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.
