Effects of Material Property and Structural Design on the Stress Reduction of the Joints in Electronics Devices

Abstract

Electronics devices consist of silicon chips, copper leads, substrates and other parts which are jointed to each other with solder, conductive adhesive or other materials. Each coefficient of thermal expansion is different and it causes strain concentrations and cracks. We analytically investigated the stress reduction structure at the edge of the joints such as Sn-Ag-Cu solder or Cu/Sn alloy between the silicon chip and copper lead. At first, we examined the influence of the joint thickness and fillet at the joint edge on the stress. In the joint without fillet, the stress at the end of the joint increased depending on the thickness of the joint. The fillet of the joint increased the stress of the Cu/Sn alloy joint and the stress was increased depending on the thickness, though the fillet decreased the stress of the solder joint. We suggested the copper lead with slits to reduce the force of constraint. We compared the effects of the structure parameters of the slits on the stress reduction. The height was a more effective parameter than the width and the pitch. In the case of solder joint, the slits of the copper lead reduce the stress more effective in the thick joint than the thin joint. However, in the case of Cu3Sn joints, the slits reduced the stress more effectively in the thin joint than thick joint.

Effects of Hybrid Structures on the Stress Reduction and Thermal Properties of Joints in Electronics Devices

“…The purpose of our study is to clarify the effect of the material and structural design on the stress reduction of the joints in electronics devices. The effects of the joint thickness, existence of the fillet and the structure of the copper lead with slits were investigated [11]. Thicker joint of solder and epoxy resin with fillet decreased the stress at the joint edge.…”