1, hot air smoothing (spray tin)

　　Hot air smoothing, also known as hot air solder smoothing (commonly known as spray tin), it is the process of coating molten tin (lead) solder on the surface of the PCB and heating compressed air to smooth (blow), so that it forms a coating layer that is resistant to copper oxidation and can provide good solderability. During hot air conditioning, a copper-tin metal intermetallic compound is formed at the joint of solder and copper. PCB for hot air finishing usually to sink in the molten solder; The air knife blows out the liquid solder before it solidifies; The air knife minimizes the meniscus of solder on the copper surface and prevents solder bridging.

　　2, organic weldability protectant (OSP)

　　OSP is a process for printed circuit board (PCB) copper foil surface treatment in accordance with the requirements of the RoHS directive. OSP is short for Organic Solderability Preservatives, also known as organic solderability preservatives, also known as Preflux in English. Simply put, OSP is a chemically grown organic skin film on a clean, bare copper surface. This film has anti-oxidation, heat shock, moisture resistance, to protect the copper surface in the normal environment no longer rust (oxidation or vulcanization, etc.); However, in the subsequent welding high temperature, this protective film must be easily removed by the flux quickly, so that the exposed clean copper surface can be immediately combined with the molten solder in a very short time to become a solid solder joint.