Which material is used in flex PCB circuits ?

[Sai teja]

Hello,
We are planning to use flexible PCB circuit in our application. Can anyone please suggest the material used in flexible PCBs ? We are looking for the flex PCB material similar to the one used in Olympus Stylus camera. I am attaching the image for your reference.

we are looking for the material which does not break on bending sharply.

Please help me in this regard.
 

   

[tooki]

Isn’t that Kapton (polyimide)?

[Sai teja]

I am new to this field. Please give me suggestions regarding the material. Our objective is to use material which is more flexible and doesn't break even on bending sharply.

[timpattinson]

Please give me suggestions regarding the material.

Isn’t that Kapton (polyimide)?

[Rerouter]

Most flex pcbs usevarious thicknesses of  kapton, because its thin, heat resistant and is resistant to stretching.

The bend radius is what you will need to figure out. The thinner the copper and kapton, the more flexible and tighter the radius can be without deformation.

However this makes it easier to tear and cant carry as much current

If you hard fold one of those cables you risk thermal cycling creating an intermittent connection later on if the copper is on the outside of the tape. Inside of the tape may face delamination

[sleemanj]

http://www.dupont.com/products-and-services/electronic-electrical-materials/flexible-rigidflex-circuit-materials/brands/pyralux-flexible-circuit.html

[TimFox]

Be careful about tearing Kapton:  a tear, once started, will propagate.  Otherwise, it is the standard material for bendable PCBs.  I first saw them inside cameras, for the contorted circuitry around the light meter, etc.

[SiliconWizard]

Polyimide substrates are the most common for flex PCBs.

Kapton is a DuPont brand, and although it's a polyimide film, not all flex PCBs are made of Kapton.

[tooki]

I didn’t say all flex PCBs are Kapton, just that the one in the image is (since it’s typical Kapton yellow).

[SiliconWizard]

I didn’t say all flex PCBs are Kapton, just that the one in the image is (since it’s typical Kapton yellow).

I know!
You were not the only one mentioning Kapton, and I was just making this point so that the author can talk with PCB manufacturers with minimal misunderstandings. Most of the manufacturers I worked with were claiming the use of polyimide. Now try specifically demanding *Kapton* and see what response you may get.

[tooki]

I didn’t say all flex PCBs are Kapton, just that the one in the image is (since it’s typical Kapton yellow).

I know!
You were not the only one mentioning Kapton, and I was just making this point so that the author can talk with PCB manufacturers with minimal misunderstandings. Most of the manufacturers I worked with were claiming the use of polyimide. Now try specifically demanding *Kapton* and see what response you may get.

I would expect it to be much the same as with Teflon (another DuPont brand), where everyone uses the brand name, not the chemical name (PTFE): you’d get what you want, perhaps with an explanation of your particular manufacturer’s brand name for it!

[amyk]

Kapton has already been mentioned, but another common one is polyester or acetate (clear).

[TheUnnamedNewbie]

For completeness I'd like to add the fact that some other flex substrates are LCP (liquid crystal polymer) and teflon, used in RF/automotive radar and such.

[jbb]

Kapton has already been mentioned, but another common one is polyester or acetate (clear).

Be aware that polyester has a lower service temperature than polyamide.  E.g. polyamide can have components soldered to it, but I don't know if polyester can.

There are some very handy tricks than can be applied to flex PCBs:

• PCB design tools are set up to make rigid PCBs.  Designing flex PCBs will involve discussions with the manufacturer about how to express your design (e.g. how do you represent where a stiffener layer is placed?)
• Stiffeners can be added to carefully define where you want to bend the FPC
• You can use FR4 (fibreglass) stiffeners to make a rigid area and solder components on
• You can get adhesive strips (i.e. double sided tape) applied by the FPC manufacturer to help with mounting
• You can choose between etched copper (more precise, finer features, more expensive) and conductive inks (coarse features, more resistance, cheaper in volume
• A conductive EMI shielding film can be added to the outside to form a very thin ground plane (it's going to be a ground plane. No tracks possible)

I've got a design guide somewhere, I'll try to post a link later today.

[KL27x]

(e.g. how do you represent where a stiffener layer is placed?)

No need to overcomplicate it. Just make a Gerber layer, draw where you want a stiffener or an adhesive and include the dimension layer, and label the file with something that indicates the purpose. I suggest "[PCB name] [rev number] - Top/Bottom Stiffener Layer" or "Top/Bottom Adhesive Layer." Just make up a unique extension. Or not. I don't think there's any manufacturer out there can't figure it out. The old "standard" extensions are pretty much obsolete, and if the manufacturer wants you to use a specific extension in the future, they will tell you.

And attach a note as to how thick of a stiffener/adhesive, and what you want it to stick to. Then let then come back to you with options... They have certain materials on hand which they prefer to work with due to sourcing/cost/familiarity. They'll be able to suggest 3M xxxx or what not that you can look up the specs on.

It's nice to know these are options. But OP, there's no need to stress about it.

Many of the major manufactures' quote system will show you at least some of these options, particularly where it comes to the board material and thicknesses available. 

IME, the minimum parameters are all the same, regarding minimum hole size and trace width without incurring extra cost, etc. Pretty much the same thing as ordering a rigid PCB, except prototypes cost more. I guess there isn't enough demand to make pooled services as efficient. In volume, the cost isn't necessarily much different.

For a cheap proto, check out ITEAD. For their cheap proto service, they do have specific extensions they request for the standard Gerber layers, but it's all detailed on the site.

[jbb]

Yes, that’s what I meant: you end up doing everything manually on ‘mechanical’ layers. So be careful when you make the Gerber files (I.e. remember to export all the layers you need) and remember to communicate with the manufacturer.

At work we actually do a big boilerplate with a layer stack drawing to indicate layer arrangement, thicknesses, via styles etc. it also includes fabrication notes and a legend of what the Gerber layers mean.

The golden Grber rule: one layer per type of thing. If you need a top stiffener and a bottom stiffener, use two mechanical layers. If you need an FR4 stiffener on the bottom layer, use another mechanical layer. If you want some adhesive tape, that’s another layer. They add up fast...

[tooki]

Kapton has already been mentioned, but another common one is polyester or acetate (clear).

Be aware that polyester has a lower service temperature than polyamide.  E.g. polyamide can have components soldered to it, but I don't know if polyester can.

Just to be clear, Kapton is a polyimide, not a polyamide, which is a totally different family of polymers.