Study of Adding Sb into Lead-free Sn-Ag Solder Joints on Metallurgical and Mechanical Properties

• Main Authors: Ming-Hung Chen, 陳明宏
• Other Authors: Hwa-Teng Lee
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/84123187913467802594

博士 === 國立成功大學 === 機械工程學系碩博士班 === 91 === The work discussed the effect of adding 1 — 2 wt% Sb on the melting point temperature, hardness, microstructure, adhesive strength and shear strength of Sn3.5Ag solder and solder joints. The effect of cooling rate on the microstructure and hardness of Sn3.5Ag solder, as well as the relationship among the total thickness of interfacial IMC (Intermetallic Compound) layers, adhesive strength and shear strength of solder joint and fractography were discussed. The solders were smelted from pure elements, i.e. Sn 99.9wt%, Ag 99.99wt%, Sb 99.5wt%, and the compositions were confirmed by ICP-AES. The results showed that adding 1-2 % Sb increased the melting point temperature of Sn3.5Ag solder, but the hardness were also enhanced. Adding Sb didn’t influence the composition of Ag3Sn that existed in the Sn3.5Ag solder, the added Sb atoms were solute into b-Sn completely. After 205°C´625h storage, the morphology of Ag3Sn that existed near the soldering interface appeared coarse plate, and the Ag3Sn that existed far away from the soldering interface appeared irregular rod. The experiment also revealed that the as-cast microstructure of Sn-Ag solder was governed by cooling rates. The microstructure changed from the ring-like structure to the dendrite structure, and finally to the chrysanthemum structure as the cooling rate slowed. The morphology of Ag3Sn also changed from needle-like to flake-like as the cooling rate slowed. The water-quenched hardness of Sn3.5Ag solder exhibited the highest hardness, and then air-cooling; the furnace cooling was the lowest. After soldering with Cu, there was a little Sb found in the interfacial Cu6Sn5 and Cu3Sn layers, which showed that adding Sb induced the Cu6Sn5 and Cu3Sn compound transforming to Cu6(Sb,Sn)5 and Cu3(Sb,Sn) non-stoichiometry compounds respectively. Adding Sb also enhanced the adhesive and shear strength of Sn3.5Ag solder joint, even after long-term thermal storage the solder joints that contained Sb still exhibited higher strength and slower strength decreasing rate. Furthermore, the bouncing phenomenon of adhesive and shear strength of solder joints occurred in all Sb-contained solder joints during thermal storage. Fractographic analysis revealed that there was a certain relationship existing among the total thickness of interfacial IMC layers, adhesive and shear strength of solder joints, and fractography. As the total thickness of interfacial IMC layers was smaller than 1.0 mm, the highest strength was obtained. The fracture occurred approximately along the interface between solder and interfacial IMC layers. The fractography appeared flat. As the thickness lay between 1.0 - 10 mm, the adhesive and shear strength of solder joints decrease rapidly, and the fractography appeared dimple morphology. Finally, as the thickness exceeded 10 mm, the strength of solder joints decreased slowly. The fracture moved to inside the interfacial IMC layers and the fractography appeared cleavage morphology.