Anti-oxidation of PCB is to coat the specified metal surface (hole and board) with an anti-oxidation organic film, namely organic solderability protection (DSP). Glicoat SMDLF2 is one of them, which maintains its solderability in the thermal cycle of forming a firm leveling technology on the metal surface of the printed board through the chemical reaction between its effective components and the copper surface.
flow
Oil removal → micro-etching overflow washing I → overflow washing II → pickling → pressurized washing I → pressurized water washing II → clean water washing III →DI washing → air knife to catch water → antioxidant dipping → air knife to catch water → overflow washing III → overflow washing IV →DI washing → strong wind blow drying → hot wind blow drying.
Oil removal and micro-etching: remove the residue, grease and oxide layer on the copper surface, and activate the copper surface.
Acid washing: further remove the copper powder on the board surface and prevent the activated copper surface from being oxidized again.
Anti-oxidation dipping: In order to form an anti-oxidation film on the board surface and inside the hole, dipping is better than spraying. Soaking at 40℃ for 60-90 seconds can get an anti-oxidation film with a thickness of 0.15-0.25um. If the concentration, PH, temperature, soaking time and other parameters are within the normal range, but the film thickness is not enough, it is necessary to add supplementary solution A for adjustment, and F2 liquid can be used without dilution. The transmission shaft should be made of lightweight materials.
Anti-oxidation process control of PCB proofing
1. The PH value is the most important factor to maintain the film thickness, so it should be measured every day. With the increase of PH value, the film thickness becomes thicker, and with the decrease of PH value, the film thickness becomes biased. If the PH value is too high, crystallization will occur. Due to the volatilization of acetic acid and the introduction of water, the PH value tends to rise, so it is necessary to add acetic acid for adjustment, and the PH value should be controlled between 3.80 and 4.20.
2. In order to keep the film thickness in the best range, the concentration of active ingredients should be kept between 90-110%, and crystallization is easy to occur if it is too high.
3. The film thickness should be kept between 0.15-0.25um as much as possible. If it is lower than 0.12um, the copper surface will not be oxidized during storage and thermal cycle. However, if it is higher than 0.3um, it will not be easily washed off by soldering flux, which will affect the performance of tin plating.
4. Under the normal conditions of various parameters, if the film thickness is too thin, make-up solution A can be added appropriately. When making up solution A, it should be added slowly. Otherwise, star-shaped oil spots will appear on the liquid surface, which is the precursor of solution crystallization. Other reasons can also cause crystallization such as high PH and high concentration. Therefore, regular observation and measures should be taken to avoid it.
5. The suction roller behind the anti-oxidation cylinder is easy to crystallize when it is not working for a long time. Therefore, when the machine is stopped, a small amount of water should be used to spray the suction roller to wash off the residue of the F2 medicine. In addition, extra rollers should be prepared for replacement. Otherwise, the roller marks will easily appear on the board surface because the rollers are used for too long.
6. As acetic acid is used in F2 liquid medicine, it is necessary to equip with an exhaust device, but excessive exhaust will cause excessive evaporation and high concentration of liquid medicine. Therefore, when the system stops working, the exhaust should be kept to a minimum and the tightness between gaps should be ensured.