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Flex PCB Manufacturing Process

Flex PCB manufacturing is an old process by now. It has reached a point where it is mature. There have been great improvements in materials and packages that make flexible PCB products more attractive. Flexible PCBs used to be limited to specific applications that required their use. Still, as technology develops and new materials come into the market, they are a viable option for most electronics applications because of their sheer flexibility. There are expectations that the market for flexible PCBs will reach about $76 billion in sales by the end of 2027.

Standard vs. Flexible PCB

The main difference between a standard PCB and a flexible PCB is the material. There are two main materials used for flexible PCBs:

ABS is an off-the-shelf plastic for general manufacturing purposes, making it easy to use. Thermoplastics are polymers that change their structure with the application of heat or pressure. This makes materials like PET and PBT highly malleable and strong, and relatively stiff. They are also used for making lightweight parts for vehicles and aircrafts.

A second difference between flexible PCBs and standard PCBs is the fabrication process. Flexible PCB manufacturing requires different procedures than standard ones. Special processes play a big role to make flex PCBs. They involve molding, laminating, surface treatment, cutting, and bonding to form a final product.

FPC Manufacturing Dynamics

Flex pcb press process

The FPC – Flexible Printed Circuit board is a new type of electronic circuit board. FPC is a thin, electrically insulated polymer film that makes it possible to print upon the conductive circuit patterns. Usually, one wraps a thin polymer coating to shield the circuit from damage.

Flexible Printed Circuits are usually used in the electrical industries. It is easy to bent and fold them without causing shorts or any other damage. Instead of rigid circuits in industrial applications, flexible circuits are being used to provide flexibility. Many devices use flexible circuit boards, including televisions, clocks, refrigerators, and phones. FPCs are less expensive than regular circuit boards and are usable in many industries without breaking or bending.

Step-by-step Flex PCB Manufacturing Process

The Flex PCB manufacturing process aims to build a PCB with flex layers. Flex PCB manufacturing is the application of flexible printed circuits. You can spread one or more electrical conductors over a flexible substrate rather than being laying out on rigid copper tracks. The advantages of utilizing flex circuits come from their low cost, small form factor, lightweight, and high flexibility in size.

In addition, we can reshape or remodel these boards to the needs of the application. Therefore, flex PCB manufacturing is especially useful in applications that require continuous modification to the board. Such can be in medical electronics, automotive electronics, and other portable and mobile devices.

The main advantages of using this type of technology are:

  • There’s less chance of creating a physical connection between two parts on the board, which increases its reliability.
  • PCBs with flex layers are less expensive to make because they can be produced in smaller quantities than regular PCBs.
  • They have less connection points, so they don’t have to be as well protected when shipping.
  • Flex PCBs are also easier to produce because there’s less chance of creating short circuits, damaging or destroying other parts.
  • A flex layer is a PCB layer with one or more flex circuits on it, making it flexible and giving it the characteristics of a sheet of paper. Other components such as ground planes, vias, and tracks become part of the board instead.

The manufacturing process of a flex PCB is different from the process of making a regular PCB. The manufacturing process includes:

Concept, Design & Prototyping

Every successful project begins with a good concept and design. It lays the foundation of how the boards will be manufactured, the required materials, etc. This step is crucial for an effective end-product that matches your original idea.

A flex PCB must follow a design that supports expansion and contraction for long periods without breaking. The design undergoes optimization for production, and adhere to smaller design rules. This means the tracks must be wider, which increases the routing complexity.

Design rules are much larger than those used for other kinds of PCBs to achieve similar performance.

We use a prototype to ensure all the components fit together and have enough space. The prototype come from the same materials and methods as the finished product.

You can make prototype boards from different types of materials such as paper, plastic, tape, metal, or aluminum foil. You can even build them on an 8 “x11” sheet of paper for a quick idea.

laser cut flex pcb Coverlay

Material Preparation

Production panels are chemically cleaned before applying a photoresist film to ensure the film will stick properly. There is protection of ultra-thin material cores by a conveyorized process in which there is transportation of cores in a thin, cylindrical package.

Flex PCBs are typically manufactured using FR4 or Rogers 4003 material, a Polyimide-based material. Material selection depends on component placement, production speeds, and solder masking requirements. A buildup process is used, where there are multiple layers of copper material deposited on a base material substrate using a stencil. The copper is then patterned and etched to create the traces and expose the internal components of the board.

Circuit Pattern Exposure

Photoresist coated panels are overlaid with circuit artwork patterns. Circuit board images are being transferred to production panels with collimated ultraviolet light. Such a step exposes both sides simultaneously, if needed.

Circuit pattern exposure is one of the major steps in the PCB build process. It is important to expose copper traces that connect internal components on the board. This process uses a stencil to create a mask for etching copper traces. Patterning and etching are typically done by masking with photomask technology.

Etching

The etching process is very important in creating surface mount boards and creating through-hole designs. We do it using sacrificial material to protect components from damage during the chemical process (etching). In addition, the etching process is a chemical process that removes unwanted material. This process is done in a plating tank using an etchant. Etchants are typically sulfuric acid-based and remove unwanted copper traces and expose pads for drill holes.

Drilling

Drilling happens after etching to create through holes on the board. After drilling, there is exposure of metal pads on the backside of the board. This allows insertion of components into the board through holes during insertion and soldering processes. Capable of high speeds, high accuracy, and small holes. Drilling systems create the desired hole patterns in production panels. In addition, laser-based systems that provide ultra-small hole solutions exist.

Copper Plating

The plating chemical removes unwanted material by filling in pads and traces on circuit boards. Gravity holds the plates on their bottom surface, giving them a flat surface to distribute the chemical evenly onto the board.

Properly leveling conductors and pad alignment of PCBs will make this process easier. The action will reduce losses in gold-plated components.

Coverlay Application

We apply polyimide coverlay panels to production panels before laminating them together. Coverlays come in play after the copper plating process to protect components from damage during drilling and soldering processes. After drilling holes through the coverlay, you apply permanent glue to enclose the components and prevent damage to the board.

Stiffener Application

Apply a stiffener to production panels in a separate process after the coverlay and before the stiffener connection to create strong interconnections between multiple layers of PCBs. Stiffeners are typically fiberglass-based. You apply localized stiffening materials prior to the final lamination process.

After curing coverlays, there is application of stiffeners to stabilize the flex PCB from warpage during soldering, bending, or high-speed inserts. A stiffener is a thin layer of copper material placed on the flex PCB after the coverlay process.

Stiffeners can be on one or both sides of the flex PCB and important as an interface between a solderable surface and an insulation layer. Stiffeners on the flex PCB to increase rigidity, where they are spring-loaded after soldering. Those on one side of the flex PCB are for use as a stand-off, where one stiffener is spring-loaded, and the other is not.

Electrical Test

flex pcb e-test

The electrical tests are for detecting any shorts that may cause board design or operation failures. Electrical testing happens after all processes are complete and after a final visual inspection of the product. This guarantees the quality and reliability of the products produced. In addition, it is important to verify the functions and functionality of internal parts, circuits, and connections of the boards. This ensures that the electronic components on the board work properly and have no short circuits or poor contact points.

We use the electrical test process to detect shorts and opens in the circuit board. The test identifies failed components and any short circuits that may happen during any of the production processes to ensure product quality. In addition, there is need for various electrical tests to ensure that the board is operating properly before shipping out.

Final Fabrication

This step includes a quality inspection, where we visually inspect the boards for irregularities, such as solder splashes or missing components. You can also test the boards during this stage to ensure they meet certain requirements essential for a customer.

Other related processes include:

Surface treatment

The surface treatment is useful in the processing of a flexible PCB to improve the product’s mechanical properties, as some of them are harder than traditional PCBs. One prepares the surface using plasma chemical vapor deposition. It happens using Plasma assisted vacuum lamination or PVD. As a result, it extends the product’s life and helps with dielectric strength when used on an FR4 substrate.

Edge Spacing (Step)

This is the most crucial step of flex circuit manufacturing. This is where all the effort put in by you during design and construction will finally pay off. The proper spacing between laminate layers makes sure that a product fits perfectly into its package or enclosure.

Trimming

You carry out the cutting/trimming process to accurately cut the excess laminate material after the laminating the circuit patterns. It happens before the product enters into final assembly.

Final fabrication consists of packaging and shipping products for use. Packaging can happen in plastic bags or metal containers depending on the manufacturer and end-use product requirement. Flex PCB manufacturing process has been a major development for electronic products. Moreso, it important for those that require flexibility, toughness, and durability.

In recent years, the emergence of new-generation devices and flexible electronics has prompted the need for flexible circuitry in many portable applications. As a result, flexible PCB is in high demand among the electronics industry and applies more in commercial products.

To have a strong presence in the electronics industry, companies have started producing these components by themselves. Recently, flex PCB manufacturing processes have undergone development to include multilayer PCBs with ten or more layers.

Types of Flex PCBs

flex pcb print silkscreen

There are two types of flex PCBs:

Multilayer Flex PCB

A multilayer flex circuit is a printed circuit that consists of several layers of conductive materials and fabricated circuits. The materials and circuits transfer electrical signals between electronic components. Such include integrated circuits and active components like diodes, connectors, switches, actuators, resistors, and capacitors. Flex PCBs are important  in various electronic applications like in-plane connectors, high-speed circuits in computers, automobiles, smartphones, and more.

Multilayer flex PCBs have one or more flexible layers on top of a regular non-flex PCB. This type of flex PCB is easy to bend or deform to meet the needs of the printed circuit board manufacturer. In addition, the  design allows for expansion and contraction without breaking after the production phase.

The Single or 1 Layer Flex PCB

1 layer flex PCB or Single-layer flex PCB has no flexible layers on top of a regular non-flex PCB. As a result, these flex PCBs undergo manufacturing process with larger design rules, making them more expensive than multilayer types.

For every (flex) layer, there are two tracks that go from one side to the other: one for each circuit (device or track). These tracks are the copper tracks and have coatings of copper foil or copper-plated copper.

Single-layer flex PCBs have a rigid core material surrounded by flexible circuits.

Multilayer flex PCBs have a solid core, with some of the circuits being flexible and other layers are rigid.

Knowing the future usage of a part is important when creating or designing a flex PCB. Most likely, the usage could be in a product that has moving parts such as an electrical device, battery pack, or smartphone.

The designer must know how the parts will move relative to each other, how they expand and contract, and what space is available.

Although flex PCBs are more expensive to produce than regular PCBs, they are becoming increasingly popular. The main reason is that they don’t have a fixed shape and you can easily bent or move them when need be. This means their performance does not deteriorate over time, even when subjected to harsh conditions such as extreme temperatures or humidity for many years.

You can accomplish Flex PCBs in a variety of ways. Due to the many choices available, there is a wide range of prices. High-end flex PCBs are expensive, but still relatively inexpensive when compared to their normal counterparts.

4 Layer Flex PCB

This is a 4 layer flexible PCB, which is very thin, cheap, and flexible. It has many alternative methods for processing because it has four layers. You can process these layers separately to allow faster processing time. Also, this type of board is useful in many products that require flexibility and durability.

Flexible Printed Circuit Boards (FPCBs) are PCBs having a two-ply structure that are very flexible, more specifically due to the nature of the form of the film stack. FPCBs are flexible and thin, thereby becoming useful in a very large range of applications. FPCBs are applicable in all types of industries, but consumer electronics, aerospace, and transportation have a higher demand for FPCBS.

The demand for flexible circuit boards is continuously increasing in the consumer electronics industry. We attribute this to new innovations regarding their use in portable electronic devices, including portable computers, cell phones, and PDAs.

2 Layer Flex PCB

The 2 Layer Flex PCB, also known as PCB2L, is a double-sided laminated construction consisting of outer layers with the core material. PCB2L originates from FR-4, but other options are available for making the PCB2L, such as Polyimide film, Teflon, and glass epoxy.

2 Layer Flex PCB is useful in the automotive electronics industry and many commercial devices. Such devices include cell phones, smartphones, TVs, power supply for air conditioners, other appliances, etc. There is combination of these boards with LCD panels to protect them from the mechanical damages caused during shipping and installation.

Flex Technology

flex pcb final quality check

Flexible PCBs play a big role in several industries, including the medical industry. For example, you find these flexible circuits in many surgical devices that can otherwise be quite heavy and fragile. Flex PCBs are typically semi-flexible, supporting most types of forces without breaking or bending.

A key benefit of Flex PCBs is their flexibility and durability. Many products and components used in electronics must be flexible because they usually need to bend and bend when placed into a product. Flex PCBs are not like standard industrial-grade circuit boards, which have rigid electrical connections. If a product needs to bend, these circuits must also be flexible.

The type of flex technology and its use determine a flex PCB’s quality. There are three different types: full, partial, and hybrid-hybrid.

Full Flex:

A full-flex PCB has all the layers on top of each other with limited movement of the flex circuits on those layers. These circuits are good for transmitters and receivers, which always stay in their original position.

Partial Flex:

Partial flex circuits have a stiffer backbone than other types and can bend or twist without damaging or breaking it. This type of circuit is essential for low-flex boards such as connectors with printed boards on them.

Hybrid Flex:

Hybrid flex circuits combine rigid and flexible circuits to create the best of both worlds. It has similar usages as a rigid PCB and you can also deform it when needed.

A flex circuit is an electrical circuit with additional insulation layers between the conductor and outer sheath. This means that it can bend without breaking or shorting out, either electrically or mechanically.

FAQs

flex pcb punching profile

Which material is present in flexible PCB?

Flexible PCBs use layered material. The most important layers are:

1. Protective layer

2. Conductive layer

3. Conductive Injector/layering material (at least one layer of this is required)

Various materials are available in the market to use in making flexible PCBs. They include Polyimide film, Glass Epoxy, Teflon film, Polyester film, and others like paper and glass fiber. However, the most popular materials used in making flexible PCBs are Polyimide film and Glass Epoxy materials.

Polyimide (PI) film is a quite popular material for flexible PCBs, particularly when using a solvent-based process. It is relatively expensive, but it has good electrical properties and mechanical stability. It also needs less time to dry out during the manufacturing process compared to other materials.

Glass epoxy is a cheap and easily available material that is also very flexible. The actual problem with using glass epoxy is that it has poor mechanical properties, so it is not good in flex circuits.

What is Coverlay FPC?

Coverlay is a material important for surface protection of the PCB. It provides protection against scratches, UV radiation, and the aging or discoloration of the board. In addition, it is washable and easy to remove.

We also refer to Coverlay as ‘photo-etched polyester film’ or ‘Flexible Printed Circuit Board Protective Film.’ The main purpose of using this material is to protect the flexible PCB from scratches, contamination, etc. However, it is useful in many other applications like in manufacturing food products to protect them from water, oil, and other contaminants.

How thick is a flex circuit?

You can make flex circuits in various thicknesses, depending on the application. Higher the thickness, lower the flexibility of the product. The most common thickness is 0.2 mm to 0.5 mm.

Final Thoughts

Flexible PCBs are the future of Electronics. These boards allow better bonding and adhesion between components, thereby improving the performance of your product. The flexible PCBs are a great solution for most small form factor devices. Flexible PCBs are a great alternative in many applications that need flexibility plus durability. These types of circuits are almost as thin as paper. You can easily put them into small spaces like notebooks, smartphones, and more (depending on how big they are). We hope this article covered everything about Flex PCB manufacturing; if you have any queries, feel free to drop us an email.