A parametric solder joint reliability model for wafer level-chip scale package

The micro-SMD is a Wafer Level-Chip-Scale Package (WL-CSP) designed to have external dimensions equal to that of the silicon device. This new package type extends flip-chip packaging technology to standard surface mount technology. The package has been successfully targeted for low pin count (less than 30), high volume applications such as cellular phones, hand-held PDAs, etc. Since the WL-CSP is typically used without underfill, solder joint reliability is of prime concern. A good understanding of the device failure mechanism when assembled on different board configurations is critical to the development of an accurate predictive model of solder fatigue. This paper presents results of a joint effort to develop a parametric predictive model of the solder joint reliability of the micro-SMD subjected to thermo-mechanical stresses. An 18 I/O micro-SMD was used as the primary test vehicle for the thermal cycling and thermal shock tests performed with different ramp/hold profiles. The parametric model developed can be extended to different pin count and die size of WL-CSPs with eutectic solder.