Etch PCBs with ferric chloride and a sponge

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Etching a printed circuit board generally takes a bit of time and uses a lot of etchant. [TechShopJim] posted a method that uses a sponge to reduce the amount of etchant used while speeding up the entire process. First, a resist is applied using either a sharpie or the toner transfer method. Using gloves to handle everything, he soaked a sponge in ferric chloride and continually wiped a copper-clad board until all the exposed copper was removed. This technique moves the etchant around more, keeping “fresh” etchant closer to the copper. If you can’t procure ferric chloride, you can also use our method that uses 2 household chemicals: hydrogen peroxide and hydrochloric acid.

Comments

  1. Sounds great! One would have to be careful to not scrub off the etch resist, but that shouldn’t be an issue if you’re just rubbing the sponge against it. Have you tried this method? I’d like to know if it’s more or less efficient than etching with an agitator, along with average times.

  2. This is really really cool.

  3. TMH says:

    Very nice.

  4. Steve Watkins says:

    This is a great post. I’d like to point out that hydrochloric acid is also known as “muriatic acid”- the stuff used to clean sidewalks, driveways, garage floors and sometimes pool PH control. Typically sold in 2 gallon jugs at lowes. ~$5

  5. CH says:

    If you use a persulphate etchant, this won’t work I don’t think, since those etchants don’t improve with agitation; They don’t form ‘contour/gradient shells’ around etch areas.

  6. cyanide says:

    wait, did he use a sharpie’s ink as a resist or did he use a sharpie to apply a resist?

  7. Steve Watkins says:

    sharpie’s ink as the resist. radio shack use to sell a kit back in the day that came with a just plain old sharpie and ferric cloride.

  8. andrew says:

    …no, the resist is toner from a laser printer. it clearly says that in the description.

  9. cynic says:

    “a resist is applied using either a sharpie or the toner transfer method.”
    Seems you need to get your eyes tested andrew.

    I’m amazed the resist puts up with being wiped, I may take up home etching if this is as convenient as it seems.

  10. Rolf says:

    “you can also use our method that uses 2 household chemicals: hydrogen peroxide and hydrochloric acid.”
    I don’t know about any of you guys, but I’m pretty sure I don’t have any hydrochloric acid laying around…

  11. @rolf Quite a few toilet cleaners have high levels of hydrochloric acid (near the 20% range). You can find a how-to here – http://www.instructables.com/id/etching_a_circuit_with_toilet_bowl_cleaner/

  12. fenwick says:

    If you’re careful, you could even do 2 sided boards with this method.

  13. Matt says:

    I have done something like this. I had the Radioshack etching kit, and I got bored waiting for it so I got out a flux brush (like a cheap little paint brush about 3/8″ wide) and brushed the etchant across the board. It was done in just a few minutes. The biggest problem was the toner, which didn’t seem to stick to the board right.

  14. pixel says:

    As I typically only make small PCBs, the biggest being Arduino shields, I have a large glass coffee jar that I etch in. I drill a hole in the corner of the pcb, tie a bit of cotton of fishing line through, and drop it in the jar. Use the jar lid to wedge the string so the pcb is off the bottom. I stand it in another shallow tray of boiling water to warn the etch, and periodically give the coffee jar a shake. Works great for single and double sided pcbs, is clean, re-usable, and easy to dispose of the etch when it needs replacing too.

  15. Josh says:

    @matt… i’ve found that be true if the board is dirty (scotch-brite pad and acetone or isopropyl), if the iron isn’t hot enough (turn it all the way up and place a sheet of paper between the iron and transfer sheet), or if there isn’t enough toner on the transfer.

    please, make sure you use gloves and safety glasses with this. ferric chloride is very nasty and will stain anything it comes in contact with, including skin.

  16. markps2 says:

    i echo the warning
    ferric chloride is very nasty and will stain anything it comes in contact with, including skin

  17. Benny M says:

    “hydrochloric acid… Typically sold in 2 gallon jugs at lowes” –Steve Watkins

    I don’t know about you Steve, but Lowes around here sells clothes.

    I’m gonna take a crack at making PCBs just for the hell of it. Wish me luck guys. Send a card to the hospital in advance, hoping that the acid burns heal up okay.

    See ya

  18. zypher says:

    I’m with Benny M on this, though the nearest lowes to me is a hardware store.

    I’ll be trying this just for the hell of it. So wish me luck.

  19. Steve Watkins says:

    Benny, Where are you?

    Clothes- Really? I was at Lowes earlier today so i checked the price and found i was wrong. It is now $6.98 without tax.

  20. cgmark says:

    I use the muriatic acid + peroxide combo . It is really cheap. The muriatic acid is sold to clean concrete, makes it really white. Do not get the etchant on stainless steel , it will ruin it. I unthinking washed off a board in the kitchen sink and now the sink has stains that cannot be cleaned off.

    I use photo glossy paper + laser printer then just soak the board in water till the paper peels away leaving the toner.

  21. Flood_of_SYNs says:

    Hydrochloric acid = Muriatic acid = Spirits of salt, it goes by a few different names.

  22. Jesse says:

    benny is likely in Australia.

    the lowes in the US is a hardware store, like home depot or Bunnings.

  23. kanamin says:

    you can use A SHARPIE?????????

    Sweet.

  24. samurai says:

    i have made quite a few PCBs using the ferric chloride method, and i can tell you that sharpies do not work for me. maybe its the copper clad, maybe not, but it dont work. =p

  25. Oren Beck says:

    surface prep is simply everything in getting resist to stick. After that it’s ultraimportant to clean/neutralize every trace of etchant. As etchants will keep on corroding. And many spent etchants are quite conductive too. Which has caused odd hard to track down intermittent flakies in high voltage or high gain circuits… Especially if humidity fluctuations make conductivity vary..

  26. ilyas says:

    hi all,
    i wanna etch the pcb…here in qatar its very hard to get the right chemical to etch the pcb like ferric chloride etc…but sufuric acid is easily available in here… my question is …is any one tried etching pcb with sulfuric acid? if so pls share your experience…will be appreciated…thanx all for reading my post…

    waiting for ur response…
    ilyas

  27. I’ve been working with FeCl for about 25 years now (I started when I was around 10 yrs old). The stuff is safe, though it stains bad. It wont hurt or burn if get it on you but the stain will last 1-3 weeks and look strange to others. Stains on cement or floors can be permanent after it dries. Ingestion? I dont know, very small amounts probably ok, but take a good gulp and it could lead to iron poisoning.

    FeCl fumes are not so much toxic as just an irritant. However, keep metal appliances and stuff nearby away, fumes could condense on them and ruin the finish. (I’ve seen it firsthand.)

    I’ve been using this guys system for a few boards:

    http://www.pulsarprofx.com/pcbfx/main_site/pages/

    much better than regular tonor transfer. After the tonor transfer you treat it with some green leaf and then the resist pattern is *very* tough to get off…as in, sandpaper has a tough time.

    I then use the sponge to etch and it is definately faster and more effecient than constant agitation. It’s all about getting the used FeCl away from the copper surface to let the fresh FeCl do its work. The sponge is also cleaner, just trust me on this. You use much less of the resist and your not adjitating it and dripping it everywhere.

    Today I am trying a new ferric chloride mix with citric acid (Edinborough mix) that is supposed to facilitate the evacuation of the used FeCl from the copper surface to let fresh FeCl at the copper. I’ll post the results.

  28. Gee Wiz says:

    @ ilyas

    Yes, sulfuric works just as well…. The reason it’s use isn’t more often indicated in the USA is difficulty locating the material in most areas. It oxidizes the copper layer and forms the bright blue solution of copper sulfate.

    Be careful with any method to etch circuit boards however.

  29. The Edinburg etch worked good. I don’t use sponge anymore though. I double bag the PCB in two zip lock bags and put the etchant inside and zip lock. I then use an artists rubber roller to squeeze the etchant accross the pcb surface. I submerge the whole thing in a bucket of hot water while I do this. The hot water heats the etchant through bag without diluting it and speeds up the process beyond belief!

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