Temperature Effect of Interfacial Fracture Toughness on Underfill for Pb-Free Flip Chip Packages

In this study, the interfacial fracture toughness between passivation layer and underfill was investigated at elevated temperatures by performing conventional four-point bending test and finite element simulation. Since the board level reflow temperature for Pb-free flip chip packaging is reaching as high as 260 degrees C, the concern about delamination at the interfaces between underfill and its surrounding components becomes a more serious reliability issue. To estimate the interfacial strength, interfacial fracture toughness at a specific mixed mode loading condition is calculated. As temperature is increased, the interracial toughness was also increased up to the glass transition temperature. Beyond the glass transition temperature, however, interfacial fracture toughness is decreased.