Characterization of molded underfill material for flip chip ball grid array packages

Flip chip technology has been utilized for more than 30 years in the field of electronic packages. It was developed to meet the requirements of excellent electrical performance, small device, high input/output (I/O) density and high speed. Underfill which is used to fill the gaps between solder bumps can enhance the fatigue life of solder bumps due to CTE mismatch between chip and substrate. Underfill materials usually need longer cure time to cure in process and with higher cost. Therefore, the molded underfill is studied to replace the capillary flow underfill for providing higher productivity, no particle setting and less expensive materials. The molded underfill material has to contain smaller filler size to fill the small gap between solder bumps and fast cured time. The development of molded underfill material is different from conventional underfill and molding compound material. The material characterization of molded underfill material was analyzed with various methods. The curing condition was measured by differential scanning calorimeter (DSC). Thermo-gravimetrical analyzer (TGA) was used to study the weight loss of materials. Thermal mechanical analyzer (TMA) was used to investigate the coefficient of thermal expansion (CTE) of the cured materials. Dynamic mechanic analyzer (DMA) was used to measure the storage modulus of the cured materials. In this paper, the curing conditions and material properties such as CTE (coefficient of thermal expansion), T_g (glass transition temperature), storage modulus and weight loss were evaluated from the measurement results for molded underfill materials. The results were also compared with conventional underfill materials and molding compound materials