Monday, May 20, 2013

a new etchant option

for the past year or so i have been etching my own PCB's. i have experimented and successfully mastered many Toner Transfer resist techniques where a reversal image is applied with heat and pressure. i have had the kind support from our printmakers who allow me to use their Edinburgh Etch tank to burn the boards. and they have been really spectacular, it gives me much pride to deliver a project module to the students with home-brewed PCB's to work upon. it brings it closer to home on multiple levels.

on friday, i was leading a seminar for my summer work group who are assisting my summer project (stay tuned). in the seminar i demonstrated the entire process: drawing a schematic, PCB layout,resist transfer, etching, and then soldering the project. our printmaking facility is shut down for the summer so i did an etch in a photo tray in the UWF FabLab. this was fine as i only needed about 5 boards and it was fresh FeCl so it went relatively quickly. it has spurred me to take the next leap for our lab and start an official 'chemistry' policy in the lab to make sure the students can follow my lead and make their own custom PCB's.

i began more etchant research as i prepare for the discussion i need to have with our Environmental Health and Safety officers. i am concerned with the protocols we will need to establish for material handling and storage. even though we will need to comply to material handling for the 'used etchant' supplies, it would be wonderful to find other processes that use less hazardous raw materials and etchants that will last long term to reduce the waste stream.

for sometime i have been aware of a Hydrochloric Acid (HCl) and Hydrogen Peroxide (H2O2) etchant that seems to have a long life according to the citizen scienctitst and nerdom around the anecdotal evidence suggests that it has a long life that actually increases etching ability as it is used and that it can be extended by adding more oxidizing reagent (H2O2) or simply bubbling air through the mixture to facilitate the oxidation. the reports are that enthusiasts are getting very long usage times reducing the amounts of materials they dispose of. this is fantastic because cupric solutions are highly toxic to the environment and biology. it has even been suggested that electroplating techniques could be used to reclaim a less soluble (less hazardous) and recyclable copper powder. other advantages of this style of etchant is that it doesn't have the horrid staining that is characteristic of FeCl. it will still wreak havoc on your stainless steel sink so you need to exercise caution.

in the past 48 hours, became aware of a small but growing number of individuals using household vinegar (or if you will acetic acid CH3COOH) and H2O2 plus a little salt (NaCl) as an etchant. this well documented in the BLONDIHACKS blog post from Feb. 2012, where the awesome Quinn Dunki details the process of design to fabrication in awesome detail. and here and Steve Hobley has run similiar experiments as detailed in blog posts from 2011. kind of cool is that he has a chemist in his family who comments on the chemical processes at work here and makes it a totally interesting read.

the remarkable point is that common vinegar runs about 5% acid by volume where a considerably stronger corrosive is usually employed.

i had to do this! tonight i returned to campus with 3% peroxide, household vinegar, and some salt. i can report that it works very well. slower than the fresh FeCl etchants, but very similar to time need when using the Edinburgh bath we have in the printmaking department. in about 30 minutes, i had etched a one ounce copper plate. as Quinn puts it "not having to deal with storage, use, and disposal of a strong acid is worth it."

i have a close associate in photography and thus access to some pretty aggressive Acetic (it is used as a stop) that we can mix down to a reasonable but higher percentage by volume. i can also get vinegar in up to 30% by volume. this is used as weed killer, but it also looks like it is a lightly regulated as a chemistry. i am also thinking of running some tests citric acid which i could pickup at the local brewing supply house. all of which could make the requirements for Health and Safety easier!

i will be running another board tomorrow morning in the resultant etchant, it should go quicker if the reports are correct. and post images... stay tuned!

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