Failure modes & effects analysis (FMEA) of flip chip devices attached to printed wiring boards (PWB)

Assembly techniques using flip chip devices on PWB and ceramic have been available for several years. When Medtronic Micro-Rel decided to introduce this technology or change some of the design, component, or process parameters, failure modes and effects analysis (FMEA) proved to be a useful tool to identify any potential design and process related failure modes. Additional purposes of an FMEA are: to determine the effects of the failure modes; to determine the root cause of the failure modes; to prioritize actions using a ranking system for failure mode effects in terms of failure mode occurrence probability, failure mode effect severity and failure mode detection probability through manufacturing; to identify, implement, and document corrective actions to address failure modes with rankings that are considered unacceptable. The purpose of this paper is to address FMEA by dividing the process into smaller pieces for manageability. Also, this report addresses preliminary FMEA performed early in the evaluation stage of flip chip devices on PWB. Many initial inputs were based on available literature, and many of the evaluations and designed experiments (DOE) performed were driven by the initial FMEA rankings. During development, six DOEs were recorded and performed, addressing various issues related to flip chip attachment. Areas reviewed included solder screening, reflow profiles of the flip chip dice, and underfill dispense parameters. The FMEA was then reevaluated after all evaluations and qualification builds were performed. These findings were used to drive design rules and process parameters.