Flex Vs. Rigid: The Ultimate Guide

About Flex Vs. Rigid, We’re at a critical point in history when technology has taken over almost every aspect of the economy.

For example, we have many PCBs with unique features and applications.

This has given rise to several debates on the best, with the latest being the flex vs. rigid PCB.

The main difference is that a rigid PCB is designed with a rigid base layer that you can’t bend, while a flex PCB is designed on a flexible base that you can easily twist, fold, and bend.

However, that’s not all. There are still more important differences worth our attention.

In this Flex vs. rigid PCB article, we explore the differences, similarities, and applications of the two.

What Is A Flex PCB?

(Someone holding a flex PCB)

This is also known as a flexible circuit board and is a printed circuitry having components that employ flexible materials. Surprisingly, these PCBs can either have or lack cover layer materials.

Since flex PCBs are flexible, you can use them in tighter and smaller spaces. Some of the applications of flex PCBs include printers, smartphones, smartwatches, and keyboards.

However, do not confuse flex PCBs with rigid-flex PCBs. The latter has some features and technologies of rigid circuit boards.

What Is A Rigid PCB?

(A rigid PCB)

A rigid PCB is what we have known traditionally to be circuit board. They’re solid and inflexible printed circuit boards that you can not flex or bend.

In most cases, these PCBs come with multiple layers, including copper, silk screen, substrate, and solder mask layers. Therefore, we join these layers together using heat and an adhesive.

Moreover, rigid circuit boards can be single-sided, multilayered, or double-sided. However, you can’t change or modify these boards after designing and fabricating them.

These PCBs find applications in computers, smartphones, and x-ray equipment.

Flex Vs. Rigid PCBs: Differences

(A person folding a PCB)

We understand that you can use both rigid and flex circuit boards to achieve the same purpose of linking several electronic components.

However, there are many differences between the two that make them have unique performance benefits and disadvantages.

Let’s consider the differences below:

Layers

The first difference comes in with the base layer, where rigid boards connect components using conductive tracks and elements on a non-conductive substrate.

Also, the non-conductive substrate has glass, offering the required thickness and strength.

Surprisingly, flex PCBs have conductive tracks on a non-conductive substrate, but the base material is flexible. Therefore, rigid boards come with FR4, while flexible ones have polyamide.

Furthermore, there are differences arising from the adhesive layers you use. A rigid circuit board doesn’t bend, thus limiting the adhesive requirements to thermal and chemical properties.

For the flex PCB, you’ll need unique adhesives that allow bending without cracking.

Flexibility

As we highlighted above, the base rigid circuit board comes with a base material that reinforces it with rigidity and strength. However, flex PCBs come with materials that allow bending into different shapes without cracking.

Conductors

We also noted that these two PCBs employ different conductors. In the case of rigid PCB, the conductive material is electro-deposited copper.

However, flexible circuit boards use rolled annealed copper to make them bend and fold with ease.

Manufacturing process

Regarding rigid PCB manufacturing, we apply a solder mask. However, for the flexible circuit board, we replace the solder mask with a coverlay or overlay.

Consequently, it protects the exposed circuitry on the board.

Cost

Generally, flex will cost more than rigid circuit boards thanks to the complexity of the design and fabrication process.

However, we understand that flex PCB can fit in tight and smaller spaces and is thus used to make most high-demand consumer products.

Therefore, electronic manufacturers will still make more revenue from flex PCB thus indirectly saving on the high costs.

Durability

We guarantee you’ll get a reasonable amount of durability from each PCB type. However, rigid PCBs come with high strength, dissipate heat, absorb vibrations, and better withstand environmental elements better.

Therefore, expect them to last longer than flexible PCBs. Surprisingly, flexible PCBs will still serve you for years without experiencing failure.

Weight

As mentioned above, rigid PCBs come with thick materials and better strength thus having a higher weight than flex PCBs.

Surprisingly, flex PCB is lightweight, making them helpful in developing small devices like watches that need lighter components.

Resistance

Flexible circuit boards withstand high levels of temperature and have less chance of succumbing to extreme environments like radiation, heat, and chemicals.

Surprisingly, rigid PCBs aren’t designed with much resistance. Consequently, they can easily warp and damage when you expose them to chemicals, radiation, and heat.

Design Sophistication

To create basic consumer electronics like toys and music keyboards, rigid circuit boards would be your best option.

Surprisingly, flex-printed boards come with sophisticated designs that make them perfect for highly complex electronics.

Furthermore, flex circuit boards are structurally versatile and thus helpful in developing innovative and compact devices.

Flex Vs. Rigid PCBs: Similarities

Despite the differences between flex and rigid circuit boards, there are similarities worth noting. For example, these boards serve the same purpose of connecting components like transistors, diodes, and resistors to create electronics.

Moreover, these circuit boards employ the same thickness, size, and components design rules. Finally, they have the same manufacturing process. If you know how to design a rigid PCB, you can easily design a flex PCB.

Flex Vs. Rigid PCBs: Applications

(A smart wearable that uses flex PCB)

Generally, we use flexible PCBs when weight and space are a major concern. Surprisingly, you can bend and fold a flex PCB to fit in tight spaces.

Moreover, they’re lightweight and thus important in circuits where traditional PCBs won’t fit.

Furthermore, flex PCBs have a high resistance to temperature and shock, therefore perfect for such use cases.

As we highlighted, these PCBs also dissipate heat faster. Therefore, we recommend them for cameras, smartphones, and smart wearables.

On the other hand, rigid PCBs are perfect for solid and traditional electronic designs where a rigid board matters. Also, they’re perfect in situations where cost efficiency is key.

We noted that using flex PCB is expensive and unsustainable for most designs. Rigid PCBs find application in computer units, power junction boxes, and transmission sensors.

Combining Flex and Rigid To Form Rigid-Flex PCBs

Combining flex and rigid circuit boards gives rise to rigid-flex PCBs. Surprisingly, these PCBs share the features and technologies of flex and rigid boards.

Although rigid-flex PCBs aren’t as flexible as flexible PCBs, you can still use them in limited and tight spaces.

Moreover, rigid-flex PCBs offer mechanical stability and 3D design freedom. Using these boards will significantly reduce your production costs.

These boards find application in control systems, consumer appliances, and telecommunication systems.

FAQ

Which is better between a rigid and flexible PCB?

There is no better or worse option between a rigid and flexible PCB. Surprisingly, each option is designed to be useful in a specific use case.

Therefore, we recommend flexible PCBs if you’re working with compact spaces and rigid PCBs for more durability and cost-effective applications.

What’s the lifespan of a PCB?

Most PCBs having proper maintenance and repair will serve you well for at least 50 years or more. However, choose a rigid PCB for more lifespan.

Can you replace a flex PCB with a rigid PCB?

No! A flex PCB is mainly used in tighter and more compact spaces. Moreover, they’re designed to function well even in extreme conditions like high temperatures.

Therefore, replacing it with a rigid option will likely render your device ineffective. Similarly, you can’t replace a rigid PCB with a flex one.

Conclusion

As highlighted, many differences between rigid and flex PCBs are worth noting. For example, It’s easier to fold and bend flex PCBs but not rigid ones.

Moreover, flexible PCBs withstand higher temperatures and resistance than rigid PCBs. Surprisingly, rigid PCBs have a higher lifespan than flex PCBs.

However, the PCBs share similarities like connecting components together, using the same design rules, and having similar manufacturing processes.

Finally, flex PCBs offer better performance, but rigid PCBs provide a cost-effective approach.

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