Why Flexible PCB need Stiffeners  ?

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 PCBs 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 .

 

When Using Stiffeners  ?

 

Stiffeners can be used to reinforce the areas where 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.

 

Stiffener 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.

 

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 

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 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 board, as follows:

 

 

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