What are flexible led pcbs?
Printed circuit boards enable seamless device functionality by connecting electronic components, and the field of flexible printed circuit technology has been constantly evolving. These circuit boards can be used in major electronics industries such as consumer electronics, the automotive industry, and the aerospace industry. With the rise of flexible led pcbs, the traditional technology of different parts of electronic devices or circuits has undergone a radical change, and due to the adaptability of connectors and their small size, flexible pcbs can significantly reduce size and cost compared to rigid pcbs.
- The flexibility of flexible led pcbs allows them to bend and flex, giving application designers and operators more creative freedom, as standard rigid circuits cannot accommodate the ability of flexible circuits to adapt to tiny or irregular shapes.
- Flexible led pcbs also have the advantage of occupying less space, thereby reducing the load on the application motherboard, and the utilization of available space can also improve thermal management, thereby reducing the amount of heat that needs to be released.
- When electronic components are exposed to continuous vibration and mechanical strain, flexible led pcbs may be safer and more robust than rigid pcbs, so traditional connection methods that rely on soldering wiring are replaced by flexible printed circuits.
Electrical devices used in various industries are susceptible to constant mechanical strain and vibration, and they all need reliable connections to operate, and this is when flexible led pcbs ensure reliability, long life, and low maintenance.
led pcbs are circuit boards used to support and connect light-emitting diodes. In other words, it is a pcb for LED chips. After receiving power, the chips emit light to operate lights or other fixtures, displays, signs, etc.
These pcb types may contain a few to hundreds of light-emitting diodes or chips. They also come in a variety of forms, depending on the required functions and application environments, such as the type of equipment.
For example, it can be a round board for lamps, a flexible light strip, or an LED matrix for panel lighting and displays. That is, a typical pcb board for LED assembly contains the following main parts:
The light-emitting diode or semiconductor device that emits light when connected to a power source
The core or substrate. This part can be made of a variety of materials, such as traditional FR4 or flexible materials, such as polyimide.
The traces that connect the diodes and other components. Usually copper
Solder mask or layer that covers and protects the surface
Silkscreen that forms component markings and other information
What are the materials of pcb?
Printed circuit board materials are the basic elements of pcbs because they provide the required foundation and shielding for multiple layers and establish electrical connections between copper-containing layers that make up certain electronic components. Flexible led pcbs use the same components as any other pcb, and the materials work in the same way.
- Base layer
Printed circuit boards are built on top of substrate layers, which are usually made of fiberglass because it is a very hard material that provides rigidity to the pcb. However, other substances can also be used as backing materials, examples of which include FR-1, polyimide, insulated metal substrates, epoxy resins, and G-11. Materials are specially designed to meet requirements such as dielectric constant and glass transition temperature, and the most commonly used substrate material is FR-4. - Conductive layer
The copper layer is the conductive layer that forms the signal lines, which are the circuits that conduct electricity. Other common conductive layer materials that can be effectively utilized are gold and silver, however, almost all conductive layers on pcb designs are composed of copper because copper is an efficient conductor of electricity. - Solder Mask
The solder mask has a thin layer of polymer coating that is placed along with the copper layer on top of the laminate. Moreover, the solder mask gives the LED flex pcb a green color and this layer helps the pcb manufacturer to solder the correct locations on the board, thus preventing the formation of solder bridges. - Silk Screen Layer
Epoxy is commonly used for silk screen printing on the circuit board, and it also acts as a reference indicator that helps in the placement of components on the board. It helps in identifying different warning indicators, and the silk screen helps in locating the test areas and manufacturer markings.
How to Choose the Right Material for Flexible led pcbs
Flexible led pcbs are becoming more and more common due to their expanding dominance in the market and rapid technological improvements. This is because LED flex pcbs can be used for a variety of purposes due to their thin, flexible, and lightweight properties. This has been made possible by the creation of innovative LED flex pcb manufacturing technologies. Since the efficiency of substrate materials affects the basic characteristics of pcbs, improving the operation of substrate materials is essential to improving the technical capabilities of pcbs.
Let’s discuss the various types of materials used in flexible led pcbs and see which characteristics are most beneficial in the production process of flexible led pcbs. 1.Film substrate material
The film substrate material is a useful material because it can serve as an insulating medium and conductor carrier between circuits, and it must also be flexible enough to bend and curl.
- The choice of substrate composition should be based on its effectiveness and economy, but for flexible copper clad laminates, PI (a thermosetting resin that becomes inflexible at high temperatures) is usually the recommended substrate medium. Because PI has excellent electrostatic properties and significant heat resistance, it can continue to maintain its flexibility and plasticity throughout the thermal polymerization process, unlike many other thermoplastic resins.
In addition to having higher stability, the improved PI material also has tear resistance and strong moisture retention. - Whether it is a flexible copper clad laminate or a rigid copper clad laminate, halogen-free environmental protection requirements are required. This is an inevitable and strict trend in the electronics industry. Six types of hazardous compounds have been banned in electronic devices including flexible pcbs.
- Adhesives are used to bond copper foil and substrate films. They can be roughly divided into four types: acrylic, PET, modified epoxy resin, and PI resin. Among them, modified epoxy resin and acrylic resin have strong adhesion and are used more.
There are thousands of materials that may be used for a pcb, and some of them are definitely suitable for the production of flexible led pcbs. This is also the reason why new flexible led pcb substrate materials are needed as the use of flexible led pcbs becomes more and more widespread.
2.Double-layer PI substrate material
When double-layer flexible CCLs are used for flexible led pcbs, they are more suitable for environmental protection and can meet the requirements of lead-free soldering by increasing the temperature because it does not contain glue that may contain halogens. There are three different methods for manufacturing 2L-FCCLs – film coating, lamination, and electroplating. After comparing the three methods, it is clear that copper foil and thinner substrate materials can be obtained at a reasonable cost, and electroplating a metal layer on a polyimide film is a simple process. Thin film coating is suitable for cheap mass manufacturing because the lamination effect is very good when manufacturing double-sided boards.
3.New copper foil
Copper or copper foil is the main conductive material used in flexible led pcbs, but alloys such as aluminum, nickel, gold and silver are sometimes used. Based on the different production processes used, copper foil is divided into two categories – rolled annealed (RA) copper foil and electrodeposited (ED) copper foil, which vary in the crystal form. The columnar array geometry of RA copper foil gives it a smooth, uniform structure that is easy to etch and roughen processes, while fish scale is a property of ED copper foil that makes the copper foil smooth, durable, and cannot be roughened or etched. When it comes to dynamic flexible led pcbs for circuit boards that require high flexibility, RA copper foil is usually used. Currently, ED copper foil is the main component of high-density flexible pcbs, and the new requirement is compatibility with mass production of pcbs with a pitch below 50 μm.
4.LCP substrate
Liquid crystal polymer (LCP) is a recently invented material that fundamentally changes the shortcomings of polyimide substrate materials. Single-sided or double-sided CCL is made by covering the thermoplastic LCP board with copper foil and continuously heating and pressing. This CCL has a water absorption rate of only 0.04% and a low dielectric constant, which can meet the requirements of high-frequency digital circuits. The advantages of TLCP include the ability to be formed and manufactured by pressing into a film, which can be used as a flexible led pcb substrate material. In addition, it can be recycled and reused after secondary processing, which is why flexible led pcbs began to use TLCP. This material also has other advantages such as low moisture absorption, high-frequency compatibility and thermal dimensional stability, and has become a sought-after material for pcb construction.
5.Halogen-free materials
WEEE and RoHS prohibit the use of six different categories of hazardous materials and the disposal of waste electrical and electronic equipment, so these regulations currently prohibit the use of lead in surface coatings and bromine used as flame retardants in pcbs. With the advancement of technology, it is now possible to use halogen-free substrates in both flexible and rigid printed circuit boards, because various flexible substrate materials (including reinforcement boards, prepregs and solder masks) are halogen-free and flame-resistant.
6.Photosensitive PI cover film
PIC emerged because standard PI cover layers could not meet flexible pcb standards, such as high density and environmental protection, and PIC also has high flexibility tolerance. Due to its strong bonding, good flexibility and high resolution, liquid PIC has been widely studied and has a variety of applications, however, limited dimensional stability is a disadvantage of PI.
7.Conductive silver paste
Printed conductive coatings have the characteristics of good connectivity, low resistance and strong adaptability. Conductive inks are mainly composed of silver particle pastes and can be printed on insulating materials, including wiring or shielding materials generated during the manufacturing process of these circuit boards. This silver paste can produce images for RFID objects, meeting the requirements of low resistance and high adaptability. Flexible led pcb components made with conductive silver paste are certified for humidity testing, high temperature storage, and high and low temperature cycle performance, and are of high value.
Applications of Flexible led pcbs
led pcb boards are adaptable, cost-effective, efficient, and offer a variety of design options. These qualities allow them to be used in many environments. Most applications are in the world of lighting. Most modern lights use light-emitting diodes, and this pcb type is standard in many lamps, from household lamps to those installed in offices and commercial or industrial facilities. Today, outdoor lighting is also gradually becoming LED-based. In the automotive field, LEDs are widely used, and most car lights use this technology. These pcbs are the backbone of advertising and other displays, supporting light-emitting chips and providing excellent heat dissipation capabilities.
