In situ study on growth behavior of interfacial bubbles and its size effect on Sn-0.7cu/Cu interfacial reaction

With the advent of lead-free soldering electronic packaging industry, there are growing concerns regarding the problems of voids in lead-free solder joints. Many researchers are eager to understand the growth, evolution and control factors of bubbles. Due to the restrictions in test conditions imposed by high temperature and opacity of soldering, one cannot directly observe and analyze the behaviour of bubbles. Moreover, bubble evolution and surface reaction effects go hand in hand with each other during soldering; so the latter should be interfering the pattern of the former and vice-versa. In this study, the growth behavior of interfacial bubbles and the effect of bubbles on interfacial reaction during a soldering process were in situ studied by the synchrotron radiation real-time imaging technology. In the scanning electron microscope, we can observe the bubbles size and its impact on the scope of IMC at Sn-0.7Cu soldering on 250°C. We found that bubbles effecting surface reaction have a the critical value and there is differentiate between different size of bubbles and its area of influence, the larger of bubbles, the greater effecting area. The closer to the bottom of the bubble, the less the Cu substrate dissolved. The effect of bubble on the IMC growth around the bubble was small, and the average IMC size decreased gradually with the increase of the distance and stabilized finally.