Experimental analysis on the mechanism of moisture induced interface weakening in ACF package

In this paper, we have determined the influence of moisture absorption to the adhesion property of ACF for flip chip interconnection. An attempt was made to quantitatively measure the interfacial fracture toughness of both silicon/ACF and FR4/ACF sandwiched specimens exposed to different humidity conditions using 4-point bending test. Evidence of crack propagating along the interface was checked by cross section images of the specimens. For moisture absorption, specimens were stored inside the humidity chamber (85^oC,85% RH) until they were fully saturated. Pressure cooker test (PCT) was performed to observe vaporization effect on the adhesion strength under real service condition. By comparing the 4-point bending test results between different humidity conditioned specimens, interface weakening by moisture absorption has been observed quantitatively and the mechanism was considered. Scanning acoustic microscope (SAM) images were taken to observe whether delamination exists at the specimen interface.