Circuit boards play an essential role in the electronics industry. This is because they are widely used to play various roles in devices such as computers, televisions, and power systems. Printed circuit boards consist of conductive tracks that interconnect components on the board. They include potentiometers, resistors, capacitors, and switches with various voltage or current levels. They are also typically used for electrical safety testing or verification.
According to JIS C5017, the Japanese industrial standard for measuring the mechanical properties of printed circuit boards, a flexible printed circuit (FPC) is a PCB with a cylindrical or rectangular shape that can change its dimensions depending on the requirements of its application. The standard classifies FPCs into two categories: rigid-type and flexible-type. Rigid-type FPCs help connect parts mechanically but cannot bend. The flexible-type FPC is a double-sided PCB that can withstand bending forces. Additionally, we mainly use it in electrical interconnection applications.
FPCs have become popular among engineers due to their easily modified and customized without any solder joints. The flexibility of the FPC allows for different retrofit solutions. It significantly reduces the cost of printing new boards for a specific application. For example, adding functionality onto the face of an existing board is easier than creating a whole new board from scratch.
Composition of an FPC PCB material
The composition of an FPC material depends on its intended application and end-use. The flexibility of the FPC relies on the material’s ability to resist cracking, warping, and mechanical damage while maintaining high conductivity. As a result, manufacturers tend to make FPC flexible printed circuits from fiberglass or FR-4 materials. It consists of a mixture of epoxy resins and glass fibers. FR-4 is a rigid board that combines both thermal and electrical properties.
1. Insulating film
It is a layer of high-density polyethylene, which is made by extruding resin through a nozzle and applying it over the substrate. The HDPE film eliminates capacitive coupling between the substrate. It also eliminates other circuits to electrically shield interconnections on top of the board. The HDPE layer also serves as a vapor barrier to prevent moisture from entering the circuit during curing.
2. Electrostatic adhesion layer
After applying the HDPE film, an adhesion layer may attach components. These components may include potentiometers and LEDs to the circuit board to improve performance or decrease cost. The adhesion layer is acrylic or polyimide and allows LEDs to bond directly to the FPC, saving materials and assembly time.
3. Conductor
We then add a conductive layer over the top of the adhesion layer. This layer could be a polyimide or epoxy resin or a printed circuit board itself. To avoid warping, we can apply the conductor to a solution that is 100 °C.
4. Enhanced board
Lastly, we add the second layer of adhesion over the conductor to further decrease flexural or cracking problems. We usually make this layer using cellulose or acrylic.
FPC circuit board fabrication
To fabricate an FPC PCB, the components are first pre-assembled onto the board and then cut to size. The FPC material is then placed inside a mold to bend without breaking. Typically, we heat the FPC material to 120 °C for approximately 1 hour. Do this to achieve the necessary stiffness, which allows the material to resist flexors and bend easily. Components are then added to the mold and subjected to pressurization, which causes them to become embedded into the FPC.
Next, we apply a layer of conducting ink over the top of the components. It helps create a smooth surface that prevents electrical resistance and improves performance.
5. Coverlay
A coverlay is a top plate made from either polyimide or acrylic. The coverlay protects the underside of the FPC material. It also serves as insulation to prevent moisture from entering the FPC material. The coverlay also has high-temperature resistance, allowing us to use it in ovens and heaters.
Why do you need to use FPC PCB
We use FPCs in applications when we require flexibility and conductivity. However, we do not use it when we need mechanical strength. Since FPCs are thin and lightweight, we use them in portable devices such as cell phones, digital cameras, and walkie-talkies. We can use them in larger devices such as peripheral and power supplies.
RayMing PCB and Assembly developed FPCs to create light products that one can design quickly without adding much weight.
1. Reduce weight and space
Since FPCs do not have terminals for electrical connectors, we can use them in devices that need to be light but need to connect the output of many components. For example, a portable GPS device can use an FPC to connect a small battery to the main unit. The main unit has an internal rechargeable battery. However, the GPS receiver also needs a power source and several other functions such as a display and buttons. The FPC provides all these components, connecting them.
2. Easy customization
FPCs are flexible, and we can cut them to the desired size. Since they are not soldered, they can be easily removed from the circuit board and modified for new uses. You can make a whole new electronic product by adding an FPC with additional components onto a board already used for another purpose. For example, we can add an FPC to connect an external battery to an existing product. They include a car radio, increasing its functionality without completely replacing it.
3. Meet dynamic flexing requirements
We use FPCs primarily on portable devices with their flexibility and low weight. They can conform to flexible products like a cell phone or cut them to the desired size for a new circuit board. These properties make them an ideal choice for use in consumer electronic products.
4. Flexing for easier installation and service
We use FPCs in solar panels for homes and buildings, satellites, power generators, and electric vehicles. One can install solar panels easily in places where they cannot build a roof, or the landscape makes it difficult. The flexibility of these FPCs means they can conform to many different environments while still providing an electrical pathway between the various components. We also use FPCs in electric vehicles. This is because they have a lightweight structure while maintaining the required strength to ensure they will not break when driven.
5. Impedance control
Manufacturers make FPCs of high-quality materials and have high electrical conductivity. So, we also use them in consumer electronic products that require impedance control. The main advantage of using FPCs instead of soldered connections is that we can easily control the impedance, which is necessary for mobile devices like cell phones.
6. Expandability
We need to expand some electronic devices such as solar panels or electric vehicles later. This is due to technological advances or improving user needs. These products can use an FPC to connect to various other components that we can add later as we require new functions.
7. Increase reliability and repeatability
When we use FPCs in solar panels, we weigh the FPCs and mechanically test them to remain steady once installed. This process ensures that the product will be reliable and operate smoothly in many different environments.
8. Thermal management
Products that we can design use FPCs with good thermal management. Since we cannot solder an FPC to the main board, we can move and replace it with another one to change its thermal properties. This process ensures that the product will always perform well.
9. Improve aesthetics
We can design FPCs to be very thin to reduce the size of the final product and make it look very nice. By printing components on a thin film instead of inside an FPC, one can achieve this. Manufacturers print the components on top of the FPC. It still appears connected to it while retaining its function and appearance.
10. Eliminate connectors
FPCs can eliminate the need for connectors because they can be easily removed and reconnected to other boards. Since there are no connectors and terminals, you do not need to disassemble the product every time you access a cable. You can then reconnect the FPC later, reducing production costs and ensuring that the product looks clean.
11. Reduce assembly cost
FPCs can reduce the assembly cost in many cases. For example, semiconductor companies need to add new components to their production lines. We can use the FPC with other components to create a circuit board. This increases the product’s functionality while decreasing production costs.
12. Increase scalability
FPCs can connect many components onto a central board to create a larger device. Since they are flexible and have low weight, we can assemble these boards into a large product that provides high-performance features.
13. Provide uniform electrical characteristics for high-speed circuitry
Since companies manufacture FPCs using the same high-quality materials and techniques as optical fiber, they provide reliable electrical characteristics for high-speed circuitry. As a result, these circuits can operate at very high speeds without becoming unstable.
14. Improve signal integrity
We can design FPCs to improve signal integrity by reducing noise and reflection. They can also enhance transmission performance and resistance to electromagnetic interference (EMI).
Flexible Circuit Options
The text above demonstrates that FPCs are ideal for various applications. Also, we can replace traditional circuit boards. The polyester (PET) and polyimide (PEEK) materials used in FPCs are conductive. So, they can connect to other circuits and components. They also provide mechanical protection for more robust products. The 1oz thick, Type-V-PET substrate used in the FPC is flexible and can carry large amounts of current. It also withstands high-temperature variations at the same time. This makes it ideal for high-power applications such as solar panels.
Layer 1
We form the “graphic overlay” at this stage. One first cleans the surface, prints the screen, and then cures it to ensure a high-quality printing process with repeatable properties. Layer 1 is where most of the modifications take place. We print the silkscreen or other overlay patterns. We do this usually in a CMYK format, using high-quality inkjet printers to ensure the sharpest possible image.
Layer 2
The lamination stage involves adding the electrical traces. This layer is an electrically conductive adhesive, laminated with the first layer to form the final FPC product. The adhesive must provide a smooth surface to achieve electrical and mechanical stability. We can achieve this via vacuum or pressure lamination, depending on how rigid or flexible the final product needs.
Layer 3
This is the essential layer, as it provides a strong mechanical bond between the first and second layers. One of the most popular adhesive options is a thin ceramic-based adhesive that provides excellent mechanical properties. We can apply this using either hand or automated systems to ensure consistent production quality at each location.
Layer 4
The final layer determines the physical look and feel of the FPCs. The thickness of this layer can vary depending on various factors. They include material type, application requirements, and production location.
We use Flexible Printed Circuits (FPCs) in many different applications such as solar panels, electric cars, and aircraft. Also, we use them in new applications such as aerial drones and wearable electronics. So, FPCs must provide reliable electrical characteristics for high-speed circuitry. The makers of FPCs use more than 20 different chip types and a wide range of specialized components to create the final product.
Difference between PET and FPC
PET is a polymer that we commonly use in FPCs. PET has a low thermal expansion, and it is also transparent, which means we can use it for solar panels or as display panels. On the other hand, FPCs are flexible for high-performance display screens or indoor uses.
Flexible Printed Circuit Board (FPC) is a flexible circuit board with low cost and significant saving of transportation space. When we apply the PCB with many components, their size becomes large. Because of the flexible key feature, the manufacture and construction of the FPC become easy.
Flexible Printed Circuit Card (FPC) combines integrated circuit (IC) and thin-film printed circuit traces. We use them to make a flexible circuit board. A flexible printed circuit card is an electronic device used to house an integrated circuit (IC).
Flexible Printed Circuits (FPC) are thin plastic sheets that we can use in applications. Some examples include solar panels, electric cars, aircraft, and new applications such as aerial drones. We make FPCs from electrically conductive, flexible plastic. One etches and prints the top layer of the plastic with various circuits and components. This helps to create circuitry that is thin enough to be flexible while also being durable.
Flexible Printed Circuit Cards (FPCs) are helpful in many different applications. They include solar panels, electric cars, and aircraft. We also use them in new applications such as aerial drones and wearable electronics. So, FPCs must provide reliable electrical characteristics for high-speed circuitry.
Trace Width Benefits
One of the enormous benefits of FPC technology is maintaining high line widths, which leads to increased performance. This performance improvement is significant for wireless applications. There is a critical difference between the time it takes for radio signals to travel from one point on the board to another and the time it takes for the signal to become disrupted by noise and interference. Higher line width allows for greater signal integrity by reducing these delays while increasing data rate and transmission range.
Another benefit of FPC technology is low dielectric constants (low εr). Compared to other materials, such as FR-4, PET allows for smaller trace widths and increased performance. Using a low εr in FPC traces also reduces line width variation, which results in improved signal integrity.
Electrical Characteristics
FPCs offer several electrical benefits that are largely due to the use of PET. As previously mentioned, PET is a low dielectric material, and, as a result, FPCs using PET can achieve lower line width variation. Reducing line width variation leads to improved noise immunity and signal integrity.
FPCs also allow for easy routing, which results in improved manufacturing yields. Low temperature co-fired ceramics (LTCC) and silicone is also helpful in the FPC process. It provides circuitry with enhanced thermal performance.
The most common FPC fabrication method is transfer printing. This is because it involves transferring electronic ink onto a surface. Then the etching away portions of the surface to create circuitry. Transfer printing allows for very high-speed processing capabilities. We might need circuits that support wireless communication (e.g., WiFi).
Manufacturing Processes
FPC manufacturing is a complex process that involves the use of many different materials and processes. We can make FPCs by transferring ink onto a flexible substrate. This creates circuits and removes substrate portions to expose the circuitry. We then transfer the ink using an ultra-sensitive printer that applies 500-800 g/cm² of pressure.
The ink used in FPC manufacturing includes a mixture of photoinitiators and photoresists. This allows for high-speed propagation. We can print the desired areas of the circuit first. Then we deposit a thin layer on top of the printed area as an etching mask. The exposed areas are then etched away using oxygen plasma to produce the desired circuitry.
The final step of the FPC manufacturing process involves cutting the circuit into appropriate shapes. The circuit must be thin enough to flex with any movement and thick enough to maintain durability and functionality. The thickness of FPCs typically ranges between 0.031 mm and 0.065 mm. However, it can also be as thin as 0.01 mm or even thinner for special applications (e.g., wearable electronics).
Applications Flexible Printed Circuit Board
FPCs have numerous applications in multiple different fields. We use FPCs in solar power cells, cell phones, vehicles, and aircraft. Many of these applications require flexible sheets that are thin and durable. So, they can survive bending, folding, or rolling.
1. Hybrid Electronics
These are a type of electronics with both organic and inorganic components. Hybrid electronics are helpful clothing or building materials with embedded electronic devices.
2. Wearable Electronics
Wearable electronics include everything from fitness trackers to glasses and other products we wear on the body. We have been using FPCs for wearable electronics. This is because of their extremely thin, flexible, and transparent properties. It makes them perfect for integrating clothing and other clothing items.
3. Wireless Communication
We have been using FPCs in many different types of wireless communication. They are good since they offer very high speed and low-power capabilities. They are essential on portable devices such as cell phones, laptops, tablets, smartphones, and more. Many of these products require flexible sheets that can bend without damaging the circuitry. Flexible FPCs enable these products to be ultra-thin and durable. They also offer a range of benefits, such as easy routing and simplified designs.
4. Connectors
We use FPCs in all connectors, including low, high and ultra-high temperature versions. FPC connectors are also essential high-speed cables. They include fiber optic cables and miniature radio frequency coaxial cables (e.g., CAT6).
5. Connector & Housings
FPCs are essential in the connector and housing industry because of their versatility and ease of use. Many companies use FPCs to connect many products, including cell phones and other portable devices. Others also use FPCs to house components such as LEDs and capacitors.
6. Printed Circuit Board
FPCs are essential in printed circuit boards (PCBs). They also work best in sheets of circuitry printed onto a flexible substrate usually made with PET or laminated silicon dioxide. FPCs are ideal for PCBs because they can withstand high temperatures. They can also easily integrate into the board and provide excellent flexibility.
7. Portable Devices
FPCs are applicable in the portable device market because of their thin and durable properties. One of the essential properties of FPCs for this market is that we can fold, roll or bend without damaging them.
8. Solar Power
FPCs are perfect for solar power because of their flexibility, thinness, and environmentally friendly properties. We use them in electronics that convert light into energy. They include solar cells, photoelectrochemical cells, and more. These cells are flexible, thin, and durable and provide high efficiency for solar power.
How much does FPC cost?
Most producers and sellers determine FPC pricing by the type of application, component, and quantity. For example, a small FPC order for a cell phone used as a business card we can price individually. On the other hand, if we use FPCs in solar cells or an aircraft control system, we could price a larger order that includes more components as one order. The FPC pricing is also affected by the type of product or component. For example, flexible FPC PCBs are essential in smaller orders than rigid FPCs. This is because of their lower setup costs and the smaller quantity of the order.
F-LGA and L-CUP are two common flexible printed circuit board types, which are perfect for various applications.
F-LGA is a type of connector commonly referred to as a micro-connector for its small size. This connector has a unique design suitable for applications. They require reliable, low-cost, and lightweight connections. F-LGA is a type of flex PCB used for high-frequency connections in mobile phones, pagers, portable telephones, video cameras, and more.
L-CUP is a connector with an LC interface designed for signal transfer between fiber optic cables used in network equipment such as routers, hubs, and switches. This connector features a high transmission rate with excellent repeatability. L-CUP is a type of flex PCB used in photovoltaic solar cells, medical devices, and aerospace equipment.
Conclusion
FPC is a flexible component used in a wide range of applications. Because of FPC’s versatility, we can use it in many different applications that need an embedded component with high durability and low cost. This flexibility and capability make FPC circuit an ideal component for many items, including solar cells and cell phones.
