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.

Inquiries related to this report should be directed to ADI.PbFree@analog.com.

Test Results

Summarized on the following pages are the test results available to date. There are 3 different sets of test conditions: JESD22A121 conditions, NEMI recommended conditions, and pre-NEMI conditions. In general, all interval read-points leading to the maximum specified durations meet the specified criteria. Note that the LFCSP package type is not within the scope of JESD201, since the plated surface is fully wetted during board mount assembly.

Table 1: JEDEC JESD22A121 Sn Whisker Test Results (Updated May 2007)

Criteria: Per JESD201 technology acceptance criteria

Table 1 Notes:
* = 1500 cyc for samples preconditioned using Pb Free reflow, 1000 cyc for samples with no preconditioning
A = No Preconditioning
C = Preconditioned using SnPb reflow
D = Preconditioned using Pb Free reflow

JESD22A121 Conditions/Criteria:

• Temperature Humidity Storage (THS) at 30°C/ 60%RH for 4000 hours
• High Temperature Humidity Storage (HTHS) at 60°C/ 87%RH for 4000 hours
• Temperature Cycling (TC) at (-55°C) to (+85°C) for 1500 cycles
• Samples: Baked at 150°C for one hour within 24 hours of plating
• Inspection: 1000 hours or 500 cycles intervals
• Criteria: Per JESD201 technology acceptance criteria (LFCSP does not fall within the scope of JESD201, since the plated surface is fully wetted during board mount assembly)

Table 2: NEMI (Pre-JEDEC) Sn Whisker Test Results (Updated July 2005)

Criteria: Maximum 50 µm

Table 2 Notes: Testing to 3000 hours abandoned in order to initiate testing per JESD22A121.

NEMI Recommended Conditions:

• Temperature Humidity Storage (THS) at 30°C/ 60%RH for 3000 hours
• High Temperature Humidity Storage (HTHS) at 60°C/ 90%RH for 3000 hours
• Temperature Cycling (TC) at (-55) to (+85°C) for 1000 cycles
• Samples: Baked for 1 hour at 150°C within 24 hours of plating, except SSOP. No preconditioning.
• Inspection: 1000 hours or 500 cycles intervals
• Criteria: Maximum 50 µm, defined in lieu of an industry standard

Table 3: Pre-NEMI Sn Whisker Test Results (Dec 2003)

Criteria: Any evidence of whiskers

Pre-NEMI Conditions/ Criteria:

• Temperature Storage (TS) at 50°C for 3 months
• Temperature Humidity Storage (THS) 50°C/ 85%RH for 3 months
• Samples: No preconditioning
• Inspection: One month intervals
• Criteria: Any evidence of whiskers, defined in lieu of an industry standard

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.