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The Differences Between Flexible Solder Masks and Coverlay FPC

The differences between a flexible solder mask and a coverlay are significant but often overlooked. A coverlay is a solid sheet of material with mechanical openings. As a result, a small amount of adhesive squeezes out. Coverlay design rules are different than those of flexible solder masks. However, they do have a few things in common.

Flexible PCB coverlay

A few differences exist between a flexible solder mask and a PCB coverlay. One is a solid sheet of material, while the other is flexible. The difference lies in the material and design rules. Generally, a coverlay overlaps the solder mask by 0.4 mm, while a solder mask overlaps by 0.2 mm. Different manufacturers have different design rules, and there are some essential things to remember when selecting a coverlay for your flex circuit.

The flexible PCB coverlay is a layer that protects the circuit board and copper foil. It serves the same function as a solder mask but adds flexibility. Its thickness is usually one mil thick, but different thicknesses are available to meet the exact design requirements. They are laminated using heat and force. Flex circuit board coverlays are more costly than rigid PCBs but are worth the extra expense.

When comparing flexible solder masks and PCB coverlay, it is essential to keep in mind the different materials and processes used. Both materials are helpful in flexible PCB applications. A flexible solder mask uses a photo-imaged liquid that adheres to the PCB. Because it is flexible, it allows larger feature openings. A flexible solder mask is also less expensive than a film-based polyimide coverlay. Flexible PCB coverlay is more versatile than a rigid PCB and offers the same functionality as a rigid PCB.

Flexible solder mask


When evaluating the pros and cons of a coverlay versus a flexible solder mask, it is essential to comprehend how they differ from each other. While both masks provide adequate protection, flexible solder masks have advantages over coverlays. These products are less expensive and have lower copper content. However, they are not ideal for tight bends or folding.

The thickness is the most notable difference between a coverlay and a flexible solder mask. With a coverlay, we must mechanically create openings so the solder can adhere to it. This can leave small gaps between the two materials; in some cases, even adhesive squeezeout can occur. In addition, the design rules for these two materials are different. Because of this, flexible solder masks often don’t adhere to a polyimide coverlay and fail to meet IPC quality standards.

A coverlay is a solid material, such as Kapton, while a flexible solder mask consists of plastic. The former combines plastic polyimides with adhesive, while the latter uses a liquid. Coverlay dams are generally ten mils thick, while solder mask dams are four mils. So if you’re using a flexible solder mask, check the dam size to ensure it’s the correct thickness.

A coverlay has a minimum opening size. The minimum size for an opening is 0.6mm. It is better to avoid openings that are too small. Otherwise, we risk damaging the coverlay during manufacturing, and the adhesive may squeeze out. It is also essential to consider the minimum distance between the trace and solder mask opening. If the overlap is too significant, the coverlay may not be able to do its job.


A flexible solder mask is a cost-effective alternative to a traditional coverfilm. It is more flexible than a coverfilm, allowing fabricators to create smaller solder pads closer together. They are also more durable than coverfilm, which can be helpful in more applications. The following compares the two materials and their relative advantages and disadvantages. Depending on the specific circuit design, a flexible solder mask may be a better choice for particular applications.

When choosing a coverlay, it’s essential to consider the benefits and drawbacks of each type. A coverlay is a solid sheet with no seams or creases. Its openings must be mechanically created and may display a small amount of adhesive. As a result, the coverlay may be more expensive than a flexible solder mask. On the other hand, a flexible solder mask can protect a more expensive PCB.

While polyimide and flexible solder masks are inexpensive, the adhesives are expensive, and a thin coverlay is better for a tight bend radius. A flexible coverlay’s thickness depends on the thickness of the copper. For example, if your copper is 1oz thick, you’ll need a polyimide coverlay of 1 mil. This material is thin enough to fit an ounce of copper but thick sufficient to encapsulate it fully.

Dielectric strength

One method of improving the dielectric strength of a flexible solvent mask is to incorporate a power source. The electrical power source can be removable or incorporated into the mask during manufacture. In addition, an electrical power source may be a DC voltage source or an electronic circuit that can vary the voltage over a specific period.

The high breakdown strength of a polymer combined with its high dielectric constant is one of the advantages of these composites. We can use these masks in the production of semiconductors and other electronics. In addition, we can change the dielectric constant of a polymer to control the amount of energy stored. The dielectric constant of polymer films can be varied by systematically varying the constituent layers of the composite.

PPC was ideal as a substrate and dielectric. Its surface energy was 47 mN m-1, and the dielectric constant was 3. PPC exhibits good compatibility with organic semiconductors. Further, it is biocompatible. Its surface energy can influence the growth of organic semiconductors. Using PPC as a substrate, researchers have been able to improve the performance of OTFTs.

EMI reduction


There are several advantages of flexible and coverlay PCB in EMI reduction projects. Both are made from epoxy-reinforced materials and provide a consistent dielectric thickness. However, flexible PCBs do not offer EMI shield layer lamination and cannot guarantee maximum protection from electromagnetic interference. On the other hand, Coverlay PCBs are more reliable and are helpful in high-frequency PCB projects.

The most effective way to minimize EMI is to shield the flex sections using a coverlay. We construct a coverlay with an EMI/RF shielding layer using a specialized film. China’s APlus and Tatsuta are good examples. These highly effective films allow for a much thinner flex construction than conventional FR-4. Shielding is significant for low-voltage circuitry, and a flex area coverlay will provide EMI/RF shielding while maintaining an electrical connection.

Coverlay is a layer of insulating film with adhesives that adhere to the copper structure. Unlike conventional solder masks, which have limited bendability, coverlay films adhere to the copper structure. Coverlay films are drilled or cut, making them suitable for small apertures. This film has limited application in finepitch SMD areas. However, the EMI/RFI protection offered by a flexible coverlay PCB is more than worth the cost of the coverlay.

Unlike rigid boards, flexible solder masks can resist EMI. This EMI-resistive solder mask is photo-imaged liquid, allowing almost the same capabilities as rigid boards. However, the flexibility of flexible PCBs requires a larger number of feature openings. Unlike coverlay, flexible solder masks do not require the assembly of multiple openings.




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