How to deal with copper exposure on PCB?

How to deal with copper exposure on PCB?

The core of electronic products is the design and manufacturing process of PCB (Printed Circuit Board), and it is crucial to ensure its quality and performance. Among the common problems that may occur during the PCB production process, PCB copper exposure is one of the problems that directly affects the electrical characteristics, reliability and appearance quality of the circuit board.

This article will provide you with a detailed introduction to what copper exposure is in PCB boards, and how to address it through scientific and reasonable methods, particularly discussing whether copper exposure can be effectively covered by soldering.

Understanding PCB copper exposure

copper exposure refers to the phenomenon where, during the PCB manufacturing process, due to factors such as design, processing, or materials, the exposed copper foil (parts other than wires, solder pads, etc.) that should have been covered by the solder mask is not completely shielded and remains exposed. This copper exposure can occur at any position on the board surface, including but not limited to vias, traces edges, and around solder pads.

The hazards of the copper exposure issue mainly manifest in the following aspects:

Electrical hazards: Uncovered copper foil may pose a short-circuit risk, especially in humid environments or situations involving foreign object contact, which may result in circuit abnormalities or even equipment damage.

Soldering issues: Excessive exposed copper surfaces can increase the consumption of solder paste during soldering, affecting soldering quality and potentially leading to soldering defects such as cold joints or bridging.

Decreased reliability: Exposed copper surfaces are prone to oxidation, reducing the corrosion resistance of the circuit board and affecting its long-term stability.

Aesthetic deterioration: From an aesthetic perspective, copper exposure makes the PCB appear irregular, affecting the product’s image.

How to Cover copper exposure?

How to Cover copper exposure?

For addressing the issue of copper exposure, there are several common methods:

Optimization of Solder Mask Design and Process

This is the most direct and fundamental approach. During the PCB design phase, it is essential to ensure precise and accurate design of the solder mask to avoid copper exposure resulting from design oversights. During production, strict control over the solder mask coating process should be exercised to ensure it uniformly and completely covers the copper surfaces that need protection.

Use of Touch-up Paint or Repair Adhesive

For PCBs already experiencing “copper exposure,” specialized solder mask or repair adhesive can be used for local repairs. These products can cure at room temperature, forming an insulating protective layer that effectively covers the exposed copper surfaces.

Selective Plating

In certain specific situations, selective plating processes can be employed to deposit a layer of another metal (such as nickel, gold, etc.) at the site of “copper exposure.” This serves the dual purpose of providing coverage protection and enhancing the local corrosion resistance.

Can copper exposure on PCBs be Covered with Solder?

Can copper exposure on PCBs be Covered with Solder?

Regarding the question of whether copper exposure can be covered with solder, the answer is: it can be done under specific conditions, but it’s not the optimal solution and requires careful handling.

Firstly, soldering can indeed cover copper exposure to some extent, preventing direct contact with the environment and reducing the risks of short circuits and oxidation. However, this method has the following limitations:

Increased costs: Additional consumption of solder paste will raise production costs, and manual intervention may be required, affecting production efficiency.

Soldering issues: Excessive accumulation of solder paste may result in uneven heat distribution during soldering, leading to soldering quality issues.

Uncertain reliability: Solder paste itself is not an ideal insulating material, and there may be a risk of insulation failure after prolonged use. Additionally, solder paste is prone to oxidation and sulfidation reactions in high-temperature and humid environments, affecting its covering effectiveness and circuit stability.

Therefore, although soldering can serve as a temporary measure for copper exposure in emergency situations, optimizing solder mask design and processes, or using professional touch-up paint, repair adhesives, selective plating, and other methods are more prudent and effective in the long run.

Conclusion

In summary, the issue of copper exposure on PCBs should not be overlooked, and effective covering should be carried out through scientifically reasonable means. While soldering can partially conceal “copper exposure,” it’s not the ideal choice due to its cost, soldering, and reliability limitations. Prioritizing the optimization of solder mask design and processes or using professional repair materials and techniques is a wise move to ensure PCB quality and performance.

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