Ultra Fast Etching - is this really safe to do !! - Page 1
Forum section: electronics / projects

author: sleemanj
author_rank: Super Contributor
timestamp: April 10, 2014, 02:17:57 pm
content: I've heard of this sponge method before, but to me it seems too aggressive, you're rubbing on the resist, it's a millisecond away from serious over etching, you've got ridiculous amounts of fumes...HCl and H202 is great, but dilute the HCl down until it's just below fuming and add only a little H202 (if it's high strength stuff, if you only have 3% stuff use it to dilute the HCl instead of extra water), much more manageable, 2-3 minutes a board, no foaming or ridiculous fumes, no sponging, just rock the board as usual. The more/stronger H202, the faster the etch will be.And don't throw the etchant out, just add a little more H202 every etch to "green it up" and it will be good as new, add a little HCl now and then too.

author: LukeW
author_rank: Frequent Contributor
timestamp: April 10, 2014, 02:47:07 pm
content: I've never used his "sponge" process before, but I have heard of people using it before with other etchants such as FeCl3in order to use small amounts of etchant solution very efficiently in contact with the board area.HCl/H2O2can be a useful, convenient, cost-effective etchant chemistry if you do a lot of etching. Nothing to dissolve in water, no heating, just at room temperature, and pour a bit of the liquid reagents in from their storage drums. So it can be quite fast and convenient.A 1:1 mixture of concentrated HCl and 50% H2O2 will react very exothermically when a lump of solid copper is added... it willboil itselfand aggressively dissolve the lump of copper.It can be very fast, and very reactive - but this is likely to damage the etch resist, probably result in a low quality board, and spit solution everywhere, make a mess, release excessive fumes etc. So don't use that to etch your boards, you really should be diluting it with water if you're starting with concentrated reagents.I think from memory something like a 3:2:1 ratio by volume of H2O and 33% HCl and 50% H2O2respectively is a rule of thumb that I used to use for good results.If you're starting with more dilute reagents, such as 6% or 12% H2O2, you may not need to water it down, just use a mixture of peroxide at that concentration and HCl and see how it goes. Try it first using a small scrap of copper-clad blank board, this will give you a feel for the concentrations needed and the reaction rate, before you put your "good" board with your resist artwork in and risk wasting it.

author: TMM
author_rank: Frequent Contributor
timestamp: April 10, 2014, 03:45:48 pm
content: I stopped using the sponge method because i found it abrasively removed sharpie 'touch ups' on toner transfers.

author: hlavac
author_rank: Frequent Contributor
timestamp: April 10, 2014, 04:11:17 pm
content: In my experience, sponge is very good with ferric chloride, it helps to remove the black residue that slows down etching a lot, making it much faster and dramatically reduces the amount of etchant needed.In addition it helps to remove any uneven etching by just rubbing it more where needed.Dip the sponge lightly in ferric chloride, rub pcb until the sponge turns from orange to green, wash out the green, squeeze dry, repeat...On the negative side, the mechanical irritation/abrasion of the etching mask pattern edges increases undercut and makes this unsuitable for high resolution patterns. You need a pretty solid, resilient mask like the one from (unretouched) toner transfer.I found the photosensitive mask I use too weak for this and thus abandoned the method in favor of the "eternal" cupric chloride method, which is nicer for environment and you can see the board while etching...