Since printed circuit boards are not your average final product, the definition of the name is somewhat confusing. For example, the motherboard of a personal computer is calLED a motherboard, not a straight circuit board. Although there is a circuit board on the motherboard, it is different, so you can't say the same when you rate the industry. For example, since integrated circuit components are mounted on circuit boards, the news media refer to them as IC test boards, but in essence, they are not equivalent to printed circuit boards. A printed circuit board is often referred to as a bare circuit board, that is, a circuit board without an upper component. In the design of PCB boards and the production of PCB boards, engineers should not only prevent PCB boards from being accidentally encountered in the manufacturing process, but also avoid design errors.
1, circuit board short circuit: because of this problem, directly lead to one of the common faults in the circuit board work, the biggest reason is that the pcb circuit board short circuit is caused by incorrect solder joint design. At this point, the circular pad can become an oval. Shape to increase the distance between points to prevent short circuits. Improper design of PCB proofing direction will also lead to short circuit board, can not work. If the SOIC foot is parallel to the tin wave, it is easy to cause a short circuit accident. In this case, you can change the assembly direction perpendicular to the tin wave. PCB boards can also short circuit, that is, automatically insert bending. Because the length of the welding wire stipulated by the industrial computer is less than 2mm, when the bending Angle is too large, the part may fall, which is easy to cause short circuit. The off-line requirement of the welding spot is greater than 2mm.
2, PCB solder joint gold: PCB circuit board solder is generally silver gray, but occasionally out of cash solder joint, the main reason is that the temperature is too high, just reduce the temperature of the tin furnace.
3. Black and granular contact on the circuit board: Black or SMAll particle contact on the printed board is mainly caused by solder contamination and excess oxide in the tin, forming too weak solder joint structure. Care must be taken not to confuse dark tin with low tin content due to the use of solder. Another cause of the problem is a change in the composition of the solder used in the manufacturing process, which contains too much impurity and requires the addition of pure tin or alternative solder. Stained glass acts as a physical change in the fiber layer, such as separation between layers. However, this situation is not a bad solder joint. The reason is that the matrix heating is too high, must reduce the preheating and welding temperature, or improve the matrix motion speed.
4. Loose or misaligned PCB components: During refusion welding, small components may float on the solder and eventually fall off the target solder joint. Possible causes of displacement or tilt include vibration or rebound of PCB welds due to inadequate board support, refurnace setup, solder paste problems, and human error.
5, open circuit board: when the trace is broken or solder is only on the pad rather than the component lead, there will be open circuit. In this case, there is no glue or connection between the component and the pcb board. Just like a short circuit, it can happen during production or welding and other operations. Shaking or stretching the circuit board or other mechanical deformation factors can damage the circuit board or solder joints. In addition, chEMIcals or moisture can cause solder or metal parts to wear, causing component conductors to break.
6, welding problems: the following are some problems caused by poor welding: solder joint interference: solder before solidification due to external interference and move. This is SIMilar to cold welding spots, but for different reasons can be corrected by reheating, cooling the spot without outside interference. Cold welding: This happens when the solder does not melt properly, resulting in rough surfaces and unreliable connections. Cold solder spots can also occur because too much solder prevents full melting. The solution is to reheat the joint and remove excess solder. Welding Bridge: This occurs when solder intersects and physically joins two leads together.
7, poor PCB circuit board is also affected by the environment: due to the structure of the PCB circuit board itself, when in an adverse environment, it is easy to cause damage to the circuit board, extreme temperature or temperature change, other conditions such as high humidity, high strength vibration, etc., are leading to the performance of the circuit board decline and even scrap factors. For example, changes in ambient temperature can cause circuit boards to deform. This can damage solder joints, bend the shape of the board, and possibly cause the copper wires on the board to break. On the other hand, moisture in the air can lead to oxidation, corrosion and rust on metal surfaces such as exposed copper wire, solder joints, pads and component leads. Accumulation of dirt, chips or debris on the surfaces of components and boards also reduces air flow and component cooling, causing the PCB to overheat and degrade performance. PCB vibration, drop, impact or bending can lead to PCB deformation and cracking, while high current or overvoltage can lead to PCB damage or components, rapid path aging.
8. Human error: Most defects in PCB manufacturing are caused by human error. In most cases, faulty manufacturing processes, incorrect component placement, and unprofessional manufacturing specifications resulted in up to 64 percent avoidance. There are defects in the product.