Study of contact degradation in final testing for BGA socket

Abstract

BGA socket is most important part in the final testing which selects the good or bad chip of BGA packages. When testing BGA-type packages using a BGA socket, the characteristic contact conditions and mechanisms of surface degradation in a low and stable contact are essential. However, the electrical contact between the pogo pin and the solder ball of the BGA-type package becomes unstable following repeated touchdown operations since particles from the package outline gradually accumulate on the crown tip of pogo pin. The contamination caused by these particles causes the contact resistance to increase. Accordingly, this study develops an experimental procedure for investigating the effect of the particle contamination on the magnitude and stability of the contact resistance. Initially, an experiment is performed to establish the contact resistance between a plated beryllium-copper (BeCu) pin at various number of touchdown. Subsequently, an experiment is conducted to investigate the accumulation of surface particles on the crown tip following multiple touchdowns of the pogo pin with the surface solder ball. The worn-out of crown tip following 6,830 and 36,580 touchdowns, respectively, is examined using a scanning electron microscope (SEM). The experimental results are then integrated to establish a suitable tradeoff between the contact resistance and the number of contacts for the time of socket clean.