Effect of Different PBO-Based RDL Structures on Chip-Package Interaction Reliability of Wafer Level Package

Abstract

In this paper, CPI (chip-package interaction) reliability of WLP (wafer level package) was investigated. PBO (Polybenzoxazole)-based RDL (redistribution layer) structure was the primary focus. Firstly, the stress distribution for PBO structures was studied by simulation. Secondly, two types of the chip with different PBO structures completed the accelerating experiments. Based on our investigation, the results of CPI reliability tests are coincident with the simulation data. It can be applied to the early prediction for the risk level of CPI reliability. Additionally, failure mechanisms were figured out for different PBO structures. Design A has the potential risk to suffer corrosion damage owing to exposed SR (seal ring) and CAS (crack stop). Design B has a four times failure rate in THT (Temperature and Humidity Test), which related to hotspots around SR. These results suggest that protecting SR and relieving hotspots effect will effectively enhance CPI reliability performance of WLP.