Fluxless Flip-Chip Bonding Process Using Hydrogen Radical

Recently the portable electronic appliances have been remarkably minimized- (in weight and thickness), the assembled electric parts have also been gotten smaller and 3- dimensional and Flip-Chip bonding with solder bump haven been widely used. The 3-dimensional mounting has been put into an actual application stage. One of the important technologies for supporting these packaging is a bonding technology. Especially the reliability in Flip-Chip bonding technology of the fine solder bump has been an important key. In the fine solder, the bump-to-bump pitch gets smaller, and the conventionally applied flux has a more difficulty in cleaning after the reflow. This problem is required establishment of a fluxless reflow technology. Recently due to environmental problems, regulations for non-application of Halogen element have been established. And the flux has also been studied for Halogen-free application. From this viewpoint, the fluxless solder bonding technology has become an important factor. As the fluxless soldering technology, up to now, the author group has made studies for development of fluxless reflow process of solder bump, while taking note of reduction capability of hydrogen radical[1][3]. In this reports, we arrange the results of fluxless reflow and bonding. And we developed a high productive method of fluxless solid state bonding in the air using the solder bump, which the oxide film reduced by hydrogen radical irradiation before bonding. These results propose a new effect that hydrogen radical irradiation is not only reduce the oxide film but also inhibit re-oxide. And we think of this effect as a decoration such as chemical adsorption on the solder surfaces by hydrogen. And we call this effect as "Surface Hydrogen Buffering Effect".