Role of materials evolution in VLSI plastic packages in improving reflow soldering performance

Cracking of surface mounted plastic packages worsens with increasing die sizes and thinner packages, both are recent trends in packaging. The precursor to failure, delamination at a leadframe to polymer interface, suggests that improvements in mold compounds, die attach adhesives and leadframe surface finishes are key elements in a solution. Identifying which specific materials properties must be improved and to what degree is a major task, followed by working with vendors to supply improved materials. In this study, the strategy is to improve all weak interfaces in parallel, rather than simply strengthen the weakest link. An excellent measurement method capable of detecting small improvements in the measured reflow soldering performance of a test package (148 PQFP) quantified both its delamination and cracking performance. These studies identified a general weakness in polymer to Ag die pad interfaces, implying that improving the adherend is mandatory