One type PCB defect caused by bad solder mask

We can see from below figure that there are 13 vias inside the footprint of the MCU on the PCB, and there is a large pad at the bottom of the MCU that connects to GND.

If the solder mask layer is not thick enough, the copper of some vias will not be covered by the solder mask ink, when the MCU is assembled by the SMT machine, the big pad of MCU will short with the vias, it will cause a disaster in the production.

How can we avoid this type defect?

1. When we design the PCB, if we find there is a big bare pad under the chips, we should not place the vias or wires under this pad;
2. If we must place the vias under the bare pad of the chips, we should find a good PCB manufacturer who can process enough thickness solder mask to keep opening circuit between the vias and bare pad.

Our company can manufacture high quanlity PCB to avoid this kind defect, and we also can provide the PCB design suggestion for customer.

A good PCB design will be helpful for mass productions.