Enhancement of underfill adhesion to die and substrate by use of silane additives

A challenge in flip-chip technology development is to improve the thermo-mechanical reliability of the flip-chip assembly. To increase reliability, an underfill encapsulant is applied to the gap between die and substrate to provide thermal-mechanical protection as well as environmental protection to the assembly. There are three main underfill material properties that contribute to thermo-mechanical reliability of the flip-chip assembly: 1) modulus, 2) coefficient of thermal expansion (CTE), and 3) adhesion. This paper deals with improving the adhesion of the underfill to die and substrate surfaces which could lead to improvements in thermo-mechanical reliability. Adhesion of the underfill to die and substrate surfaces can be enhanced by addition of silane coupling agents to the underfill. This paper presents results on shear strength as a measure of adhesion strength for underfill bonded to alumina and FR4 with solder mask.