Correct PCB pad design is crucial to effectively weld components to the circuit board. For bare pad assembly , there are two common welding methods -- SMD (Solder Mask Defined) and NSMD (Non-Solder Mask Defined), each with its own characteristics and advantages.
SMD refers to the resistance layer opening is less than the metal pad welding process. This process reduces the possibility of the welding plate falling off during welding or dewelding. However, the disadvantage is that the method reduces the copper surface area that can be used for solder joint connections and reduces the space between adjacent pads. This limits the thickness of the trace lines between the pads and may affect the use of through-hole.
NSMD refers to the welding plate process in which the opening of the resistance layer is larger than that of the welding plate. This process provides greater surface area for solder joint connections and greater clearance between solder pads (compared to SMD), allows for wider line width and more through-hole flexibility, but NSMD pads are more likely to fall off during welding and disassembly. Even so, NSMD still has a better welding firm performance and is suitable for solder joint sealing pads.