Metal Migrations Outside the Package During Accelerated Life Tests

Various large-scale integrated (LSI) ceramic and plastic packages are stressed through different accelerated life tests including temperature, humidity, hostile gases, and bias. Migration phenomena are observed after biased tests, with metal dendritic growth from the cathodic pins and large corrosion areas around the anodes. When no bias is applied only corrosion areas which could affect any pin are evidenced. The metals found to migrate are Ni, Cu, Sn, and Ag. The influence of hostile gases proves dominant through solubility control in the anodically corroded areas. The effect of residual contamination on the substrates is also described. Physical failure mechanisms are investigated through the accelerated tests results and data from defective components in service conditions. It appears that silver migration is the main concern and that the use of Ag package technology should be severely limited. The temperature-humidity bias tests are more convenient to predict package life time in service conditions in order to provide a reliable quantitative evaluation.