PCB News - PCB Immersion Gold Circuit Board Oxidation Analysis and Improvement Countermeasures

PCB Immersion Gold Circuit Board Oxidation Analysis and Improvement Countermeasures

In response to the common problem of poor oxidation of immersion gold boards in the PCB circuit board industry, the circuit board factory has set up a discussion group with participants including quality, craftsmanship, customer service and suppliers to discuss and improve this issue. After a week of on-site observation and experimentation, this problem has been comprehensively improved. The following is an analysis of the oxidation of PCB immersion gold circuit boards, and the following improvement measures have been implemented after discussion:

2. Description of oxidation of immersion gold circuit board:
Immersion gold circuit board oxidation is the contamination of the gold surface with impurities, and the impurities attached to the gold surface become discolored after oxidation, 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.
Through observation, it is found that the oxidation of gold plate 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 and dirty table surface, directly touching the position of the gold plate pad, backing plate contact pollution, etc.; The similar oxidation area is large and may appear on multiple adjacent pads at the same time, and the appearance color is lighter and easier to clean.
2. Half plug hole, small area oxidation near the via hole; this type of oxidation is due to the fact that the liquid in the via hole or half plug hole is not cleaned or the water vapor remains in the hole. The liquid medicine slowly diffuses along the hole wall to the gold surface during the storage stage of the finished product. Forms dark brown oxide;
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; this kind of oxidation area is small, usually appearing at the corners of individual pads, and it 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 pollutant for washing after gold sinking and washing with finished plate washer is microbial fungi, especially the tank body using DI water is more suitable for fungus propagation, the best inspection method is bare hand touch The dead corner of the groove wall, see if there is a slippery feeling, 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.
3. Analysis of the oxidized fishbone diagram of the immersion gold board (according to human, machine, material, law, and circle):

Analysis of oxidized fishbone diagram of immersion gold board (according to human, machine, material, law, ring)

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