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Poor Wetting
Poor solderability of the pins can be caused by poor or thin plating or long storage times. Solderability of tin/lead pins normally is a function of the plating thickness or the plating and the base materials. In the case of brass pins the pin must first be plated with a 1-3um layer of copper before the tin/lead is applied, if not zinc from the brass will affect the solderability very quickly. Solderability is also related to thickness, if a coating of 0.005um is present it should provide in excess of one year's storage life. This coating thickness is relevant for any base materials. The example shown is not a plating issue, it was caused by the printed board resin on the corner of the pins. If you look carefully you can see that only the corners of the pins has failed to wet. During pin insertion the four corners of the pin have made an interference fit with the single sided board causing resin to smear along the corners. When looking at any defects don't jump to conclusions, look at a number of defects using 10x magnification and just take a few minutes to think about the whole process not just soldering. Poor Hole Fill 065.tif c In the example one hole has filled and the second has not, which should indicate the problem is less likely to be a printed board problem. Close examination shows that the solder has solidified on one hole due to the thermal demand of the component. By raising the pre heat or by increasing wave contact time this problem should be simply overcome.