Experimental Test And Reliability Of Cu Wire Interconnecting With Au Plating Layer Using Microresistance Welding

With the development of Electronic devices, it asks smaller, multifunctional and high reliable. Because of the need for high density packaging, the microjoining technology are facing of challenge. Hand-tin soldering is often used in the interconnection of electronic devices, but it has many disadvantages like inefficient, hard to control quality, dry joint, burr, trailing as well as intermetallic compound evolution. A faster and more reliable joining method should be proposed to reach the need. Therefore, parallel gap resistance welding is put forward. The welding process and joint reliability are studied in this paper.Orthogonal experiment table was established to study the optimal parameters. Tensile force and shear force were tested to study the mechanical property. Range analysis and variance analysis were adopted to study the influence of each parameter. Joining mechanism was studied by cross section analysis. Reliability tests including of thermal shock, random vibration, heat aging and electric heat aging were all studied. At last, ANSYS software was used to study the parallel gap resistance welding theory, and also the simulation of thermal shock, random vibration and electric heat aging were studied to find the weak region of joint.The results showed the optimal parameters were electrode force of 0.56N-0.84 N, welding voltage of 0.45V-0.5V, welding time of 16ms-20 ms. The maximum value of tensile force was up to 28 g, while the shear force was 187 g. With the increasing of heat input, the joint shapes respectively were rectangular joint, figure 8 joint, rectangular joint and elliptic joint. The composition on the interface of Cu wire/Au plating was solid solution, and there was no intermetallic component. In optimal range of parameters, the bonding mechanism was solid state bonding. The joint would melt when overheated, but no nugget was formed. In thermal shock test, the joint resistance and tensile force just changed a little. In heat aging test, the joint resistance raised rapidly with the production of oxidation on Cu wire, but raised slowly after a few days. In random vibration test, no fracture appeared at the neck region. After electric heat aging for 180 h, the joint resistance raised greatly and separation was produced at partial of Cu wire/Au plating interface, which indicated the joint was failure. The finite element analysis of parallel gap resistance welding results shows the highest temperature region was at the center of Cu wire/Au plating interface, which was up to 938℃. The highest electric current density was also at the center of Cu wire/Au plating interface, but the biggest equivalent stress was on the sides of interface. The thermal shock simulation results indicated the weak region was at the junction of joint neck and interface. The electric-thermal simulation results indicated the current piled up at the joint neck, meanwhile the neck suffered the biggest equivalent stress. In model analysis, resonance was mainly produced at the Cu wire, because of nearly no constraint at the end of wire. In the simulation of random vibration, the biggest equivalent stress was at the junction of joint neck and bonding interface, but it was only 0.77 MPa which was much less than the joint failure strength.