Lets see if I can remember the redox stuff from chemistry.
The HCL/H202 is just the starter, the real etchant is the Cupric Chloride (+2 oxidation state)you eventually end up with. Initially the HCL/H202 etch the copper off the board forming Cuprous ions (+1 oxidation state)in the solution. Then more H202 is added or O2 is bubbled through the solution to oxidizes the Cuprous ions back to Cuperic ions. As the quantity of copper in solution increases more HCL must be added to keep the chloride ions in balance with the ever increasing copper in solution. You actually make more etchant with every board etched. There has been extensive postings about this process and how to replenish and regenerate the etchant. My understanding is that 3% H202 adds too much water and dilutes your etchant. For best results use 30% if you can find it.
Cu + CU++ ---> 2CU+ the etching equation
http://www.pcbfab.com/chemistry-of-the-cupric-etchCraig
--- In Homebrew_PCBs@yahoogroups.com, "N2CUA" <n2cua@...> wrote:
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> Is there any issues with mixing etching solutions
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> From 30% HCL / 30% H2O2 to the right concentrations/ ratios
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> And mix together and store that way ?
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> Or is there an issue with it becoming weaker just sitting around ..
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> Randy - N2CUA
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> [Non-text portions of this message have been removed]
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