Interfacial reaction of Sn-Ag-Cu-Ni solder/Cu joints by laser process

With the miniaturization of electronic productions and the use of heat sensitive electronic components,the traditional reflow soldering often has difficulties. As an alternativesoldering process, a laser reflow process has been recently proposed and a laser process has been introduced into the industry for practical use because of its unique properties such as localized and noncontact heating, rapid rise and fall in temperature, and ease of automation and robotization. However, there has been limited discussion for the basic phenomena and performance of the joints heated by this laser process. In this study, Sn-3.0 mass%Ag-0.5 mass% Cu solder and Sn-3.0 mass%Ag-0.5 Cu-0.1Ni solder balls with a diameter of 0.76 mm were used. Cu pads that had a thickness of 35 $\mu$m and a diameter of 0.6 mm and were used as the substrate. The interfacial reaction between a Ni added solder and a Cu pad heated by laser process and the microstructure of soldered joint after heating and after isothermal aging was investigated. In the as-heated condition, a quite thin IMC layer was formed at the interface and Ni element was included in the IMC in the case of the laser process. It was found that the growth of Cu3 Sn layer between the Cu pad and Cu6 Sn5 layer during isothermal aging was suppressed in the case of Sn-Ag-Cu-Ni solder.