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PCB Etching with a Sponge

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Hon1nbo

Tue Jul 14 2009, 03:12PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

I found a neat article via Hackaday that shows how to etch PCBs using a sponge to save material and time.

here

klugesmith

Tue Jul 14 2009, 08:47PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

I am skeptical about the claim of etching faster than a traditional agitated bath. The cited article says nothing quantitative about Cu thickness, etchant concentration and temperature, etc. Nor offers any explanations or reasoning. Has anyone here tried the sponge method, or is planning to? [edit] After reading the comments on hackaday page, I'm less skeptical. Figure it could do well in a race against other DIY methods, though not against commercial double-sided spray etchers.

The wet sponge approach reminds me of electrolytic etching, using a simple salt solution aided by electric current. It's been used (in a bath) to etch through stainless steel sheets, for DIY pulse-jet reed valves. In sponge form (actually wet paper towel), I've used it with mimeograph stencil material to mark hard metal parts in just a few seconds -- see

for a commercial version.
Would work on PC boards up to the point where the first land area becomes electrically isolated.

Killa-X

Wed Jul 15 2009, 12:30AM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Klugesmith wrote ...

I am skeptical about the claim of etching faster than a traditional agitated bath. The cited article says nothing quantitative about Cu thickness, etchant concentration and temperature, etc. Nor offers any explanations or reasoning. Has anyone here tried the sponge method, or is planning to? [edit] After reading the comments on hackaday page, I'm less skeptical. Figure it could do well in a race against other DIY methods, though not against commercial double-sided spray etchers.

The wet sponge approach reminds me of electrolytic etching, using a simple salt solution aided by electric current. It's been used (in a bath) to etch through stainless steel sheets, for DIY pulse-jet reed valves. In sponge form (actually wet paper towel), I've used it with mimeograph stencil material to mark hard metal parts in just a few seconds -- see

for a commercial version.
Would work on PC boards up to the point where the first land area becomes electrically isolated.

I can't say when but I'll give it a shot sometime with a scrap peace of copper if you want. Sometime this week. Unless someone beats me to it I'll let you know how it goes. And to test it comparing to my agitator, I'm not going to heat it, I'm going to do the same exact thing, Bring it out of garage, And go for it. My agitator took around 15-20 mins due to radioshack ferric chloride being slightly less powerful. But I'll still try this.

edit: Ok, It does work faster. I used a very crappy print (rushing, did like 30 secs of ironing) and then I went in the garage, took a sponge, got the corner wet (solution in jar) and moved back and forth on it faster with not much pressure. It did work, the center was getting green, but I accidentally droped my board, and it fell into water. I have a feeling this is why it didnt work for the rest of the board. I got water on the sponge, water does help slow the reaction, and well, wasnt as fast.

I only did a 1X1 inch board, and it did turn out besides the sides due to me dropping it. But i did work on it longer than 2 minutes. But at least it beats 15+ minutes. I'll still try it tomorrow or so when I can have more time. I'll try thin traces because i noticed those can be destroyed fast. So tomorrow, I'll post pictures up on the forums of my "larger-spent-time" board. thanks.

klugesmith

Wed Jul 15 2009, 06:00AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

I tried it tonight with 3 modifications:

1) scrubbed gently with a very soft toothbrush instead of a sponge. The brush might do an even better job of replacing depleted etchant with fresh material at the working surface. But might be harder on fine patterns of resist material.

2) Instead of getting out the ferric chloride & making a mess, I used a strong solution of table salt, 1/4 inch deep in an aluminum dish, with electricity from a benchtop power supply.

3) No resist pattern at all. I etched one corner of a scrap of one-sided copper-clad material. (unknown foil thickness), until a 1/2-inch-wide triangle of laminate was exposed.

Dipped the board corner until it touched bottom (without metal-to-metal contact). Connected power supply, set to 15 volts with maximum current of 0.55 amps. Things got fizzy & yucky fast, as I worked the brush. Timing was not at all scientific, but I think it took less than 3 minutes. There might be some thin traces of copper left that lost their metallic connection to anode supply, so if this were a real PCB it would need real etchant to finish up.

Killa-X

Wed Jul 15 2009, 07:41PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

Tryed it today with a circuit of a 555 tester, it went slower today, maybe it was colder yet, but once I got a spot of yellow (board color) showing, it went very fast. There seems to be a way to do it. I noticed when i had a spot going, i bearly put any pressure at all and it went off. Idk its a very confusing way. I like it because it's less hassle and way less messy. I found this way clean :)

And for disposal, my bottle says to mix with Wash soda, and you can dump it down the drain after it sits for awahile, so I useed super wash soda, and let it go for awhile, and yeah :) Just following the etching solution directions.

Picture! (The 1.0 at the bottom failed, I knew sharpie couldn't be near as good!)

Conundrum

Tue Jul 21 2009, 09:00PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

yeah, i saw that. the brush modification is pretty cool.

perhaps someone can automate the process to etch pcbs super fast using a servo and spare (cleaned) soldering iron sponge?

also, used ampersulf should work well.
-A

Killa-X

Tue Jul 21 2009, 10:41PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

The other way I saw today was a bubble tank.

Looks like it works, and it does make it a kinda-more clean method. You just have to bubble the ferric chloride with the board in it, and he made a valve to remove all the fluids

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