Shear Resistance Strain Of The Solder Joints Under Tensile And Temperature Cycling Conditions

The reliability of the Lead-free solder joints is a hot spot in the field of today's electronic packaging research. The electrical measurement methods for studying the reliability of the Lead-free solder joints have broad development prospects as a result of the advantage of real-time measurement, fast and low-cost. In this paper, the micro-electrical-resistance strain characteristics of the lead-free solder joint under the shear creep or the thermal cycle condition were studied by the method of combining the theoretical deduction, the experiment and the simulation. Under the shear creep condition, the theoretical calculation formula of the micro-electrical-resistance strain was obtained by the theoretical derivation, from which the theoretical curves of the micro-electrical-resistance strain were obtained. The theoretical curves and the experimental curves are in good agreement, and both are consistent with the classic creep curve. Compared the micro-electrical-resistance strain of the solder joints with eight different thickness, an optimum thickness 0.25mm was found for making the minimum electrical-resistance strain and the best creep performance. On the other hand, the creep strains of the solder joints with the above-mentioned eight different thicknesses were simulated by the finite element method, and an optimum thickness 0.25mm was also obtained. A quantificational relationship between the micro-electrical-resistance strain and the solder joints thickness was obtained according to the experimental data. The quantificational relationship between the creep strain and the solder joints thickness was obtained according to the data of FEM. The quantificational relationship between the creep strain and the electrical-resistance strain was obtained by combining the experimental data and the FEM data. Under the thermal cycle condition, the theoretical calculation formula of the micro-electrical-resistance strain was obtained by the theoretical derivation. Corresponding theoretical curves of the micro-electrical-resistance strain were constructed, which were analyzed by comparing with the experimental curves. The effects of the temperature cooling and rise rate, the temperature range were discussed respectively based on the theoretical formula. The micro-electrical-resistance strain of the solder joints with shear tensile loading under thermal cycle condition were studied, which was compared with the electrical-resistance strain under the single thermal cycle condition. Finally, a preliminary study about the relationship between electrical-resistance strain and damage was carried out. The quantificational relationship between the electrical-resistance strain and the damage was obtained by theoretical deduction. Corresponding damage curves were obtained by combining the theoretical formula and experimental data, and they are consistent well with the damage curves which were discussed in the literature. It indicated that the micro-electrical-resistance strain is an effective parameter for studying the damage of the Lead-free solder joints.