inemi Lead-Free Alloy Characterization Program Update: Thermal Cycle Testing and Alloy Test Standards Development

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1 inemi Lead-Free Alloy Characterization Program Update: Thermal Cycle Testing and Alloy Test Standards Development Chair: Greg Henshall, HP Co-Chair: Stephen Tisdale, Intel October 21, 2011

2 Authors Julie Silk and Bill Jones; Agilent Richard Coyle and Joe Smetana; Alcatel-Lucent Ahmer Syed; Amkor Jasbir Bath; Bath Technical Consultancy Mike Osterman and Elviz George; CALCE Tae-Kyu Lee; Cisco Ranjit S. Pandher; Cookson Richard Parker; Delphi Joelle Arnold, Nathan Blattau; DfR Solutions Jennifer Nguyen; Flextronics Mark Currie and Srini Chada; Henkel Gregory Henshall, Jian Miremadi, Aileen Allen; Hewlett-Packard Fay Hua and Stephen Tisdale; Intel Jeffrey Lee, Graver Chang, IST Keith Sweatman and Keith Howell; Nihon Superior Sze Pei Lim and Weiping Liu; Indium Dave Godlewski and Haley Fu; inemi Bill Barthel and Ursula Marqez de Tino; Plexus Derek Daily; Senju

3 Project Team Members 20 companies; 55 individuals Solder alloy suppliers, component suppliers, EMS providers, OEMs

4 Outline Background and Objectives Thermal Fatigue Reliability Alloy Test Requirements and Standards Summary and Conclusions

5 Near-eutectic SAC allowed industry to meet RoHS deadline of July 1, 2006 Industry adopted SAC 305 & other near eutectic alloys as the standard Pb-free alloys during the RoHS transition Selected by industry consortia balancing many factors Major factors included: Relatively low melting point Reasonable thermal fatigue reliability Selected prior to understanding impact of composition on mechanical robustness and copper dissolution Further optimization anticipated Typical Sn-Ag-Cu (SAC) microstructure

6 SAC305/405 functional but not the optimal Pb-free solution Problems with SAC305/405 include: Poor drop/shock performance for BGAs, especially on Ni/Au surfaces Expense of Ag is driving the desire to reduce Ag content $660/lb August 30, 2011 (Tin ~ $10.80/lb) Wave solder bar main concern Poor barrel fill on thick boards for some surface finishes Copper dissolution Hot tearing and other surface phenomena create inspection issues & possibly unnecessary rework Fracture surface showing intermetallic layer left, no solder Cu Ni IMC Gregorich, et al., IPC/Soldertec Global 2nd International Conference on Lead Free Electronics (2004). Solder

7 Addressing issues with alloy alternatives led to expanding alloy choice Alloys Sn1.0Ag0.5Cu (SAC105) SAC205 Sn-3.5Ag Sn0.3Ag0.7Cu+Bi (SACX) Sn0.3Ag0.7Cu+Bi+Ni+Cr (SACX) SAC Ni+0.5In SAC Co SAC Ge SAC Ni (LF35) SAC Ni+0.05In Sn-3.5Ag La Sn-0.7Cu Sn0-4Ag0.5Cu + Al + Ni SAC Ce Sn-2.5Ag-0.8Cu-0.5Sb Sn-0.7Cu-0.05Ni Sn-0.7Cu-0.05Ni + GE (SN100C) SAC Ti SAC Mn 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) Wide range of alloy choices is both an opportunity and a risk

8 Concerns with alternative alloys There is no perfect alloy there are concerns with every alloy Concerns with alternative alloys include: Technical issues Manufacturing and rework Reliability (thermal fatigue, drop/shock, bending, etc.) Copper dissolution New alloys may or may not solve all problems of SAC305 Non-technical issues Supply chain management Cost of ownership Industry management (part number changes, standards on dopants, etc.) SAC305 SAC305 7

9 Pb-Free Alloy Characterization Project focused on addressing high priority knowledge gaps 2008 inemi assessment of key areas where knowledge is lacking High Priority Knowledge Gaps Advantages and disadvantages of specific alloys Composition limits for microalloy additions; ranges of effectiveness Standard method to assess new alloys; standard data requirements Consistency of testing methods, including test vehicles & assembly, test parameters, etc. Establish the microstructural characteristics of specific alloys Long term reliability data for new alloys, particularly low Ag & microalloyed Lack of thermal cycle data for evaluating new alloys; benchmark to Sn-Pb and SAC 305/405 inemi Alloy Characterization Project Focus Areas 8

10 Outline Background and Objectives Thermal Fatigue Reliability Alloy Test Requirements and Standards Summary and Conclusions

11 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 10

12 Overview of industry efforts to generate thermal fatigue data Industry Working Group (complete) Alcatel-Lucent Working Group Jabil Working Group (ATC complete) 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 Effects of thermal cycle profile Data for common commercial alloys Quantitative acceleration factors Impact of package type 11

13 Alloys under test Cell No. BGA Ball Alloy Trade Name Solder Paste Comments 1 Sn-37Pb Eutectic Sn-Pb Sn-37Pb Control 2 Sn-0.7Cu+0.05Ni+Ge SN100C SN100C 0% Ag joint 3 Sn-0.7Cu+0.05Ni+Ge SN100C SAC305 Impact of [Ag] 4 Sn-0.3Ag-0.7Cu SAC0307 SAC305 Impact of [Ag] 5 Sn-1.0Ag-0.5Cu SAC105 SAC305 Impact of [Ag] 6 Sn-2.0Ag-0.5Cu SAC205 SAC305 Impact of [Ag] 7 Sn-3.0Ag-0.5Cu SAC305 SAC305 Impact of [Ag] 8 Sn-4.0Ag-0.5cu SAC405 SAC305 Impact of [Ag] 9 Sn-1.0Ag-0.5Cu+0.05Ni SAC105+Ni SAC305 Impact of dopant 10 Sn-2.0Ag-0.5Cu+0.05Ni SAC205+Ni SAC305 Impact of dopant Impact of 11 Sn-1.0Ag-0.5Cu+0.03Mn SAC105+Mn SAC305 dopant Doped commercial 12 Sn-0.3Ag-0.7Cu + Bi + X SACX0307 SAC305 alloy 13 Sn-1.0Ag-0.5Cu SAC105 aged SAC305 Effect of aging 14 Sn-3.0Ag-0.5Cu SAC305 aged SAC305 Effect of aging 15 Sn-1.0Ag-0.7Cu SAC107 SAC305 Impact of [Cu] Doped commercial 16 TBA SACi SAC305 alloy Pb-free alloys plus Sn-Pb control Systematically investigate impact of Ag content Impact of common dopants, such as Ni Alloys becoming fairly common in practice Impact of aging Paste alloy is SAC305 except as noted in red

14 ATC test vehicle 0.8mm pitch 192 CABGA Large die 475x475 mils Ball size: 0.46mm 0.5mm pitch 84 CTBGA Large die 200x200 mils Ball size: 0.3mm Balling performed by Premier Semiconductor 6-layer board 16 parts of each type per bd. 16 parts per test cell 84 CTBGA 192 CABGA One daisy-chain per part In-situ monitoring Over 3000 parts under test 13

15 Temperature ATC thermal profile definition for consistency Nominal T hi Actual T hi Temperatures measured on parts! (NOT air temperature) Ramp Rate N Nominal T low Actual T low Consistency is the critical issue Time

16 Temperature ATC thermal profile use of IPC-9701 standard Nominal T hi Dwell starts here Actual T hi max +5C Dwell start N Dwell time Dwell end Dwell ends here IPC-9701A Table 4.1: = +5/-0 for peaks. Time

17 Standardized solder joint failure definition First event : 1 st occurrence of a resistance measurement 1000 ohms 9 or more additional events within 10% of the number of cycles for the first event Follows IPC-9701 for event detectors; also use for data loggers Example 1 st event Failure 9 events Example 1 st event at 1000 cycles 9 more events within 100 cycles of the 1 st event Failure defined to be at 1000 cycles

18 Thermal cycle test overview and status Test Profiles and Status as of 21 Sept 11 Full factorial structure for determination of acceleration factors Impact of T min, T max, T, and dwell time Interactions among the three main variables (T max, T, dwell time ) Two additional profiles Long dwell Test alloys for harsh environment applications Auto, aerospace, military Profile No. Company Cycle (Min/Max/Dwell) Date Started Cycling Current Cycle # 1 ALU 0/100/10 3/21/ IST 25/125/10 7/22/ Henkel -40/100/10 7/27/ Nihon -15/125/10 8/3/ ALU 0/100/60 2/10/ HP 25/125/60 5/12/ HP -40/100/60 5/31/ CALCE -15/125/60 5/2/ CALCE -40/100/120 6/15/ Delphi -40/125/10 8/24/ Began cycling: March 2011 Est. completion: Dec

19 Outline Background and Objectives Thermal Fatigue Reliability Alloy Test Requirements and Standards Summary and Conclusions

20 Lack of test standards creates risk and slows adoption of new alloys Risks of not having standard test data CSP Package 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 PCB CSP Package 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 PCB Incomplete solder joint formation for a 1% Ag ball alloy assembled at the low end of typical Pb-free reflow process window.

21 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

22 Approach to developing alloy test standards 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.). Reliability tests should include at least: Accelerated thermal cycling Mechanical shock (drop) Other tests still being discussed 21

23 Multi-step process for developing industry standard alloy tests HP Specifications inemi Recommendations Align with SPVC Develop IPC standards Complete Some SPVC Members Critical Stakeholders Relevant Standards Body SPVC = Solder Products Value Council (solder suppliers)

24 Status of industry standards development for testing of new alloys HP Acceptance Specifications* inemi Recommendations Alignment of inemi and SPVC/IPC Recommendations IPC Standards Development Basic Material Properties Board-Level Reliability Impact on Mfg. Process Complete Complete Complete Complete Complete Started Nearly Complete Started Not Started Pending Early Draft Not Started * HP has specifications that include all three topic areas. One each for: Wave solder and mini-pot rework Surface mount reflow (paste) BGA spheres

25 Outline Background and Objectives Thermal Fatigue Reliability Alloy Test Requirements and Standards Summary and Conclusions

26 Summary and conclusions Pros and cons of second generation alloys Second generation Pb-free alloys provide an opportunity to address issues with near-eutectic SAC Concerns about thermal fatigue performance and management of alloy change identified as top priorities to address inemi investigating thermal fatigue performance Generating substantial data on new alloys Data will enable development of quantitative life prediction models Alloy test standards inemi is leading industry efforts to drive standardization of alloy testing Goal is to enable use of new alloys with minimal reliability risks Progress has been made in the development of standard testing methods, but work remains before IPC standards are available 25

27 contacts: Bill Bader Bob Pfahl