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Multi-Axis Loading Impact on Thermo-Mechanical Stress-Induced Damage on WLCSP and Components With Via-in Pad Plated Over (VIPPO) Board Design Configuration

The impact of uneven strain distribution induced by mixed via in pad plated over (VIPPO) configuration in thick printed circuit boards is investigated. To identify the tension and compression strain during thermal cycling, BGA components with 0.5mm pitch and 300µm diameter solder joints were tested with -40 to 125oC thermal cycling profile. Boards with conventional dog-boned pad configuration are compared with all VIPPO pad and unevenly distributed VIPPO pad configuration boards. It is identified that specific pad design parameters degrade the thermal cycling performance over 46% from a characteristic life cycle perspective. The additional tension and compression, a multi-axis straining was also observed in fully conformal coated WLCSP, which was identified with Electron-backscattered diffraction (EBSD) imaging. The degradation mechanism and the multi-axis loading condition due to the uneven distributed VIPPO configuration along with the conformal coating induced degradation mechanism are presented and discussed.