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TRANSCRIPT
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
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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
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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.
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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 ([email protected])
− Greg Henshall ([email protected])
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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
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