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.
Electronics devices consist of silicon chips, copper leads, resin or ceramics substrates and which are jointed to each other with solder, conductive adhesive or other materials. Each coefficient of thermal expansion is different and it causes strain concentration and cracks. The solder easily deformed by the difference of the thermal expansion and it relieved the stress on the devices however the epoxy resin of the conductive adhesives are harder. So we suggested the composed joint including the relaxation layers of low elastic material. The shear strength and elongation of the epoxy resin joint, silicone rubber joint and the composite joint of the two materials were investigated. The analytical study was carried out to clarify the stress reduction effect of the design of the relaxation layer in the composite joints. The parameters such as the width, height, pitch and the distance of the relaxation layer from the joint edge are investigated. The high relaxation layer close to the joint edge effectively reduced the stress of the joint. The stress reduction effect appeared in the different pitch of the layers.
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