Today let's review the popular mistakes in PCB design.
The pad overlap means hole overlap, it leads to hole damage in drilling process because one hole will be drilled more than once.
If two holes overlapped in multi layers PCB, the overlapped connecting pad will be treated as isolation pad after negative film is painted, then must throw away.
Abuse of circuit layer
Design lots of useless circuits in different layers, for example a normal 4 layers PCB but in design there are over 5 layers circuits layer which leads to misunderstanding.
Be lazy in designing. If using Protel, draw the circuits which is in every layer in board layer and then add remarks in board layer too. Then in the light painting stage, the remarking line is missed because board layer is not chosen, or, result in short circuit because choosing board layer including remarking line. So it is a must to keep the circuit layer complete and clear.
Irregular design. For example set the component in BOT layer and soldering in TOP.
Locate legend disorder
Design legend on pad or SMD soldering terminal, it makes the circuit test and components soldering difficult.
Small legend makes the silk screen difficult. Oversized legend makes the letters overlap.
Drill size in single side pad
There usually do not have drill in single sided pad, if there must be a drill marking, then the size should set to zero. If a drill size is set other than zero, then a drill locate will generate in drilling data, then create problem.
Draw pad using filling block
It may pass the DRC exam if you use filling block to draw pad, but it is not okay for production. Because it can't generate soldering data, then it will be covered with solering resis oil.
Unclear outline design
Some designer draw outline in keep layer, board layer and top over layers, and these outline layers are not identical, then PCB manufacturers do not know which one is correct.
Too close between outline and large area copper
The minimum gap between large area copper and outline should be 0.2mm, to ensure the copper is well protected and the soldering resists do not fall in outline shaping process.