“Making the move to Lead Free”
A Comprehensive DFM
Lead Free Overview
Legislative Overview
Processing Materials
Component Selection
Printed Circuit Boards
Surface Mount Technology
Through Hole
Mechanical Assembly
Logistic, Repair and Inspection
Compliance
Legislative Overview
– Restriction on the Use of Certain Hazardous Substances in Electrical and
Electronic Equipment (RoHS) (Europe, July 2006)
• Bans the use of lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs)
(Some exceptions noted until 2010)
– Directive on Waste Electrical and Electronic Equipment (WEEE) (Europe, Dec
2006)
• Mandates reuse and recycling of electrical and electronic equipment
– Acts of Pollution Control in Electronics Production (China, July 2006)
• Mirrors WEEE and ROHS legislation
– Electronic Waste Recycling Act of 2003 (California, Jan 2007)
• Prohibits electronic devices covered under ROHS from being sold or offered
for sale in the state
RoHS Legislation Overview
Reporting Threshold
(ppm of material containing the substance)
Substance
1000
Lead
1000
Polybrominated diphenyl ether (PBDE) flame retardants
1000
Polybrominated biphenyl (PBB) flame retardants
1000
Mercury
1000
Hexavalent chromium (Cr+6)
75
Cadmium
Some exceptions are:
•Mercury (Hg) in compact fluorescent lamps not exceeding 5 mg per lamp.
•Lead (Pb) in the glass of: cathode ray tubes, electronic components, and fluorescent tubes.
•Lead (Pb) as an alloying element in steel containing up to 0.35% lead by weight, aluminum
containing up to 0.4% lead by weight, and as a copper alloy containing up to 4% lead by weight.
•Lead (Pb) in electronic ceramic parts (e.g., piezoelectronic devices).
•Lead (Pb) in high melting temperature type solders (i.e., tin-lead solder alloys containing more
than 85% lead).
•Batteries
Processing Materials
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The removal of lead raises major challenges in all areas of assembly. Everything from PCB
finishes, component leads/surfaces plating, solder paste selection, reflow profiling, wave
soldering, rework, etc will have to adopt to the new materials and process changes.
In addition to PCB materials, finishes and laminates, conformal coatings must also comply
with the RoHS directive in order to consider the completed assembly RoHS compliant.
Conformal coating labeling must comply with IPC-CC-830B if assembly marking space
permits
Labeling materials must be capable of surviving multiple reflows at lead free temperatures in
addition to complying with RoHS legislation. Polyimide and high temperature inks are
typical.
Processing temperatures are generally higher, wetting is reduced, BGA voiding is higher,
moisture sensitivity levels are exaggerated. In addition to concerns from lead contamination.
• SAC has different creep properties than SnPb (tin/lead). Long term reliability test
acceleration factors are not fully understood.
• Mechanical properties may vary with reflow parameters, especially at higher Ag (silver)
contents or in mixed solder situations.
• Surface Mount Technology (SMT): tighter soldering process controls and different
inspection criteria apply
• Wave Solder: higher temperatures, new equipment, bath contamination concerns
• Rework: higher temperatures. Risk of damage to neighboring parts, reduced thermal
cycling.
Processing Materials: Solder
– Leaded solder
– Eutectic 63% Sn 37% Pb
• Solidus: 183ºC Liquidus: 183ºC
• Peak Temperature 210-220 ºC, TAL: 30-90 sec.
– Lead Free solder
– SAC 305 (96.5% Sn, 3.0% Ag, 0.5% Cu)
• Solidus: 217ºC Liquidus: 227ºC
– SACX 307 (99% Sn, 0.3% Ag, 0.7% Cu)
• Solidus: 217ºC Liquidus: 228ºC
• Peak Temperature 230-250 ºC, TAL: 30-90 sec
– Flux
• Lead Free fluxes have been reformulated to increase activation temperature
to ensure proper fluxing at higher temperatures. Generally higher residues
are present, no clean fluxes selected comply with IPC J-STD-004A –
Requirements for Soldering Fluxes ROL0 and ORL0 for SMT and Wave
respectively.
Processing Materials: Tool
– Higher corrosive tin content requires some equipment retrofitting for
wave solder machines.
– Generally higher zone reflow ovens are required to control the ramp rate
to the higher reflow temperatures.
– Wave pallets materials require higher temperature materials such as
Durostone (350ºC), as opposed to FR-4 G10 or G11 (250ºC).
– Stencil apertures design guideline changes to compensate for reduce
wetting, increased tomb stoning and different surface finishes.
– Dedicated soldering irons capable of high thermal recovery and control
as well as limiting lead contamination.
– Increased moisture migration equipment for increased moisture
sensitivity of components
– Increased X-ray utilization for BGA voiding control.
– Data infrastructure additions to address lead free logistics and physical
separation, handling and labeling requirements.
Component Selection
– Parts changed to become RoHS compliant must undergo an added level of
scrutiny to ensure product quality and reliability.
• Components must not only be lead free, but RoHS compliant.
• Lead free crosses likely will have increased moisture sensitivity level (MSL)
ratings and may introduce more restrictive processing methods
• Component body resistance to higher temperatures is also a concern and
may result in higher premiums for components for higher temperature
epoxies (Max 260ºC is typical)
• Higher processing temperatures degrade some components, fuses, crystals
and some capacitors are among high risk items. Fuses may blow at lower
values, crystals lose tolerance, electrolytic/polymer capacitors may degrade,
ceramic capacitor and ferrite beads subject to micro-cracking.
• Depending on the manufacturer, component terminations come in a variety
of metrology and react differently with the different chemistries. (See
approved finishes)
• Marking must comply with IPC-1066 2nd level interconnect.
Component Selection
PREFERRED APPROVED FINISHES (“e2” category solder finishes)
– 100% Matte Tin (Sn) *
– Matte Tin (Sn) over Alloy 42 (FeNi) with or without Copper (Cu)
– Matte Tin (Sn) over Copper (Cu) *
– Tin-Copper (Sn/Cu)
– Tin-Silver (Sn/Ag) with a minimum Ag content of 1% by weight over Copper (Cu)
or Alloy 42 (FeNi)
ALTERNATE “e4” APPROVED FINISHES
– Noble metal plating with the exception of Silver (Ag)
– Palladium-Silver (Pd/Ag)
– Tin-Nickel (Sn/Ni) **
– Nickel-Palladium (Ni/Pd)
– Nickel-Gold (Ni/Au)
– Nickel-Palladium-Gold (Ni/Pd/Au)
ALTERNATE “e6” APPROVED FINISHES
– Tin-Bismuth (SnBi) with concentrations of Bi between 2-3% by weight over
Copper (Cu), Nickel (Ni) or Alloy 42 (FeNi)
*
Requires tin whisker mitigation technique by manufacturer
**
Recommended for connector terminations
Printed Circuit Boards (PCB)
– Current PCB material FR-4 (Tg 140) are not suitable for lead free
processing, new materials must be used to be able to survive multiple
reflow and increased plated through hole (PTH) reliability due to
increased Z-axis expansion and potential PTH reliability.
– High performance FR-4 with a Tg between 170 -180 degrees C or other
suitable material should be selected for lead free conversion for greater
margin of safety in rework and multiple thermal cycling requirements. In
addition, the base resin must comply with the RoHS directive
– Laminates must also be changed as higher processing temperatures
could break the polymeric bonds within the materials, current laminate
moisture content will lower Tg also well as the potential for solder mask
/ marking discoloration. New resins are on the market to meet your lead
free needs
– Marking requirements must comply with IPC-1066 (See Compliance)
Printed Circuit Boards (PCB)
–
There are a number of lead-free surface finishes available on the market, your particular
application, technology and volume will determine the right surface finish for your particular
design.
• Lead free HASL should be used for low layer count boards with no fine pitch (<= 20
mil), no press-fit, no wire-bonding or card-edge connections. Low tech, low to medium
volume boards should consider this finish as the preferred lead-free surface finish.
NOTE: This finish is not backwards compatible with leaded processing and should NOT
be selected for applications which will switch between leaded and lead-free.
• Immersion Tin should be used on low to medium layer boards with no fine pitch (<= 20
mil), no wire bonding, no card-edge connections but contains press-fit. Low tech, low to
medium volume boards containing press-fit should consider this finish as the preferred
lead-free finish.
• Immersion Silver should be used for medium layer count boards containing fine pitch
(<=20 mil), possible aluminum or gold wire bonding, no press-fit or card-edge
connections. Medium to high tech, low to high volume boards with fine pitch but no
card-edge connections should consider this finish as the preferred lead-free surface
finish. NOTE: This finish is not backwards compatible with leaded processing and
should NOT be selected for applications which will switch between leaded and leadfree.
• ENIG should be used for low to high layer count board containing fine pitch (<=20 mil),
require gold bonding, press-fit or card-edge connection. Medium to high tech, low to
high volume boards with fine pitch and card-edge connections should consider this
finish as the preferred lead-free surface
Surface Mount Technology
– Stencil alignment becomes more vital due to reduce wetting, global
fiducials are important. Proper aperture design significantly reduces
common defects.
– Paste in hole technology guidelines must also be changed to
compensate for the reduced wetting. Lead application may not be valid
for lead free.
– Proper component selection is vital to a successful and high yielding
lead free assembly. Conflicting termination finish selection, max peak
temperatures and moisture sensitivity levels may result in a poor overall
lead free assembly.
– Reduced wetting and increased surface tension increases tomb stoning,
offset and solder ball occurrences. Machine placement accuracy is
emphasized with lead free.
– Similar to pallets, SMT fixturing must similarly be able to withstand the
higher processing temperatures.
– Controlled ramp rates and high temperatures typically result in slower
reflow speeds and slight cycle time reductions.
Through Hole
– Increased solder surface tension at wave may change wave pallet
opening incident angles, in addition to proper material selection.
Aluminum and metal hold downs should be avoided at higher
temperatures.
– Lead free flux residues are inherently harder to remove and cleaning
represents increased cost. No clean flux is SMTC standard, increased
flux residues should be expected with lead free.
– Lead contamination at either wave or hand solder can severely effect
solder joint reliability in addition to expensive remedial lead removal.
– Gold plated through hole lead finish should be avoided due to the
reduced wetting and nickel-tin lead finishes are recommended.
– Component bodies must be able to withstand high lead free processing
temperatures, these requirements are exaggerated for thinner PCBs.
– Lead free component typically rated for a 1-2 thermal cycles and rework
may cause scrap. Solder iron temperatures, BGA rework and touchup
must be avoided as much as possible, robust processes begin at the
design stage.
Mechanical Assembly
– Immersion Tin and ENIG are the recommended PCB finish for press-fit
and swage hardware. Alternate finishes may result in PCB shearing
and poor electrical connections. Review your plating requirements to
ensure proper connections.
– Metal enclosures, custom assemblies and hardware similar to
components must also comply with RoHS legislation.
– Adhesives and additional chemicals must be reviewed for RoHS
compliance.
– Cadmium is a common metal plating, lead containing paint must be
replaced, flame retardant materials must be checked for PBB and PBDE
content. Custom designs should be reviewed with manufacturers early
in the transition to ensure compliance.
– Packaging materials, manuals, CD and ink must also be reviewed for
compliance.
Logistics, Repair and Inspection
– All lead free assemblies must comply with IPC-A-610 Rev. D –
Acceptability of Electronic Assemblies Class 2 to be considered
acceptable.
– Increased BGA voiding has been documented with lead free alloys over
leaded alloys and as such may require additional X-ray inspection to
ensure quality solder joints.
– Existing AOI programs for leaded assemblies will be required to be
reprogrammed to compensate for physical and visual difference
between leaded and lead free solder joints. Parallel assembly
chemistries will require two programs for production and additional
programming charges will apply for lead free programs.
– SAC 305 alloy will be used for all touch repairs. BGA balls must be
replaced with SAC 305 to be reused on lead free assemblies.
Components rated for a single thermal cycling must be replaced during
touch to mitigate reliability concerns.
– Any touchup, or replacement of components on lead free assemblies
with leaded solder or components must have the lead free identification
permanent obscured.
Compliance
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Component Declaration
• Manufacturer Material Declaration Sheets (MDS) may be used a evidence of
compliance with RoHS requirements and may require additional infrastructure to
support. Depending on your ISO certification, these may be required for both internal
and external lead free compliance audits.
PCB
• If the base resin and reinforcement matrix used in making the bare printed board is
halogen free, the label/marking “HF” shall be noted on the bare printed circuit board
identification label. If no “HF” is present, a halogen-containing base resin and
reinforcement matrix is assumed.
Solder Finish
• The following categories are meant to describe the lead-free 2nd level interconnect *
terminal finish/material of components and/or the solder paste/solder used in the
assembly
Compliance
Solder Finish Category
Description
E1
Tin-Silver-Copper ( )
E2
Other Tin (Sn) alloys (i.e. SnCu, SnAg, SnAgCuX, etc.) (No Bismuth (Bi) or Zinc (Zn))
E3
Tin (Sn)
E4
Precious metals (i.e. Silver (Ag), Gold (Au), Nickel-Palladium (NiPd), NiPdAu, but no Sn)
E5
Tin-Zinc (SnZn), SnZnX (No Bismuth (Bi))
E6
Contains Bismuth (Bi)
E7
Low temperature solder (<150°C) containing indium (Id) but no Bismuth (Bi)
Conformal Coating
• When conformal coatings are applied, and if assembly-marking space
permits, or if contractually required by purchasing agreement, coatings
may be labeled/marked per IPC-CC-830B as follows;
– ER – Epoxy Resin
– UR – Urethane Resin
– AR – Acrylic Resin
– SR – Silicone Resin
– XY - Paraxylylene
Compliance Examples
– A Pb-free identification label shall only be used when the
components/devices and/or board assemblies are lead free. It is
recommended the label be a minimum of 22 mm x 25 mm with the
minimum diameter of the circle being 18 mm.
– A 2nd level interconnect label confirms of the 2nd level interconnect only
and is affixed to containers holding printed circuit boards/assemblies the
category field describes the solder paste/solder used in the board
assembly. The “maximum assembly temperature” field, if blank does
not apply. It is recommended that the Pb-free label be a minimum of 75
mm by 50 mm.
Lead Free Compliance Standards
– Commodity Standards
• JEDEC JESD22-B102D - Solderability
• IPC J-STD-020B - Moisture / Reflow Sensitivity Classification for
Nonhermetic Solid State Surface Mount Devices
• JEDEC JESD22-A113 – Preconditioning of Nonhermetic Surface
Mount Devices prior to Reliability Testing
• IPC-9503 – Moisture Sensitivity Classification for Non-IC
Components
• IPC J-STD-002B – Solderability Tests for Component Leads,
Terminations, Lugs, Terminals and Wires
• IPC J-STD-033A – Handling, Packing, Shipping and Use of
Moisture / Reflow Sensitive Surface Mount Devices
• IPC-1066 or JEDEC JESD97 – Marking, Symbols and Labels for
Identification of Lead-Free and other Reportable Materials in LeadFree Assemblies, Components and Devices
• IPC J-STD-003A – Solderability Tests for Printed Boards
Lead Free Compliance Standards
– Assembly Standards
• IPC-9504 – Assembly Process Simulation for Evaluation of Non-IC
Components
• IPC J-STD-004A – Requirements for Soldering Fluxes
• IPC J-STD-005 – Requirements for Soldering Pastes
• IPC-A-610D – Acceptability of Electronic Assemblies
• IPC J-STD-001CS – Space Applications Electronic Hardware
Addendum to Requirements for Soldered Electrical and Electronic
Assemblies
• IPC J-STD-006A – Requirements for Electronic Grade Solder Alloys
and Fluxed and Non-fluxed Solid Solders for Electronic Soldering
Applications