Fan-out PoP Solder Joint Reliability Investigation by System Power Cycling

A new fan-out PoP (package on package) package was developed and validated on a high perform phone system through SMT and PoP DRAM attached process optimization followed by system power cycling test to ensure dozens of failure parts per million (DPPM) level system's defect failures in field.The cracked solder balls were found at the highest heat resource area and cross-section showed solder ball crack filled with underfill material in system power cycling test. The observed solder ball crack symptom quite matched with the failure mode found from failure chips in field. It revealed that, for underfill materials, the curing condition was found being the most dominant factor since, with longer curing condition, both underfill materials used were able to have system passed 100,000 cycles without failure, a 2.5~4X improvement. From our studies, a desirable smart phone SoC (system on chip) package system assembly and underfill process was validated by system power cycling. The identified system process conditions were also confirmed through the real-life use of the product without any failures. The proposed system level stress methodology and experimental results shall be a good reference to package solder joint reliability enhancement.