WELCOME to: A Practical Guide to Achieving LeadFree Electronics Assembly

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WELCOME toA Practical Guide to Achieving
Lead-Free Electronics Assembly
Pb
AIM info_at_aimsolder.com www.aimsolder.com www.lead
free.com
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Goal Achieve Lead-Free Soldering

• Apparatus
• Purchasing
• Engineering/Design
• Maintenance
• Quality
• Abstract To successfully achieve lead-free
  electronics assembly, each participant in the
  manufacturing process, from purchasing to
  engineering to maintenance to quality, must have
  a solid understanding of the changes required of
  them.
• This pertains to considerations regarding design,
  components, PWBs, solder alloys, fluxes,
  printing, reflow, wave soldering, rework,
  cleaning, equipment wear tear and inspection.

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Concerned Parties
components
PWBs
solder alloy
flux
handling
design
purchasing
engineering
maintenance
quality
printing
reflow
wave
rework
cleaning
inspection
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Agenda

• 1. Introduction to Lead-Free Electronics Assembly
• 2. Materials Issues
• 3. Process Issues and Advice

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• Introduction to Lead-Free Electronics Assembly

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Why Do Solders Contain Lead?

• Reduces the melting temperature of tin.
• Forms eutectic at 183C
• Increases the strength and ductility of tin.
• Increases thermal fatigue resistance.
• Tin/lead solders have been used for THOUSANDS of
  years.

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Why Is Electronics Being Targeted for Lead
Removal?

• Solders account for only lt 2 of the total
  worldwide lead consumption.
• World Lead Consumption per product
• 0.49 Solder for Electronics
• 0.70 Solder (excluding electronic solder)
• 2.77 Miscellaneous
• 0.72 Pipes, Traps and Extruded Products
• 0.72 Brass, Bronze Billets and Ingots
• 1.13 Casting Metals
• 1.40 Cable Covering
• 1.79 Sheet Lead
• 4.69 Ammunition
• 4.78 Paint, Glass, Ceramic, Pigments Chemicals
• 80.81 Storage Batteries

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Why Is Electronics Being Targeted for Lead
Removal?

• The soldering process does not present immediate
  exposure problems.
• Process by-products are easily recycled.
• Mixed evidence regarding the threat of
  electronics products if disposed of in landfills.
• Electronics was thought to be a quick and easy
  fix.

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What is lead-free?
?

• There is a new draft of the guidance document
  outlining the Maximum Concentration Values of the
  banned substances in RoHS. The EU TAC working
  group have unofficially agreed on the text but
  have not yet adopted it officially.
• The main text is
• For the purposes of Article 5(1)(a) a maximum
  concentration value of 0.1 by weight in
  homogeneous materials for lead, mercury,
  hexavalent chromium, polybrominated biphenyls
  (PBB) and polybrominated diphenyl ethers (PBDE)
  and of 0.01 weight in homogeneous materials for
  cadmium shall be tolerated.
• Homogeneous material means a material that can
  not be mechanically disjointed into different
  materials.
• References to 'unit' have been removed and
  'single' material is now 'different materials'

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Lead-Free Soldering Driving Forces

• Europe
• North America
• Japan

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WEEE Directive

• Ratified January 2003.
• The WEEE (waste electrical and electronic
  equipment) directive covers products made with
  heavy metals, such as mercury, lead, cadmium and
  hexavalant chromium, as well as certain
  brominated flame-retardants.
• The WEEE directive lays down measures which aim,
  as a first priority, at the prevention of waste
  electrical and electronic equipment, and in
  addition, at the reuse, recycling and other forms
  of recovery of such wastes so as to reduce the
  disposal of waste.
• More

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WEEE Directive

• Being implemented because The amount of WEEE
  generated in the Community is growing rapidly.
  The content of hazardous components in electrical
  and electronic equipment (EEE) is a major concern
  during the waste management phase and recycling
  of WEEE is not undertaken to a sufficient
  extent.
• WEEE mandates producers to make products easily
  recycled, separate collection of EEE products,
  and states that convenient facilities should be
  set up for the return of WEEE, including public
  collection points, where private households
  should be able to return their waste at least
  free of charge.
• This goes into effect January 2006 (recently
  pushed back from August 2005).
• By 31 December 2006 at the latest, a rate of
  separate collection of at least 4 kg on average
  per inhabitant per year of waste electrical and
  electronic equipment from private households must
  be achieved. A new target rate to be set at a
  later date is to be achieved by 31 December 2008.

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WEEE Scope

• 1. Large household appliances
• 2. Small household appliances
• 3. IT and telecommunications equipment
• 4. Consumer equipment
• 5. Lighting equipment
• 6. Electrical and electronic tools (with the
  exception of large-scale stationary industrial
  tools)
• 7. Toys, leisure and sports equipment
• 8. Medical devices (with the exception of all
  implanted and infected products)
• 9. Monitoring and control instruments
• 10. Automatic dispensers

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RoHS Directive

• The RoHS (restriction of the use of certain
  hazardous substances in electrical and electronic
  equipment) directive bans the materials covered
  under the WEEE scope.
• It states that Member States shall ensure that,
  from 1 July 2006, new electrical and electronic
  equipment put on the market does not contain
  lead, mercury, cadmium, hexavalent chromium,
  polybrominated biphenyls (PBB) or polybrominated
  diphenyl ethers (PBDE).
• Guidance on put on market may be found at
  http//europa.eu.int/comm/enterprise/newapproach/l
  egislation/guide /document/1999_1282_en.pdf
• Placing on the market is the initial action of
  making a product available for the first time on
  the Community market, with a view to distribution
  or use in the Community. Making available can be
  either for payment or free of charge.
• The directive pertains to electronics products
  produced in or imported into the EU.

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Why WEEE and RoHS?

• Both prohibition of materials and recycling are
  being proposed simultaneously because
• it remains to be seen whether other Member
  States attain the collection target in the medium
  term. As a consequence, the substitution of the
  hazardous substances is the only feasible way to
  reduce the presence of these substances in the
  waste stream.
• and
• Even if WEEE were collected separately and
  submitted to recycling processes, its content of
  mercury, cadmium, lead, chromium VI, PBB and PBDE
  would be likely to pose risks to health or the
  environment Restricting the use of these
  hazardous substances is likely to enhance the
  possibilities and economic profitability of
  recycling of WEEE and decrease the negative
  health impact on workers in recycling plants.

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RoHS Scope

• 1. Large household appliances
• 2. Small household appliances
• 3. IT and telecommunications equipment
• 4. Consumer equipment
• 5. Lighting equipment
• 6. Electrical and electronic tools (with the
  exception of large-scale stationary industrial
  tools)
• 7. Toys, leisure and sports equipment
• 8. Automatic dispensers

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RoHS Exemptions (pertaining to lead in
electronics only)

• 5. Lead in glass of cathode ray tubes,
  electronic components and fluorescent tubes.
• 7. Lead in high melting temperature type
  solders (i.e. tin-lead solder alloys containing
  more than 85 lead),
• lead in solders for servers, storage and
  storage array systems (exemption granted until
  2010),
• lead in solders for network infrastructure
  equipment for switching, signalling, transmission
  as well as network management for
  telecommunication,
• lead in electronic ceramic parts (e.g.
  piezoelectronic devices).
• lead in solders for servers, storage and
  storage array systems, network infrastructure
  equipment for switching, signalling, transmission
  as well as network management for
  telecommunications (with a view to setting a
  specific time limit for this exemption) as a
  matter of priority in order to establish as soon
  as possible whether these items are to be amended
  accordingly.

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EU Debates RoHS Exemptions

• The outcome of a March 2005 EU Commision TAC
  meeting concerning RoHS exemptions was the
  reaffirmation of its original decision to let the
  exemptions stand defying a EU Parliment request
  to "re-examine" their decision.
• MEPs adopted a resolution calling for the
  Commission to "reexamine" its December 2004
  decision to adopt additional RoHS exemptions at a
  March 16 meeting. The Parliament and the
  Commission's debate over the deficient
  collaboration on decision-making has increased
  confusion and uncertainty over the exemptions
  process.
• Questionable exemptions include solders to
  complete a viable electrical connection between a
  semiconductor die and carrier within IC flip chip
  packages compliant pin connector systems
  coating materials for c-ring thermal conduction
  modules in optical and filter glass and solders
  consisting of more than two elements for
  connection between the pins and the package of
  microprocessors with a lead content of more than
  80 and less than 85 by weight.
• The Commission has insisted that it acted in
  accordance with the law, but a campaign group
  within the Parliament is urging member states to
  reject the exemptions. In February 2005, the
  Parliament challenged all of the decisions made
  by the Commission, representing member state
  governments via the TAC since RoHS' enactment,
  based on not having been consulted. Some MEPs
  have branded the exemptions "illegal," and legal
  action from the Parliament could be possible.

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Additional Exemptions

• This Directive does not apply to spare parts for
  the repair, or to the reuse, of electrical and
  electronic equipment put on the market before 1
  July 2006.
• Automotive is covered under a separate directive
  (ELV) and solders are currently exempted.
• Military, aviation and some other industries are
  not covered under WEEE/RoHS.

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North America

• Compliance with EU legislation driving the issue.
• No pending federal legislation.
• Some U.S. states considering legislation.
• Lead reporting issues.
• 20 pound/year limit
• Fear of litigation.

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IPCs Position Statement

• The US electronics interconnection industry,
  represented by the IPC, uses less than 2 of the
  worlds annual lead consumption. Furthermore, all
  available scientific evidence and US government
  reports indicate that the lead used in US printed
  wiring board (PWB) manufacturing and electronic
  assembly produces no significant environmental or
  health hazards
• Nonetheless, in the opinion of IPC, the pressure
  to eliminate lead in electronic interconnections
  will continue in the future from both the
  legislative and competitive sides. IPC encourages
  and supports research and development of
  lead-free materials and technologies
• These new technologies should provide product
  integrity, performance and reliability equivalent
  to lead-containing products without introducing
  new environmental risks or health hazards. IPC
  prefers global rather than regional solutions to
  this issue, and is encouraging a coordinated
  approach to the voluntary reduction or
  elimination of lead by the electronics
  interconnection industry.

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JapanJEIDA Roadmap toward the introduction of
the lead-free solders

• This is the roadmap not for completing the
  lead-free soldering, but for introducing it.
  However, it is desirable to vigorously take part
  in the activity, considering the fact that the
  vast amount of annual electronics wastes is about
  to surpass the capacity of the waste treatment
  plant in our country.
• First adoption of lead-free solders in
  mass-produced goods 1999
• Adoption of lead-free components 2000
• Adoption of lead-free solders in wave
  soldering 2000
• Expansion of use of lead-free components 2001
• Expansion of use of lead-free solders in new
  products 2001
• General use of lead-free solders in new
  products 2002
• Full use of lead-free solders in all new
  products 2003
• Lead-containing solders used only
  exceptionally 2005

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Japanese Household Electronics Recycling Law

• Mandates that producers reclaim household
  electronics goods such as air conditioners and
  refrigerators that contain lead.
• (Passive lead-free solders legislation)

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Japanese Lead-Free Soldered Assemblies
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China

• Considering mirroring the EU legislation.
• Perhaps without the exemptions (!)

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Resistance to Changing to Lead-Free Soldering

• Cost
• Reliability Concerns
• Unproven Environmental Benefits

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Costs

• Lead is cheap, Replacing it is not.
• New designs?
• Special components?
• New equipment?
• Nitrogen?
• Retraining
• Seminars
• Research
• Testing
• Questionable reliability

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Raw Cost of Metals Comparison

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Reliability Concerns

• Solder joint quality
• We know what tin-lead does
• The data sample size for lead-free is not nearly
  as large as that for tin-lead.
• Component and substrate temperature damage
• As a result of the higher temperatures of
  lead-free solders
• A component's internal thermal damage may not be
  detectable by electrical tests the internal
  damage eventually may trigger a field failure.

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Unproven Environmental Benefits

• There is no evidence of lead leaching out from
  electronic waste (like PCB assemblies) into the
  water table.
• Substitute alloys contain silver - inert in
  itself, but scientists now suspect that lower
  doses of silver compounds over longer periods of
  time may have subtle but worrisome effects on
  fish and other aquatic organisms, affecting the
  reproductive system in sensitive species.
  Researchers are investigating the effects of
  chronic silver exposure on aquatic life.
• Lead will be replaced by other metals that may be
  more environmentally damaging to mine and
  extract.
• More energy will be used to make solder joints -gt
  more pollution global warming.

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Regardless of the Resistance . . .

• Lead-Free is happening.
• Current Lead-Free Status
• Millions of lead-free units in Japan.
• 65-70 of all soldering is lead-free
• The rest of Asia is also moving very fast.
• North America and Europe are in trials.
• Manufacturers need to prepare for lead-free
  assembly starting NOW.

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• Materials
• Issues

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Areas of Concern

• Components
• PWBs
• Flux
• Solder Alloys

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Component Concerns

• Lead Finish Options
• Availability / Materials Management
• Reliability
• Moisture Sensitivity Level (MSL) Rating
• Wetting
• Tin Whiskering

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Common Component Lead Finish Options

• Matte Sn for passives
• Matte Sn, Ni/Pd/Au for lead frames
• Sn/Ag/Cu for balls
• Sn/Bi popular in Japan

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Component Availability Concerns

• Although vendors are offering some lead-free
  parts your selection will be far more restricted
  than in the past.
• Single-source for a part?
• A part that is not quite the one you want?
• No source at all?
• Change in lead-times?
• More expensive?
• Purchasing needs to work in close conjunction
  with Engineering/Design and vendors to ensure
  that the lead-free parts needed are available
  compatible with the manufacturing process.

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Component Availability StatusTier 1 EMS
Provider's Survey
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Component Materials Management Concerns

• Some components are changing to lead-free WITHOUT
  their part changing.
• Part Management / Tracking
• Termination Finish
• Temperature and MSL Rating
• Labeling and Marking
• Materials Handling / Inventory

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Component Reliability Concerns

• The higher melting temperatures of the lead-free
  solders that are coming into use mandate
  components that can withstand the increased
  temperature stresses of the soldering process.

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Component Reliability Concerns

• A component's internal thermal damage may not be
  detectable by electrical tests. This compounds
  the problem.
• The internal damage eventually may trigger a
  field failure.
• Popcorning will be more likely during second side
  reflow.

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Component Wetting

• Different materials have different wetting
  characteristics.
• Any solderability issues with Sn/Pb soldering
  will be exacerbated by lead-free soldering.
• Engineering should consider wetting when
  specifying component finish.
• Designers should be aware of reduced
  solderability on second-side reflow and
  through-hole processes.

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Component MSL Rating

• Industry testing has demonstrated that there is
  no generic solution for maintaining an ICs MSL
  with a higher reflow profile
• MSL degrades with an increase of peak reflow
  temperature.
• Degradation of MSL may increase with increasing
  profile dwell above 200C
• Will result in an increased need to pre-bake
  parts and could require more stringent storage
  methods.
• Storage and handling procedures may need
  adjustment.

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Tin Whiskering

• Finishes can be susceptible to the spontaneous
  growth of single crystal structures known as tin
  whiskers, which can cause electrical failures
  ranging from parametric deviations to
  catastrophic short circuits.
• No clear mechanism of growth is known.
• An industry wide, standardized accelerated test
  to show the propensity of whisker growth has
  NOT been defined yet.
• Continues to be an oft-argued subject.
• Proponents of matte tin argue that whiskering is
  a result of the plating process, and not
  necessarily inherent to pure tin. They
  demonstrate that whiskering can also occur with
  Sn/Bi, etc.
• Others suggest that a dopant is needed to offset
  the whiskering.
• Most Japanese manufacturers utilize Sn/Bi finish
• Mitigation methods have been proposed but not
  agreed upon.

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Tin Whiskers Growth RatesWhisker growth after
temperature cycling (-40C/85C, 5K/min, 30
minutes dwell time) comparing bare components and
modules (soldered with SnAgCu and SnPbAg).
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Tin Whiskering

• Engineering should pay close attention to this
  issue.
• NEMI, JEDEC, and IPC have committees working on
  this issue now.

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PWB Materials

• Must ensure board materials can withstand reflow
  temperatures without warpage, sag, or
  delamination.
• Some FR4 will discolor at higher temperatures.
• Via cracking on thick substrates is a possibility
• Higher Tg material may be required.
• Tg The temperature at which an amorphous
  polymer changes from a hard and relatively
  brittle condition to a viscous or rubbery
  condition.
• High temperature materials may be required
• Low temperature material has a Tg around 140?C
• High temperature material has a Tg around 170?C

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PWB Surface Finishes

• Several surface finish options have been
  available and used widely for years.
• ENIG - Au/Ni
• OSPs
• Immersion Sn, Ag
• Lead-Free HAL
• Each is viable for certain applications.

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Impact of Solder Finishes
Production dot solderability test pattern with
tin/silver/copper
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Impact of Solder Finishes
Nickel/Gold
OSP
Silver
Tin
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PWB Materials

• Must ensure board materials can withstand reflow
  temperatures without warpage, sag, or
  delamination.
• Some FR4 will discolor at higher temperatures.
• Via cracking on thick substrates is a possibility
• Higher Tg material may be required.
• Tg The temperature at which an amorphous
  polymer changes from a hard and relatively
  brittle condition to a viscous or rubbery
  condition.
• High temperature materials may be required
• Low temperature material has a Tg around 140?C
• High temperature material has a Tg around 170?C

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PWB Materials

• The current high Tg FR4 laminates most widely
  offered to the North American market consist of
  Tg 170 Dicy resin system and Tg170 Phenolic resin
  system (huge in Asia but not so widely used or
  offered in North America). There is also Nelco
  -13 which is a modified epoxy resin system that
  yields a Tg of 210.
• Experience has shown that the standard Dicy Tg
  170 resin system is adequate for most lead free
  applications. However, it is not "robust".
• Sometimes rework or multiple passes in the higher
  temperature lead free processes can damage the
  material.
• It is well known that the Phenolic Tg 170 resin
  system has a higher Degradation Temperature and
  therefore can withstand more thermal excursions,
  but it is not as widely offered in North America.
• Nelco has a material which is designed for high
  speed applications which boasts a Tg of 210. This
  material is very robust for lead free
  applications but is more expensive than the other
  resin systems listed above.

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Flux Considerations

• The particular flux in use will continue to have
  a great impact on an assemblys manufacturability
  and reliability.
• Select flux chemistries (paste, liquid flux and
  cored wire) suitable for lead-free processing and
  your particular application. As with alloys,
  what is suitable for one manufacturer may not be
  for another. One should consider
• Activation temperature
• Activity level
• Compatibility with alloy
• Reliability properties
• Higher solids/activity liquid fluxes may be
  required.
• Evaluation of new fluxes may be required.

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Lead-Free Alloys
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Drop-In Replacement?

• NCMS Study
• Multiyear, multimillion study in the 1990s that
  examined lead-free solders.
• 70 alloys studied to find a drop in lead-free
  solution.
• The result There is NO drop in solution

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Alloy Requirements

• Low Cost
• Non-hazardous
• Mechanically reliable
• Thermal fatigue resistant
• Relatively low processing temperature
• Compatible with a variety of lead-bearing and
  lead-free surface coatings

• Good wetting
• All base elements available in sufficient supply
• Easily repairable
• Good thermal and electrical characteristics
• Compatible with current equipment and chemistries
  
• Available in all solder forms

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Elements to Avoid for Widespread Use

• Bismuth- embrittlement, poor fatigue resistance,
  secondary eutectic of 96C formed if exposed to
  lead.
• Indium- cost, supply, poor resistance to
  corrosion and rapid oxide formation during
  melting.
• Zinc- corrosivity, oxidation, ease of use
• Cadmium, Gallium, Germanium, etc.

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Most of the lead-free alloys currently available
are rich in tin

• Many of these are binary alloys that have been
  used for years in non-electronic applications.
• Many of these alloys offer advantages over Sn/Pb
  alloys.
• However, these benefits vary greatly among the
  various lead-free alloys.

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Common Lead-Free Alloys

• Sn42/Bi(/Ag1)
• Sn/Ag/Cu
• SN100C

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Sn42/Bi(/Ag1)

• 138C Melting Temperature.
• Ag-containing alloy has proven to be viable for
  certain consumer electronic applications.
• Superior fatigue resistance compared to Sn/Bi
• HP has done a lot of work with this alloy.
• Not viable for many applications due to its low
  melting temperature.

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Tin-Silver-Copper Alloys

• Despite a confusing patent situation and
  continuing questions about reliability, the
  tin-silver-copper family of alloys has earned a
  great deal of positive response from various
  industry consortia and organizations in recent
  years and the majority of manufacturers plan on
  implementing one of these alloys.
• In general, this family of alloys demonstrates
  relatively low melting points, good reliability
  characteristics, and, depending upon the exact
  composition, reasonable cost.

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Sn/Ag/Cu vs. Sn63/Pb37

• In order to learn how Sn/Ag/Cu alloys would
  perform as a substitute for the traditional
  tin/lead solder, a comparison of the physical
  properties of Sn/Ag/Cu and Sn63/Pb37 was made.

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Physical Properties

• Tensile Sn63 Sn/Ag/Cu
• UTS (ksi) 4.92 5.73
• Yield Strength (ksi) 4.38 4.86
• Youngs Modulus (msi) 4.87 7.42
• Elongation 52.87 50.00
• tested per ASTM E-8
• Compression Sn63 Sn/Ag/Cu
• Elastic Modulus (msi) 3.99 4.26
• YS (ksi) 4.52 4.33
• Stress 25 /u (ksi) 7.17 8.54
• Hardness 10.08 13.5

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When the curves of mild stresses affected on
Sn/Ag/Cu and Sn63/Pb37 are overlaid, they are
virtually identical.
64
Sn/Ag/Cu has demonstrated the ability to be more
adaptable to a wide range of stresses than
Sn63/Pb37.
Sn/Ag/Cu Sn/Pb
65
Thermal and Electrical Properties

• Sn/Ag/Cu Sn63/Pb37
• Thermal Diffusivity 35.82/-.18mm2/s
• Specific Heat 218.99 J/(kg.K) 150.0J /(kg.K)
• Thermal Conductivity 57.26 W/m.K 50.0 W/m.K
• Electrical Resistivity 1.21 E-7ohm.m 1.45
  E-7ohm.m
• Electrical Conductivity 8.25M(ohm-1m)
• Testing performed by ITRI UK

66
Intermetallic Growth Rates

• Another area of concern relates to the
  intermetallic growth rates.
• Sn/Ag/Cu is more resistant to Cu intermetallic
  growth.

67
Wave Solder Drossing

• Sn/Ag/Cu and Sn/Pb are very similar.
• Sn/Cu produces substantially more dross.

68
Solder Joint Reliability Testing

• How an assembly will survive after it has been
  soldered with a tin-silver-copper alloy must be
  determined before implementing an alloy for
  production.
• It should also be understood that solder joint
  reliability is dependent upon several factors
  other than solder alloy, including solder joint
  geometry, fatigue severity and soldering surface
  finish.
• Furthermore, tin-silver-copper alloy fatigue
  resistance has been proven superior to tin/lead
  under certain testing condition, but inferior
  under other conditions.

69
Solder Joint Reliability Testing
70
Solder Joint Reliability Testing
71
But Which Sn/Ag/Cu Alloy?

• Most of the industry will use an Sn/Ag/Cu alloy.
• But which one?
• As there are several different alloy formulations
  within the tin-silver-copper family, background
  information is necessary to determine if any
  particular alloy is best suited for the broadest
  range of applications.
• IPC SPVC Presentation.

72
Microstructure Comparison

• Concern about Ag3Sn needles (platelets) found
  in the microstructure of Sn/Ag3.8/Cu0.7 and
  Sn/Ag4.0/Cu0.5
• Not found in Sn/Ag3.0/Cu0.5
• Potential reliability problem?

Sn95.5/Ag3.0/Cu0.5
Sn96.5/Ag4.0/Cu0.5
73
Ag3Sn Needles (Platelets)
74
Microstructure Comparison

• The image to the right is of the Ag3Sn forming as
  large plates attached to the interfacial
  intermetallics. This results in plastic strain
  localization at the boundary between the Ag3Sn
  plates and the bounding b-Sn phase.
• Adverse effects on the plastic deformation
  properties of the solidified solder have been
  reported when large Ag3Sn plates are present.
• It also has been suggested that silver segregates
  to the interface and weakens it by poisoning.
  The brittle fracture is exacerbated by gold
  contamination.

75
IPC SPVC

• Studying the different Sn/Ag/Cu alloys.
• So far have found no difference between
  manufacturability, metallography, or reliability.
• Thermal Shock and Thermal Cycling Testing being
  run now.
• No differences found thus far.
• IPC SPVC Reliability Report and Analysis
  completed January 2005
• If no differences between the alloys, will
  recommend SAC305
• IPC SPVC Presentation.

76
IPC SPVC Reliability Testing ProgramProgram
Elements
77
IPC SPVC Reliability Testing ProgramProgram
Elements
78
IPC SPVC Reliability Testing ProgramProgram
Elements

• Base line metallographic analysis of completed
  assemblies.
• The characterization involved
• X-Ray Fluorescence measurement of the
  immersion silver plating thickness on test
  vehicles
• Transmission x-ray examination of solder joints
• Solder joint cross sectioning and optical
  microscopy
• Base Line Analysis Complete

79
IPC SPVC Reliability Testing ProgramProgram
Elements

• Example of Analysis

80
IPC SPVC Reliability Testing ProgramProgram
Elements

• Results of Base Line Metallographic Analysis
• (including XRF, transmission x-ray, SEM/EDX, and
  optical microscopy)
• Good quality solder assembly on all test
  vehicles.
• No discernable solder joint differences between
  SAC alloys.
• Size and shape of SAC alloy solder joints not
  significantly different than SnPb joints.

81
IPC SPVC Reliability Testing ProgramProgram
Elements

• Thermal Cycling
• The thermal cycle profile proposed reflects the
  IPC test regimen and consists of a low
  temperature soak of 0?C for 10 minutes with a
  temperature increase ramp up to 100?C with a high
  temperature soak of 10 minutes prior to a ramp
  down to the low temperature. The total cycle is
  expected to take approximately 60 minutes or
  less.

82
IPC SPVC Reliability Testing ProgramProgram
Elements

• Thermal Shock Exposure
• The thermal shock test profile is very similar to
  the JEDEC prescribed exposure. It consists of a
  low temperature -40?C soak for 5 minutes followed
  by a transition to the high temperature of 125?C
  with a high temperature soak for 5 minutes and
  finally transitioning back to the low
  temperature. This cycle would be repeated
  continuously. The total cycle time is estimated
  to be approximately 45 minutes.

83
Alloy Comparison Conclusion

• Several processing and reliability issues are
  associated with Sn/Cu.
• In addition, difficulties arise when using two
  alloys for PCBA
• Since there are no advantages in terms of
  processing, reliability, or availability for the
  high-silver Sn/Ag/Cu alloys as compared to the
  low-silver alloys, it is only logical to utilize
  the less expensive of these for use in all
  soldering applications.
• Several low-silver Sn/Ag/Cu alloys are available
  from solder manufacturers throughout the world.
• This is what JEIDA has recommended for widespread
  use to Japanese manufacturers.
• These alloys provides users with the advantages
  of the Sn/Ag/Cu family of alloys, and thus
  eliminate the problems associated with Sn/Cu
  alloys and a dual-alloy process.

84
SN100C Alloy

• SN100C was developed by Nihon Superior in Japan
  and offers high-throughput and the lowest cost of
  ownership as compared to any other lead-free
  solder alloy.
• Does not contain costly silver or bismuth.
• Bridge-free and icicle-free soldering.
• Smooth, bright, well-formed fillets without
  micro-cracks.
• Good PTH penetration and topside fillet
  formation.
• Low copper pad erosion.
• Low drossing.
• Does not require a nitrogen atmosphere.
• Low aggressiveness to soldering equipment.
• Reliable joints (no reported failures in 6 years
  of field service).

85
SN100C Alloy

• Availability
• Bar Solder
• Solder Bath Top-Off Alloy (SN100Ce)
• Solid and Flux Cored Wire Solder
• Other forms such as Solder Paste, Spheres, and
  Preforms are also available.
• Successfully Tried and Tested
• Leading electronics manufacturers throughout the
  world have used SN100C with outstanding results.
  To date, millions of circuit boards have been
  assembled with the SN100C family of solders in
  all types of products.

86
SN100C Alloy

• Customer experience over several years is that
  the TOTAL cost of running a standard wave
  soldering machine with SN100C when all factors
  are taken into account can be up to one third the
  cost of running the same machine with
  tin-silver-copper alloys.
• The actual saving in each case will depend on the
  number of factors that apply, but the cost of
  running a line with SN100C is always lower than
  the cost of running the same line with
  tin-silver-copper.

Annual Cost per Wave Solder Machine of Running
Sn-Ag-Cu (1) and SN100C (2)
87
SN100C Test Data
88
SN100C Test Data
89
SN100C Wave Soldering Recommendations
90
Solder Surface Comparison
91
Sn-37Pb
SN100C
92
Sn-37Pb
SN100C
93
Sn-37Pb
SN100C
94
Tin-Lead Lead-Free Compatibility

• The question of what happens to a lead-free
  solder joint if it becomes contaminated with lead
  is important because during the transition to
  lead-free soldering it is very likely that
  tin/lead parts will still be used in a great deal
  of production.
• In fact, exposure to lead from boards, components
  and repair operations could happen for years.

95
Transition to Pb-FreeAvoiding Board Mixing

• As long as both Sn-Pb and lead-free products are
  built in the same factory, it is important that
  the two board process types be kept separate.
• It is risky when the same product is being built
  in both SnPb and Pb-free versions at the same
  facility.

96
Transition to Pb-freeAvoiding Board Mixing

• Recommendations
• Mark Pb-free products in some way, so that they
  are easily identifiable.
• Visibly mark dedicated machines or lines.
• Set up and identify separate rework workstations
  for SnPb and Pb-free boards.
• When boards are returned to a line after being
  taken to an off-line area (like debug, rework,
  failure analysis, or measurement for process
  control), take extra care to confirm that the
  boards are the correct type.

97
Lead-Free Backward Compatibility Process

• Manufacturers convert to lead-free components
  and/or PWBs before lead-free solder is used.
• This is OK no reliability problems reported.
• There is some concern about mixing lead-free BGAs
  with a tin-lead process.
• This process can result in a non-uniform
  microstructure that can impact solder joint
  integrity.

98
Lead-Free Forward Compatibility Process

• Board Assembly process has been converted to Lead
  free
• Some components and/or PWBs still contain Lead
• What problems can occur?

99
Lead Contamination

• Unfortunately, in the past the presence of lead
  in lead-free alloys has been presumed to be
  acceptable.
• The logic behind this was that tin and lead are
  soluble in a lead-free system.
• However, what has been overlooked is that the
  intermetallic crystalline structures in lead-free
  systems are not soluble and will precipitate at
  lead boundaries.
• Thus, when using a lead-free alloy to solder to
  Sn/Pb coated component leads, Pb can actually
  create voids in the solder joint that can result
  in joint failure.

100
Lead Contamination

• An example of what can also occur is with
  bismuth-bearing alloys, as bismuth and lead form
  pockets with a secondary eutectic of 96C.
• This is a well documented occurrence and could
  have obvious negative effects on reliability if
  an assembly is exposed to any thermal stress.

101
Field Failures from Lead Contamination

• All of the lead as an impurity in a solder joint
  goes to the last area of the joint to cool.

102
Field Failures from Lead Contamination

• The lead forms a ternary alloy of tin/lead/silver
  that melts at 179?C. This alloy surrounds the
  grains of the lead-free alloy.
• This intergranular phase exhibits poor adhesion
  to the lead-free alloy, causing grain separation.
  
• So, try not to not mix lead-free solder with
  leaded parts!

103

• Process Issues
• and Advice

104
Process Considerations

• You have finally confirmed that the parts,
  materials and equipment to be used in your
  lead-free assembly are available, suitable and
  reliable for your application.
• Now its time to get your process optimized in
  order to achieve maximum throughput and
  reliability.
• Paste Handling
• Printing
• Reflow
• Wave Soldering
• Rework Repair
• Cleaning

105
Paste Handling

• Shelf-lives with lead-free pastes may be reduced
  as compared to tin/lead, and storage conditions
  may be slightly more stringent.
• Alloy dependent.
• Some pastes require freezing.
• However, in general, the same rules as with
  tin/lead apply.
• Prevent/minimize exposure to heat and humidity.
• Allow paste to come to room temp before using.
• Do not mix old and new paste.

106
Printing

• As compared to tin-lead solder pastes, lead-free
  pastes should exhibit similar features on the
  stencil and many equipment set points should
  transition well.
• However, implementation of lead-free solder paste
  does necessitate some critical, often overlooked
  adjustments, as well as provides an opportunity
  to review and fine-tune several key printing
  parameters.

107
Stencil Apertures

• Many manufacturers currently use reduced
  aperture-to-pad ratios to prevent bridging and
  solder beading.
• Due to differences in the solderability
  characteristics of lead-free circuit board
  finishes and the inability of lead-free solders
  to spread as well as tin-lead, reduced stencil
  apertures may need to be opened up back to a 11
  aperture-to-pad ratio.
• This ratio should not result in bridging because
  density differences between lead-free and
  tin-lead solder pastes results in less slump with
  lead-free pastes.

108
Cycle Times

• Some lead-free pastes have shown a propensity to
  stick to squeegee blades after the print cycle.
• This is a result of the different densities of
  tin-lead and lead-free alloys.
• To combat this, print cycle times may need to be
  slowed.
• By slowing the print cycle time, any solder paste
  sticking to the squeegee blades should fall back
  onto the stencil prior to the next print stroke.

109
Squeegee Pressure

• Squeegee pressure is the downward pressure
  exerted by the squeegee blade onto the stencil
  surface during the print cycle.
• The squeegee pressure required for lead-free
  pastes is often higher than that for tin-lead.
• A typical starting point for squeegee pressure
  for a lead-free solder paste is 1.5 to 2 lbs. of
  pressure per linear inch of printable area.

110
Squeegee Pressure

• Squeegee pressure should be adjusted to just high
  enough to achieve a good, clean, topside wipe of
  the stencil surface.
• Leaving paste behind on the stencil surface can
  promote poor aperture release, torn prints,
  insufficient solder coverage and premature paste
  dry out.

111
Lead-Free Solder Paste Printing Requirements

• Easy to achieve clean stencil wipe
• Do not clog apertures, even on fine-pitch
  applications
• Prints high-speeds without slumping or
  insufficients
• Long stencil life
• Compatible with enclosed paste deposition systems
• Long tack time for batch operations

112
Lead-Free vs. Tin-Lead Solder Paste Comparison

• Same flux chemistry used in conjunction with Sn63
  and SAC305.
• Metal load optimized for each alloy.

113
Print Height Consistency Analysis30 boards were
printed and a specific pad was chosen to
determine the print height consistency between
boards.
Sn63 SAC305
114
Consistency of Print Volumes During Standard to
High-Speed Printing
Sn63 SAC305
115
Tack Characteristics

• Tack versus Time at Ambient Conditions (72F
  (22C) at 40 RH) over 24 hours.

Sn63 SAC305
116
Tack Characteristics

• Tack versus Time at Humid Conditions (72F (22C)
  at 75 RH) per IPC-TM-650.

Sn63 SAC305
117
Lead-Free Solder Paste Fine Pitch Printing
QFP 0.020 pitch
0201 Components
8 mil gap
01005 Components
118
Fine Pitch Printing Without Slumping
.06mm gap
IPC Slump Test Pattern
119
Placement

• Should not be affected significantly.
• Tack time and force are dictated by the
  particular solder paste in use.
• Accuracy is more critical because lead-free
  alloys do not self-correct as well as tin-lead
  alloys.

120
Reflow Profiling

• Most lead-free alloys require higher reflow
  temperatures than tin/lead
• Sn/Ag/Cu _at_ 240C 5C.
• Some components may be exposed to temperatures as
  high as 260C due to ?T
• Challenges
• Minimize ?T
• Maximize wetting
• Solutions
• Optimize reflow profile (including cooling)
• Equipment changes

121
Reflow Profiling
122
Reflow Profiling
123
Reflow Profiling - Voiding

• Voiding can be more prevalent with lead-free
  alloys.

124
Reflow Ovens

• Most modern reflow ovens can provide the
  necessary heat for lead-free soldering.
• However, whether this equipment can also tightly
  control the reflow profile parameters (minimize
  ?T) should be investigated.
• Nitrogen may also need to be utilized to
  compensate for difficult-to-wet parts and poorer
  wetting solder alloys.
• Nitrogen generally will help in lead-free
  soldering. Nitrogen use probably will increase
  due to the broader process window it provides
  when utilizing lead-free alloys.

125
Reflow Process Cost Comparison

• Energy consumption has been found to vary
  significantly between solder alloys, primarily
  due to the difference in melting points and the
  corresponding changes in the reflow profile
  design parameters.
• Testing has indicated that soldering with SnAgCu
  alloys will result in an 11 percent increase in
  reflow energy use.

126
Wave Soldering

• May require a higher pot temperature than
  tin/lead 255-265C
• May require a change in liquid fluxes to
  compensate for the poor wetting of some alloys
  and high thermal stresses of the wave process.

127
Wave Soldering Equipment

• Most modern wave solder machines can provide the
  necessary heat (preheat and wave) for lead-free
  soldering.
• Nitrogen blanket may be required, depending upon
  the alloy selected.

Chip
Main
1
2
3
128
Wave Soldering Equipment

• Many high-tin alloys rapidly dissolve the
  materials often used in wave solder equipment.
  SS pots, nozzles, impellers, etc will need to be
  replaced with cast iron, titanium, or a special
  coating.
• Wave soldering equipment manufacturers have had
  success using a Melonite coating over SS.
• Equipment Impacts of Lead Free Wave Soldering,
  Morris and OKeefe. APEX 2003.

Pics from TWI/UK
129
If You Choose Not to Change Your Pot

• Here are the solder changeover steps

130
Typical Lead-Free Wave Profile
131
Wave Soldering Drossing

• Sn/Ag/Cu and Sn/Pb are very similar.
• Sn/Cu produces substantially more dross.

132
Lead-Free Automatic Soldering Equipment Pot
Maintenance Issues

• Different proposals have been suggested for
  lead-free wave soldering.
• One option is to use the Sn/Cu0.7 alloy for wave
  soldering and Sn/Ag/Cu for surface mount.
• Another idea is to use a low silver (lt3.0Ag)
  Sn/Ag/Cu alloy for all applications.
• A third is to use a high silver content (gt3.8Ag)
  Sn/Ag/Cu alloy.
• Unfortunately, it appears that whichever process
  is implemented, wave solder pot maintenance could
  be problematic.

133
Copper Limits

• As discussed, some alloys pick up copper at
  different rates than others.
• Over time, however, all the alloys seem to reach
  approximately 2 copper at 530F (276C).
• Clearly, an agreed upon industry specification
  for lead-free pot maintenance is needed as a
  guideline for the users of these alloys.

134
Impurity Limits

• The chart shown has been developed from empirical
  studies and metallurgical evidence. As is shown
  here, the upper limits for copper in the pot is
  1.5. Above this point the alloy becomes sluggish
  and at 1.9 to 2 precipitation in the pot starts
  to occur, which can lead to damage to the wave
  pump and baffles.

135
Traditional Cu Build-Up Removal

• Copper is a well-understood contaminate in the
  Sn63/Pb37 alloy for automatic soldering
  applications.
• If the copper level in pots becomes too high, the
  solder may suffer from poor flow as well as
  experience embrittlement issues.
• In a standard Sn63/Pb37 wave pot, as impurities
  such as copper build up, these form
  intermetallics with the tin.
• This intermetallic build up can be systematically
  removed by reducing the temperature of the solder
  pot to 370F (188C) and allowing the pot to sit
  undisturbed for gt 8 hours.
• The density of the Cu6Sn5 intermetallic is 8.28,
  while Sn63/Pb37 is 8.80, allowing most of the
  Cu6Sn5 to float to the top of the pot after a few
  hours of cooling. After this the top of the pot
  is skimmed and new solder is added to bring up
  the level. This typically will maintain copper
  levels below 0.3 and can maintain the copper
  level in the 0.15 range.

136
The Lead-Free Problem

• Unfortunately, whether Sn/Cu or Sn/Ag/Cu is
  implemented for wave soldering, the density of
  both alloys is less than Cu6Sn5.
• Approximately 7.39 versus 8.28.
• Therefore, instead of the intermetallics floating
  off and easily being removed as when in
  Sn63/Pb37, the intermetallics sink and are
  dispersed through the lead-free alloy in the pot.
  
• To add to these problems, as lead-free
  electronics assembly becomes increasingly
  popular, more organic coated (OSP) copper boards
  will be utilized. This could result in more
  copper exposure to the wave.

137
The Result?

• The result and biggest problem of all of the
  above is that solder pots could need to be dumped
  more often, leading to a complete change over of
  the wave pot.
• This obviously is costly, time consuming and
  unwanted.

138
Then What To Do?

• A procedure for separating copper intermetallics
  from lead-free pots has to be developed.
• How?
• Use pots that can drain from the bottom
• Catch copper intermetallics into a net placed
  in the bottom of the pot after cooling down pot
• Utilize another pot
• Avoid OSP boards and top off the pot with Sn or
  Sn/Ag bars.

139
Lead-Free Hand Solder Rework FlowRemains the
same as with tin/lead

SMT Components
Through Hole Components
Identify Defective Component
Identify Defective Component
Remove Defective Component Using Soldering Iron,
Tweeze or Hot Air Tool
Remove Defective Component Using A Solder Sucker
Solder Wick Pads
Clean Residual Solder Out Of Holes
Solder New Component With Soldering Iron
Solder New Component With Soldering Iron
Inspect Clean Site
Inspect Clean Site
Retest
Retest
140
Rework and Repair

• Operators must be trained for lead-free rework,
  as lead-free solders do not flow as well as
  tin/lead.
• Stronger cored wire fluxes are required.
• All rework should use the same lead-free solder
  alloy as originally used on the solder joint.
• If more than one alloy is in use in the
  production process, operators should be trained
  to use the correct wire for each part.
• An 800F tip temperature and/or working at a
  slower speed will reduce common lead-free hand
  soldering defects such as bridging and pad
  lifting.

141
Rework Equipment

• It is necessary to ensure that the desoldering
  and soldering stations are suitable for lead-free
  processing, i.e. can reach the necessary
  temperatures for lead-free soldering.
• Lead-free soldering can wear out tips at a much
  higher rate than tin/lead.

142
Common Lead-Free Hand Soldering Rework Problem

• Solder bridges.
• Working slower and using 425C/800F solder tips
  helps correct these problems.

143
Cleaning

• In general, flux residues from lead-free solders
  are still cleanable.
• Water soluble residues may be cleaned in water,
  no-cleans and RMAs with a saponifier or
  cleaning solvent.
• However, it has been found that an increase in
  pressure, cleaning times and/or cleaner
  concentrations often is necessary.
• Cleaning chemistry companies are developing
  lead-free compatible cleaners.
• The efficiency of the cleaning equipment,
  strength of the cleaner, melting point of the
  alloy being used and thermal stability and
  propensity of the flux to char all effect the
  cleanability of an assembly.

144
Inspection

• Lead-free solder joints look different
• They are generally dull grainy
• This does not necessarily mean that they are
  weaker than tin/lead joints.
• AOI equipment will need to be recalibrated.
• Higher rate of false failures possible.
• X-Ray
• Density of lead-free solders is less, contrast is
  not as good as with Sn/Pb

145
Inspection

• Inspection personnel must be trained on what to
  look for when inspecting lead-free solder joints
• IPC-A-610D Is under review.

146
Solder Appearance Comparison
Tin-Lead
Lead-Free
147
Solder Appearance Comparison
Tin-Lead
Lead-Free
148
Solder Joint Appearance
149
Solder Joint Appearance
150
Solder Joint Appearance
151
Solder Joint Appearance
152
Solder Joint Appearance
153
Solder Joint Appearance
154
Lead-Free Solder Joint Appearance
Sn/Ag/Cu Chip Resistor
Sn/Ag/Cu Chip Capacitor
Sn/Ag Transistor
155
Pin Probe Testing

• Current test fixture settings could possibly
  damage lead-free solder joints.
• Tips may probably wear out faster.
• The higher reflow temperatures may make probing
  through pin probeable flux residues more
  difficult. This could warrant changing flux
  chemistries or cleaning in some cases.
• Test pads may be more difficult to probe due to
  increased oxidation during higher reflow
  temperature processes.

156
Lead-Free Overview Conclusion

• Lead-free electronics assembly is achievable.
• It is being done NOW.
• It is a complicated process that requires a
  strong understanding of the changes required of
  each person involved in the manufacturing
  process.

157
Conclusion

• Lead-free electronics assembly is achievable.
• It is being done NOW.
• It is a complicated process that requires a
  strong understanding of the changes required of
  each person involved in the manufacturing
  process.

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158
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