Carbon Fiber PCB questions - Page 1
Forum section: electronics / projects

author: RobertBG
author_rank: Regular Contributor
timestamp: December 08, 2015, 11:01:40 pm
content: Hi,I've been looking into transferring a existing design over to carbon fiber for a limited edition run.I'm no stranger to composites but this is a little beyond my level and while I know it can be done,I'm not finding much about it.Most of the things I've found just have power traces run inside and not much as far as actual boards go.It is a single sided through hole design but there is one newer model that is SMD I hope to do later on.Would surface mount be a better way to go?How do they hold up in high heat applications?What difference is there between the two?Is it going to be a issue to have a board house use my existing board files?What sort of design considerations are there if it is possible.I'm sure there is a lot that I'm forgetting but the idea is to essentially have the boards manufactured and then put together the final product here in the States.It was something that was originally designed and made here and we're looking to relaunch the line and bring it back stateside with as much made here as possible.Lastly I'm not averse to farming things out I'd prefer to try and do as much in house as a learning project.Thanks

author: brabus
author_rank: Frequent Contributor
timestamp: December 08, 2015, 11:26:59 pm
content: Hi Robert,Well, being carbon conductive, we have to do our best to keep the traces insulated from the substrate; if you go for a completely SMD approach, I guess it would be easier --> no THT holes requiring insulation at all. If you still need some THT stuff, I suggest you to contact the manufacturer and find out how they approach this. The only one in EU I know that can handle similar stuff isSomacis.Regarding heat resistance, I guess it all depends on how much we are talking about. Carbon fiber itself is pretty tolerant, but the epoxy bonding the traces to the substrate may not like it. My guess is that heat resistance of a normal fiberglass PCB is far better. But again, in which temperature range are we?Maybe this can do the trick: develop your PCB on a thin flex substrate,as clear as possible, and then glue it to the carbon fiber with an optically clear adhesive. In this way you will be limited to SMD anyway, but insulation and robustness will be by far better. Plus, you can keep the carbon panels untouched, no drills and no etching at all. If the bonding is well done, the traces will seem to be printed directly on carbon.Don't forget to post some pics, when it's done!

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 08, 2015, 11:43:30 pm
content: Multilayer PCBs are made with thin layers of prepreg sheet - not sure if it comes with copper already on, so it may be possible to create a layup of carbon fibre and a surface layer of PCB prepreg, which could then be etched after curing.

author: IconicPCB
author_rank: Super Contributor
timestamp: December 09, 2015, 12:17:39 am
content: Mike,Mas lamination is a possibility.A couple of sheets of prepreg on top of carbon fiber layer topped off with copper sheet.We use copper sheet which has been pretreated with adhesive so that it can be laminated.I would imagine the carbon fiber laminate would need to be treated to enhance adhesion of prepreg.

author: ConKbot
author_rank: Super Contributor
timestamp: December 09, 2015, 06:58:33 am
content: Are you trying to stick a PCB onto a CF sheet or, embed it into it? If you're not doing RF or high frequency stuff, than I think a conformal coating on a PCB would go a long way for you. Use a coating that you can bond to well. (Acrylic or epoxy based? I doubt a silicone based one will be easy to bond to) Once its coated, go with whatever you would normally do for bonding stuff to the CF, just mind the curing temperatures. If you have tall components to deal with, and your laying up your own CF, then perhaps a die or laser cut pre-preg would help you support them right without adding lumps?If youre already doing CF work yourself, if you can get the PCB into a formfactor that you can use directly, I suspect it will be a lot cheaper than getting a PCB fab to lay up some pre-preg on a CF core.

author: RobertBG
author_rank: Regular Contributor
timestamp: December 09, 2015, 04:27:28 pm
content: They are audio amplifiers,2 class A/B are the through hole designs and I also have the designs and rights to a few class D's but I'm only interested in the one class D at this point in time for this project.So they do get pretty toasty.I realize at some point for profitability I may have to go surface mount but at this point it's all about reintroducing the product and it's simply a side project at the moment.brabus, Thanks for the links,that is similar to one idea I had.I've also been experimenting with laser cutting the carbon fiber for through holes prior to layup and it's been promising but I'm hesitant to spend the money on a laser cutter just yet.ConKbot, As far as trying to stick a PCB onto a CF sheet or, embedding it goes. We hope to get as close to a real carbon fiber pcb as possible due to us being a manufacturer of composite parts,the last thing we need is a fake CF product for marketing.Ideally it would be embedded but the more I research the more difficult it seems.Right now a real possibility would be to finish a black PCB off with a laser cut prepreg cf sheet topped with a clear sheet of some kind or layer of resin and the copper traces on top of that.I think I could cut the holes in the CF large enough to expose the through hole pads and vacuum bag it in house.It'll be labor intensive but seems like it should work.A little mold release on the pads would keep the resins from sticking but tying in the top layer traces might prove difficult.I think it's time to look into something small I can use as a test bed for laying up my own boards.I also don't see any reason why I cant use aramid/Kevlar for layup other than cost.There is very little info out there that I've found on board layup manufacturing.Anyone have any recommendations on where to look?Also if anyone has recommendations for little projects that use multi layer through hole pcb's that I could adapt to trying to figure this out.I'd really appreciate it.

author: ConKbot
author_rank: Super Contributor
timestamp: December 09, 2015, 07:53:49 pm
content: Quote from: RobertBG on December 09, 2015, 04:27:28 pmThe main PITA with carbon fiber will be if its conductive, if you can use a high resin low carbon type layup and get the resistance sufficiently high it could be workable as a PCB core material. When PCBs are made, the though holes are plated, so you'd end up with resistance between each though hole if its not high enough resistance. If you're open to using kevlar, then stuff gets a lot easier. If you can find a experimental/small run PCB manufacturer that's willing, plating the though hole may be possible.The least cheaty but not full CF/kevlar PCB would be to get your circuit put on a flex, bond the polyimide to the core. With CF with a high enough resistance, or kevlar, you could even drill the holes for though hole components. It would look like a single sided PCB, but you could get a multi-layer flex made if you want/need. All the strength would be provided by the composite, though hole components would still be going though it.

author: RobertBG
author_rank: Regular Contributor
timestamp: December 09, 2015, 09:55:23 pm
content: Thanks for the help so far,I really think I should be able to use a kevlar combo by cutting the through holes back a little extra on the carbon fiber outer layer and filling the void with resin during the vacuum bagging process.If not the clear substrate is definitely doable but I have some ideas in mind for further down the line that would benefit from the first method if I can get it to work.Thanks for the help so far,it's got me back on the right track

author: coppice
author_rank: Super Contributor
timestamp: December 10, 2015, 12:51:07 am
content: Quote from: ConKbot on December 09, 2015, 07:53:49 pmI worked with Kevlar PCBs in the early days of surface mount for defence systems. Kevlar has a similar thermal coeff of expansion to ceramic packages, so it has good thermal compatibility with military grade devices. It is thermally a poor match to most plastic packages, though, so you will probably have horrible thermal stresses in a typical commercial grade board. It really blunts drills, too.

author: RobertBG
author_rank: Regular Contributor
timestamp: December 10, 2015, 04:01:58 pm
content: coppice,We learned the hard way about what it can do to drill bits and cutting toolsWe worked on a bid for some ballistic panels and they had to be drilled for installation.I'd like to forget what we spent on drill bits for that one but since then we try and cut holes before layup and either use inserts or back fill them with resin and redrill after layup.Before layup you can take metal tubing in the size of the hole you need and sharpen it and either smack it with a hammer or use a press to do multiple holesAlthough I'm hoping to build or find a cnc laser cuter in the near future.

author: Ian.M
author_rank: Super Contributor
timestamp: December 10, 2015, 04:26:38 pm
content: Quote from: RobertBG on December 08, 2015, 11:01:40 pmI have one question: Why?It has similar issues to IMS (aluminium core) PCBs which are basically SMD only. To do through hole, you would need to find a board house that will work with you to drill oversize and epoxy fill all PTH holes before drilling them to size and plating them.I hope its not just for aesthetics: Its not even going to look very good as the glasscloth prepreg will obscure the characteristic weave of carbon cloth, so you would have little benefit over simply using black soldermask.

author: RobertBG
author_rank: Regular Contributor
timestamp: December 10, 2015, 06:35:56 pm
content: Quote from: Ian.M on December 10, 2015, 04:26:38 pmIan.M,the reasons are twofold,In short,I'm trying to use a limited edition to help create some hype for the products relaunch and get some needed exposure.I know a black mask would give the same look without the headaches or cost,but with a high end niche product where cost is not the driving factor we can afford to spend a little money in return for the exposureNow without getting into too many details it's also going to be valuable R&D exercise for a product we've been working on for some time in our primary field.For us it makes good business sense if we can make it happen.R&D is not cheap and anytime we can offset it with a marketable product we feel it's worth trying.Hopefully that explains why the troubles are worth it to us.

author: wraper
author_rank: Unknown
timestamp: December 10, 2015, 06:52:59 pm
content: Quote from: RobertBG on December 10, 2015, 06:35:56 pmSurely you will get some exposure because of the ridiculous reliability and/or performance. The single fact that it is conductive is a no go by itself. Guess someone need to sell some gold plated insulators for audiofools. The fact they do not insulate doesn't matter.EDIT: seriously put that carbon fiber somewhere else. For example, enclosure. Then advertise it as some new technology of full body electromagnetic shield (conductive).It's like making gearbox of the car from some premium wood. Yes it is premium material, but will it give some premium experience? (I guess not).

author: Ian.M
author_rank: Super Contributor
timestamp: December 10, 2015, 07:02:20 pm
content: Might make a really nice heated bed for a 3D printer!Otherwise, I would regard it as unsafe for anything except extremely low current low voltage circuits with all supplies current limited off-board so that a short to board substrate cannot cause dangerous overheating.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 10, 2015, 07:06:39 pm
content: One of the reasons you do not see carbon fiber PCBs is shedding of conductive fiber fragments when drilling.I had an audio product in a high strength, high carbon, case. We quickly learned to keep the drilling/cutting operations away from the electronics assembly area. Drill bit lifetime would be very short, as well.There are multilayer boards with heat conducting carbon cores under development, however it is a lamination, not a classic PCB.You could look athttp://www.stablcor.com/However, it is a carbon-carbon layer, not a carbon outer surface.http://www.stablcor.com/data/STABLCOR_Presentation.pdfSteve

author: RobertBG
author_rank: Regular Contributor
timestamp: December 10, 2015, 11:05:30 pm
content: Quote from: wraper on December 10, 2015, 06:52:59 pmIt's obvious that you cant see the benefit of adding strength to something in order to use it as a integral part.Or that someone might use a product to offset their research and development costs.Because you conveniently neglected to quote that aspect,but we both know that your comment was a jab at me

author: Nerull
author_rank: Frequent Contributor
timestamp: December 10, 2015, 11:16:15 pm
content: All the strength in the world won't do you any good if you put copper on top of a conductive material, and making your PCB support any significant load is going to result in a nightmare of broken solder joints...but maybe that's part of the plan too. Sell completely ridiculous concepts to idiots and then you get to consistently charge them for repair costs every few months. Win-win!Why not just make your PCB out of steel? Carbon is only strong in tension, its also quite brittle. Steel doesn't have that problem.

author: Ian.M
author_rank: Super Contributor
timestamp: December 10, 2015, 11:18:03 pm
content: Its full of potential problems, and you can get the same increase in strength and stiffness for less weight of carbon fibre by using the carbon fibre to make a frame for the board, but *IF* appearance isn't a primary concern, you don't have any HF circuits which would induce eddy currents in the carbon cloth, you skin it with FR4 for isolation, and you can find a board house that will work with you to customise their process, to provide PTH isolation from the substrate, and who has a supplier who can provide chemically compatible carbon fibre epoxy prepregs, its viable.

author: RobertBG
author_rank: Regular Contributor
timestamp: December 11, 2015, 12:53:31 am
content: Thanks for the ideas guys.........it seems like as soon as someone hears "audio"or anything closely related all of the haters jump on the bandwagon and neglect to actually read anything.Quote from: Nerull on December 10, 2015, 11:16:15 pmI'm completely aware of carbon fibers strengths,weaknesses and the fact that it conducts electricity.We manufacture and selll quite a bit of the stuffI also guess you glazed over the part where I also planned to use Kevlar or another aramid in the layup.Since the peanut gallery missed it the first time,I said thanks to those that had helped.I actually have heard back from a supplier that is quite interested.They currently do power distribution boards for drones and hopefully we'll have working solution in the near future.

author: Ian.M
author_rank: Super Contributor
timestamp: December 11, 2015, 01:02:54 am
content: Don't joke about steel as a PCB substrate:Its been doneover 30 years ago.(Steel coated with vitreous enamel with AgPd metallic ink tracks.)

author: coppice
author_rank: Super Contributor
timestamp: December 11, 2015, 03:45:42 am
content: Quote from: Ian.M on December 11, 2015, 01:02:54 amWhy mess about with steel? Just use ceramics and AgPd ink to make your PCBs. There was a lot of work with that approach in the early days of SMD work for defence applications. Think of it as a PCB that looks like a large ceramic PGA package.

author: SeanB
author_rank: Super Contributor
timestamp: December 11, 2015, 04:44:29 am
content: Flexible Polyamide board laminated to a precut carbon fibre board, and with large clearance holes for the through hole parts, with the through hole side being done with brass PCB rivets. That way you have the look and strength of the carbon fibre, and the rivets provide the mechanical hold for the through hole stuff like leads. You will have to have a larger clearance on the board around the holes, but this should work and look reasonable, as you do have the ability to do the required lamination work in house for the final resin work. If not flexible polyamide you simply use a very thin FR4 board ( thinnest the PCB fab can etch and drill) and simply bond to the carbon fibre, using a black soldermask to reduce the visual spoil of the carbon fibre.

author: rjeberhardt
author_rank: Regular Contributor
timestamp: December 11, 2015, 11:59:57 am
content: Quote from: RobertBG on December 11, 2015, 12:53:31 amNot at all. On the contrary you seem to think that different = better.Yes carbon fibre composites have some advantages. I'm using it for the pendulum in a precision regulator clock. For an audio amplifier pcb however the only advantage could be advertising hype.Russell

author: nukie
author_rank: Frequent Contributor
timestamp: December 11, 2015, 01:45:58 pm
content: Pyralux aka flexible pcb plus adhesive

author: RobertBG
author_rank: Regular Contributor
timestamp: December 15, 2015, 08:21:24 pm
content: Quote from: rjeberhardt on December 11, 2015, 11:59:57 amLike I said,you see one aspect andneglectto read the rest.What you failed to read or realize is that it is being used as a test bed for another product.Yes in this instance it is solely for looks but the plan is to take what we learn doing this for "the look" and implement it into a patented product where space and weight are the driving factors in the designs and market.This is simply to use a product line I'm partners with to absorb some R&D costs.Yes looks will help sell the product but that is not the reasoning behind this.I may not even bring the audio product to market,to me it is nothing more than a test bed to learn how to integrate something into our main line of products.Last but not least to the folks screaming "it's conductive,it'll never work" etc, in order to talk trash and hear themselves speak.Could you please go and tell that to all the companies manufacturing aluminum PCB's

author: Berni
author_rank: Super Contributor
timestamp: December 16, 2015, 08:06:19 pm
content: The whole idea seams a bit strange to me to be but it can be done.You can buy aluminum or copper core PCBs that are double sided with vias on them (Or even internal layers if you really wanted). How its done is that a very thin layer of prepreg is glued on to an aluminum plate. If you want vias on it then they drill holes bigger, fill them and then create the actual metalised hole as usual. Had such boards done before.I assume you can just use carbon fiber panels instead of sheet metal as the core but the PCB wont look any different visually except for the fact that it will be black at the cut off edge where a aluminum core board would normally look shiny. Perhaps a bit of the pattern would show trough if using a fairly transparent solder mask.