Printed circuit boards are widely categorized into two major classes: flexible PCBs and Rigid PCBs. Flex PCBs can be further classified into multi-layer PCBs, double-sided PCBs, and the single-sided PCBs. There are also quality classes referred to as Class 1, 2 and 3. The Class 3 PCBs have the highest quality requirements as compared to the other classes.
The difference in the quality classes for each of the PCB classes determines the inspection method you can use. A vast number of electronics use the rigid double-sided PCBs and the multi-layer PCB's. This guide will, therefore, focus on the rigid and multi-body PCBs. The panel is then inspected, carried out to determine if the quality of the end product meets the design requirement.
There are standard inspection procedures for all types of PCBs. Visual inspection is top on the list of inspection items. General electrical inspection and the general technological inspection are also methods of inspection used for the PCBs.
Visual inspection requires holding a printed circuit board with veneer calipers and inspecting it with a magnifying glass. You can check out for the board thickness, compatibility of the board with other electric connectors, and the adherence to the dimensions provided in the design. Other features that can be determined by visual inspection include the surface roughness and the general surface quality. Character quality such as the firmness of other components on the circuit board can also be checked.
Under the general electrical inspection, there are several two approaches that you can possibly take:
Connectivity test - Here you connect the board to a multimeter and focus on the conductive patterns created on the board. This test also ensures that the circuit board meets its specific objective.
Insulating performance test - This specific test checks the insulating resistor on the planes. The insulating performance of a PCB determines how long it lasts while in use.
General technological inspection checks for the plating and solderability qualities of the circuit board. Wetting performance of the soldering joints is done to determine the soldering quality. There are many more types of technological inspection that can be done depending on the components on the board.
Common causes of breakdowns in electrical devices are due to poor quality of the metalized vias. The quality of metalized vias is very crucial in the performance of both double-sided PCBs and the multi-layer PCBs too. This type of inspection checks into the electrical performance for open and closed circuit states of the board. The resistance change rate between the layers of the board is also not supposed to surpass 10%. Metalized vias inspection combines both mechanical and visual inspection.
The inspection of circuit boards is an important element in ensuring that they meet desired requirements and working life. After the assembly of the PCB, only those that meet the requirements fully are released for shipping.