Research Of Low Temperature Bongding Technology Based On Micro-Cones Arrays

With the development of a variety of high-density micro-electronics packaging technology, the electronic interconnection faces great challenge. Currently, there are a variety of ways to compactly connect multiple chips using peripheral wiring technologies, but the package density of IC is limited by the wire-bonding technology, these methods will gradually turn to the Face to Face type interconnection. And the requirement of the temperature of the interconnection will become more and more strongly with the increasing of the number of chips and the pin wiring. High temperature will seriously affect the reliability of the packaging.So we developed a new low temperature bonding technology based on the micro-cones arrays. The micro-cones arrays had special surface of the needle crystal structure in the Z order. It could get extremely high bonding strength because of the physical biting cooperation when the arrays combined with other materials. This method included three key parts: first, the preparation of the Ni micro-cones arrays on the surface of bump and the soft solder on another surface; second, the relevance and timeliness hot bonding; the third, heat treatment technology. Our laboratory developed the method of preparation of Ni micro-cones arrays by directional electrodepositing which is simple and low-cost. It provided the necessary condition for this low temperature bonding technology. And then, we made soft solder and the micro-cones arrays embedded integration through appropriate hot bonding, achieve the chemical combination by heat treatment to get more reliable performance. In this paper, we studied the effect of the morphology of the micro-cones arrays, the hot bonding technical parameter (such as the bonding temperature and pressure, etc.) and the time of the heat treatment to the bonding strength. And we also investigated the elements of the combination of the joints.The main points are summarized as follows:1. When the size of needle-like crystal grow up to 500nm-800nm which controlled by adjusting the time of electrodeposition, the micro-cones arrays are embedded better in the solder for a better combination. The gold-plated process for an antioxidant layer can improve the bonding strength.2. The inserted combination is achieved after hot bonding. And the bonding strength of the joints is significantly increased with the bonding temperature and pressure. When the bonding temperature is higher than 180℃and the pressure is higher than 550gf/p, the increase of the bonding strength tend to gentle.3. Because of the surface hardness of SnAgCu solder is lower than the SnZn solder, the bonding strength of SnAgCu joints is higher than SnZn joints by this low temperature bonding method.4. The bonding strength is significantly increased after heat treatment to achieve a chemical combination. The behavior of diffusion in tin-nickel interface is based on the non-reaction-diffusion and supplemented by the reaction-diffusion. So there is no brittle intermetallic compound lay which existed in the traditional reflowed process. It is possible that the compound is Ni3Sn4 which is predicted by the heat formation of intermetallic compounds models.5. The micro-cones arrays promote the diffusion between Ni and Sn because of the micro-nano-structure on the surface which has a high activity and a large number of grain boundaries.This paper introduces this new low temperature bonding technology based on Ni micro-cones arrays, and provides a new green method of electronic interconnection for 3D high-density packaging.