NSA Just Emailed A Wench To The International Space Station
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Gallium itself melts at too low a temperature; you don't want your PC board melting when you touch it.
Hence the "like Gallium". :) Elemental Gallium would not work, but an unspecified alloy with a melting point low enough to be printed without destroying the substrate, yet high enough to not melt when used...that could work. I don't know if that is feasible, I am no metallurgist...and I never stay at Holiday Inn Express.
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an unspecified alloy with a melting point low enough to be printed without destroying the substrate, yet high enough to not melt when used...that could work.
As I said in the next sentence, an alloy with a suitable melting point could almost certainly be devised. The melting point of gallium is too low, and alloying it with a little of almost anything else will lower it further. However, it will hit a minimum at some ratio, and increasing the proportion of the other metal further will raise the melting point until it is eventually that of the pure other metal. Somewhere on that curve is a temperature, and corresponding alloy ratio, in the desired range. Whether that alloy would be suitable in other ways would be a topic for further research.
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So someone ahem changed wRench to wench...cute... :P
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All this just to create something in a single process. Many metals can already easily be electro-deposited and photo-etched very cheaply and with amazing precision.
3D printing is not poised to replace all other hobbyist manufacturing technologies, regardless of what Kickstarter says. It's great for making medium resolution plastic parts for low cost, or a wider range of parts for a higher cost. But, once you get above a few thousand dollars, you go from "let's see what we can do with one machine" to "let's use the process that makes us the most money for this task" and a 3D printer becomes just another station in a fabrication shop.
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Many metals can already easily be electro-deposited and photo-etched very cheaply and with amazing precision.
And copper certainly fits both of those, at least on earth. Going back to the original topic, that processing might or might not be practical on the ISS.
a 3D printer becomes just another station in a fabrication shop.
It would certainly be overkill for a 1- or 2-sided board. For a one-off complex, multi-layer board, it might or might not be a sensible way to make all the layers in proper alignment; there's no way to unless someone does at least some preliminary analysis.
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Also, something similar to Gallium could provide the conductivity, with a suitably low melting point. Some manner of conductor like silver suspended in a plastic or epoxy matrix would likely be a better choice. Provided that a change in manufacturing processes could get the resistance down to a suitable level.
I'd actually been thinking about something with lots of graphite suspended in it, perhaps using a printing mechanism more like inkjet printing than extruding? The conductivity might not be as high as copper, but it could be enough for the kinds of circuits that printing might make more sense to make.
Through-hole vias
One of the advantages of using 3D printing would be that there would be no need for the result to be flat at all. That PCBs are flat now is a side-effect of the process used to manufacture them. Provided you've got some sort of printable conductor (and an insulating matrix) you can make any old shape you want. A consequence of this would be that you wouldn't need any through-hole vias at all; the conductive elements could be routed through the body of the matrix directly.
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A consequence of this would be that you wouldn't need any through-hole vias at all; the conductive elements could be routed through the body of the matrix directly.
Heat dissipation could be come a bit of an issue. it's easy to bolt heatsinks onto a flat PCB, bit so easy to do that when the component you want to heat sink is buried in a 3D matrix. It's a solvable problem, yes but it is also a problem that we don't have with SL-PCBs and ML-PCBs can side step it by making all the ICs that get hot on the outside layer or by building in heatpipes to redirect the heat to where it can be removed via heatsink.
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Yes; it's probably best considered to be a totally different discipline to PCB design. (For example, you could incorporate channels for flowing water continuously through the matrix for heat removal without any risk of it ever coming into contact with the conductors.)
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i'd argue that it would then need to be integrated into PCB design. there's not good designing the worlds most elegant 3D PCB and then having the heat engineer saying that they're gonna need to drive a whopping great heat transfer conduit right through the heart of your PCB so that you don't end up cooking the PCB to death....
when you can print 3D PCBs then heat dissipation becomes a paramount concern to the circuit designer. otherwise things don't work so good.
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Provided you've got some sort of printable conductor (and an insulating matrix) you can make any old shape you want. A consequence of this would be that you wouldn't need any through-hole vias at all; the conductive elements could be routed through the body of the matrix directly.
Yes, you could eliminate the need for holes to route the conductors through the matrix. However, you still need a process where you can print the matrix and conductors together, either at the same time, or on alternate passes of the print head, which was the main point of that discussion.
graphite suspended in it, perhaps using a printing mechanism more like inkjet printing than extruding? The conductivity might not be as high as copper, but it could be enough
See my mention of "copper paint" earlier in the thread. Same idea, but better conductivity, and no more difficult to implement. The resistance of graphite traces would be, perhaps, an order of magnitude higher, which would degrade the performance of almost any kind of circuit, with no offsetting benefit that I can see.making all the ICs that get hot on the outside layer
I don't think @dkf was suggesting embedding components in the matrix. You could potentially print passive components — resistors, capacitors, inductors — but ICs are beyond the capabilities of 3D printers, and are likely to remain so for a rather long time; see the earlier discussion. You could, I suppose, have a robotic pick-and-place mechanism that would attach components to the board as it's being built around them, but I don't see a reasonable use case for that.It seems to me you might be thinking of something like a graphics card with multiple boards, and components between them (yes, heat dissipation is an issue), rather than a ML-PCB. The multiple layers are just copper-substrate (usually fiberglass-reinforced epoxy)-copper-substrate-copper-substrate-copper for however many layers, the whole thing only 2 or 3mm thick. Components are attached to the outside surface(s); there's no place inside to put them. That's what I've been talking about throughout this discussion, and I think that's what the other participants have been talking about, too.
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3D PCBs
I'm still not seeing a good use case for these. Unless you're planning to attach the components as you're printing the PCB, assembly is going to be hard/ridiculously hard/impossible, depending on the shape. As you've pointed out, heat dissipation becomes an even bigger problem that it already is. Conventional PCB manufacturing scales well from one-off to mass production; 3D printing doesn't.
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Unless you're planning to attach the components as you're printing the PCB
that was the idea actually.
and it would never work for mass production but just like emailing a wrench to the ISS it could be useful for specialized applications like space.
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