The Comparative Study of High and Low Temperature Cure Polyimide For Wafer Level Package With Ultra-Thick Re-distribution Copper Layer

摘要

In this investigation, two different negative photosensitive polyimides are selected and compared for WLP with different thickness of copper re-distribution layer (RDL) $12mu mathrm{m}, 15mu mathrm{m}$ and $mathrm{18} mu mathrm{m}$. One is high temperature cure polyimide with curing temperature >350°C which is the baseline used for typical WLP. The other is low temperature cure polyimide with curing temperature <250°C, the features of lower intrinsic residue stress and wafer warpage are expected for this polyimide. The four-layer fan-in WLP test vehicle (two polyimide layers, one RDL metal layer and one UBM layer) with minimum RDL line/space $12/12mu mathrm{m}$ and ball pitch $350mumathrm{m}$ is designed to screen the process and reliability capabilities of both polyimide interested. The thickness of 1^{st & 2nd polyimide layer in the four-layer WLP is optimized for ultra-thick RDL application and kept the same for the two different polyimides in this evaluation to compare the planarity performance on ultra-thick RDL and reliability performance. The performance of all the study legs coated by high and low temperature cure polyimide have been evaluated by employing board level temperature cycle test (TCoB). Besides, the component level reliability (CLR) include Thermal Cycling Test (TCT), High Temperature Storage (HTS) and unbiased Highly Accelerated Temperature and Humidity test (uHAST) are also demonstrated to verify the stack-up adhesion stability and robust of the two different polyimide on ultra-thick RDL.}