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An Overview of Flexible Printed Circuit Boards

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Thur, Jun 18, 2020

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The flexible printed circuit boards, or FPC, are initially designed to replace the original wire connections in an innovative way. The difference is in the end design, fabrication, and functionality. The unique set of rules is of core importance in flexible circuits. Designed from flexible material it doesn’t affect anything in the workflow and it is efficient enough. The FPCB contains a very thin layer of copper that is usually appearing metallic on the first look.

 In 1950 with this innovation in design FPCB the way we built electronics. Now flexible circuits are used in many industries such as automotive, cell phones, laptops, LCD televisions, and antennas.  There are many different kinds of flexible circuits such as one metal layer, multilayer, double-sided and rigid-flex circuits.  To illustrate further, some of them do not have the components attached. But even when there are, the components are considered to be from a flexible family. Flexible printed circuit  ( FPC) is always referring to the same flexible design and  photolithographic technology is at the core of this innovation.

Features of Flexible Circuit Board

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The innovative flexible circuits design many advantages that have been discovered and applied in the industrial field of work. With the market growing some of these advantages include:

Component Assembly - The service mount capability and trough hole that this design offers is a remarkable electrostatic and protective packaging.

Air Gap  - The technology of flexible circuits rapidly increased the flexibility that is mainly achieved by layers with one main advantage “unbinding”. This is an essential aspect of the flexible circuit assembly, allowing the layer to freely flex.

Controlled Impedance  - The engineers finally understood to control the impedance of traces which is responsible for increasing the signal switching speeds and with that in mind now, instead of simple interconnections in the modern digital circuitry are used transmission lines. Today’s end - designs are manufactured in a way that is increasing the speed and minimizing the electrical reflections. This way they ensure no errors between the transitions and the track interconnections. On the other hand, a perfectly designed and optimized controlled impedance can allow great control of the material of the cable and its physical dimensions. With the controlled impedance the requirement of flexible circuit materials is now not a barrier for the industry in order to be able to uniform in both thickness and electrical properties. It is essential to be perfectly designed by the manufacturers and optimized as per its application.

Penalization  - This feature allows the circuit to be durable in components assembly and more specifically during the wave soldering process and in a popular manufacturing segment “pick & place”. Once the panel is completed the circuit is ready for the assembly of the end product.

Pressure Sensitive Adhesives (PSAs) - These types are used in projects and applications that a portion of the circuit has to be extra secured to a specific condition or location in the final product. The assembly process includes a releasing of the liner that is peeled away and the adhesive that remains exposed is allowing the manufacturer to press the circuit in its place and keep it there as long as needed.

Shielding   - Securing is applied when there is a demand for it in the limits of electrostatic and electromagnetic interferences. The shielding can be solid or electromagnetic. Both of the materials are insulating signal lines and any noise.

Manufacturing of Flexible Printed Circuit Board

In general, the flexible printed circuit boards are created by a photolithographic technology one sheet at a time. There is, however, a more efficient way that manufacturers are adopting called R oll T o R oll ( RTR ). Basically, the photolithographic technology is the whole production process, step by step. We will briefly review each step in order to get a basic understanding.

1. Shearing  - The first step is material utilization. The material is being a cutter and adjusted as per the desired end-design.

2. Computer Numerical Control (CNC)  - Basically, CNC is the drilling process. In order for the FPCB to fit the customer's desires, specific holes are being drilled on the board's surface.

3. Plating through hole  - In order for the pattern connection between the layers to be realized, a plated copper on the hole-wall is placed after the drilling. It is done this way because both the top and bottom latter are not conductive.

4. Dry film lamination  - It is laminated to create an etching layer of resistance.

5. Exposure  - The laminated film is driven onto the foul in order to create an exposure area.

6. Development  - Ultraviolet UV light is cast directly on the dry film. This way the exposure area will be polymerized and hardened.

7. Etching  - After the development step, the manufacturers remove the non-exposure area by chemical reaction.

8. Stripping  - The dry film covering is removed which leaves the circuit pattern exposed.

9. Automated Optical Inspection (AOI)  - AOI tested checks the quality of the printed board.

10. Coverlay pre-lamination  - After the AOI check, the board is covered with an insulation layer called “overlay”.

11. Hotpress  - Then the board passes through a hot press machine which forms adhesion between the overlay and the copper.

12. Metal finish  - The bonding area gets coated in order to protect the terminator’s function.

13. Test  - Functional test of the finished circuit design.

Different Types of Flexible Printed Circuit Board Layering

With all the benefits and capabilities in mind along with rigid-flex, we will now take a look at the other different layering types in flexible circuits.

Single-Sided Flexible Circuit

This is the general single-layer design for flex circuits that are laminated in a thin surface of copper. A chemical etching is applied to the copper layer, in order to produce a specific pattern according to the requested design. For environmental protection and insolation, a polyimide overlay is later added to the circuit.

Double-Sided Flexible Circuit

This layering type is called double-sided because the flex circuit has two conductive layers. The interesting thing here is that traces can be created on both sides, specifically for customer requirements. Sides are connected wherever needed by placing a-holes designed in the copper plate. They are famous for the connection between the layers.

Multi-Layer Flexible Circuit

This is the circuit where the combination of several single and double-sided circuits happens. They are a great solution where manufacturers are facing major issues with the circuits with fewer layers. Many individual requirements can be covered and handled flawlessly by the multi-layer circuit design in combination with the high-end manufacturers.

How PCBONLINE Stands Out from FPC Manufacturing Competitors

A manufacturer with a great reputation and background in all types of printed circuit boards, including flexible rigid including all the latest innovations is PCBONLINE. Visiting their outstanding BLOG   is a great way to learn more and more, in order to customize your own design and add as many requirements and configurations as you want before purchase. They provide real-time feedback with professional opinions and quotes, PCB fabrication, assembly, and components sourcing.

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At PCBONLINE , only high-quality management systems are used for every material and electronic component. They are using only reliable and proven sources for ensuring the reliability of your terminal products. They always aim to exceed your expectations by taking the advantages one step further in your service.

When working with them you can expect:

1.  High-quality PCB raw materials with flexibility, ensuring the quality of the source.

Cover Film : TaiFlex, APLUS, RCCT

Material : Dupont, TaiFlex

PI reinforce : UBE, TaiFlex, SKC

Electromagnetic membrane : Fang Bang, Toyo, Sankei

2.  Professional research and development department, with a production and quality management team with years of experience in flexible circuits fabrication.

3.  A variety of different production types as CTP, flexible PCB led strip, Biological recognition, automotive, and more…

4.  Best cost solution deliverable from a variety of different design materials and expert evaluation of manufacturability in the end-design product.

5.  Team of professionals available at your services 24/7

6.  Strictly following the IPC standards in order to ensure the quality of the shipments.

7.  Fast delivery time provides the customers with marketing advantages.

PCBONLINE's online quotation to the public. Register free and you will be rewarded with $100 off coupons to buy custom PCB/PCBA/electronic components. Click the "online quote" button or contact PCBONLINE by email now.