The pad is connected to the through hole. The wires between the mounting pad connection vias should in principle be soldered. In the absence of solder mask, solder joint defects may occur such as less soldering, cold soldering, short circuit, not welding, and tombstoning.
The solder mask design between the pads, the solder resist pattern specification should be in accordance with the specific component solder joint distribution design: between the pads, such as the use of window-type soldering, resulting in short circuit between the pads, between the pads are designed as pin independent soldering, and there is no short circuit between the pads during soldering.
The component solder mask pattern size is not appropriate, too large solder mask graphic design, mutual "shadow" resulting in non-resistive soldering, so that the component spacing is too small.
There are no solder masks under the components. There are no solder masks under the SO16 components. The solder on the vias after wave soldering may affect the reliability of IC soldering and may cause short circuit of components. And other defects.