Since the printed circuit board is not a general terminal product, the definition of the name is slightly confusing. For example, the motherboard for the personal computer is called the motherboard, and cannot be directly called the circuit board. Although there is a circuit board in the motherboard, It's not the same, so when you evaluate the industry, you can't say the same thing. For example, because the integrated circuit parts are mounted on the circuit board, the news media called him an IC board, but in essence he is not equivalent to a printed circuit board. We usually say that the printed circuit board refers to the bare board - that is, the board without the upper components. In the process of PCB board design and circuit board production, engineers not only need to prevent PCB boards from being accidentally encountered during manufacturing, but also need to avoid design errors.
1, Short circuit of the circuit board: For such problems, one of the common faults that directly cause the circuit board to work, the biggest cause of the short circuit of the PCB is the improper design of the solder pad. At this time, the circular pad can be changed to an ellipse. Shape, increase the distance between the point and the point to prevent short circuit. The design of the PCB proofing part direction is not appropriate, and it will also cause the board to be short-circuited and unable to work. If the foot of the SOIC is parallel to the tin wave, it is easy to cause a short circuit accident. In this case, the direction of the part can be modified to be perpendicular to the tin wave. There is also a possibility that the PCB will be short-circuited, that is, the automatic plug-in bends. Since the IPC stipulates that the length of the wire is less than 2 mm and the part is likely to fall when the angle of the bending is too large, it is easy to cause a short circuit, and the welding point needs to be more than 2 mm away from the line.
2, The PCB solder joint turns golden yellow: In general, the solder of the PCB circuit board is silver-gray, but occasionally there are golden solder joints. The main reason for this problem is that the temperature is too high, and only the temperature of the tin furnace needs to be lowered.
3, Dark and granular contacts on the board: Dark or small grained contacts on the PCB, mostly due to solder contamination and excessive oxides in the tin, forming a solder joint structure too brittle. Care must be taken not to confuse 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 itself used in the manufacturing process changes, the content of impurities is too much, and it is necessary to add pure tin or replace the solder. The stained glass acts as a physical change in the fibrous layer, such as separation between layers. However, this situation is not a bad solder joint. The reason is that the substrate is heated too high, and it is necessary to reduce the preheating and soldering temperature or increase the substrate traveling speed.
4, Loose or misaligned PCB components: During reflow soldering, small parts may float on the molten solder and eventually get out of the target solder joint. Possible causes of shifting or tilting include vibration or bounce of components on the soldered PCB due to insufficient board support, reflow oven settings, solder paste problems, human error, and the like.
5, Open circuit board: An open circuit occurs when the trace breaks, or when the solder is only on the pad and not on the component leads. In this case, there is no glue or connection between the component and the PCB. Just like a short circuit, these can also occur during production or during welding and other operations. Shaking or stretching the board, dropping them or other mechanical deformation factors can damage traces or solder joints. Also, chemical or moisture can cause solder or metal parts to wear, causing component leads to break.
6, Welding problems: The following are some of the problems caused by poor soldering practices: Disturbed solder joints: The solder moves before solidification due to external disturbances. This is similar to a cold solder joint, but for different reasons, it can be corrected by reheating and the solder joint is cooled without being disturbed by the outside. Cold welding: This happens when the solder does not melt properly, resulting in rough surfaces and unreliable connections. Cold solder joints can also occur because excess solder prevents complete melting. The remedy is to reheat the joint and remove excess solder. Solder Bridge: This happens when the solder crosses and physically connects the two leads together. These may create unexpected connections and short circuits that may cause the components to burn out or blow the wires when the current is too high. Pad, pin or lead is not wet enough. Too much or too little solder. A pad that is raised due to overheating or rough soldering.
7, The badness of the pcb board is also affected by the environment: due to the structural reasons of the PCB itself, when it is in an unfavorable environment, it is easy to cause damage to the circuit board. Extreme temperature or temperature changes, other conditions such as excessive humidity and high-intensity vibrations are factors that cause the performance of the board to be reduced or even scrapped. For example, changes in ambient temperature can cause deformation of the board. This will destroy the solder joint, bend the shape of the board, or it may also cause the copper trace on the board to break. 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, debris or debris on the surface of components and boards also reduces air flow and cooling of the components, causing PCB overheating and performance degradation. Vibrating, dropping, hitting or bending the PCB can cause it to deform and cause the crack to appear, while high current or overvoltage can cause the PCB to break down or cause rapid aging of components and paths.
8, Human error: Most of the defects in PCB manufacturing are caused by human error. In most cases, wrong production processes, incorrect placement of components and unprofessional manufacturing specifications result in up to 64% avoidable. Product defects appear.
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