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Flexible PCB – Flexible Circuit, referred to as flex PCB or FPC board. It is made into conductor circuit patterns using light pattern expose transfer and etching processes on the surface of a flexible substrate. The surface and inner layers of double-sided and multi-layer circuit boards are electrically connected through metalized holes. The surface of the circuit pattern is protected and insulated by the PI and glue layer.
Flexible PCB is mainly divided into single-sided flex PCB, double-sided Flex PCB, ,4 layer flexible pcb and other multi-layer flexible board, rigid-flexible PCB board
Rayming is flex pcb manufacturer that provide 1- 12 Layer Flexible PCB Manufacturing services for both quick turn prototypes and production quantities. also we provide Flexible circuit fabrication and assembly services, Our Engineer provide free DFM Checking.
Flexible printed circuit boards provide excellent electrical performance, meet the design needs of smaller and higher-density mounting, and reduce assembly processes and enhance reliability. Flexible circuit boards are the only solution to meet the miniaturization and mobility requirements of electronic products. It can be bent, wound, folded freely, and can withstand millions of dynamic bending without damaging the wire.
It can be arranged arbitrarily according to the space layout requirements. It can also be moved and stretched arbitrarily in three-dimensional space to integrate component assembly and wire connection. The flexible printed circuit can significantly reduce the volume and weight of electronic products. Furthermore, it is suitable for developing electronic products in high density, miniaturization, and high reliability.
Features of Flexible Circuit PCB
- Short: Short assembly time (Reduce 30% hand wiring), All lines are configured, eliminating the need to connect redundant cables.
- Small: smaller than PCB (Rigid board), It can effectively reduce the product volume and increase the convenience of carrying.
- Light: Lighter than rigid PCB, Can reduce the weight of the final product.
- Thin: Thickness is thinner than rigid PCB, It can improve the softness and strengthen the three-dimensional assembly in a limited space.
What are the advantages of flexible PCB?
Flexible PCB is printed circuits made of flexible insulating substrates and have many advantages over rigid PCB:
1. Flexible circuit boards can be bent, wound, and folded freely. It can be arranged according to the space layout requirements. Itcan also be moved and expanded in three-dimensional space, which allows us to achieve the integration of component assembly and wire connection.
2.The use of FPC can greatly reduce the volumeand weight of electronic products(up to 70% saving). It is suitable for the development of electronic products in the direction of high density, miniaturization, and high reliability. Therefore, FPC has been widely used in aerospace, military, mobile communications, laptops, computer peripherals, PDAs, digital cameras, and other fields or products.
3.flexible printed circuit boards also has the advantages of good heat dissipation and solderability, easy assembly and low overall cost, etc. The soft and hard combination design also makes up for the slight deficiency of the flexible substrate in the component carrying capacity to a certain extent.
4.Wiring errors eliminated.
5.Improves electronic packaging – Gives designers the ability to solve packaging and interconnect issues based on the ability to form, bend, and move.
6.Interconnect solution – Reduces the number of interconnects (wire, cables, connectors, PCBs).
7.Electrical integration – Tailored solutions can be created based on the myriad of material choices, plating, and designs.
5 Differences between Rigid PCB with Flex PCB
Flexible PCB Also known as flexible circuit boards,Is rolled with copper or Electrolytic copper as the material,Flexibility is very good, Bending resistance.
Normally we talk about PCB Called rigid board,
The FPC called the fpc flexible printed circuit .Small and medium-sized flexible circuits/s design follows Rigid circuit board design,
But not completely The same with rigid circuit board.Specific differences can be summarized as the following aspects:
1. softness
A standard for flexible circuit boards Is to require good flexibility,
Flexible printed circuit board Three-dimensional space is very important,Because of bending and flexible applications
Can save space and reduce the board layer,Mostly single-sided.Hard board material is Requirements more excellent,
With compression,Wear-resistant high temperature and other characteristics,So the limitations of the space,Common Multilayer PCB.
2. the carrying capacity of the line
Compared with the rigid circuit board,Flexible PCB is Poor,Anything from a straight line to a corner Or different line width changes,Should be smooth transition.We can see a lot Flex PCB with snake-like alignment. The same line width from the hard board Of the current carrying capacity Much stronger than the soft board,So we common
flexible circuit boards applications ,In the place of smaller current,Such as mobile phone cable.
3. the pad design
In the periphery of the pad,There is one from the flexible pcb material changes.Board This area is the soft board
More likely to damage the conductor.Therefore, the pads should be avoided In the region prone to bending.Rigid board does not need to emphasize this problem.
4. the shape of the plate
Regardless of the soft board hard board
Shape will be a variety of,
Flexible pcb fabrication in shape On the general preferred rectangle,So you can better save the substrate,Leave at the edge of the board
Enough free margins, In the shape,
General solution made of circular
Than the sharp inner angle is better,
The inner solution of the light shape is easy
Causing the plate to tear.
Rigid board is a fixed mode,
Depending on the shape of the product.
5. the thickness of the board
FPC is thinner than Rigid board,
Conventional hard board thinnest to do
To 0.2mm has been very good,
While the flexible printed circuit boards Can be thinner than paper,
So in many areas or
There is a good space for development.
From the above can see the Flex PCB
And Rigid boards are different,
Each have their own fields.
Making use of tablets or smartphones comes easy. However, have you ever considered the components? Among these components is the flex circuits.
In this guide, we’ll be teaching you what you need to know about flexible printed circuit board. We will be focusing more on the major characteristics of this PCB.
What Does Flexible PCB Mean?
Flexible printed circuit boards are the best solutions for electronic requirements. You can also refer to them as flex circuits board, flexible circuits, and flex pcb. Basically, this is a PCB that can flex. For this reason, there are different forms with most especially in functionality, design, and fabrication.
Basically, flex circuits are made up of a dielectric layer and a metallic layer bond together. You can make use of many conductive metals; however, the most common of these conductors is copper. Let us consider some of the benefits of flex pcb manufacturer
Benefits of Flexible PCB
The technology of flex pcb offer different possibilities for different products and designs. Its flexible nature is included among the most desired attributes of connectors, wires, cables, and PCBs. Below are some of the benefits of making use of flex circuit .
- Reduction in the overall size and weight
- It reduces the device’s weight by about 70%
- Improves electronics’ packaging
- Allows you to solve issues relating to packaging and interconnection. This is because it can move, form, and bend.
- It is a solution to interconnects; this is because it lessens the amount of interconnects like wires, connectors, pcbs, and cables.
- Conformity as the material’s slender nature makes the production of 3D packages possible
- Electrical integration: Creating custom solutions is easy, making it possible to base your design on different options of materials. Asides from this, you can choose from the different plating procedures and designs.
- Power or ability to handle heat dissipation – flexible printed circuit can withstand high temperatures. Therefore, they are useful for applications having high power.
- Mechanical and electrical repeatability
- Saves costs – you can save about 30% of the cost involved in hard wiring, as well as other processes involved in the flex rigid assembly
- Saves space by about 30%
- They are more reliable because they lack wiring errors
Types of Flexible Printed Circuit Boards
Flex circuits boards come in different types. The type to choose depends on whatever mode of application you’re using.
Single Layer flexible circuit boards
This flex circuit is made up of one conductive layer on one side of the printed circuit board. Actually, it is made up of one layer of copper between polyimide dielectrics. Holes may be formed in the base film. You can do this by soldering so as to allow the passing through of component lead.
Single layer PCBs can find their way through without cover layers or cover coats. However, the major practice in manufacturing this flexible circuit boards usually involves the cover layer.
The amount involved in fabricating this flexible circuit board is high compared to that of rigid PCBs with single layers.
Double Sided flexible circuit boards
This type is made up of two conductive layers, and between them has polyimide insulation. The outer part may either be left open or cover it using a copper pad.
Other elements can be added to the double sided flexible PCB. These elements include stiffeners, pins, and connectors. Some major applications of double sided flexible PCBs include:
- Shielding applications
- Dense surface mounting applications
- Ground and power plane applications
- LCD modules, digital cameras, among others
Multi-layer Flexible PCBs
This has to do with combining several double and single sided fpc flexible printed circuit. These multiple layers are dependent on shielding and/or surface mounted technologies and complex interconnections in order to keep them together.
This type of flexible PCB offers the most effective and efficient solution regarding design challenges. You will therefore need them to:
- Shield applications
- Power ground and plane applications
- EMI/RFI shielding
- Control impedance
- Route the density and layer of a circuit that cannot be done on just one layer
- Increase a circuit’s density
Rigid-Flexible PCB
This connection combines both the rigid and flexible circuit technologies. Majority of rigid flex circuits have multiple layers of flexible circuits which are all connected to one strong and rigid board. This connection can be external or internal; this depends on the application’s nature.
This flexible circuit is often in a state of flex and they may be found on bends. This connection is a bit more challenging because it must be done in a 3D space. This ensures that the design has more spatial and greater efficiency.
Flexible Printed Circuit Board Material
A flexible circuit’s elements must meet the material’s life expectancy and requirements. Asides from this, the material must work with other flexible circuit boards parts. This ensures the circuit’s reliability and manufacturing ease.
In summary, the material’s performance must be improved in order to improve the circuit’s performance. While assembling a flexible PCBs, you’ll need different materials. Let’s consider these materials.
Substrate Overlay
The film and the substrate’s function depend on the insulation medium and conductor carrier. In addition, the substrate must have the curling and bending ability.
Usually, flexible PCB material include the PET (polyester) films and the PI (polyimide) film. Asides from this, other polymer films can be found like aramid, polyethylene naphthalate, PTFE, and more.
The substrate material should be picked up due to the performance and cost of the material. The most common type used by flex pcb manufacturers is the Pi polyimide. It can survive extremely high temperatures thereby getting rid of any possible melting. Also, it can stay elastic and flexible after thermal polymerization.
Conductor Materials
The use of conductor materials, which will supply current efficiently, is needed. In the majority of flex circuits, copper is the major conductor used.
Copper serves as a very effective conductor and is readily accessible too. You can also acquire copper at a low rate compared to some other materials.
Heat dissipation also joins electrical conductivity in requiring a reliable heat conductor. Materials that can remove heat from your flexible circuit can be used. The amount of current the copper will conduct depends on its thickness. Other conductor types that you can consider include Cupronickel, BeCu, and stainless steel.
Adhesives
There are adhesives between the copper and polyimide film in all fpc pcb. You may utilize two major adhesives, which includes acrylic and epoxy. This adhesive material must have the required strength to withstand copper’s high temperatures.
Insulators
With insulators, users are protected from shock whenever electric current passes through the conductor or copper. The best material to serve as an insulator is the polyimide film. Regarding rigid flex printed circuit boards, you’ll combine prepreg and FR4 in the rigid part.
Specification of flexible circuit boards
In designing a flexible circuit, there are some specifications to consider. These specifications will assist the flex pcb manufacturer to know what should be included.
Number of Layers
Flex circuit are of different types. This is why specifying the type that suits your needs is necessary. The different board types come with different numbers of layers. With respect to your specifications, the number of layers could be one, two, or multiple.
This is available in different forms. There’s no particular surface finish for specific applications. With this, you are given the freedom of selecting from the surface finishes available in the industry. These include Gold and Soldering, Immersion Tin, Immersion Silver, Hot Air Solder Level, Organic Coating OSP, Electrolytic tin plating, and more.
Solder Mask
This is also referred to as solder stop mask coating or solder resist. They are available in different forms. It’s important you specify the solder mask type needed and where you want or need it.
You can either place it on both sides of your flex PCB or on one side. Your flex PCB fpc type will also guide you on where the solder mask should be placed.
Copper Weight
This is also very important. The copper’s weight will be determined based on your application. Take note that the flexibility can be compromised by the copper’s weight. Therefore, make sure you don’t compromise on the design’s flexibility.
Spacing
Spacing affects the design’s functionality greatly. With small spacing, the functionality may be compromised, which may cause the whole circuit to experience short circuiting. Make the specifications of your device as wide as possible. The wider it is, the higher your device’s functionality.
Hole Sizes
The holes should be tighter to prevent any issues with drilling. This ensures the mounted components on the substrate are tighter whenever the circuit is flexing.
Quality Tests
Your design has to pass through this process. Quality tests reveal how well your design will function.
Quality Compliance
This makes sure that the design adheres to the quality standards set by the different bodies. The major quality standards that the design must comply with include ISO 9001:2000 and RoHS.
Conclusion
By now, we are sure that your knowledge of flex circuit is top notch. Now, you can make your own designs with assistance from your manufacturer. So, what are you waiting for? Get started today!
Disadvantages of Flexible PCB
1. High one-time initial cost: Since the flex circuit is designed and manufactured for special applications.The initial circuit design, wiring,and photographic masters require higher costs. Unless there is a particular need to apply a flexible printed circuits boards, it is usually best not to use it in a small amount of application.
2. It is difficult to change and repair the flex circuit boards: Once the flex circuits is created, it must be modified from the original design or the light drawing program. The surface is covered with a protective film, which must be removed before repair and restored after repair. Due to the above, it is a relatively difficult task.
3. Size is restricted: flexible printed circuits boards are usually manufactured by a batch method when they are not commonin the industry. This is why they cannot be made very long and wide due to the limitation of the size of production equipment.
4. Improper operation and easy damage: Improper installationand operationcan cause damage to the flexible circuit. As a result, its soldering and rework need to be operated by trained personnel.
Main Raw Materials of FPC
The main raw materials include: 1. base materials, 2. cover film, 3. reinforcement, 4. other auxiliary materials.
1) Substrate of flex pcb
1.1 Adhesive substrate
Adhesive substrates are mainly composed of three parts: copper foil, adhesive, and PI. There are two types of single-sided substrates and double-sided substrates. The material with only one side of copper foil is a single-sided substrate, and the material with double-sided copper foil is a double-sided substrate.
1.2 Adhesive-free substrate
The non-adhesive substrate is the substrate without the adhesive layer. Compared with the ordinary adhesive substrate, the middle adhesive layer is missing and composed of copper foil and PI. Thus, the non-adhesive substrate is thinner than the adhesive substrate. It also has other advantages, such as better dimensional stability, higher heat resistance, higher bending resistance, and better chemical resistance. Currently, it has been widely used.
Copper foil: At present, the commonly used copper foil thickness has the following specifications, 1 oz, 1/2 oz, 1/3 oz. A thinner copper foil with a thickness of 1/4 oz is also on the market. However, this kind of material is currently used in China and makes ultra-circuit (line width and line spacing are 0.05 mm and below) products. With the increasing requirements of customers, materials of this specification will be widely used in the future.
2) Cover film
It is mainly composed of three parts: release paper, glue, and PI. In the end, only the glue and PI remain on the product. The release paper will be torn off during the production process and will not be used again (its role is to protect the glue from foreign matters).
3) Flexible PCB Stiffener
The stiffener is a specific material used for FPC. It is used in a specific part of the product to increase the support strength to enhance the “soft” characteristic of FPC.
At present, The commonly used reinforcement materials are as follow:
- FR4 stiffener: The main components are glass fiber cloth and epoxy resin glue, which are the same as the FR4 material used in PCB.
- Steel sheet stiffener: The composition is steel, which has strong hardness and support strength.
- PI stiffener: The same as the cover film, consisting of PI and release paper. However, the PI layer is thicker, and it can be produced from 2 MIL to 9 MIL.
4) Other auxiliary materials
- Pure glue: This adhesive film is a heat-curing acrylic adhesive film composed of protective paper/release film and a glue layer. It is mainly used for layered boards, rigid and flexible boards, and FR-4/Steel sheet reinforcement board, which plays a role in bonding.
- Electromagnetic protective film: Paste on the board surface for shielding.
- Pure copper foil: Only composed of copper foil, mainly used for hollow board production.
6 Types of FPC
Flexible printed circuits types have the following six distinctions:
- Single flex PCBs: Only one side has circuits.
- Double-sided flex PCB
- Hollow board: Also known as window board (opening on the finger surface).
- Layered board: Two-sided circuit (separate).
- Multilayer flex PCBs
- Rigid-flexible PCB board: Acombination of flex board and rigid board.
Design Analysis of Flexible PCB
The structural design of the flex PCBs is also critical. As some PCB designers do not know enough about the characteristics of flexible printed circuits, the FPC designed is prone to stress concentration problems, which may cause the problem of FPC circuit breakage.
The left FPC design diagram below shows the cover film’s endpoints on the upper and lower sides are designed on the same cross-section. The double-sided adhesive also ends at the same point, which will form a stress-concentrated cross-section. The edge of the insulating layer (cover film, Polymide) of the cable, as shown on the right side of the figure, staggered 1.0 mm to avoid stress concentration and breaking of the flexible cable. However, pay attention to whether the underside of the 1.0mm flexible PCB solder pads are still pressed on the PCB solder pads. Avoid short-circuit with test points or vias nearby.
Let’s look at another illustration. The designer sets the HotBar flexible printed circuits on the edge of the board. The diagram on the left shows the original design. The soldering pad of the HotBar flex circuit falls on the edge of the PCB. However, after production, we’ve noticed a common occurrence of flex PCB fracture, which is concentrated at the edge of the protective insulating layer (cover film). After further analysis, it is found that there is a stress concentration point at the edge of the PCB and the edge of the insulating layer of the flex circuits .
Firstly, to improve the stress concentration point, the strategy is to move the soldering pad of the soft board inside the PCB slightly. Secondly, add double-sided tape, and extend the insulating layer of the soft board forward to cover the stress concentration point of Yuanlai. In this way, not only the strength of the soft plate is strengthened, but the original stress concentration point is also eliminated. After the modifications were applied, the problem of the flexible printed circuits fracture is not detectable.
How do you make a PCB flexible?
The flexible circuit board is highly reliable and made of polyimide or polyester film as the base material. Referred to as a soft board or FPC, it has high wiring density, lightweight, and thin thickness.
Pre-production treatment
There must be a complete and qualified production process to make a good-quality flex PCBs. From pre-processing before production to final shipment, every procedure must be strictly implemented. In the production process, in order to prevent excessive open and short circuits from causing low yield or reduce the problem of Flex PCB scrap and replenishment caused by process problems such as drilling, calendering, and cutting, and to evaluate how to select materials to achieve customer use The best effect flexible circuit board. Pre-production treatment is vital.
Before production, in pre-processing, three aspects need to be processed and complete by engineers. The first is the flexible PCB engineering evaluation, mainly to evaluate whether the customer’s flex pcb can be produced. Secondly, the engineers will review the company’s production capacity to see if it can meet the customer’s technical and pricing requirements. If the engineering evaluation passes, then materials preparation will begin immediately to meet the production process. Finally, the engineer processes the customer’s CAD structure drawing, Gerber data, and other engineering documents to suit the production environment and specifications of the equipment. Then regular production process continues by the delegation of production drawings and MI (engineering process card) to the production department, document control, purchasing, and other departments.
1) Manufacturing Process of Double-Sided Flex PCB
Cutting → Drilling → PTH → Plating → Pre-treatment → Pasting Dry Film → Alignment → Exposure → Development → Graphic Plating → Stripping → Pretreatment → Pasting Dry Film → Alignment Exposure → Development → Etching → Stripping → Surface Treatment → Paste the cover film → Pressing → Curing → Immersion of nickel gold → Printing characters → Shearing → Electrical test → Laser profile or Punching → Final inspection → Packaging → Shipment
2) Manufacturing Process of Single-Sided Flex PCB
Cutting → Drilling → Pasting Dry Film → Alignment → Exposure → Developing → Etching → Stripping → Surface Treatment → Covering Film → Pressing → Curing → Surface Treatment → Immersion Nickel Gold → Printing Characters → Cutting → Electrical Measurement → Laser profile or Punching → Final Inspection → Packaging → Shipment
3) Process Characteristics of flex circuits
- Surface treatment: Immersion gold, OSP, Gold plating, HASL/LF
- Profile: Manual shape, CNC (numerical control machine) cutting, Laser cutting
- Substrate copper thickness: 1/3 ounce, 1/2 ounce, 1 ounce, 2 ounces, 4 ounces
4) Detector
The characteristics of the material of the flexible circuit board have a wide range of applications. To more effectively reduce the volume and achieve a certain degree of accuracy, the characteristics of the three-dimensional space and the thin thickness are better applied to digital products, mobile phones, and notebook computers. The instrument used for flexible circuit board (FPC) testing is an optical image measuring instrument.
What are flexible circuits used for?
The characteristics of the material of the flexible circuit board have a wide range of applications. To more effectively reduce the volume and achieve a certain degree of accuracy, the characteristics of the three-dimensional space and the thin thickness are better applied to digital products, mobile phones, and notebook computers. The instrument used for flexible circuit board (FPC) testing is an optical image measuring instrument.
Communications
Consumer Electronics
Automotive
Medical
Industrial
Aerospace
Military
Transportation
RayMing is an experienced flex PCB manufacturer, able to handle up to 12 layer flex PCB manufacturing and different stiffer requirements (PI, FR4, Aluminum).