Case study of leakage/short on PCB after biased-HAST

Abstract

After HAST of WLCSP devices mounted on PCB, several short and leakage failures were observed. Non-destructive technique, lock-in thermography (LIT) was applied to localize the fault on PCB. Thereafter, physical failure analysis (PFA) was performed. It revealed solder contamination between the solder bumps of PCB as cause of the failures.