PCB Technical - PCB Board Design and Manufacturing Common Problems and Optimisation Strategies

In the pcb board design and manufacturing process, engineers have the arduous task of preventing accidents in the manufacturing process, but also to avoid design omissions. The purpose of this article is to summarise and analyse the PCB manufacturing of common problems, in order to provide useful reference for the industry's design and manufacturing work.

Problem 1: PCB board short circuit is one of the common failures, it will directly lead to the board can not work properly. Short circuit for a variety of reasons, need to be analysed one by one. According to the North Soft Semiconductor Laboratory study, the solder pad design is not reasonable is the first factor leading to short-circuit, in this regard, can be changed to oval round pads, and increase the distance between the solder joints, in order to avoid short-circuit. In addition, PCB parts of the direction of the design is not appropriate will also trigger a short circuit, such as the foot of the SOIC if the parallel with the tin wave, it is easy to lead to a short circuit, at this time should be adjusted to the direction of the parts, so that it is perpendicular to the tin wave. In addition, the automatic plug-in foot bend may also cause short-circuit, because the IPC requires the length of the line foot 2mm below, and the angle of the foot is too large when the parts are easy to fall off, so you need to make sure that the solder joints away from the line at least 2mm above. In addition, the substrate hole is too large, the temperature of the tin furnace is too low, the board can be soldered poorly, solder mask failure, board contamination, etc. is also a common short-circuit reasons, engineers can be based on the actual situation of one by one to check.

Problem 2: PCB boards appear dark or granular joints, usually due to solder contamination or oxide mixing too much, resulting in weak solder joint structure. It should be noted that this is to be distinguished from the use of low tin content of solder resulting in dark colours. Another reason is that the composition of the solder has changed during the production process and impurities have increased, in which case it is necessary to add pure tin or replace the solder. In addition, the stained glass from the fibre layer of physical changes, such as interlayer separation, but not a bad solder joints, but the substrate is too high due to heat, you need to reduce the preheating and soldering temperature or speed up the substrate travel speed.

Problem 3: PCB solder joints show golden yellow is not a normal phenomenon, usually solder should be silver-grey. The main reason for the gold-coloured solder joints is the temperature is too high, at this time only need to reduce the temperature of the furnace can be.

Problem 4: the impact of the environment on the PCB board should not be ignored. Due to the special structure of the PCB, vulnerable to damage in harsh environments. Extreme temperatures, excessive humidity, high intensity vibration and other factors may lead to board performance decline or even scrap. For example, changes in ambient temperature can cause board deformation, which in turn can damage solder joints, bend the board shape, or cause copper traces to break. Moisture in the air can cause oxidation, corrosion and rust on metal surfaces such as exposed copper traces, solder joints, pads and component leads. Dirt, dust or debris build-up can reduce air flow and cooling of components, resulting in degraded PCB overheating performance. Vibration, dropping, hitting or bending the PCB can deform it and create cracks, while high currents or overvoltages can break through the PCB or cause rapid deterioration of components and pathways.

Problem 5: PCB open-circuit means that the traces are broken or the solder just stays on the pads without being connected to the component leads, resulting in no connection between the component and the PCB. Open circuit may occur during production, soldering or other operations, vibration, stretching, dropping and other mechanical deformation factors may damage the trace or solder joints. Also, chemical corrosion or moisture can cause solder or metal parts to wear out, leading to component lead breakage.

Problem 6: During the reflow process, small components may become detached from the target solder joint due to the buoyancy of the molten solder, causing looseness or misalignment. This can be due to solder vibration or popping caused by inadequate board support, improper reflow oven settings, solder paste problems, or human error.

Problem 7:Poor soldering practices can cause a host of problems. Disturbed solder joints, which form when external disturbances cause the solder to move before solidifying, are similar to cold solder joints but have a different cause, and can be corrected by reheating and ensuring that the joints are undisturbed as they cool. Cold soldering, on the other hand, occurs when the solder fails to melt correctly, resulting in a rough surface and an unreliable connection, and is remedied by reheating the joint and removing the excess solder. Solder bridging is a condition where solder crosses and physically connects two leads together, which can create unintended connections and short circuits that can lead to component burnout or burned out alignments. In addition, insufficient pad wetting, too much or too little solder, and pad lifting due to overheating or rough soldering are also issues of concern.

Problem 8:Human error is a major source of defects in PCB manufacturing.Incorrect production processes, component misplacement, and unprofessional manufacturing practices are responsible for up to 64% of avoidable defects. As circuit complexity and the number of production processes increase,so does the potential for defects, especially in densely packaged components, multiple circuit layers, fine alignments, surface-soldered components, and power and ground planes.Despite the desire of manufacturers and assemblers to produce defect-free PCB boards, challenges in the design and production process can lead to ongoing problems. Typical problems and results include short circuits,open circuits and cold solder joints due to poor soldering; poor contact and poor performance due to misalignment of layers; arcing due to poorly insulated copper trace wires; risk of short circuits due to copper trace wires being too close to the pathway;and bending and fracturing due to insufficient board thickness.

The design and manufacture of PCBs requires meticulous attention to detail, and in the face of challenges such as short circuits,soldering defects and environmental adaptability, the design process and pcb manufacturing technology need to be continuously optimised. In the future, we look forward to colleagues in the industry to seek innovation, work together to improve the performance and quality of PCBs, and contribute to the prosperity of electronic technology.