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Old 22nd June 2003, 11:49 PM   #1
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kiwi_abroad's Avatar
Join Date: Sep 2001
Location: Wellington, New Zealand
Question Etching 4oz PCB boards

Hi All,

I'm looking into purchasing some double coppper clad boards from Digikey, for a power amplifier, and I see the board size I'm after costs the same for both the 2oz and 4oz copper.

My question is, will there any drawbacks to getting the 4oz PCB? Will there be any problems with etching, undercutting of the track or likewise? I think 4oz will only be beneficial for the electronic side of things. The amplifier will be around 150W for a sub-amp.

After thinking about this, I came up with another question, is there a formula to work out how much etchant I will need to properly etch the board. eg If I'm etching a 4oz (or 2oz) double sided board, and I'm removing 50% of the copper (maybe worked out from the PCB design software), then how much Ammonium Persulphate will I need to etch the board in reasonible time without wasting too much, or without the etchant 'running out of bite'

Thanks, Adrian
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Old 23rd June 2003, 12:54 AM   #2
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JOE DIRT®'s Avatar
Join Date: Apr 2003
Location: Brantford, ON
formula is the same....etching time is just increased....also with 4 oz boards finer traces are harder to do without pro a test run and you will see the results for yourself....I have never needed to use that heay of a board because all my transistors have been remotely mounted and a 2 oz board can carry alot amperage on short traces

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Old 28th June 2003, 03:35 PM   #3
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Location: Salt Lake City
Keep the solution warm as it will speed up the etching process and make undercutting less of a problem.
We have a local PCB manufacturer that does plated on traces that can handle 100 amps current if anyone is into building a really serious amp!! They make alot of them for Hill AFB.
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Old 28th June 2003, 05:46 PM   #4
jleaman is offline jleaman  Belgium
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Here you go sorry for the bad pic ill look for more in my thousands of picture's..

it is a home made tank that i built for etching. In it is a fish tank heater and a fish tank bubble creator. at the very bottom. What you do is put air through the bubble creator at the bottom and it creats soft bubbles to flow over the board that is hanging in the enclosure. if it is heated and bubbles are used it speeds things up alot and helps etch the board in all places not just a few.. any questions please ask..

Also i use amonium persalphate.
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Old 28th June 2003, 09:09 PM   #5
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The bubbling method works very well. What I do is to float the PCB on top of warm solution. This way the heavier dissolved copper falls away fom the board being etched and there is always clean solution in contact with the copper to be etched. The result is very quick etching, sometimes about 15 min for 1 oz material.
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