Moisture-Induced Die Stresses in PBGA Packages Exposed to Various Environments

Plastic Ball Grid Array (PBGA) technology has been proven to be one of the most popular packaging solutions with many advantages in thermo-electro-mechanical performance, reliability as well as cost effectiveness. While a number of studies have been conducted to investigate the package reliability using a wide range of experimental methods such as thermal cycling, thermal shock, vibration, drop test, etc., there are quite limited studies on the effects of moisture on PBGA packages. The mold compound and PCB substrate are two primary components in PBGA package; they however absorb moisture when subjected to high humidity environment, generating stress changes in the package die and potentially causing delamination in the package interfaces. In this study, the effects of moisture on die stresses in Plastic Ball Grid Array (PBGA) packages have been characterized. On-chip piezoresistive sensors were used to measure moisture-induced device side die stress in the packages under three different moisture conditions (65% RH and 65 °C; 85% RH and 85 °C, and 95% RH and 95 °C). The measurements were carried out in both absorption and desorption process to evaluate the reversibility of the moisture effects. In addition to the experimental measurements on package level, a study on the moisture properties of the BT substrate and mold compound in the PBGA was completed. The moisture properties (Diffusivity D, Saturated Concentration C _sat , and Coefficient of Moisture Expansion β) of each material were experimentally obtained. Finally, a finite element numerical simulation was performed to validate the experimental results. The moisture properties obtained earlier were used in the model. Good agreements between numerical predictions and experimental results were observed.