The reliability evaluation of (PTH hole) negative wetting phenomena in lead free process used OSP coated PCB by using thermal cycle testing

摘要

Negative wetting is a common phenomenon in SMT wave solder process, especially happened when the size of the component is big, such as electrolyze capacitors. The cap of the electrolyze capacitors is like a heat sink and it lowers down the lead temperature of the top of the component during SMT wave solder process and that often causes negative wetting phenomenon on the PTH (Planting through hole) area. However, this negative wetting phenomenon is unwelcome on SMT products because the negative wetting shape of the solder area might have stress concentration and possibly cause reliability problem. Moreover, this kind of negative wetting phenomenon is difficult to inspect via X-ray, and it consumes SMT factories lots of time and resources to control and solve this problem. This thesis discussed the reliability evaluation on the negative wetting phenomenon by using thermal cycle testing and evaluated the behavior after ATC aging condition on the negative wetting solder area by optical microscope and scanning electron microscope. The reliability of barrel fill on PTH area was also discussed in this study. With the experiment, we could simulate different solder phenomena in the PTH area for the reliability evaluation and observe the result of negative wetting and low barrel fill PTH solder area after thermal cycle test. The goal of this thesis is trying to understand if it has reliability impact when there are negative wetting and low barrel fill on the PTH solder area.