Problem 1: PCB Short Circuits
Short circuits are one of the most common failures that directly cause a PCB to stop functioning. There are multiple causes for this issue, which we will analyze one by one.
The primary cause of a PCB short circuit is improper pad design. In such cases, changing the circular pads to oval ones and increasing the distance between pads can help prevent shorts. When designing the pad layout, it’s crucial to follow industry best practices to ensure that signal integrity is maintained and that no unintended connections are made.
Another potential cause is improper component orientation. For instance, if the leads of a SOIC (Small Outline Integrated Circuit) component are parallel to the solder wave, it can easily lead to a short circuit. In this case, adjusting the component's orientation so that the leads are perpendicular to the solder wave can prevent the issue.
A third possibility for short circuits is bent component leads during the automated insertion process. According to IPC standards, the lead length should be less than 2mm to prevent components from falling off. However, if the bending angle is too sharp, it may result in a short circuit. Ensuring that the leads are at least 2mm away from the traces can help prevent this issue.
Beyond these causes, other common factors may lead to short circuits, such as oversized via holes, low soldering temperatures, poor solderability of the PCB surface, defective solder mask layers, and contamination of the PCB surface. Engineers should carefully examine these factors to troubleshoot and eliminate the root cause.
Problem 2: Dark or Granular Solder Joints
When dark-colored or granular solder joints appear on a PCB, it is often due to contamination of the solder paste or excessive oxidation in the solder alloy, which results in brittle solder joints. This issue should not be confused with dark-colored solder caused by low-tin-content solder paste.
Another contributing factor is a change in the composition of the solder used during manufacturing, with excessive impurities leading to solder defects. To address this, pure tin or high-quality solder paste should be used. It’s also important to adjust the preheating and soldering temperatures to avoid excessive heating that could cause physical damage to the PCB, such as fiber delamination between layers.
Problem 3: Yellowish Solder Joints
Normally, solder joints on PCBs appear silver-gray, but occasionally, they may turn gold or yellow. The primary cause of this issue is excessive temperature during the soldering process. To resolve this, lowering the soldering oven temperature can correct the issue and prevent further defects.
Problem 4: Environmental Factors Affecting PCB Quality
The inherent construction of a PCB makes it susceptible to damage in unfavorable environments. Extreme temperatures, temperature fluctuations, excessive humidity, and high-intensity vibrations can all lead to performance degradation or even failure of the PCB. For instance, changes in ambient temperature can cause the PCB to warp, potentially damaging solder joints, causing board warping, or even leading to copper trace breaks.
Humidity in the air can cause oxidation and corrosion on exposed metal surfaces like copper traces, solder pads, and component leads. Dirt, dust, or debris that accumulates on the PCB’s surface can impede airflow and cooling, leading to overheating and decreased performance. Additionally, vibrations, drops, impacts, or bending of the PCB can cause physical damage, such as cracks. Overcurrent or overvoltage conditions can lead to PCB breakdowns or rapid aging of components and traces.
Problem 5: PCB Open Circuits
Open circuits occur when a trace is broken, or when the solder only adheres to the pad but not to the component leads. This problem can occur during manufacturing, soldering, or other handling procedures. Vibration, stretching of the PCB, or mechanical deformations, such as dropping the board, can damage the traces or solder joints. Additionally, chemical exposure or moisture can cause solder or metal components to wear away, leading to broken component leads and open circuits.
Problem 6: Loose or Misaligned Components
In the reflow soldering process, small components may float on the molten solder and eventually detach from the intended pads. Misalignment or shifting of components may occur due to insufficient PCB support, improper reflow oven settings, solder paste issues, or human errors during assembly. Ensuring proper solder paste application and adequate support during reflow is crucial to preventing this issue.
Problem 7: Soldering Issues
Several problems can arise from improper soldering practices:
Interfered Solder Joints: External disturbances cause the solder to move before it solidifies, similar to cold solder joints. Reheating the joint can correct this issue, ensuring that the solder solidifies without external interference.
Cold Solder Joints: This occurs when the solder does not melt properly, resulting in a rough surface and unreliable connection. Cold solder joints may also occur due to excessive solder, which prevents complete melting. Reheating the joint and removing excess solder can fix this issue.
Solder Bridges: This happens when solder crosses and forms an unintended connection between two leads. This can cause shorts and component damage when high current flows through the unintended paths. These bridges should be carefully inspected and removed before the final assembly.
Pad Issues: Insufficient wetting of component leads or pads can result in poor solder joints. Too much or too little solder can also cause problems, as can pads being lifted due to overheating or rough soldering.
Problem 8: Human Errors
Many defects in PCB manufacturing arise from human error. Incorrect manufacturing processes, improper component placement, and lack of adherence to production standards account for up to 64% of avoidable defects. The likelihood of defects increases as circuit complexity and manufacturing processes become more intricate, such as with densely packaged components, multilayer circuits, fine traces, surface mount components, and power/ground planes.
Despite the best efforts of manufacturers or assemblers to produce defect-free PCBs, certain challenges during the design and production processes lead to ongoing issues. Typical problems include poor soldering, misalignment of layers, inadequate insulation of copper traces, traces that are too close together, insufficient board thickness, and physical board deformation or cracking.
At PCBYES, with over 5 years of experience in PCB prototyping and fabrication, we understand the intricacies of PCB production. Our team of experienced engineers ensures that every design, assembly, and manufacturing process meets the highest standards. By adhering to these standards and performing thorough quality checks, we work diligently to minimize defects and maximize the quality of each PCB produced.
