What are the advantages and disadvantages of PCB spray tin board?

What are the advantages and disadvantages of PCB spray tin board?

Tin spraying is a step and process flow in the production process of PCB board. To be specific, the PCB board is immersed in a molten solder pool, so that all exposed copper surface is covered by solder, and then the excess solder on PCB board is removed by a hot air cutter. Because the surface of the printed circuit board is the same as the solder paste, the welding strength and reliability are better. However, due to its processing characteristics, the surface flatness of tin spraying is not good, especially for BGA and other packaging types of small electronic components. Due to the small welding area, if the flatness is not good, it may cause short-circuit and other problems. Therefore, it is necessary to have a good flatness process to solve the problem of tin spraying plate. Generally, the chemical gold-plating process (not the electronic gold-plating process) is selected, and the principle and method of chemical replacement reaction are used for reprocessing to increase the thickness of the nickel layer of 0.03~0.05um or 6um to improve the surface flatness.

Advantages:

1. Good wetting during the welding of components, easier to solder.

2. The exposed copper surface can be avoided from corrosion or oxidation.

Disadvantages:

It is not suitable for welding small gap pins and small components, because the surface flatness of spray tin plate is poor. Solderbead may occur in PCB manufacturer's processing, which may cause short-circuit to finepitch components. When using two-side SMT process, because the second side has been through a high temperature reflow welding, it is very easy to produce Solderbead or similar water droplets falling into spherical tin points affected by gravity, resulting in uneven surface and affecting the welding problem.

With the development of technology, PCB samples in the industry has appeared the tin spraying technology suitable for QFP and BGA with smaller assembly spacing, but the practical application is less. At present, some PCB samples use OSP process and gold immersion process instead of tin spraying process; The development of technology also makes some factories adopt the process of tin sinking and silver sinking, and the trend of lead free in recent years, the use of tin spraying technology is further restricted.