Guide to PCB Stiffeners

One of the popular types of printed circuit boards that Millennium Circuits Limited offers are flexible circuit boards. If you’ve used flex PCBs before, you know how useful they can be. Flex circuit boards allow you to outfit products with circuitry when the design of those products won’t admit a rigid circuit board, so they’re invaluable for many electronics applications.

However, flex printed circuit boards have their drawbacks, one of which being that they may not be rigid in places that actually need stiffness — PCB stiffeners were created for these situations. When you’re working with flex circuit boards, you often need flex PCB stiffeners. You may not be familiar with PCB stiffeners, or you may have an idea what they are but not be entirely sure how to apply them. So, what are PCB stiffeners, and how do they work?

How Do PCB Stiffeners Work

It’s important to understand that the PCB stiffener is not an integrated part of the electrical circuit board design — it exists to offer mechanical support. A stiffener is called for when you need:

  • Greater thickness in your flex circuit in certain areas
  • To constrain bend areas to specific predefined locations
  • To meet ZIF connector specifications
  • To strengthen specific areas of the board
  • To support other components or connectors

When you need a rigid area in your flex circuit, to protect components or connectors that are attached there, you can add a stiffener. This will stop the circuit from bending and protect the integrity of the part’s solder joint.

What Are Flex PCB Stiffeners Made Of?

Naturally, if you’re going to add PCB stiffeners to your design, you need to give some consideration to what they’re made from. PCB Stiffeners, like much of the flex PCB, are usually made of FR4. The thickness of the stiffener can range from .008” to .059”.

Typically, when manufacturing your flex board and using PCB stiffeners, you want to make the stiffener as thick as you possibly can given the design. The thicker the PCB stiffener is, the more support it will be able to offer. Not all PCB stiffeners in a design must be the same thickness. If you need to increase thickness, you’ll usually use polyimide stiffeners, adding a thin layer of polyimide at the contact fingers. However, trying to make a thicker PCB to avoid using a ZIF stiffener will probably result in a board that’s more rigid than you want it to be.

In certain situations, you may use other materials, such as stainless steel or aluminum, for your PCB stiffener. As you might imagine, these materials are more expensive, but you do get better rigidity and heat sinking properties. While there are some very specific situations where it will be to your advantage to use one of these more expensive materials, most manufacturers feel the benefits don’t not merit the added cost with flex PCBs.

How to Apply a PCB Stiffener

Make sure when attaching your PCB stiffeners with plated-through hole components that the stiffener is on the same side of the board where you’re inserting the component, so you can access the solder pads. You can attach stiffeners to both sides of a part, but the assembly will require an array configuration review to make sure you won’t run into any complications during the assembly process.

Typically, you’ll use heat and pressure to attach the stiffener to the circuit through thermal bonding. You can also attach PCB stiffeners with a pressure sensitive adhesive.

Understanding PCB Stiffeners

While it may feel like PCB stiffeners are complicating your printed circuit board design, they enable your flex circuit boards to function much more effectively in a wider range of applications. You have many options for combining various stiffener types in your PCB design to get the result that you want.

If you’re not clear on how PCB stiffeners can work for you with your flex boards, or about the many ways you can use PCB stiffeners in a single board, the experts at MCL will be happy to discuss it with you. Our specialists can go into detail about stiffeners themselves and discuss flex board alternatives for using stiffeners effectively. Contact us to learn more.