Analysis of a new BGA THB failure and study on its mechanism

An electrical overstress (EOS) short failure was observed on ball grid array (BGA) package during the temperature humidity bias (THB) stress test. The cause of the EOS short failure has been identified to be attributed to 3 factors, i.e. the VDD/VSS copper lines of the BGA substrate which have been laid out closely at the same side of the substrate, the solder resist crack and the high humidity nature of the THB stress test. To resolve this problem, the BGA substrate layout has been redesigned so that the close pairs of the VDD/VSS copper lines are separated into two opposite sides of substrate. No EOS short failure was observed on the BGA package with new substrate design after the THB stress test.