November13th, 2012

Aileen Allen and Greg Henshall Hewlett-Packard Co.

Solder Alloy and Flux Materials Management from an OEM Perspective

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We will cover… •  Background and Problem •  Pb-free Alloys

• Long term solder joint reliability • New (low-Ag) alloy testing and acceptance

•  Solder paste and flux chemistries • HP’s qualification process • Halogen-free

•  Summary and Conclusions

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Issues with SAC305/405 •  Industry adopted SAC 305 & other “near eutectic”

alloys as the standard Pb-free alloys during the RoHS transition

•  Alloy optimization followed to address: • Poor drop/shock performance for BGAs − Mainly an issue for portables/handhelds − Brittle fracture failures on Ni/Au surfaces

• Expense of Ag is driving the desire to reduce Ag content − $560/lb – Oct, 2012

(Tin ~ $10/lb) − Wave solder bar main concern

• Poor barrel fill on thick boards for some surface finishes

• Copper dissolution

Ni Cu

Solder

IMC

Fracture surface showing intermetallic layer left, no

solder

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Wide range of alloy choices is both an opportunity and a risk

Alloys Sn1.0Ag0.5Cu (SAC105)

SAC205

Sn-3.5Ag

Sn0.3Ag0.7Cu+Bi (SACX)

Sn0.3Ag0.7Cu+Bi+Ni+Cr (SACX)

SAC 305+0.05Ni+0.5In

SAC255+0.5Co

SAC107+0.1Ge

SAC125+0.05-0.5Ni (LF35)

SAC101+0.02Ni+0.05In

Sn-3.5Ag + 0.05-0.25La

Sn-0.7Cu

Sn0-4Ag0.5Cu + Al + Ni

SAC305 + 0.019Ce

Sn-2.5Ag-0.8Cu-0.5Sb

Sn-0.7Cu-0.05Ni

Sn-0.7Cu-0.05Ni + GE (SN100C)

SAC105 + 0.02Ti

SAC105 + 0.05Mn

Sn-3.0Ag-1.0Cu

• SAC is Sn-Ag-Cu •  SAC305 is Sn-3.0Ag-0.5Cu •  SAC105 is Sn-1.0Ag-0.5Cu •  SACX is SAC with small quantities of dopants added

• Partial list of Pb-free solder alloys used commercially or being investigated for BGA/CSP balls

• Most new alloys have low silver content (or none at all)

Addressing issues with alloy alternatives led to expanding alloy choice

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Industry focus on two gaps 2008 iNEMI assessment of key areas where knowledge is lacking

Industry Focus Areas

Standardized test methods

Solder joint reliability

Long Term Solder Joint Reliability

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Questions to answer about thermal fatigue performance of new alloys

1.  How does the performance of low-silver alloys compare to that of eutectic Sn-Pb and SAC305?

2.  What is the quantitative impact of Ag concentration?

3.  What is the impact of dopants? 4.  Does relative performance among

alloys depend on the package type? 5.  How do the thermal fatigue conditions

impact acceleration behavior?

Impact of alloy composition on thermal fatigue life in the field

difficult to judge

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Overview of Industry Efforts •  Generate data to predict alloy thermal fatigue performance

Industry Working Group

Alcatel-Lucent Working Group

Jabil Working Group

iNEMI Alloy Characterization

Impact of Ag concentration Impact of Ag concentration & dopants

Rapid results through using existing test

materials

Comparison to Sn-Pb

Mixed Sn-Pb/Pb-free joints Data for common commercial alloys

Effects of thermal cycle profile Quantitative acceleration factors

Impact of package type

Complete Complete Complete Continuing

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IWG: Low Ag alloys may perform worse than high Ag alloys

•  0/100 °C accelerated test conditions

•  BGAs with SAC105 have lower performance than high-Ag alloys

•  BGAs with Sn-3.5Ag and SAC305 perform similarly

•  Comparison to eutectic Sn-Pb not established

Data of Henshall et al., APEX 2009

0/100°C 10 min. dwells

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Jabil: Experimental Materials & Procedures Solder Ball Alloys Studied:

•  SnPb: Sn-37Pb •  SAC 305: Sn-3.0Ag-0.5Cu •  SACX 0307: Sn-0.3Ag-0.7Cu + Bi + X •  SAC 105: Sn-1.0Ag-0.5Cu •  LF35: Sn-1.2Ag-0.5Cu + 0.05Ni •  SAC 205: Sn-2.0Ag-0.5Cu

Mixed and Unmixed Solder Joints Manufactured: •  Eutectic Sn-Pb paste with eutectic Sn-Pb components •  SAC305 paste with Pb-free components •  Eutectic Sn-Pb paste with Pb-free components

Four BGA Package Types: (0.5 mm to 1.27 mm pitch; 84 to 600 I/O)

Two Thermal Cycle Profiles •  0 to 100 °C, 10 minute dwells, 10 °C/min ramp rate •  -40 to +125 °C, 10 minute dwells, 10 °C/min ramp rate

Unmixed

Sn-Pb Baseline Pb-free Baseline

Low Ag

Mixed

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Jabil: Effect of % Ag on Characteristic Life (0/100 °C profile)

•  Low-Ag joints out perform Sn-37Pb in 0/100 °C test

•  Characteristic life increases with [Ag] for all packages

•  Alloy rank order maintained for all packages

Henshall et al., SMTAi 2010, APEX 2011

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Jabil: Effect of % Ag on acceleration factors

•   Accelera*on  for  Sn-‐37Pb  joints  less  than  all  Pb-‐free  alloys    •   Under  typical  IT  equipment  field  condi*ons,  low-‐Ag  alloys  may  outperform  Sn-‐37Pb      

Accelera*

on    

0.5  mm  CSP  0.8  mm  CSP  1.0  mm  PBGA  1.27  mm  SBGA  

Accelera*on  =    N63(0/100  C)    

N63(-‐40/+125  C)    

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iNEMI: Thermal cycle test overview

Profile  No.   Company  

Cycle  (Min/Max/Dwell)   Status  

Current  Cycle  #  

1   ALU   0/100/10   Complete   12900  

2   IST   25/125/10   Complete   9946  

3   Henkel   -‐40/100/10   Complete   6200  

4  Nihon/  

DfR  Solu*ons   -‐15/125/10   In  Progress   5575  

5   ALU   0/100/60   In  Progress   6100  

6   HP   25/125/60   In  Progress   4319  

7   HP   -‐40/100/60   In  Progress   3957  

8   CALCE   -‐15/125/60   In  Progress   2860  

9   CALCE   -‐40/100/120   In  Progress   1717  

10   Delphi   -‐40/125/10   Complete   3175  

Test  Profiles  and  Status  as  of    Sep  ‘12  

•   Two  package  types  •   192  CABGA  

• 16  ball/paste  alloy  combina*ons  •   Sn-‐37Pb,  SAC305  controls  •   0-‐4%  Ag  and  various  levels    of  microalloys/dopants  

• Results  presented  in    four  SMTAi  2012  papers    (iNEMI  Pb-‐Free  Alloy    Characteriza*on  Project  Reports)    

 Began  cycling:  March  2011    Est.  comple9on:  Dec.  2012  

•   84  CTBGA  

New Alloy Testing and Acceptance

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Lack of test standards creates risk and slows adoption of new alloys •  Risks of not having standard test data

• High melting point alloys will shrink an already small process window; need data to establish practical process limits

• Alloys formulated to meet specific goals not consistently tested to determine general suitability − Example: low-Ag alloys tested for improved

mechanical shock performance but thermal fatigue reliability not evaluated

•  Risks of not having standard test methods • Data from one valid experiment may not be comparable to another (data not “portable”)

• Test results may not directly correlate with OEM concerns − Data must enable alloy acceptability decisions

•  Example: Bulk properties not sufficient to predict solder joint thermal fatigue life

Incomplete solder joint formation for 1% Ag ball alloy assembled at the low end of a Pb-free reflow process window

CSP Package

CSP Package

PCB

PCB

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HP Qualification Process •  Objectives:

• Evaluate alloy performance consistently and improve reproducibility • Enable data comparisons between different alloy assessments (portable data)

• Use industry data and test methods where ever possible

•  Test methods divided into three areas: • Basic material properties •  Impact to PCA reliability •  Impact to PCA manufacturing

•  Tests must focus on alloy performance and results must not be overwhelmed by other parts of the assembly (laminate properties, board design, etc.).

• Test vehicles & materials are specified • Controls specified: lowest performing currently-used solder solutions

•  Tests must be economical

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Managing Solder Alloys at HP •  HP has 3 alloy evaluation specifications:

− Bar solder: EL-MF862-09 – Wave and Miniwave Alloys − BGA spheres: EL-MF862-10, – BGA/CSP Solder Ball Alloys − Solder paste: EL-MF862-11 – Reflow Paste Solder Alloys

•  Approved Materials List (AML) of Solder Alloys •  Given the variable performance of low-Ag alloys as a function of

board thickness/PCA complexity, AML will have different approved solutions for different classes of HP products

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Multi-step process for developing industry standard alloy tests

HP  Specifica*ons  

iNEMI  Recommenda*ons  

Align  with  SPVC  

Develop  IPC  standards  

SPVC = Solder Products Value Council (solder suppliers)

Complete   Led  by  HP  Some  SPVC  Members  

Cri*cal  Stakeholders  

Relevant  Standards  Body  

•  Data need to be “transferable” or “portable”

•  Data collected at one lab need to be useful for acceptability assessments around the industry

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Status of industry standards development for testing of new alloys

Basic Material Properties

Board-Level Reliability

Impact on Mfg. Process

HP Acceptance Specifications*

Complete Complete Complete

iNEMI Recommendations

Complete Complete Started

Alignment of iNEMI and SPVC/IPC Recommendations

Nearly Complete Pending Not Started

IPC Standards Development

Pending Early Draft Not Started

Solder Pastes and Fluxes

Fluxes must meet basic requirements so that our products can meet

customer expectations for quality and reliability.

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Yield and Reliability

•  Process yield is critical to EMS

•  Reliability is critical to OEM • HP requirements are weighted towards reliability

•  November  19,  2012  Copyright © 2012 HP All rights reserved.

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HP Management of Paste/Flux Materials for Reliability •  HP Approved Materials List (AML) based on reliability criteria

• Qualified at the corporate level

•  Detailed qualification test procedures, separate for paste and flux materials

•  Main Test: electrochemical migration testing

• Goal: Screen out fluxes that may cause electrochemical migration and SIR failures in products

November 19, 2012

Copyright © 2012 HP All rights reserved.

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HP Electrochemical Migration Test EL-EN861-00 •  Test conditions

•  50°C/90%RH /5V bias test conditions •  28 day test period • Defined flux application methods •  In-situ measurement, frequent monitoring

•  Multiple surface finishes tested for different failure modes

•  Individual materials and combinations are tested

• Rework materials need to pass unactivated (without heat)

•  Pass/Fail: • Resistance after 3 days ≥ 108 Ω • No more than a decade

resistance drop over the life of the test November 19, 2012

Copyright © 2012 HP All rights reserved.

IPC-A-25A 12.5mil pattern

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Types of Failures in EL-EN861-00

•  Two typical failure mechanisms: • ECM • Corrosion

•  More failures with halogen-free (HF) fluxes

November 19, 2012

Copyright © 2012 HP All rights reserved.

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Green Screen for Assessing Replacements for Restricted Substances in Electronics •  Green Screen is a key tool HP uses for

alternatives assessment when replacing a restricted substance

•  Enables identification of better materials, not just minimum acceptable

•  Green Screen results are only part of decision, but initial hazard screening eliminates certain options early in assessment process

•  HP continues to use Risk Assessment, LCA, and Carbon Footprint tools to complement

November 19, 2012 Copyright © 2012 HP All rights reserved.

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HF Fluxes to be Green Screened 2013

•  HP specifications will be revised to require Green Screen of all constituents to 100ppm

•  May require full material disclosure under NDA

• Compartmentalized data handling • Third party assessor option

•  Initially information only, but will become pass/fail

• White lists of better options within a functional class of chemicals

November  19,  2012  

Copyright © 2012 HP All rights reserved.

Summary and Conclusions

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Summary and conclusions •  Pros  and  cons  of  second  genera*on  alloys    

−  Second  genera*on  Pb-‐free  alloys  provide  an  opportunity  to  address  issues  with  near-‐eutec*c  SAC  

−  Industry  results  indicate  that  for  the  majority  of  IT  products,  thermal  fa*gue  concerns  should  be  minimal  with  alternate  alloys  (full  accelera*on  factors  pending)  

•  Alloy  test  standards  −  Progress  has  been  made  in  the  development  of  standard  tes*ng  methods,  but  work  

remains  before  IPC  standards  are  available  

•  The  HP  ECM  test  EL-‐EN861-‐00  has  been  an  effec*ve  screening  tool  at  the  material-‐level  because  it  is  predic*ve  of  flux-‐related  failures  

•  Very  effec*ve  at  elimina*ng  electrochemical  migra*on  failures  in  products  

•  Important  for  halogen-‐free  materials  

•  Halogen-‐free  fluxes  to  be  Green  Screened  in  2013  to  assess  for  hazardous  substances  

•  Contact  Info:  −  Aileen  Allen  (aileen.allen@hp.com)  

−  Greg  Henshall  (greg.henshall@hp.com)    

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Acknowledgements

•  HP  Alloy  Team:  Kris  Troxel,  Jian  Miremadi,  Elizabeth  Benedeko,    Helen  Holder  

•  IWG  Team:  Jasbir  Bath  •  Jabil  Working  Group:  Quyen  Chu    •  iNEMI  Team:  Elizabeth  Benedeko  •  Michael  Roesch,  Keith  Newman  

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Questions?

Back Up Slides

Electrochemical Migration Test Comparison

HP EL-EN861-00 2.6.3.3 B (06/04) (SIR) 2.6.3.7 (03/07) (SIR) 2.6.14.1 (09/00) (ECM)

Conditions 50°C, 90%RH 85°C, 85%RH 40°C, 90%RH 40°C, 93%RH, 65°C, 88.5%RH, 85°C, 88.5%RH

Period 28 day (672h) 168 hours 72 hours 500 hours

Coupon IPC-A-25A IPC-B-24 IPC-B-24 or AABUS IPC-B-25 (B or E) or IPC-B-25A (D)

Pattern 0.318 mm [12.5 mil] 0.4 mm line/0.5 mm space 0.4 mm line/0.5 mm space 0.318 mm [12.5 mil]

Surface finish

unpreserved bare copper, immSn, immAg unpreserved bare copper unpreserved bare copper

untreated, bare copper, unless surface finish is being evaluated

Paste application

print with 0.15mm stencil print with 0.2mm stencil not defined / AABUS not defined / AABUS

Liquid application 40uL for wave

no defined application amount or method

no defined application amount or method / AABUS

no defined application amount or method / AABUS

Unactivated condition

rework fluxes tested unactivated comb-up option only not defined / AABUS no unactivated test

Bias 5V 45–50V DC 5V 10V

Measurement In situ -100v DC In situ

same as bias, power disconnected from coupons before measurement

Measurement frequency 10 min measure at 24, 96 and 168h 20 min measure at 96 and 500h

ECM Results (L Fluxes)

– 227 L fluxes tested according to EL-EN861-00 and submitted to HP for review

•  197 passed •  30 failed (excludes improper tests)

– Fewer failing materials being submitted now that flux suppliers are more familiar with the requirements and tests more established

– Increase in HF failures

Copyright © 2012 HP All rights reserved. 33

Efforts underway to develop solder alloy test standards

– Key assumption: alloy acceptability may vary by industry sector, product type, and company BUT testing methodology and data requirements are largely the same

IS Standardized

tests and reporting

IS NOT Standardized

P/F criteria

Underlying data needed to evaluate new alloys are similar even if acceptance criteria vary by industry, by

company, by product

Manufacturability Required Tests Pass/Fail for new alloy acceptability Wetting balance curves

Per J-STD-003: Performance of the new alloy ≥ SAC 305

Manufacturing DoE for: -  BGA ball alloys -  paste alloys

Proper SJ formation (IPC 610D) within HP process window for BGAs and leaded components (paste only)

IMC at 3x reflow (250°C peak T, TAL 120 sec) ≤ 7 µm

Cu dissolution at 3x reflow (250°C peak T, TAL 120 sec) of New alloy ≤ SAC 305

Manufacturing DoE for wave alloys

Proper SJ formation (IPC 610D) within HP process window

Cu dissolution of New alloy ≤ SAC 305