The Difference Between HASL and Immersion Tin

　　The base purpose of PCB surface treatment is to ensure good solderability or electrical properties. Since copper is oxidized in the air, the composition of copper will becomes impure, PCB surface treatment is required for copper. There are many kinds of PCB surface treatment processes, and different processes will affect the cost of the final PCB processing. Now, let’s talk about the difference between HASL and Immersion tin.

　　HASL: It is to soak the PCB into the molten tin-lead. After PCB surface is covered with enough tin-lead, the excess tin-lead is scraped off with hot air to enhance the continuity and solderability of the PCB pads. It is thicker, typically between 50 and 150 microns. The main purpose of HASL is to prevent oxidation, effectively separating the copper surface from the air.

　　Immersion Tin: As the name suggests, it is chemically plated with a layer of tin on the PCB pad. It is thinner, typically between 10 and 30 microns. It is a surface treatment process that protects the surface of the pad. The main purpose of Immersion tin is to prevent oxidation, better to make SMT tin fusion, and protect the surface copper foil (PAD position).

　　In SMT, HASL on the PCB does not need to be tinned, but Immersion tin on the PCB need to be tinned. Therefore, in terms of cost, HASL is lower than that of the Immersion tin.

　　Moreover, the two kind of tin must also be different in composition. HASL is usually made of tin alloy, which is divided into lead and lead-free. Because pure tin has a high melting point, it will never be used. Immersion tin is made of tin salt and is formulated into an acidic solution containing tin.

　　So, we’ve known HASL and Immersion tin have many difference. When we learn more about each process, we can clearly know which PCB surface treatment is applied to the PCB produced. Of course, in addition to these two, there are other surface treatment processes. Next, we will talk about the role of other PCB surface treatment processes.

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