The eight common problems of PCBs and their solutions.

In the design and manufacturing process of PCBs, engineers need to prevent unexpected issues during production and avoid design errors. This article summarizes and analyzes common PCB problems, aiming to provide some assistance for your design and manufacturing efforts.

Problem 1: PCB Short Circuits

Short circuits are a common failure that can directly cause a PCB to malfunction. There are several reasons for this issue, which we will analyze individually.

The primary cause of PCB short circuits is improper pad design. Changing circular pads to oval shapes and increasing the distance between pads can help prevent shorts.
Inadequate orientation of PCB components can also lead to short circuits. For example, if the leads of an SOIC are parallel to the solder wave, this can easily cause a short circuit. Adjusting the component orientation to be perpendicular to the solder wave can mitigate this risk.
Another possible cause of short circuits is bent leads from automatic insertion. IPC standards dictate that lead lengths should be under 2mm; if leads bend too much, components may fall off, leading to shorts. Therefore, solder points should be at least 2mm away from traces.
In addition to these three reasons, other factors can cause short circuits, such as oversized substrate holes, low soldering oven temperatures, poor solderability of the board, solder mask failure, and surface contamination. Engineers can compare these causes with the occurrences of faults for troubleshooting.

Problem 2: Dark or Granular Solder Joints on PCB

Dark or granular solder joints on PCBs are often due to solder contamination or excessive oxides, leading to brittle joint structures. This should not be confused with dark solder from low-tin content solder.
Another reason for this problem is a change in the composition of the solder used during manufacturing, leading to excessive impurities. Pure tin may need to be added or the solder replaced. Additionally, physical changes such as layer separation in the substrate can occur due to overheating, which may require lowering preheating and solder temperatures or increasing substrate travel speed.

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Problem 3: PCB Solder Joints Turning Gold

Typically, solder on PCBs appears silver-gray, but occasionally, golden solder joints may appear. The main cause of this is excessive temperature, which can be remedied by lowering the solder oven temperature.

Problem 4: Environmental Impact on PCB Defects

Due to the structural nature of PCBs, they can be easily damaged in adverse environments. Extreme temperatures or unpredictable temperature changes, excessive humidity, and high-intensity vibrations can all lead to reduced performance or even failure of the board. For example, changes in environmental temperature can cause deformation, damaging solder joints or copper traces.
Moisture in the air can lead to oxidation, corrosion, and rust on metal surfaces, including exposed copper traces, solder joints, pads, and component leads. Accumulation of dirt or debris on components and PCB surfaces can hinder airflow and cooling, resulting in overheating and performance degradation. Vibration, drops, impacts, or bending of the PCB can deform it and create cracks, while high current or overvoltage can lead to breakdowns or rapid aging of components and traces.

Problem 5: PCB Open Circuits

Open circuits occur when traces are broken or when solder is only on the pad and not on the component leads. In such cases, there is no adhesion or connection between the component and the PCB. Like short circuits, these issues can arise during production, soldering, or other operations. Vibration or stretching of the circuit board, dropping it, or other mechanical factors can damage traces or solder joints. Additionally, chemicals or moisture can wear down solder or metal components, leading to broken component leads.

Problem 6: Loose or Misaligned Components

During the reflow soldering process, small components may float on the molten solder and eventually detach from their target solder joints. Causes of misalignment or tilting may include insufficient support for the PCB, incorrect reflow oven settings, solder paste issues, and human error, all of which can lead to vibrations or bouncing of components on the soldered PCB.

Problem 7: Soldering Issues

Several problems can arise from poor soldering practices:

• Disturbed Solder Joints: External disturbances can cause solder to move before it solidifies. This is similar to cold solder joints but has different causes; it can be corrected by re-heating and ensuring that solder joints cool without interference.
• Cold Joints: This occurs when solder does not melt properly, leading to rough surfaces and unreliable connections. Excess solder can prevent full melting, resulting in cold solder joints. The remedy is to reheat the joint and remove excess solder.
• Solder Bridges: This occurs when solder crosses and physically connects two leads, potentially creating unintended connections and short circuits, which can lead to component failure or burnt traces under high current.
• Pads: Insufficient wetting of pins or leads, improper solder amounts, or pads raised due to overheating or rough soldering.

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Problem 8: Human Error

Most defects in PCB manufacturing are caused by human error. In many cases, incorrect manufacturing processes, misplacement of components, and unprofessional standards lead to up to 64% of avoidable product defects. The likelihood of defects increases with circuit complexity and the number of manufacturing processes due to factors like densely packaged components, multiple circuit layers, fine traces, surface-mounted components, and power and ground planes.
While every manufacturer or assembler hopes to produce PCBs without defects, various challenges in design and production can lead to persistent PCB issues.
Typical problems and outcomes include: poor soldering leading to short circuits, open circuits, and cold solder joints; misalignment of board layers causing poor contact and overall performance issues; inadequate insulation of copper traces leading to arcing; traces being too close to paths, increasing the risk of shorts; and insufficient board thickness leading to warping and breaking.

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