What is OSP process?
Regarding the surface treatment of PCB production, we introduced Hot Air Solder Leveling earlier. Hot Air Solder Leveling removes excess materials, but PCB production, from the first process to the final end, requires many processes. It takes a long time and the substrate will rust when exposed to the air. So, how to protect the substrate from damage? FASTPCBA gives you a brief introduction.
OSP (Organic Solderability Preservatives), also known as copper protective agent, is essentially to act as a barrier between copper and air. The process is: on the surface of bare copper, a chemical method is used to grow a layer of organic film. This film has anti-oxidation, thermal shock resistance, and moisture resistance to protect the copper surface from rust, oxidation, and sulfide in a normal environment. Wait. However, in the subsequent welding high temperature, this protective film must be easily removed by the flux quickly, so that the copper surface can be combined with the molten solder in a very short time to become a strong solder joint.
The process of OSP is: degreasing-micro etching-pickling-pure water cleaning-organic coating-cleaning, which is easier than other surface treatment processes. The purpose of micro-etching is to form a rough copper surface to facilitate film formation. The thickness of the microetching directly affects the film formation rate. Therefore, to form a stable film thickness, it is very important to keep the thickness of the microetching stable.
It is best to use DI water for washing before film formation to prevent the film formation liquid from being contaminated. It is also best to use DI water for washing after film formation, and the PH value should be controlled between 4.0-7.0 to prevent the film from being polluted and damaged. The film should not be too thin or too thick, it is more appropriate between 0.2-0.5um.
OSP has three types of materials: Rosin, Active Resin and Azole. The most widely used OSP is the azole OSP. The azole OSP has been improved for about 5 generations, which are named BTA, IA, BIA, SBA and the latest APA.
BTA (Benzotrichlorazole) is a white, light yellow, odorless, crystalline fine powder. It is stable in acids and alkalis, and is not prone to oxidation-reduction reactions. It can form stable compounds with metals. However, BTA is sensitive to humidity, has a short inventory life (3 months), cannot withstand repeated heating, and its performance is not very good. AI (alkylimidazole) is transparent, difficult to detect, and not used in large amounts.
ABI (Alkylbenzimidazole) can produce complex compounds with copper atoms to prevent oxidation of the copper surface. It is compatible with all kinds of solder pastes and has a positive effect on solderability. SBA has significantly strengthened its protection and heat resistance. Its heat resistance can withstand three reflow treatments, which is currently the mainstream of OSP supply.