Solid-Liquid InterDiffusion (SLID) Bonding, for Thermally Challenging Applications

Solid-Liquid InterDiffusion (SLID) bonding is particularly suited for high-temperature applications, since SLID bonds can tolerate higher temperatures than the bonding temperature. SLID uses a layered binary metal structure, which reacts to high-temperature stable intermetallics at normal solder temperatures. Hence, high-temperature stability is achievable for a process at moderate bonding temperatures. Alternatively, low-temperature SLID bonding (bonding down to ~100 °C) allows bonding of temperature-sensitive components and materials, without restricting the application temperature range. Cu-Sn is the most mature SLID system. We show optimized Cu-Sn SLID bonding for vacuum encapsulation of MEMS devices. Au-Sn SLID has superior oxidation resistance, and we demonstrate that Au-Sn SLID has excellent reliability when bonding thermally mismatched chips and substrates. We demonstrate Ni-Sn SLID bonding, as well as the low-temperature alternatives Au-In and Au-In-Bi. For Cu-Sn, Au-Sn and Au-In SLID, we show experimental evidence for the high-temperature stability predicted from phase diagrams.