Reliability assessment of flip chip on board connections

This paper describes the reliability performance of flip chip on board assemblies. A test vehicle consisting of 6 flip chip components was designed and assembled. In building the samples of these assemblies, the following design factors were included: solder bump alloy, die size, mounting pad type and underfill filler loading. Most of the samples passed the minimum requirements specified in JEDEC standards for steady-state temperature humidity testing, high temperature storage and power cycling tests. On the other hand, failures were noted in the temperature cycling testing. It was found that substrate quality, such as solder mask aperture alignment, is critical in achieving good reliability performance. Among the design factors studied, the underfill filler loading is the most critical factor in determining the reliability performance. Samples constructed of different solder bump alloys, different die sizes and different mounting pad types, when encapsulated with high underfill filler loading, passed a 3,000 cycles temperature cycling test. Failure analysis showed that solder joint cracking was the major failure mode in the temperature-cycling tested-samples. Other failure modes included underfill cracking and underfill delamination.