PCB Tech - Do you know the PCB organic protective film OSP process?

The PCB must take protective measures on the copper surface to be soldered to ensure solderability, but for high-density PCBs, traditional spray tin processing cannot meet the surface treatment requirements of many high-density assembly. The industry introduced the so-called Entek process many years ago, but the formulation and industrial environment requirements were not mature at that time, and its weather resistance period was very short, ranging from a few hours to two or three days. Therefore, the application at that time was mainly placed in the case of direct production and use in some factories, which was not an appropriate option for some professional PCB manufacturers.

However, due to the improvement of subsequent formulations, the trend pressure of lead-free assembly, the cost advantage and the high-density structure of the product, the current development of organic solder mask has made certain achievements.

The organic solder mask formulations that are normally sold on the market are mainly products prepared based on organic formulations such as BTA, AI, ABI, etc. Because these organic substances have many different molecular structures, the relevant manufacturers have classified their pharmaceutical properties as confidential, and users can almost only understand and evaluate the effects of PCB production.

The general organic solder mask has a thickness of about 0.4um to achieve the purpose of multiple fusion welding. Although it is cheap and simple to operate, it still has the following shortcomings:

1. OSP is transparent and difficult to measure and difficult to inspect visually

2. Too high film thickness is not conducive to low-solid content and low-activity no-clean solder paste operations, and CU5SN6 IMC that is conducive to bonding is not easy to form

3. Many times of assembly must be operated in a nitrogen-containing environment

4. If there is partial gold plating and then OSP, the copper contained in the operating bath may be deposited on the gold, which will cause problems for some products

The most famous of these products is represented by the copper protection agent sold by ENTHON, which is dissolved in methanol and aqueous solutions. The product name is CU-XX as the code name, and different applications have different titles. BTA is a white, light yellow, odorless, crystalline powder. It is very stable in acid and alkali, and is not prone to oxidation-reduction reactions. It can form stable compounds with metals. This mechanism can produce a protective film with the processed copper surface to prevent rapid oxidation of bare copper to maintain solderability.

The common feature of these organic compounds is that they can produce appropriate complexes with copper, so that copper can not be oxidized and can maintain soldering properties. At present, there are three types of such product systems: acetic acid system, formic acid system, and rosin system. Since the rosin system must be cleaned after assembly, it is not easy to clean, so there are very few users. Most of the liquid medicine system is operated to increase the growth rate, and it is not easy to control the PH value because of the rapid evaporation of water. Generally, an increase in pH will cause IMIDAZOLE to become insoluble and crystallize. Therefore, the pH must be adjusted back to achieve improvement.