We have developed a modified accumulated damage model that can be used to predict the fatigue lives in solder joints in electronics devices. Our model calculates the fatigue life of solder based on the damage that accumulates during crack propagation using a finite element method and corrects for the influence of element size on the calculated life using Hutchinson–Rice–Rosengren singularity theory. We predicted the fatigue lives of two types of solder joints in Ball-Grid-Array (BGA) packages during thermal cycling tests: one is conventional solder bumps and the other is Cu-cored solder bumps. The predictions agreed well with the experimental results, which indicates that our model can effectively predict fatigue life in solder joints.

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A corrosion test was carried out for copper substrates with a plated nickel undercoat and plated gold top surface, and the influence of the nickel-plating conditions on corrosion resistance was investigated by varying the kind of plating bath and the current density. The samples were characterized by X-ray photoelectron spectroscopy (XPS), electron-probe microanalysis (EPMA) and focused ion beam/scanning ion microscopy (FIB/SIM). From those results, it was confirmed that a Watt's bath was more effective for corrosion resistance than a sulfamic acid bath, and the crystallite size of the nickel plated with the Watt's bath was smaller than that with the sulfamic acid bath. From the EPMA results and the values of standard free energy of formation (ΔG_f°), the main corrosion products on the surface appeared to be nickel and copper compounds including the sulfate ion, which was not affected by the nickel-plating conditions.

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