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Copper wire deposition

Posted by rocket_scientist 
Copper wire deposition
March 03, 2010 01:06PM
One of the possible ways to manufacture a PCB board using a reprap is to press heated copper wire onto a thermoplastic substrate. It turns out that this has been done before, and there is a US Patent for this technique, which has no expired. But it means that we can build on this technique if it turns out to be a good way to build the boards needed.

The patent refers to insulated wires going point-to-point with no concern for routing or layers. The insulation would have to be cut or melted off at each end, and the copper wire bonded to the pad. I believe that patent calls for plated through holes to be made first before the board is wired. This can be done with a drill (milling head with small diameter bit) and then a riveting type head that will make a through hole with a rim on both sides. The wire is likely very thin, at least for signal wires, so spot welding the end of the wire to the through hole rivet would provide the needed electrical and mechanical connection.

For SMD, I think we would need to press a 'pad' of hot copper onto the board, then spot weld the wire(s) to it. I am not sure what range of pad sizes that would be needed. It could be of a thin ribbon and have a cutter cut off a piece, then place the piece. Or a tape of pieces that would feed through the placement head like the old cap guns. The advantage to the ribbon approach is that it can be cut to different lengths, and may be a less expensive to make in bulk.

Mike

Edited 1 time(s). Last edit at 03/03/2010 06:23PM by rocket_scientist.

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Re: Copper wire deposition
March 03, 2010 03:16PM
The problem I can see with this are that it is an all or nothing approach. What I mean is, unless you get the entire process automated, it will be far less convenient than the laser print then iron then etch method. With this approach, you still have to place all the parts, which is either done painstakingly by hand, or with a hugely complex tool to take parts of varying size and manipulate them into place. While I'm still concentrating on printing plastic parts, my thoughts are as follows:

The laser print/iron/etch method is an extremely easy way to print pcbs. I know opinions will vary on this, but I think blank pcbs are a suitably "low-level" material; they're cheap and widely available.

I'll admit to not having tried it, but I get the impression that adding solder paste to each pad is very fiddly without a mask. I think a reprap would be ideal for this, make a paste extruder that gets its information from the eagle files or whatever, place the etched pcb on the build area, and it wouldn't need a terribly accurate reprap to place the solder paste adequately.

Drilling pcb holes is likely to be possible with a high speed motor and tiny drill bit.

For placing components, I personally don't reckon the larger ones (electrolytic caps, transistors, switches) would be worth placing by machine. Humans are so much better at things like working out how long to cut the leads, knowing which pins to nudge to get an ic to fit etc. For my money, its the small smd parts that would save the most time. As most are roughly the same size (resistors, leds, capacitors), you could stack them in the appropriate order into a dispensing tube, get the reprap to hover over the location, then drop each one by one. With so many people making heated beds, it might not be too difficult to design them for the rapid heatup and cooldown needed for reflow soldering.

While making sure each head knows how to align itself might be tricky, I would think it would be possible to make the pcbs have a distinctive mark in each corner, so a simple sensor on the tool head could work out where it was.

Now I'll admit there are some serious advantages to your approach, what with being able to make 3d circuits and the like, but I know I could never make a machine to do the job that way, and my way is within my skillset. Several of the design challenges are already being worked on (paste extruder, drill head), which would help. I know I've rather gone off topic, apologies ^^
Re: Copper wire deposition
March 03, 2010 05:52PM
I share all your concerns. Right this minute, the laser printer route is much easier and faster. I use this kit to make them better with the transfer paper and laminator, but I have also made boards using my iron and ironing board. My goal here is to start discussions that will lead to better future models. I am trying for the Gada prize, and my plan is for a 4 head machine, and the conductive material will be solder paste, not copper wire, unless I come up with some much better ideas between now and then.

Mike


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Re: Copper wire deposition
March 03, 2010 09:17PM
You rocket scientists realize that there's an entire forum for printing wires embedded in plastic, right? smiling smiley

[dev.forums.reprap.org]

The spoolhead guys are working on something pretty similar for a few months now:

[objects.reprap.org]

And Rhys Jones printed a working circuit with solder almost a year ago:
[blog.reprap.org]

I'm not saying you shouldn't work on this, just though I'd point out some of the prior work that's been done in the area. Maybe you could team up with the folks already working on these concepts.

Wade

Edited 1 time(s). Last edit at 03/03/2010 09:20PM by Wade.
VDX
Re: Copper wire deposition
March 04, 2010 12:38AM
... i've already posted some comments in the SpoolHead-wiki ...

Actually i'm developing a diode-laser toolhead capable of cutting thin foils, sintering, melt solder or braze.

With such a laser and a solderpaste-dispenser (or look at the atached images here) embeded in a spoolhead positioning wires you should be able to draw and solder all needed connections in a PCB - either DIP or SMD ...


Viktor
Re: Copper wire deposition
March 04, 2010 09:28AM
No, Wade, I was completely ignorant of the whole forum. I will switch to writing there. I have been pulling ideas out of my original GADA forum team submission posts to make less confusing, individual titled discussions on each idea. But I have only just found this forum last Thursday, and have not read all the sections yet.

VDX, that looks like a fun expansion item to add!

Mike


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