The cost of PCB tin plating is relatively low because it only applies a thin layer of tin on the pads, whereas tin coating involves covering the entire board, including the traces.
As the name suggests, PCB tin plating is a chemical process where a thin layer of tin is deposited on the pad area. This layer is typically 10–30 microns thick and serves mainly to prevent oxidation, making it more suitable for SMT (Surface Mount Technology) soldering. In fact, this method is similar in purpose to other surface finishes like OSP (Organic Solderability Preservative). However, it still requires tinning before SMT assembly.
PCB tinning, on the other hand, is a physical process where a thicker layer of tin—usually 50–150 microns—is sprayed onto the board. This method is not required during SMT, but it allows for easier soldering by applying tinned solder directly.
The composition of the two tins also differs. PCB tin plating uses tin salts dissolved in an acidic solution, while tin coating is typically an alloy, either with lead or lead-free. Pure tin is rarely used due to its high melting point.
Chemical tin, also known as immersion tin, is a surface finish used to protect the copper pads on the PCB. It works similarly to other finishes like OSP, immersion gold, or immersion silver, all of which are designed to preserve the copper surface and ensure good solderability.
Tin plating, in contrast, is a process used by PCB manufacturers to protect the copper lines and holes before etching. Once the etching is complete, the tin is removed, and the board moves on to the next stage, such as solder mask printing. Because of this, the tin plating process is not commonly seen in SMT assembly houses.
Understanding the differences between these two processes helps in selecting the right finish for your PCB based on the manufacturing and assembly requirements. Whether you're looking for cost-effectiveness, solderability, or long-term protection, choosing the correct surface treatment can significantly impact the performance and reliability of your final product.
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