Study Of The Reliability Of Power Device With SnAgCu Lead-free Attachment

With the development of electrical product and its wide application, our dependency on the electrical product becomes more and more high. Meanwhile, lead pollution is focused by the whole global people. So how to product lead-free devices is the challenge all electrical manufacturers must face. Then the lead-free electrical product's reliability and process are the main topic. Void in sold joint is the main factor in the failure of electrical device, and it also is the main question of the reliability. This paper focused on the SnAgCu lead-free soldering and improvement of the process.First, the bad effects of sold voids in SnAgCu attachment on function was studied though the failure analysis of power device, and the failure mechanism was that, when the device was working, the stress existed around the void and micro-crack was induced. Then micro-crack was spread and enlarge, and that would induce the Electrical Over Stress or destroy the device completely.Second, thermal resistance of power device was investigated by Finite Element Method. The results showed that voiding percentages had significant effects on heat dissipation. And when voiding is about 50%, the thermal resistance increase 16.12%.Third, the process and factors of SnAgCu lead-free solder voids formation were studied. In present experimental design and process parameter window, the effects of solder paste type, print mask type and reflow profile were more significant, and the largest void rate was excess 10%. And we find poor wetting and the volatized flux gas at the solder joints is the key to increase voiding rate.Last, the study of the improvement of the process was followed. Heat factor was introduced in optimization of the reflow profile to decrease the solder void. The results exhibit when hot factor was between 1500~2000, the solder voiding would be the least.