Tin Whisker Test Method Development

Published

October 12, 2021

Author(s)

Valeska Schroeder, P Bush, Nick Vo, Maureen E. Williams

Abstract

In response to legislation banning Pb from electronics, any component suppliers plan to implement tin-based lead-free surfaces finishes to replace current Sn-Pb finishes. The industry needed a test for assessing the susceptibilty of tin-based finishes to tin whisker formation and growth. The tin whisker test group of the interNational Electronics Manufacturing Initiative (iNEMI) proposed a set of test that were standardized by JEDEC Solid State Technology Association (Once known as the Joint Electron Device Engineering Council), as JESD22-A121. However, further test optimization was needed to validate and verify proposed iNEMI tests to determine whether tests could differentiate between surface finishes, to investigate the connection between short tern and long term tests, and to determine optimal inspection intervals and test durations. In the current work 15 surface finishes were evaluated in iNEMI's three proposed environmental test conditions. These finishes were evaluated for whisker presence and length in scanning electron microscope (SEM) every 1000 hours or 500 cycles for a total of at least 9000 hours of isothermal testing and 3000 thermal cycles. Test results showed that thermal cycling and high temperature/humidity testing could grow whiskers for all Pb-free Sn-based finishes, while few finishes exhibited whiskers at 10000 hours in an air-conditioned office environment. Short term testing could not be used to predictive the relative ranking of finishes based on whisker length. However, incubation time may be a predictor of performance in different environments. Moreover, JEDEC inspection intervals of 1000 hours and 500 cycles and total durations of 4000 hours and 1500 cycles are reasonable. Finally, the results described in this paper were used to change the JEDEC tin whisker test method from the original iNEMI proposal by decreasing the humidity of the high temperature humidity test, controlling the ambient test condition at 30C and 60% RH, and increasing the number of leads per samples (sample size) for inspection.

Citation

IEEE

Pub Type

Journals

Keywords

leadframe package, Pb-free, surface finish, tin whiskers, whisker growth

Citation

Schroeder, V. , Bush, P. , Vo, N. and Williams, M. (2021), Tin Whisker Test Method Development, IEEE (Accessed April 20, 2024)