PCB

Causes of bad pcb


PCB board short circuit

This is one of the common faults that cause the PCB board to fail to work, and there are many reasons for this problem.

1. The biggest cause of PCB short circuit is improper solder pad design. At this time, the round solder pad can be changed to an oval shape to increase the distance between points to prevent short circuits.

2. Inappropriate design of the direction of the PCB parts will also cause the board to short-circuit and fail to work. For example, if the pin of the SOIC is parallel to the tin wave, it is easy to cause a short-circuit accident. At this time, the direction of the part can be appropriately modified to make it perpendicular to the tin wave.

3. There is another possibility that will cause short-circuit failure of the PCB, that is, the automatic plug-in bending foot. As the IPC stipulates that the length of the pin is less than 2mm and there is concern that the parts will fall when the angle of the bent leg is too large, it is easy to cause a short circuit, and the solder joint must be more than 2mm away from the circuit.

In addition to the three reasons mentioned above, there are also some reasons that can cause short circuit failures of the PCB, such as too large a hole in the substrate, too low temperature of the tin furnace, poor solderability of the board, failure of the solder mask, and board surface Contamination, etc., are relatively common causes of failure. Therefore, many tests need to be carried out during the production process of PCB to ensure the high quality of PCB.

PCB open circuit

When the trace is broken, or when the solder is only on the pad and not on the component leads, an open circuit can occur. In this case, there is no adhesion or connection between the component and the PCB. Just like short circuits, these may also occur during production or welding and other operations. Vibration or stretching of the circuit board, dropping them or other mechanical deformation factors will destroy the traces or solder joints. Similarly, chemical or moisture can cause solder or metal parts to wear, which can cause component leads to break.

Dark and grainy contacts appear on the PCB board

The problem of dark color or small-grained joints on the PCB is mostly due to the contamination of the solder and the excessive oxides mixed in the molten tin, forming the solder joint structure too brittle. Be careful not to confuse it with the dark color caused by the use of solder with low tin content. Another reason for this problem is that the composition of the solder used in the manufacturing process has changed, and the impurity content is too high. It is necessary to add pure tin or replace the solder. The stained glass causes physical changes in the fiber build-up, such as separation between layers. However, this situation is not due to poor solder joints. The reason is that the substrate is heated too high, and it is necessary to reduce the preheating and soldering temperature or increase the speed of the substrate.

boards are also affected by the environment

Due to the structure of the PCB itself, it is easy to cause damage to the PCB when it is in an unfavorable environment. Extreme temperature or temperature fluctuations, excessive humidity, high-intensity vibration and other conditions are all factors that cause the performance of the board to be reduced or even scrapped. On the other hand, moisture in the air can cause oxidation, corrosion and rust on the metal surface, such as exposed copper traces, solder joints, pads and component leads. Accumulation of dirt, dust or debris on the surface of components and circuit boards will also reduce the air flow and cooling of the components, causing PCB overheating and performance degradation. The production conditions of PCB factories need to be very strict, and the temperature and humidity must be controlled to prevent losses.

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