The choice of PCB surface coating technology for SMT soldering in SMT processing mainly depends on the type of final assembled components, and the surface treatment process will affect the production, assembly and final use of PCB. The following briefly introduces the selection basis of PCB solderability surface coating.

When selecting the solderable surface coating of the PCB in the patch processing, the selected solder alloy composition and the use of the product should be considered.

1. Solder alloy composition

The compatibility of PCB pad coating and solder alloy is the primary factor in choosing PCB solderable surface coating (plating). This directly affects the solderability and connection reliability of the solder joints on both sides of the pad. For example, Sn-Pb hot air leveling should be selected for Sn-pb alloy, and hot air leveling for lead-free metal or lead-free solder alloy should be selected for lead-free alloy.

2. Reliability requirements

Products with high reliability requirements should first choose the same hot air leveling as the solder alloy, which is the best choice for compatibility. In addition, high-quality Ni-Au (ENIG) can also be considered, because the connection strength of the interface alloy Ni3Sn4 between Sn and Ni is the most stable. If ENIG is used, the Ni layer must be controlled to be> 3 µm (5 to 7 µm), and the Au layer must be ≤ 1 µm (0.05 to 0.15 µm), and solderability requirements must be put forward to the manufacturer.

3. Manufacturing process

When choosing the PCB solderable surface coating (plating) layer, the compatibility of the PCB pad coating layer and the manufacturing process should also be considered. Hot air leveling (HASL) has good weldability, can be used for double-sided reflow welding, and can withstand multiple welding. However, since the surface of the pad is not flat enough, it is not suitable for a narrow pitch. OSP and immersion tin (I-Sn) are more suitable for single-sided assembly and one-time soldering process.