Flex circuits are slowly becoming more relevant than their rigid counterparts.

Flex circuits allow for a lot more freeform integration, which is useful when designing some of the more complicated circuits that are in high demand in today’s world of electronics.

Designing a flex circuit can be very complicated, and this is what can turn some designers off.

However, there are many rules and considerations for designing flexible circuits. You must be familiar with them to overcome the challenges of flexible circuit design. Please come with me now. Let me tell you should pay attention to the problem.

Flex Circuit Design

1、What is Flex Circuit Design, and why do Their Designs Get Complicated?

What is a flexible circuit

Image 1: What is a flexible circuit

To develop a system that optimizes flex circuit designs, you should first understand what a flex circuit design is.

True to their name, flex circuits are flexible.

Conventional circuits are rigid and follow stringent design procedures that are very limited in their design integration.

Flex circuits eliminate this predicament by allowing freeform integration of elements through all dimensions of a PCB’s space. It allows you a more massive draw of materials to use when designing.

However, just because you are designing a flex circuit does not mean you can do whatever you want. There are still rules that must be made aware of, guides to follow, and just like with rigid circuits, you need to put flex circuits together with the proper software.

Flex circuits follow different rules for being optimal than rigid circuits. If you are not aware of this, you will struggle with designing them.

Also, if you are using flex circuit design software that might not match up to the available guides for your flex circuits, you will not have an easy time.

You do have a little more room for creativity when it comes to flex circuits. But there are still some rules of thumb to follow that can optimise the design process for flex circuits.

This part of the TV show “How to Make” gives you a deeper understanding of the differences between rigid and flexible boards.

https://www.youtube.com/watch?v=C-2ysGoCRoo

2、Rules to Follow When Designing Flexible Circuits

Just because you are designing a flex circuit does not mean you have free reign over how you can design it.

There are still rules that you need to follow to make sure you are designing an optimal flex circuit. While designing a flex circuit frees you up from a lot of limitations that you face with rigid circuits, there are certain things that you should do and things that you should not do.

Make sure that the dimensioning and tolerancing of your flex circuits are as perfect as they can be. It helps prepare your flex circuit for manufacturing.

Proper dimensioning and tolerancing means that you should provide individual dimensions only once then committing to the dimensions and checking them, stating all dimensions as clearly as possible, and provide dimensions for any of the features shown in a profile.

Flex circuits are designed to be functional. Avoid using the same materials that made your rigid circuit look nice. You are not trying to impress people with a flex circuit; you want the flex circuit to outperform a rigid circuit.

Instead of using thicker copper for better conduction, flex circuits use wider copper for more consistent conduction. If you are not familiar with working with wider copper materials, you may want to learn to do this before designing your flex circuit.

These are just a few things that you should and should not do when designing flex circuits. Keep them in mind when you are browsing through flex circuit design guides and pursuing design software.

Flex Circuit Design

Image 2: Copper layerings. Flex circuits use copper that is wider, not thicker like in rigid circuits.

3、Factors to Consider When Designing Flexible Circuits

Materials, design guides, and the effectiveness of design software are indeed important to any flex circuit. But there are a few more things to consider when designing a flex circuit.

Flex circuits use different materials than rigid circuits do. Because of this, you’ll need to consider the heat dissipation, the base materials used, and the bending radii that are involved in the flex circuits.

Heat dissipation in a flex circuit is much different than it is in a rigid circuit. It is possible to dissipate heat in a flex circuit through something called a hybrid heater, where heat dissipation from only one side of the circuit board. You’ll want to familiarise yourself with this kind of concept when you begin designing flex circuits.

The second thing you should consider is the basic material.

Flex Circuit Design

Image 3: A detailed look at a flex circuit. Three key factors to consider when designing a flexible circuit.

There are three common base materials in a flex circuit: 1PI Polyimide, PET polyester, and liquid photo-imageable solder mask (aka LPS). These have different properties about the flex circuit.

Polyimide and polyester have similar properties about flex circuits. They both yield high dielectric strength, but they require precutting. LPS contains all the through holes that you will ever need in a flex circuit, but they are not as mechanically robust as polyester or polyimide base materials.

The last factor considered is the bend radius. Because flex circuits are not rigid, they can bend. It means you need to determine a minimum bending radius as well as know whether your flex circuit can be optimized with dynamic bending or with a bending and retention solution.

Most bending and retention solutions involve the thickness of the circuit and how many sides and layers the course has. Working with those numbers will give you a minimum bending radius.

Dynamic bending is generally only used with single layer flex circuits. Dynamic bending entails creating a bending radius upwards of 40 times the thickness of the course.

4、Challenges and Problems That are Faced When Designing a Flex Circuit

Flex Circuit Design

Image 4: Screenshot of design software. Inconsistencies involving design software are one of a few challenges that flex circuit designers face.

Like with any other kind of circuits, some challenges need to be overcome when designing flex circuits.

One challenge that you are going to face when designing flex circuits is taking the time to find design software that is effective and responsive. You can get away with a few flaws with design software for rigid circuit design software, but there is no way that you can get away with any when it comes to flex circuit design software.

Flex circuits entail a completely different utilisation of materials when compared to their rigid counterparts, even though both use the same materials in their design. It is the crux of the challenges that flex circuit designers face.

Flex Circuit Design

Image 5: FR4 used as a base on a rigid circuit.

For example, how many rigid circuits bend? None of them. Even the concept of bending radii and folding designs can be very challenging for anybody who isn’t also aware that circuit bases could bend or fold.

Getting used to working with polyimide bases instead of FR4 bases is also a significant challenge. Although FR4 for a flexible circuit, they are used as stiffeners and not plates.

The concept of a stiffener does not even exist in rigid circuitry, and this is yet another challenge that anybody new to flex circuits face. Inflexible channels, stiffeners function as support in areas where connectors and other components are applied.

These stiffeners built into the rigid circuit. Flex circuits do not.

Rigid and flex circuits often use similar materials. The only difference is that these materials need to be customized for a flex circuit if you initially used them for rigid circuits.

5、What Can OurPCB Offer You in Terms of Flex Circuit Materials?

To design a flex circuit, you’ll need to customize whatever materials you currently use for your rigid circuits.

The conductive layers of most flex circuits are fragile, and they require a flexible dielectric film because of this.

There are two ways you can obtain a flexible dielectric film.

First, you can order it directly. Doing this is extremely costly, and considering the alternatives, doing this is also unnecessary.

The other way is to send in whatever film you have so that it can be customized.

It is what OurPCB has done. We work on materials that are not suitable for flex circuits and prepare them for flex circuit design.

Our turnaround time is much shorter than most other PCB manufacturers. Anybody who gets their circuit materials serviced by us also gets instant discounts and also becomes part of all of our customers like to participate in the rewards program.

The dielectric film is one of many circuit materials that we can modify for flex circuits. We can work on other elements that might need to be customized for flex circuits.

6、Conclusion

Directly ordering materials that are ready for flex circuits can not only be difficult to acquire but can also be costly.

Fortunately, you do not need to order materials for flex circuits directly. Our customising materials to make them compatible with flex circuits is one of our major services.

Different than other PCB manufacturers who perform services, you will not need to wait for a quote from us. We quote immediately, which will save you time and also give you peace of mind when requesting services from us.

You should find an order form at the bottom of the page. Let us know whenever you need to get any materials ready for a flex circuit design, and we will work with you.