Analysis of common causes of PCB board defects

PCB boards always encounter various problems during the design and production process, such as PCB board short circuit, dark and granular contacts on the PCB board, board bending, etc. In this article, 2PCB and everyone will learn about some common causes of PCB board defects.
PCB board short circuit

This is one of the common faults that directly causes the PCB board to fail to work. There are many reasons for this problem. Let’s analyze them one by one below.

1) The biggest cause of PCB short circuit is improper solder pad design. At this time, you can change the circular solder pad to an oval shape to increase the distance between points to prevent short circuits.
2) Improper design of the direction of PCB parts will also cause the board to short-circuit and fail to work. For example, if the SOIC pin is parallel to the tin wave, it will easily 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 can also cause PCB short circuit failure, that is, automatic plug-in bending feet. Since IPC stipulates that the length of the wire pins should be less than 2mm and there is concern that the parts will fall off when the angle of the bent pins is too large, it is easy to cause a short circuit, so the solder joints need to be separated from the circuit by more than 2mm.

In addition to the three reasons mentioned above, there are also some reasons that can also cause short-circuit failure of PCB boards, such as too large holes in the substrate, too low temperature of the solder furnace, poor solderability of the board surface, failure of the solder mask, and board failure. Surface contamination, etc., are relatively common causes of failures. Engineers can compare the above causes with the failure situations to eliminate and check them one by one.

PCB open circuit
Opens occur when traces break, or when solder is only on the pads and not on the component leads. In this case, there is no adhesion or connection between the component and the PCB. Just like short circuits, these can also occur during production or during welding and other operations. Vibrating or stretching the boards, dropping them, or other mechanical deformation factors can damage traces or solder joints. Likewise, chemicals or moisture can cause the solder or metal parts to wear away, causing component leads to break.

Dark and granular contacts appear on the PCB
Dark or granular contact problems on the PCB board are mostly caused by the solder being contaminated and too much oxide mixed in the molten tin, resulting in a solder joint structure that is too brittle. Be careful not to confuse it with the dark color caused by using solder with low tin content.
Another reason for this problem is that the composition of the solder itself changes during the manufacturing process, and the impurity content is too much. Pure tin needs to be added or the solder needs to be replaced. The stained glass undergoes physical changes in fiber lamination, such as separation between layers. But this situation is not a bad solder joint. The reason is that the substrate is overheated, and the preheating and soldering temperatures need to be reduced or the substrate traveling speed needs to be increased.

PCB solder joints turn golden yellow
Generally, the solder on the PCB board is silver-gray, but occasionally golden solder joints appear. The main cause of this problem is that the temperature is too high. At this time, you only need to lower the temperature of the tin furnace.

Defects on the board are also affected by the environment
Due to the structure of the PCB itself, it is easy to cause damage to the PCB board when it is placed in an unfavorable environment. Extreme temperatures or temperature changes, excessive humidity, high-intensity vibration and other conditions are all factors that can lead to reduced board performance or even scrapping. For example, changes in ambient temperature can cause the board to deform. This will damage solder joints, bend the shape of the board, or possibly cause copper traces on the board to break.

On the other hand, moisture in the air can cause oxidation, corrosion and rust on metal surfaces such as exposed copper traces, solder joints, pads and component leads. Accumulation of dirt, dust, or debris on component and circuit board surfaces can also reduce air flow and cooling of components, causing PCB overheating and performance degradation. Vibrating, dropping, hitting or bending the PCB will deform it and cause cracks, while large current or overvoltage can cause the PCB board to breakdown or cause rapid aging of components and pathways.


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