PCB Etching and some chemistry

[Refrigerator]

TPTB seem to be making high strength H2O2 harder to find because of the "OMG!! Terrorism!!!" stuff. Useful for producing acetone peroxide, an easily made (but dangerously unstable) explosive compound that contains no nitrogen, and therefore can avoid detection by many explosive sniffers.

You mean TATP? I use that stuff to detonate my ANFO.   

[westfw]

TPTB == "The Powers That Be"
TATP == "Acetone Peroxide"

[T3sl4co1l]

TPTB don't like TATP ^

[skyline_stu]

Haven't used Ferric Chloride or the other persulfates for donkeys years. Why ?

FeCl3 is too messy, expensive, hard to clean up, a bit slow sometimes.
Persulfates are waaaaaaay too slow for my needs.

6% H2O2 and conc. HCl works great in equal volumes (a little goes a long way).
Fresh mix etches in about 2 minutes.
Gentle agitation is suggested as the bubbles formed can attack your resist.
I often do prototypes in 5 thou or less widths. (photographic process).
Hardest part in these thin traces is waiting for the photoliths to arrive.
Other etchants undercut or have poor edge definition when at this scale.

The remaining green solution is a great etchant too, You can let it evaporate to a concentrated liquid or even crystalise it.
Next time add a little fresh HCl and peroxide and etch in a few minutes again.

If you need to neutralize it, add washing soda (sodium carbonate) or bi-carb soda until it stops fizzing. You end up with a solid copper salt that can be more easily disposed of and salt water.

 If your solution goes brown when adding the acid and peroxide together, don't worry. It's just iron contamination in the acid - and that acts a like a catalyst !!!

Avoid doing this in your room, the fumes will attack you and ANYTHING metal.

[akis]

Ammonium Persulphate comes in as a white powder which you mix with tap water. £7 pounds (about $11 USD) for 1Kg of powder to make 10 lt of solution. eg http://www.ebay.co.uk/itm/1Kg-Ammonium-Persulphate-98-PCB-etch-Etchant-/161014761335?pt=UK_BOI_Medical_Lab_Equipment_Lab_Supplies_ET&hash=item257d3a4777

I typically use 700ml in a plastic tub to etch my boards. The plastic tub is stackable, and I place it inside another tub full of very hot water, that allows me to keep the etching solution at 50C more or less.
eg http://www.amazon.co.uk/Whitefurze-Ladies-Shoe-Storage-Pack/dp/B003M2XI84/ref=sr_1_1?ie=UTF8&qid=1412586333&sr=8-1&keywords=whitefurze+box

Ammonium Persulphate is quite safe to use compared to the other etching chemicals. You can stick your hands in the solution and it is fine, you can spill it on the floor, in the sink, just wash away with water, it does not stain. Very easy and safe to work with.

Also it will not over-etch, and will not eat into the resists because it is slow, so even after it is done (visual inspection), you can leave it for another 30 minutes and nothing will happen.

It is a bit slow (needs about 1 hour at 50C) and it can be even slower if at room temperature but that's the price to pay for the extra conveniences.

[zagnut]

my favorite has always been 2 parts 3%peroxide to 1 part 32% hydrochloric acid.  cheap, easy to find and works fast without any nasty surprises.

i usually mix just enough to cover the board while laying flat and gently wipe the surface with a foam brush.