Reliability of small BGAs in the automotive environment

In this work, the under-the-hood reliability of smaller PBGA packages has been evaluated in the automotive thermal cycling environment. Various methods of enhancing reliability have been explored including increased BT substrate thickness, the utilization of NSMD pads on the BGA component, alternative PCB plating finishes, and the use of underfill encapsulants. A set of test boards was assembled with several 15 and 17 mm body size BGA components from two different vendors. In addition to non-underfilled parts, the enhancements achieved with four different underfill encapsulants have been explored. Larger 23 mm BGAs have also been included in the test matrix as a control/reference. The assembled test vehicles have been subjected to 6000 thermal cycles over the range -40 to 125 °C, and the daisy-chain resistances of the various components were monitored throughout the testing. Logged failures have been statistically analyzed using two parameter Weibull models. The analysis results have allowed the board level reliabilities of the examined BGA components to be compared and ranked, and the reliability enhancements achieved with various underfills to be accessed. Detailed failure analyses have also been performed to find the locations of solder joint fatigue crack growth, and to identify other failure modes occurring in underfilled parts.