Enhancement of underfill performance for flip-chip applications 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. The fast-flow method is currently the most widely used method for applying the underfill to the gap. This method dispenses the underfill along one or two sides of the die and allows the underfill to fill the gap by capillary flow. There are two major opportunities for improvement of the fast-flow method of underfilling: flow time and cure time. This paper presents work on enhancement of the underfill viscosity and wetting properties by silane coupling agents to decrease the time to underfill the die. Viscosity, contact angle measurements, and flow time in a simulated flip-chip are used to test the effects of the additives in the underfill. Also, adhesion of the underfill to die and substrate surfaces can be enhanced by addition of silane coupling agents to the underfill. Adhesion is important in the reliability of the flip-chip assembly. This paper presents results on shear strength as a measure of adhesion strength for underfill bonded to alumina and FR4 with solder mask.