1. Methods and status quo of copper surface oxidation in PCB production

1.1 Copper deposition -- anti-oxidation of the whole plate after plating

Generally, after copper plating, most of the board will go through:

(1) 1-3% dilute sulfuric acid treatment;

(2) 75-85℃ high temperature drying;

(3) Then the socket or laminated plate is placed, waiting for the dry film to be pasted or the wet film to be printed for graphic transfer;

(4) In this process, the board will need to be placed for 2-3 days, more than 5-7 days;

(5) At this time, the plate surface and the copper layer in the hole have already oxidized into "black".

Before figure transfer, the copper layer on the board is usually processed in the form of "3% dilute sulfuric acid + grinding brush". The hole only depends on the treatment effect of pickling, and the hole in the front of the drying process is difficult to achieve the ideal effect; Therefore, because the hole is often not completely dry and contains water, the degree of oxidation is much more serious than the plate surface, and the stubborn oxide layer can not be achieved by pickling alone. This may lead to the board after graphic plating, etching caused by no copper hole and scrap.

1.2 Anti-oxidation of the inner layer of multilayer board

Usually, after the completion of the inner line, it is developed, etched, de-coated and 3% dilute sulfuric acid treatment. Then through the way of film storage and transfer and wait for AOI scanning and testing; Although in this process, operation, transport and so on will be particularly careful and careful, but the surface of the board is inevitably such as finger prints, stains, oxidation points and other defects; A large number of false points will be generated during AOI scanning, and the test of AOI is carried out according to the scanned data, that is, all scanned points (including false points) have to be tested, which leads to the low efficiency of AOI testing.

2. Some discussion on introducing anti-oxidant on copper surface

At present, many PCB suppliers have introduced different copper surface antioxidants for production; The main working principle is: the use of organic acids and copper atoms to form covalent bonds and coordination bonds, mutual substitution into chain polymer, on the surface of copper to form a multi-layer protective film, so that the surface of copper does not occur REDOX reaction, does not occur hydrogen, so as to play the role of oxidation prevention. According to our use situation and understanding in actual production, the copper surface antioxidant generally has the following advantages:

a. Simple process, wide application range, easy to operate and maintain;

b. Water-soluble process, free of halide and chromate, conducive to environmental protection;

c. It is simple to remove the generated anti-oxidation protective film, just need the conventional "pickling + brushing" process;

d. The generated anti-oxidation protective film does not affect the welding performance of the copper layer and almost does not change the contact resistance.