Study On IMC Growth In SnAgCu/Cu Interfacial

Because of the lead and lead contained compounds' toxicity to human body and the environment and the restriction of legislation, solders without lead have become the tendency of the electronic packaging materials. At present, most of lead-free solders are Sn-based binary or ternary alloys with adding non-toxic and non-volatile elements, such as Ag, Zn, Cu, Bi, In and so on. But in the application process of lead-free solders there are many problems, one typical question is the thick Cu-Sn intermetallic compounds (IMCs) formed due to the rapid react between Sn from the Sn-based lead-free solders (Sn concentration above90%) and the traditional Cu substrate. And thick Cu-Sn IMCs may reduce the mechanical and the thermal fatigue performances of electronic products, and correspondingly reduce the service life of the products. So it is very important to research the rule of IMC growth and how to reduce the speed of IMC growth.The research indicated that in a very short time of soldering, a thin layer of IMC formed at the interface. And the thickness increased with the soldering time. In initial 90s, the IMC growth was controlled by grain boundary diffusion mechanism, and the growth speed was relative quick. With the increase of IMC thickness, the growth mechanism was gradually controlled by volume diffusion, and the growth speed slowed down.The butt-joints were aged at 125℃, 150℃, 175℃for 400h, where the IMC growth was also controlled by diffusion in solid-state. The Cu3Sn appeared while aged at 150℃and 175℃. But when the joint was aged at 125℃Cu3Sn couldn't be found. According to the relationship between the IMC thickness and different time and temperature, the active energy that was fitted is 81kJ/mol.In the thermal cycling test, it was found that the IMC growth at low intensity temperature impact (-25~125℃) was slower than that at high intensity temperature impact (-40~125℃). This was mainly because that the thermal cycling influenced the IMC microstructure at interface. And compared with the thickness at aging, the IMC growth slower at the same temperature.