Flip chip on board: assessment of reliability in cellular phone application

Flip chips are generally seen as a potential future "packaging" option providing an alternative to chip scale packages. In this work, the reliability of flip chip assemblies was analyzed using daisy chain test components on a schematic test vehicle designed to emulate a cellular phone environment printed wiring board (PWB). The flip chip components were assembled in a standard surface mount technology process, where the flip chip bumps were first dipped in a flux film. A test matrix consisting of a number of flip chip test components with different input/output configurations, PWBs, fluxes, and underfills was built up. The assemblies were tested for potential damage to the flip chips and their interconnects by thermal cycling and by mechanical shock in a drop. After testing, the root causes of the failures were analyzed. As a separate task, the stress/strain generation that occurs in the flip chips in the drop test was analyzed using simulation, in order to find the critical locations on the test PWB.