HAST evaluation of organic liquid IC encapsulants using Sandia´s assembly test chips

Accelerated aging (HAST) experiments were conducted with special-purpose corrosion test chips (ATCs) in both bare die form and with various liquid encapsulants: epoxy, silicone and silicone elastomer, or silicone gel. The purpose of the experiment was to show what incremental improvement in die corrosion resistance was provided by the encapsulants and to determine the failure modes for the two types of samples. The test conditions were 140°C/85% RH (relative humidity) and +40-V bias on outer tracks with respect to the center track. In the case of nonencapsulated parts, median lifetimes of about 1000 h were observed for the best passivations, with the predominant failure mode being triple track corrosion on the die. In the case of the encapsulated parts, the failure mode depended on the encapsulant type. Several of the silicone gel materials showed excellent HAST (high accelerated stress testing) performance, with only a few percent failures at the 1 100-h point