1.Through hole opening, when the electronic component is in wave soldering, spraying tin on the inner wall of the hole will increase the hole’s current capacity.
2.In the factory processing, if the copper sinking process is not completed, there will be some holes conducting Defective, tinned through-hole windows are opened, and it is sufficient to insert metal feet up and down for welding during maintenance, which is more convenient for maintenance.
3.Single-sided and double-sided pcb have such requirements, and multi-layer boards generally do not require ordinary windows to open through holes.