Lead Free Material Selection Guide

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Lead FreeMaterial Selection Guide

• UniLine
• Hermann Löns 27 31199 Diekholzen
• Tel [phone] Fax [phone]
• pcb_at_uniLine.de www.uniLine.de

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What is RoHS / WEEE?

• Waste Electrical and Electronic Equipment
• Restrictions of Hazardous Substances
• Substances maximum level by mass

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Requirements to the PCB

• Base material
• FR-4 meets RoHS requirements
• Surface finish
• All the popular alternatives to HASL with lead
  complies with RoHS.

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PCBs for Lead Free Soldering

• Important base material parameters
• Tg Glass Transition Temperature
• Td Decomposition temperature
• T260/T288 Time to Delamination
• CTE

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Glass Transition Temperature, Tg

• The Tg of a resin system is the temperature at
  which the material transforms from a relatively
  rigid or glassy state, to a more deformable or
  softened state.
• Tg is important to understand since the
  properties of base materials are different above
  the Tg versus below the Tg.

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Decomposition temperature, Td

• The decomposition temperature is a measure of
  actual chemical and physical degradation of the
  resin system. This test uses thermogravimetric
  analysis (TGA), which measures the mass of a
  sample versus temperature.
• The decomposition temperature is reported as the
  temperature at which 5 of the mass of the sample
  is lost to decomposition

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Time to Delamination

• The time to delamination is a measure of the time
  it takes for the resin and copper, or resin and
  reinforcement, to separate or delaminate. This
  test utilizes TMA equipment to bring a sample to
  a specified temperature and then measures the
  time it takes for failure to occur.
• With Pb-free assembly temperatures reaching
  260oC, the T260 test has become a much more
  relevant measure of performance.

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Coefficient of Thermal Expansion CTE

• CTE values are important since they influence the
  reliability of the finished circuit.
• Other things being equal, less thermal expansion
  will result in greater circuit reliability as
  less stress is applied to plated holes

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Conclusion

• Standard FR-4 complies with RoHS
• A wide range of surface finishes that complies
  with RoHS is widely available.
• Lead Free soldering have a great impact on the
  material
• Tg is not a sufficient parameter to select
  materials for lead free soldering!

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What impacts the selection?

• Assembly requirements
• Application requirements
• PCB manufacturing process
• Copper / layers
• Holes and plating
• PCB thickness
• Mixed materials

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Soldering process

• Number and type of soldering processes
• For each soldering we need
• Type of soldering
• Peak temperature.
• Repair/replacement/selective soldering
• Standard profiles
• Wave IEC 61760
• Reflow JSTD020C

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Solder alloys

• SAC305
• Solders at 235-240 0C
• Copper erotion
• SN100C
• Solders at 260-270 0C
• Less copper erotion
• Better flatness/brighter/less bridges?

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Application requirements

• Mechanial demands
• High mechanical demands one step up
• Thermal demands
• High thermal demands one step up

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Application requirementsEnvironmental aspects

• Vibration
• Re IVF report Brittle Fractures
• Heat
• Material breakdown
• Cycling (viaholes)
• Moisture
• Delamination

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Manufacturing process

• Core
• Prepreg
• Pressing parameters
• Copper surface cleanliness roughness
• Plating - hole quality and copper adhesion

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Copper - layers

• Copper distributes heat!
• More copper more heat more challenge
• 1,6 mm standard ca 6-8 layers 1 oz Cu
• Thicker copper per layer
• More layers per board thickness
• Planes in outer layers

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Holes and plating

• Holes distributes heat into the board!
• Blind via/ buried via extra bonding cycle
• Each extra bonding cycle one step up
• Microvia can be 1-2 extra bonding cycles
• Smaller holes weaker holes
• Aspect ratio gt 81 - requires better Z CTE
  control high material performance.

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PCB Thickness

• Thickness gt 1,6 one step up
• Related parameters
• Hole aspect ratio
• Base copper thickness,
• Number of layers
• Plating thickness

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Mixed materials

• HF applications
• Bow Twist
• Balanced build
• Increased plating thickness
• Rigid Flex
• High performance material must be used!
• If possible, avoid Covercoat inside rigid part.
• Balanced build
• Increased plating thickness

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Laminate properties

• Fibre Glass Resin FR-4
• Different types of Resin
• Standard Dicy cured FR-4
• Mid Performance Dicy Cured
• Mid Performance Phenolic Cured
• High Performance Dicy Cured
• High Peformance Phenolic Cured

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IPC 4101B Lead Free

• IPC-4101B/99. High Tg FR-4, inorganic fillers,
  brominated flame retardant
• IPC-4101B/101. Low Tg FR-4, inorganic fillers,
  brominated flame retardant
• IPC-4101B/121. Low Tg FR-4, no fillers,
  brominated flame retardant
• IPC-4101B/124. High Tg FR-4, no fillers,
  brominated flame retardant
• IPC-4101B/126. Very high Tg, inorganic fillers,
  brominated flame retardant
• IPC-4101B/129. Very high Tg, no fillers,
  brominated flame retardant

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Laminate Performance GuideStandard PCB
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Material selection guide
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Material selection guide
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Material selection guide
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Material selection guide
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Material selection guide

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Selection guide - Features...
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Selection guideApplication demands.
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PCB finishes for RoHS and Lead Free Soldering
UniLine Hermann Löns 27 31199
Diekholzen Tel [phone] Fax 05121
267815 pcb_at_uniLine.de
www.uniLine.de
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Topics

• RoHS requirements to the PCB finish
• Lead Free soldering requirements
• Alternatives
• Today

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RoHS requirements to the PCB finish

• Material content
• Increased heat in soldering process

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RoHS requirements to the PCB finish

• Substances maximum level by mass
• Lead                                    lt 1000
  ppm / 0,1
• Hexavalent Chromium lt 1000 ppm / 0,1
• Mercury                              lt 1000 ppm
  / 0,1
• Cadmium lt 100 ppm / 0,01
• Polybrominated Biphenyls (PBB)    lt 1000 ppm /
  0,1
• Polybrominated Diphenylethers (PBDE) lt 1000 ppm /
  0,1
• Levels measured by mass in any "homogenous
  substance" - defined as any substance that can be
  mechanically separated into an isolated substance

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Lead Free Alternative Finishes

• Lead Free HASL
• Silver
• Tin
• OSP
• ENIG
• ENIG OSP
• Flash Gold

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Lead Free HASL

• Several alloys used
• SAC 305
• SAC 308
• SN100CL (Nihon Superior Balver, ANSAN etc.)
• Can we mix soldering and HASL alloys? Yes..(?)
• Concerns
• Flux compatibility
• 1 extra heat process
• Flatness

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Chemical Tin

• Chemistry is under development
• White tin
• Silver doped tin
• Concerns
• Thickness enough for solderability, but
• Whiskers thick tin can give whiskers!
• Inter metallic layer (time and temperature)
• Handling (in all stages)
• Complex process control
• Via plugging
• Compatibility to Flux and soldermask

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Chemical Silver

• New chemistry released 2005
• Thickness improved
• Concerns
• Handling (in all stages)
• Sensitive to light
• Process control
• Compatibility to Flux
• Dendrites
• Markets Parts of Europe and USA

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OSP

• Development through 20 years
• Process control simple!
• Concerns
• Sensitivity to thermal cycles
• Shelf life
• Handling
• Markets Japan South East Asia USA.

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Chem. NI-AU

• Process control
• mature process long experience.
• Concerns
• Plugged via design black pad
• BGA brittle fractures
• Handling with care
• Markets Europe