Evaluation, optimization, and reliability of no-flow underfill process

The advent of no-flow fluxing underfills for Flip Chip on Board application has required a new investigation of optimal processing for increased reliability. This research provides a systematic development of optimal process parameters for 3 currently available fluxing underfills. The impact of the dispensing pattern on void formation is determined. A DOE is utilized with dispense pattern at 3 levels, and speed at 2 levels. Metrics include material voiding, and fillet shape. Low temperature cure is used to isolate the effects of dispensing by avoiding any volatility of a standard reflow cure. The impact of the placement process is determined. A second DOE involves varying placement force, speed, and dwell time at 2 levels. Metrics include underfill voiding, solder voiding, and electrical yield. The results of these two experimental studies will be used to choose an optimal placement process for each material, to be used in further optimization of the reflow process.