Coffin‐Manson equation of Sn‐4.0Ag‐0.5Cu solder joint

Abstract

PurposeThe purpose of this paper is to fit Coffin‐Manson equation of Sn‐4.0Ag‐0.5Cu lead free solder joint by using results of solders joint reliability test and finite element analysis. Also to present a novel device for solder joint reliability test.Design/methodology/approachTwo‐points bending test of Sn‐4.0Ag‐0.5Cu lead free solder joint was carried out at three deflection levels by using a special bending tester that can control displacement exactly by a cam system. The failure criterion was defined as resistance of solder joint getting 10 percent increase. The X‐section was done for all failure samples to observe crack initiation and propagation in solder joint. Finite element analysis was presented with ANSYS for obtaining shear strain range, analyzing distribution of stress and strain and supporting experimental results.FindingsThe experimental results indicate that the fatigue life decreased obviously with the displacement increased. By using optical microscope and SEM photographs, two kinds of failure mode were found in solder joint. The majority failure mode took place at the bottom corner of solder joint under the termination of resistor initially, and propagated into the solder matrix. Another failure mode was delamination. It appeared at the interface between the termination of resistor and its ceramic body. The distribution status of stress and strain in solder joint and the calculation results of shear strain range at different deflection levels were obtained from simulation result. The Coffin‐Manson equation of Sn‐4.0Ag‐0.5Cu lead free solder joint was fitted by combining experimental data with result of finite element analysis.Originality/valueThis paper presents Coffin‐Manson equation of Sn‐4.0Ag‐0.5Cu solder joint with two‐points bending test. An effective and economical device was designed and applied.