1. Pad design

　　(1) When designing plug-in component pads, the pad size should be designed appropriately. If the solder pad is too large, the solder spreading area is large, and the formed solder joints are not full, while the surface tension of the smaller solder pad copper foil is too small, and the formed solder joints are non wetting solder joints. The fit gap between the aperture and the component lead is too large, which is prone to false soldering. When the aperture is 0.05-0.2mm wider than the lead and the diameter of the solder pad is 2-2.5 times the aperture, it is an ideal welding condition.

　　(2) When designing solder pads for SMD components, the following points should be considered: in order to eliminate the "shadow effect" as much as possible, the solder end or pin of SMD should be facing the direction of the tin flow to facilitate contact with the tin flow and reduce false soldering and solder leakage. For smaller components, they should not be placed behind larger components to avoid solder leakage caused by larger components obstructing the contact between the tin flow and the solder pads of smaller components.

　　2. PCB sampling flatness control

　　Wave soldering has a high requirement for the flatness of printed boards, generally requiring a warpage of less than 0.5mm. If it exceeds 0.5mm, leveling treatment should be carried out. Especially for some printed boards with a thickness of only about 1.5mm, their warpage requirements are higher, otherwise welding quality cannot be guaranteed. The following precautions should be taken:

　　(1) Properly store printed boards and components, and minimize the storage cycle during welding. Copper foil and component leads free of dust, grease, and oxides are beneficial for forming qualified solder joints. Therefore, printed boards and components should be stored in a dry and clean environment, and the storage cycle should be minimized as much as possible.

　　(2) For printed boards that have been placed for a long time, their surface generally needs to be cleaned to improve solderability, reduce false soldering and bridging. For component pins with a certain degree of surface oxidation, the surface oxidation layer should be removed first.