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'[EE]: Reprap circuit printing'
2008\11\25@220641 by Brendan Moran

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The second generation of reprap is supposed to support printing
circuit.  The method proposed is printing low-melt metal such as field's
metal or woods metal.  This has a number of drawbacks, the low
melt-point is generally incompatible with any form of power electronics
since high temperatures could cause melting, woods metal is toxic and
the alternative, field's metal, melts at an even lower temperature.  
Because the molten metal has high surface tension, it must be poured
into channels rather than being extruded onto a smooth surface.


Based on these issues, I've been looking for another solution for
printing conductive material.
The broad requirements for the material are these:
1. Must be printable, that is it must be possible to load a syringe up
with the material, squeeze it out onto the substrate, and let it cure.  
Two-part compounds would be alright provided that a mechanism for
clearing the print nozzle is practical.
2. Must be conductive, at least as conductive as gold (Ag>Cu>Al>Au)
3. Must be readily available, this material should be something that can
be made easily or purchased easily.  Ideally, I'd like it to be less
expensive than conductive epoxy. ($26 for 6mL seems pricey to me)
4. Must not require high temperature baking (>150C)
5. Should not require lengthy cure time, this will slow fabing
significantly on complex parts
6. Ideally, should be solderable


There are four broad possibilities I've found:
1. Conductive particle suspensions, such as conductive epoxies.
2. Conductive thick films
3. Conductive ceramics
4. Conductive polymers such as polyacetylene

Conductive epoxies seem promising, but they are quite expensive due to
the silver content.  Still, this seems like the most immediately viable
option

I've not been able to find much information on thick films, conductive
ceramics, or conductive polymers.  I have found information relating to
some of the properties of polyacetylene, but no melting points, etc.
which are necessary to consider integration into a reprap.

I'd like to know if I've missed something obvious or if there's another
material out there which fits this bill.  Reprap could have a great
future before it if we can get past these initial growing pains.

Thanks,
Brendan

2008\11\25@231946 by Dr Skip

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A few come to mind:

http://www.mgchemicals.com/products/8420p.html

http://parts.digikey.com/1/parts/956980-conductive-pen-std-tip-3oz-cw2200stp.html

http://www.circuitspecialists.com/prod.itml/icOid/825

Frys and RadioShack also have ones similar.

3M makes a copper foil tape with conductive adhesive too. They probably have
other conductive items as well along the line you're looking at.

-Skip



Brendan Moran wrote:
{Quote hidden}

2008\11\26@002018 by Brendan Moran

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I've looked at the conductive pens.  They have a resistivity of 0.2Ohm
mils, which is 5.08x10^-6 ohm meters.  For comparison, nichrome wire, a
common heating element, has a resistivity of 1.10x10^-6 ohm meters.  
Nickel, Tungsten, Calcium, Aluminium, Gold, and Copper are all on the
order of 10^-8 ohm meters.

Those pens are only used for touchups because they introduce a lot of
resistance into a trace.  If I were to use pens, it would require very
careful power delivery.

3M may have the requisite product, but I haven't found it yet.

Thanks for the suggestions.

Brendan
Dr. Skip wrote:
{Quote hidden}

2008\11\26@083926 by Martin

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Brendan Moran wrote:
> The second generation of reprap is supposed to support printing
> circuit.  The method proposed is printing low-melt metal such as field's
> metal or woods metal.  This has a number of drawbacks, the low
> melt-point is generally incompatible with any form of power electronics
> since high temperatures could cause melting, woods metal is toxic and
> the alternative, field's metal, melts at an even lower temperature.  
> Because the molten metal has high surface tension, it must be poured
> into channels rather than being extruded onto a smooth surface.

What about engraving? There are ways of creating gerbers that use
single-width lines to separate signals rather than large copper-free
areas so the device wouldn't have to cut out large amounts of copper.
-
Martin

2008\11\26@103713 by William \Chops\ Westfield

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On Nov 25, 2008, at 7:06 PM, Brendan Moran wrote:

> The broad requirements for the material are these:
> 1. Must be printable, that is it must be possible to load a syringe up
> with the material, squeeze it out onto the substrate, and let it cure.
> Two-part compounds would be alright provided that a mechanism for
> clearing the print nozzle is practical.
> 2. Must be conductive, at least as conductive as gold (Ag>Cu>Al>Au)
> 3. Must be readily available, this material should be something that  
> can
> be made easily or purchased easily.  Ideally, I'd like it to be less
> expensive than conductive epoxy. ($26 for 6mL seems pricey to me)
> 4. Must not require high temperature baking (>150C)
> 5. Should not require lengthy cure time, this will slow fabing
> significantly on complex parts
> 6. Ideally, should be solderable

Wow.  Let me know if you find anything!  I would assume that no such  
thing exists, or it would be in common use.  After all, things like  
(industrial) inkjet printing or powder coating are a lot easier than  
the sort of chemical etching process used to make PCBs for modern  
electronics!  (Although, even with magic ink, you'll STILL have plated-
through hole issues, and track size issues...)

> There are four broad possibilities I've found:
> 1. Conductive particle suspensions, such as conductive epoxies.
> 2. Conductive thick films
> 3. Conductive ceramics
> 4. Conductive polymers such as polyacetylene

I think Conductive thick films tend to require high-temperature firing  
after they've been deposited.  That's why they go on ceramic substrates.

If by "conductive ceramics", you mean things like "MetalClay"; that's  
even worse.  These are fine nobel metal particles in a polymer base  
(not unlike your conductive epoxies), so they're very expensive AND  
they require a high-temperature firing to remove the base, AND they  
shrink 30%+.

You'd probably be better off looking for an etchant-resitant ink/
plastic that you can lay down on conventional copper clad; to be  
processed in the usual way afterward.

BillW

2008\11\26@110939 by Bryan Bishop

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On 11/25/08, Brendan Moran <spam_OUTannirackTakeThisOuTspamshaw.ca> wrote:
> The second generation of reprap is supposed to support printing
> circuit.  The method proposed is printing low-melt metal such as field's
> metal or woods metal.  This has a number of drawbacks, the low
> melt-point is generally incompatible with any form of power electronics
> since high temperatures could cause melting, woods metal is toxic and
> the alternative, field's metal, melts at an even lower temperature.
> Because the molten metal has high surface tension, it must be poured
> into channels rather than being extruded onto a smooth surface.

One of the big deals about RepRap is that it's designed ad-hoc,
meaning this stuff wasn't thought about in terms of "this component,
which would make it self-replicating, can't be made because we're
starting with _blah_ material, which can't be made by that other
component". Let me briefly explain-- Freitas previously published in
"Advanced Automation for Space Missions" and "Kinematic
Self-Replicating Machines" (KSRM) about this problem of
closure-engineering, which requires a little foresight on behalf of
the designers (to make a long story short, there's an 'open
manufacturing' mailing list out there working on a system to evaluate
a design for 'closure'):

Excerpts from KSRM on "closure engineering" --
http://groups.google.com/group/openmanufacturing/msg/4ff7a92e2425dde2

This doesn't immediately answer your question, of course, because it's
more long term rather than the "pick a material, any material and run"
method that you're asking help with.

In the beginning of integrated chips and the semiconductor industry,
guys were using huge sheets of wax and lenses from cameras bought from
down the street, and the circuits were millimeter scale, not
micrometer scale. While we're clearly not going to write out a digital
circuit at this large of a scale, it might still allow for analog
circuits. Ben Lipkowitz and I have been interested in clay pit
clanking replicators because of this, the aluminum and silicon being
useful for the glass or possibly other ways at getting very simple
circuits, maybe.

Another idea floating around is microfluidic logic, either through the
shrinky-dink methods where you throw it into an oven and it shrinks
down to size, or through the more conventional fluidics like you see
inside of pond assemblies when you break those down.

And then there's graphene and nanocrystals. The nanocrystal synthesis
methods are getting pretty interesting. To my knowledge there's no
simple semiconductor nanocrystal synthesis method, but I do know of a
few --
heybryan.org/~bbishop/docs/nano/eznanoparticles/
.. requiring low temperature plasmas, though. :-/ CNTs require CVDs,
which is a big turn off for a clanking replicator IMHO.

Graphene might be interesting however. You can use scannng tunneling
microscopes or atomic force microscopy to very delicately position
graphene into the circuits that everybody has been raving about:
http://heybryan.org/graphene.html

There are amateurs (or professionals?) who have worked on building
ridiculously simple piezo-actuated STM setups for ~$100 with things
like broken speakers and some screws.
http://heybryan.org/instrumentation/instru.html

The resolution isn't quite down to what would be needed for graphene
transistors (10 nm). That's a fairly large expectation for amateur STM
equipment; presumably the overall system needs to be more robust than
relying on 10 nm accuracy of tacky/hacky equipment. ;-)

Uh, there's probably a number of other materials I'm not remembering.
http://heybryan.org/semiconductor.html

{Quote hidden}

Good luck. One area that you might want to look into is proteins and
biological material. These could be grown and harvested, but the trick
is finding something sufficiently conductive and not requiring a lot
of specialty chemicals for feedstock, harvesting, that sort of thing.
(remnants of the "self-replicating bioreactor" concept - even the
plastic tanks would be made from the cell membranes, heh).

{Quote hidden}

Yeah, so to help solve the growing pains, just to throw in an ad here
I guess :-), what the OSCOMAK/SKDB and other projects (Freitas?) are
doing is this simple 'manufacturing web' where processes and materials
are cross-referenced to detail which process requires what. This then
allows a search algorithm to go through and do 'dependency checking'
much like in the debian APT system. Imagine going through and just
"fishing out" a replicating mechanism from the possibility space. At
the moment some aspects of the project have NSF funding for cyber
repositories for open hardware designs, so things are moving well.

Best of luck,

- Bryan
http://heybryan.org/
1 512 203 0507

2008\11\28@102008 by Brendan Moran

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Bryan Bishop wrote:
{Quote hidden}

The point of the approach that I am taking is simple: I want the two
materials used, conductor and filler, to be similar.  This leads to a
large number of capabilities which are not otherwise possible.  
Conductive polymers seem like a really great approach to acheive that.
{Quote hidden}

I'm not sure how microfluidics are relevant to printed circuits
{Quote hidden}

Sorry, are you actually suggesting building an atomic force microscope
onto reprap?  Not that AFM isn't cool or anything, but it seems like a
pretty big hammer for a mighty small nail.
{Quote hidden}

There are a few possibilities I've found now.
1. Polyaniline seems to be a very good conductor, but it's typically
used in thick film applications.  It's possible that polyaniline,
polyacetylene or some proprietary polymers could be mixed into PLA to
make a conductive PLA. I like this one the best.
2. I've found one supplier or conductive plastic.  The conductivity is
provided by stainless steel fibres, so the conductivity is lower than
I'd like, but it still could work.  
www.3ninc.com/conductive_plastic_master_batche.htm
3. Thick film is still an option.  The local uni has a thick film expert
whom I'm going to talk to in a few weeks about the project.  If he has
some ideas, I should be up and running.
4. As I've been searching, conductive silver ink--not conductive
epoxy--keeps coming up.  I've found a few better options on using it, so
it's now a viable option too, the drawback being that it really needs
conductive epoxy as solder.

Brendan

2008\11\28@110103 by Bryan Bishop

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On Fri, Nov 28, 2008 at 9:19 AM, Brendan Moran <annirackspamKILLspamshaw.ca> wrote:
>> Another idea floating around is microfluidic logic, either through the
>> shrinky-dink methods where you throw it into an oven and it shrinks
>> down to size, or through the more conventional fluidics like you see
>> inside of pond assemblies when you break those down.
>>
>
> I'm not sure how microfluidics are relevant to printed circuits

Microfluidic logic would be an alternative to printed circuits if that
happens to fail in your investigations.

{Quote hidden}

No, I am not. Your original intentions seemed to be "make reprap more
thoroughly replicate itself", so you have to admit that this might
mean a re-design of many components until you can find something that
"for sure" replicates. I know that you were looking just for a method
of printing out circuits, but it's conceivable that the direction that
reprap has started from and is going down doesn't lead to a quick
replication solution.

{Quote hidden}

Feel free to post your linkdumps and references that you're reading.

- Bryan
http://heybryan.org/
1 512 203 0507

2008\11\29@054203 by Mike snyder

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On Tue, Nov 25, 2008 at 10:06 PM, Brendan Moran <.....annirackKILLspamspam.....shaw.ca> wrote:

{Quote hidden}

1. Wonder if there is some material that once applied to a board could
serve as a catalyst to let copper adhere - think copper/nickel/zinc
plating via a catalyst

2. Check out LPKF site http://www.lpkf.com/products/3d-mid/index.htm,
they seem to have developed a process to create molded interconnects
and maybe there is a similar material that can be applied and
subsequently baked or processed via a laser to activate

3. Maybe look at a wire warp type model where the various layers of
the PCB are simply wire-wrapped with posts to solder components to?
Might not be the most elegant but for prototyping might be a way to
go??

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