Know More About Flex PCB Coverlay film

Flexible printed circuit boards (Flex PCBs) are highly reliable and excellent PCBs made of polyimide or polyester film as the base material. Commonly known as soft boards or Flex PCBs, they possess features such as high wiring density, lightweight construction, and thin thickness. They find extensive application in mobile phones, notebook computers, PDAs, digital cameras, LCM, and other electronic products.

The protective film used on Flex PCBs is called Coverlay (CVL). It consists of various components such as curing agents, methyl ethyl ketone, thinners, and rubber, with the specific proportions varying based on the requirements.

Commonly used flex pcb cover film thicknesses are：

• 1/2mil=12.5+15=27.5um;
• 1/2mil=12.5+25=37.5um;
• 1mil=25+25=50um;
• 2mil=25*2+30=80um;

Flex pcb coverlay film function

Generally, the function of the cover film (CVL) can be considered as follows: it protects the circuit, prevents dust accumulation, provides anti-fouling and anti-static protection by shielding the circuit from exposure to air, and helps prevent oxidation and corrosion of the copper foil. The cover film is applied in areas where gold plating is not required. Additionally, in Surface Mount Technology (SMT), the cover film serves the purpose of a solder mask.

1. The Flex PCB cover film, commonly referred to as a protective film, serves to safeguard the circuit against oxidation and damage.
2. It shields the copper foil from exposure to the air, preventing oxidation of the copper foil.
3. The cover film is applied to areas that do not require gold plating, serving as a protective cover during subsequent surface treatments.
4. In subsequent Surface Mount Technology (SMT), the Flex PCB cover film functions as a solder mask.

Flex pcb coverlay film advantages and disadvantages

Flex PCBs, as flexible boards, also offer advantages such as good heat dissipation, weldability, easy installation, and low overall cost. The design of flexible boards with a combination of soft and rigid areas helps compensate for the slightly limited component bearing capacity of the flexible substrate.

Advantages

Mondo Technology will discuss the advantages and disadvantages of Flex PCB coverlay:

1. The use of Flex PCB can significantly reduce the size and weight of electronic products. It is suitable for meeting the demands of high density, miniaturization, and high reliability in electronic product development. As a result, Flex PCB coverlay has found widespread applications in aerospace, military, mobile communications, laptops, computer peripherals, PDAs, digital cameras, and other fields or products.
2. Flex PCBs can be freely twisted, bent, and folded. They can be arranged according to spatial layout requirements and can move and expand in three-dimensional space, achieving integration of component assembly and wire connection.
3. Flex PCBs also offer advantages such as good heat dissipation, weldability, easy installation, and low overall cost. The combination of soft and rigid design also helps compensate to some extent for the slightly lower component bearing capacity of the flexible substrate.

Disadvantages

1. Changing and repairing Flex PCBs can be challenging. Once a Flex PCB is manufactured, any modifications or repairs require altering the base drawing or the light drawing program, which is not a straightforward task. The PCB’s surface is covered with a protective film that needs to be removed for repairs, followed by restoration, making it a relatively difficult job.
2. High initial cost: Flex PCBs are designed for specific applications, resulting in high costs for initial circuit design, wiring, and photographic plate production. Unless there is a specific need for Flex PCBs, it is generally not recommended for use in low-volume applications.
3. Scale limitations: Flex PCBs are typically produced using intermittent processes, which limits the size of production equipment and makes it challenging to manufacture very long and wide boards. Improper handling during installation can easily damage the delicate soft circuitry. Soldering and rework of Flex PCBs require trained personnel to ensure proper operation.

Flex pcb coverlaly film bonding method

1. Inspect the covering film and film for any missing punches, missing drillings, multiple drillings, flushes, or excessive burrs. Clean the surface dust using an encapsulation cleaning machine.
2. Prepare and clean the work surface, and position the cover film to be cleaned on the board along with the electric soldering iron and other tools.
3. Check the board to be laminated for oxidation, debris, or dust. If any of these issues are found, address them through rework or cleaning before proceeding with the lamination process.
4. Follow the process requirements and MI (Manufacturing Instruction) data to accurately position and paste the cover film. Align the “C” marked line on the board with the pad or alignment hole. For boards with pads, ensure even exposure of the pads when applying the cover film.
5. Proper cover film removal technique: Place the cover film on a light table with the release paper facing up and the cover film facing down. Press one side of the cover film with one hand and slowly peel off the release paper.
6. Once the cover film is aligned with the “C” marking line on the board, use an electric soldering iron to fix it securely, preventing any shifting or detachment. Take care not to burn the product while fixing the cover film with the soldering iron.
7. For single-sided lamination, process the film board at a temperature between 160°-165°. After passing through the machine, allow it to cool down. Then, remove the film release paper and perform self-test based on the alignment holes.

Precautions for lamination of flex pcb coverlay film

1. Wear gloves and finger cots throughout the entire operation, leaving only the two thumbs exposed to prevent oxidation of the board surface and fingerprints.
2. Maintain a clean process environment to avoid any foreign matter on the board’s surface or inside the composite board.
3. Be vigilant during inspection: ensure the cover film is undamaged, without burrs, and suitable for lamination. If any abnormalities such as board surface wrinkles, shrinkage, fog, or scratches are observed, promptly provide feedback and address them.
4. Avoid wearing bracelets, watches, and other metal jewelry while working to prevent scratching the board surface.
5. When electroplating all circuit boards with tin or gold, ensure that the cover film leaves exposed edges for the plating process.
6. Pay attention to the proper handling of the soldering iron, making sure not to exceed the handle to prevent burns.

What does flex pcb coverlay film windowing mean?