Micro-thermocompression Bonding Mechanism and Modeling for Electronics Devise Interconnection

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Process mechanism of wire bonding and fine lead bonding used in pakaging of microelectronics was studed. Deformation processes during these thermocompression bonding without ultrasonic vabration are simulated by a numerical model which is based on the finite element technique. The growth process of interfacial contact between wire surface and lead frame is also analyzed. If the contact interface is fixed then the lateral wire surface expands simultaneously with folding to the lead frame, producing the perimeter bond. On the other hand, if the contact interface can slide, the center of contact area largely expands and the lateral wire surface does not extends. It follows that the interfacial contact area tends to be fixed but not to slide when the perimeter bond is produced even if strong metallic bond is not achieved at the center. The wire reduction greater than 0.5 is required for ensuring the strong perimeter bond formation. This is supported by the experimental rsults.The interfacial contact area is governed mainly by the wire reduction. If the reduction is kept constant then the tool with a groove increases the contact area somewhat larger than the flat tool, although the groove tool decreases the rate of wire deformation. We further discuss the size limit of wire bonding, taking into account the perimeter bonding mechanism.With respect to lead bonding, effect of pad thickness and hardness on the interfacial deformation was investigated. In paticular, pad thickness effect largely change the interfacial deformation and the stress distribution on the interfaces between pad and lead andbetween pad and substrate. This was supported by experimental data.Moreover, solid state micro room temperature bonding of fine golid wire was tried. Ultra high vacume condition and the bonding surface activated by ion beam make this bonding possible. We cannot ignor the elastic deformation around bond interface. The reduceing process of elastic stress distribution was modeled.