Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!usc!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!hplabs!hpl-opus!hpnmdla!donrm From: donrm@hpnmdla.hp.com (Don Montgomery) Newsgroups: sci.electronics Subject: Re: Etching PCBs ?? Message-ID: <7380015@hpnmdla.hp.com> Date: 16 Mar 91 01:36:44 GMT References: <1991Mar08.084952.7323@lynx.CS.ORST.EDU> Organization: HP Network Measurements Div, Santa Rosa, CA Lines: 73 Here's my $0.02 worth after many years of making pc boards in the kitchen: excerpts from the responses- > Then clean and coat a copper-clad board; we use steel wool >and soapy water, rinsing and blow-drying with compressed air. ^^^^^ Be careful here. Some soaps leave stearates on the board and the resist will slough off, particularly the real Kodak KPR. If in doubt, use a degreaser, but make sure it's not contaminated. > Bake for 15 minutes or air-dry for 3 hours (longer is better). I bake my boards in the oven at the lowest setting. Place a muffin fan (150 F or so won't hurt it) to displace any temperature gradients that occur. Let the board air-dry enough to evaporate the volatiles before placing in the oven or you may be picking the door off the floor or out of the wall. Close the door to keep the ambient (and oven) light out. One interesting note: Positive photoresist (like Shipley) that devel- ops with potassium hydroxide solution requires humidity during the dry- ing process. I fretted over this for hours with one failure after another when using a new electric oven. Previously, I had used a gas oven that raised the humidity by virtue of combustion products. One of the ChemE's here at work told me what I was doing wrong... >solution. FeCl will cheerfully etch through copper, stainless >steel, you name it (and stains your hands and clothes a terrible You ought to see what this stuff does to aluminum! Post your results to rec.pyrotechnics. I have also used ammonium persulfate (with a mercury chloride catalyst) as an etch. It's only advantage is you can tell how "used" the solution is as it turns blue from the dissolved copper sulfate. The stuff is very poisonous (due to the catalyst) and should probably be avoided. >plate the board. Tin-plating can be done by dipping in an electroless >plating solution, silver plating by rubbing with 'Cool-Amp' powder with The electroless tin-plating works great, but requires a VERY clean board. Touch it with your fingers and it won't plate in that area! Also, be careful of silver plating pc boards that are going to be used in a high humidity. They tend to grow dendrites that short out everything in sight. > After inspection, drill the holes with a carbide drill >(typically #61 size). Proper drill spindle speed is in the 10k-40kRPM >range. A Dremel tool is the way to do this in small lots (and you Dremel makes a dandy little drill press fixture that works just great for this. You can drill a lot of holes in a hurry. >The absolutely *best* method I have ever found is to use "Twinkle" brand >copper cleaner (intended for use on the bottom of Revereware pots and such) >and warm water and a sponge, according to directions. The "Twinkle" will >chemically clean off the oxides, and leave you with copper so pure it's >almost pink in color! This method works great! You can use any brand of copper cleaner that contains phosphoric acid. >DON'T use steel wool, as it will scratch (gouge, really) the surface, which >creates channels for the etchant to run under the resist. Boy, this is the absolute truth. If you're running 0.031 inch or smaller lines, you WILL have trouble!! Don Montgomery donrm@hpnmdla.HP.COM The usual disclaimers apply.