Development of a New Multi Layer Substrate Bonding Technology using Ag-Sn Liquid Phase Sintering Process (First Report) -Investigations of Diffusion Processes-

Abstract

In order to construct the multi layers IVH (Interstitial Via Hole) structure with only one time hot pressing, we have developed the new diffusion bonding technology. In this paper, the sintering process of Ag-Sn mixed powders (Ag/Sn:65/35 mass%) between copper foils in IVH with hot vacuum pressing was investigated, and the effect of temperature on the respective diffusion reactions was discussed. Ag and Sn formed Ag₃Sn up to 473 K with the solid diffusion reaction. At 483 K, Ag particles disappeared completely and the mixed compact consisted of Ag₃Sn and excess Sn. Cu-Sn diffusion reaction between excess Sn and copper foil commenced at 493 K. Excess Sn was consumed completely below 573 K. The liquid phase of Sn contributed not only to Cu-Sn diffusion bonding but also to Ag₃Sn sintering. As a result of hot pressing above 573 K, the mechanical properties were improved without large grain growth of Ag₃Sn (about 4 μm).