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What Are Flex PCB Stiffeners ?

What Are Flex PCB Stiffeners ?

Sometimes it is necessary to enforce some parts of the flexible circuit board or FPC with stiffeners. PCB stiffeners are used to make a certain part of the board rigid so it can be easier to add/solder interconnects or components to the stiffer part.

The PCB stiffener is not an electrical piece of the PCB. It is simply applied with the purpose to provide mechanical support to the printed circuit board during the assembly process. Furthermore, the PCB stiffeners include an increase in abrasion resistance, reinforcing of solder joints, and better handling of the board for the automated process of pick-and-place.

here are 3 main types of PCB stiffeners – Polyamide (PI) stiffenerFR4 stiffener, and aluminum/stainless steel stiffener. These materials are most commonly used on projects requiring increased stiffness and heat dissipation.

The PI stiffeners are a cheaper alternative to FR4. On the other hand, if manufacturers are looking for heat sinking properties and better rigidity, they use stainless steel or aluminum stiffeners.

  • Polyamide (PI) Stiffener

PI stiffeners are commonly used to increase the thickness of the ZIF connector, where fingers contact and provide full support. This way it allows tolerances in bending thickness and contours the component at the contact. The finger area bend thickness tolerance is typical +/- 0.002″ and the width profile is +/- 0.003″. Also, PI stiffeners are used to limit the bending ability of specific PCB areas to prepare an installation in the final assembly. The most common area to enhance would be the hole locations to provide additional wear resistance whenever wear problems occur.

Polyamide stiffener is an excellent option for solder resistance and high bond strength. The most preferred locations for stiffeners application are on the backside of the insertion gold fingers. Sometimes you can simply pick the part of the PI stiffener that is not laminated or attached to the FPC body and easily insert the flexible printed circuit connector fingers into the ZIF socket or connector.

Chart 1 FPC with PI stiffene

FR-4 Stiffener

FR-4 can be the CCL of the rigid printed circuit board and is the most common material used for the PCB stiffeners application in and flex circuits. The main purpose of adopting an FR4 stiffener includes:

1. Providing flat enough support when the flexible PCB is in the pick-and-place and reflow processes.

2. Plated-through hole (PTH) components, it is important for the stiffeners to be placed on the same side of the flex PCB in which the components are inserted to allow direct access to solder pads. In some cases, the customer wants to save money in the turnkey process of the project assembly, and in order for manufacturers to do so, they add an FR-4 frame on the border of the panelized PCB to successfully replace the SMT carrier.

Chart 2 FR4 stiffener

In some flexible printed circuit board designs, the diameters of the hole of FR-4 stiffeners are the same as the FPC. The holes will be extremely difficult to be attached, and it could result in dis-alignment. As a leading flex circuit manufacturer, LingtechPCB always ensures that the holes on FR-4 stiffener bigger than those related holes on FPC to ensure good alignment.

Stainless Steel/Aluminum Stiffener

Stainless steel/aluminum stiffeners are usually used for flexible circuit designs requiring anti-corrosion resistance, capability, robustness, and formability. The stainless steel/aluminum stiffener in flexible circuits is always added to the connecting fingers to stiffen the flexible printed board to facilitate assembly.

Chart 3 Stainless steel stiffener

Multiple PCB Stiffener

Whenever applying PCB stiffeners, manufacturers ensure that the stiffener overlaps the bored overlay by .030” to relieve stress. In this case, the overlay acts as a solder resist for the flexible printed circuit board. Also, the same exact stiffener thickness should be maintained whenever using multiple stiffeners. After the process is completed, the stiffener strengthens the solder joints due to the increased abrasion resistance.

In fact, an advanced custom PCB manufacturer LingtechPCB can easily do with various PCB boards requiring the above stiffeners. Our PCB company fully understands the difficulties of the designing side to get the board to stay in spec, so we offer tech support to customers.

Why choose LingtechPCB for PCB Requiring Stiffeners:

We provide high-quality flexible PCB that can apply stiffeners.

We offer tech support to help customers deal with issues in stiffeners.

Professional Gerber and BOM check ensure the success of PCB and end production.

In all, LingtechPCB is an advanced circuit expert providing one-stop PCB solutions for customers.

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