Homebrew PCBs

Stefan,

We never tried using hydrochloric acid in our shop so I don't have 
any ideas on that process. Most PWB shops electroplate a metallic 
resist such as tin or solder and the etchant must be compatable with 
this resist. The copper background is etched but the tin or solder 
plated areas remain after etching. 

Sulfuric/peroxide etchants will darken the solder plating but won't 
etch through thus leaving the circuitry well defined and ready for 
solder reflow. 

I'm not certain if the hydrochloric acid based etchants will 
precipitate copper as a crystal but I assure that the sulfuric types 
will. They are also very easy to operate. I don't remember the 
peroxide consumption but it wasn't too bad since we also added a few 
ounces per day of stabilizers. 

For hobby and small volume use just make up the initial batch, heat 
it up, add a few ounces of peroxide whenever you want to etch and 
you're ready to go. When the copper content grows to around 8-10 
ounces per gallon it will start to form crystals at room temperature.

Scrape these crystals out of the tank, add a few ounces of sulfuric 
acid and peroxide and start etching. Sulfuric acid will only be 
consumed when the crystals are formed. The main consumable will be 
hydrogen peroxide. 

If stabilizers are used the peroxide consumption is not bad at all. 
Technical grade peroxides already have some stabilizers and are a 
light yellow color. Food grade peroxides are clear and will be 
consumed faster as they have no stabilizer.

If the etching bath is run at lower temperatures the peroxide will 
last much longer but the etch rate will slow down. This is no big 
deal for the occasional prototype. We ran our etch tank at 115 
degrees F with an etch rate of about 3 to 5 minutes for half ounce 
copper laminate. When the rate slowed down the operator just added a 
little peroxide to increase the rate. It usually took about a half 
gallon addition to speed up a fifty gallon etch tank. I'll try to 
find my notes on acid and peroxide consumption per square foot of 
etched copper and post that information later.

I made our stainless etching racks from 316 stainless steel and they 
lasted over twenty years. Some of the welds on the rack handles 
showed some surface corrosion but only because I goofed and welded 
them using 304 rods. I used a plasma cutter and tig torch to make the 
racks. The PVC tank took quite a beating and finally started cracking 
after twenty or so years but the plastic was not damaged by the 
etchant.

The electrowinning cell used lead anodes because they were inert in a 
sulfuric acid bath. That's why lead anodes are used in many sulfuric 
anodizing tanks. I'm sure they give out over time but they do have a 
very long service life. 

I now only make boards for my own products and other very small 
production runs. The etchant is ferric chloride in a small spray 
etcher. I use dry film resist or electroplated gold as an etch 
resist. If we started up large production again I would go back to 
using the sulfuric peroxide because it's so easy to use.

Tom

--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan 
<stefan_trethan@g...> wrote:
> hi tom!
> 
> really great method!
> 
> i wanted to ask if you may figure out the amount of hydrogen 
peroxyde consumed (and also if the etchant 
> was used very often which i assume or seldom. if one uses a 
soultion with H2O2 seldom (once a week or 
> so) i believe all of the H2O2 has vanished in between and needs 
replacement. the 10% you state for 
> initial use seems quite similar to the amount needed by my hcl h2o2 
method. but interesting would be if 
> it is used up very quick, then it would become more expensive with 
less using rate.
> i know you only adjusted it via etching rate but if you may 
remember at least one time, like after some 
> holydays or so, when you haven't used the bath some days if it 
needed the full 10%?
> 
> i'm also wondering if the copper also falls out when using 
hydrocloric acid and hydrogen peroxyde. it 
> never fell out in my etchant but maybe the concentration is yet too 
low (concerning only 35micrometer 
> copper thickness)...
> 
> also your description of electrowinning is very nice. that is 
exactly what i hoped for.
> i'm wondering which reason there is for the lead plates?
> why lead?
> 
> 
> 
> another question: you have obviously used stainless steel in your 
etchant, how did it resist?
> perfect or was there some agression?
> 
> 
> i see only one disadvantage of your method compared to the 
hydrocloric acid and this is availability of 
> sulphuric acid. it is much, much easier to get the hydrocloric acid 
here. it is sold in many stores, for 
> household use. sulphuric acid is only available in special stores. 
but if one needs hydrogen peroxyde he 
> has to go there anyways (if not getting it from hairdressing 
supply)..
> 
> 
> i find your method very interesting but it would be more 
comfortable to stay with a hydrocloric 
> process... i will try if there also falls out the copper if i let 
it cool down.. (i always put the 
> etchant back into its bottle after useage, so it the copper 
concentration was diluted immediately).
> 
> many thanks, was a great help to mee.. also some satisfaction that 
somebody else thought of electrolysis 
> and did try it (even if it showed to be not comfortable).
> 
> 
> regards
> stefan