OSP has developed through five main stages so far, from the first generation benzotriazole (BTA) to the second generation alkyl imidazole (IA), and the third generation phenyl imidazole (BIA), the fourth generation of substituted benzimidazole (SBA) and the fifth generation of high temperature resistant lead-free soldering arylphenyl imidazoles (APA). The fourth generation developed in 1997 is currently commonly used. Substituting benzimidazole (SBA), the fifth generation has become the main target of research in the PCB industry.
The reaction principle of the OSP process is that chemicals such as "phenyltriazole" BTA (Benzo-Tri-Azo) form a layer of complex compounds on the clean copper surface. Protective organic copper film (both 0.35μm or 14μin). Firstly, it can protect the copper surface from rusting due to external influences; secondly, its film can be quickly removed by dilute acid or flux before welding, so that the bare copper surface can still show good solderability instantly; therefore The official scientific name is "organic soldering flux" which focuses on the latter function.