OSP is the abbreviation of Organic Solderability Preservatives. The Chinese translation is organic solder mask, also known as copper protector. It is also known as Preflux in English. Simply put, OSP is a chemically grown organic film on a clean bare copper surface. This film has anti-oxidation, thermal shock resistance and moisture resistance. It protects the copper surface from normal environment. Rusting (oxidation or vulcanization, etc.); however, in the subsequent high temperature of soldering, the protective film must be easily removed by the flux, so that the exposed clean copper surface can be melted with solder in a very short time. Immediately combine to form a strong solder joint.
In fact, OSP is not a new technology. It has actually been more than 35 years old and is longer than SMT history. OSP has many benefits, such as a flat surface, no IMC formation between the copper of the pad, allowing solder and copper to be soldered directly during soldering (good wettability), low temperature processing, low cost (less than HASL), Less energy use during processing, etc.
OSP has three main types of materials: Rosin, Active Resin and Azole. The most widely used is azole OSP. The azole OSP has been improved for about five generations, namely BTA, IA, BIA, SBA and the latest APA.

Disadvantages of PCB board OSP process

The downside of the OSP process is that the resulting protective film is extremely thin and prone to scratching (or scratching) and must be carefully handled and operated.
At the same time, the OSP film (which refers to the OSP film on the unwelded lands) after many high-temperature soldering processes may cause discoloration or cracking, affecting solderability and reliability.
The solder paste printing process should be well mastered because poorly printed boards cannot be cleaned using IPA or the like, which can damage the OSP layer.