Critical Factors in Thru Hole Defects
By Ernie Grice
Vice President of Sales
Kurtz Ersa North America
Production needs us
Soldering Zone
Production needs us
Thru Hole Soldering Challenges
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Selective solder masks – High potential for defects!
7 mm !
Small but deep Cut-outs are requiring a higher wave .
Effect: More turbulent wave with more dross creation.
Difficult to control the contact time => higher failure rate can be expected
Solution from Ersa: Programmable wave height in the solder program
.
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Selectiv Solder Masks – lead free wave process !
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Typical Thru Hole Defects:
•
•
•
•
Bridging – Component Orientation, Lead Length, Pitch, Design
Topside Hole Fill – Layer Count, Thermal Demand, Lead to Hole Ratio, Design
Solder Balls – Flux and solder mask
Insufficient Solder – Flux, Contamination
All of These factors can be resolved and more easily managed with Selective
Soldering.
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Content Thermal Demand
• Fundamentals and the Physics of Solder Joints
• Thick Copper Technologies
• PCB Layout - Theory and Practice of Heat Traps
• Soldering defects
• Preheating Process
• Soldering Trials – Parameters and Results
• Conclusion
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
What is a “Good Quality” Joint?
Goal: 100% Through hole filling
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Target conditions of the IPC A 610
Target – Class 1, 2, 3
There is 100% fill
This is easy to inspect, there is no
cause for any speculation
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Acceptable conditions of the IPC A 610
Acceptable – Class 1, 2, 3
Minimum 75% fill
Question:
How to inspect 75% ??
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Error Pattern – insufficient solder and possible consequences
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„core“ – conditions at a solder joint to achieve „good quality“
Heat capacity
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Glasübergangstemperatur TG
/734 F
/644 F
/617 F
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Specification temperature of FR4 laminates versus process window
Resistance to Soldering Heat
Soldering:
SAFE
UNSAFE
T288
DESTRUCTIVE
TD
(320°C – 390°C)*
T300
* Depending on the specification
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Starting damage of PCB-laminate due to high solder temperature
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Delamination
Copper dissolution
Delamination
Resin recession
© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Copper leaching
If a solder joint requires
additional heat, the solder
temperature should be
increased incrementally and
very careful. At high solder
temperatures, copper leaches
very fast, in the worst case the
complete pad leaches into the
solder (see above).
Increase wetting time before increasing solder temperature
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Influence of the layout on the heat management of a solder joint
TTop > TM-Sol
Capillary gap size
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Copper connected to the
plated through-hole
Influences of the
PCB-Layout
on
soldering results
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Selective Soldering by miniaturized solder waves
Heat transfer by flowing solder
within a limited area
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Energy transfer into a solder joint with 100% connection to a copper layer
FhG ISIT
ERSA
Massive heat flow into Cu-layer
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Energy transfer into a solder joint with heat trap present
ERSA
Reduced heat flow into Cu-layer
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FhG ISIT
Heat Traps and their Mode of Action on Printed Circuit Boards
 Heat traps reduce the heat carrying cross section to those copper layers
attached to the joining location
 Retaining the heat energy in the joining location is improved
 The joining location heats up more quickly
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Desired Effect
Heat Traps - Layout recommendations
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Insufficient usage of top side heaters
When the top side heaters can‘t transfer
sufficient energy to heat up the boards
top side, all the energy to heat up the
solder joint (PCB + pin) must be
transfered from the bottom side of the
assembly.
To ensure a rapid heat up of the solder
joint, thermal support vias transfer a large
amount of heat additionally to the PCB
top side.
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Heat Traps for Busbars- Layout Recommendations
X
X
Dimension:
d4
X
X
d2
d3
d1
d 1 ≤ d 2 + d3 + d4
Please Note: The cross sectional area of the bus bar is reduced by
the drillings!
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Layout recommendations
Heat traps to reduce
the heat flow into a
massive copper
layer. This layout is
recommended for all
layers of a PCB.
Thermal support vias to
improve the transfer of
heat up to the PCB top
side.
Reducing the heat capacity
of a busbar. Reducing the
diameter lowers the heat
flow from the pin into the
busbar.
Note that for all above layout recommendations, the current density
has always to be taken into consideration !
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Layout – Capillary Action with Wave- and Selective Soldering
Ratio of diameter pin – through-hole
capillary gap
To increase the transfer of heat into the plated through-hole, it is recommended to
work on the upper limit of the capillary gap.
In power electronics the gap is 0,25 – 0,30 mm
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Calculating the hole diameter for square pins
A = pin dimension
G
D = A x √2
G = required for insertion
D
dH = D + (2 x G)
G
A
dH
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Possible Sources of Defects in the Selective Soldering Process
• Soldering System related
• Component related
Same Error Pattern!
Typical Error Pattern in Practice
• Non-Wetting
• Insufficient Capillary Rise
 Layout
• Bridging
 Layout
• Copper Leaching
• Pad- and/or Fillet Lifting
• SMDs Desoldered
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 Layout
Conclusion
• Selective soldering of thick copper PCBs with mini wave
systems is possible.
• The layout of the PCB plays of crucial role - especially the
connection of inner layers to THTs and the ratio of pin to hole
diameter.
• The specification of the PCB laminate has to be adapted to
the higher solder temperatures.
• The delamination temperature TD is especially critical !
• The more copper layers are in the board, the smaller will be
the process window for soldering.
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Conclusion
 The board layout has a large influence on the capillary rise and
the formation of bridges
 The cause variables in the layout are
• Pad size / Contact spacing
• Pin length
• Plating of PTH joined to copper layers
• Size of capillary gap
• Distance between THT and SMD
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The Process: Flux (F) – Preheat (PH) – Soldering (S)
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FLUXING METHODS:
• Drop Jet Fluxer – Airless system. Precise Deposition. 2mm Dot Size.
Programmable Flux Amounts per joint. No Clean, Water Soluble and Rosin
Up to 15% solids.
• Ultrasonic Fluxer – Precise Deposition. Good for Spraying Rows. Good for
High Solids Rosin Fluxes.
• Spray Fluxer – Good for use of Chip Wave Style nozzle in selective.
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Preheating: Top and Bottom
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Preheating Multilayer Boards – Telecommunication (24 Layers)
T--∆T

T +++
If, for multi-layer assemblies, thermal energy is supplied only from one side (lower side), then
the heat has to travel, layer by layer, from the bottom up through the board.
Since each layer absorbs energy, a temperature gradient exists from bottom to top of the
board. Therefore, to achieve a uniform and homogeneous heating of the board, a
correspondingly long time has to be accepted.
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Preheating: Multi-layer Boards with IR from bottom
LP Bottom Side – Surface Temperature
ΔT 30K
Critical!
160°C
LP Top Side
Temperature
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Long Preheat Time 140s
IR Preheater only from
bottom side, with
maximum power (100%) !
Preheating: Multi-layer Boards with IR from bottom
LP Bottom Side – Surface
Temperature
ΔT 20K
High!
150°C
LP Top Side
Temperature
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Very Long Preheat
Time 190s
IR Preheater only from
bottom side, with reduced
power (66%) !
Preheating Multilayer Boards - Telecommunication (24 Layers)
T +++
∆T

T +++
If multi-layer boards are supplied with thermal energy from both sides, the heat penetrates
the board simultaneously from top and from bottom. As a result, the temperature gradient is
very small, and the board warms up uniformly and homogeneously at a much faster rate. At
the same time, the stress experienced by the lower side is reduced, and the danger that the
flux is damaged during the preheat process is minimized.
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Preheating: Multi-layer Board with IR from bottom + convection from top
LP Bottom Side – Surface
Temperature
ΔT 10K
Not Critical! 140°C
Preheating from bottom
and from top, with reduced
power (65%) !
LP Top Side
Temperature
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Short Preheat
Time 110s
Forced Convection Top side pre-heating
The use of Multijet Forced
Convection Optional Top
side pre-heating guarantees
a constant PCB temperature
during the entire selective
soldering process.
This guarantees that each
solder joint is made under
the same thermal conditions.
Highly recommended for
heavy, multilayer PCBs
which require a long process.
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Copper Dissolution and The Need For Preheat
Interaction Plot for Voiding
Board
Thick ness/Surface
Finish
1
2
1 = .093" 106AX-HT OSP
2 = .093" ImAg
5
0
10
Cu Dissolution
Voiding
10
Interaction Plot for Cu Dissolution
Board
Thick ness/Surface
Finish
1
2
1 = .093" 106AX-HT OSP
2 = .093" ImAg
5
0
260
270
280
Pot Temperature
290
260
0 = Low Voiding (0% - 5%)
5 = Medium Voiding (5% - 10%)
10 = High Voiding ( >10%)
270
280
Pot Temperature
290
0 = No Dissolution
5 = Slight Dissolution
10 = Total Dissolution
Interaction Plot for Hole Fill
Hole Fill
10
Board
Thick ness/Surface
Finish
1
2
1 = .093" 106AX-HT OSP
2 = .093" ImAg
5
0
260
270
280
Pot Temperature
290
0 = 0% - 25% Hole Fill
5 = 25% - 75% Hole Fill
10 = 75% - 100% Hole Fill
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
The more thermal energy you have in
your board, the lower your pot temperature
And dwell time can be in order to achieve a
Good solder joint. No preheat or not enough
Preheat warrants higher pot temps and
Higher dwell times in order to topside fill
On thermally challenging boards.
The Soldering Module: Things to Consider….
• Single Point or Multi-dip
• Moving Pot or Moving the Board
• Positional Accuracy of the Gantry
• Pumping Mechanism for Wave Height
• Dual Alloy Capable
• Fidicual Recognition
• Board Warpage Detection
• Nozzle Types and Sizes
• Nozzle Cleaning
• Keep out Areas
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Multi-dip
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Single Point XYZ
Multi-Dip Tooling
Pros:
• Fast Cycle Times
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Cons:
• Dedicated Tooling
• Change Over time
• Tooling Cost
• Universal Dwell time for all joints
• Requires Larger Keep out Area
• More N2 Consumption with Hood
Reflowlöten
Configuration - Single Solder Nozzle
- Constant solder flow over the complete nozzle
surface – no preferred direction for solder to drain
- Continuous heat transfer into the solder joint during
the solder process
- No orientation of the component to the solder
nozzle required
- No layout constraints for the orientation of the
components
- Suitable for a wide variety of solder alloys
- Individual Wave Height and Dwell Time per Joint
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Moving the Board or the Pot
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Gripper Systems moves the entire PCB
with a gripper system, one PCB at a time.
Only Localized top side preheat possible.
- moving only the solder
pot is 50% faster.
- no risk of vibration
during cooling.
- moving solder pot does not
require component fixing.
- top side preheating keeps PCB
temp. constant during soldering.
- a machine with segmented
process steps can handle up to 6 PCBs
at the same time!
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© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
A D V A N T A G ES:
B
C
For soldering the square socket
just program a line and move the
solder nozzle from
A to B
B to C
C to D
D to A
and peel off
A
D
It is not required to either turn
the board or the solder nozzle,
or to change any angles.
A recommended orientation of
the components is unnecessary
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Repeatability is Critical
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Reflowlöten
Design of Solder Bath
- Maintenance-free design with electro-magnetic
solder pump
- No mechanical movable part in the solder bath
- Precise wave height due to continuous circulation
of solder
- Outstanding repeatability of solder process (no
impeller)
- No adjustment after servicing the solder bath
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Reflowlöten
Monitoring - Solder Bath
- Solder wave height is
measured
- Solder level in bath is
monitored / Solder wire
feeder option
- Solder temperature is
exactly controlled
- N2 atmosphere assures
stabile process
conditions
play video
click button
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Solder Module
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Reflowlöten
© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Reflowlöten
Configuration Solder Module Z - variable
Different nozzle geometries
Variety of Alloys
- Both solder bath can be raised, separately and individually, on the axis up to the required
working height (z- direction)
- Depiction of mode of operation with two identical nozzles but different alloys.
- Depiction of mode of operation with two nozzles of different geometries and identical
solder.
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Reflowlöten
Configuration Solder Module Y- variable
- The distance of solder bath 1 to solder bath 2 can be adjusted on the axis system in the
y-direction.
- Set-up for simultaneous soldering of two assemblies of a multi-up panel.
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Reflowlöten
Solder Snap-Off with Wettable Nozzle Surfaces
F1= Wetting Force
F2= Capillary Force
F3= Gravity
F4= Adhesive Forces
- Solder snap-off, the point in the process when the solder breaks off
from the solder joint, is positively assisted by the adhesive force F4,
which is generated by the wettable surface of the nozzle.
- This adhesive force, in conjunction with gravity F3, enables the solder
to properly drain off from the solder joint after having formed it, and
to eliminate bridging and shorts.
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Reflowlöten
Solder Snap-Off with Wettable Nozzle Surfaces
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Standard Snap-Off
Controlled Snap-Off
- forms convex solder joints
- forms concave solder joints
© by Ersa GmbH| Layout_Selectiv.ppt | AT.JFR.29.11.2013
Reflowlöten
Automatic Nozzle Activation:
• Automatic, preventive activation of the
nozzle surface to prevent the surface from
dewetting.
• The uniform wetting of the outer surface of
the solder nozzles is essential for a stable
process and constant soldering results.
• By a charging screw adipic powder will be
applied on the solder nozzle in a specified
interval.
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Fiducial and Board Warpage
The need for fiducial Recognition and Board Warp Detection is highly
Dependent on the Assembly.
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Min. distance of a single solder point from the adjacent SMD pad or from the conveyor*
BE
Pad
Bohrung
Pin
Scrap edge
3 mm
 3 mm
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 6 mm
Off-centre positioning possibility of the solder wave
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Minimum Distance of a multi-row connector to the adjacent SMD Pads*
Pad
Component
 1 mm
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Through Hole
Keep out area around dual and multi row solder joints (pitch 2.54 mm)*
Blue = Required keep out area
A = distance between pads
B = distance between pads
≥ 1 mm
≥ 2 mm
This recommendation should be used
for all double and multi row layouts,
starting with a pitch of > 2,54 mm.
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keep out areas around selective solder joints
No keep out areas or solder
thieves required!
X
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Programming Methods
• Joystick Teach :
• Pro – Easy to use
• Con- VERY Time consuming and Machine is not producing while
teaching, Requires live product
• Offline Programming:
• Pro – Machine runs production while programs created offline, Easy to
Use, Auto routing and cycle time calculations, CAD DXF or JPG, Very
Accurate!
• Con- Need Computer Knowledge
• Data Entry
• Pro- Can be done while machine is running
• Con- Requires hand measurements, VERY Time consuming.
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• Scale Image
Result:
Scaled and rotated
image
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• 3D-View of Blocking Zones
Visual Monitoring due
to 3D-View
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• Optimized Line
• Optimized Cycel Times
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• Multi Panel
• Profils can be easy
duplicated
• Time optimized
programming for
multi panels
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• Parameter-Set Up
Selection can be done
in the graphic or in the
Set-Data-List
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Thank you for your attention!!!
We hope we can work with you for your soldering needs.
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