Research On NiPdAu Pre-plated Frame Copper Wire Bonding

With the deep development of electronics packaging technology, micro-electronicindustry is keeping on pursuing high-density, miniaturized package as well as low-cost, low-pollution manufacturing process. To meet these develop demands, Pre-plated frame copperwire bonding technology come into our eyes. As the pre-plated frame copper wire bondingprocess has a short manufacturing cycle, lower environment pollution and what is most is thecost benefit, it is considered to be the most promising candidate to replace the golden wirebonding process, and copper wire bonding technology based on pre-plated frame has becamea popular IC manufacturing trend. However, because of the new bonding materials couple andthe immature bonding process, the current NiPdAu pre-plated frame copper wire bondingprocess has a low bonds yield and fast capillary wear problem.In present paper, the specific copper wire bonding samples based on the NiPdAu pre-plated lead frame was investigated. First researched the basic properties of the bondedmaterials, such as the copper wire, NiPdAu pre-plated frame, and then studied the reliabilityproblems that might exist in the bonding process and analyzed the bonding mechanism.Finally, to improve the bonding quality, a new post heat treatment was introduced to the pre-plated frame copper wire bonding process.Copper wire and NiPdAu pre-plated frame were two of the most important materials inour research. For the copper wire, the oxidation was a university problem, palladium-platedcopper wire could promise a better bonds appearance than that without palladium plated. Forthe NiPdAu pre-plated frame, the surface roughness was a key factor. It was found theNiPdAu pre-plated frame with a rougher surface could get a strength bonds, but with a fastercapillary wear. While reduced the rough a little, the capillary life had a significantimprovement, though the bonds strength also reduced, but not seriously. As both the copperwire and the NiPdAu pre-plated frame were very hard, when they were bonded together, thehardness-match was also very important.For the NiPdAu pre-plated frame copper wire bonding process, the biggest problem wasappeared in the second bond. During the bonding process, copper oxidation, bonds lift off, bond irregular in shape and so on were quite common. The wire pull test showed the secondbond had a poor adhesion between the copper wire and the NiPdAu surface while use thegeneral bonding parameters, but when enhance the bonding parameters, it would cause theheel crack in the second bond. The factors which influent the bonds reliability included thebonding parameter and the capillary type.NiPdAu pre-plated lead frame copper wire bonding process and its interface formationmechanism were analyzed. The cross-section with the microstructure morphology of the wirebonds indicated that the low reliability of the second bonds were caused from two aspects: Asthe copper wire and the NiPdAu lead frame surface were hard, the interface diffusion is poor,and there is almost no growth of intermetallic compounds appeared, which result in the pooradhesion. If enhance the bonding parameter, as the copper wire was working-harden sensitive,the higher bonding parameters caused the damage in the copper wire.A new post heat treatment process was introduced to improve the NiPdAu pre-platedlead frame copper wire bonding process. For the pre-sealed wire bonding product, a5-10minheat treatment at the temperature of200°C could significantly improve the bonding strength.