Mechanism of Cu5Zn8 layer act as a diffusion barrier layer

The development of lead-free in electronic packaging field brings many new problems, Interfacial intermetallic compound (IMC) formed at the interface of Sn and the substrate is an important factor for the reliability of soldering joints, which will seriously decrease the reliability of solder joints for its brittleness. Cu5Zn8 shows low cost, low melting point and better mechanical properties than Cu6Sn5. In the present study, scallop-like Cu5Zn8 was used as diffusion barrier layer between lead-free solder alloy and cooper substrate. Effect of the diffusion barrier layer for reflowing with several holding temperature and times was investigated. In addition, the Cu element diffusion behavior and the thickness change of IMC layer for different soldering temperature and time. The conclusions were summarized as follows: 1) From the results, conclusions can be drawn as The IMC layer initially preparation on cooper substrate acting as a diffusion barrier layer between lead-free solder alloy and cooper substrate is feasible. 2) the average thickness of IMC layer increase as the soldering time and temperature increase on both Cu substrate and Cu5Zn8 substrate. 3) For the same soldering time and temperature, the average thickness of IMC layer is thinner for Cu5Zn8 substrates than Cu substrate. 4) Cu5Zn8 layer can effectively restrain elements diffusion in Sn9Zn soldering joints.