Fracture mechanics study on the intermetallic compound cracks for the solder joints of electronic packages

The crack behavior of the intermetallic compounds (IMCs) for the solder joints of electronic packages under the thermal cycling test conditions was analyzed using the finite element method in this research. A flip-chip plastic ball grid array package was selected as the analysis target. The two-dimensional in-elastic finite element method was employed to calculate the fracture mechanics parameters at the crack tip; such as the modes I and II stress intensity factors. Two locations were considered herein to initiate the crack: the first one was on the interface between the IMC and the copper pad (interfacial cracks); and the other one was at the inner part of IMC (IMC cracks). Furthermore, the effects of crack length and thickness of IMC on the crack tip parameters were also studied in this investigation. In the numerical simulation, the properties of the solder joint and the underfill were assumed to be elastic–plastic–creep and viscoelastic, respectively. The sub-modeling technique was used in the finite element analysis to reduce the computational time and the crack tip parameters were obtained using the simulated results of the displacement field near the crack tips. The results show that for both interfacial cracks and the IMC cracks, the modes I and II SIFs decrease as the length of crack increases, and the decreasing trend becomes more stable when the cracks propagate longer except for the variation of the mode II SIF for IMC cracks. Furthermore, the thickness of the IMC has slight effect on the magnitudes of SIFs under the conditions of constant crack lengths.