Au-(In-Bi) and Ag-(In-Bi) Metallic Bonding for Temperature Sensitive Materials

Solid-liquid interdiffusion (SLID) bonding based on Au-(In-Bi) and Ag-(In-Bi) metal systems has emerged as a potential approach for low-temperature metallic bonding of temperature sensitive materials, such as substrates for flexible, wearable electronics and piezoelectric materials. This work uses eutectic In-Bi with extremely low melting temperature
$(\mathbf{T}_{\mathrm{m}})$
of 72.7 °C, sandwiched between Au or Ag, these metals being commonly used as electrodes on flexible substrates and piezoelectric materials. We have demonstrated metallic bonds for both Au-(In-Bi) and Ag-(In-Bi) at temperatures as low as 90°C. Using bonding temperatures above 110°C accelerates the diffusion process remarkably, resulting in the final bonds comprising quasi-layered (Au,Ag)-In IMCs sandwiched between (Au,Ag) layers, with Bi pockets enclosed by the IMCs and/or (Au,Ag) at the centre of the bondline. We demonstrate the feasibility of bonds with no low
$\mathrm{T}_{\mathrm{m}}$
In-Bi IMCs (89–110 °C), all Bi being present as elemental Bi (
$\Gamma_{\mathrm{m}}$
271°C). Such a bond has a theoretical thermal stability defined by the high-temperature stable (Au, Ag)-In IMCs. This paves the way for using these low-temperature SLID bonds in the assembly of temperature sensitive materials as well as in high-temperature applications.