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Why Flex PCB need Stiffeners  ?

Flex PCB stiffener is to Strengthen the hardness of flex PCB,We use 3 types stiffeners for flex pcb ,  Fr4 stiffener,PI stiffener,Aluminum stiffener

Flexible PCB -Flexible Printed Circuits  are made of thin dielectric substrate & high ductility metal foil, flexible pcb can be bent or folded and used in static and dynamic applications.

Flexible PCB Stiffeners
Flexible PCB Stiffeners

The demand for flexible PCB is increasing in all business segments with especially strong demands from medical, military and industrial markets. Since the volumes normally are quite small for these segments ,RayMing works with a number of  high-mix, low-volume Flexible PCB order  that fit the technology and volume requirement. RayMing Group set very strong team to support different volume demand on different industry .

What is Flexible PCB?

Flexible printed circuit boards, also called Flexible PCB or Flex PCBs, derive their name for their ability to enable the circuitry to be designed to fit the electronic device or product, as opposed to building the device to conform to the circuit board. Flex boards are characterized by a distinctly patterned printed circuitry and component arrangement highlighted by a malleable base material.

When we talk about Flexible PCB , will consider the connect with other device , At this time, we will  consider using stiffeners in Flexbile PCB Design

Normally Flex PCB Stiffeners  material :  Fr4, PI , Aluminum .

Aluminum Flex PCB stiffener

Aluminum  stiffener

Stiffeners can be used to reinforce the areas where electronic components will be assembled, but not where the board will flex. If your board requires stiffeners on both sides of the flex, it may require two laminations. Also keep in mind that stiffeners require their own prepreg lamination cycle, and certain stiffener materials require an additional lamination cycle as well. They add thickness to your board, and impact both cost and manufacturing time. However, there are certain cases where stiffeners are required.

Flexible-only PCBs can withstand fewer components than rigid-flex. The rigid part of rigid-flex can also be as complex as a traditional rigid Circuit Board. Stiffeners are occasionally laminated the same time as the coverlay.

When Using Stiffeners  ?

Stiffener Raw Materials for Flexible PCB

Stiffeners are typically made of FR-4 or Kapton. Kapton is often used when the end of the flex must be thickened and inserted into a ZIF connector. However, the use of Kapton requires a separate lamination cycle. FR-4 stiffeners can be done within the same lamination cycle.

FR4 Stiffener
FR4 Stiffener

Route And Retain With Stiffeners For Flexible PCB
When routing and retaining arrays, the same material as the stiffener will simply be extended into the array. This rigidizes the array.

Flex PCB Stiffeners Are Required When:

Components are near or in an active, or dynamic, flex zone
Component size and weight will import stress onto the flex
A large number of SMT pads make planarity critical
Connectors that require repeated insertions or assemblies require a stiffener, or something to help alleviate the stress of pads.

Stiffeners Are Not Required When:

Small “static” components do not exert a large amount of strain on the flexible of the PCB.There are no components in the flex region.

Tips of Flexible PCB Design 

Polymind PI Stiffener

Polymind PI Stiffener

1.What are the advantages of using flex versus cables?

Flex provides several advantages to cables. We’ve covered the pros and cons of both in our article Flex Circuits Fit Where Cables Cannot. Flex’s higher upfront cost will dramatically reduce cost in the long run. Cables can take several weeks to go through production, while flex PCBs can be completed in several days. In short, using flex eliminates or completely decreases cable cost, reduces rigid flex assembly time, and produces a lighter end-product.

2.What are the preferred hole and pad sizes for flexible PCBs?

Flex material, like Kapton, does not drill as well as regular materials. 10 mils and above is preferred for minimum size, only in the flex. Rigid-flex specs are similar to rigid board specs. Pad size, plating process for flex is barrel-only (hole wall). Flex holes are not plated on the surface because it needs to flex, and because it is necessary to keep the electrodeposited copper off the surface.

3.Flex Prepreg Materials

No-flow prepreg is the preferred bonding material for joining flex and rigid materials. This is most commonly found in standard FR-4 or Polyimide.

4.What are the alternative prepreg materials for joining flex and rigid materials?

No flow pre-preg is the preferred bonding material. Available in either standard FR-4 or Polyimide.

5.What does a real stackup look like? (Not four signal layers, plane layers needed)

The plane layers for the flex are the same as the would be for the rigid board. This board would be turned into a 6 layer pcb board, as follows:

The world of electronics and circuit boards is a fascinating one. It seems small but proves comprehensive in every aspect. Consequently, it can become challenging when the time comes to get yourself a printed circuit board or any other allied PCB product like stiffeners. However, in a global community where information sharing is the order of the day, the confusion has to stop. Therefore, in this article, and in light of all these, the focus will center on stiffener PCB, also inferred as PCB stiffeners. It should help you navigate the murky information world of printed circuit boards.

Printed Circuit Board Stiffener

Stiffener PCB is a typical term you will encounter in the printed circuit board assembly process. It can include FPC stiffener, stiffener flex PCB, etc. So what does the term stiffener PCB entail? It implies a printed circuit board fitted with stiffeners. Stiffeners come as a necessary component for flex and rigid-flex printed circuit board designs. You would appreciate by now how crucial flex PCBs can become, especially in outfitting circuitry in products that would ordinarily not permit rigid printed circuit boards. However, these flex PCBs need some strength or stiffness to function properly, something that becomes a reality with PCB stiffeners.

Diverse types of PCB stiffeners exist. It predominantly includes fr4 stiffener and polyamide stiffeners, though aluminum and stainless steel stiffeners also exist. The material used in the stiffener often corresponds to your printed circuit board design requirements, especially when thickness and the extent of flexibility get factored in. For instance, a flex PCB stiffener may require an fr4 material to ensure flexibility of the board gets maintained besides also providing the necessary strength to the flex part. Therefore, the type of PCB you decide to settle on plays a fundamental role in determining and guiding the type of PCB stiffener you eventually opt for. However, it becomes necessary to note that most PCB stiffeners get composed of rf4 or polyamide material.   

Fr4 is composed of a woven glass-fiber laminate complete with an epoxy resin. At the same time, polyamide gets produced by a high-temperature polymer that gets formed into a thin sheet or layer. Several layers can always get stacked up to achieve greater thickness. One typical polyamide product used as a stiffener is Kapton, especially when the flex end needs thickening for insertion into the ZIF connector. However, stiffener materials transcend fr4 and polyamide. You can also use materials such as aluminum and stainless steel as your printed circuit board stiffeners. It becomes crucial to note that the latter two come at higher prices than the fr4 and polyamide materials. Further, they ensure greater thickness, unlike the fr4-based stiffener.   

Printed circuit board stiffeners, while crucial, do not form part of the integrated electrical circuit board design. It primarily exists to provide mechanical support and become vital in particular instances. Such instances include where you want to limit bend areas, where you need to enhance the thickness of specific board areas, and where you need to strengthen particular board areas. Additionally, it also becomes essential when you need to support connectors or other components of the printed circuit board. Consequently, the stiffener will preserve the circuit board from bending besides ensuring the integrity of the circuit board part’s solder joints.  

If you want to buy a stiffener PCB, then canvassing and understanding these numerous aspects become key.   

Benefits of the Diverse Types of Stiffener Materials

  • FR4 Stiffeners. It provides flat and sufficient support for the flex printed circuit board, especially during the pick-and-place and reflow process. Additionally, the fr4 material, while sturdy enough, comes at a more affordable price compared to other stiffener materials like stainless steel.
  •  Stainless steel stiffeners. It offers excellent features such as form ability and resistance to corrosion, robustness in diverse temperature ranges, and compatibility. However, it is crucial to note that customization of the stainless steel stiffener happens to post the submission of the Gerber file, with the lead time also stretching by a further few days (normally three to five days)
  • Polyimide stiffeners. It provides high bond strengths and excellent solder resistance. The polyimide stiffener also allows for simple or easy insertion of the FPC connector fingers.

Rigid-Flex and Flex Printed Circuit Board Stiffener

Flex and rigid-flex printed circuit board uses have diverse and documented significance when it comes to application. It, therefore, proves unsurprising that a lot of circuit board designers opt for these PCBs to cater to their electronic circuit needs. Because of this, stiffener flex PCBs have become common. So are you interested in stiffener PCB but have no idea how to go about it?

Getting yourself the correct stiffener PCB, especially when it comes to flex and rigid-flex PCB designs requires an understanding of your design needs besides the anticipated application area. It becomes necessary because of the diverse functions of the PCB stiffener, which can either work to your advantage or disadvantage based on where it gets applied. Therefore, once you settle on the type of printed circuit board to design, it becomes prudent to determine the type of stiffener to apply and where to apply it on the board to maximize your PCB’s functionality.

Functions of Stiffeners in Rigid-Flex and Flex PCBs

As already detailed, stiffeners are not an integral part of the printed circuit board. Therefore, their functions revolve around the following.

  • It provides mechanical support for certain areas of the printed circuit board, especially those containing surface mount technology and PTH components.
  • Stiffeners maintain the authentic thickness of the flex PCB
  • It supports the printed circuit board connectors and components
  • Stiffeners ensure the restriction of the PCB’s flexible parts to the required rigid area according to the specifications detailed
  • It facilitates the better handling of flimsy and thin circuit boards
  • Stiffeners keep specific areas of the rigid-flex and flex circuits stable and flat
  • It meets the ZIF or zero insertion force connector specifications
  • Stiffeners enhance the bend radius of the circuit at flex and rigid intersections. Consequently, it eliminates the stress subjected on the flex part when bended
  • It also retains and routes arrays when extended into the array

Knowledge of the functions of PCB stiffeners thus becomes instrumental before deciding to pick and shop for one for your PCB design. Additionally, it becomes necessary to comprehend why your flex or rigid-flex printed circuit board needs a stiffener. Here, it would help if you considered the following.

Why Your Flex or Rigid-Flex PCB Needs a Stiffener

  • If you want to place components on the flex zone
  • When the weight of the components you place in the flex zone exerts pressure on the PCB’s flex material.
  • Whenever a requirement of developing a rigid and flat surface on the flex to place SMT pad components exist
  • If you have connectors that need numerous insertions and a need to reduce stress on the pads  

The standard thickness of a PCB stiffener often ranges from 0,002 inches to 0.059 inches. However, it’s also prudent to note that Kapton stiffener thickness ranges from 0.002 inches to 0.010 inches, while the thickness of stiffeners for rigid PCBs can range from 0.008 inches to 0.059 inches. The thicker a stiffener proves, the more structural support it provides. However, diverse types of printed circuit boards require specific stiffener thicknesses.

If you need any qualified advice and service regarding stiffener PCBs and other circuit board needs, then RayMing PCB and Assembly Company prove an ideal one-stop shop. You will get relevant and dependable advice, excellent manufacturing, fabrication, and assembly services, besides getting incredible around-the-clock customer care while at it.  

How to Utilize a Printed Circuit Stiffener

It is crucial to consider certain aspects of using a PCB stiffener. For instance, you have to consider positioning the stiffener on a similar side to which the flex components get inserted for PTH (plated through-hole) components. It will permit you to access solder pads on the flex PCB. Alternatively, it is possible to attach stiffeners on either side of the part, though this requires a review of the array configuration.

When we need an assembly array, especially for flex designs, it becomes cost-effective and standard to incorporate an fr4 stiffener through the array border, leading to a rigid array. Consequently, it allows for a similar run-through of parts during the automated assembly as it happens for rigid PCBs. Further, it eradicates the need for extra tooling plates, and so on.

What happens during this process entails the application of pressure and heat in a process inferred as thermal bonding. The process attaches the stiffener to the circuit board. However, it is also possible to attach printed circuit board stiffeners by using pressure-sensitive adhesives. Adhesives that prove popular for this work fall under either thermally-bonded adhesives or pressure-sensitive adhesives. However, the choice you end up with should be guided by diverse performance requirements such as chemical resistance, thermal exposure, and adhesion to diverse materials.             

The Distinction between Rigidized and Flex-Rigid Printed Circuit Board

The distinction between rigidized and flex-rigid PCBs becomes hazy most times for a lot of people. However, rigidized PCBs imply a flexible printed circuit board bonded with an fr4 stiffener to provide it with some rigidity during the assembly process. On the other hand, rigid-flex circuit boards come as a hybrid between flex and rigid circuits containing both flexible and rigid substrates that get laminated together.

Additionally, no traces exist on the rigid segment of a rigidized flex, and it also includes pads. The rigid section only provides strength to the location or flex. Conversely, the rigid-flex printed circuit board contains flex and rigid segments with traces connected through holes. It, therefore, implies that in this case, the aim is to provide connection and not structural support to the rigid-flex printed circuit board.

Stiffener PCB Considerations

Printed circuit board stiffeners act as crucial yet non-integral parts of the PCB. Because of this, you have to consider the following when it comes to deploying it on your preferred flex or rigid-flex printed circuit board.

  • It becomes essential to ensure that stiffeners overlap and are barred to cover-lay by 0,030inches to relieve pressure or stress.
  • It also proves crucial to maintain similar thickness, especially in instances where you are deploying several stiffeners.

Benefits of using Printed Circuit Board Stiffeners

We have covered the functions of printed circuit board stiffeners, but it becomes obvious that their deployment accrues some benefits. So how can you benefit from using a PCB stiffener?

  • Stiffeners (of whatever type) strengthen the solder joints, and this leads to an increase in abrasion resistance.
  • Additionally, stiffeners can become helpful in relieving the existing strain on the flex part besides helping with heat dissipation.  

How to Pick the Best Stiffener PCB Manufacturing Company

Picking the correct manufacturer of stiffener PCB can go a long way in determining the cost and quality of printed circuit boards. Therefore, if you want a stiffener PCB, it becomes pivotal to assess and pick a suitable manufacturer who will not satisfy your PCB needs but help you throughout the production process. So what criteria should you use in determining a top and qualified stiffener PCB company?

  • Consider the company’s profile in offering quality and diverse stiffener PCB products and services become a key indicator, especially when you want to contract a top manufacturer.
  • It also becomes pivotal to check the company’s quality management systems certifications to ensure that it has the capacity, pedigree, and resources to source for and produce quality stiffener PCB products for your needs.
  • Another crucial aspect involves the company’s adoption and flexibility concerning technological advances. If the company has new and state-of-the-art equipment and technologies, it implies producing quality and high-end PCB products attuned to your expectations.
  • Cost. A top manufacturer of printed circuit boards should have in-house sourcing mechanisms for their stiffeners to reduce the costs as much as possible. You do not want to incur extra expenses on account of the contracted company sourcing for stiffeners from other providers, which increases the total cost of the manufacturing and assembly process.

If you want a top-notch manufacturer that can guarantee you excellent quality of diverse stiffener PCB, then do not look beyond RayMing PCB and Assembly.       

Bottom Line

Stiffeners get used in the event you want a rigid area of the flex circuit. It also applies to the protection of connectors and components attached. Such significance and other benefits of a PCB stiffener make it necessary to get it from the best PCB manufacturer. Therefore, I hope the article has presented sufficient and helpful information to guide you to understand everything about PCB stiffeners. Additionally, you now know where to get your stiffener PCB production from moving forward.

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