Functional testing of printed circuit boards, how to look at printed circuit boards

1. Find out the general working principle, working process and signal flow of the electrical circuit, and the position of the main components and core components on the PCB board.

2. It is recommended to look at the PCB board along the signal flow, looking forward (such as starting from the high-frequency head and looking backwards) or looking backwards (such as looking backwards from the speaker), and sometimes the combination of the two is also suitable for the analysis of some circuits. The circuit must have branches, at this time to see the branches separately, if there are too many branches, you can mark to distinguish the branches that have been seen, but also can be stopped at the mark, first look at other branches or other parts of the circuit, when the analysis to the original pause, even if the analysis is completed when the circuit is paused.

3. It is best to look at the direction of the power supply and the ground wire first, and at the same time note the position of the power supply and the ground wire, when you analyze the component, one end of the component is connected to the power supply or ground wire, even if you finish reading. Along the edge of the circuit board, the copper foil strip with the largest area, the copper skin where the heat sink is connected, etc. (generally the negative pole) is the ground wire. If these characteristics are not obvious, you can look at the filter Li Peibo capacitor of the power supply (for positive power supply), that is, the negative connection of the electrolytic capacitor is the negative or ground wire of the circuit.

The level of PCB engineering production can reflect the design level of the designer, and can also reflect the production process ability and technical level of the printed board manufacturer. At the same time, because PCB engineering production integrates computer-aided design and auxiliary manufacturing, extremely high precision and accuracy are required, otherwise the electrical performance of the final on-board electronic products will be affected, and errors may be caused in serious cases, which will lead to the scrapping of the entire batch of printed board products and delay the manufacturer's contract delivery time, and suffer economic losses. Therefore, as a PCB project maker, we must always remember that our responsibility is heavy, do not take it lightly, and be careful, serious, careful, and serious.

When working with PCB design files, you should double-check: Does the received file comply with the rules set by the designer? Can it meet the requirements of the PCB manufacturing process?

Are there any anchor markers? Is the route layout reasonable? Whether the distance between wire and line, wire and component pad, wire and through hole, component pad and through hole, and between through hole and through hole is reasonable and can meet production requirements.

Are there any conflicts between components in 2D and 3D space? Does the size of the printed board match the processing drawing? Whether the graphics (e.g., icons, annotations) added to the PCB graphics will cause a short circuit in the signal.

Make and modify some undesirable line shapes. Is there a process line on the PCB? Whether the solder mask meets the requirements of the production process, whether the size of the solder mask is appropriate, and whether the character mark is pressed on the device pad, so as not to affect the quality of the electrical system.