关键词: 中低温焊料, Sn-In-Bi-（Ag, Cu）五元合金, 熔点, 可靠性, 金属间化合物

Abstract: The warping deformation of chips and substrates at elevated soldering temperatures has been recognized as a critical issue, giving rise to welding defects such as head-on-pillow (HoP), Non-wet- open (NWO), and solder ball bridging (SBB). As a result, traditional medium and high temperature solders, like SAC305, have been demonstrated to be insufficient for large-scale chip soldering processes, as they fail to meet the requirements of such processes. Moreover, the reliability of low melting point Sn-Bi solder remains unsatisfactory. To address the conflict between melting point and reliability, this study proposes a reduction in the melting point of Sn-Ag-Cu solder (to 194.1 ℃) through the addition of In, Bi, while ensuring that its alloy structure does not form a low melting point phase. Simultaneously, according to the solder joint reflow and high-temperature ageing of the organization evolution, drop resistance, high-temperature ageing, temperature cycling, such as the reliability of the evaluation of optimising the content of Ag, the paper puts forward a series of recommendations. The results show that the reflow temperature of the newly developed medium-low temperature Sn-In-Bi-(Ag, Cu) solder can be decreased by 20-25 ℃ compared to SAC305. Additionally, due to the suppression of the coarsening of the intermetallic compound granular phase and the strengthening of the matrix, the reliability of the solder joints is superior to that of the SAC305 alloy.

Key words: low to medium temperature solder, Sn-In-Bi-(Ag,Cu), five-membered alloys, melting point, reliability, intermetallic compound