PCB gold plate oxidation

　　The oxidation of the submerged gold plate is the contamination of the gold surface by impurities, and the impurity attached to the gold surface changes color after oxidation, which leads to the gold surface oxidation that we often say. In fact, the gold surface oxidation statement is not accurate, gold is an inert metal, under normal conditions will not occur oxidation, and impurities attached to the gold surface such as copper ions, nickel ions, microorganisms in the normal environment is easy to oxidize to form gold surface oxides.

　　Through observation, it is found that the oxidation of gold plate has the following characteristics:

　　1, improper operation causes pollutants to adhere to the gold surface, such as: with unclean gloves, finger cover contact with gold surface, gold plate and unclean table, pad contact pollution; Such oxidation area is large, may appear on multiple adjacent pads at the same time, and the appearance color is lighter and easier to clean.

　　2, poor water quality causes impurities in the water body to adsorb on the gold surface, such as: washing after sinking gold, washing machine washing; Such oxidation area is small, usually appears at the edges and corners of individual pads, showing obvious water stains; Water droplets will be retained on the welding pad after the gold plate is washed. If the water body contains more impurities, the water droplets will quickly evaporate and shrink to the corners when the plate temperature is higher. After the water is completely evaporated, the impurities will be solidified in the corners of the welding pad. The main pollutants in washing after sinking gold and washing machine are micro-bacteria, especially the tank using DI water is more suitable for bacterial propagation. The best test method is to touch the dead corner of the tank wall with bare hands to see if there is a feeling of lubricity. If so, the water body has been polluted.

　　3, half plug hole, through the hole near a small range of oxidation; This kind of oxidation is due to the liquid in the hole or the half-plug hole is not cleaned or the residual water vapor in the hole, the liquid medicine slowly diffused along the hole wall to form a dark brown oxide on the gold surface during the storage stage of the finished product;

　　4, the analysis of the customer return board, found that the gold surface density is poor, the nickel surface has slight corrosion phenomenon, and the oxidation contains abnormal element Cu, the copper element is very likely due to the poor density of gold nickel, copper ion migration caused by such oxidation removal, still grow, there is a risk of reoxidation