Board level reliability and surface mount assembly of 0.35mm and 0.3mm pitch wafer level packages

Board level reliability studies have been performed on wafer level packages (WLP) on various die sizes with 0.35mm and 0.3mm ball pitches. The 0.35mm pitch test vehicles included 4mm × 4mm, 5mm × 5mm, and 6mm × 6mm package sizes. The 0.3mm pitch test vehicles were 3mm × 3mm and 4mm × 4mm. All test vehicles were fully populated ball arrays. The parts were assembled at 2 different suppliers. All of the WLPs studied passed drop shock. All of the test vehicles passed board level temperature cycle initially except for the 6mm × 6mm. The SMT process optimization included variations of stencil aperture ratios. These modifications impacted temperature cycling reliability. The reliability of the largest package size was improved from this optimization.