On-Chip Diffusion Bonding creates Stable Interconnections Usable at Temperatures over 300°C

Abstract

In this paper, we present a conceptual design of an on-chip solder stack to connect silicon devices faster and more reliable. Almost all electronic devices rely on solder layers to provide electrical, mechanical, and thermal connections between components. We improve the solder connection with industry-standard solder parameters of 300°C and some minutes of soldering time. An ideal solder connection is composed of intermetallic phases (IMPs) at the interfaces between device and solder, and substrate and solder. Typically, a thin region of Sn-based solder remains between the two IMP layers at the interfaces. IMPs of copper (Cu) and tin (Sn) are Cu6Sn5 and Cu3Sn. The formation of IMPs is decisive for a good mechanical connection because of their high melting point and mechanical stability. To achieve these requirements, we implement the solder stack as a transient liquid phase bonding (TLPB) system. To realize durable interconnections, we use the diffusion of a high-melting first component in a second component, which is liquid at solder process temperature. Ongoing diffusion leads to the formation of IMPs with a melting point above process temperature, resulting in a solidification of the connection at constant temperature. By this isothermal solidification, the solder connection becomes more durable against mechanical and thermal load and is usable at temperatures exceeding 300°C.