Copper Foil Peeling Up

by Shirley
(Oklahoma)

I've noticed on 2 of my projects that a couple of places where the copper foil comes unadhered to the glass after I apply the flux. Am I putting on too much flux, or should I be using paste flux? I think I'm burnishing the foil well before soldering. I hope you can tell me what I'm doing wrong. Thanks!

Answer

You may not be cleaning the glass well enough before you apply the foil. If there is any grinder dust, oil from your cutter, or oil from you skin on the glass, the foil could lift after you solder it.

Even though you burnish very well, the foil isn't stuck down tightly. Flux gets under the foil, or water from cleaning gets under the foil and it lifts off the glass.

Try wiping each piece with a cloth dampened with alcohol before you foil it. The alcohol cleans the glass and it also seems to make the foil stick better. Don't use enough alcohol to make the glass wet, just enough that it cleans the glass and it evaporates by the time you start foiling.

The only other reason the foil could be lifting is that the foil is defective and has spots where there isn't any or very little adhesive. This is quite unlikely, but I have seen it happen. Check the roll of foil as you're using it, to see if that could be the problem.