Homebrew PCBs

I did another test. This time I simply put clean copper 
metal in the 20% acid and bubbled lots of air through it. It 
took just over 3 hours to completely dissolve the copper and 
produce a deep green colored cupric chloride etching solution.

makeup data:

40 ml of  26%wt HCl acid
20 ml of water
8.7 grams of copper.


Here are some pictures of the test.
First pic is after 5~10 minutes, the second is after 2 hours.
http://www.alphalink.com.au/~seychell/CuCl2_prep03_5minutes.jpg
http://www.alphalink.com.au/~seychell/CuCl2_prep03_2hours.jpg

I haven't got a picture of the final solution, the camera 
got taken away.

Some notes:
* Its clear that atmospheric oxygen feeds the reaction, so 
more air that comes into contact with the solution the 
faster the copper dissolves. Fine bubbles are a *BIG* 
advantage here. A previous test showed it takes about 48 
hours when bubbling large bubbles from the end of a hose.

* The reaction accelerates as copper is dissolved. Initially 
the solution goes from clear to slightly green, then slowly 
becomes an olive brown in 1 hour, then to a dark brown in 
rather quickly there after. After 2 hours the reaction rate 
is enough to generate a significant amount of heat. This 
heat further accelerates the reaction. I thermally insulated 
the vessel and measured the temperature stabilized to about 
20\ufffd above ambient (38\ufffdC). Heat loss would of occurred from 
the air passing through the solution.

* For some strange reason the bubbles produce an increasing 
amount of foam as more of the copper dissolves, until at the 
very end when the solution is green (i.e. no copper(I) 
remaining) the foam gets to a stage that its difficult to 
control. You may need up to 100 mm of head room for the 
foam. All of the experiments I've done had this exact same 
effect.
I suspect the foam has an advantage because it would 
increase the air contact area to the solution.


Adam

Hi Adam - my chemist friend (who, incidentally, grew up near Bondi
beach) advised me some time ago to try this recipe. I did not get past
trying some copper in muriatic acide, and, expecting a quick reaction
and getting none, giving up. (He had no idea about the time frame
required, and no suggestions about what to do next). Here is his
recipe, FWIW:

"Dissolve 67 grams of copper in 100 gms muriatic acid solution (the
38% stuff). You could use an excess of copper to make sure all the HCl
is consumed, but make sure you can remove the residual copper. Add 100
gms muriatic acid and bubble the bejeezus out of it until it turns
green. Add an additional 90 gms of muriatic acid solution and 606 gms
of water and you should have about 900 mils of the recipe mentioned in
the Rex Allers article."

I think he got the 38% figure for the HCl from the article, since the
muriatic acid available in hardware stores here is 20 Baume, about 30%.

I don't know if that is helpful or not. He develops plastics for
Dupont, so this is off the beaten track for him.

Thanks for the idea for pumps for hydroponics - I will check  it out

Grant

--- In Homebrew_PCBs@yahoogroups.com, adam Seychell
<adam_seychell@y...> wrote:
> I did another test. This time I simply put clean copper 
> metal in the 20% acid and bubbled lots of air through it. It 
> took just over 3 hours to completely dissolve the copper and 
> produce a deep green colored cupric chloride etching solution.
> 
> makeup data:
> 
> 40 ml of  26%wt HCl acid
> 20 ml of water
> 8.7 grams of copper.
[snip]
> 
> Adam

grantfair2001 wrote:
> Hi Adam - my chemist friend (who, incidentally, grew up near Bondi
> beach) advised me some time ago to try this recipe. I did not get past
> trying some copper in muriatic acide, and, expecting a quick reaction
> and getting none, giving up. (He had no idea about the time frame
> required, and no suggestions about what to do next). Here is his
> recipe, FWIW:
> 
> "Dissolve 67 grams of copper in 100 gms muriatic acid solution (the
> 38% stuff). You could use an excess of copper to make sure all the HCl
> is consumed, but make sure you can remove the residual copper. Add 100
> gms muriatic acid and bubble the bejeezus out of it until it turns
> green. Add an additional 90 gms of muriatic acid solution and 606 gms
> of water and you should have about 900 mils of the recipe mentioned in
> the Rex Allers article."
> 
> I think he got the 38% figure for the HCl from the article, since the
> muriatic acid available in hardware stores here is 20 Baume, about 30%.
> 
> I don't know if that is helpful or not. He develops plastics for
> Dupont, so this is off the beaten track for him.


HCl won't react with Cu without oxygen present. The initial 67g 
Cu + 100g 38% HCl won't do anything. It also don't need to be 
that complicated or precise (see my the post of my latest test) .
 From what I recently learned, 1 liter of etchant can be prepared 
by placing approximately 140g +-15% of copper into a thermally 
insulated container (i.e. your cooler box) fitted with a sparger 
for producing fine air bubbles. Add 1 liter of 6.0 +-15% Molar 
HCl (or 20% wt or 220 g/L). Ideally the copper should be fully 
immersed, but not essential. Cover the container and bubble air 
through the solution until solution becomes deep green.
See pictures and description from by previous post for more info.

For horizontal etching you may need to have large bubbles as 
small bubbles may simply trap foam under the PCB and slow 
agitation. The fine bubbles then only be used for air 
regeneration. You can include a few air stones in addition to the 
PVC pipes for producing large bubbles for horizontal etching. I 
have never tried etching this way.

Adam

Hello Group,
I am a new subscriber to the group and have been following the thread for a
few days. I closed down my etching services about two years ago, providing
hobbyists and business small runs of single and double sided boards. I never
mixed my own chemicals. Always purchased etchant in bulk (Ferric Chloride).
The conversation on making your own etchant is very interesting. I wish that
I had found a group like this several years ago.
Grant's comments about muriatic acid made me recall that when I was in a
pinch and the order of etchant had not arrived, I had to come up with a way
to extend the life of what I was using. It is a good old trick to run down
to the local hardware store and get some muriatic acid to add to the
etchant. This would keep you going for awhile so that you did not have to
stop the production line and it did not give you undercutting problems as
some remedies might.

Best regards,
Mike Putnam

----- Original Message -----

From: "grantfair2001" <grant.fair@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Monday, April 21, 2003 12:10 AM
Subject: [Homebrew_PCBs] Re: Cu + HCl -> CuCl2 : part 3


> Hi Adam - my chemist friend (who, incidentally, grew up near Bondi
> beach) advised me some time ago to try this recipe. I did not get past
> trying some copper in muriatic acide, and, expecting a quick reaction
> and getting none, giving up. (He had no idea about the time frame
> required, and no suggestions about what to do next). Here is his
> recipe, FWIW:
>
> "Dissolve 67 grams of copper in 100 gms muriatic acid solution (the
> 38% stuff). You could use an excess of copper to make sure all the HCl
> is consumed, but make sure you can remove the residual copper. Add 100
> gms muriatic acid and bubble the bejeezus out of it until it turns
> green. Add an additional 90 gms of muriatic acid solution and 606 gms
> of water and you should have about 900 mils of the recipe mentioned in
> the Rex Allers article."
>
> I think he got the 38% figure for the HCl from the article, since the
> muriatic acid available in hardware stores here is 20 Baume, about 30%.
>
> I don't know if that is helpful or not. He develops plastics for
> Dupont, so this is off the beaten track for him.
>
> Thanks for the idea for pumps for hydroponics - I will check  it out
>
> Grant
>
> --- In Homebrew_PCBs@yahoogroups.com, adam Seychell
> <adam_seychell@y...> wrote:
> > I did another test. This time I simply put clean copper
> > metal in the 20% acid and bubbled lots of air through it. It
> > took just over 3 hours to completely dissolve the copper and
> > produce a deep green colored cupric chloride etching solution.
> >
> > makeup data:
> >
> > 40 ml of  26%wt HCl acid
> > 20 ml of water
> > 8.7 grams of copper.
> [snip]
> >
> > Adam
>
>
>
> 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/
>
>

Hi Mike , welcome to the list. The ferric chloride is well know 
among DIY PCB etching. The air regenerated CuCl2 etching is new 
to me and seems like a nice etchant once understood how it 
behaves. This is why I've been working out ways of producing it 
from copper metal and HCl, both are cheap and easily available 
(two key rules for us hobbyist). It turns out to be very easy to 
prepare your self and quite tolerant to varying operating 
parameters, such as free HCl, and Cu content. Theoretically it 
can etch 2 sq.ft of single sided 1 oz PCB materal per liter of 
solution before needing readjustment with acid and water.

I'm interested in methods of getting a uniform etch across the 
board. I've tried several different vertical bubble etch tanks 
and I'm not happy with etch consistency. Have you tried floating 
the PCB and hit it with bubbles ?

Adam

Mike Putnam wrote:

> Hello Group,
> I am a new subscriber to the group and have been following the thread for a
> few days. I closed down my etching services about two years ago, providing
> hobbyists and business small runs of single and double sided boards. I never
> mixed my own chemicals. Always purchased etchant in bulk (Ferric Chloride).
> The conversation on making your own etchant is very interesting. I wish that
> I had found a group like this several years ago.
> Grant's comments about muriatic acid made me recall that when I was in a
> pinch and the order of etchant had not arrived, I had to come up with a way
> to extend the life of what I was using. It is a good old trick to run down
> to the local hardware store and get some muriatic acid to add to the
> etchant. This would keep you going for awhile so that you did not have to
> stop the production line and it did not give you undercutting problems as
> some remedies might.
> 
> Best regards,
> Mike Putnam
> 
> ----- Original Message -----
> From: "grantfair2001" <grant.fair@...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Monday, April 21, 2003 12:10 AM
> Subject: [Homebrew_PCBs] Re: Cu + HCl -> CuCl2 : part 3
> 
> 
> 
>>Hi Adam - my chemist friend (who, incidentally, grew up near Bondi
>>beach) advised me some time ago to try this recipe. I did not get past
>>trying some copper in muriatic acide, and, expecting a quick reaction
>>and getting none, giving up. (He had no idea about the time frame
>>required, and no suggestions about what to do next). Here is his
>>recipe, FWIW:
>>
>>"Dissolve 67 grams of copper in 100 gms muriatic acid solution (the
>>38% stuff). You could use an excess of copper to make sure all the HCl
>>is consumed, but make sure you can remove the residual copper. Add 100
>>gms muriatic acid and bubble the bejeezus out of it until it turns
>>green. Add an additional 90 gms of muriatic acid solution and 606 gms
>>of water and you should have about 900 mils of the recipe mentioned in
>>the Rex Allers article."
>>
>>I think he got the 38% figure for the HCl from the article, since the
>>muriatic acid available in hardware stores here is 20 Baume, about 30%.
>>
>>I don't know if that is helpful or not. He develops plastics for
>>Dupont, so this is off the beaten track for him.
>>
>>Thanks for the idea for pumps for hydroponics - I will check  it out
>>
>>Grant
>>
>>--- In Homebrew_PCBs@yahoogroups.com, adam Seychell
>><adam_seychell@y...> wrote:
>>
>>>I did another test. This time I simply put clean copper
>>>metal in the 20% acid and bubbled lots of air through it. It
>>>took just over 3 hours to completely dissolve the copper and
>>>produce a deep green colored cupric chloride etching solution.
>>>
>>>makeup data:
>>>
>>>40 ml of  26%wt HCl acid
>>>20 ml of water
>>>8.7 grams of copper.
>>
>>[snip]
>>
>>>Adam
>>
>>
>>
>>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/
>>
>>
> 
> 
> 
> 
> 
> 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/ 
> 
>

I'm wondering if anyone has thought about spray etching...

this may give uniform etch, may be very fast and may also regenerate the etchant.
but i have no idea if you can prevent a cheap pump from being eaten away soon.
the plastic pumps i know have a permanent magnet exposed to the fluid as rotor. and i believe nylon 
bearing.
but this may also be too complicated and even dangerous (etchant jet...)..

i also have thought of building a vertical tank with sort of rails on the side to slide adjustable 
bubbling nozzels, not only to bubble from bottom, you sayd it etches the bottom side faster so 
additional bubbling towards the upper part may help? i have no idea if anyone can direct the bubbles 
close enough to the board. it may also help to place a plastic "bubbling guide wall" near the copper 
plate which directs the bubbles up very close to the board, i believe it is slower on the upper not 
because of chemical reasons (oxygen lower etc.) but rather becasue the bubbles simply "shake up" the 
fluid more on the bottom edge.. and then rise up in growing distance from the board. i have not seen 
this, you have, if my assumption is wrong please correct me.

i believe this vertical etching would also be more efficient in bubbling as it should get out more 
oxygen of each bubble.

one solution for preventing the horizontal etched board from floating on foam and thus slowing down the 
etch may be to fix it down there in the fluid.
i have seen this in old foam etch machines, you simply make a holder of plastic like in vertical etching 
but lay it down in there, when proper constructed it holds the needed height. you may add some mechanism 
to lift it up and safely get the clad in and out..
i believe this would be very easy to build of some plastic rods and some plastic sheeting (10mm thick or 
more)


22.04.2003 05:07:09, Adam Seychell <adam_seychell@...> wrote:

>Hi Mike , welcome to the list. The ferric chloride is well know 
>among DIY PCB etching. The air regenerated CuCl2 etching is new 
>to me and seems like a nice etchant once understood how it 
>behaves. This is why I've been working out ways of producing it 
>from copper metal and HCl, both are cheap and easily available 
>(two key rules for us hobbyist). It turns out to be very easy to 
>prepare your self and quite tolerant to varying operating 
>parameters, such as free HCl, and Cu content. Theoretically it 
>can etch 2 sq.ft of single sided 1 oz PCB materal per liter of 
>solution before needing readjustment with acid and water.
>
>I'm interested in methods of getting a uniform etch across the 
>board. I've tried several different vertical bubble etch tanks 
>and I'm not happy with etch consistency. Have you tried floating 
>the PCB and hit it with bubbles ?
>
>Adam
>
>Mike Putnam wrote:
>> Hello Group,
>> I am a new subscriber to the group and have been following the thread for a
>> few days. I closed down my etching services about two years ago, providing
>> hobbyists and business small runs of single and double sided boards. I never
>> mixed my own chemicals. Always purchased etchant in bulk (Ferric Chloride).
>> The conversation on making your own etchant is very interesting. I wish that
>> I had found a group like this several years ago.
>> Grant's comments about muriatic acid made me recall that when I was in a
>> pinch and the order of etchant had not arrived, I had to come up with a way
>> to extend the life of what I was using. It is a good old trick to run down
>> to the local hardware store and get some muriatic acid to add to the
>> etchant. This would keep you going for awhile so that you did not have to
>> stop the production line and it did not give you undercutting problems as
>> some remedies might.
>> 
>> Best regards,
>> Mike Putnam
>> 
>> ----- Original Message -----
>> From: "grantfair2001" <grant.fair@...>
>> To: <Homebrew_PCBs@yahoogroups.com>
>> Sent: Monday, April 21, 2003 12:10 AM
>> Subject: [Homebrew_PCBs] Re: Cu + HCl -> CuCl2 : part 3
>> 
>> 
>> 
>>>Hi Adam - my chemist friend (who, incidentally, grew up near Bondi
>>>beach) advised me some time ago to try this recipe. I did not get past
>>>trying some copper in muriatic acide, and, expecting a quick reaction
>>>and getting none, giving up. (He had no idea about the time frame
>>>required, and no suggestions about what to do next). Here is his
>>>recipe, FWIW:
>>>
>>>"Dissolve 67 grams of copper in 100 gms muriatic acid solution (the
>>>38% stuff). You could use an excess of copper to make sure all the HCl
>>>is consumed, but make sure you can remove the residual copper. Add 100
>>>gms muriatic acid and bubble the bejeezus out of it until it turns
>>>green. Add an additional 90 gms of muriatic acid solution and 606 gms
>>>of water and you should have about 900 mils of the recipe mentioned in
>>>the Rex Allers article."
>>>
>>>I think he got the 38% figure for the HCl from the article, since the
>>>muriatic acid available in hardware stores here is 20 Baume, about 30%.
>>>
>>>I don't know if that is helpful or not. He develops plastics for
>>>Dupont, so this is off the beaten track for him.
>>>
>>>Thanks for the idea for pumps for hydroponics - I will check  it out
>>>
>>>Grant
>>>
>>>--- In Homebrew_PCBs@yahoogroups.com, adam Seychell
>>><adam_seychell@y...> wrote:
>>>
>>>>I did another test. This time I simply put clean copper
>>>>metal in the 20% acid and bubbled lots of air through it. It
>>>>took just over 3 hours to completely dissolve the copper and
>>>>produce a deep green colored cupric chloride etching solution.
>>>>
>>>>makeup data:
>>>>
>>>>40 ml of  26%wt HCl acid
>>>>20 ml of water
>>>>8.7 grams of copper.
>>>
>>>[snip]
>>>
>>>>Adam
>>>
>>>
>>>
>>>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/
>>>
>>>
>> 
>> 
>> 
>> 
>> 
>> 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/ 
>> 
>> 
>
>
>
>
>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/ 
>
>
>

----- Original Message -----

From: "Stefan Trethan" <stefan_trethan@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Tuesday, April 22, 2003 9:59 AM
Subject: Re: [Homebrew_PCBs] Re: Cu + HCl -> CuCl2 : part 3


> I'm wondering if anyone has thought about spray etching...
>
> this may give uniform etch, may be very fast and may also regenerate the
etchant.
> but i have no idea if you can prevent a cheap pump from being eaten away
soon.
> the plastic pumps i know have a permanent magnet exposed to the fluid as
rotor. and i believe nylon
> bearing.
> but this may also be too complicated and even dangerous (etchant jet...)..
>

I think that spray etching is used by most of the PCB manufacturers.

I've often wondered whether ultrasonics would be useful. We used ultrasonic
cleaning where I worked many years ago with very high-power units. The
cavitation  produced on the surface of the copper should give very rapid
removal. The effect of the etchant on the transducers needs to be solved, of
course, perhaps by coupling them to the base of the tank, so they aren't
exposed.

Leon
--
Leon Heller, G1HSM
leon_heller@...
http://www.geocities.com/leon_heller

Just an idea for pumping etchant...

What about a peristaltic pump?
The ones I have seen use a silicon rubber tubing and good for all sorts  
of fluids.


Simon Whitehead

On Tuesday, Apr 22, 2003, at 10:45 Europe/London, Leon Heller wrote:

>
> ----- Original Message -----
> From: "Stefan Trethan" <stefan_trethan@...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Tuesday, April 22, 2003 9:59 AM
> Subject: Re: [Homebrew_PCBs] Re: Cu + HCl -> CuCl2 : part 3
>
>
>> I'm wondering if anyone has thought about spray etching...
>>
>> this may give uniform etch, may be very fast and may also regenerate  
>> the
> etchant.
>> but i have no idea if you can prevent a cheap pump from being eaten  
>> away
> soon.
>> the plastic pumps i know have a permanent magnet exposed to the fluid  
>> as
> rotor. and i believe nylon
>> bearing.
>> but this may also be too complicated and even dangerous (etchant  
>> jet...)..
>>
>
> I think that spray etching is used by most of the PCB manufacturers.
>
> I've often wondered whether ultrasonics would be useful. We used  
> ultrasonic
> cleaning where I worked many years ago with very high-power units. The
> cavitation  produced on the surface of the copper should give very  
> rapid
> removal. The effect of the etchant on the transducers needs to be  
> solved, of
> course, perhaps by coupling them to the base of the tank, so they  
> aren't
> exposed.
>
> Leon
> --
> Leon Heller, G1HSM
> leon_heller@...
> http://www.geocities.com/leon_heller
>
> ------------------------ Yahoo! Groups Sponsor  
> ---------------------~-->
> Make Money Online Auctions! Make $500.00 or We Will Give You Thirty  
> Dollars for Trying!
> http://us.click.yahoo.com/yMx78A/fNtFAA/i5gGAA/bGYolB/TM
> --------------------------------------------------------------------- 
> ~->
>
> 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/
>
>
>
>
>
Simon Whitehead
4 Colleton Crescent
Exeter
Devon EX2 4DG
England
01392 217873
s.whitehead@...

Adam, yes I know what you mean about the vertical hobbyist kit tanks. The
air holes are spaced too far apart in them. Actually, I did try a homemade
horizontal bubbler once. The bubbles would not move across the copper evenly
and caused areas of the copper to etch faster than others. In some cases the
bubbles would stay in one place and cause the etchant to not react with the
copper.
 I used a vertical tank that I built like a fish aquarium only much thinner.
It was made of glass panels and was sealed with the same RTV material used
for aquariums. I made it wide enough so that I could get one hand down to
the bottom so that I could perform maintenance when needed. It was tall
enough to hold 12X12 panels, to give you an idea of dimensions. The air for
the bubbler was provided by a small compressor, although other means will
also work. About the bubbler: In fish stores you can find cheap devices to
create a wall of tiny bubbles in your fish tank. I used a few of these glued
(RTV) onto the bottom of the etch tank. On mine, I had to use a small needle
and poke a few larger holes to get something better than a mist. These
devices are made of some type of cardboard material, so it is easy. A very
even layer of holes provide a wall of bubbles that produce very good results
on the panels. Some experimentation here is needed the first time.

Mike

----- Original Message -----

From: "Adam Seychell" <adam_seychell@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Monday, April 21, 2003 8:07 PM
Subject: Re: [Homebrew_PCBs] Re: Cu + HCl -> CuCl2 : part 3


> Hi Mike , welcome to the list. The ferric chloride is well know
> among DIY PCB etching. The air regenerated CuCl2 etching is new
> to me and seems like a nice etchant once understood how it
> behaves. This is why I've been working out ways of producing it
> from copper metal and HCl, both are cheap and easily available
> (two key rules for us hobbyist). It turns out to be very easy to
> prepare your self and quite tolerant to varying operating
> parameters, such as free HCl, and Cu content. Theoretically it
> can etch 2 sq.ft of single sided 1 oz PCB materal per liter of
> solution before needing readjustment with acid and water.
>
> I'm interested in methods of getting a uniform etch across the
> board. I've tried several different vertical bubble etch tanks
> and I'm not happy with etch consistency. Have you tried floating
> the PCB and hit it with bubbles ?
>
> Adam