Solder mask is exposed to the pads used, it is often said that the green oil, oil is actually digging holes in the green, the green oil does not need to cover the pads and other exposed areas. Proper cleaning can get a suitable surface features.

HASL solder coating HAL (commonly known as HAL) process is first dipped on the PCB flux, then dipping in molten solder, and then from between two air knives by compressed air with a knife in the heat air to blow off excess solder on printed circuit board, at the same time eliminate excess solder metal hole, resulting in a bright, smooth, uniform solder coating.
Gold Finger, purpose-designed Edge Connector, plug the connector as board liaison foreign exports, and therefore need to cheat the process. Chose gold because of its superior conductivity and oxidation resistance. However, because the cost of gold applies only to cheat so high, local gold plated or chemically.