PCB surface coating technology refers to the solderable coating (plating) layer and protective layer for electrical connection other than the solder resist coating (and protective) layer.
Classification by use:
1. For welding: Because the surface of copper must be protected by a coating layer, otherwise it is easy to oxidize in the air.
2. For connectors: electroplating Ni/Au or chemical plating Ni/Au (hard gold, containing P and Co)
3. For wire welding: wire bonding process
Hot air leveling (HASL or HAL)
The method of flattening the PCB coming out of the molten Sn/Pb solder by hot air (230℃).
1. Basic requirements:
(1). Sn/Pb=63/37 (weight ratio)
(2). Coating thickness at least>3um
(3) Avoid the formation of non-solderable Cu3Sn. The reason for the formation of Cu3Sn is insufficient tin, such as the Sn/Pb alloy coating is too thin, the solder joint is composed of solderable Cu6Sn5-Cu4Sn3--Cu3Sn2-non-solderable Cu3Sn
2. Process flow
Remove the resist-board cleaning-printing solder mask and characters-cleaning-applying flux-hot air leveling-cleaning
