Evaluation of Damage of Stainless Steels during Lead-free Wave Soldering

摘要

The damage of stainless steels used for wave solder bath by contact with molten lead-free solder is a severe problem in assembly of electronic components on printed wiring boards. The principal cause and estimated process of damage was demonstrated based on the former studies. To observe the maximum damage of stainless steel specimens, a micro-focus X-ray CT scan test was adopted. After immersion in molten solder for predetermined periods, the specimens were withdrawn from the molten solder bath. The relatively clear CT images can be obtained by this method. The comparison test to find the correlation between the CT scan image and the corresponding cross sectional photograph revealed that there was a good correlation between the CT scan image and the corresponding cross sectional observation. The micro-focus X-ray CT scanning equipment is believed as an appropriate method to find out the maximum damage in stainless steel after contacting with molten lead-free solder. The damage of stainless steels was enhanced by the rise of test temperature, immersion time in molten solder and increase in rotation rate of specimen in molten solder. Even the use of CT scan method, the relatively large scattering of observed data was still existed indicating the irregular reaction between stainless steel and solder.