PCB Tech - Immersion gold pcb board oxidation analysis and improvement methods?

It is conceivable that for the circuit board industry, the most common problem is the poor oxidation of the immersion gold PCB. For this situation, the following improvement measures have been implemented after discussion:

1. Picture of Immersion Gold Board with Poor Oxidation:

2. Description of Immersion Gold Plate Oxidation:
The oxidation of the gold-immersed circuit board of the circuit board manufacturer is that the surface of the gold is contaminated by impurities, and the impurities attached to the gold surface are oxidized and discolored, which leads to the oxidation of the gold surface that we often call. In fact, the statement of gold surface oxidation is not accurate. Gold is an inert metal and will not be oxidized under normal conditions. Impurities attached to the gold surface such as copper ions, nickel ions, microorganisms, etc. are easily oxidized and deteriorated under normal conditions to form gold surface oxidation. Things.

3. Through observation, it is found that the oxidation of immersion gold circuit board mainly has the following characteristics:
1. Improper operation causes contaminants to adhere to the gold surface, such as: wearing dirty gloves, finger cots contacting the gold surface, gold plate contacting with dirty countertops, backing plates, etc.; this kind of oxidation area is large and may occur at the same time On multiple adjacent pads, the appearance color is lighter and easier to clean;
2. Half-plug hole, small-scale oxidation near the via hole; this kind of oxidation is due to the yao water in the via hole or half-plug hole not being cleaned or residual water vapor in the hole, the yao water slowly diffuses along the hole wall during the storage stage of the finished product Dark brown oxide is formed on the surface of gold;
3. Poor water quality causes impurities in the water body to be adsorbed on the gold surface, such as: washing after gold sinking, washing with finished plate washer, such oxidation area is small, usually appearing at the corners of individual pads, which is more obvious Water stains; after the gold plate is washed with water, there will be water droplets on the pad. If the water contains more impurities, the water droplets will quickly evaporate and shrink to the corners when the plate temperature is higher. After the water has evaporated, the impurities will solidify At the corners of the pad, the main pollutants for washing after immersion in gold and washing with the finished plate washer are microbial fungi. Especially the tank with DI water is more suitable for fungus propagation. The best inspection method is bare hand touch. Check if there is a smooth feeling on the dead corner of the groove wall, if there is, it means that the water body has been polluted;
4. Analyzing the customer's return board, it is found that the gold surface is less dense, the nickel surface is slightly corroded, and the oxidation site contains an abnormal element Cu. This copper element is most likely due to the poor density of gold and nickel and the migration of copper ions. After this kind of oxidation is removed, it will still grow, and there is a risk of re-oxidation.