Zot
Printed Circuit Division
Advanced Electronic Interconnect Solutions for the Future
Printed Circuit Guide & DFM

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
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Capabilities & Approvals
Plant List
PCB Manufacturing Flowchart
Design for Manufacture Section
Best Practice Guides
Prototype • Quick-Turns • Production
Quick Turnaround Specialists 24 Hrs to 7 Days
PTH
Multilayer
Rigid, Flex, Rigid-Flex
High Density Interconnects
RF and Microwave
Commercial & Military
On-site Engineering Consulting
Collaborative Research and Development
BS EN 9100 (AS9100)
BS EN 123 000
UL Approval Certificate No: E76334
IPC 600 Application Specialists
WWW.ZOT.CO.UK
Ver. 23/3/14
Zot Printed Circuit Guide
Overview
Material
Standard
Capabilities
Prototype
Capabilities
Other
Standard
Capabilities
Prototype
Capabilities
FR4 – High TG Isola 370HR, VT47
Y
Y
Blind & Buried Microvia
Y
Y
FR4 - Mid TG Ventec VT 481 , IS 400
Y
Y
Buried Resistors
Y
Y
FR4 - Low TG
Y
Y
Conductive/Non Conductive hole fill
Y
Y
Polyimide – various options
Y
Y
Copper filled via – via in pad
Y
Y
PTFE – Rogers 3000
Y
Y
Multi copper weight PCB
Y
Y
Rogers 4000 series
Y
Y
Depth Control Drill & Rout
Y
Y
Arlon
Y
Y
Countersink
Y
Y
Omega Ply
Y
Y
Back Drilling
Y
Y
Halogen Free
Y
Y
Impedance (Single Ended & Differential)
+/-10%
+/-5%
DuPont – Pyralux AP/FR/LF
Y
Y
Scoring
Y
Y
Other Flex material – on request
Y
Y
PCB Edge Bevelling
Y
Y
Ask
Laser Direct Imaging
Y
Y
Mixed Dielectrics & Hybrid constructions
Y
Y
Sequential Lamination
Y
Y
Embedded Components
For any material not on list please
contact Technical Manager
Insulated Metal Substrate (IMS)
Y
Y
Surface Finishes
Microvia Features
ENIG
Y
Y
Capture / Target pad size = Drill +[x]
0.200mm
0.150mm
Lead Free HASL
Y
Y
Glass reinforced Dielectrics
Y
Y
Leaded HASL
Y
Y
Maximum Aspect Ratio
Y
Y
Immersion Silver
Y
Y
Minimum Microvia hole size
0.125mm
0.075mm
Electrolytic Nickel /Gold ( All over &
Edge connectors)
Y
Y
Stacked Microvia
Y
Y
Y
Y
Y
Y
Cad Net-list testing (ipc-356A)
Y
Y
Computer Aided test Engineering work
stations
Y
Y
Selective & Multiple Surface Finish
Y
Y
Immersion Tin
S
S
ENEIPG
S
S
Solid copper plate Microvia ( via-in-pad
applications)
State of the art Depth drill to +/- 10
micron Depth
Electrical Test
S = subcontract, this will add to lead-time
Standard Features
Electrical Test compliance to IPC-9252
Y
Y
0.400mm
0.300mm
0.400mm
0.300mm
Maximum Panel Size
574mm X
406mm
574mm X
406mm
Flying Probe pitch
Minimum Panel Thickness
0.400mm
0.100mm
Standard SMD pitch
Maximum Panel Thickness
3.2mm
6.00mm
Maximum PTH Aspect Ratio
8:1
15:1
Quality System & Certifications
Maximum Copper weight
3oz
6oz
Maximum Layer Count
2-18
18-32
Minimum Core Thickness
0.100mm
0.075mm
Minimum Dielectric
0.065mm
0.045mm
Minimum Drill size (pth)
0.200mm
0.150mm
BS EN 9100:2009 (Rev C)
ISO 9001:2008
UL Certificate No. E76334
BS EN 123000
IPC-600,6011 / 6012 / 6013 / 6016
Unless otherwise stated default is Class 2
IPC –A-600 Application Specialist Certified
ISO 13485
ISO 14001
Soldermask Registration
+/- 0.100mm
+/-0.037mm
Copper feature to PCB edge
+/-0.200mm
+/-0.150mm
Minimum Track & Space – Outer*
0.100mm
0.050mm
Minimum Track & Space – Inner*
0.100mm
0.050mm
*’ Base copper weight dependant
www.zot.co.uk
2
Zot Printed Circuit Guide
Introduction
About Zot
We were established in 1975, and service the needs of all sectors of the worldwide electronics industry. We continue to
build on our industry relationships through our policy of continual investment year-on-year in the latest PCB
technologies, and are recognised as one of the leading pcb manufacturing companies in the Europe.
For an overview of the company please visit : www.zot.co.uk
WHAT CAN THE PCB DIVISION DO?
We specialise in producing small to medium batch quantities from 24 hour turnaround. Standard turnaround is typically
10 to 12 working days. We understand the need for maintaining our customer’s competitiveness, therefore we also offer
offshore volume supply options, utilising our experience in monitoring and testing to ensure that offshore enjoys the
same quality systems as in-house production.
Whether the design is plated through hole, controlled impedance, backplanes, bonded heatsinks, multilayer to 24
layers+, microvia, buried/blind via, or even flexi-rigid, we have the experience and ability to produce your design.
Our manufacturing processes use state of the art pcb manufacturing equipment such as Laser Direct Imaging, Soft Touch
flying probe testing, 4 slot innerlayer tooling and environmentally friendly direct legend printing. These processes and
others, allow us to hold very tight tolerances.
What Makes The Pcb Division Different?
Our PCB Division not only enjoys over 30 years of experience in the small to medium scale development and production
of PCBs, but also maintains a client portfolio which stands as testament to the company's long-term reliability. In many
cases our clients who have been with the business for over a decade. We believe this is due to the company's efforts to
recognise and meet the particular needs of each customer.
Quality is key to the PCB division but not at the expense of price. We pride ourselves on the ability to deliver on time, to a
competitive budget, with quality that will encourage repeat business.
Front End Engineering Ability
We have a wealth of front end engineering ability, most of our Front End Engineers, have been in the Printed Circuit
Industry for 20 years. The combined front end experience of our tooling engineers is over 150 years, this with the
combination of sophisticated computer systems ensures we have the right knowledge to engineer your design for
manufacturability, and help design quality in. All designs are fully design rule checked, and verified to net lists during
engineering and subsequent automatic optical inspection and electrical testing of your product. Our tooling department
is manned 24 hours a day.
We have 2 tooling sites, 1 in our main site in Musselburgh, and another site in the West of Scotland, these all work as
virtual offices.
Production Facilities
Our production facility is well manned with a highly skilled and knowledgeable workforce, and our equipment purchasing
strategies ensure that our state of the art production facility is well equipped with the latest in pcb manufacturing
technologies, such as imaging processes like Laser Direct Imaging and soft touch probe testing, and with our fundamental
commitment to quality, delivery and service, with continuous improvement programmes utilising a variety of process &
quality control tools, backed up with our fully equipped laboratory, ensures our customers of an outstanding service from
a world class manufacturer.
All processes are controlled by various quality methods, including Cp & Cpk, preventative maintenance schedules, critical
characteristics, every possible variable & attribute is monitored and controlled. This is also backed up with a well
equipped Laboratory, covered 24 hours a day.
www.zot.co.uk
3
Zot Printed Circuit Guide
Zot PCB Manufacturing Flow Chart
Engineer
Data Transfer from Customer
&
Create
Tooling
Data Engineer &
DRC
Data Prep & DFM
Materiel Issue
Chemical Clean
Create
Inner
Layer
Tracking
Laminate
Laser Direct Image
Develop/Etch Inners
AOI Inners
Alternative Oxide
Lay-up & Bond
Drill
Holes
Drill
Desmear
Direct Metalisation
Plate Holes
and Create
Outer
Tracking
Laminate
Laser Direct Image
Develop
Pattern Plate
Etch/Strip
A.O.I. Outers
Apply
Solder
Mask
and
Legend
Pumice & Print SR
Photoprint P/I
Develop P/Image
Direct Legend Print
Final Cure
Electrolytic Gold
Solder Level
Electrical Test
Imm. Gold/Tin/Silver
CNC Score
Process are controlled by
SPC, Critical
Characteristics, totalling
1,000s of process and
product checks
Prt Peelable
Apply
Solderable
Finish
Cut to
Size
Router
Final Inspection
Insp and
Test
Electrical Test
Despatch
Despatch to Customer
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4
Zot Printed Circuit Guide
Sending Data for Quotations
Our preferred method of quotation is to provide us with a set of ODB++ or Gerber files.
Please note if you do not specify, we will use our standard default, i.e. if finish is not specified, we will
assume Lead free HASL.
In order to increase the speed and quality of our quotation process we employ the use of
sophisticated data analysis/modelling and costing software.
Because most of the interaction is automated, this leads to a faster and more accurate quote.
We can even see what the board will look like when it is finished, i.e see the microvias in the pads of
the BGA shown.
This data is then imported into our costing system
A quotation is then emailed to you.
www.zot.co.uk
5
Zot Printed Circuit Guide
Introduction
The following are our capabilities & approvals; this is split into sections, dependant on the
attribute/variable specification.
Key to Colour Coding
This is the next step in our
capability improvement.
programme
This is the Qualified limits of our
current production
This is our Standard Production,
which is produced on a daily basis
Notes
1. Where we have stated “ ----- “, in the columns, it means that at this point we have no active
plans to alter/improve our capability.
2. We are always working on improving our capability, by adopting new processes/procedures,
and investing in more capable equipment, therefore if you require something, out with the
stated capability below, then contact us, as we now may be capable of your requirement.
3. Standard Production : We are doing this type of work on a daily basis, with good yields.
4. Qualified Limits : This is the current qualified limit of our production, where we can get
acceptable yields, but this type of attribute/variable, requires extra attention, and can only be
achieved using specialised processes & equipment, such as Laser Direct Image Soldermask
features.
5. Next Step : This is the next step we will be taking in our capability improvement, this is
currently under development and outwith our current capability.
6. When designing a board always go for the largest feature possible, i.e.
a) If the track to track pitch is 0.300mm, do not design with 0.100mm tracks and 0.200mm
space, design with 0.150mm tracks and 0.150mm space.
b) If you have a 0.80mm pad, use a via hole of 0.40mm, and not a 0.25mm via, as this can affect
price.
c) Always try to balance annular ring with track spacing with track pad.
As part of our continual improvement programmes, we are constantly updating, and adding new
sections to this document, however we will not be advising the holders of this document, as this is
not possible.
Please visit www.zot.co.uk, to check the revision level of your document.
www.zot.co.uk
6
Zot Printed Circuit Guide
Circuit Feature– Minimum / Maximum
Attribute
Minimum Track Width
Minimum Track Space
Maximum Hole Aspect Ratio
Minimum Drilled Hole
Minimum Track to Board Edge External
Minimum Track to Board Edge –
Internal
Minimum Internal Plane
Clearance
Minimum Annular RingOuterlayer
Minimum Annular RingInnerlayer
Maximum Copper – Internal
Maximum Copper – External
Impedance Control
Standard
Production
Development
/Prototype
Future
Development
0.100mm
0.100mm
8:1
0.200mm
0.200mm
0.075mm
0.075mm
12.5:1
0.150mm
0.150mm
0.050mm
0.050mm
15:1
0.10mm
0.10mm
0.300mm
0.200mm
0.15mm
0.300mm
0.200mm
0.15mm
0.075mm
0.050mm
0.025mm
0.100mm
0.075mm
0.050mm
105um
105um
+/- 10%
210um
210um
+/- 5%
-----420um
------
Notes
Minimum Track to Board Edge – External : This is closest track to edge without cutting tracks.
www.zot.co.uk
7
Zot Printed Circuit Guide
Legend Attributes
Attribute
Standard
Production
Minimum Legend Feature
0.125mm line
Size
Legend to Copper Pad
0.150mm
Clearance
Number Serialisation
Yes
(traceability marking)
Standard Legend Colour is White.
Development
/Prototype
Future
Development
0.075mm line
-------
0.100mm
-------
Yes
Soldermask Attributes
Attribute
Minimum Solder Mask Dam
(Green,Red,Blue,Clear)
Minimum Solder Mask Dam
(Black, White, Yellow)
Minimum Soldermask
Standard
Production
Development
/Prototype
0.075mm
0.050mm
0.100mm
0.075mm
0.015mm
UL Approval
Yes
Others available on
request
Yes
Halogen Free
(< 900ppm)
IPC-SM-840
Yes
Yes
Yes
Yes
Minimum Soldermask
Oversize
LDI Soldermask Compatability
0.075mm
0.037mm
No
Yes
Thickness over Tracks
Future
Development
0.025mm
Standard Soldermask is Green, other colours available.
www.zot.co.uk
8
Zot Printed Circuit Guide
Registration Tolerances
Attribute
Circuit Side to Side
Layer to Layer
Circuit to Drill Hole
Circuit to Board Edge
Soldermask to Circuit
Legend to Circuit
Drill to Datum Hole
Primary Drill : Hole to Hole
Primary Drill to Secondary
Drill
Primary Drill to Routered Hole
Countersink/Counterbore
Postional
Standard
Production
Development
/Prototype
Future
Development
+/- 0.150mm
+/-0.125mm
+/-0.100mm
+/- 0.200mm
+/- 0.100mm
+/-0.100mm
+/- 0.100mm
+/- 0.100mm
+/- 0.150mm
+/-0.100mm
+/-0.100mm
+/- 0.075mm
+/- 0.15mm
+/- 0.037mm
+/- 0.075mm
+/- 0.075mm
+/- 0.075mm
+/- 0.100mm
+/- 0.050mm
+/- 0.050mm
+/- 0.050mm
+/- 0.10mm
+/- 0.025mm
------------------+/-0.075mm
+/- 0.150mm
+/- 0.200mm
+/- 0.100mm
+/- 0.150mm
+/-0.075mm
-------
Zot Minimum Drill Size Capability
Based on 18um (1/2oz) Base copper
Board Thickness (mm)
Minimum Drill Size (mm)
Finished Hole size (Cu = 25um)
Aspect Ratio (>10:1 increases
difficulty and Reduced yield)
External Annular Ring - IPC Class 2
(mm)
External Annular Ring - IPC Class 3
(mm)
External Pad Size - IPC Class 2 (mm)
External Pad Size - IPC Class 3 (mm)
Internal Pad Size - IPC Class 2 (mm)
Internal Pad Size - IPC Class 3 (mm)
Antipad (hole to copper internal)Level 1 0.250mm (mm)
Antipad (hole to copper internal)Level 2 0.200mm (mm)
Antipad (hole to copper internal)Level 3 0.150mm (mm)
Minimum
Optimum
Optimum
Minimum
Optimum
Minimum
Optimum
1.6
0.15
0.1
1.6
0.2
0.15
1.6
0.25
0.2
2
0.2
0.15
2
0.25
0.2
2.4
0.2
0.15
2.4
0.25
0.2
10.7:1
8:1
6.4:1
10:1
8:1
12:1
9.6:1
0.111
0.111
0.116
0.122
0.122
0.132
0.132
0.161
0.373
0.473
0.403
0.453
0.161
0.423
0.523
0.453
0.503
0.166
0.483
0.583
0.503
0.553
0.172
0.444
0.544
0.474
0.524
0.172
0.494
0.594
0.524
0.574
0.182
0.465
0.565
0.495
0.545
0.182
0.515
0.615
0.545
0.595
0.650
0.700
0.750
0.700
0.750
0.700
0.750
0.550
0.600
0.650
0.600
0.650
0.600
0.650
0.450
0.500
0.550
0.500
0.550
0.500
0.550
Reduced
Yield
Increased
Cost
www.zot.co.uk
Reduced
Yield
Increased
Cost
Reduced
Yield
Increased
Cost
9
Zot Printed Circuit Guide
Board Dimension(s)
Attribute
Maximum Board Size
Minimum Board Thickness
Maximum Board Thickness
Minimum Core Thickness
Maximum No. of Layers
Board Size X & Y - Tolerance
.Board Size H.T.E. X & Y Tolerance
Score to Board Edge
Score to Score
Score Residue
Countersink/Counterbore
Depth
Finished Hole Size
- Drilled
Finished Hole Size
- Routered
Minimum Copper in Holes
Standard
Production
Development
/Prototype
Future
Development
574mm x 416mm
0.40mm
3.20mm
0.100mm
12 Layers
+/-0.20mm
+/-0.25mm
574mm x 416mm
0.10mm
6.00mm
0.075mm
30 Layers
+/-0.10mm
+/-0.20mm
------------------0.050mm
> 24 Layers
------+/-0.15mm
+/-0.20mm
+/-0.20mm
+/-0.10mm
+/-0.10mm
+/-0.15mm
+/-0.15mm
-----+/-0.075mm
+/-0.10mm
+/-0.10mm
-----------
-0.00mm/
+0.100mm
+/-0.20mm
-0.00mm/
+0.075mm *
+/-0.15mm
-0.00mm/
+0.05mm *
+/-0.10mm
20um
Others available as
requested
------
------
------
0.50%
-------
Meets IPC-6012
Table 3-3
Minimum Copper in Holes
Microvia
Bow & Twist
12um
Meets IPC-6012
Table 3-3
0.75%
* = Surface Finish and Diameter Dependant
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10
Zot Printed Circuit Guide
As the copper thickness increases, then the minimum track width, that can be produced also
increase.
Track Width
Base Copper Thickness
Printed Circuit Substrate
Minimum Track Widths to Base Copper Thickness
Attribute
9um Foil
Standard
Production
0.10mm
Development
/Prototype
0.075mm
Future Development
18um Foil
0.125mm
0.100mm
0.075mm
35um Foil
0.150mm
0.125mm
-----
70 um Foil
0.225mm
0.150mm
-----
105 um Foil
0.275mm
0.200mm
-----
140um foil
0.300mm
0.200mm
-----
175 um Foil
0.375mm
0.250mm
-----
210um Foil
0.450mm
0.300mm
-----
0.050mm
Note
1. Copper tracks on copper thickness greater than 18um foil, are etch compensated.
2. Minimum Track space after etch compensation is 0.100mm
3. We also compensate track widths on 18um and 35um base, this is dependant on track width/space
ratio.
www.zot.co.uk
11
Zot Printed Circuit Guide
Finishes Available
These are the following Finishes available, they are all produced in house, and the thickness plated.
Coated is verified by X-Ray Fluorescence on each batch processed
Attribute
RoHS
Standard
Development
Future
Compliant Production
/Prototype
Development
Lead Free HASL
Yes
3 – 20um
------
------
------
------
1.0um –
1.50um
0.25um –
0.50um
3.0um – 7.0um
------
------
------
------
0.05um – 0.15um
------
------
------
0.5um – 5um
------
Meets IPC 6012
Table 3-2
Leaded HASL
NO
3 – 20um
Meets IPC 6012
Table 3-2
Immersion Tin
Yes
Immersion Silver
Yes
Electroless Nickel
Yes
Immersion Gold
Yes
Electrolytic Nickel
Yes
0.05um –
0.10um
3.0um – 7.0um
Electrolytic Gold
Yes
1.5um – 3.0um
ENIPIG
Yes
As specified
------
Electrolytic Nickel and Gold are available as selective plating, or as all over plating.
Electrical Test
Attribute
Standard
Production
Development
/Prototype
Future
Development
Minimum pitch
Test voltage
Isolation
Continuity – Flying probe
0.200mm
10 volts
10 Mohm
10 ohm
0.100mm
Up to 500volts
10 Mohm – 25Mohm
1 ohm to 2 kohm
None
none
none
none
QFP = Quad Flat Pack, BGA = Ball Grid Array
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12
Zot Printed Circuit Guide
Peelable Soldermask
Attribute
Standard
Production
Peelable Soldermask
Thickness
Peelable Soldermask
Registration
Development
/Prototype
 300um
Future Development
 300um
+/- 0.50mm
------
+/- 0.20mm
------
Carbon Ink
Attribute
Standard
Production
Development
/Prototype
Future Development
Carbon
12 ohms
Other Values
upon On Request
------
+/- 0.20mm
0.300mm
+/- 0.15mm
0.200mm
------------
Surface Resistivity
Sheet Resistance
Carbon to Circuit
Minimum Carbon
Feature
The following Soldermask Colours are available
Soldermask Colour
Halogen Free
U.L. Approved
Approved for
BS Release
Green – Halogen Free
Green
Black
Blue
Red
Yellow
White
Yes
NO
NO
Yes
Yes
NO
NO
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Notes
1. Preferred Soldermask Colour is GREEN.
2. Direct Legend Printing only available in white, photoimageable legend available in all colours
above.
3. Halogen Free defined as less than 900ppm total halogens
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13
Zot Printed Circuit Guide
Laminate
The following Table represents the laminates which we can manufacture, in the respective board
product types, available in single sided, pth and multilayer. If the laminate you require is not listed
below, please contact our technical department for more information.
FR4 Materials
Dicy Cured Fr4 : SN-L41, De117, N4000-6, PCL 240, PCL370, FR4-ML, FR4-RD, FR4, De104
De104i, 104-TS, 1755C (R1650C P/P), IS410, VT-481,370HR, N4000-29, R1566 (R1551P/P), VT-47TC
Fr4 H/Free = R1566, De156
All Fr4 Type Materials
Other PCB Laminates
Polyimide: N7000 series, P95,96,97, VT-901
Arlon Diclad
Aramid
PTFE Laminates
Metal Backed Laminates
Rogers type Laminates
R03000 Series PTFE Ceramic
R04000 Series
RT/duroid® 5000 PTFE Glass Fibre
RT/duroid® 6000 PTFE Ceramic
TMM® Hydrocarbon Ceramic
ULTRALAM® 2000 PTFE Woven Glass
ULTRALAM® 3000 Liquid Crystalline
Flexible Materials
Dupont
Espanex
If you require a laminate that is not listed above, please contact us.
www.zot.co.uk
14
Zot Printed Circuit Guide
Quality Approvals
Quality System Approval
Quality System : BS EN 9100 (AS9100)
British Standards Product Approval
BS EN 123 000
BS EN 123 100
BS EN 123 200
BS EN 123 300
Assessment Level C
Registration No: M1052 IECQ-CECC
Certificate No: E086/CA
Underwiters Laboratory Approval
UL Approval Certificate No: E73364
IPC Certification
IPC-A-600 Application Specialist
Notes
1. Copies of BS Release certificates and Scope are available upon request.
Limitation of Approvals - The following is the scope of our BS EN123000 Approval
BS EN 123000 Attribute/Variable
Hot Air Solder Level - Leaded
Hot Air Solder Level – Lead Free HASL
Immersion Silver
Immersion Tin
Electroless Nickel, Imm.Gold
Electrolytic Gold
Approved for BS
Release
Yes
Yes
Yes
No
Yes
Yes
(2.5um gold on 5um Nickel – Contacts Only )
Photoimageable Soldermask
Photoimageable Legend
Direct Legend Print
Peelable Soldermask
Minimum Track Width
Minimum Space
Minimum Hole Size
Maximum No. of Layers
Aspect Ratio
FR4 Laminate Family
Yes
Yes
Yes
Yes
0.100mm
0.100mm
0.20mm
24
12.5:1
Yes
Board Size
584mm x 432mm
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15
Zot Printed Circuit Guide
Underwriters Approval ( UL Approval ) Limitations : File no: E76334(M)
UL Approval – Finishes & Coatings
Approved for
UL Release
Lead free HASL
Yes
Leaded HASL
Yes
Immersion Tin
Yes
Immersion Silver
Yes
Electroless Nickel / Immersion Gold
Yes
Electrolytic Gold
Yes
Soldermask – All Colours
Yes
Legend
Yes
Carbon
No
Peelable Soldermask
Yes
UL Approval – Conductor Pattern
Limit
Maximum Operating Temp
UL 796 (DSR )
UL Flame Class
Minimum Edge Conductor
Minimum Conductor
Maximum Unpierced Area ( Outer )
(<105um Base Copper )
Maximum Unpierced Area (Outer )
(>105um Base Copper )
Maximum Unpierced Area ( Inner )
Minimum Core Thickness
Minimum Board Thickness
Maximum Copper Weight
130c
All
V-0
0.050mm
0.150mm
150mm Diameter
UL Approval – Board Types/Materials
FR4
Sequential Multilayer Build
Polyimide
Rogers/Getek/Aramid
Flexibles & Flexi-rigids
114mm Diameter
210um Diameter
0.100mm
0.80mm
210 micron
Approved for
UL Release
Yes
Yes
Yes – UL 94V-1
No
No
General Specification
Unless otherwise stated we work to I.P.C. 600 ( Latest Revision )Class 2, and I.P.C. 6012.
Certified IPC 600 Application Specialist
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16
Zot Printed Circuit Guide
Zot Flexible
Why use Flex & Flex-Rigid Technology?
Flex& flex-Rigid PCB’s have been widely used in a variety of applications and markets for many years
where space and size is critical to its function as an interconnect either between connectors or to other
rigid PCB’s. At Zot Printed Circuits we are seeing more and more customers migrate to flex& flex-Rigids
due to the benefits of its construction, some examples as follows:
•3d interconnect
•1 part component (as opposed to multiple rigid pcb’s and wiring looms)
•increased reliability
•space saver
•reduced labour costs at assy
•fully tested as a 1pc component
FLEX CIRCUIT TYPES FOR OPTIMAL INTERCONNECTION
Different types of flex circuits offer different advantages. Some offer lower cost, while others increase functionality. Zot Printed
Circuit has invested heavily in advanced manufacturing equipment and Engineer/Operator training to meet the needs of this
market. Learn more about the circuit types available for your application below:
Single-layer IPC 6013 Type I
One conductive layer either bonded between two insulating layers or uncovered on one
side. Access holes to conductors may be on either one or both sides.
Access holes on both sides of a single-layer are more expensive since the substrate must be
drilled or laser defined separately.
Double-layer IPC 6013 Type 2
Two conductive layers with an insulating layer between; outer layers may have coverlayers or exposed pads. Plated through-holes provide connection between layers.
Access holes in cover-layers or exposed pads without cover-layers may be on either or
both sides; vias can be covered on both sides.
Multi-Layer IPC 6013 Type 3
Three or more flexible conductive layers with flexible insulating layers between each
one; outer layers may have cover-layers or exposed pads.
Plated through-holes provide connection between layers.
Access holes in cover-layers or exposed pads without covers may be on either or both
sides. Vias can be through, blind or buried.
Rigid Flex IPC 6012 Type 4
Two or more conductive layers with either flexible or rigid insulation material as
insulators between each one; outer layers may have covers or exposed pads.
Rigid-flex has conductors on the rigid layers, which differentiates it from multilayer
circuits with stiffeners. Plated through-holes extend through both rigid and flexible
layers.
Access holes in cover-layers or exposed pads on rigid features may be on either or both
sides. Vias or interconnects can be fully covered for maximum insulation.
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17
Zot Printed Circuit Guide
Flexi Rigid Capability
The following is our flexi-rigid capability, this is different from our normal capability.
See Note 1
Attribute
Panel Size
Minimum Track Width
Maximum no. of Layers
Maximum Thickness
Track to Flexi Rigid Tail –Note 1
Minimum Internal Annular Ring
Minimum External Annular Ring
Minimum Flexible Core Thickness
Flex Materials
Standard
Production
18 x 12
0.125mm
10
2.40mm
1.00mm
0.150mm
0.150mm
0.025mm
Dupont – AP
Dupont – LF
Espanex
Tori
Development
/Prototype
24x18
0.100mm
16
3.00mm
0.45mm
0.100mm
0.100mm
Future
Development
0.075mm
----4.00mm
----0.150mm
0.100mm
-----
Notes
1. The minimum that a pad or track can be to the start of the flexible tail is shown above on the
diagram, and in the table.
2. Flex – Rigid can be combined with HDI designs for the ultimate solution. Please contact us for
details at Data@zot.co.uk. See below for HDI capability.
www.zot.co.uk
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Zot Printed Circuit Guide
Flexible PCB Benefits
•Flex Properties
–Heat dissipation, shock and vibration resistant
–Electrical characteristics: predictable and controllable (impedance, cross-talk, noise)
–Versatile shape enables 3-dimensional configurations
•Weight and Size
–Allows dramatic reduction of electronics package size and weight (up to 75% compared to rigid and
round wire configurations)
•Cost effective
–Designed to eliminate board to board interconnects or board to wire connections (the most
common failure points in electronic assemblies)
–Easier to install or replace (removes human-error associated with point to point wire assemblies)
•Durability
–Bend & straighten up to 500 million times without a failure–Unmatched performance for
applications with repetitive motion
–Polyimide is known for its dimensional stability, dielectric strength
and high heat resistance
Flex Board Applications
Defence and Aerospace
•Replacing many wire harnesses for ruggedized applications, flexible circuit boards are able to
survive hostile environments.
•Weight reduction paired with increased reliability.
•Field serviceability.
Medical
•Dramatic reduction of overall electronics package size.
•Weight reduction enables handheld and portable devices.
•Resistance to chemically aggressive environments enables implantable devices.
Industrial Controls
•With the ability to bend and straighten millions of times without a failure, flex circuits provide unmatched performance for applications with repetitive motion.
•Durability and reliability in aggressive environments.
Consumer Electronics
•Weight reduction is key for hand-held devices, personal computing, GPS, cell phones.
•Stability of materials for high volume manufacturing.
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Zot Printed Circuit Guide
The Basics: Materials
Copper Clad Laminates
•Rolled Annealed (RA) copper
•Electro-Deposited (ED) copper
•¼ oz (ED) to 3 oz Cu weights
Flex Materials are certified to IPC-4202,
4203 and 4204
Kapton® -DuPont's trademark for polyimide film
Pyralux® -DuPont's trademark for flexible circuit
materials (Cu clad laminates, coverlays and
bonding adhesives)
Coverlay –Kapton coated with adhesive on one
side (insulating material that is applied over a
conductive pattern on the outer surface of the
pcb)
Bondply –Kapton coated with adhesive on both
sides
•Adhesiveless copper clad laminate
–AP (excellent thermal, chemical, electrical and
mechanical properties) ideal for rigid flex and
multilayer flex
•Acrylic Adhesive Based clad laminates
–LF (High Reliability) Avionics
–FR (Fire Retardant) Commercial Grade, UL 94 V0
•Stiffeners –FR4 or other material that is bonded
to the FCB to provide mechanical support
•Rigid Multilayer Materials for Rigid- Flex
Constructions:
.FR4
.Polyimide
.RF Materials, Reinforced PTFE
TYPICAL PROPERTIES OF DIELECTRIC MATERIAL FOR FLEXIBLE PRINTED CIRCUITRY
PROPERTY (TYPICAL)
UNITS
REPRESENTATIVE TRADE NAME
POLYIMIDE
POLYIMIDE
(Adhesiveless)
POLYESTER
KAPTON
KAPTON
MYLAR
PHYSICAL
Thickness Range
mil
0.5 to 5
1-6
2-5
Tensile Strength (@25° C)
psi
25,000
50,000
20,000 to
35,000
Break Elongation
%
70
50
100,000 psi
4.3
.7
5
Tear Initiation Strength
lb/in
1000
700-1200
1000 to 1500
Tear Propagation Strength
g/mil
8
20
12 to 25
Good
Good
Good
Strong Alkalis
Poor
Good
Poor
Grease and Oil
Good
Good
Good
Organic Solvents
Good
Good
Good
Water
Good
Good
Good
Sunlight
Good
Good
Fair
Fungus
Non-nutrient
Non-nutrient
Non-nutrient
% (24 hours)
2.9
.8
<0.8
Service Temperature (min/max)
degree C
-125/+200
-125/+200
-60/+105
Coefficient of Thermal Expansion
(@22°C)
PPM/degree C
20
20
27
%
<0.3
0.04-0.02
<0.5
Tensile Modulus (@25° C)
60 to 165
CHEMICAL
Resistance to:
Strong Acids
Water Absorption (ASTM D570)
THERMAL
Change in Linear Dimensions
(100° C, 30 min)
ELECTRICAL
DIELECTRIC CONSTANT (ASTM D150) 1MHz
3.4
3.4
3
DISSIPATION FACTOR (ASTM D150) 1MHz
0.01
.003
0.018
6000
1.0E+16
6000
1.0E+16
3400
1.0E+1
DIELECTRIC STRENGTH (ASTM D149)
@ 1 mil thickness
Volume Resistivity (ASTM D257)
V/mil
ohm-cm
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20
Zot Printed Circuit Guide
Design Considerations
Minimum Bend Radius
•For single and double sided flex the
minimum bend radius should be 6 times
the overall thickness.
•For multilayer and rigid flex, the minimum
bend radius should be 12 times the overall
thickness.
•Critical area is the inside of the bend
where delamination, dielectric and
conductor fractures can occur.
•Failures in the compression area
(Inside of the bend) may go undetected
until after the FCB is in service.
•This is the most common mechanical
failure mechanism for a flex board and it
can happen with just one excessive fold of
the board.
•Elevated PCB temperature during bending
is not recommended.
Designer Tips:
.Even distribution of copper features in the
bend area.
.Power & ground planes on the outside of the
bend and cross-hatched.
.For border-line conditions there is no
substitute for a mechanical mock-up that can
be destructively tested after bend.
Flex Tear Prevention
•Second most common mechanical failure
mode for flex and rigid-flex.
•Can be caused by mis- handling as well as
fatigue from repetitive motion.
•Tear Stops: unterminated (or grounded)
conductors placed at or near corners to
stop tear propagation, may run the entire
length of the board.
•Rounded Corners: where possible inside
radii should be .030” or greater. Eliminate
sharp edges wherever possible.
Designer Tips:
.Avoid 90 degree corners, applies to inside and
outside corners.
.Avoid mechanical stress build-up caused by uneven circuitry. Route traces with rounded or 45
degree corners in critical areas.
.Allowspace for tear stops in the vicinity of
inside corners.
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21
Zot Printed Circuit Guide
Design Considerations
Balanced Circuitry
•Allows mechanical stress to distribute
evenly when circuit is flexed repeatedly
perpendicular to the conductors.
•Absolutely necessary for any dynamic flex
applications (single sided, double sided and
multi-layer), highly recommended for all
constructions.
•Prevents higher stress conditions to
develop around isolated traces or other
copper features.
Designer Tips:
.Balance geometry of copper vs. void areas as
much as possible.
.Add un-terminated (or grounded) copper pour
to even distribution if necessary.
.Adjust width of flex area to avoid large void
areas if possible.
Maximize Conductor Widths
•Tear Drops (Pad Fillets): improve mechanical and
electrical reliability for both innerlayer and
outerlayer connections.
•Improved reliability when drills are not perfectly
centred on pads.
•Tear drops can be added globally in CAM (requires
customer approval).
•“Anchoring Spurs” to be used on outerlayer pads
only to help prevent lifted pads during soldering
operations.
•Improve manufacturability, increase yield, lower
PCB costs.
Designer Tips:
.Use wider traces where possible, also helps
balancing copper/void areas.
.Add or require tear drops to all inner and outer
layer pads (including SMT pads).
.Add anchoring spurs or square copper pads
with round coverlay opening when possible.
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Zot Printed Circuit Guide
Design Considerations
Strain Relief Fillets
•Two-part epoxy fillet applied to rigid-flex
interfaces or stiffener-flex interfaces.
•Rigid, semi-rigid and flexible (most
popular) formulations are available based
on the amount of hardener used.
•Prevents conductor strain when bent near
the rigid to flex transition area.
•Fully encapsulates prepreg flow or
“squeeze-out” for rigid flex boards. This
prevents those sharp edges to pierce the
softer flex material.
Designer Tips:
Strain relief fillets are usually specified by a
note in the Fab drawing, for example:
“Apply Eccobond 45, colour black at interface
marked, top and bottom sides. Eccobond fillet
must not extend more than .100” from rigidflex interface”
The “I-Beam” Effect
•This condition takes place when traces
from 2 or more adjacent layers are running
overlapping each other.
•Increases non-uniform stress build-up
when the board is flexed perpendicular to
the traces.
•Applies to both innerlayers and
outerlayers equally.
•Creates “high” and “low” areas during
coverlay or multilayer lamination that can
lead to inadequate fill of adhesive at the
foot of the trace (micro-voids).
•“Staggered” conductor routing is
necessary for dynamic flex applications and
recommended for all constructions.
Designer Tips:
.Stagger traces for adjacent conductors where
possible
.Use power / ground plane to break up the
“I-Beam” effect when overlap routing cannot be
avoided.
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23
Zot Printed Circuit Guide
Design Considerations
Distance from Rigid-Flex Interface
•Recommended minimum distance is 50
mils from the edge of the hole to the rigidflex interface.
•Prepreg is pre-routed .020” inside the
interface edge to allow for flow as it
changes from B to C Stages.
•Coverlay and flex bondply are also routed
.020” inside the interface line.
•Allow for the barrel of the hole to be
drilled through the area of the board where
prepreg flow can be controlled and the
laminate is stress free.
•Larger holes affect the material more than
smaller diameter holes and need to be kept
even further from interface.
Designer Tips:
Keep all holes an absolute minimum of 50 mils
from the rigid-flex interface
Controlling Adhesive Squeeze-Out
•Coverlay materials require 1 mil of
adhesive for every ounce of copper weight
on the surface layers.
•Adhesive flow under normal conditions is
3-4 mils per mil of thickness, can be up to 6
mils per mil.
•Use copper pad as a “dam” to limit
coverlay flow onto the pad.
•Where a trace enters a pad there will be
additional coverlay flow, this should be
taken into account for fine pitch BGAs, tight
SMT devices or wire-bond pads.
Designer Tips:
.Avoid coverlay-defined pads
.Coverlay annular ring = pad size + .005”
.Allow for additional flow where a trace enters a
pad.
www.zot.co.uk
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Zot Printed Circuit Guide
Design Considerations
Designer Tips:
.Run conductor’s perpendicular
to bend direction.
.Straight conductors in the
dynamic flex area, if this can’t be
avoided use rounded corners.
.Balanced conductors.
.Symmetrical stack up.
.Thin, adhesiveless dielectric
materials.
.1 ounce rolled annealed copper.
.Absolutely no plated through
holes in the flex area.
.Avoid surface plating in the flex
area.
.Loose leaf construction.
Dynamic Flex Applications
•Any lack of symmetry in the design will increase the
chances of stress build-up in the flex area.
•1 ounce copper performs better than ½ ounce copper.
•Thin dielectric performs better than thick dielectric.
•Any imperfection will cause premature failure; flex area
should be “pristine”
www.zot.co.uk
25
Zot Printed Circuit Guide
Impedance Control
Impedance Control
•Impedance is the single most important
transmission line property used to
determine the performance of a high-speed
circuit
•Impedance can be controlled with several
different configurations and by using
Characteristic, Differential, and Coplanar
models.
•Transmission lines are signal carrying
circuits composed of conductors and
dielectric material configured to control
high frequency or narrow pulse type signals
•Two types of transmission lines
configurations used to control impedance:
–Micro-strip -conductor is above a ground
plane.
–Stripline –conductor is running between
two ground planes
•Impedance is controlled through:
–Conductor width
–dielectric thickness
•Flex Materials have advantages over rigid
laminates based on:
–Non-hybrid dielectric .more uniform local
Dk.
–Better controlled dielectric thickness.
www.zot.co.uk
26
Zot Printed Circuit Guide
Zot HDI
High Density Interconnect
Zot Printed Circuits is a UK based manufacturer of High Density Interconnect PCBs (HDI PCBs). Our HDI
capabilities include advanced depth control drilling, blind and buried vias, fine lines and spaces,
sequential lamination, via-in-pad technology. We have provided microelectronic pcbs with fine pitch
devices down to 300 microns, using 75 micron drilled via-in-pad technology and thin build-up materials.
Modern electronic designs are becoming more and more slim and portable. The use of more complex
components with very high Input /Output (I/O) count have pushed PCB fabricators to evolve to use new
techniques for creating smaller vias and have also pushed them to develop new processes, or re-tool old
ones. These processes include revised methods of producing holes from the conventional drill, to
processes such as laser drilling. Reduction of the via hole size will allow the designer to significantly
increase the routing density through the use of vias in surface-mount technology (SMT pads), which will
in-turn minimize the size and weight of the product to improve the electrical performance of the system.
These types of boards are generically called High-Density Interconnects (HDI).
Multilayer technology allows the designer to sequentially add additional pairs of layers to form a
multilayer core. For designs with a dielectric element which has copper foil both on the top and bottom
we use our advanced drill machine to produce holes on the inner layers which then go on to the imaging
and etching process. This added approach for HDI design typically is called the Sequential Build-up (SBU).
SBU printed circuit boards are commonly described as 1+N+1,2+N+2..etc.Where N is the number of
layers that constitutes the formed inner core. One and two, etc. are the number of added layers. At Zot
we can currently produce boards that are 3+N+3.
Fabricating with solid metal vias is our method of metallization on Interconnect Via holes(IVHs). It not
only provides the stacked vias a stronger interconnection but also helps in obtaining better thermal
management as well, which in-turn significantly increases the board reliability under severe operational
circumstances.
HDI Capability
www.zot.co.uk
27
Zot Printed Circuit Guide
HDI general description
Printed circuit board with a higher wiring density per unit area than conventional printed circuit boards (PCB).
They have finer lines and spaces (≤ 100 μm), smaller vias (<150 μm) and capture pads (<400
μm), and higher connection pad density (>20 pads/cm2) than employed in conventional PCB technology.
IPC-2226 definition of Microvia:
A blind hole with a diameter of less than or equal to 150 μm having a pad diameter of less than or equal to
350μm formed by either laser or mechanically drilling.
IPC-T-50H:
High Density Interconnect (HDI) A generic term for substrates or boards with a higher circuit density per unit
area than conventional printed boards
At Zot we use mechanical drilling down to 0.120mm diameter, for smaller microvia laser drilling is used.
IPC-2226 defines HDI in 6 classes
Type I 1(C) 0 or 1(C)1 – Currently Manufactured at Zot – See Capability table below
 Defines a single Microvia layer on
either one or both sides of core.
•Core can be multilayer, rigid or flex.
•Core is typically manufactured using
conventional PWB techniques.
•Uses both plated microvias and plated
through holes for interconnection.
•Employs blind, but not buried vias.
Type II 1(C) 0 or 1(C)1 – Currently Manufactured at Zot – See Capability table below
•Defines a single microvia layer on
either one or both sides of core.
•Core can be multilayer, rigid or flex.
•Core is typically manufactured
using conventional PWB techniques.
•Uses both plated microvias and
plated through holes for
Interconnection.
•Employs blind and buried vias.
Type III 2 ≥ (C) ≥0 – Stacked Microvia
Currently Manufactured at Zot – See Capability table below
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28
Zot Printed Circuit Guide
•Defines at least two layers of
microvia layers on either one or
both sides of core.
•Core can be multilayer, rigid or
flex.
•Core is typically manufactured
using conventional PWB
techniques.
•Uses both plated microvias
and plated through holes for
Interconnection.
•Employs blind and buried vias.
Type III 2 ≥ (C) ≥0 – Staggered Microvia
Currently Manufactured at Zot – See Capability table below
•Defines at least two layers of microvia
layers on either one or both sides of
core.
•Core can be multilayer, rigid or flex.
•Core is typically manufactured using
conventional PWB techniques.
•Uses both plated microvias and
plated through holes for
Interconnection.
•Employs blind and buried vias.
Type IV ≥ 1 (P) ≥0 – Limited manufacturing capability, please enquire for more details
•Defines to have at least one
Microvia layer on either one
or both sides of core.
•Core is typically
manufactured using
conventional PWB techniques.
•Uses both plated microvias
and plated through holes for
interconnection.
•Uses a passive core not
electrically connected, used
normally for CTE
management.
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29
Zot Printed Circuit Guide
Type V Coreless – No current manufacturing capability, please enquire for more details
•Uses thin “cores” which uses
both plated microvias and
conductive paste
interconnections.
•Uses B-stage resin system
prepregs where conductive
material locally have been
placed.
Type VI Construction – No current manufacturing capability, please enquire for more details
•A construction where
connections are build up without
normal plating.
•The connections are formed with
conductive ink, or other type of
conductive material.
•Examples as ALIVH (Any-Layer,
Inner Via Hole )and PALAP
(Patterned Prepreg Lay Up
Process ) both Japanese
inventions.
Zot Microvia & Through Via Capability
www.zot.co.uk
30
Zot Printed Circuit Guide
Aspect Ratio
Level A
Production
High Yield
Standard cost
Level B
Prototype
Level C
Advanced Prototype
Microvia Plating aspect ratio
<0.5:1
(k + j)/ a
<5:1
(2k + Board
Thickness) / h
<5:1
(2r + q) / o
>0.5:1 to 1:1
(k + j)/ a
>5:1 to 10:1
(2k + Board
Thickness) / h
>5:1 to 10:1
(2r + q) / o
>1:1
(k + j)/ a
>10:1
(2k + Board
Thickness) / h
>10:1
(2r + q) / o
Through via hole aspect ratio
Buried via aspect Ratio
Symbol
Feature
Level A
Level B
Level C
a
b
c
Microvia diameter at target land ( no plating)
Microvia diameter at capture land ( no plating)
Microvia target land size = (a + 2x annular ring) +
(1)
FA
FA for c =
Microvia capture land size = (b + 2x annular ring)
(1)
+ FA
FA for d =
Internal conductor trace width
Internal conductor spacing
External conductor trace width
External conductor spacing
Through via land size = (h + 2x annular ring
(1)
width) + FA
Through via diameter (no plating) (1.6mm thick
board)
Through via diameter (no plating) (2.0 mm thick
board)
Through via diameter (no plating) (2.4 mm thick
board)
Minimum through via hole wall plating thickness
(2)
Dielectric thickness (HDI blind microvia layer)
External Cu foil thickness
Minimum blind microvia hole plating thickness
Minimum buried microvia hole plating thickness
Minimum buried via hole wall plating thickness
Buried via diameter (no plating)
(1)
Buried via land size = (o + 2x annular ring) + FA
Buried via core thickness (excluding outermost
conductors)
Buried via Cu foil thickness (outermost layer)
Core board thickness (excluding conductors)
Staggered via pitch
100 μm
180 μm
100 μm
75 μm
120 μm
100 μm
75 μm
100 μm
100 μm
200 μm
150 μm
100 μm
125 μm
125 μm
125 μm
125 μm
100 μm
75 μm
100 μm
100 μm
75 μm
75 μm
75 μm
75 μm
250 μm
200 μm
150 μm
300 μm
250 μm
200 μm
350 μm
300 μm
250 μm
25 μm
70 μm (1080)
18 μm (1/2oz)
25 μm
70 μm (1080)
12 μm
25 μm
55 μm (106)
12 μm
100 μm
75 μm
<75 μm
18 μm (1/2oz)
12 μm
12 μm
d
s
t
e
f
g
h
h
h
i
j
k
m
m’
n
o
p
q
r
u
(1)
(2)
FA = Fabrication allowance which considers process variations required to fabricate printed circuit board.
Measured from top surface of layer 2 Cu to bottom surface of Layer 1 Cu
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31
Zot Printed Circuit Guide
Design rules
• Always aim for symmetrical build-ups even if μvias not are needed on both sides.
• Aspect ratio on blind hole should be kept well below 1:1, preferred 0.7:1
• When using 2 levels of μvias, keep the copper balance good, fill out empty areas with ground plane,
so the amount of resin is enough to make a good encapsulation of the tracks.
Example of to high aspect ratio on μvia
Design rules - HDI plus 1
No
A
B
C
D
Description
Entry Pad Size
Microvia size
Dielectric Thickness
Capture Pad Size
Recommended
300um
100um
60-80um
300um
www.zot.co.uk
Capability
250um
100um
60-80um
250um
Remark
L1
STD
STD
L1
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Zot Printed Circuit Guide
Design rules - HDI plus 2 (staggered µvia)
No
A
B
C
D
E
Description
Entry Pad Size
Microvia size
Dielectric Thickness
Capture Pad Size
Microvia pitch
Recommended
300um
100um
60-80um
300um
400um
Capability
250um
100um
60-80um
250um
350um
Remark
L1
V1-2 & V2-3
L1-L2 & L2-L3
L2 & L3
STD
Design rules - HDI plus 2 (stepped µvia)
No
A
B
C
D
E
F
Description
Microvia size
Microvia size
Dielectric Thickness
Capture Pad Size
Entry/Capture Pad Size
Entry/Pad Size
Recommended
200um
100um
60-80um
300um
400um
400um
Capability
200um
100um
60-80um
250um
350um
350um
Remark
V1-2
V2-3
L1-L2 & L2-L3
L3
L2
L1
Design rules - HDI plus 2 (stepped µvia)
No
A
B
C
D
E
Description
Microvia size
Entry pad size
Dielectric Thickness
Capture Pad Size
Anti-Pad Size
Recommended
200um
100um
60-80um
300um
400um
www.zot.co.uk
Capability
200um
100um
60-80um
250um
350um
Remark
V1-3
L1
L1-L3 max
L3
L2 min
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Zot Printed Circuit Guide
Design rules - HDI plus 2 (stacked µvia)
No
A
B
C
D
Description
Entry pad size
Microvia size
Dielectric Thickness
Capture Pad Size
Recommended
300um
200um
60-80um
400um
Capability
250um
200um
60-80um
350um
Remark
L1
V1-2 & V2-3
L1-L2 & L2-L3
L2&L3
µvia between L2- L3 need to be copper filled
µvia between L2- L1 optional to be copper filled
Design rules - HDI plus 2 (µvia on buried pad)
No
Description
Recommended
A
Entry pad size
300um
B
Microvia size
200um
C
Dielectric Thickness
60-80um
D
Capture Pad Size
400um
E
Buried Hole size*
300um
*Core thickness dependant, see above for aspect ratio
Capability
250um
200um
60-80um
350um
200um
Remark
L1
V1-2
L1-L2
L2
Note:
a. Always keep dielectric spacing for blind vias as low as possible ;
1 x 106 prepreg (54 micron) or 1 x 1080 prepreg (70 micron) are the best for manufacturing, to
increase reliability and reduce cost.
b. Maximum Sequential Pressing = 4 pressing Cycles.
c. Blind microvia can be copper filled or resin filled and copper plated over, please ask for
details.
www.zot.co.uk
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Zot Printed Circuit Guide
Via in PAD Technology – Copper Filled Microvia
With the ever increasing miniaturisation of components, and the need to put more in a smaller
space, we have commissioned a process, which can fill microvias with copper to plate them shut.
Using Vias in pads on BGAs without
plating them shut can lead to voids in
the solder joints
This technology is typically used in BGAs to put the via in the pad enabling greater routing of signal
tracking, and removing the problem of voids in the solder joint caused by air entrapment during the
printing of solder paste, that could be trapped in the non-filled via.
What Via configuration can we copper fil.
In order to plate vias shut, the via needs to be no more than a certain depth drilled and no more than
a certain diameter, in order not to overplate the outerlayer circuitry.
It is possible to plate shut other depth/diameters, however we would then need additional
planarization processes to reduce outerlayer copper weight for etching the final circuit pattern.
Created by
Outer Copper
Drill Size
Hole Diameter - Top
of Tapered Holes
Drill Depth
1*106
1*1080
2*106
12
12
12
120
150
200
105
116
170
85
100
140
132
2*1080
12
250
185
170
Copper Via
Fill
Dielectric (micron)
55
70
100
Default
YES
Possible
Reduced yield
Increase cost
Possible
Reduced yield
Increase cost
Larger dielectrics are possible to copper fill, please
ask for advice
Definition of a Plated Shut Via.
We define a plated shut via, as having a dimple less than 10 microns.
www.zot.co.uk
35
Zot Printed Circuit Guide
Zot IPC 4761 Via Plugging Guide
IPC-4761 - Summary of Specification
IPC-4761 reflects IPC's work towards standardizing the via plugging process. To summarize, this document
classifies 7 different types of via plugs. Two of these are dedicated to the use of dry film soldermask, which now
has only limited usage and applications.
From what we know, this usage is primarily limited to older military applications. The remainder, we would
separate between via plugging and Via-in-Pad as these two types of via plugs serve very different purposes.
Historically, and even continuing to today, the requirement for via plugging in designs has simply been called out
as "via must be plugged", with some diligent designers calling out that they must be plugged with an epoxy.
Overall, this is a very ambiguous callout that IPC-4761 serves to lend discipline and clarity to.
Here's a summary of the different types of via plugs called out in this document:
Photographic Examples of Various Types of Via Plugging
Since we are a provider of commercial printed circuit boards, we most often encounter the middle grouping of
via plug types (III, IV, V, & VI), which we be the focus of this article. Reviewing the IPC 4761 document from Type
III through Type VI, I can't help but think that this is somewhat of a dangerous document. Based on my
experience in plugging vias, I would say that types III and IV are nothing but an incremental step on the way to
achieving a Type V or VI via.
Now, it's very easy to look at a cartoon picture and say "That's what I want!" and include that in your fabrication
notes. It's whole other story when you actually have to achieve in real life what the nice cartoon depicts. With
larger via sizes (0.016" and up) in a 0.062" typical thickness PCB, achieving a Type V or VI via plug is not too
difficult--though still time consuming. However, trying to screen a low shrinkage ink into a 0.012" via (and often
down to 0.008") and fill it entirely is a much more difficult target to hit. Given the difficulties in achieving a Type
VI(b) via fill, IPC should almost create a Type VI(c), which depicts the attempt at a Type VI in which the plugging
ink only fills a portion of the via, and the rest of it is filled with soldermask. While this may not be technically
correct, I would wager that this is what most actual boards look like given the difficulty in achieving a full plug.
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36
Zot Printed Circuit Guide
Assuming that my statement is correct in that typical Type VI via fills come out as per the above depiction, it
would be worthwhile for
IPC to generate tests of this outcome for long-term reliability.
Via Plugging Process Description
The primary challenge is trying to force the required volume of ink into that small of a hole. To get a better
understanding of the challenge, it is important to understand the process by which the ink is applied. The fisrt
step is to create a screen through which the plugging ink is passed into the hole. The screen is prepared by
applying an emulsion over the entire working area. This emulsion is a photoimageable ink that reacts to UV light.
We then image the emulsion with a dot pattern that replicates the locations of the vias to be plugged. Once
imaged and developed, the emulsion will remain in all areas in which plugging ink is not required. The areas over
the vias will be free of emulsion ink, allowing a path through which the ink can travel through the screen and
into the vias.
The total thickness of the screen is typically 0.004". Including the emulsion, the total may be approximately
0.006". Each stroke of the squeegee will theoretically push this thickness of plugging ink into the hole. Therefore,
if this assumption holds true, then a minimum of 10 strokes will be required to fill a hole in a panel thickness of
0.062". In practice, we have seen smaller vias holes (e.g., 0.012" and smaller) require up to 20 strokes and even
with this we have found that not all vias are fully plugged.
In summary, requiring a Type V or VI fully plugged via can add significant cost to cover both labor & machine
time, as well as fallout at both the fabricator and end user should the PCBs be rejected for not achieving a full
plug.
This begs the question, "Why do I need a fully plugged via?"
Concerns Over Type III & IV Via Plugs
The IPC-4761 document takes the opportunity to explain why one should be concerned over each time of via
plug. They do also make a note on Type V and VI via plugs in that there should be a concern in the complexity of
obtaining a complete fill. There must have been a PCB fabricator on the committee who spoke up.
However, I'll take this opportunity to address the concerns listed over solely the Type III & IV via plugs and
attempt to alleviate those. Important note: I will focus on the effect of the concern in the end, deliverable
product.
Concern 1: Via plug should not be used with bare copper hole walls
Why not? This is one of the fundamental issues I have with certain specifications. It would be ideal to know why
or why isn't a particular feature good for a PCB. Other times it would be great to know what testing or test
results lead to a particular specification. In this case, I would argue that a via that is plugged only from one side
would result in the exposed copper being coated with the final finish. Often, if this particular feature type isn't
compatible with a final finish, it will result in other rejectable anomalies such as exposed copper on the surface
due to skip plating.
In the cases where the plug is from both sides and you have exposed copper in the barrel, the concern is,
understandably, oxidation of the plated hole wall resulting in a latent failure. My experience so far is that surface
copper is covered with either soldermask or a plating to keep the copper from being exposed to air. In the case
of a 2-sided plug, there would be air in the via, but it would be stagnant. My question to the IPC board would be
"Is there a diminished impact of the air trapped in the via as opposed to constantly replenished air against
copper?". I think it would be great if they came up with a test for this. One idea would be to create a daisy chain
coupon with a 2-sided plug and measure the resistance at start. Then you could either thermal cycle or keep at
high temperature / high humidity and measure at 250-hour increments. Any vias that cause a change in values
can then be cross sectioned to determine if the root cause of failure was oxidation of the hole wall.
www.zot.co.uk
37
Zot Printed Circuit Guide
Concern 2: Outgassing / Blow-Outs
Agreed. But this is a failure mode that the bare board would be rejected for. If the PCB has a HASL finish, then
any outgassing concerns would be evident on the bare board as the thermal shock in this process is much
greater than that incurred during PCB assembly. If it survives this process, then it should be considered rugged
enough to last for the rest of the product's life cycle. Furthermore, if there is a conformal coating / potting
process during final assembly, then concerns of exposed copper potentially do not apply. However, this may still
be a concern for non-HASL finishes. In any event, this should be pointed out in the IPC document and not for the
user to discern.
Concern 3: Removal of chemistries
The concern here is that the higher the aspect ratio, the more concern there should be of the removal of
chemistries. Agreed. However, this is a bare board concern. Dragging chemistries from one bath to another in
most immersion processes results in "skip plating", which manifests itself in exposed surface copper. This is a
rejectable PCB characteristic and would never make to the finished product anyway. In the case of a HASL finish,
the only chemistries the board should see after the plugging process should be RO Water, which is typically dried
out in final washing. Again, it would be great to know exactly which chemistries are of concern so that PCB
fabricators can work together with their customers to alleviate.
Summary
In summary, while I think this standard did a great job of explaining the differences between the types of
available via plugging, I think it needs more work to really define to the end user when each type of plug should
be allowable or not. Also, there should be cross qualifications (e.g., a type VI backward qualifies as meeting Type
III or IV, etc.). If there's anyone out there willing to put together the testing methodology, I'm more than happy
to build the test vehicles.
www.zot.co.uk
38
Zot Printed Circuit Guide
Overview of Outer layer Circuit Pattern
C
A
B
A
B
F
I
D
G
H
E
L
J
Features
K
Dimensions
Standard Production
Prototype/Development
Via Pad / Line Spacing (min)
0.100mm
0.075mm
Solder Mask Clearance (min)
0.075mm
0.037mm
Solder mask Dams (min)
0.075mm
0.050mm
Via Pad Size
0.350mm
0.250mm
Via Hole Size (min)
0.200mm
0.150mm
Line Spacing (min)
0.100mm
0.075mm
Line Width (min)
0.100mm
0.075mm
SMT Pad Spacing (min)
0.250mm
0.175mm
SMT Pad Width (min)
0.200mm
0.175mm
Solder mask Dams (min)
0.075mm
0.050mm
BGA Pad Size (min)*
0.600mm
0.550mm
BGA Hole Size (min)*
0.300mm
0.250mm
A
B
C
D
E
F
G
H
I
J
K
L
*BGA Via in Pad
www.zot.co.uk
39
Zot Printed Circuit Guide
Overview of Inner layer Circuit Pattern
E
A
F
G
B
C
D
Dimensions
Features
Standard
A
B
C
D
E
F
G
H
H
Pad edge-to-Pad edge Spacing (min)
Line Width (min)
Line Spacing (min)
Via Pad / Line Spacing (min)
Pitch of Vias (min)
Pitch of Vias (min) 1 Track between
Pitch of Vias (min) 2 Tracks Between
Track to Hole (min)
www.zot.co.uk
0.100mm
0.100mm
0.100mm
0.100mm
0.588mm
0.733mm
0.965mm
0.30mm
Prototype /Development
0.075mm
0.075mm
0.075mm
0.075mm
0.381mm
0.533mm
0.685mm
0.15mm
40
Zot Printed Circuit Guide
Standard Multilayer Builds
The following pages, the figures we use for prepreg thicknesses & the standard constructions we use,
where the Customer does not specify the build. Builds are shown to 12 layer, we are British Standard
BS EN123000 approved to 24 layer.
If the Customer specifies the build then we will use that build.
When specifying the build the Customer should specify the Dielectric Thickness, between the layers,
and the copper weight on each layer, as well as other critical information such as laminate
type/grade, Tg, Td, Z expansion etc..
If the product is Controlled Impedance we will be analysing the build using our Controlled Impedance
Software to establish that the right values have been designed into the build, if we find it is incorrect,
then we will contact the Customer and make them aware of this.
Dielectric Spacing
When a customer states a dielectric spacing between layers, this is achieved by the following use of
prepreg mixes.
Grade
Inches
Metric
106
0.002"
0.055mm
Dieletric Thickness
Required
60 micron
80 micron
100 micron
120 micron
160 micron
180 micron
200 micron
240 micron
250 micron
260 micron
280 micron
300 micron
320 micron
340 micron
350 micron
380 micron
400 micron
1080
0.0025"
0.070mm
2113
0.0035"
0.09mm
2116
0.0045"
0.115mm
7628
0.007"
0.175mm
1st Option
2nd Option
1x1080
1x2113
1x2116
2x1080
1x1080 and 1x2116
2x2113
1x2116 and 1x2113
1x2116 and 1x2165
1x7628 and 1x2113
1x7628 and 1x2113
1x7628 and 1x2116
2x2116 and 1x2113
2x2116 and 1x2113
3x2116
2x7628
1x7628 and 1x2116 and 1x2113
1x7628 and 2x2116
None
None
1x1080 and 1x106
1x2165
1x7628
1x7628
1x2165 and 1x2113
2x2113 and 1x1080
3x2113
3x2113
2x2113 and 1x2116
1x7628 and 1x2165
2x2165 and 1x1080
2x2165 and 1x2113
4x2113
3x2165
2x2113 and 2x2116
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Zot Printed Circuit Guide
Default Multilayer Build Constructions
Where a multilayer build is not specified, we default to the most cost effective construction. ( combination of
prepregs and cores )
Our Standard defaults builds are 1.60mm thick, with 35um internal copper and 35 um finished external
copper.
Cost effective construction can only be used where there is sufficient prepreg available to encapsulate the
innerlayer tracking.
Importance of Prepreg Selection
The function of the prepreg is to provide an insulation layer and fully encapsulate the innerlayer copper.
Insulation (Dielectric Breakdown)
The actual dielectric breakdown is typically 1,000 volts per 1 thou ( 25 microns ) of Prepreg
This means that was use a minimum of 100 um of prepreg, breakdown is 4,000 volts plus.
With some constructions using a lot more, values are typically 40 volts per Micron of prepreg.
Encapsulation of Innerlayer Tracking
Prepreg prior to pressing is basically a glass cloth impregnated with a B stage epoxy resin which is then heated
to a liquid state under pressure, this then encapsulates the innerlayer tracking, however it must be
remembered that all prepreg styles have different thicknesses and resin percentages, and circuit patterns
have different amounts of areas to be encapsulated with the resin.
The actual resin when liquid does not move very far, so "AVAILABLE RESIN " is a major issue to good
encapsulation of innerlayer patterns.
Typical Prepreg Resin % are as follows
Style
106
1080
2113
2116
7628
7628HR
Pressed
Thickness
0.050mm
0.066mm
0.090mm
0.115mm
0.175mm
0.200mm
Resin
%
75.00%
61.00%
56.00%
53.00%
42.00%
48.00%
Cost
+76%
Base
+14%
Base
+12%
+20%
As you can see 106 are the thinnest and most expensive, typically this should only be used when you are trying
to create a high layer count in a thin construction or when “available resin” is a major issue.
As you can also see 2116 is just under twice the thickness of 1080, but they are the same price, and the
“available resin “ is similar.
Although 7628 or 7628HR ( HR = high resin content ) is by far the most cost effective prepreg, it has the lowest
available resin.
4 Layer
6 Layer
Separation
Ly1 – Ly2
No
Issue
< 25%
Copper Area
8 Layer
< 25%
Copper Area
10 Layer
No
Issue
12 Layer
No
Issue
Separation
Ly3 – Ly4
No
Issue
<126%
combined
Copper Area
<126%
combined
Copper Area
<44%
combined
Copper Area
<44%
combined
Copper Area
Separation
Ly5 – Ly6
Separation
Ly7 – Ly8
Separation
Ly9 – Ly10
Separation
Ly11 – Ly12
< 25%
Copper Area
<126%
combined
Copper Area
<44%
combined
Copper Area
<44%
combined
Copper Area
www.zot.co.uk
< 25%
Copper Area
<44%
combined
Copper Area
<44%
combined
Copper Area
No
Issue
<44%
combined
Copper Area
No
Issue
42
Zot Printed Circuit Guide
Zot Engineering Ltd - Laminate Grading for Lead Free Soldering
Material
Tg
Z
Expansion
Td
T260
T288
Dicy Cured Fr4
<140°C
4.10%
300°C
5 mins
0 mins
Std FR4
De104i
140°C
130°C
4.10%
3.20%
300°C
340°C
5 mins
>60 Mins
0 mins
>10mins
VT-481
IS410
150°C
170°C
2.5%-3.1%
3.50%
345°C
350°C
>60 Mins
>60 Mins
>10mins
>10mins
VT-47
N4000-29
370HR
175°C
180°C
180°C
2.2%-2.8%
3.00%
2.70%
345°C
350°C
350°C
>60 Mins
>60 Mins
>60 Mins
>10mins
>10mins
>10mins
R1566
150°C
2.40%
330°C
>60 Mins
>10mins
The above laminates have the ability to withstand Lead Free Assembly Soldering Processes.
Different characteristics of the laminate affect its ability to withstand assembly processes.
A combination of the above parameters gives the laminate its final Lead Free grading.
Standard – Dicy Cured
This is where the customer specifies dicy cured (non lead free laminate) as the laminate requirement
Standard FR4
This is used where the customer only states Fr4 as the laminate requirement, in these cases the material used,
may be upgraded.
Tg
Z Expansion
Td
T260
T288
N/A
<=4.1%
Td >=300c
T-260 >=5mins
T-288 >= 0 mins
Lead Free Laminate Low Technology
This is where the customer states RoHS compliant, Lead Free Laminate, this is selected as the starting level.
Ability to withstand up to 3 Lead Free Cycles
Tg
Z Expansion
Td
T260
T288
N/A
<=3.8%
Td >=330c
T-260 >=60mins
T-288 >= 10 mins
Examples of Laminate type are 104-TS, R1755, VT-481
Lead Free Laminate Medium Technology
Ability to withstand up to 4 Lead Free Cycles
Tg
Z Expansion
Td
T260
T288
N/A
<=3.5%
Td >=330c
T-260 >=60mins
T-288 >= 10 mins
Examples of Laminate type are IS410, VT-481
Lead Free Laminate High Technology
Ability to withstand up to 6 Lead Free Cycles
Tg
Z Expansion
Td
T260
T288
N/A
<=3.0%
Td >=330c
T-260 >=60mins
T-288 >= 10 mins
Examples of Laminate type are IS420, 370HR, R1566, and N4000-29, VT-47
Notes
1. This is a guide only, users of these materials, are advised to carry out their own analysis, to ascertain the
ability of the laminate to withstand their assembly processes.
2. The Tg does not play a significant role in the ability of the laminate to withstand the Lead Free
soldering process, therefore we have not included this as a Critical factor. Tg is only critical in
high temperature operating conditions, such as engine management etc…
3. Customers are requested to specify performance characteristics, rather than specific laminate type when
ordering boards from Zot Engineering.
It is worth noting that all laminates are RoHS and WEE Compliant
www.zot.co.uk
43
Zot Printed Circuit Guide
IPC Specification for Base Materials for
Rigid and Multilayer Printed Boards – IPC
4101B
This specification covers the requirements for base materials (laminate and prepreg) to be used
primarily for rigid or multilayer printed boards for electrical and electronic circuits. This
document contains more than 50 separate specification sheets and now uses search terms to
allow the user to find similar groups of materials from these specification sheets. This standard
provides the user with additional information and data on printed circuit board materials that
are better able to withstand the newer assembly operations employing higher thermal
exposures, including those assembly practices that utilize the now commonly-encountered lead
free solders.
Y
De104i
IS410
IPC4101B/129
IPC4101B/128
IPC4101B/126
IPC4101B/121
Y
Y
Y
Y Y Y Y Y
Y
R1755
VT-481
IPC4101B/101
IPC4101B/99
IPC4101B/98
IPC4101B/97
IPC4101B/94
IPC4101B/83
IPC4101B/42
IPC4101B/41
IPC4101B/40
IPC4101B/30
IPC4101B/29
IPC4101B/28
IPC4101B/ 26
IPC4101B/25
IPC4101B/24
IPC4101B/ 21
For the following materials, please see the IPC4101B/ No. Primary in Blue
Y Y
Y Y
Y Y
Y Y
Y
R1566
Y Y
Y Y
370HR
VT-47
Y
Y
Y Y
N4000-29
Y
Y Y
Y
Y
Y
IS420
Y Y
Y
Y Y Y Y
Y
Y
Y Y
Y
Y
De156
N4000-7
Y
Y Y
N4000-11
Y
Y
Y Y
Y
Getek
Y
IS620
Y Y Y
Y Y Y
Y Y Y
P95/P25
P96/P26
N7000
N4000-13
Y
Rogers 4003 = IPC-4103/10, Rogers 4350 = IPC-4103/11, Espanex = IPC-4204/11 Dupont = IPC-4204/11
Where customers do not specify IPC-4101 slash no.s or other performance or material requirements
requirements, we adopt our internal grading system.
www.zot.co.uk
44
Zot Printed Circuit Guide
Complex Printed Circuits
How are these made
At Zot we manufacture from the smallest simplest 1 layer single sided board to complex large
20 layer plus boards with multiple ball grid arrays etc…..
It is obvious that the simplest of pcb manufacturing processes can produce simple single sided
boards, however in order to manufacture large complex 20 layer plus designs, we need to ensure
that we are using state of the art advanced manufacturing equipment and production
techniques.
All products manufactured by Zot, are initially engineered for manufacture, and grouped into
levels for manufacturability, which then decides what processes will be applied to what level of
product complexity.
The most accurate system for
imaging printed circuits in the
world
Examples are as follows
Circuit Imaging – Innerlayer and outerlayer
All our circuit layers are imaging using the most accurate and fastest method of producing
circuit layers, this is “ Laser Direct Imaging “(the fastest and most accurate system in the
world), this is an exceptionally accurate method of circuit imaging, it aligns images to less than
25 um in positional accuracy relative to the mean position of the drilled image. At times of peak
loading, the simplest technology are photoprinted, using the conventional pcb imaging process,
but this tends to be standard pcb designs, complex designs are always laser direct imaged on all
circuit layers.
Drilling
Our latest acquisition completes our
strategic purchasing plan to be able to
manufacture H.D.I. printed circuit designs.
Our drill is capable of drilling holes 50um in
diameter to a controlled depth +/- 12um,
using 300,000 rpm spindle. This therefore
guarantees our ability to drill the most
demanding of pcb designs.
www.zot.co.uk
45
Zot Printed Circuit Guide
Via in Pad Fill
With the ever increasing demands on real estate of pcbs, and the miniaturisation of devices, we are
commissioning a via in pad – via fill plating line.
This is especially important when the via in pad, is situated in the centre of a BGA pad. This then
reduces the issues associated with voids created during the assembly process at the BGA bal to
solder paste to pcb pad junction.
Soldermask
There is a limit to what you can successfully soldermask, using standard pcb manufacturing
techniques, this limit is dependant on the size of the board/manufacturing panel in relationship to
the soldermask oversize.
Soldermask oversize, should be initially optimised to ensure most effective over size, this is achieved
by taking the space between the pad and the track that must not be exposed and halving the space(
= soldermask oversize). This is the optimum soldermask oversize to maximise yield.
When this is less than or equal to the following we consider Laser Direct Imaging the soldermask, it
should be noted however that this technique is considerably slower than conventional soldermask
photoprint, and more expensive, but has the greatest possible registration ability.
Process/board dimension
Photoprint Soldermask
Laser Direct Image Soldermask
200mm
>=0.0375mm
<0.0375mm
300mm
>=0.0450mm
<0.0450mm
400mm
>=0.0525mm
<0.0525mm
500mm
>=0.0650mm
<0.0650mm
Before employing LDI ensure soldermask is properly optimised, as most designs do not require the
accuracy of the LDI process.
BGAs can be size for size, but
first optimise soldermasks, before
stating this requirement, as these
must be LDI imaged
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46
Zot Printed Circuit Guide
Electrical Test
Most of our lower qty and complex boards are tested on a soft touch, flying probe tester, the touch is
that soft, it leaves NO test witness mark on the test pad, leading to a pad which can be more
effectively assembled.
Boards shown on left is uBGA, the pitch
between the pads is 250 microns, with 50
micron track and space.
There are no test witness marks as probes
are soft touch and leave NO test mark
With this level of soft touch flying probe
technology, we are future proof, as this
machine can test complex board designs,
that would have 100um pitch bgas.
Multilayer Registration of Layers
Where designs require tighter control of the registration of the innerlayers, we use a
Multiline 4 slot tooling registration system, this gives the best registration of all layers.
This registration is optimised and enhanced further, using a sophisticated software
system linked to all our registration measurement enabled machines. Known as “Xact”
this then measures any misregistration of all inner layers, before drilling this allows
optimum alignment of drilling for optimum registration on all layers. As predictive
tool Xact builds up a database of all materials and builds and allows you to predict
layer stretch and movement, allowing optimum layer adjustment in pre-production
leading to superior registration and ultimately superior final product quality and
reliability.
We employ various production inspection techniques as the complexity of the board increases.
www.zot.co.uk
47
Zot Printed Circuit Guide
Controlled Impedance
We are able to do the following impedance designs, for impedance designs, we create the build,
verify the data, and then calculate the impedance requirements of the copper tracks, and dielectric
requirements.
A coupon is then designed for each impedance track on each layer and then built into and tested on
the production panel.
Examples of Impedance designs are as follows
Outerlayer
Single Ended
Impedance
Innerlayer Single
Ended
Impedance
Outerlayer
Differential
Impedance
Innerlayer
Differential
Impedance
There are many other types of impedance designs (practically 100 designs in total), the
designs shown above are the most common.
www.zot.co.uk
48
Zot Printed Circuit Guide
Multi Copper Weight Technology
A unique solution to the issue with heat and power
With the increasing demands on the printed circuit board for effective heat dissipation and power,
we have developed a process where we can create 2 different copper weights on the outer layer of
the same pcb. Allowing sophisticated circuitry and power/heat dissipation on the same layer, this is
known as MCW ( Multi Copper Weight).
Graphical Representation shown above is not to scale
You can still have 210um innerlayers, with 35um outerlayers, with parts of the outerlayer circuitry
with very heavy copper eg. 300um. The heavy copper areas are part of the circuitry, and can have the
usual plated holes, plated to the requires of IPC.
Example of Board Microsection.
300 um
70 um
35 um
Please Note:
This is dependant on the design of the printed circuit board, and certain design rules
must be applied to enable the use of this selective build up technology.
Please contact us, if you require more information
www.zot.co.uk
49
Zot Printed Circuit Guide
Embedded Resistor Technology
Because of the need to increase the density and reliability of pcb’s, we have commissioned a process
for embedding the resistors as part of the circuitry on the inner and outerlayer circuitry.
OhmegaPly® is a thin film Electrodeposited-On-Copper NiP metal alloy. (RESISTORCONDUCTOR
MATERIAL) that is laminated to a dielectric material and subtractively processed to produce planar
resistors. Because of its thin film nature, it can be buried within layers without increasing the
thickness of the board or occupying any surface space like discrete resistors.
Electrical Advantages
Improved line impedance matching, Shorter signal paths and reduced series inductance, Eliminate the
inductive reactance of the SMT device, Reduced cross talk, noise and EMI
PCB Design Advantages
Increase active component density & reduced form factors,Improved wireability due to elimination of
via.Improved reliability due to elimination of solder joints.
Improved Reliability
Low RTC of <50 PPM, Life testing: 100,000 hours = +2% at 110° C, Stable over wide frequency range: tested
beyond to 20+ GHz, Lead-free compatible
Economic Advantages
Elimination of discrete resistors, Improved assembly yield, Board densification and/or size reduction, Board
simplification (double sided SMT to single sided SMT, potential layer and via count reduction, Deliver tested
board to the assemblers
Minimal Risk
Over 30 years of use, Predictable, Design: Know how to achieve target with simple formula (L/W x Rs), Proven
long term reliability
Resistors could be embedded into the innerlayer circuitry under outerlayer
components
For further information, please contact us.
www.zot.co.uk
50
Zot Printed Circuit Guide
Design Guidelines for Heavy Copper Weights
The two main problems with boards that contain heavy copper weights are the reduction in the track
widths and the encapsulation of the tracks with soldermask on the outer layers, and encapsulation with
resin on the innerlayers.
Heavy Copper weights are those greater than 70 micron
Actions Required : Soldermask
Therefore all copper weights greater than 70 microns should be double coated with soldermask to
achieve a minimum of 50 microns of soldermask on top of the tracks, this also helps with the elevated
soldering temperatures/time, that are used when soldering heavy copper weights.
Actions Required : Legend
Try to keep the legend away from the spaces between tracking as it is difficult to reproduce the text.
Legend can be
imaged on top
of tracks
Try not to have
legend being
imaged here
Opens areas are
no problem to
image legend try
to keep at least 5
mm from
tracking edge
Etch Compensation
When we are processing heavy copper weights we etch compensate the copper image too allow for the
reduction of the pattern during the etching process, the table is as follows
Copper Weight
Minimum
Feature
3 oz ( 105um )
4 oz ( 140um )
5 oz ( 175um )
6 oz ( 210um )
7 oz ( 245um )
8 oz ( 280um )
9 oz ( 315um )
10 oz ( 350um )
0.010”
0.014”
0.018”
0.022”
0.026”
0.030”
0.034”
0.038”
Minimum
Space to allow
for Etch Comp.
0.016”
0.018”
0.020”
0.022”
0.024”
0.026”
0.028”
0.030”
Etch
Compensation
0.010”
0.012”
0.014”
0.016”
0.018”
0.020”
0.022”
0.024”
The Etch Compensation factor is added to ALL copper features, these include ALL pads, Surface
Mount Devices, Lettering etc…
When we receive files for heavy copper weights, we alter the Gerber Files to compensate for the track
reduction.
6 oz Copper
The minimum track width for 6oz micron copper is 0.55mm, which requires a minimum space of 0.55mm
as we need to add 0.40mm for etch compensation which increases the track width to 0.95mm, with a
space of 0.15mm, during etching this returns to approx. 0.55mm track/space.
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51
Zot Printed Circuit Guide
Innerlayer Circuit Patterns with Heavy Copper Weights
With heavy internal copper, we need to restrict the amount of open area of the circuit, this helps with
flatness and with encapsulation of the internal conductors with reson.
Basically we need to add filled planes to areas between tracking, try not to have more than 5mm of open
bare laminate. See Below
This is 5mm gap
This is copper fill
This copper fill is 5 mm from edge of board. This ensures that as much resin as possible can be used to
ensure encapsulation of copper conductors.
Using our available resin calculator, we will establish the % of copper on the internal layer, and ensure
that there is sufficient resin in the prepreg used to encapsulate the internal tracking, these will also be
pressed inside a vacuum press.
We will then simulate the build
in our available resin calculator
which will take into account the
copper thickness, the copper
are, then take the prepreg to be
used to ensure there is
sufficient resin in the prepreg,
to fill the areas between the
tracks/pads.
To ensure maximum resin,
there must be greater than
150% available.
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52
Zot Printed Circuit Guide
Layer count by Thickness
Multilayers can be created in a variety of thickness from 0.20mm to 6.00mm.
It should be noted however that the standard PCB Thickness is 1.60mm up to
Board Type
Single Sided/
Double Sided & PTH
4 Layer
6 layer
8 Layer
10 Layer
12 Layer
14 Layer
16 Layer
18 Layer
20 Layer
22 Layer
24 Layer
Minimum Thickness
0.10mm
Maximum Thickness
6.00mm
Minimum Dielectric
N/A
0.30mm
0.40mm
0.60mm
0.80mm
1.00mm
1.20mm
1.60mm
1.80mm
2.10mm
2.20mm
2.40mm
6.00mm
6.00mm
6.00mm
6.00mm
6.00mm
6.00mm
6.00mm
6.00mm
6.00mm
6.00mm
6.00mm
80 microns
80 microns
80 microns
80 microns
80 microns
80 microns
80 microns
80 microns
80 microns
80 microns
80 microns
Notes
1. It is possible to manufacture thinner pcbs, however there are minimum dielectric concerns,
the minimum dielectric on the above builds is 0.80um and is based on 18um copper,
increasing copper thickness will increase the minimum thickness, especially as the layer count
increases.
2. If you do not have a specific thickness requirement, then inform us of this, and we will ensure
that the board is build with the most cost effective dielectric.
3. The minimum thickness is based on a well balanced design, it may be necessary to add
additional layers of prepreg, if there are large open areas on design, as these will need more
available resin, alternative adding internal supplementary patterns, will increase availability of
resin.
4. Minimum Dielectrics are created by either a 0.080mm core, or by 2 sheets of 106 prepreg,
constructions, came be made thinner, by using 1 sheet of prepreg.
If required, please do not hesitate to contact us, with any issues regarding builds, build thickness ,
dielectric spacing etc……
www.zot.co.uk
53
Zot Printed Circuit Guide
Board Finish
Because of the RoHS Directive (2002/95/EC, effective July 2006), there has been/is a major change in
the Electronics Industry, the predominant finish of Leaded (63/37) HASL, has to be replaced with an
alternative finish that does not contain Lead or any of the other banned substances.( unless your
product is exempt )
First Step towards Lead free Soldering and Ultimately RoHS Compliance
The first step we would suggest is to change the finish from Leaded HASL to one of the following
finishes.
The following graph shows how we and our customers have changed from the predominant Leaded
HASL finish to Lead Free HASL finish.
This is for all products, as you can historically HASL finish was approx. 80% of our board finish, with
the introduction of the RoHS directive, a large portion of our customers, have had to change board
finish, from the non RoHS compliant finish to another finish, most have changed from Leaded HASL
to Lead Free HASL.
Since January 2005, ( this was the point we started to look at the RoHS directive ), we have shipped
3,000,000 circuits, over 1,000,000 of these were Lead Free HASL.
% Circuits by Finish
100%
90%
LEAD FREE HASL (
SN100CL )
80%
Imm. Tin
60%
Imm. Silver
50%
Imm Nickel Gold
40%
H.A.S.L.
30%
All Over Gold
20%
10%
03/2009
02/2009
01/2009
12/2008
11/2008
10/2008
09/2008
08/2008
07/2008
06/2008
05/2008
04/2008
03/2008
02/2008
01/2008
12/2007
11/2007
10/2007
09/2007
08/2007
07/2007
06/2007
05/2007
0%
04/2007
Percentage
70%
Month
% BGAs by Finish
All Over Gold
2.4%
Imm Nickel Gold
71.7%
Imm. Silver
14.3%
LEAD FREE HASL ( SN100CL ) 11.5%
Total:
100.0%
As you can see, all finishes
have boards produced
with BGAs, however by
far the most popular is
Electroless Nickel/
Immersion Gold.
Sum of SOrderDetail.CircuitQuantity
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Zot Printed Circuit Guide
Board Finish Property Table
Property
Thickness
Hot Air
Solder
Level
(Reference
Purposes)
<20um
Hot Air
Solder
Level –
Lead
Free
<15um
Immersion
Silver
Immersion
Tin
Electroless
Nickel
/Immersion
Gold
All Over
Electrolytic
Gold/Nickel
0.15um0.40m
0.50um –
1.50um
Nickel : 3um7um
Gold:0.040.10um
Flat
Ni: 3um-7um
Gold : 0.50um
– 5.0um
Topography
Not Flat
Not Flat
Flat
Flat
Solderability
Solder Joint
Shelf life
Very good
Cu - Sn
18 mths
Very Good
Cu - Sn
18 Mths
Good
Cu - Sn
6 - 12 mths
Very Good
Sn - Ni
24 months
Very Good
Sn – Ni
24 months
0.5mm /
0.020"
Good
Poor
0.5mm /
0.020"
Good
Poor
Any
Good
Cu - Sn
6 - 12
months
Any
Any
Any
Very Good
Good
Good
Good
Very Good
Excellent
Very Good
Excellent
No special
Handling
Low
Good
No special
Handling
Low
Good
Handle with
care
Medium
Good
Handle with
care
Medium
Excellent
No
No
No
YES
Al & Au
YES
No
YES
Handle with
care
High
Not
recommended
Al
YES
Handle with
care
Very High
Not
recommended
Al
YES
Environmental
Issues
YES
No
No
YES
No
No
Zot Preference
1
1
2
3
4
5
Min. SMT Pitch
Ionic Cleanliness
Fiducial
recognition
Handling
Cost
Press fit
connections
Wire bonding
RoHS compliant
Flat
Notes
1. Zot Preference : shown in order of cost, 1 being lowest, and in order of RoHS Compliant replacement
2. In house :We produce all of the above finishes in house & are measured by XRF Fluorescence
3. Boards Containing BGAs (Ball Grid Arrays) : Because of the flatness issues with HASL finishes and
the possibility of ball grids being required to be removed/reworked, we would suggest using one of the
immersion finishes.
4. Hand Soldering: It is worth noting that a lot of today’s boards are still hand soldered, this obviously
leads to a lot of handling, immersion finishes require a far greater degree of control over handling
procedures. Leaded HASL still requires control but is far more resilient to handling
Our Recommendation
Nothing solders like solder, it is the most cost effective finish we produce. Therefore we would suggest
that anyone who previously used Leaded HASL, should select the replacement of Lead Free HASL, it
performs the same, looks the same, it’s the same cost, and it is a backward compatible RoHS compliant
finish.
www.zot.co.uk
55
Zot Printed Circuit Guide
Premium Delivery - Ready for Despatch Calculator
The following tables represent, when a job is planned to be ready for despatch.
This is dependant on the time of day the files and order is received as well as the service requested
Please note the following
1. Sameday Service ( less than 24 hours ) by special arrangement
2. Normal Premium service is for files & order received before 3pm
for that day to count
3. This is only a guide, as actual ability to achieve required service is dependant on the size of the job.
Order and data received
between
Friday post 9am >
Monday Pre 11am
Monday post
11am > Tuesday
Pre 11am
Tuesday post
11am >
Wednesday Pre
11am
Wednesday post
11am > Thursday
Pre 11am
Thursday post
11am > Friday
pre 9am
delivery is one day after
despatch
Courier Despatch
Courier Despatch
Courier Despatch
Courier Despatch
Courier Despatch
1 day service
Tuesday 17:00
Wednesday 17:00
Thursday 17:00
Friday 17:00
2 day service
Wednesday 17:00
Thursday 17:00
Friday 17:00
3 day service
Thursday 17:00
Friday 17:00
4 day service
Friday 17:00
5 day service
6 day service
7 day service
8 day service
Standard Sevice
(W2)Monday
17:00
(W2)Tuesday
17:00
(W2)Wednesday
17:00
(W2)Thursday
17:00
(W2)Monday
17:00
(W2)Tuesday
17:00
(W2)Wednesday
17:00
(W2)Thursday
17:00
(W2)Friday 17:00
(W2)Monday
17:00
(W2)Tuesday
17:00
(W2)Wednesday
17:00
(W2)Thursday
17:00
(W2)Monday
17:00
(W2)Tuesday
17:00
(W2)Wednesday
17:00
(W2)Thursday
17:00
(W2)Monday
17:00
(W2)Tuesday
17:00
(W2)Wednesday
17:00
(W2)Thursday
17:00
Premium
Rates
100%
80%
70%
60%
(W2)Friday 17:00
50%
(W2)Friday 17:00
Monday 17:00
40%
(W2)Friday 17:00
Monday 17:00
Tuesday 17:00
30%
Monday 17:00
Tuesday 17:00
Wednesday
17:00
20%
Order confirmation and data must be received before 11 am on day 1, for standard sevice.
(W2) = Following week
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56
Zot Printed Circuit Guide
Delivery Service to Board Construction Type
The following service to layer construction is based on small to medium qty, for an exact
determination of minimum lead time, please contact us, as this is also dependant on production &
tooling loading at time order is placed
This is only a guide, as actual ability to achieve required service is dependant on the size of the job
48 Hr Service
72 Hr Service
5 Day Service
7 Day Service
Standard Service
1 & 2 Layer
4 Layer
6 Layer
8 Layer
10 Layer
12 Layer
14 Layer
16 – 20 Layer
20 – 24 Layer
Flexible
Flexi-Rigid
Blind uVia
Blind/Buried uVia
Sequential Build
24Hr Service
Construction
Type
Sameday Service
Service Type
Yes
Yes
Yes
No
No
No
No
No
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
10 Days
10 Days
10 Days
10 Days
10 Days
10 Days
10 Days
15 Days
15 Days
15 Days
15 Days
15 Days
15 Days
15 Days
Service also being dependant on material availability, we stock approx. £200,000 of laminates &
prepregs. So under normal material requirements, materials should be in stock
The following finishes / additional coatings are all produced in house and do not add to lead time
Leaded HASL, Lead Free HASL, Electroless Nickel Immersion Gold, Immersion Tin, Immersion Silver,
Edge Gold contacts, All over deep gold plated.
Peelable Soldermask, Carbon Ink, MicroVia drilling, Copper filled Vias, Embedded Resistors
www.zot.co.uk
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Zot Printed Circuit Guide
Effective Panelisation & Cost Reduction
The material that printed circuits are manufactured on, is an expensive laminate, it is
important that the most is made of this by effective panelisation.
In purchasing larger quantities of board, one of the most effective methods to reduce board cost (
and we are always looking at this ), is to ensure that we are effectively using the manufacturing panel
that the board is being manufactured on.
A 1 mm decrease on your carrier, can have a substantial effect on the price of the board.
Remember you are not buying circuits you are buying the manufacturing panel, that the board is
being made on, ensure you are maximising this.
Ineffective Use of PCB Manufacturing Panel
This is poor Carrier utilisation, the carrier and the boards on the carrier are not effectively using the
working area of the panel
Cost Effective Use of Manufacturing Panel
The following carrier panelisation is a far more effective use of this carrier, by fitting in more circuits
per carrier, you get the a substantial reduction in board cost.
! Remember you are paying for the utilisation of the manufacturing panel !
This has a profound affect on the price of your boards.
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Zot Printed Circuit Guide
Effective Panelisation
Effective Working Areas of panel sizes and examples of effective good carrier sizes.
All our standard panels, are a 100% utilisation from the sheets that the laminate suppliers produce,
in pcb production we have extra tooling and test coupons added to panels, however it is still possible
to get 80% effective utilisation of the pcb manufacturing panel
Panel Size
S/Sided, PTH
Multilayer
Resin Filled, Blind & Buried,
Working Area
working Area
Impedance
working Area
18” x 12”
16.81” x 10.81
16.81” x 10.25”
14.0” x 8.0”
18” x 16”*
16.81” x 14.25”
14.0” x 12.0”
24” x 12”*
22.81” x 10.25”
20.0” x 8.0”
24” x 18”
22.81” x 16.81”
22.81” x 16.25”
20.0” x 14.0”
*Multilayer only
The above is to give you an approximation, for exact utilisation of your design contact us
It must be noted that the size of the circuit/carrier, the router cutter size, the complexity of the
board, the shape of the board, whether it is scored or not affects the actual working area.
Obviously as an assembler you do not want the carriers to large ( difficult to assemble )or too small
(costly to assemble), as a PCB Manufacturer, we do not want to large a carrier, as this greatly
increases the possibility of scrap in the carrier ( very dependant on complexity of board design).
Examples of Effective carrier sizes
If you are going to standardise your assembly process on standard carrier panelisation, we strongly
recommend you speak to us to ensure that your standard panelisation is an effective use of our
standard panels.
www.zot.co.uk
59
Zot Printed Circuit Guide
Default Specification
We supply to a vast range of companies, from very large OEM/CEM to very small ( and
just as important ) users of printed circuits.
Because not all of our customers fully understand the various specifications regarding
print circuit boards, we have a standard set of defaults.
If you do not specify the following requirement, we will quote/manufacture using the
following. This will be stated on the quotation.
Board Thickness = 1.60mm +/- 10%.
Laminate Type = First Grade Lead free Compatible Laminate
Copper Weight = 35um Inners and Outers
Build = Zot Standard Build ( can be altered dependant on board design )
Soldermask Colour = Green
Legend Colour = White
Single Circuits ( unless requested by default to panelise or panelisation requested )
Finish = Lead free HASL
Edge Gold Finger plating = Minimum of 1.50um, Nickel minimum of 3um.
Inspection to I.P.C. 600 Class 2.
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60
Zot Printed Circuit Guide
Soldermask for Gold Edge Connectors
Below shows an edge connector, and what to avoid.
The desired design is to have the soldermask up to the edge connector, with at least 0.050” from
top of fingers to pads free of soldermask, to allow for masking
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Zot Printed Circuit Guide
Legend Best Practice Fact Sheet
Attribute: Legend Clearance from Copper Pad.
The printed circuit imaging processes require a tolerance on their relative positions from each layer to each layer. The
placement of the legend relative to the circuit and soldermask is one of these processes, there has to be (where possible)
sufficient clearance to allow for slight misregistration (legend is typically registered with 0.004” (0.10mm) of relative
position) of these layers relative to each other, whilst still producing a quality product. However it is possible if the circuit
is slightly misregistered in the +X direction and the legend could be misregistered in the –X direction, potentially causing
legend on the pads.
Unless otherwise stated, the legend files should be amended (clipped) to remove the possibility of legend on the copper
pad. Legend/Annotation is like soldermask, if it is on the solderable pad area, then it cannot be soldered. The following is
an example of legend design. If possible keep the legend markings as far as possible from the copper pad.
The three examples shown have the designed clearance with 100um misregistration
The following is an example of insufficient clearance - As you can see from the 3 examples, when the legend is size for
size there is a strong likelihood of legend on the pads, and the picture above shows a 100um misregistration on the
legend only.
Pink is overlap
of Legend on pad
The following shows what is the desired minimum ( 100um clearance) - even with a very small oversize of 0.10mm it
creates a condition where the legend can be misregistered and there is no legend on the pad
No Legend on pads
The following shows the Target condition – (150um Clearance )
0.002” clearance
from copper
The minimum line on a legend is 0.005” (0.125mm), although, line widths of 0.003” can be produced, however it is
difficult to read such fine lined text.
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Zot Printed Circuit Guide
Adding Tear Drops to Pad/Track Intersection
With up to 250,000 internal connections in a multilayer, with some of the tracks intersectioning the
pad being only 80um x 18um in diameter ( only 33% of a human hair ) add tear drops as these ensure
a greater probability of a full pad intersectioning the plated hole wall and not just the track
Tear Drops Added.
We have a sophisticated testing system and software analysis for measuring layer alignment to
datum, however in reality no pcb manufacturer can guarantee all 250,000 connections have 0.002”
clearance to pad track intersection, give the board a better chance and tear drop the connection.
Unless instructed not to, we tear drop all via connections.
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Zot Printed Circuit Guide
Effect of Copper Area on Innerlayer in Relationship to Available Resin
The resin of the newer lead free laminates does not flow as well as the older Fr4 resin
systems, they also have the added issue of a far lower interlaminar bond as well as the
added problem of the water pressure being twice for lead free soldering as for leaded
soldering. This has increased the issues of delamination see in printed circuits across
the entire industry.
The main areas of concern are
Internal areas free of copper : the larger the area the greater the issue
On high layer counts : Stacked low areas.
Heavier copper weights : Require more resin to fully encapsulate the resin
On the newer lead free laminates the resin does not flow as readily leading to issues of
air entrapment or resin starvation
Example of Issue on Bare Board
Small areas where there are air pockets, which
when heated during assembly expand and
overcome the inter laminar bond of the prepreg
Example of Sample Area after Assembly
As you can see this expands a lot ( causing
delamination
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Zot Printed Circuit Guide
Example of too large an area to encapsulate
As mentioned newer lead free epoxy resin systems, do not move far when they are
turned to a liquid during the bonding of printed circuits.
This can cause issues where there may be enough resin to encapsulate the entire
circuit, but locally there are issues of larger open areas.
Where these areas are greater than say 10mm square, they can require more resin to
encapsulate than is available.
Example of Insufficient Resin
There is only a certain amount of resin in prepregs, prepreg styles have different resin %, different
thicknesses, and therefore a different cost to create a certain dielectric thickness
Because resin does not move far when it turns to a liquid state in the press, we use 150% as our
warning limit, and 100% as our stop limit.
This is only rectified by either increasing the copper area ( adding internal supplementary pattern ) or
by decreasing the prepreg thickness and increasing the no. of prepregs to create the same dielectric
50% Copper fill, all above 150% resin fill. ( no action )
15-25% Copper fill, all border line, just above 150% resin fill. ( no action )
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Zot Printed Circuit Guide
5% Copper fill, all failed, below 150% resin fill. ( ACTION REQUIRED )
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Zot Printed Circuit Guide
Supplementary Patterns
This is the additional of copper patterns to the internal and external layers, these are non functional
but they will increases both yields of board manufacturer, and at the assembly of product.
Supplementary patterns are only added to boards where the customer has given a global
authorisation, otherwise permission is applied on a job by job basis.
Internal Supplementary Patterns – Solid is Best
The main purpose of these, is by increasing the copper in the isolated layers, it then increases the
availability of the resin from the prepreg to encapsulate the innerlayer circuitry.
Which can reduce issues with blistering, Delamination, air voids, low areas, foil wrinkling.
We can add this to your layers, and will gave a clearance of 2mm ( 0.080” ) from copper circuitry or
holes. Using solid copper as fill, ensures maximum availability of prepreg, and also less issues with
AOI of layers.
Because there is not a lot of copper
on layers 3 & 4, it requires more
prepreg to fill gap between layers,
leading to a possibility of low spots
or voids
By adding internal supplementary
patterns, you decrease the
possibility of low spots and increase
the available resin, thereby making
the board a more reliable build
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Zot Printed Circuit Guide
External Supplementary Patterns
The main purpose of this to fill the areas of the board with no circuitry, which then has a profound
effect on a reduction in short circuits ( problem with pcb manufacture), and reduces the variation of
plating thickness in the holes, leading to an easier board to assemble, as well as evening out the
plating on the tracks, which affects the impedance.
Look inside a pc and boards usually always have supplementary patterns added, as this greatly
affects the yield of certain board designs.
Outerlayer supplementary patterns should be at least 30% copper.
Benefits to the PCB Manufacturer
 Easier control of plating thickness in holes
 Less short circuits in isolated areas of overplating
Benefits to Customer
 More consistent thickness of copper in holes leading to better reliability at assembly, and
better control of hole size for press fit connectors etc…
 Controlled impedance tracks will be more evenly plated, leading to a more consistent
impedance match.
The helps the electrolytic copper
plating operation, by evening out
variations in circuit density per area,
leading to a far superior plated board
Board with areas greater than a 25mm diameter with no tracking, should be filled where possible,
typically with a 2mm clearance to circuitry.
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Zot Printed Circuit Guide
Soldermask Oversize
Basically the soldermask oversize should be the half way point between the pad and the tracking that
is to be encapsulated with soldermask.
It’s the best balance for any possible misregistration, and minimising any soldermask on the pad.
If the spacing between the pad and the track is 0.004” ( 100um, 0.10mm), then the soldermask pad
should be the same size oversize on the circuit pad, so that the soldermask has a 0.002” oversize,
leaving 0.002” for soldermask misregistration
Optimised mask ring/clearance i.e.
8thou pad to track = 4thou ring
6thou pad to track = 3thou ring
2thou pad to track = 2thou ring.
Note
It is possible to manufacture boards with a soldermask oversize of little as 0 to 0.0015”, however in
order to ensure compliance with the inspection requirements of IPC, then we would have to Laser
Direct Image the soldermask image, this is however a costly and slow process.
99% of the jobs we produce can be soldermasked using conventional techniques as long as the
simple rules above are applied.
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Zot Printed Circuit Guide
Track width between pads of BGA
Unless there is a design reason ( Impedance tracks ), then there should be a balance between the
width of the track and the spacing from track to bga pad along with a adequate clearance on the
soldermask.
The above picture shows a board design where there was no impedance control, yet the track
were far to wide in comparison to both the track to pad spacing and the soldermask oversize..
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Zot Printed Circuit Guide
Soldermask Dams
These are the dams( or bars ) of soldermask between the SMD pads
The ability of a pcb manufacturer to reproduce these dams effectively is affected by a lot of process
control factors, one of the factors affecting the reproduction of these soldermask dams is the colour
(& density) of the customers requested soldermask colour.
Basically soldermask is separated into two main categories transparent and opaque soldermasks.
Transparent Soldermask Colours : Green, Red, Transparent Blue, Yellow,
The minimum solder resist bar should be set at 2.5 to 3thou for standard production but can be
reduced to 2thou for smaller prototype/development batch quantities, however this is only for green
and other transparent coloured soldermasks
The other issue is that the Green soldermask dams, will be better adhered to the pcb.
Soldermask Colours : Black & Opaque Blue
Basically the UV cannot fully polymerise the ink at the base, causing it to be undercut at soldermask
develop.
This is a problem with fine soldermask dams, especially on darker pigment soldermask ink, this
means that darker pigment soldermasks, cannot hold the same minimum soldermask feature and as
increase the energy
Soldermask Bar Missing
The following Shows the minimum soldermask dams and desired oversize
Soldermask Type
Transparent ( Green, Red, Yellow, Blue )
Opaque ( such as Opaque Blue, Black)
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Zot Printed Circuit Guide
Profiling
Minimum Radius
Try to avoid stating 0.50mm as a radius as this requires the use of a smaller diameter cutter, 1mm,
which will substantially increase the cost, and time to rout the final pcb.
Where a sharp corner is required, specify the profile, so that the sharp corner is created by
overshooting, rather than the use of a small cutter.
Overshoot into circuit to produce
sharp corner
Another way is to drill a hole in the place you require a sharp corner, then us a 2.40mm router cutter
Profiling – Plated Edges or Very large plated Holes
Edges of the pcb can be plated, this only requires you to specify what edge you wanrt plated, (
remember to extend you innerlayer
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Zot Printed Circuit Guide
ZOT PCB DIVISION PLANT LIST
Planning & Estimating
PCP2 and Ucam Integrator Computerised estimating/ planning/ shop loading system.
6 workstations networked to 20 shop floor data terminals.
Remote Tooling Site 1
Mania-Barco Ucam Software - 3 Seats
Remote Tooling Site 2
Mania-Barco Ucam Software - 2 Seats
P.C.B. Tooling Department in a Controlled environment
Barco BG 7304 Laser photo plotter with scanning facilities
Mania-Barco Ucam Software - 5 Seats
Barco Auto Fixture
Kodak film processor
Drilling & Routering Department
5 off single and twin spindle Automatic Prosys Wessell Drills
3 off Pluritec Single Spindle Automatic Drills
1 off 2 headed Schmoll Depth Drill Drill (2010)
1 off 1 headed Schmoll Depth Drill Drill (2011)
1 off 1 headed Schmoll XRC X-Ray drill (2012)
Glenbrook X-ray inspection Equipment
3 off S.E.L. R100-S Router DNC linked
EX200 Excellon Drill/Router machine 3 heads DNC linked
LHMT SCM411 CNC Scoring Machine (2012)
Multilayer Department
Luaffer Lamination press
Fully Automated cold transfer Luaffer Vacuum Lamination press (2012)
Komtek Press
Printprocess Targomat and Rivomat
DIS PRS 77 L/U Direct Optical Registration Induction welding (2012)
Multiline 4 Slot tooling Post Etch Punch
Orbotech Discovery AOI – ( 2010)
New Custom Build Cleanroom Layup Area (2012)
Xact PCB Registration system (2012)
Wet Processes
Hollmuller Innerlayer Etch and Resist Strip Line
Hollmuller Horizontal Alternative Oxide Line
Hollmuller Horizontal Desmear
Pola Massa Deburring and power wash (2010)
Automated Pattern Plating Line
Pulse Plating rectification all copper cells
Electrolytic copper via Fill Plating Line (2009)
Horizontal Direct Metallisation Line
Adam Pill Plating Resist developer and Etch Line
Innerlayer Chemical Cleaning Line
Various Video Magnification inspection equipment
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Zot Printed Circuit Guide
Photomech Class 10,000 Cleanroom
Youngwha Automatic Cut Sheet Laminator (outer layer)
Automatic Cut sheet Laminator(Innerlayer)
ORC and DSR Little John Exposure machines
Orbotech Laser Direct Imaging Paragon 6000
Teknek CM8 Clean Machine (2012)
SDI Clean Machine (2012)
Soldermask/Legend Department
I.S. Pumice Scrubber
Circuit Automation DP - 1500 Dual-Sided LPISM Coating
Verticure Conveyorised Oven
Semi-automatic Printer - 2 off
Olec 8KW Exposure Machine
Cirgraphics Supercool Exposure Machine
IS Conveyorised solder resist developer/dryer
Orbotech – Sprint 8, Direct Legend Printer – ( 2010)
Surface Finishing Area
Lantronix 45 degree Lead Free HASL Hot Air Solder Levelling line
Lantronix Leaded HASL Hot Air Solder Levelling line
Automated Immersion Silver Line
Automated Electroless Nickel/Immersion Gold
Immersion Tin Line
Deep Electrolytic Nickel/Gold line (Hard gold)
Electrical Test / Final Inspection
2 off ATG A5cf Soft Touch Flying Probe (2012)
Mania Fault Stations - 3 off ( 3.2 Software )
Polar CTS 500 S Controlled Impedance Measurement
Visual Inspection Stereo Dynascope
Detagging & Vacuum Packing Station
Laboratory
Fisher X-ray Fluorescence Measuring Equipment
Computerised Chemical Analysis & Recording Software
Video Microscope & Microsectioning Equipment
Atomic Absorption & various Chemical Analysis
U.V. Spectrophotometer
Tri-Moore Solderability Tester
Accelerated Ageing & Peel/Pull Tester
Sanyo Environmental Chamber
Multicore Ionic Contaminometer
Effluent treatment
Using multiple automated effluent filtration
and control systems.
Completely contained Waste storage and Transfer
New Carbon Filtration for < 0.1ppm metal discharge
Exceeding local government limts.
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Zot Printed Circuit Guide
Best Practice Guide
Possible Issues with the Transition from Leaded to Lead Free Soldering
Delamination
With the assembly of most printed circuit boards, moving towards Lead Free assembly, there is a
substantial increase ( 20c to 50c) in the temperature profile that a pcb laminates sees. Due to this
increased temperature, pcb laminates have been chemically altered to withstand this increase,
however this has come with a adverse effect.
Although the new laminates can withstand the lead free temperatures, far greater than the older
dicy cured laminates, however they have a reduced interlaminar bond between the resin to resin,
and resin to glass.
As I am sure you are aware there is moisture in printed circuit boards ( 0.2% by weight), this moisture
when heated (to 270c) expands , the water pressure increases(to over 600 psi), this can overcome
the bond at critical laminates interfaces, leading to a defect called “ delamination “.
Going from Leaded solder profiles to Lead Free solder profiles typically causes the water to double in
pressure.
If you are not seeing issues of delamination, then carry on, as you have done. The following is only to
help customers understand and overcome the problem.
The delamination can occur at the following interfaces
1. Resin to innerlayer copper
2. Resin to resin interface
3. Resin to glass interface
The delamination of the resin to copper is a pcb manufacturing fault, the following actions are for
resin to resin and the resin to glass interface.
Basically the delamination issue is caused by the moisture inherent in the pcb being heated up, thus
causing the water to expand, if there is enough water and heat, then this water pressure overcomes
the bond between the resin/resin/glass in the laminate and causes it to weaken and then come
apart.
To identify if this is the issue, carefully cut out the area and look at the two faces which have
delaminated, if there is resin on either side, then this is most likely caused by the water pressure
overcoming the chemical bond of the resin system.
PCB storage prior to assembly is now an important issue.
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Zot Printed Circuit Guide
Solutions
The solution to the problem of the delamination is to prevent moisture from getting into the board,
however if this is not possible, then the remedy to remove the moisture is to bake the boards.
Baking the bare printed circuit boards
If there is moisture inside the board, an effective solution is to bake the boards prior to assembly,
however this procedure will minimise the delamination, but if boards are over stoved, then the final
solderability of the board can be effected, with some finishes being worse than others.
A minimum temperature of 100 to 110c is required to drive out the moisture, the higher the
temperature the greater the possibility of affecting the solderability, the greater the time the greater
the effect on the solderability.
There try to bake at 110c for the minimum time needed to remove moisture, normally 2 hours is
sufficient.
Board Finish
Suggested
Bake Maximum Suggested
Temperature
Bake Time
Leaded HASL
100 to 110oC
3 hours
Lead Free HASL
100 to 110oC
3 hours
Electroless Nickel/Imm Gold
100 to 110oC
3 hours
Immersion Silver
100 to 110oC
3 hours
Immersion Tin
100 to 110oC
2 hours
The maximum time/temperature is a complex combination of various factors, such as oven type,
cleanliness of air, time, temperature, board finish, So for actual time and temperature, it is advisable
to carry out your own evaluation tests.
Recommended shelf life of package
The precise pre-assembly shelf life is highly dependant on a variety of specific environmental factors,
although this can range from days to months, the general recommended shelf life ,once the pcb
package is opened, is approx. 1 week, when stored and maintained at or below 30C and 60% RH.
It is recommended that opened packages of pcbs, be resealed for future use.
The moisture saturation point is typically 7 days, however 50% of the moisture uptake can be picked
up in the first 24 hours.
PCBs should not be stored in an environment where the temperature exceeds 30c and the relative
humidity exceeds 60% RH,
For further information, please email : Data@zot.co.uk
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Printed Circuit Division - Contact Details
Sales Area Representatives
North England - Business Development / Sales
Name:
E-Mail:
Mobile:
Drew Smith
Business Development Manager
DrewSmith@zot.co.uk
0774 251847
South - Sales Engineer
Name:
E-Mail:
Mobile:
Daniel Priest
Southern Sales Engineer
DanielPriest@zot.co.uk
07725 226515
Scotland - Sales Engineer
Name: Bill Bachop
E-Mail: BillBachop@zot.co.uk
Tel:
0131 653 4618 (Direct Line)
Fax: 0131 653 6025
Mob: 07725226577
International Sales
Internal PCB Sales Contact
PCB Internal Sales/ Global Procurement
Name: Bill Bachop
E-Mail: BillBachop@zot.co.uk
Tel:
0131 653 4618 (Direct Line)
Fax: 0131 653 6025
Mob: 07725226577
PCB Division Key Personnel
General Manager
Name: Gordon Falconer
E-Mail: gordonfalconer@zot.co.uk
Tel:
0131 653 4626 (Direct Line)
Fax: 0131 653 6025
Mob: 07725226585
PCB Quality Manager
Name: Neil Richardson
E-Mail: neilrichardson@zot.co.uk
Tel:
0131 653 4622 (Direct Line)
Fax: 0131 653 6025
Mob:
Technical Manager
Name: Gary Kerr
E-Mail: garykerr@zot.co.uk
Tel:
0131 653 6834 (Direct Line)
Fax: 0131 653 6025
Mob: 07725226581
Front End Engineering & Test Manager
Name: Robert Brown
E-Mail: rabbrown@zot.co.uk
Tel:
0131 653 4616 (Direct Line)
Fax: 0131 653 6025
Mob:
Website: www.zot.co.uk
Zot Engineering Ltd, Inveresk Industrial Park, Musselburgh, EH21 7UQ,
East Lothian, Scotland, Tel: 0131 653 6834, Fax: 0131 653 6025
Email: data@zot.co.uk
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Notes :
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