Effects of Heating Rate During ACFs Curing Process on Material Properties and Thermal Cycling Reliability of Flip Chip Assembly

In this study, effects of heating rate during ACF curing processes on material properties such as thermo-mechanical properties and rheological properties of ACFs were investigated. Generally, material properties of polymers change with the process conditions such as temperature, time, frequency, and so on. As the heating rate increased, coefficient of thermal expansion (CTE) of ACFs increased, and storage modulus and glass transition temperature (T_g) of ACFs decreased. ACF material property changes were due to cross-linking density which is related with ACFs density. Contact resistance of ACFs flip chip assembly was dependent on heating rates. As the heating rate increased, the contact resistances of ACFs flip chip assemblies decreased. The decrease in contact resistance was due to larger ACFs conductive particle deformation. In addition, effects of heating rates of ACFs on thermal cycling (T/C) reliability of flip chip assemblies were also investigated. As the heating rate increased, the contact resistances of ACF flip chip assemblies rapidly increased during the T/C test. T/C reliability test result was analyzed by the shear strain estimation which is closely related with ACFs material properties and the gap between a chip bump and a substrate pad. As a summary, effects of heating rate on ACFs material properties and thermal cycling reliability were investigated. T/C reliability test result was analyzed in terms of the shear strain. Based on the results, the guidelines of ACFs curing process during flip chip bonding processes were suggested.