Shear Tension Of Lead-free Solder Joints Creep Resistance Strain Relations

Damage caused by creep is an important factor in the failure of lead-free solder joints. Research the creep behavior characteristic is significant to analysis the solder joints mechanical properties, predict its life and guide its recipe selection. It is difficult to detect the creep of soler joint directly by using the traditional methods because of its small size. Micro-resistance testing method has been proven feasible in the solder joints creep measurement as the trend of the solder joints resistance change is consistent with its creep. However, the specific relationship between electronic-resistance strain and creep is not yet clear. In this paper, the relationship between them has been deduced theoretically by establishing a solder joint equivalent crack damage model based on damage mechanics. Then base on the SCM platform by using four-probe micro-resistance measurement method and a high-resolution digital camera which is used to capture the image of solder joint deformation a real-time testing system was established, by which the resistance change and the creep of the solder joints can be measured synchronously in the shear tension conditions. During the tests the resistances and shear creep images of samples can be recorded in PC database automaticly. According to compare the shear creep images with the initial image of the solder joint the creep value can be got. In this paper the solder joint samples was produced by Sn96.5Ag3.0Cu solder. A large number of experimental data was analysised and optimized by using Origin software and the expermental results were compared with the theoretical results. Then some of the experimental phenomena and the differences between experiment and theory are discussed. The main conclusions are as follows:1) Both the "shear creep-time" graphs and "electronic-resistance strains-time" graphs can be divided into linear growth phase and exponential growth phase. In the linear growth phase the rate of shear creep is faster than electronic-resistance strains, while in exponential growth phase the rate of shear creep is slower than electronic-resistance strains; 2) With the increase of "h/S" (solder joint thickness divided by its cross-sectional area), the disparity in change rates of shear creep and electronic-resistance strains widens firstly and narrows lately, while the disparity in critical points of them narrows firstly and widens lately; 3) The relationship between creep shear creep and electronic-resistance strains is not linear simply, but to be divided into three stages. In the first stage it is linear, in the second stage it is exponential and in the third stage it is power.