Abstract
Deformations of a Si-epoxy-FR4 (simplified flip chip) structure under thermal testing were inspected with a real-time Moire technique. Specimens without cracks and specimens with a crack at the silicon-epoxy interface were prepared. The measurement results showed that the maximum deformation appeared at the edge. When the specimen was cooled to 20 °C, there was residual plastic deformation in the specimen. The creep effect was more dominant in the FR4-epoxy interface. Upon cooling to 20 °C, the specimen experienced partial strain recovery. To characterize the behavior of the interfacial crack, stress intensity factors KI and KII, and the strain energy release rate G in the vicinity of the crack tip were calculated using the measured deformations to conduct a quantitative study. It was observed that a sharp strain gradient occurred at the crack tip. KI and KII were dependent on temperature, and G was dominated by KI for the interfacial crack in the specimen.
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