First, check the flatness of the PCB surface. The PCB surface should be smooth and flat, without any bumps or blemishes. There should be no cracks, scratches, or damaged areas on the surface.
 
Second, look at the silk screen. On a high-quality PCB, the silk screen should be clearly legible, without any blurring or missing parts. The text and markings should be neatly aligned, without any deviations or tilts.
 
Third, check the ink. Ink is not just for beautifying the PCB surface, but more importantly, it serves as a permanent protective film for the PCB, effectively protecting the circuitry from minor friction and damage. Using high-quality ink can enhance the reliability and lifespan of the PCB.
 
Fourth, look at the solder pad treatment. Whether it's a spray-on or other process, the solder pad treatment should be uniform and complete, especially for the corners of the IC. The solder pads should be neatly arranged, without any obvious misalignment or offset.
 
Fifth, check the BGA solder pads. Professional PCB manufacturers will use special processes when handling and optimizing BGA solder pads to ensure that the solder pads are full and round.
 
These five points can help you initially assess the quality of the PCB. However, for more in-depth testing, professional testing equipment and techniques will be required.