PCB Stiffeners: An Extensive Guide

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Jun 24, 2020|Product Innovations and Design, Technological Advancements and Materials

A printed circuit board is an essential part of technology as we know it today. Without them, our favorite devices would be useless.

In the evolution of PCBs, there have been many advancements and changes that allow us to better enjoy electronics. Many of the components that go into creating a PCB are simply a solution borne out of evolution. One such critical part is a PCB stiffener.

What is a PCB Stiffener?

PCB stiffeners are not an original part of a PCB. They are something added later to the board as support. They have many jobs, from strengthening parts of the board to allowing for better handling of the board. It essentially is a way to make a PCB circuit board more durable so that it can stand up to the demands put upon it through manufacturing and use.

What is a Busbar?

Circuit board stiffeners and busbars cause some confusion. They are the same thing with one difference. Every busbar is a board stiffener, but not every stiffener is a busbar. A PCB busbar has the addition of a dielectric coating. It can conduct power. Most of them are brass or copper, and they can have multiple layers.

Why Do Flex and Rigid-Flex PCBs Need Stiffeners?

To really understand PCB stiffeners, we need to look at flex and rigid-flex PCBs.

A flexible PCB has a malleable base material. It allows you to design the circuitry to fit the device. The need for PCB stiffeners on flex boards is evident due to the nature of the design. There will always be areas that require more support than the base material can supply.

What is a rigid-flex PCB? This type of board has some areas of strengthened base, while others are malleable. Areas on the board that require extra support will not bend, while the areas that do not need support can bend.

Since the manufacturer builds support into the printed circuit board, you may think this type of board will not need stiffeners. However, that is untrue. Even a rigid-flex board can benefit from extra strengthening once all components are in place.

You may find that answering the questions, how do you make flex PCB, and how are rigid-flex PCBs made, can make this clearer because you will see how each board functions and why someone may feel the need to add in a PCB stiffener.  

Advantages of Using PCB Stiffeners

There are three main advantages to using PCB stiffeners in your board design:

     * Strengthening

     * Rigidity

     * Conductivity

Strengthening

Because you can place a stiffener in many different areas of a board, it provides the ability to add support anywhere you need. If you have a stack of boards, you can use a stiffener to prevent sagging and to stop shorts from occurring between boards. They can act as flex circuit board connectors to ensure a strong overall collection of boards. You also can use it to correct a warped board or simply add more support in a weak area.

Rigidity

The whole point of a stiffener is to prevent bending of the board. Adding this enables you to also eliminate or minimize vibrations throughout the board. Rigidity is also essential when you need to solder, which naturally weakens the board. You can combat this with stiffeners. In addition, you need the board to lie flat to avoid failures.

Conductivity

When you use a busbar, you gain connectivity on the board, along with the extra support. It allows you to get a two-for-one benefit.

PCB Performance with Stiffeners

Board stiffeners can improve performance. They help to alleviate stress that can impact the way components work and the overall function of the board. They also positively impact reliability.  

Without stiffeners, a PCB is very weak. The stiffeners protect every component by providing strengthen. They allow for spot strengthening, which is essential since trying to reinforce the whole board will fail because its own weight would be too much to keep it rigid.

In short, stiffeners allow a circuit board to do its job and to be a durable part of a device that won’t break down from wear before its useful life is over.

How to Attach PCB Stiffeners

Since you can see that you will usually have to use stiffeners in your PCB, you should understand how to attach them correctly. As you know, if you do not do it the right way, you could damage your board or cause other issues that make the board not function properly.

The most common way to attach a stiffener is on the same side as you adhere the component. You can also connect them to the sides of a component.

You attach them with thermal bonding. It is also possible to use a pressure-sensitive adhesive.

PCB Stiffener Materials

You will need to choose your stiffener based on its material. Different applications will call for different approaches to ensure the right stiffness and cohesion with nearby components.

As mentioned, if you use a busbar stiffener, it will be metal because it has to conduct electricity. So, you need a conductive metal, such as copper.

Other metal options include aluminum, which can conduct electricity but does a poor job of it. It also will build up hear, so be cautious of using it. Another choice is stainless steel, which is another good choice for a busbar.

You can also go with non-metal options, such as polyimide or FR4. Do note that FR4 stiffeners may have some metal components.  

PCB Stiffener Sizes

The size of your PCB stiffeners is also an important consideration since you need them to fit within the board with your other elements. Also, size impacts weight. If you add too many heavy stiffeners, it is going to cause issues. However, a thicker stiffener will offer more support. What thickness you choose depends on your design and what will fit in the space you have with the other components.

You may find you use some thicknesses more often than others, including 0.020″, 0.031″, 0.039″ and 0.059″. You’ll have choices that go from 0.008″ to 0.059″.

Wrapping Up PCB Stiffeners

Now that you know the answer to the question, what is a stiffener in PCB, you can make sure you implement the use of them in your PCBs. Stiffeners play an essential role that you cannot discount. Trying to bypass their use is often detrimental to your overall design and the function of your board. Understanding them allows you to use them correctly and effectively.