A Design Guide for Flexible Printed Circuits

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Wed, Jan 01, 2020

Flexible printed circuits have a number of benefits and applications in the world of electronics. However, to be able to use a flexible printed circuit, you have to know the steps you need to take to design one. Read this step-by-step guide to better understand the process of creating a flexible printed circuit design.

STEP ONE: DECIDE WHAT TYPE OF FLEXIBLE PRINTED CIRCUIT YOU WILL NEED

There are multiple types of flexible printed circuits you can use, depending on what you’re needing. This is important because it will determine your design. To help you better understand, here is a bit about each of the five main types of flexible printed circuits:


·  Single-sided flexible circuit:  This design has a single conductive layer with an insulating layer that can be on one or both sides of the circuit. It may also have a protective coating but isn’t required to have one.

·  Double-sided flexible circuit:  These circuits have two layers made of a conductive material. At times, these circuits contain holes where components can be placed and soldered. Since the components are laying within the material, it maintains its flexibility.

·  Sculptured flexible circuit:  This circuit is sculpted in a unique way to fit a certain area or connect to another component that is uniquely shaped. The thickness of the conductive material on this will vary as the shape varies.

·  Multilayer flexible circuit:  This type of circuit contains several layers of conductive material. Much of the circuit is laminated several times, with only components and holes remaining visible.

Rigid-flex circuit :  A combination of a traditional printed circuit board and a flexible circuit, this features strips of flexible materials that branch off from a more rigid board. 

What you choose will depend on the device that the circuit will be going into and the space inside of that device.

 

STEP TWO: DESIGN IT

Although the flexible circuit is made of different materials, the design process for a traditional printed circuit board.

You need to take a number of things into consideration. To begin, you need to decide where your components will go. This will be crucial in where holes are drilled for the components. The spacing of components will also likely be impacted by your design choices. Although flexible circuits are much more tolerant of heat, keep heat distribution in mind.

Be sure to also leave some space between your components so your design will work effectively.

You also need to decide how wide your lines or pathways will need to be. In many cases, flexible circuits are added to traditional printed circuit boards to continue pathways to other components. This means that the energy currents will be traveling along these pathways to reach these components. If you aren’t careful, you could design the lines to be too small. This can cause your flexible circuit to overheat or cause incompatibility between your printed circuit board and your flexible circuit. There are several calculators online that can help you determine the width of your lines depending on the amount of energy that will be flowing through the circuit.

 

STEP THREE: DETERMINE THE APPLICATION OF THE FLEXIBLE CIRCUIT

There are two types of applications for flexible circuits: static and dynamic. Depending on which one you need to use, you may have to adjust your materials or the type of flexible circuit you need to use.

Static flexible circuits are usually manipulated by being bent once to fit into an area. However, a dynamic flexible circuit is bent multiple times either prior to use or during use. Knowing which application will be employed will be crucial in making a flexible circuit that is best for the device you’re making it for.

 

STEP FOUR: MAKE A MOCK-UP

After you’ve made the design concept, it is time to make a mock-up. It is suggested that you use software or at least a model you created to do this. Make sure that your mock-up is to scale with the actual flexible circuit. Creating this mock-up will help you to space out your components and help you to avoid mistakes that could lead to disastrous results.

 

STEP FIVE: CONSIDER YOUR LAYERS

Even though flexible circuits are thin, they are composed of a number of layers that are laminated together. These layers include

·  A base material. In many cases, this material is copper or another conductive material.

·  A top and bottom cover. These are usually polyimide.

·  An FR-4 material.

·  An adhesive to keep it all together.

 

STEP SIX: CREATE AND TEST

Now that you know what type of circuit you need, its application, and the layers you will need, it is time to take your mock-up and turn it into the real deal. Thankfully, the manufacturing process is almost always automated, so you don’t have to worry about making mistakes.

However, machines can make a mistake too. After the manufacturing process, it is crucial that the flexible circuit is tested to assure that it performs its functions. If something is wrong, you may have to troubleshoot and re-manufacture the flexible circuit to find the issue.

 

THINGS TO CONSIDER

While these are your four main design steps, you need to consider a few other things.

Remember that you want the heat within the flexible circuit to distribute as evenly as possible to avoid overheating. It may be easy to say, “because of its thinness and the materials it is made of, it won’t overheat.” You should still take precautions.

Remember also that you are designing this to fit into a compact area. You should take into consideration the final device that this will be put into so that you can effectively design the flexible circuit for that space.

 

CONCLUSION

This guide should prove helpful as you begin the design process for your flexible circuit. Be sure to take all of these steps into consideration during the process. It can be difficult, but flexible circuits are an integral part of so many electronics, so it is worth the extra effort.