Ag-(In-Bi) Solid-Liquid Interdiffusion Bonding

Solid-liquid interdiffusion is a metallurgical bonding technique, suitable for assembly of temperature sensitive materials. We identify Ag-(In-Bi) as meeting the low-temperature bonding requirements, theoretically as low as 73 degrees C. This work focuses on understanding the bonding process and the interactions between the metal elements. Ag-(In-Bi) was bonded using an eutectic In-Bi foil at both 150 degrees C and 180 degrees C. The resulting bondlines were layered as Ag/Ag9In4/AgIn2/In-Bi compounds/AgIn2/Ag9In4/Ag. At some sections the phase growth of AgIn2 or Ag9In4 bridged the bond. Because of this bridging of gamma-Ag9In4, temperature stability of similar to 480-570 degrees C, is readily possible. The majority of the remaining Bi was located within large pockets near the middle of the bondline, and the minority as precipitates in protruding arms. Mechanisms for these Bi precipitates and intermetallic arm growth are discussed, and the evidence indicates that dissolution and surface planarity play important roles in their formation.