Etching question:

[MikeH]

I ordered some copper blanks, but I accidentally bought the 2-sided variety (Grrr!!).  I'm guessing my only option to use them would be to etch the entire second side off, otherwise I'd have a high likelyhood of shorting the whole circuit out, no matter how well I insulated the top side.  Which really sucks because it's a waste of etchant, but I guess I'll only use it for very small boards.  Would you recomend I etch both sides at the same time, perhaps by proping the board up on some toothpicks?  Or should I etch each side individually, while covering the other with resistant? 

[Narcosynthesis]

sandpaper it?

etching needs to be a lot more precise, hence the chemicals and masks and so on, but if you need the whole side off, takinging some sandpaper to it should do the trick

David

[MikeH]

That's a good idea.  Why didn't I think of that?  I love this forum...

[David]

Instead of dunking your board, why don't you try CAREFULLY brushing etchant onto the side of the board you want to remove the copper from?  Don't brush all the way to the edges.  Let the edges etch off when you do the "good" side of your board.

Let us know if it works.  Could be another weapon in the ol' arsenal...

[MetalGod]

Instead of dunking your board, why don't you try CAREFULLY brushing etchant onto the side of the board you want to remove the copper from?  Don't brush all the way to the edges.  Let the edges etch off when you do the "good" side of your board.

Let us know if it works.  Could be another weapon in the ol' arsenal...

you could use spraypaint on one side to mask the copper - that way you could protect the side you want to use.

[MikeH]

I thought about just doing that, but I'd have to insulate the compnent leads from the top sheet of copper.  Once I drilled the holes for the leads, the copper would be exposed, and not matter how well I tried to shield the leads from the copper, the whole damn thing would just short out.

[Paul Perry (Frostwave)]

It might be possible to peel the copper off one side, if the adhesive can be melted by a heat gun..... I havn't tried this, it might be a very bad idea.....
Really, I'd just leave it there & waste the etch, myself.

[sfr]

I've done this once before - (I made the same mistake that you did!) do my P'N'P as normal, and then carefully drill the component holes before etching.  (The P'N'P is remarkably resiliant, but I'd still be careful centerpunching for the holes and clamping the board)

After I've done that, I know where all the component leads are.  I took small round stickers (somewhere inbetween a 1/4 and an 1/8 inch diameter - they had smiley faces on them - it's important to get the smiley faced ones for the best tone in your build.  Preferably N.O.S. if you can find them   ) from the drug store, and placed them over all the holes for the leads.  Then I painted on a heavy layer of acrylic paint over the back side.  after that had gotten a bit of tack to it, I peeled off the stickers.  Etched the board as normal.  (Took a bit longer because of the two-sided nature, and was a little more difficult to watch both sides.)  Worked relatively well.  After I was done populating the board, went and checked everywhere for shorts before applying power.  Had no problems. 

Next board I did with that copper, I just took a belt-sander to it and took all the copper off one side.

Another option, if you have smaller circuits to do is to just mount all your components on the top, (sort of like how SMDs are done) without going through-hole.  I wouldn't want to do anything huge like this, but I've done it for simple boosters and several Millenium bypass boards.  The nice thing about this is you can then mount the small board with double stick tape with no problems. (If this description doesn't make sense, there's picturs of something similar at Tonepad - look at "populating an amp board" under the "photoessays" section.)

I've even done small circuits in the fashion of the above without even etching - making sort of my own "stripboard" variant by taking a hacksaw and slicing vertical "breaks" in the copper on top of the board.  I would credit where I saw this idea first if I could remember -  I think it was the op-amp tutorial pages at ESP Audio.