| Summary: | 碩士 === 國立清華大學 === 化學工程學系 === 101 === Soldering is one of the most important joining technologies in electronic products. During the soldering processes, the molten solders wet the substrates first, and then solidify with lowering temperatures. The phases formed at the joints are critical to the properties of the solder joints. Sn-Ag solders are widely used commercial solders. It has been found that a small amount of cobalt addition can effectively reduce undercooling and improve its mechanical properties. Nickel is the most commonly used diffusion barrier, and (Co,Ni) has also been investigated as possible diffusion barrier material. In the soldering process with Sn-Ag-Co alloys and (Co,Ni) barrier layer, in addition to the formation of intermetallic compounds by interfacial reactions, substrate dissolution occurs, and a Sn-Ag-Co-Ni melt is formed. Understanding of the Sn-Ag-(Co)/(Co,Ni) interfacial reactions and the solidification behaviours of Sn-Ag-Co-Ni melts are important. Liquidus projection is an essential tool for the understanding of solidification behaviours. This study thus investigates the Sn-Ag/Co interfacial reactions and the liquidus projection of Sn-Ag-Co-Ni ternary system at the Sn-rich corner. Since there is no information of the liquidus projection of the Sn-Co-Ni system which is an important constituent ternary system of the Sn-Ag-Co-Ni, this study also studies the liquidus projection of the Sn-Co-Ni system. The results indicate the primary solidification phases of the ternary Sn-Co-Ni system are all terminal solid solution phases and binary compounds which are Sn, CoSn3, CoSn2, CoSn , (Ni,Co)3Sn2, (Ni,Co), Ni3Sn4 and Ni3Sn, respectively. Co3Sn2 and Ni3Sn2 form a solid solution, and no ternary compound is found as the primary solidification phase. At the 90at.%Sn and 95at.%Sn of the Sn-Ag-Co-Ni quaternary system, there are four primary phase regions which are Ag3Sn, CoSn2, CoSn and Ni3Sn4.The Sn-Ag/Co couples reacted at 250oC reveal that the CoSn3 phase is the primary intermetallic compound formed at the interface. The reaction rate is lower with Ag addition. Two reaction layers, CoSn3 and Ag3Sn, are formed in the couples reacted at 200 and 150oC.
|
|---|
