Different customers have different requirements of the size and thickness of PCB. So you can check the size and thickness of the PCB to decide whether it complied with your standard or not.
If the product is far from your requirements, then we can say this is not a good product.
B. Surface of PCB
Every PCB has covered printing ink on the surface to perform the function of insulation. Hence we can learn the PCB board China is good or not from the surface. Bad one will be short of ink and off-color.
C. The welding line of PCB
The PCB is produced for welding components, if it is welded badly and components lost easily, it will influence the application of products. So PCB boards China with strong welding line is extremely important, and one PCB with strong welding line means the good quality of it.
What wrote above explained in detail of the three ways of distinguishing PCB boards China from its appearance, hope it will help you when you are doing business with PCB manufacturers in China.