Homebrew_PCBs

Why not try etching with a sulfuric acid and hydrogen peroxide
mixture? We used this for years in a commercial shop with excellent
results. The solution makeup is easy, 15% technical grade sulfuric
acid, 10% hyrogen peroxide (35% grade), 75% water. This solution can
be heated to 100 to 120 degrees F. and it's ready to use.

One way to remove copper is to plate it out. This is called
"electrowinning". Use lead plates for anodes and stainless steel
sheets for the cathodes. The plated copper will peel off the
stainless sheet if the edges are masked off with plating tape. The
tape keeps copper from plating around the edges of the stainless
sheet. After plating just flex the sheet and the copper peels off.

My electrowinning tank had three lead sheets as anodes with two
stainless steel sheets in between as cathodes. A 500 amp rectifier
was used with the positive connection to the lead plates and negative
connection to the stainless steel plates. A much smaller system could
be made for hobby use.

We transferred the solution to this tank on Friday afternoons and let
it plate all weekend. On Monday we transferred the plated out
solution back to the etching tank and started over. When using this
method only the hydrogen peroxide had to be replenished to bring the
etching rate up to speed.

This seemed like a lot of work so after a while we went back to
simply cooling off the working solution and letting the copper fall
out. Copper will drop out as copper sulfate crystals when the
solution is cooled to around 60 degrees F.

We sold these crystals to a chemical recycler and never once
generated any waste from this process. The same working solution was
used for over seven years without replacement and etched many
thousands of square feet of boards.

All tanks, racks and hardware can be made of stainless steel, PVC,
polyethylene or polypropylene plastic. Don't use nylon or delrin as
they fall apart after a short time.

I made all of our tanks from PVC plastic using a hot air plastic
welding torch. My torch was made by Seelye Electric Company and was
expensive but I see a direct copy of this torch being sold by Harbor
freight for around $40. You also need a very small air compressor.
The welding pressure used is around 2 psi or less. Air is used for
PVC but nitrogen must be used for most other plastics.

Analysis is by titration, however, in all the years we ran this
process we never once analyzed the working solution. After dropping
out copper sulfate crystals we just added some sulfuric acid and
hydrogen peroxide until the etch rate was correct. We used a scrap
piece of laminate and timed the etch rate. It was real easy to run
this etching system with minimal problems.

For a hobby system I would just use a plastic bucket and glass
aquarium heater. When the solution is saturated the copper sulfate
crystals will drop out and can be collected for resale or used as
make up salts for a copper electroplating tank etc.

Tom

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




17.04.2003 15:54:12, "twb8899" <twb8899@...> wrote:

>Why not try etching with a sulfuric acid and hydrogen peroxide
>mixture? We used this for years in a commercial shop with excellent
>results. The solution makeup is easy, 15% technical grade sulfuric
>acid, 10% hyrogen peroxide (35% grade), 75% water. This solution can
>be heated to 100 to 120 degrees F. and it's ready to use.
>
>One way to remove copper is to plate it out. This is called
>"electrowinning". Use lead plates for anodes and stainless steel
>sheets for the cathodes. The plated copper will peel off the
>stainless sheet if the edges are masked off with plating tape. The
>tape keeps copper from plating around the edges of the stainless
>sheet. After plating just flex the sheet and the copper peels off.
>
>My electrowinning tank had three lead sheets as anodes with two
>stainless steel sheets in between as cathodes. A 500 amp rectifier
>was used with the positive connection to the lead plates and negative
>connection to the stainless steel plates. A much smaller system could
>be made for hobby use.
>
>We transferred the solution to this tank on Friday afternoons and let
>it plate all weekend. On Monday we transferred the plated out
>solution back to the etching tank and started over. When using this
>method only the hydrogen peroxide had to be replenished to bring the
>etching rate up to speed.
>
>This seemed like a lot of work so after a while we went back to
>simply cooling off the working solution and letting the copper fall
>out. Copper will drop out as copper sulfate crystals when the
>solution is cooled to around 60 degrees F.
>
>We sold these crystals to a chemical recycler and never once
>generated any waste from this process. The same working solution was
>used for over seven years without replacement and etched many
>thousands of square feet of boards.
>
>All tanks, racks and hardware can be made of stainless steel, PVC,
>polyethylene or polypropylene plastic. Don't use nylon or delrin as
>they fall apart after a short time.
>
>I made all of our tanks from PVC plastic using a hot air plastic
>welding torch. My torch was made by Seelye Electric Company and was
>expensive but I see a direct copy of this torch being sold by Harbor
>freight for around $40. You also need a very small air compressor.
>The welding pressure used is around 2 psi or less. Air is used for
>PVC but nitrogen must be used for most other plastics.
>
>Analysis is by titration, however, in all the years we ran this
>process we never once analyzed the working solution. After dropping
>out copper sulfate crystals we just added some sulfuric acid and
>hydrogen peroxide until the etch rate was correct. We used a scrap
>piece of laminate and timed the etch rate. It was real easy to run
>this etching system with minimal problems.
>
>For a hobby system I would just use a plastic bucket and glass
>aquarium heater. When the solution is saturated the copper sulfate
>crystals will drop out and can be collected for resale or used as
>make up salts for a copper electroplating tank etc.
>
>Tom
>
>
>
>
>Be sure to visit the group home and check for new Bookmarks and files:
>http://groups.yahoo.com/group/Homebrew_PCBs
>
>To unsubscribe from this group, send an email to:
>Homebrew_PCBs-unsubscribe@yahoogroups.com
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>

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

hmm two questions arised now:

first i have to inform myself about stabilizers and how long they may be useful to conserve the H2O2. i
don't assume they would help if there is one week between the prototypes.


the second issue is regenerating the fluid with air oxygen, i'm really wondering if this would also work
with this etchant.
when using hydrocloric it converts Cu2Cl2 to CuCl2 and the CuCl2 does thake the copper off the pcb and
gets Cu2Cl2 (as i have understand it). but in your bath CuSo4 builds.. have no idea how this all works
together and if your solution may be regenerated with air oxygen.. my chemistry knoweledge is bad..

i also wonder if the "battery liquid" sold at car shops is clean sulphuric acid and can be used or not.



regards
stefan

18.04.2003 16:41:15, "twb8899" <twb8899@...> wrote:

>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
>
>
>
>
>Be sure to visit the group home and check for new Bookmarks and files:
>http://groups.yahoo.com/group/Homebrew_PCBs
>
>To unsubscribe from this group, send an email to:
>Homebrew_PCBs-unsubscribe@yahoogroups.com
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>

Stefan Trethan wrote:

> hmm two questions arised now:
>
> first i have to inform myself about stabilizers and how long they may be useful to conserve the H2O2. i
> don't assume they would help if there is one week between the prototypes.

Stefan, you might be interested reading articles on
http://www.h2o2.com/ :)

>
>
> the second issue is regenerating the fluid with air oxygen, i'm really wondering if this would also work
> with this etchant.
> when using hydrocloric it converts Cu2Cl2 to CuCl2 and the CuCl2 does thake the copper off the pcb and
> gets Cu2Cl2 (as i have understand it). but in your bath CuSo4 builds.. have no idea how this all works
> together and if your solution may be regenerated with air oxygen.. my chemistry knoweledge is bad..

From what I've read the reaction of copper with sulfuric
acid / hydrogen peroxide does not require air. The overall
reaction is
Cu + H2O2 + H2SO4 -> CuSO4 + 2H2O

I don't have any experience with this etching, so but I
don't think its fast as (CuCl2+HCl) or FeCl3 etching. I
believe its used commercially for 'microetching' and etching
with solder plating resists, just as Tom (twb8899) explained.

I've been playing around with a type of etching solution
that theoretically just consumes water and air. I copied it
from an old patent, and is based on the widely used
ammonical chloride enchants. It replaces the ammonia with
monoethanolamine (MEA), so it doesn't smell, or evaporate
gas. I got 1 liter of MEA form an place that prepares
industrial cleaning chemicals. Its used in some detergents.

approximate concentrations of the solution I made up is.
100g/l ammonium chloride
200g/l cupric chloride
200g/l MEA
pH 7 to 8

I'm guessing the overall reaction is

Cu + O + H2O -> Cu(OH)2

Note:, the copper in solution is always at saturation, so
the Cu(OH)2 produced falls out as a sludge.

Yes, I confirmed it worked by etching a relatively large
chunk of copper in just 100 ml of solution and although it
took a week, it etched away, creating a lot of copper(II)
hydroxide sludge. I drained off the solution into another
container and bubbled air through it for about a day. Then
it etched a tiny piece of 1/2 oz PCB in about 30 minutes at
room temperature. The sludge is messy and it could prove
difficult to separate efficiently, so I wouldn't recommend
it as a hobby etchant. I'm guessing this is also the reason
its not used commercially.

Adam