Package Substrate Die Pad Roughening Innovative Solution to Strengthened Die Attach Adhesion

Abstract

Poor die adhesion to substrate resulting to stray dice issue for the MEMS package was encountered. This die bond failure mechanism has a downstream effect specifically on the mold process. The presence of the stray die resulted to mold compound leakage outside the tool cavity due to planarity not achieved. The mold compound that leaks affected the overall package thickness, thus exposing the wires. Using the Design of Experiment methodology, the team generated different simulations and validations to resolve the stray die problem. Based on the simulation and experiments, it was established that an optimum substrate roughness is necessary to achieve a better adhesion between the Die adhesive and the substrate.  This paper presents a systematic study on how the substrate roughness can improve the adhesion of Die Attach film (DAF) to the substrate thereby resolving the Stray Die problem.  Results showed that the die adhesion strength on the substrate increases as the substrate surface roughness increased from Ra 0.05 um to Ra 1.5 ~ 2.0 mm. Consequently, the rejection rate of stray dice was eliminated. This new learning will be used to establish a standard on surface roughness for substrate-based material that can be applied to new packages.