PCB Blog - Discussion on Antioxidation of Copper Surface in PCB board Production

At present, in the operation cycle of copper sinking, whole PCB board electroplating and pattern transfer in the production process of double-sided and multi-layer PCB boards, the oxidation problem of the copper layer on the board surface and in the holes (from the small holes) seriously affects the pattern transfer and operation. The production quality of pattern plating; in addition, the increase of AOI scanning false points caused by oxidation of the inner layer board, which seriously affects the test efficiency of AOI, etc. Such incidents have always been a headache in the industry, and now we will solve this problem and use copper Do some research on antioxidants.

1. The method and current situation of copper surface oxidation in the current PCB board production process
1.1 Immersion copper - anti-oxidation after electroplating of the whole board
Generally, most boards after copper immersion and whole board electroplating will undergo: (1) 1-3% dilute sulfuric acid treatment; (2) high temperature drying at 75-85 °C; Paste dry film or print wet film for graphic transfer; (4) During this process, the board needs to be placed for at least 2-3 days, and as long as 5-7 days; (5) At this time, the board surface and the copper in the hole The layer has long since oxidized to "black". In the pre-treatment of the pattern transfer, the copper layer on the board is usually treated in the form of "3% dilute sulfuric acid + grinding". The inside of the hole is only treated by pickling, and it is difficult for the small holes to achieve the desired effect in the previous drying process; therefore, the oxidation degree of the small holes is often higher than that of the small holes due to incomplete drying and moisture. The surface of the board is much more serious, and the stubborn oxide layer cannot be removed by pickling only. This may cause the board to be scrapped because there is no copper in the hole after pattern plating and etching.

1.2 Anti-oxidation of the inner layer of the multilayer board
Usually, after the inner layer circuit is completed, it is developed, etched, stripped and treated with 3% dilute sulfuric acid. Then it is stored and transported by means of film separation and waiting for AOI scanning and testing; although during this process, operation, transport, etc. will be very careful and careful, it is inevitable that there will be fingerprints, stains, oxidation spots, etc. on the board surface. Defects; a large number of false points will be generated during AOI scanning, and the AOI test is carried out based on the scanned data, that is, all scanning points (including false points) AOI must be tested, which leads to the test efficiency of AOI very low.

2. Some discussions on the introduction of copper surface antioxidants
At present, many PCB board potion suppliers have launched different copper surface antioxidants for production; our company also has a similar product, which is different from final copper surface protection (OSP) and is suitable for PCB board production. The copper surface anti-oxidation syrup in the process; the main working principle of the syrup is: the use of organic acids and copper atoms to form covalent bonds and complex bonds, and replace each other into a chain polymer, forming a multi-layer protective film on the copper surface, so that the There is no oxidation-reduction reaction on the surface of copper, and no hydrogen is generated, which plays an anti-oxidation role. According to our use and understanding in actual production, the copper surface antioxidant generally has the following advantages:
1) The process is simple, the scope of application is wide, and it is easy to operate and maintain;
2) Water-soluble process, free of halides and chromates, which is beneficial to environmental protection;
3) The removal of the resulting anti-oxidation protective film is simple, only the conventional "pickling + grinding" process is required;
4) The resulting anti-oxidation protective film does not affect the welding performance of the copper layer and hardly changes the contact resistance.

2.1 The application of anti-oxidation after copper sinking - whole board electroplating
In the process of copper sinking - after the whole plate electroplating, "dilute sulfuric acid" is changed to "copper surface antioxidant", and other operation methods such as drying and subsequent insertion or stacking remain unchanged; during this process , a thin and uniform anti-oxidation protective film will be formed on the surface of the board and the copper layer in the hole, which can completely isolate the surface of the copper layer from the air, prevent the sulfide in the air from contacting the copper surface, and make the copper layer oxidized and blackened. ; Under normal circumstances, the effective storage period of the anti-oxidation protective film can reach 6-8 days, which can fully meet the operation cycle of general factories. In the pre-treatment of pattern transfer, only the usual "3% dilute sulfuric acid + grinding" method can be used to quickly and completely remove the anti-oxidation protective film on the board surface and in the hole, without any impact on the subsequent process.

2.2 Application of anti-oxidation in the inner layer of multilayer boards
The procedure is the same as the conventional treatment, just change the "3% dilute sulfuric acid" in the horizontal production line to use "copper surface antioxidant". Other operations such as drying, storage, and transportation remain unchanged; after this treatment, a thin and uniform anti-oxidation protective film will also be formed on the board surface, which completely isolates the surface of the copper layer from the air, so that the board surface will not be oxidized. At the same time, it also prevents fingerprints and stains from directly contacting the board surface, reducing false points in the AOI scanning process, thereby improving the testing efficiency of AOI.

3. Comparison of AOI scanning and testing of inner layer boards treated with dilute sulfuric acid and copper surface antioxidants respectively
The following is a comparison of the results of AOI scanning and testing of the inner layer boards of the same model and batch number treated with dilute sulfuric acid and copper-surface antioxidants, respectively, with each 10PNLS.
Note: From the above test data, it can be known that:
1) The number of AOI scanning false points of the inner layer board treated with copper surface antioxidant is less than 9% of that of the inner layer board treated with dilute sulfuric acid;
2) The AOI test oxidation point of the inner layer board treated with copper surface antioxidant is: 0; while the AOI test oxidation point of the inner layer board treated with dilute sulfuric acid is: 90.

4. Summary
In short, with the development of the circuit board industry and the improvement of product grades; the copper-free scrapping of small holes caused by oxidation and the low test efficiency of inner and outer layers of AOI, all need to be vigorously solved in the production process of PCB boards; and copper surface The emergence and application of antioxidants have provided a good help to solve such problems. It is believed that in the future PCB board production process, the use of copper surface antioxidants will become more and more popular.