Qualification of plastic ball grid array packages for space applications

The reliability of plastic ball grid array packages (PBGAs) has been characterized and PBGAs have been qualified for space flight hardware using highly accelerated stress testing (HAST). We have used PBGAs with ASIC die as test vehicles for accelerated life testing to determine the storage life of the PBGAs. Degradation of the die encapsulant material (glob-top) was selected as the failure criterion because electrical failure was not detected until significant delamination of the encapsulant was observed during a step stress life test. The activation energy, E-a, for encapsulant degradation was determined from an Arrhenius plot of two temperature conditions with the absolute humidity kept constant. The exponent, n, for partial pressure of water was determined from the log t(50) vs. partial pressure of water plot. The, activation energy, E-a, was determined to be 0.47 eV, and the exponent, n, was determined to be 2 We have established an empirical model for PBGA failure time prediction. The median time to failure of the PBGAs at 35degreesC and 90% RH is estimated to be 11, 000 years.