Solder joint reliability of a polymer reinforced wafer level package

Wafer level packages (WLPs) have demonstrated a very clear cost-advantage vs. traditional wire-bond technologies, especially for small components that have a high number of dice and I/O per wafer. Solder joint reliability of traditional WLPs is the weakest point of the technology. The ability of the solder joint to survive the required thermal cycle testing has limited WLP use to products having relatively small die sizes and a small number of I/O. To increase solder joint reliability without underfill new technologies needed to be developed. To address this need, the K&S Flip Chip Division has developed a polymer reinforcement technology called Polymer Collar WLP^TM. Polymer Collar WLP utilizes a polymer reinforcement structure surrounding the solder joint and it has demonstrated a full 50-60% increase in solder joint life in various sets of TC (thermal cycling) tests. The strengthening mechanism of the polymer collar is well understood and was documented after the second TC test.