When placed an order of PCBs (printed circuit boards), you should spend time to considerate the basic factors including PCB board substrate material, layer count, board size, board thickness, copper thickness, surface finish, solder mask, silkscreen, blind vias, buried vias, through-hole plating, SMT and so on. When all the factors are checked and confirmed with the engineers, we highly recommended sample tested before the real fabrication of your PCB boards. If all things go well, fabrication could be started right away. However, it may need to do some modification if customer is not satisfied with the sample.