PCB design common eight problems and solutions, you learned?

In the process of PCB design and production, engineers not only need to prevent PCB boards in the manufacturing process when the accident, but also need to avoid the emergence of design errors. This article summarizes and analyzes these common PCB problems, I hope to be able to bring some help to the design and production work.

Problem 1: PCB short circuit

This problem is directly caused by the PCB board can not work one of the common failures, and the causes of this problem have many reasons, the following we analyze one by one.

Caused by PCB short circuit is the biggest reason for improper design of the welding pad, this time you can change the round welding pad to oval, increase the distance between the point and the point, to prevent short circuits.

PCB parts of the direction of the design is not appropriate, will also cause the same board short-circuit, can not work. Such as SOIC feet if parallel to the tin wave, it is easy to cause short-circuit accidents, at this time you can properly modify the direction of the parts, so that it is perpendicular to the tin wave.

There is also a possibility that will cause PCB short-circuit failure, that is, the automatic insertion of bent feet. Due to IPC regulations in the length of the foot 2mm below and worry about bending the foot angle is too large when the parts will fall, it is easy to cause a short-circuit, you need to leave the line of soldering points more than 2mm.

In addition to the three reasons mentioned above, there are a number of reasons that can lead to PCB board short-circuit failure, such as the substrate hole is too large, the tin furnace temperature is too low, the board can be soldered poorly, solder-resistant film failure, board contamination, etc., are more common causes of failure, engineers can compare the above reasons and the occurrence of failures to rule out and check the situation one by one.

Problem two: PCB board appears dark and granular joints

PCB board appears dark or into a small granular joint problem, mostly due to the solder is contaminated and dissolved tin mixed with too much oxide, the formation of solder joints structure is too brittle. Be careful not to be confused with the use of low tin content of the solder caused by the dark color.

Another reason for this problem is that the composition of the solder used in the manufacturing process itself changes, too much impurity content, need to add pure tin or replace the solder. Stained glass from the physical changes in the fiber layer, such as layers and layers of separation occurs between the phenomenon. But this situation is not a bad solder joint. The reason is that the substrate is overheated, need to reduce the preheating and soldering temperature or increase the substrate traveling speed.

Problem three: PCB solder joints into a golden color

In general, the PCB board solder is silver gray, but occasionally there are golden yellow solder joints appear. The main reason for this problem is that the temperature is too high, at this time only need to lower the temperature of the tin furnace can be.

Problem 4: the board’s bad also affected by the environment

Due to the construction of the PCB itself, when in an unfavorable environment, it is easy to cause damage to the PCB board. Extreme temperatures or temperature variations, excessive humidity, high-intensity vibration and other conditions are factors that lead to reduced performance or even scrap of the board. For example, changes in ambient temperature can cause deformation of the board. As a result, solder joints will be damaged, the board shape will be bent, or the copper traces on the board may be broken.

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. The buildup of dirt, dust or debris on component and board surfaces can also reduce airflow and cooling of components, leading to PCB overheating and performance degradation. Vibration, dropping, hitting or bending the PCB can deform it and cause cracks, while high currents or overvoltages can cause the PCB to be punctured or lead to rapid aging of components and pathways.

Problem 5: PCB open circuit

An open circuit occurs when the trace is broken, or when the 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 the manufacturing process or during soldering and during other operations. Vibrating or stretching the boards, dropping them or other mechanical deformation factors can damage the traces or solder joints. Similarly, chemical or moisture can cause solder or metal parts to wear out, leading to component lead breakage.

Problem 6: Loose or Misplaced Components

During the reflow process, small components can float on the molten solder and eventually detach from the target solder joint. Possible causes of displacement or tilting include vibration or bouncing of components on the soldered PCB due to inadequate board support, reflow oven settings, solder paste issues, human error, etc.

Problem 7: Soldering Problems

The following are some of the problems caused by poor soldering practices:

Disturbed solder joints: The solder moves before it solidifies due to external disturbances. This is similar to a cold solder joint but has a different cause and can be corrected by reheating and ensuring that the solder joint cools while it is free from outside disturbances.

Cold Soldering: This occurs when the solder does not melt correctly, 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 the excess solder.

Solder Bridges: These occur when solder crosses and physically joins two leads together. These have the potential to form unexpected connections and shorts that may cause components to burn out or burn out alignments when the current is too high.

Solder Pads: Insufficient wetting of pins or leads. Too much or too little solder. Raised pads due to overheating or rough soldering.

Problem 8: Human error

Most defects in PCB manufacturing are caused by human error. In most cases, faulty production processes, misplacement of components and unprofessional manufacturing practices are the cause of up to 64% of avoidable product defects. The likelihood of defects increases with the complexity of the circuit and the number of manufacturing processes due to the following: densely packaged components; multiple circuit layers; delicate alignments; surface-soldered components; power and ground planes.

Although every fabricator or assembler wants to produce PCB boards that are free of defects, there are just so many design and production process challenges that result in constant PCB board problems.

Typical problems and results include the following: poor soldering can lead to short circuits, open circuits, cold solder joints, etc.; misalignment of layers can lead to poor contact and overall poor performance; poorly insulated copper traces can lead to arcing between traces; placing the copper traces too tightly against the pathways can easily lead to the risk of short circuits; and insufficient board thickness can lead to bending and fracturing.

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