Wednesday, October 14, 2009


Copper Plating Wire Glue

I suggested previously that it might be possible to create PCB's by copper plating wire glue to create a low resistance section of track. Also, parts of the glue may be buried beneath plastic to maintain a high resistance, by preventing the plating process in order to make resistors. Anyway, I made a small PCB on our commercial machine, which consisted of a 3mm diameter channel that was later filled manually with the glue. Anyhow, after connecting the PCB to the positive terminal of a power supply and a small copper pipe to the negative, I left it overnight in some copper sulphate solution, with the power supply left at 0.1A (higher currents do speed things up, but the results aren't as tidy):
Anyway, it seemed to work, and after a few attempts there were some important findings:
  • The resistor shown was roughly 10mm long and its resistance came to 2kΩ, so it looks like wire glue has a sufficiently high resistance to make useful resistors. Unsurprisingly the copper plated sections had a resistance of 0Ω, and could be soldered to very easily (unlike the circuit produced using the solder extruder).
  • The track needs to be connected to the power supply both before and after each "resistor". Otherwise, the track is only plated up to the buried section of wire glue.
  • The entire copper plating process is much more even if a small amount of sulphuric acid (car battery acid) is added to the copper plating solution.
  • We need to be able to make several sections of track per PCB, and it is going to be a bit of pain to connect each section to the power supply. As an alternative, I included a small "bridge" whereby the track is only supported by a small section of ABS, such that it is easy to snap out afterwards to create two independent tracks. It seemed to work (see pic below), although its not as clean as I would like, but a support material extruder would help with this enormously.
  • It is very important to leave the wire glue to dry sufficiently (at least a few hours). I did make a few attempts where the glue was not completely cured, and virtually no plating was achieved, even when left overnight.
  • I did try producing the PCB using PLA on Darwin - it seems our infill settings result in the structure being porous. Of course, this could be easily remedied by altering the settings. However, if we change the infill such that some parts of the structure are porous and some aren't, we can allow the copper sulphate solution to seep into the structure; allowing track to be plated that is contained within plastic. This may prove very useful later on if we ever get around to doing things in 3D.

Now where is that paste extruder.....

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Wow, some great experimentation! Great job putting some wheels on this -- those are very nice pictures and results!
There are some ways to plate metals through non-electrical means, such as boiling, which would make it significantly easier to plate more complex circuits.

I've personally been experimenting with a few things from:
They have a few methods for plating various things with tin, and I think that description #6 (near the bottom) would be easiest. (Assuming plastic can widthstand boiling)

I'm sure there are similar processes to plate with copper.
Sorry to keep droning on about the same idea, but how about combining the electro-plating idea with tracks drawn by a conductive ink pen plotter?

That one is quite expensive since the ink is loaded with silver and it costs £22 but only promises to make 100ft of track. (~£1.40 per meter) but maybe as you intend to electro-plate the track anyway you could get away with a less conductive ink loaded with carbon?
>conductive ink pen plotter

Adrian tried this earlier this week, but hasn't blogged it. The conclusions are exactly the same, and it did indeed work. The only problem with it was that it doesn't tend to draw the track very evenly.He needed to draw over each section of track repeatably to build an even surface.
Why not use the reprap to lay down abs or what-have-you and then etch the exposed copper the way you'd normally etch it? Forest blogged about it a while back
>Why not use the reprap to lay down abs or what-have-you and then etch the exposed copper the way you'd normally etch it?

Short term the method you suggest is probably the best solution. However, in the future it has been penciled in to attempt to produce some simple electronic components. I think if we are to do this, wit would make life alot easier if we can produce the PCB using an additive method.
may be is out of topic yet but are you planning something with negative-resistors or other posible semiconductors experimental materials?
>are you planning something with negative-resistors or other posible semiconductors experimental materials?

No plans as yet but three years is a long time....That being said, I don't want my PhD to focus solely on electronics either.
As a matter of cheap and always available material, have you considered using human hair as a conductor?

Of course, I am kidding... almost. See the story of this Nepali who invented a solar panel using human hair as a photo-sensitive semi-conductor :

Building such 3rd-world oriented solar panels using a reprap would be a cool project indeed.
Talking of cheaper materials, I found this

Where he claims to make cheap conductive glue.

@Sig that article is a Hoax BTW.
Thanks Giles, I have given this method a try, but on my first attempt the resistance was far to high for any plating to be achieved. My plan is to get the wire glue solution up and running, and then experiment with the graphite/adhesive mixture to find the equivilent resistivity...
Hi. Have you heard about a conductive ink they have developed:

I don't know if this substance may be useful now. But it looks promising.

If printing these circuits is possible, it would be feasible to start experimenting with resistors and very small capacitors very flat and painted in the pcb.
Moving on slightly from the conductive glue and looking at a copper plating solution.

I have been messing about with etching PCB's using cupric chloride solution.

It pretty much does as suggested and you are presented with ever increasing quantities of copper chloride.

I whipped up a starter from peroxide and brick acid and so far have had passably good results. I am not really operating a precision process anyway though.

Given that this process makes a copper salt solution in abundance.

I guess it stands to reason that it is usable as a copper plating solution for use in electro plating.

This is a better method of use than trying to dispose of it some other way, and given the price of copper is a way to recycle scrap copper, from wherever it can be scrounged as well as recycle the copper etched from PCB's.

The major drawback is that using this stuff to electroplate liberates chlorine.... So the gasses either need recovering somehow to make more hydrochloric acid or must be vented safely away.

Thoughts for what they are worth.
Ulp sorry guys I pasted in the wrong URL you want this one for the cupric chloride info.
Zach mentioned that there are some ways to plate metals through non-electrical means (I believe the term is Electroless plating) Electroless copper plating is possible, I came across this:
You mentioned one of the problems with electroplating is having to connect each section of the track to the power supply. Have you considered automating the process of placing an electrode tip at various points on the PCB?

I.e. you would place the eletroplating dish with electrolyte on the reprap machine, the reprap would have a conductive tip toolhead which would move to different places during the plating process.

of course the obvious disadvantage is that you can only apply current to one section of track at a time, meaning that the plating process will take longer overall.
>Have you considered automating the process of placing an electrode tip at various points on the PCB?

I don’t think this will work. The problem is that the circuit board actually floats in the copper sulphate so actually has to be held under the surface to ensure the solution comes into contact with the board.
I must say, having created a few boards using this method I think it’s too fiddly for most people to be practical. That being said, I still think wire glue is a suitable material for resistors. Time for a different approach I think……

It may be possible to use a technique similar to plating pens but modified to work in a pen holder on a reprap.

For the basic idea take a look here :-

Change the gold salts for copper salts and use an annular electrode in stead of the croc clip and you may have a go-er.

It would be very controllable and you would be able to selectively copper plate without needing to initially encapsulate the elements you wanted to keep as resistors.

Turning the current on/off in conjunction with pen up/down would give you a very fine degree of control and minimise wastage.
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