Processing of no-flow fluxing underfill for flip chip assembly

For the past few years, the flip chip on board technology has grown quite rapidly. The underfill materials used in the process have been one of the most important factors responsible for that explosive growth. Development of new material systems will increase flip chip market growth provided they reduce manufacturing time and enhance reliability. Among these new materials are no-flow fluxing underfills. Properly formulated, these underfills can significantly decrease manufacturing cost by eliminating the fluxing process, the underfill flow process, and the underfill cure process. In addition, when the proper process window is defined, these new materials can provide enhanced reliability for the flip chip assembly. This work provides a characterization and process window evaluation of no-flow fluxing underfill material systems and performs a critical failure mode analysis of flip chip structures using no-flow fluxing underfills. The three main process areas included in the processing window are underfill dispensing, flip chip placement, and assembly reflow. The two main metrics are interconnect yield of the assemblies and percent voiding of the no-flow underfill materials.