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- January 30, 2023
- PCB knowledge
- (0)
- 06 mins
Flex circuit -an ultimate guide for you to get started
A flex circuit is also known as a flexible printed circuit board. It is a PCB meant to be twisted and turned in various ways. Its main composition is a thin, flexible material that you can fold and bend. A flex circuit is used in many electronic devices.
There are many applications where a conventional rigid PCB might not work well. Such examples include devices with a small form factor and those that need to be bended and folded frequently.
A flex circuit can also be applied in high-density, high-speed applications where a rigid circuit would be impractical due to heaviness.
What is flex circuitry?
Flex circuitry is a flexible, twistable, and foldable printed circuit board. They are made using a flexible substrate and have conductive traces on one or both sides. The amount of space present or the complexity of the circuit will determine whether to use a single-layer or multilayer flex circuit.
While the flexible substrate can be from polyimide, the conductive traces can come from gold, silver, or copper.
Flex circuitry has several applications, including in consumer electronics such as laptops, smartphones, wearable devices, and many more. It is also applied in the medical, military, and aerospace sectors. Automotive and industrial applications equally rely on flex circuitry.
How thick is a flex circuit?
The thickness of a flex circuit will highly rely on the materials used and its specific design. Thickness typically ranges between a few hundred micrometers to a few millimeters. The number of layers within the circuit determines the thickness. Other factors that equally affect the thickness of a flex circuit include the thickness of the conductive traces, specific application requirements, and the thickness of the substrate material.
Typically, single-layer flex circuits are thinner than their multilayer counterparts. Therefore, when designing an electronic device, all considerations must be put into place – including the thickness of the flex circuit.
What are the flex circuit materials?
A flex circuit is made up of different materials, including the following:
- Coverlay – it protects the surface of the flex circuit and the conductive traces. It is made up of PET or polyimide.
- Adhesive material – bonds different layers of the flex circuit. It attaches it to other components within the circuitry. Acrylic and epoxy are examples of the most used adhesives.
- Conductive material – creates the traces found on the flex circuit. Gold, silver, and copper are some examples of conductive materials used.
- Substrate material – this is the base of the flex circuit. It offers structural support for the circuit. Typical substrates include PET, polyimide, and PEN.
- Other materials – some other materials that can make up a flex circuit include stiffeners, vias, and connectors.
What are flex circuits used for?
Flex circuits have various applications across different industries and sectors. Aside from consumer electronics, they are also used in the medical, military, and aerospace sectors. Here’s a list of the uses of a flex circuit:
- Test and measurement equipment.
- Telecommunications equipment.
- Industrial control gadgets.
- Automotive industry.
- Consumer electronics.
- Military applications.
- Aerospace equipment.
- Medical devices.
Flex circuit design
There are numerous PCB layout software and tools to assist with flex circuit designing. These tools include design rule-checking software, simulation tools, and CAD software. However, working with an experienced flex circuit manufacturer would be best. This will help you ensure that the design meets the application’s requirements. It will also guarantee successful manufacturing.
When designing a flex circuit, it is essential to follow certain principles. Here are some important ones to have in mind:
Cost
How much will the project cost? The design should meet the project’s budget, bearing in mind materials, manufacturing processes, and other factors.
Manufacturing
What’s the feasibility of manufacturing the design while considering the availability of materials and cost?
Signal Integrity
Minimize signal loss and crosstalk. The signal integrity should remain intact during the expected range of operations.
Durability
The circuit should easily withstand environmental factors such as mechanical stress, temperature, and humidity.
Flexibility
The circuit must be flexible enough to contain bending and the expected range of motion.
Circuit Layout
Plan the layout in such a way that it functions as intended. In addition, it should meet the set requirements of its application.
How is a flex circuit made?
When manufacturing a flex circuit, the following steps are necessary:
- Design is the first step, which involves creating a detailed design of the circuit.
- Material selection – what follows is the selection of the materials that make up the flex circuit.
- Circuit patterning – using a photolithography process, a circuit pattern is created.
- Etching – The pattern created is transferred to the conductive material using an etching process.
- Laminating – using heat and pressure, the flexible substrate is bonded to the rigid backing material in the lamination process. This ensures durability and mechanical strength.
- Drilling – drilling holes on the flex circuit allow easy mounting of components.
- Plating – plating with a layer of copper or any conductive material helps protect against corrosion and boost electrical conductivity.
- Soldering – the soldering process helps to attach PCB components to the circuit.
- Testing – the last step is to perform various tests on the flex circuit and check for errors. It should meet the required standards and specifications.
How do you solder a flex circuit?
Soldering involves melting low-melting-point metal to ensure a permanent bond between two metallic surfaces. When soldering a flex circuit, here’s what you need to know:
- Solder quickly and minimize the amount of heat.
- Use flux to improve the wetting of the solder.
- Use a heat sink or other preferable protective measures to prevent damage from the soldering heat.
- Use a soldering iron tip to apply heat to a specific area and prevent overheating surrounding areas.
- Use a low-temperature soldering process to prevent any damage to the circuitry.
The general process of soldering a flex circuit is as follows:
- Clean surfaces to be soldered and soldering iron tips.
- Apply flux to the joint area.
- Apply solder to the joint area using the soldering iron tip.
- Allow it to cool.
- Inspect and test for errors.
How to find a flex circuit manufacturer?
Here are some of the ways you can use to find a credible flex circuit manufacturer:
- Attend trade shows to meet manufacturers and understand their capabilities.
- Search online for credible manufacturers within your locality or even globally. Look for companies with experience and an excellent online reputation from verified customers.
- Ask for referrals from industry associations and friends. They can recommend a good manufacturer who has assisted them in the past.
Also, when you’re selecting a flex circuit manufacturer, ensure you tick the following checklist:
- Experience.
- Lead time.
- Cost.
- Capabilities.
- Quality.
Request quotes from various manufacturers and compare their quotes with their capabilities as you make a decision.
Flex circuitry is a flexible, twistable, and foldable printed circuit board. They are made using a flexible substrate and have conductive traces on one or both sides.
The thickness of a flex circuit will highly rely on the materials used and its specific design. Thickness typically ranges between a few hundred micrometers to a few millimeters. The number of layers within the circuit determines the thickness. Other factors that equally affect the thickness of a flex circuit include the thickness of the conductive traces, specific application requirements, and the thickness of the substrate material.
- Coverlay
- Adhesive material
- Conductive material
- Substrate material
- Other materials
Final thoughts
So, that’s everything you need to know about a flex circuit. At IBE, we understand that you have expectations and need to meet them. That is why we offer our in-depth experience to our esteemed customers. Talk to us about your PCB and PCBA needs so that we can advise you accordingly. You can also request a quote from us or ask any queries. Then, we are ready to hear from you.
