Reliability evaluation of custom and standard surface mount plastic encapsulated microcircuits for military avionics applications

This paper will focus on thermal cycling and moisture susceptibility of plastic encapsulated microcircuits for use in military avionics digital processing modules. Today's avionics designs often use low profile Standard Electronics Module-Size E (SEM-E) modules, which preclude the use of through-hole microcircuit technology. This fact pushes the design selection of microcircuits to surface-mount, thin, small outline packages (TSOPs), small outline J-leaded (SOJ) packages and Plastic Ball Grid Array (PBGA) packages. For this study, two series of accelerated tests were conducted for the purpose of evaluating the moisture and temperature cycling susceptibility of standard as well as custom, plastic encapsulated microcircuits. The first group (hereafter referred to as CR1) consisted of 1248 commercially available plastic integrated circuits (ICs), representing 19 different part types from 9 different manufacturers. The second group (referred to as CR2) included 17 custom Application Specific Integrated Circuits (ASICs), and a mix of standard microcircuits that did not get into the first test group. All of the above microcircuits were reflow solder-attached to test circuit boards on an automotive electronics assembly line. The test boards were then subjected to a series of accelerated tests for the purpose of evaluating thermal cycling and moisture susceptibility of the plastic SMT ICs. The test results are summarized and the failure analysis results are presented. An assessment of expected lifetimes are made for each of the test environments based on acceleration factors, using currently acceleration models[1]. The acceleration factors and levels of stress testing are presented, as well as the methods for extrapolating the accelerated test conditions to typical military avionics application conditions. Finally, a summary failure rate calculations are presented which are based on data from this testing as well as from component manufacturing reliability testing.