OpenServo.com

[guru]

I thought you might be interested in this since I think most everyone here does thier own pcbs.

I figured out a way (after hearing some rumors it was possible) to through plate vias and thru holes using a liquid from a car defroster repair kit. The kit cost about 10$ US and I got it at Advanced Auto Parts.

After etching both sides of the pcb, but before drilling, I placed a large sticky label over the pcb (mine were transparent like scotch tape). I then setup my cnc machine and drilled all the holes. Using the conductive liquid from the defroster repair kit and an old business card of my wife's ex-coworker/stalker I squegied the liquid accross the pcb over all the drill holes. I then used a vacuum on the pcb bottom side to suck the liquid through the holes.

The sticker of course protects the top and bottom of the pcb from getting any conductive liquid on it. How conductive is it? very! The paper I was using as a drop cloth got soaked with the liquid and at about 5 inches the resistance was 0.002 ohms. The vias turned out to be about .015ohms.

Some caveats:
* The liquid drys in seconds, too fast, when it is spread thin...so by the time I suck it with the vacuum its usually already pretty solid. Some holes seem to suck it through via hydrostatic pressure (?)
* Though you can do a little at a time, probably better to put most all the bottle on (its an extremely small vile), the liquid stays liquid when thick so it spreads well. Doing a little at a time seems to spread to thin.
* Some holes were clogged with liquid, some were clear. More often the clear ones work, the clogged ones dont!

For my first board, I think I have about 60% connected...not bad IMO. I will make a vacuum table to place the pcb on, this way, when I am spreading the liquid it is instantly sucked through the pcb. Probably get close to 100% this way. I will also get some tinning solution, if will add an extra leyer of conduction and should also lower the impedance.


My pcb had 10 mil traces and via holes using a #72 drill. Many of the vias worked. Normal through holes like 2.54mm headers also worked, even some large holes worked. Typically the through holes were the best as they were big enough to clear the liquid through without getting clogged. However, with the vacuum table, it should suck the #72 vias fine.

I welcome your suggestions. I haven't perfected the technique for sure. Any other ideas?

My cnc machine drilled the holes like a charm! love'n it! ...and routed the board out too.

I used the toner transfer method to create the pcb. I just bought the transfer paper, the TRF foil and the TIA laminator from the guy at www.pulsarprofx.com...this method rox! It is so much better transfer than iron and tonor...the TRF foil applied over the tonor really resists the etchant. This method can easily etch 8mil, they claim it can do 6mil with practice.

If I can master the thru hole I am all set!

Colin

[kbb]

An interesting idea. If the defroster repair kit liquid is setting too fast, how about silver paint?

http://www.maplin.co.uk/module.aspx?moduleno=36275

Maybe too expensive?

It is many years since I made a PCB (not that many were made), I used to put thin copper wire thru the holes and then solder both sides. This would be time consuming for a board with lots of holes, but then unless you are in production, possibly not a problem?

Kevin.

[ginge]

Hmm very interesting idea. It just so happens that I have some of that stuff (got it from eurocarparts) I just ran a test on some scrap and it seems to work ok-ish. With some practice and a good vacuum bed, maybe.

Usually I just pay for a prototype board these days. The stuff I work on is either impossible to make at home, or it is small enough to make it on stripboard. This may possibly change my mind, especially as I am starting to experiment with milling my pcbs.
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http://www.headfuzz.co.uk/
http://www.robotfuzz.co.uk/

[guru]

kbb: I am all to used to soldering wires in the via holes. Yes, my boards can be pretty large, My last board had 540 holes and it was *largely* surface mount. I had a real fun time soldering those little vias. I used a large board area to try and cut down on needed via usage too. Even for through hole parts sometimes its tough to solder both sides, like the 7 digit segment displays I just did, the displays are all melted from trying to get the top soldered. I will look at the silver paint, thanks.

ginge: Your always on board with my little expirements! Remember the LCD pcb developer? Seriously though, I am all for pcb houses too. But it gets expensive when you have a lot of projects you want to do. My boards are getting so complex they require 4 or more layers too. I need to be largely sure my design/schematics are correct by breaking it into small parts and testing first. I've decided I need a good pcb prototyping system with through hole plating and I'm resolved to make something that really works. I may make a electroless plating station, but if this defroster stuff works good, then it's the simpler and safer choice.

I am making the vacuum table today, I will post my results.

[guru]

ginge: Also, I tried the pcb isolation/engraving method too. Although my machine is definately capable, I couldnt get any software to work well. The best, *by far^10*, is the Eagle power tools converter. It worked like a charm, but I use Altium DXP which I like for it's complex board features. All the gerber to gcode programs I could find either crash or don't convert it well. I started my own code and I can understand the complexity of the algorithm. pulsarprofx.com 's toner transfer method works so well though, and is so quick and easy, that I've given up on using the engraving method, at least for now. The toner method, with the green foil, can easily do 8mil traces, pretty tough to do with engraving.

If you have any suggestions on the isolation routing I'm all ears though!

I made an NC drill file to GCode converter if you are interested. The program is not refined yet, but it's looking and working good. It's written in C# and should run on Linux too under mono -- I should say, I will get it to run under Linux as well. Mono is installed by default in Ubuntu. I am also working on a similar tool to convert a board outline to gcode. Simple concept, but you have to reorder the gerber data or you will get strange tool paths.

[ginge]

heh. I'm always up for trying something that assuming works, will make my life easier

"I made an NC drill file to GCode converter if you are interested. " Sounds good. Just out of interest is it any better than say, those poor eagle PCB to GCODE scripts?
_________________
http://www.headfuzz.co.uk/
http://www.robotfuzz.co.uk/

[reefer]

I also have the problem to get the NC drill data out of Altium Designer. How its going with your Converter? Is it working?

Sincerely,
Matthias

[cdvs]

Here is my solution: DiyPbcVias dot com

[nuten]

I placed a large sticky label over the pcb (mine were transparent like scotch tape).................
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