Tin whisker test method development

The International Electronics Manufacturing Initiative (iNEMI) proposed a set of tests that were subsequently standardized by the Joint Electron Device Engineering Council (JEDEC) Solid State Technology Association as JESD22A121. However, further optimization was needed to validate and verify proposed iNEMI tests to determine whether these test methods could differentiate between component surface finishes, to investigate the connection between short-term and long-term tests, and to determine optimal inspection intervals and test durations. In the current work, 15 surface finishes were evaluated using iNEMI's three proposed environmental test conditions. These finishes were evaluated for whisker presence and length using a scanning electron microscope (SEM) every 1000 h or 500 accelerated thermal cycles for a total of at least 9000 h of isothermal testing or 3000 accelerated thermal cycles. Test results showed that thermal cycling and high-temperature/humidity testing could grow whiskers for all Pb-free Sn-based finishes, while only a few finishes exhibited whiskers after 10 000 h in an air-conditioned office environment. 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 to 30 °C and 60% relative humidity (RH), and increasing the number of leads per sample and number of samples (sample size) for inspection.