Effects of underfill thickness on mechanical properties and fracture behavior of Si/underfill/Si adhesion structures

Abstract

In this study, two types of commercial underfill materials are used to prepare a simplified Si/underfill/Si adhesion structure with the decreasing underfill thickness of 200, 100 and 50 μm, respectively. The underfill thickness effects on the mechanical performance and fracture behavior of the underfilled Si/underfill/Si structures are studied comprehensively, in which the Si/underfill/Si adhesion structure is designed to mimic the die/underfill/interposer structure widely employed in actual 2.5D/3D integration packages. Results demonstrate that fracture mainly occurs in Si/underfill/Si adhesion structures by two modes, i.e., interface delamination and mixed mode of interface cracking and internal fracture in the underfill, and the probability of two fracture modes occurring in the adhesion structures does not seem to show obvious difference. The decrease in underfill thickness from 200 to 100 and then to 50 μm seems to have little influence on shear strength of the adhesion structures, but the adhesion structures with interface delamination mode show obviously higher shear strength than the structures with the mixed fracture mode. A comparison of the shear strength between the adhesion structures prepared by two underfills suggests that T g may be the main factor affecting the adhesion performance of the underfill and its adhesion structures.