In the process of PCB board design and production, engineers not only need to prevent accidents during PCB board manufacturing and processing, but also need to avoid design errors. This article summarizes and analyzes these common PCB problems, hoping to bring some help to your design and production work.
Problem 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, and we will analyze them one by one below.
The biggest cause of PCB short circuit is improper pad design. At this time, the circular pad can be changed to an oval shape, and the distance between points can be increased to prevent short circuit.
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 pin of SOIC 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.
There is also a possibility that the short-circuit fault of the PCB can also be caused, that is, the bent feet of the automatic plug-in. Since IPC stipulates that the length of the wire pin is less than 2mm and the part is worried that the part will fall when the angle of the bent pin is too large, it is easy to cause a short circuit, so the solder joint needs to be separated from the wire by more than 2mm.
In addition to the three reasons mentioned above, there are also some reasons that can lead to short-circuit faults on the PCB, such as too large a hole in the substrate, too low temperature of the tin furnace, poor solderability of the board surface, failure of the solder mask, board Surface pollution, etc. are relatively common causes of failures. Engineers can compare the above reasons with the failure situation to troubleshoot and check one by one.
Problem 2: Dark and grainy contacts appear on the PCB
The problem of dark or small granular joints on the PCB is mostly due to the contamination of the solder and too much oxide mixed in the molten tin, resulting in a too brittle solder joint structure. Care must be taken 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 changes, and the content of impurities is too much, so pure tin needs to be added or replaced. Stained glass has 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 it is necessary to reduce the preheating and soldering temperature or increase the speed of the substrate.
Problem 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 cause of this problem is that the temperature is too high. At this time, it is only necessary to lower the temperature of the tin furnace.
Problem 4: The badness of the board is also affected by the environment
Due to the structure of the PCB itself, when it is in an unfavorable environment, it is easy to cause damage to the PCB board. Extreme or fluctuating temperatures, excessive humidity, high levels of 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 deformation of the board. This will destroy the solder joints, bend the shape of the board, or possibly cause an open circuit in the copper traces on the board.
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 the surface of components and boards can also reduce air flow and cooling of components, causing the PCB to overheat and degrade performance. Vibration, dropping, hitting or bending the PCB will deform it and cause cracks, while high current or overvoltage will cause the PCB board to be broken down or cause rapid aging of components and pathways.
Problem 5: PCB open circuit
An open circuit occurs when a trace is broken, or when the solder is only on the pad and not on the component lead. 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 boards, dropping them, or other mechanical deformation factors can damage traces or solder joints. Likewise, chemicals or moisture can cause solder or metal parts to wear away, causing component leads to break.
Problem 6: Loose or misplaced components
During the reflow process, small components can float on the molten solder and eventually break away from the intended solder joint. Possible reasons for shifting or tilting include vibration or bouncing of components on the soldered PCB due to insufficient board support, reflow oven settings, soldering problems, human error, etc.
Problem 7: Welding problem
Here are some problems that can arise due to poor soldering practices:
Disturbed Solder Joint: Movement of the solder before it solidifies due to external disturbances. This is similar to a cold solder joint, but for a different reason, and can be corrected by reheating and keeping the solder joint cool without external disturbance.
Cold Soldering: This occurs when the solder does not melt properly, resulting in rough surfaces 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 excess solder.
Solder Bridge: This occurs when solder crosses over and physically connects two leads together. These have the potential to form unintended connections and shorts that can burn components or blow traces if the current is too high.
Pad: Insufficient pin or lead wetting. Too much or too little solder. A raised pad due to overheating or rough soldering.
Problem 8: Human Error
Most of the defects in PCB manufacturing are caused by human errors. In most cases, wrong production processes, wrong placement of components and unprofessional manufacturing specifications lead to as many as 64% of avoidable product defects. The potential for defects increases with circuit complexity and number of production processes due to the following: densely packed components; multiple circuit layers; fine traces; surface soldered components; power and ground planes.
Although every manufacturer or assembler hopes to produce PCB boards without defects, there are several design and production process problems that cause PCB board problems.
Typical problems and results include the following: poor soldering can cause shorts, opens, cold solder joints, etc.; misalignment of board layers can cause poor contact and overall poor performance; Arcing occurs between wires; placing copper traces too closely to vias risks short circuits; and boards not thick enough can lead to bending and breaking.
