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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.

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 optimize the design process for flex circuits.

What are the rules of flexible PCB design?

Just because you are designing a flex circuit does not mean you have free reign over creating it. There are still rules that you need to follow to make sure you are designing an optimal flex circuit. While creating 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 tolerance of your flex circuits are as perfect as they can be. It helps prepare your flex circuit for manufacturing. Proper dimensioning and tolerance means that you should provide individual dimensions only once, then committing to the dimensions and checking them, stating all measurements as clearly as possible, and offer sizes to any of the features shown in a profile.

Flex circuits are designed to be functional. Avoid using the same materials that made your rigorous course look nice. You are not trying to impress people with a flex circuit; you want the flex circuit to outperform a fixed rotation. Instead of using thicker copper for better conduction, flex circuits use more expansive copper for more consistent conduction. If you are not familiar with working with broader 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.

Factors to Consider When Designing Flexible Circuits

Materials, design guides, and the effectiveness of design software are indeed crucial 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 course. It is possible to dissipate heat in a flex circuit through 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 raw material. 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 and 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.

What are the challenges of flexible PCB design?

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 finding 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 to get away with any when it comes to flex circuit design software.

Flex circuits entail an utterly different utilization 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. For example, how many rigid circuits bend? None of them. Even the concept of bending radii and folding designs can be 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 are 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.

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