Main Factors Affecting Film Thickness in OSP Process of PCB Surface Treatment

The main factors affecting PCB OSP film thickness:

1. The concentration of the main components of OSP: Alkylbenzimidazole or similar components (imidazoles) are the main components in the OSP liquid, and the concentration is the fundamental factor in determining the thickness of the OSP.

2. Organic acid: The addition of organic acid can increase the solubility of alkylbenzimidazole in aqueous solution and promote the formation of complex protective film. However, too much dosage will dissolve the protective film deposited on the copper surface, so it is very important to control the added value of organic acid (that is, the pH value). When the PH value is too high, the solubility of alkylbenzimidazole will decrease, and oily matter will precipitate out, which is unfavorable for dipping. If the PH value is controlled reasonably, a dense, uniform, and moderate thickness complex film can be obtained. If the pH value is too low, the solubility of the complex film will increase, which will dissolve the complex deposited on the copper and fail to form a film with the required thickness.

3. Dip coating time: Under certain conditions of OSP bath composition, temperature and pH value, the thickness of the complex protective film will start to rise linearly with the increase of dip coating time, and then slowly with the extension of time. After a certain period of time, the film thickness basically did not increase.

4. Pre-soaking: Pre-soaking can prevent harmful ions such as chloride ions from damaging the OSP tank solution. Moreover, there is an appropriate amount of copper ions in the prepreg solution, which can promote the formation of the complex protective film and shorten the dip-coating time. It is generally believed that due to the presence of copper ions, the alkylbenzimidazole and copper ions have been complexed to a certain extent in the pre-flux solution. When this kind of complex with a certain degree of aggregation is deposited on the surface of copper to form a complex film, a thicker protective layer can be formed in a short time, thus acting as a complexing accelerator. However, the content of alkylbenzimidazole or similar components (imidazoles) in the prepreg is very small. In addition, excessive copper ions will cause the prepreg solution to age prematurely and need to be replaced. The main function of the OSP prepreg cylinder is to accelerate the formation of the OSP film thickness and deal with the impact of other harmful ions on the OSP cylinder. It is recommended to improve the performance of the syrup and try not to use the prepreg tank as a routine process link. This can reduce costs.