PCB open circuit is a problem that PCB manufacturers will encounter almost every day, which has been perplexing production and quality management personnel. The problems caused by it are filling materials due to insufficient shipment quantity, delivery delay and customer complaints, which are difficult to be solved by industry insiders.

The PCB open circuit is actually two points (A and B) that should be connected, but not connected.

Four PCB open circuit features

1. Repetitive open circuit

It is characterized by the same open circuit at the same place on almost every PCB board, which is repeated many times, and the number of exposure negatives is the same. The formation reason is that the exposure plate has defects in the same position as the open circuit of the board. In this case, the exposure plate must be scrapped, and the AOI detection of the first and last boards should be strengthened to ensure that the first PCB board is correct before exposure.

2. The gap open

The characteristic of this open circuit is that there is a notch in a wire, and the remaining line width is less than or equal to 1/2 of the normal line width because of the notch, usually in a fixed position, showing repeated phenomenon. It is also caused by a defect in the exposure plate, so that the PCB board also has a gap in the same position of the wire. Petter PCB xiaobian suggests that the way to eliminate is to change a new exposure film, and strengthen the AOI detection in the exposure process.

3. Vacuum open circuit

In a certain area, there are several wires showing thinning phenomenon (gradually thinning), some are open, some are not open, but the wires are too thin (less than the minimum wire width required by the customer) and have to be scrapped. The reason for this defect is that the contact between the film and the dry film used by the PCB manufacturer for exposure is not close enough, and there is air in the middle, that is, the vacuumization is not good after the exposure table is closed, and the vacuum degree cannot meet the requirements, which leads to the wire thinning or open circuit during exposure.

4. Scrape open

Its characteristic is to be able to see the trace that the wire is scratched by the external force obviously, also thus causes the open circuit. The cause is due to improper operation (for example, the wrong way to take the board during PCB production) or the cause of the machine, and the wire is bruised to form an open circuit.

Due to the complex causes of the outer circuit defects, there are many possible cases, which are not listed here, but most of the defects occur in copper clad plate, film, dry film and other materials, or in the exposure, development, etching and other processes abnormal.