Mechanical, thermal and electrical analysis of a compliant interconnect

Ball grid array (BGA) package styles use solder balls as an electrical interconnect between packages and application boards. Solder balls are rigid and tend to fracture under thermal fatigue and/or shock loading. Metalized polymer spheres (MPS) offer a more compliant interconnect, compared to solder balls, thereby increasing the thermal cycling fatigue life. A reduction in thermal and electrical performance can be expected for MPS interconnects as a result of its lower thermal conductivity and an higher electrical resistance. A 5% and an 8% increase in MPS thermal resistance was measured for a carrier array ball grid array (CABGA) package and a plastic ball grid array (PBGA) package, respectively, compared to eutectic solder balls. However, this small reduction was offset by large gains in the solder joint life. A 4.5X increase in the mean thermal fatigue life was measured for a wafer level chip scale package (WLCSP) using MPS interconnects compared to eutectic solder balls. A first-order model showed that eutectic solder balls provide greater process margin in the presence of package and board warping compared to MPS interconnects.