Electronic Design - Make your pcb design less detours

Make your PCB design less detours

In the process of PCB board design and circuit board production, engineers not only need to prevent accidents in the PCB board manufacturing process, but also need to avoid design errors. The eight factors common to PCB manufacturers are summarized and analyzed, hoping to bring some help to everyone's design and production work.

Problem 1: Circuit board short circuit: For this kind of problem, it is one of the common faults that directly cause the circuit board to not work. There are many reasons for this board problem. The following editor will lead you to understand and analyze one by one. The biggest cause of PCB short circuit is improper solder pad design. At this time, the round solder pad can be changed to an oval shape to increase the distance between points to prevent short circuits. Inappropriate design of the direction of the PCB proofing parts will also cause the board to short-circuit and fail to work. For example, if the pin of the SOIC is parallel to the tin wave, it is easy to 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 another possibility that will cause short circuit failure of the PCB, that is, the automatic plug-in bent foot. As the IPC stipulates that the length of the pin is less than 2mm and there is concern that the parts will fall when the angle of the bent leg is too large, it is easy to cause a short circuit, and the solder joint must be more than 2mm away from the circuit.

Problem 2: PCB solder joints become golden yellow: Generally, the solder on PCB circuit boards is silver-gray, but occasionally golden solder joints appear. The main reason for this problem is that the temperature is too high. At this time, you only need to lower the temperature of the tin furnace.

Problem 3: Dark-colored and granular contacts appear on the circuit board: Dark-colored or small-grained contacts appear on the PCB. Most of the problems are caused by the contamination of the solder and the excessive oxides mixed in the molten tin, which form the solder joint structure. crisp. Be careful 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 has changed, and the impurity content is too high. It is necessary to add pure tin or replace the solder. The stained glass causes physical changes in the fiber build-up, such as separation between layers. But this situation is not due to poor solder joints. The reason is that the substrate is heated too high, so it is necessary to reduce the preheating and soldering temperature or increase the speed of the substrate.

Problem 4: Loose or misplaced PCB components: During the reflow soldering process, small parts may float on the molten solder and eventually leave the target solder joint. Possible reasons for the displacement or tilt include the vibration or bounce of the components on the soldered PCB board due to insufficient circuit board support, reflow oven settings, solder paste problems, and human error.

Problem 5: Circuit board open circuit: When the trace is broken, or the solder is only on the pad and not on the component lead, an open circuit will occur. In this case, there is no adhesion or connection between the component and the PCB. Just like short circuits, these may also occur during the production process or during the welding process and other operations. Vibration or stretching of the circuit board, dropping them or other mechanical deformation factors will destroy the traces or solder joints. Similarly, chemical or moisture can cause solder or metal parts to wear, which can cause component leads to break.

Problem 6: Soldering problems: The following are some problems caused by poor soldering practices: Disturbed solder joints: Due to external disturbances, the solder moves before solidification. This is similar to cold solder joints, but the reason is different. It can be corrected by reheating, and the solder joints are not disturbed by the outside when they are cooled. Cold welding: This situation occurs when the solder cannot be melted properly, resulting in rough surfaces and unreliable connections. Since excessive solder prevents complete melting, cold solder joints may also occur. The remedy is to reheat the joint and remove the excess solder. Solder bridge: This happens when solder crosses and physically connects two leads together. These may form unexpected connections and short circuits, which may cause the components to burn out or burn out the traces when the current is too high. Insufficient wetting of pads, pins, or leads. Too much or too little solder. A pad that is elevated due to overheating or rough soldering.

Problem 7: The badness of the PCB board is also affected by the environment: due to the structure of the PCB itself, it is easy to cause damage to the circuit board when in an unfavorable environment. Extreme temperature or temperature fluctuations, excessive humidity, high-intensity vibration and other conditions are all factors that cause the board's performance to decrease or even scrap. For example, changes in ambient temperature will cause deformation of the board. Therefore, the solder joints will be destroyed, 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 the metal surface, such as exposed copper traces, solder joints, pads, and component leads. Accumulation of dirt, dust or debris on the surface of components and circuit boards can also reduce the air flow and cooling of the components, causing PCB overheating and performance degradation. Vibration, falling, hitting or bending the PCB will deform it and cause the crack to appear, while high current or overvoltage will cause the PCB to be broken down or cause rapid aging of components and pathways.

Problem 8: Human error: Most of the defects in PCB manufacturing are caused by human error. In most cases, wrong production process, wrong placement of components and unprofessional manufacturing specifications can cause up to 64% to avoid Of product defects appear. Due to the following reasons, the possibility of defects increases with the complexity of the circuit and the number of production processes: densely packaged components; multiple circuit layers; fine wiring; surface soldered components; power and ground planes. Although every manufacturer or assembler hopes that the PCB board produced is free of defects, but there are so many design and production process problems that cause continuous PCB board problems. Typical problems and results include the following points: Poor soldering can lead to short circuits, open circuits, cold solder joints, etc.; misalignment of the board layers can lead to poor contact and poor overall performance; poor insulation of copper traces can lead to traces and traces There is an arc between the wires; if the copper traces are placed too tightly between the paths, the risk of short circuits is easy to occur; if the thickness of the circuit board is insufficient, it will cause bending and fracture. In addition to the reasons mentioned above, there are also some reasons that can cause short circuit failures of the PCB board, such as too large a hole in the substrate, too low temperature of the tin furnace, poor solderability of the board, failure of the solder mask, contamination of the board, etc., Are relatively common causes of failures. Engineers can compare the above causes and the circumstances of the failure to eliminate and check one by one.