Possible Ideas for Multi-Layered PCBs

Discussion in 'General Discussion' started by Archimedes, Sep 26, 2014.

  1. Hello All.
    After running into these guys at the World Maker Faire in New York and getting into a long discussion about the printer, possibilities and more, the conversation drifted towards the possibility of Multi-Layered PCBs. I came up with a few ideas and they suggested that I ran them by y'all on the forum. Here goes...

    First idea:
    - Take a UV quick-curing fiberglass resin (possibly fiberglass repair goop) and apply a thin layer over the current circuit. If the fiberglass had a low enough viscosity, it could be sprayed on instead of having to be extruded.
    - After the fiberglass is applied, a UV light (preferably attached to the print head) would do a sweep of the board.
    - To bind the next layer to the fiberglass, a thin layer of quick-dry epoxy could be sprayed on top of the fiberglass.
    - Ideally, the printer would print into the layer of epoxy making it more secure and thinner (negligibly but still...).
    - UV light used again to cure the epoxy (hopefully UV curable)

    Second Idea:
    - Use a non-conductive adhesive that could be printed onto i.e. Industrial Grade double sided tape (can be purchased in 6 inch (or more) widths easily covering most boards)
    - The adhesive would need to be applied by hand so more babying would be required, but it would much less complex mechanically.

    Those are the current ideas. Have at it.
  2. Michael Reed

    Michael Reed Staff Member

    Hey Archimedes,

    Thanks for your suggestions! It's nice to hear that these problems are consuming other people's minds too haha.

    We have a similar project that we are working on right now but this idea seems something that would be a lot more simple. We'll have to try and get some fibreglass resin to see if we can test it out - the only thing it lacks is the ability to leave holes for vias. The issue that we're least clear on a solution for at the moment is a good method for binding the ink down onto the insulative layer.

    Your suggestion of a quick-dry epoxy may be viable, the main issue being that printing the tracks leaves a reasonable amount of water as a by-product. At the moment the printer uses a contact absorbent roller to remove this but if the board was covered in epoxy, this would cause problems.

    The double sided tape is an interesting idea we haven't tried yet - it would provide a nice thin layer. Plus the layers would all be translucent which would just be bad ass. It would have the same problem of sticking to the absorbent roller though and if you use a material that can't deal with high temperatures, it means you won't be able to solder to the board. But multi-layered boards would be cool even if they relied on Conductive Silver Epoxy, z-axis tape etc.
  3. Vias could be problamatic. The only thing that I can think of right now is copper crimping tubing. If you were to mill out the vias (with a pcb bit after the print) and then insert a small piece of tubing, that might work. The hole would need to be small enough to friction hold (still viable as nobody is going to be hitting it with a hammer) the tube and as to not interfere with the traces.
    While copper crimping tubing may not work, I think that inserting something afterwards would be much easier than trying to design away to make a layer go around the via.
  4. Thought of another idea for vias. If you sprayed down epoxy in a row/column method, it would allow you to create a square space for vias. For example, if you have a 1/16 inch via an inch from both the left and bottom side, you'd spray epoxy horizontally from 0 to 31/32 of an inch (assuming that the distance is measured from the center of the via), and then continue to spray from the 1 1/32 inch point to the end of the board. To finish the layer, you'd spray vertically using the same stop and start locations as before. This technique could be applied for any number of vias and would leave spaces for the conductive ink. It also means that you can have selective vias (i.e. a via only going from layer 4, 3, 2 for example) and not have to drill a physical hole in the board. While this technique would theoretically make the layers twice as thick, the thickness could be controlled by changing the amount of epoxy (or whatever) sprayed down.
  5. Michael Reed

    Michael Reed Staff Member

    The methods we were focussing on the moment mostly involved finding chemicals that we could apply in an inkjet cartridge because that would be the most practical with what we already have set in place for the Argentum. Though recently I did a tour of a local electronics manufacturing house and they had a machine performed a CNC controlled spray of a UV curing lacquer material (used to just environmentally protect the boards etc). This made me think that a controlled spray head may be do-able.

    The upside to that style of deposition is that you have a wider range of available viscosities (opening up the possibility for these kinds of materials) & you can deposit it very quickly but the downside is you need an entirely new tool-head, the infrastructure to support it and you lose a lot of your resolution.

    For now, we'll probably focus on getting something 'inkjettable' because this would allow us to print insulative materials in the same resolution as the conductive materials and would make tiny blind vias (this is the name for the vias with no drilling you described) a piece of cake.

    By the same token, we would love to get onto something like this afterwards too & if you (or anyone else) wants to experiment with it yourself before us, that would just be gravy.
  6. One last question... How hard would it be to add another roller designed to apply a thin layer of insulative material over the circuit?
  7. Michael Reed

    Michael Reed Staff Member

    Hmmm not easy I would wager. The roller was something that was already very frustrating to put in (while still making everything able to be laser cut and not losing heaps of print area). Maybe it's possible to have like a semi automated process where you swap the roller out for something solid and squeeze down the insulative material in front of it...

    But by the time you swap the roller and make sure everything is still lined up and then have code that makes assumptions on where it pushes the material etc. you might as well just use a credit card like piece to squeegee it over by hand. Perhaps that's not the worst thing in the world though.
  8. Other ideas:
    1) Only place non conductive layer where you want a cross over track ie in local areas under this track. This would be a good first step and is the normal method on ceramic thick film circuits
    2) Jet a fluid like Tippex (UK brand name for a white typo correction fluid) that air dries - the problem here is the settling of any solids
    3) Jet a water based polymer like acrylic - drying time would be longer
    Ariel likes this.
  9. i was going to ask you about this (or similar): if i were to buy one of the cartesian printers i would need the conductive layer to be masked and covered except surrounding the SMT pads.
  10. Michael Reed

    Michael Reed Staff Member

    Hey Luke,

    We don't have it up and running yet unfortunately - development timeframe took a bit of a setback as we moved everyone to different offices around the world (I'm currently typing from Shenzhen, China). I can say that we probably won't be looking down the path of a spray head (ie. something not an inkjet cartridge).

    There are some UV curing inks that are potentially compatible with our cartridges (after some tweaking) that we're just beginning to look into now. But as yet, we don't have any concrete evidence as to how viable/useful/affordable the end result will be.

    I'm not working on it myself but I can guarantee that if we make something viable that will automatically apply a solder mask, we will definitely post a bunch about it on Facebook/Twitter/the Blog. I'll try and remember to post anything super cool here though.

    PS I really want to be working on this myself too - so don't worry, I'll keep the pressure on the guys looking into it.

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