| With the large scale integrated circuit developing in the direction of high density、 high integration and small size, how to improve the qualified rate of product and its reliability is the key technology and core scientific problem in the development of modern electronics manufacturing. There are many factors that can effect its reliability, the void is recognized as one of the main failure reason in solder joint. It is generally thought that flux and others volatile generate some gas trapped in molten solder during reflow soldering process. Therefore, to improve the reliability of electronic devices, in-depth understanding of solder voids in size、 shape、 distribution、 formation mechanism and control factors is very important and urgent. This involves the bubbles formation、 grew up、 movement and its subsequently merged and other related problems.This article choose Sn-0.7Cu and Sn-3.5Ag lead-free solder as research object, using Synchrotron Radiation Real-time Imaging Technology observation the evolution behavior of soldering interfacial bubbles. We found that solder interfacial bubble has great effect on the growth of interfacial IMC, bubbles affects IMC growth behavior by influencing the atom diffusing and the IMC growth also effects bubble evolution. The main conclusions are as following:(1) The bubble heterogeneous at liquid/solid interface was easier than homogeneous, both of them has the same critical radio that was However, for the critical volume, there was From the experiment we got the value of f(θ) between 0.5 to 1, it follows that the bubble’s Homogeneous nucleation of critical volume was 1 to 2 times larger than the heterogeneous nucleation. After its nucleation on the interface, using Synchrotron Radiation Real-time Imaging Technology observation found that its volume was proportional to the soldering temperature, In the heating stage, its volume increased with the rising of temperature. The increased of volume made the adjacent bubbles touching with each other and merging into a big bubble. Besides, a merged bubble grew into spherical finally under the action of surface tension. (2) The evolution of soldering interfacial IMC and bubbles influenced with each other. The experimental results showed that the copper at the bottom of the bubble was higher than other place. Besides, The IMC located in the bottom of bubbles was larger than other areas. effecting area became larger with the size of bubble increasing. Real-time observing the soldering interfacial reaction showed that the growth of IMC could effect the bubble’s shape. When the thickness of the IMC exceeded to the center of interfacial bubbles, bubble’s shape changed from spherical state to oval state. After the IMC surrounding the bubble dissolved, the bubble will recovery.(3) Under the condition of thermal-migration, using the synchrotron radiation real-time imaging technology to observe, the hot end and cold end began to grow With the increased of soldering temperature. Until the initial stage of heat preservation, under the effect of thermal-migration the dissolved copper diffusion from the hot end to the cold end that resulted in IMC significantly asymmetric growth. This kind asymmetric growth resulted in migration of interface bubble. The bubbles moved from the hot end to the cold end and attached at the top of the IMC which has been growing on the cold end. |
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