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Tin Whisker Summary

Introduction

In response to the industry's move towards lead-free ("Pb-Free") RoHS compliant semiconductor components, Analog Devices (ADI) has selected 100% matte tin (Sn) as the Pb-Free plating finish for the majority of its lead-frame based packages.

Although matte tin plating is widely used in the industry, some segments have expressed concern about the possibility of tin whisker formation in high-reliability applications. This concern has prompted recent industry research on tin whisker growth mechanisms and acceleration factors.

Because of the complexity of tin whisker formation, test methods that repeatedly and reliably predict tin whisker growth have been difficult to define.

However, industry research has led to the recent publication of two Joint Electronic Devices Engineering Council (JEDEC) standards on tin whisker growth, JESD22A121 (Test Method for Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes) in May 2005 and JESD201 (Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes) in March 2006.

ADI and other semiconductor suppliers have adopted these standards to evaluate tin whiskers for various package types assembled across subcontractor sites.

Along with testing for tin whiskers in accordance with the JEDEC standards, ADI minimizes the risk of tin whisker growth by strictly controlling the tin plating processes at our subcontractor sites. ADI has also implemented process enhancements which further reduce the risk of tin whisker growth. Specifically, plating thickness is controlled to a minimum of 400 microinches (10µm) and a post plating bake of 1 hour at 150°C within 24 hours of plating is performed at all of our subcontractor sites. Both of these process enhancements are industry accepted practices for mitigating tin whisker growth.

This report summarizes tin whisker test results from ADI and its subcontractors based on the JEDEC test standard, the NEMI recommended (pre-JEDEC) test conditions, and the pre-NEMI test conditions. Overall, the results indicate ADI Pb-Free RoHS compliant products perform very well under the specified test conditions.

Test Results

Summarized in the following tables are the test results to date. There are three different sets of results based on the test conditions available at the time of testing. Table 1 lists the results using the JEDEC industry standards JESD22A121 and JESD201. Table 2 shows results using NEMI recommended test conditions and criteria based on customer input. Table 3 summarizes early results using test conditions defined before the JEDEC industry standards or the NEMI recommendations.

Table 1: Sn Whisker Test Results based on JEDEC JESD22A121 (June 2009)

Samples baked at 150’C for one hour within 24 hours of plating. Inspections performed at intervals of 1000 hours or 500 cycles. Criteria based on JEDEC JESD201 technology acceptance testing.

Package Preconditioning Temperature Humidity Storage, 4000 Hrs (30/60%RH) High Temperature Humidity Storage, 4000 Hrs (55'C/85%RH) Temperature Cycle, 1500 Cyc (-55/+85'C)
Criteria: Maximum 20 um (Class 1a) Criteria: Maximum 40 um (Class 2) Criteria: Maximum 45 um (Class 2)
LFCSP No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
LQFP No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
MQFP No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
MINISO No precon refer to QSOP results refer to QSOP results Acceptable
Precon @ 215-220'C refer to QSOP results refer to QSOP results Acceptable
Precon @ 260'C refer to QSOP results refer to QSOP results Acceptable
PDIP No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
PLCC No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
PSOP No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
QSOP No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
SC70/ SOT143/ SOT23-3Ld No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
SOIC_N No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
SOIC_W No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
SOT223 No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
SOT23 No precon refer to QSOP results refer to QSOP results Acceptable
Precon @ 215-220'C refer to QSOP results refer to QSOP results Acceptable
Precon @ 260'C refer to QSOP results refer to QSOP results Acceptable
SSOP No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
TQFP No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable
TSSOP No precon Acceptable Acceptable Acceptable
Precon @ 215-220'C Acceptable Acceptable Acceptable
Precon @ 260'C Acceptable Acceptable Acceptable

Table 2: Sn Whisker Test Results based on NEMI Recommendations (July 2005)

All samples baked at 150’C for one hour within 24 hours of plating with the exception of SSOP. No preconditioning was done before stress tests. Inspections performed at intervals of 1000/2000 hours or 500 cycles. Tests with durations less than 3000 hours were discontinued in order to initiate testing per JEDEC JESD22A121 standard. Criteria defined in lieu of an industry standard.

Package Duration (1000 cyc or
3000 hrs minimum)		 Temperature Humidity Storage
(30/60%RH)		 High Temperature Humidity
Storage (60'C/90%RH)		 Temperature Cycle
(-55/+85'C)
Criteria: Maximum 50 um Criteria: Maximum 50 um Criteria: Maximum 50 um
LFCSP 1000 cyc -- -- Acceptable
2000 hrs Acceptable Acceptable --
4000 hrs Acceptable Acceptable --
LQFP 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
2000 hrs Acceptable Acceptable --
4000 hrs Acceptable Acceptable --
MQFP 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
2000 hrs Acceptable Acceptable --
4000 hrs Acceptable Acceptable --
MINSO 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
3000 hrs Acceptable Not performed --
PDIP 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
PLCC 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
PSOP3 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
QSOP 1000 cyc -- -- Acceptable
4000 hrs Acceptable Acceptable --
SC70 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
3000 hrs Acceptable Not performed --
SOIC_N 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
SOIC_W 1000 cyc -- -- Acceptable
4000 hrs Acceptable Acceptable --
SOT23 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
3000 hrs Acceptable Not performed --
SSOP 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
TQFP 1000 cyc -- -- Acceptable
2000 hrs Acceptable Acceptable --
4000 hrs Acceptable Acceptable --
TSOT 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
3000 hrs Acceptable Not performed --
TSSOP 1000 cyc -- -- Acceptable
1000 hrs Acceptable Acceptable --
4000 hrs Acceptable Acceptable --

Table 3: Sn Whisker Test Results before NEMI/ JEDEC Recommendations (December 2003)

No preconditioning was done before stress tests. Inspections performed at intervals of one month. Criteria defined in lieu of an industry standard.

Package Temperature Storage (50�C), 3 months Temperature Humidity Storage (50�C/85%RH), 3 months
Criteria: any evidence of whiskers Criteria: any evidence of whiskers
LFCSP No whiskers No whiskers
LQFP No whiskers No whiskers
MQFP No whiskers No whiskers
MINISO No whiskers No whiskers
SOIC_N No whiskers No whiskers
SOIC_W No whiskers No whiskers
SOT23 No whiskers No whiskers
TQFP No whiskers No whiskers
TSSOP No whiskers No whiskers

References

Dittes, M., P. Oberndorff P., Petit, L., "Tin Whisker Formation - Results, Test Methods and Countermeasures," Proceedings of 53rd Electronic Components & Technology Conference 2003, p. 822-826.  http://www.st.com/stonline/leadfree/etct.pdf

Galyon, George T., "Annotated Tin Whisker Bibliography and Anthology," IEEE Transactions on Electronic Packaging Manufacturing, 28(1), January 2005.  http://thor.inemi.org/webdownload/newsroom/TW_biblio-July03.pdf

iNEMI Tin Whisker User Group, "iNEMI Recommendations on Lead-Free Finishes for Components Used in High- Reliability Products,"
Version 4 (12-1-06).   http://thor.inemi.org/webdownload/projects/ese/tin_whiskers/Pb-Free_Finishes_v4.pdf

JEDEC standards, JESD22A121 Test Method for Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes and JESD201 Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes.  http://www.jedec.org/download/search/22a121-01.pdf,  http://www.jedec.org/download/search/JESD201.pdf

Oberndorff, P. J. T. L., M. Dittes, L. Petit, C. C. Chen, J. Klerk, and E. E. de Kluizenaar, "Tin Whiskers on Lead-free Platings," Semicon Southwest 2002.  http://www.st.com/stonline/leadfree/plating.pdf

Oberndorff, P., M. Dittes, P. Crema, and S. Chopin, "Whisker Formation on Matte Sn Influencing Factors and Mitigation An Update," Proceedings of IPC/JEDEC Lead Free Conference, Dec 2004.

Osenbach, J. W., R. J. Shook, B. T. Vaccaro, A. Amin, B. D. Pottieger, K. N. Hooghan, and P. Ruengsinsub, "The Effects of Board Assembly Reflow Processing on Sn Whisker Formation on Electroplated Matte Sn on Cu Alloy Lead Frames," Proceedings of IPC/JEDEC Lead Free Conference, March 2004.

Osenbach, John W., Richard L. Shook, Brian T. Vacarro, Brian D. Potteiger, Ahmed N, Amin, K. N. Hooghan, P. Suratkar, and P. Ruengsinsub, "Sn Whiskers: Materials, Design, Processing, and Post-Plate Reflow Effects and Development of an Overall Phenomenological Theory," IEEE Transactions on Electronic Packaging Manufacturing, 28(1), January 2005.

DISCLAIMER: All statements, information and data provided herein are believed to be accurate and reliable. Please note that whisker growth testing, acceptance criteria and test methods are not fully developed and may not reflect your operating conditions. Information and data contained herein is not applicable to all ADI products and is subject to change without notice. All statements, information and data herein are presented without guarantee, warranty or responsibility of any kind, whether expressed or implied.