In the process of PCB design and production, engineers not only need to prevent accidents during PCB manufacturing, but also avoid design errors. This article summarizes and analyzes these common PCB problems, hoping to bring some help to your design and production work.
1. PCB board short circuit
This problem is one of the common faults that will directly cause the PCB board to fail to work. There are many reasons for this problem. We will analyze them one by one below. The biggest cause of PCB short circuit is improper design of the pads. At this time, the circular pads can be changed to oval, and the distance between the points can be increased to prevent short circuits.
Improper design of the direction of the PCB parts will also cause the board to short-circuit and fail to work. For example, if the foot of 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.
There is another possibility that will also cause a short circuit fault of the PCB, that is, the automatic plug-in bending. Since the IPC stipulates that the length of the wire feet is less than 2mm and the parts will fall off when the angle of the bending feet is too large, it is easy to cause a short circuit, and the solder joints need to be separated from the circuit by more than 2mm.
In addition to the three reasons mentioned above, there are other reasons that can lead to short-circuit failure of PCB boards, such as too large substrate holes, too low tin furnace temperature, poor solderability of the board surface, failure of solder mask, board failure, etc. Surface contamination, etc., are relatively common causes of failure. Engineers can compare the above causes and failures to eliminate and check them one by one.
2. Dark and granular contacts appear on the PCB
The problem of dark or small grained joints on the PCB board is mostly due to the contamination of the solder and the excessive mixing of oxides in the molten tin, resulting in a brittle solder joint structure. Care must be taken not to be confused with the dark color caused by the use of solder with a low tin content.
Another reason for this problem is that the composition of the solder used in the manufacturing process changes, and the impurity content is too high, so pure tin needs to be added or the solder needs to be replaced. Spotted glass causes physical changes in fiber lamination, such as separation between layers. But this is not a bad solder joint. The reason is that the substrate is overheated, and it is necessary to reduce the preheating and soldering temperature or increase the speed of the substrate.
3. PCB solder joints turn golden yellow
Under normal circumstances, the solder of the PCB board is silver-gray, but occasionally there are golden-yellow solder joints. The main reason for this problem is that the temperature is too high. At this time, it is only necessary to lower the temperature of the tin furnace.
Fourth, the bad board is 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 in an unfavorable environment. Extreme temperatures or temperature fluctuations, excessive humidity, high-intensity vibration, and other conditions are all factors that lead to reduced board performance or even scrapping. For example, changes in ambient temperature can cause the board to deform. This will destroy solder joints, bend the shape of the board, or may also cause copper traces on the board to open.
On the other hand, moisture in the air can cause oxidation, corrosion and rusting of metal surfaces such as exposed copper traces, solder joints, pads and component leads. The buildup of dirt, dust, or debris on components and board surfaces can also reduce component air flow and cooling, resulting in PCB overheating and performance degradation. Vibration, dropping, hitting or bending the PCB can deform it and cause cracks, while high current or overvoltage can cause the PCB to break down or cause rapid aging of components and vias.
Five, PCB open circuit
An open circuit occurs when a trace breaks, or when the solder is only on the pad 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 soldering and other operations. Vibrating or stretching circuit boards, dropping them, or other mechanical deformation factors can damage traces or solder joints. Likewise, chemicals or moisture can cause wear on solder or metal components, which can lead to breakage of component leads.
6. Looseness or dislocation of components
During the reflow process, small parts can float on the molten solder and eventually come off the target solder joint. Possible reasons for shifting or tilting include vibration or bouncing of components on the soldered PCB board due to insufficient board support, reflow oven settings, solder paste issues, human error, etc.
7. Welding problems
Here are some problems caused by poor soldering practices:
Disturbed solder joints: Solder moves before solidification due to external disturbance. This is similar to cold solder joints, but for different reasons, which can be corrected by reheating and guaranteeing that the solder joints cool without outside interference.
Cold Soldering: This occurs when the solder does not melt properly, resulting in a rough surface and unreliable connections. Cold solder joints can also occur due to excess solder preventing complete melting. The remedy is to reheat the joint and remove the excess solder.
Solder Bridge: This occurs when solder crosses and physically connects two leads together. These have the potential to create unexpected connections and shorts that can cause components to burn out or burn traces when the current is too high.
Pads: Insufficient wetting of pins or leads. Too much or too little solder. Pads that have been raised due to overheating or rough soldering.
8. Human error
Most of the defects in PCB manufacturing are caused by human error. In most cases, wrong production process, wrong placement of components and unprofessional manufacturing specifications lead to as many as 64% of avoidable product defects. The reason why the likelihood of defects increases with circuit complexity and number of production processes is due to the following: densely packaged components; multiple circuit layers; fine traces; surface-soldered components; power and ground planes.
Although every manufacturer or assembler hopes to produce a PCB board that is free of defects, there are several design and production process difficulties that cause PCB board problems.
Typical problems and results include the following: poor soldering can lead to shorts, opens, cold solder joints, etc.; misalignment of board layers can lead to poor contact and poor overall performance; poor copper trace insulation can lead to trace-to-trace conditions. Arcing between wires; placing copper traces too close to vias creates a risk of short circuits; under-thickness of the board can lead to bending and breaking.
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