Research On The Sn-Zn-Ag(Ni) Solder For Soldering Aluminium And Copper Substrates

To realize the Al/Cu soldering in air-condition, refrigeration and electric industries, etc, Sn-9Zn alloys with Ag element and Ni element addition were used to solder aluminum and copper. The effects of alloy composition on the properties of the solder and the Al/Cu soldering joint were studied.The results showed:1 The melting points of the Sn-9Zn-xAg solders increase with adding Ag element. AgZn3 intermetallic compound(IMC) is formed in the solder and AgZn3 becomes big and coarse with the increase content of Ag element,. Ni element has no significant effect on the melting point of the solder, but the melting range is increased. The Ni5Zn21 intermetallic compound is formed in the Sn-9Zn-xNi solder, and the AgZn3 phase becomes big and coarse when increasing Ni content.2 When the Ag element is added into the Sn-9Zn solder, the wettability on the copper and aluminum get a little worse. and the wettability of the Sn-9Zn-1.5Ag solder is the best than other Sn-9Zn-xAg solders, even on the aluminum substrate the wettability of Sn-9Zn-1.5Ag solder is better than that of the Sn-9Zn solder. When Ni element is added into the solder, the wettabilities of the Sn-9Zn-xNi solder on the copper are improved while the wettability on the aluminum substrate get worse.3 The Al4.2Cu3.2Zn0.7 intermetallic compound is formed at the interface of Sn-9Zn and Cu substrate in the Al/Sn-9Zn/Cu joint. When Ag element is added into the solder, the formed AgZn3 would aggregation on the layer of Al4.2Cu3.2Zn0.7 IMC. When Ni element is added into the solder, the formed Ni3Sn4 and Al3Ni mixed IMC would distribute in the solder matrix.4 The needle-like Al-Zn-Sn solid solution is formed at the interface of the Sn-9Zn solder and aluminum substrate, which would enhance the bonding force between the solder and the aluminum substrate. With the increase content of Ag and Ni element, the needle-like Al-Zn-Sn solid solution would become thin and small, the AgZn3 IMC and Ni3Sn4, Al3Ni mixed IMC become big and coarse.5 Due to the brittle nature of AgZn3 or Ni3Sr4,Al3Ni mixed IMC formed with the addition of Ag or Ni element, the shear strength of the Al/solder/Cu joint would gradually degrade, the fracture occur in the solder matrix, and the style of fracture is ductility fracture.6 When the intermetallic compound AgZn3 or Ni5Zn21 are formed, the rich-Zn phase would decrease, the selective corrosion of the solder would reduce and the corrosion resistance would be improved. When adding proper content of Ag or Ni element, the degressive rate of the shear strength of Al/Cu joint after corrosion would degrade and the corrosion resistance of the Al/solder/Cu joint will be enhanced.