Thoughts on tt etching and soldering
2007-09-03 by Dennis Waggoner
New to the group first I want to thank all of you for your help. The techniques described here have helped me very much. Second I would like to share my best techniques on making my own pcbs. Many if not all I discovered from this group collective thoughts. So this is probably more of an affirmation than a discovery. I've found that the printer makes all of the difference from success to failure. I had an old Epson Laser 1000 that I was using and as the toner got lower and lower I found that it became impossible to make any toner transfers that I could even use. I purchased a new Dell 1720 and now it's difficult to even make a tt with imperfect results. I'm currently down to 12 mill traces with no problems and with probably try 10mils but I believe that is going to be the limit for me. (See my photos called dwags projects). I use an old iron and PressNPeel. PressNPeel is a lot cheaper if you order from their website 20 sheets for 33 dollars. And for my low volume this is great. As for iron on techniques it is a learned exercise but I have found that the color of the traces through the blue transparency of PressNPeel gets darker and less fuzzy. That change in appearance corresponds with a correct transfer of the toner and signals an end to the iron heat and pressure. Heat can be checked with thermometer if you have one find the heat setting that corresponds with about 300 deg F. For etching I use Hydrogen Peroxide (Wal-Mart 1qt for 99 cents) and Muratic Acid 4.99 a gallon. In the summer I mix three parts H202 to one part HCL and in the winter I usually mix two to one. The removal of copper works quicker if you can expose the copper to air and let the etching completely drain off then submerge and do again. Takes about 10 minutes to etch a 4x6 1oz copper pcb. Muratic acid is very strong and I urge you unless you are familiar with strong reagents please study safety and storage and waste removal of the etching before you use this technique. I always have a five gallon bucket full of water nearby incase of any accidents or spills when I am etching. After etching I remove the toner with acetone wash in a cold solution of soapy water to remove any traces of acidity dry and then coat with a light coat of Shellac. This prevents the copper from oxidizing and makes soldering a dream. Make sure you use shellac and not a lacquer or varnish. Shellac has a low melting point 180 deg F and makes an excellent protective insulating coat for the bottom of the pcb. I only know of one manufacturer of Spray shellac Zinsser and sometime you can find it at Lowes. Or you can order it online After the shellac has dried drill out the holes. I found a great source of drills on ebay you get 50 carbide ring drills for 32.00 shipping included. They come in 10s of .024, .029, .033, .035, and .045 diameter onpasinc.com out of Ohio. If you make your entire pad holes diameter less than the diameter of the drill you intend to use the etched hole in the center of the pad with act as a center punch and the drill with find the exact center. Start it slowly and let the pcb move slightly to accommodate the centering process. Soldering is straight forward. As you apply heat to the pad you will see the shellac boiling away this gives you an indication of where and how much heat is being applied. When it boils away you have perfect unoxidized copper exposed that can be soldered without any additional flux. After the board is assembled I usually brush vigorously with a small bronze brush. This dulls the solder to a mate finish and makes any imperfections or bad weld very easy to spot with a magnifying glass and removes all flux spatters. Finally after the board is tested and everything works correctly I give it a final heavy coat of shellac. Again Thanks for all of your help and I hope these comments help someone new to this group Dennis