Low-temperature solders have wide applications in integrated circuits and micro-electromechanical systems packaging. In this article, a study on Ag-In solder for chip-to-chip thermocompression bonding was carried out. The resulting joint consists of AgIn 2 and Ag 9 In 4 phases, with the latter phase having a melting temperature higher than 400°C. Complete consumption of In solder into a Ag-rich intermetallic compound is achieved by applying a bond pressure of 1.4 MPa at 180°C for 40 min. We also observe that the bonding pressure effect enables a Ag-rich phase to be formed within a shorter bonding duration (10 min) at a higher pressure of 1.6 MPa. Finally, prolonged aging leads to the formation of the final phase of Ag 9 In 4 in the bonded joints.

Low temperature hermetic wafer bonding using In/Sn interlayer and Au/Ni/Cu metallization as the high-melting-point ͑HMP͒ components was reported, wherein the thin Ni layer was introduced as a buffer layer to prevent solder consumption after their deposition. 8 in. wafer to wafer bonding was achieved at 180°C for 20 min under 5.5 Mpa. Voids free seal joints composed of high temperature intermetallic compounds were obtained with good hermeticity. Present results show that the buffer layer is the key to ensure high yield hermetic wafer bonding when the low-melting-point solder was deposited directly on the HMP component.

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