Flexible circuit board is a printed circuit made of PI or PET as the substrate, which has high reliability and excellent flexibility. By embedding circuit design on flexible thin plastic sheets, a large number of precision components are stacked in narrow and limited spaces to form flexible circuits. This circuit can be bent and folded freely, and has good heat dissipation. And it is lightweight and small in size, and is easy to install, breaking through traditional interconnect technology. In the structure of flexible circuits, the materials used are insulating films, conductors, and adhesives.
The coverlay on a flexible circuit board is a thin film material composed of an organic chemical plastic film (the same insulating material as the substrate) and an adhesive.
What are the functions of Flexible PCB coverlay?
Printed circuits and wires on flexible circuit boards are fragile and susceptible to mechanical, chemical, and environmental damage. The coverlay provides excellent protection:
1. Dustproof, anti-fouling and anti-static. Protect copper foil circuits from exposure to air, and prevent oxidation and corrosion of copper foil.
2. Cover the subsequent surface treatment, such as covering areas that do not require surface treatment with overlay.
3. It plays a role as solder mask in SMT. During the welding process, the coverlay acts as a solder mask to prevent solder bridging, ensuring the accuracy and reliability of the welding.
4. Enhance the structural strength of flexible circuit boards and improve their mechanical properties during use.
What are the types of Flexible PCB coverlay?
The coverlay is generally composed of three layers: insulation material, adhesive, and release paper. The main colors include yellow, white, black, transparent, etc. In order to meet the special requirements of some customers, the PCB coverlay can also be made in rainbow, green and other colors, but the price is higher. In addition to the original color of the material, other colored coverings are coated with an additional layer of ink on top of the insulation material, which increases the thickness of the covering. There are three common types of covering materials:
1. Polyimide film (PI)
In the flexible PCB filed, coverlay is an essential protective layer and an important guarantee for the stable performance of circuit boards. The PI film is made of high-performance material polyimide, which has good flexibility and reliability. This type of coverlay can easily handle the bending and folding of circuit boards, while also being resistant to high temperatures and able to work stably under extreme conditions. The PI coverlay is also very wear-resistant and can effectively resist dust, wear, and minor scratches, protecting conductive circuit from external influences. For high-performance circuit boards, PI film is like an invisible protective cover, ensuring that the circuit can work properly in various environments. Flexible PCBs with PI coverlay are usually used in high-end electronic products in aerospace, defense and other fields.
The thickness of the PI layer: 0.5mil, 1mil, 2mil, etc;
The thickness of the adhesive layer: 15um, 20um, 25um, 35um, 50um, etc.
2. Polyester film (PET)
PET is a polyester material with good transparency, insulation, and mechanical strength. As a PCB coverlay, it can provide good insulation performance for flexible PCBs. Usually, the thickness of PET film is between 12.5-50μm. PET film has a relatively low price, it can meet various process requirements. Flexible PCB with PET coverlay are widely used in normal electronic devices and consumer electronics products, such as mobile phones, tablets, digital cameras, etc. Different colors of PET films have slightly different properties.
3. Polytetrafluoroethylene film (PTFE)
PTFE film is also called Teflon film, can provide good protection for circuit components in high temperature, chemical, and radiation environments. The flexible pcb with PTFE coverlay are suitable for manufacturing electronic products in extreme environments, such as chemical equipment, pneumatic, gas-liquid flow meters, various level gauges, etc.
How to choose a suitable Flexible PCB coverlay?
Choosing the appropriate PCB coverlay requires comprehensive consideration of factors such as the circuit board usage environment, material characteristics, manufacturing process, and cost. The main points are as follows:
1. Understand the cost, requirements, environment, and failure modes of flexible PCBs to avoid excessive design or insufficient protection.
2. Choose the appropriate coverlay material based on the usage scenario, taking into account parameters such as thickness and flexibility of the coverlay, as well as performance.
3. Choose experienced flexible PCB manufacturers or suppliers who can provide practical and feasible solutions in terms of technology, quality, cost, and other aspects.
How to use the PCB coverlay reasonably?
Reasonable use of PCB coverlay can ensure its protective performance and lifespan in flexible circuit boards. Here are some key steps and suggestions:
1. Before applying the coverlay, thoroughly clean the surface of the circuit board to remove dust, oil, and other impurities to ensure the adhesion of the coverlay.
2. Accurately align the coverlay and circuit board to avoid bubbles and wrinkles. Using positioning tools can help ensure the precise position of the coverlay.
3. Apply pressure evenly during film bonding to ensure good adhesion. You can use pressure rollers or manual rollers to help eliminate bubbles.
4. According to the requirements of the coverlay, heating may be necessary to promote the curing and adhesion of the film. Follow the temperature and time recommendations provided by the manufacturer.
5. After coverlay bonding, check for bubbles or wrinkles and make necessary adjustments. Cut the coverlay beyond the edge to ensure that it completely covers the circuit board without affecting the connection points or pads.
6. The PCB coverlay should be stored in a dry and cool place, avoiding high temperatures and moisture. Be careful when handling the coverlay to avoid scratching or contaminating the surface of the film.
Through the above steps, the coverlay can be effectively used to ensure its protective effect and performance in flexible PCB.
Flex Plus (Xiamen) Co., Ltd. is a manufacturer specializing in the production of flexible circuit boards. The products cover single sided flex PCB, double sided flex PCB , multilayers flex PCB, rigid-flex PCB, split and dual access (back bare) flex PCB, sculpturer flex PCB and other types of flexible circuit boards, which can meet the needs of customers for all kinds of products.
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