The cost of PCB tin plating is relatively low because it only applies tin to the area above the pads, whereas tin coating covers both the pads and the copper traces.
As the name suggests, PCB tinning involves chemically depositing a thin layer of tin on the pad area. This process creates a very thin layer, typically between 10 to 30 microns thick, primarily to prevent oxidation and improve solderability during SMT (Surface Mount Technology) processes. In fact, this is similar to other surface finishes like OSP (Organic Solderability Preservative), which also serve the same purpose. Tin is required for proper soldering in SMT.
PCB tinning, on the other hand, is a physical method where a thicker layer of tin is sprayed onto the board, usually ranging from 50 to 150 microns. Because of its thickness, it’s not directly used for SMT. Instead, solder paste is applied over the tinned areas during the soldering process.
The composition of the two tins is different. The tin used in PCB tinning is typically a tin alloy, often containing lead or being lead-free. Pure tin isn’t used due to its high melting point. In contrast, the chemical tin used in immersion tin is made from an acidic solution containing tin salts.
Immersion tin, also known as chemical tin, is a surface finish that protects the copper pads on the PCB. Like OSP, immersion gold, and immersion silver, it helps preserve the copper surface before soldering. It's mainly used in the early stages of PCB manufacturing.
Tin plating, however, is a different process. It's used by PCB manufacturers to protect the copper lines and holes before etching. After etching, the tin is removed, and the board proceeds to the next stage, such as solder mask printing. Therefore, tin plating is not commonly found in SMT production facilities.
Understanding these differences can help in choosing the right surface finish based on the application, cost, and performance requirements of the PCB.
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