Two test specimens are developed to measure interfacial fracture toughness in flip-chip assemblies. The specimens consist three layers of silicon chip, underfill and circuit board. Two symmetric edge cracks are embedded along the interface either between the chip and the underfill or between the underfill and the circuit board. The specimens are subjected to four-point-bend loading and critical loads are obtained. Analytical solutions for energy release rate have been derived for these two specimens and used to obtain the toughness from the measured critical loads. These specimens have been used to evaluate material combinations of chip passivation, underfill and solder mask for desired interfacial strength.

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