Muratic/peroxide etch
2010-08-31 by Jim
I have made a etch agitator that is a mechanical resonant system. It is a 48 inch long, 2 inch wide and 3/4 inch thick wood board. On one end, it is driven by a reciprocating (up/down) scroll saw. The pivot for the resonant system is at 36 inches from the scroll saw. This leaves 12 inches on the load end (etch container). The mass of the 12 inch end with the etch cup filled with 100 milliliters of etch solution and the mass of the 36 inch end becomes resonant at some RPM (Recips Per Minute). When I run the scroll saw at about 400 to 600 up/downs per minute, the assembly becomes resonant and the agitation becomes INTENSE. I have not ever had boards etch so fast and even before. Using the 2 parts 3% hydrogen peroxide and 1 part of 29% hydrochloric acid (muratic acid), my boards etch completely in 90 seconds. I do this at about 75 degree outside temperature on my patio. There is some heat liberated in the process so the etch solution gets maybe to 90 degrees F. Using a rocking agitation (by hand) takes about 15 to 20 minutes to etch the same size board. The high etch rate seems to eliminate the under cutting I get with the slow 15 minute etch rate. 6/6 mil traces come out smooth. I have never achieved such good etching before using the hand agitation method. I save the "used" etch solution in a half gallon glass jar. The jar has gotten full and its color was a light emerald green color. I added copper scraps to the jar and allowed the solution turn dark green (could not see through it). I strained the solution into into another jar and put a air stone in the solution with an small air pump, air bubbled the dark green solution and it turned back to an bright emerald green solution. Using this solution in the super agitator, after 15 minutes, the copper was just starting to clear. Is this green solution supposed this much slower than a fresh H2O2/HCL solution. In the super agitator, there is a LOT of liquid surface area and I pump fresh air through the container to keep a fresh supply of oxygen. I have not seen an etch rate comparison between the two types of solutions (fresh and green) but I did expect the green solution to etch as fast as the fresh solution. It isn't even close!! I am looking for comments as to why the SLOW etch rate of the emerald green solution.