Homebrew_PCBs

Hi there, I'm new to etching PCBs and to the group.

Faced with some pretty tarnished copper clad I took the same approach
that I use for cleaning copper bottomed cookware, namely lemon juice
and a scotchbrite pad. Cleaned up all the oxidation very easily! Not
knowing if the lemon juice would leave any residue behind I finished
off by wiping the board with rubbing alchohol.

Just wondering if anyone else has tried lemon juice and/or has any
thoughts on how suitable it is for cleaning copper clad pcb material.

Not lemon juice, but citric acid was a common antitarnish when stripping print and etch innerlayers in caustic. Amines work better as an antitarnish, but they form complexes with dissolved copper and makes waste treatment very expensive. It reacts with the copper and forms a layer that resists oxidation reasonably well. After stripping these boards went through a black or red oxide treatment to enhance adhesion in multilayer boards. I seem to remember one or two shops that used citric acid in a chem clean line and I don't remember any adhesion problems with the photoresist.

----- Original Message -----
From: Tom
To: Homebrew_PCBs@yahoogroups.com
Sent: Friday, December 03, 2004 2:03 PM
Subject: [Homebrew_PCBs] Cleaning copper with lemon juice




Hi there, I'm new to etching PCBs and to the group.

Faced with some pretty tarnished copper clad I took the same approach
that I use for cleaning copper bottomed cookware, namely lemon juice
and a scotchbrite pad. Cleaned up all the oxidation very easily! Not
knowing if the lemon juice would leave any residue behind I finished
off by wiping the board with rubbing alchohol.

Just wondering if anyone else has tried lemon juice and/or has any
thoughts on how suitable it is for cleaning copper clad pcb material.










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[Non-text portions of this message have been removed]

Earl T. Hackett, Jr. wrote:

> Not lemon juice, but citric acid was a common antitarnish when stripping print and etch innerlayers in caustic. Amines work better as an antitarnish, but they form complexes with dissolved copper and makes waste treatment very expensive. It reacts with the copper and forms a layer that resists oxidation reasonably well. After stripping these boards went through a black or red oxide treatment to enhance adhesion in multilayer boards. I seem to remember one or two shops that used citric acid in a chem clean line and I don't remember any adhesion problems with the photoresist.

I'm having a hard time stopping freshly electroplated copper from
tarnishing when the panels dry. The cause cannot be a sulfuric acid
residue problem since it tarnishes even after neutralization and
excessive rinsing with DI water.
How was the citric applied to prevent the antitarnishing ? Do you know
the process details for antitarnish, what is the critic acid
concentration, are the boards rinsed before drying ?

Adam

In commercial shops copper was almost always pattern plated followed by tin, tin/lead, or in the case of HP, nickel gold plating. If you wanted solder mask over bare copper the tin plating was stripped after the base copper foil was etched. Plating copper over the whole board just meant you had more to etch. So antitarnish after copper plate was never much of a question.

The plating chemistry in most acid copper baths contained amines. They were present to provide leveling, grain refinement and to reduce stress. As a by product, they were pretty good antitarnish agents as well.

In your case, the best place to put an anti tarnish is in the second rinse following the plating bath. If you have realy hard water, consider making solutions with DI water from the super market. This was a rairity in the industry, but I did run into it a couple of times. Citric acid at 3 to 5% by weight should do the job. The first rinse should be a quick dip and a slosh around to remove the gross plating solution. Let the board drain off fairly well so you don't carry much plating solution over with the board and stick it in the second rinse. Slosh it around for a couple of minutes and rinse again in running water. A final DI water rinse is not a bad idea.

Monoethanol amine seems to be available over the web. I've seen it but can't remember where. It is much more effective than citric acid. Again 3 to 5 % by either weight or volume (it's a liquid with a specific gravity just a bit lower than water) in the second rinse.

----- Original Message -----
From: Adam Seychell
To: Homebrew_PCBs@yahoogroups.com
Sent: Friday, December 03, 2004 5:19 PM
Subject: Re: [Homebrew_PCBs] Cleaning copper with lemon juice


I'm having a hard time stopping freshly electroplated copper from
tarnishing when the panels dry. The cause cannot be a sulfuric acid
residue problem since it tarnishes even after neutralization and
excessive rinsing with DI water.
How was the citric applied to prevent the antitarnishing ?
Do you know the process details for antitarnish, what is the critic acid concentration, are the boards rinsed before drying ?

Adam



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[Non-text portions of this message have been removed]

--- In Homebrew_PCBs@yahoogroups.com, "Earl T. Hackett, Jr."
<hacketet@c...> wrote:

> In commercial shops copper was almost always pattern plated followed

by tin, tin/lead, or in the case of HP, nickel gold plating. If you
wanted solder mask over bare copper the tin plating was stripped after
the base copper foil was etched. Plating copper over the whole board
just meant you had more to etch. So antitarnish after copper plate
was never much of a question.


I've had good luck with Cameo copper cleaner (for pans) and a PUR
water filter. A small amount of Cameo in soft water seem to polish
the surface enough that the toner sticks well.

It is important to rinse the board until the water "sheets" over the
entire surface and the PUR filter helps quite a bit if you have hard
water.

Curt

Thanks for the information.

I tried a couple more boards and this time skipped the rubbing
alchohol wipedown after the lemon juice scrub. It may have helped and
certainly didn't hurt. I changed a few other things and went back to
the MultiProject paper, so I don't know which change was most
important. But I'm fairly pleased with the result, it's the best toner
to copper transfer I've gotten yet. Only problem is the pinholes left
by the printer, but touchup with a sharpie isn't too hard.


--- In Homebrew_PCBs@yahoogroups.com, "Earl T. Hackett, Jr."
<hacketet@c...> wrote:

> Not lemon juice, but citric acid was a common antitarnish when

stripping print and etch innerlayers in caustic. Amines work better
as an antitarnish, but they form complexes with dissolved copper and
makes waste treatment very expensive. It reacts with the copper and
forms a layer that resists oxidation reasonably well. After stripping
these boards went through a black or red oxide treatment to enhance
adhesion in multilayer boards. I seem to remember one or two shops
that used citric acid in a chem clean line and I don't remember any
adhesion problems with the photoresist.

Earl T. Hackett, Jr. wrote:

> In commercial shops copper was almost always pattern plated followed by tin, tin/lead, or in the case of HP, nickel gold plating. If you wanted solder mask over bare copper the tin plating was stripped after the base copper foil was etched. Plating copper over the whole board just meant you had more to etch. So antitarnish after copper plate was never much of a question.
>
> The plating chemistry in most acid copper baths contained amines. They were present to provide leveling, grain refinement and to reduce stress. As a by product, they were pretty good antitarnish agents as well.
>
> In your case, the best place to put an anti tarnish is in the second rinse following the plating bath. If you have realy hard water, consider making solutions with DI water from the super market. This was a rairity in the industry, but I did run into it a couple of times. Citric acid at 3 to 5% by weight should do the job. The first rinse should be a quick dip and a slosh around to remove the gross plating solution. Let the board drain off fairly well so you don't carry much plating solution over with the board and stick it in the second rinse. Slosh it around for a couple of minutes and rinse again in running water. A final DI water rinse is not a bad idea.
>
> Monoethanol amine seems to be available over the web. I've seen it but can't remember where. It is much more effective than citric acid. Again 3 to 5 % by either weight or volume (it's a liquid with a specific gravity just a bit lower than water) in the second rinse.
>

Thanks for the tips Earl, I do not know what the ingredients are in the
brightening additives I'm using, but they don't seem to help the tarnish
problem at all. I have both monoethanol amine (MEA) and citric acid
laying around the workshop. I'll try adding small amount of citric in
the rinse as you suggested. There is a triple cascaded rinse tank
following the acid copper plating. I also use these same rinse tanks for
rinsing off the ammonium persulfate microetch. After plating, the panels
are rinsed followed by application of dry film photoresist by wet
lamination. Would citric acid residue effect dry film ? MEA on the
other hand is alkaline and will probably be fatal to dry film. I did
read somewhere MEA can be used as dry film stripper.
I'll let you know what happens.

Adam

We often used citric acid as an anti tarnish after electroless copper. The dry film was applied on the scrubbed copper surface and then went on to dry film lamination. The scrubbing was sufficient to produce a fresh copper surface. The citric acid only prevented tarnish in the pores of the electroless deposit.

Interestingly, one of the adhesion promotors used in dry film formulations is an aliphatic amine. I can't think of the particular chemical, but it wasn't MEA. The theory was that it would find its way to the surface, form a copper complex, and provide a chemical bond with the photoresist. The photoresist has acid groups all along the polymer chain. Aqueous processing dry films just have more that the old solvent process films. With the amine anchored to the copper, the acid group reacts with it and forms an ionic bond very much like amonium acetate. As long as the system is dry this is a very strong bond. Over development would cause the bond to fail. Getting the adhesion level just right was always a tradeoff. If you made it too strong you have great development latitude, but stripping was slow and had the potential to leave residues. Too weak and development becomes touchy, but it would strip quickly and cleanly.

Formulations have changed over the last 20 years and there may be more robust adhesion systems in modern dry films.

----- Original Message -----
From: Adam Seychell
To: Homebrew_PCBs@yahoogroups.com
Sent: Saturday, December 04, 2004 2:53 PM
Subject: Re: [Homebrew_PCBs] Cleaning copper with lemon juice



Thanks for the tips Earl, I do not know what the ingredients are in the
brightening additives I'm using, but they don't seem to help the tarnish
problem at all. I have both monoethanol amine (MEA) and citric acid
laying around the workshop. I'll try adding small amount of citric in
the rinse as you suggested. There is a triple cascaded rinse tank
following the acid copper plating. I also use these same rinse tanks for
rinsing off the ammonium persulfate microetch. After plating, the panels
are rinsed followed by application of dry film photoresist by wet
lamination. Would citric acid residue effect dry film ? MEA on the
other hand is alkaline and will probably be fatal to dry film. I did
read somewhere MEA can be used as dry film stripper.
I'll let you know what happens.

Adam



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[Non-text portions of this message have been removed]

Hi there
Ive never tried Lemon Juice however i remember i think from Mr.
Wizard, (remember him?) a good way to clean copper.
Take some white vinegar, (red wine vinegar also works) and mix in
some table salt.

This is your copper cleaner. Drop your board into a shallow tray
with some of this stuff and watch the tarnish vanish. Rinse well with
water. Get it all off or it will just start to corrode later.

This removes tarnish, but won't pollish, A good pencil eraser may be
used to burnish the copper traces.


A little thing to remember, Being vinegar and salt, one would assume
that this is a safe substance, and it is... BUT once you use it to
clean copper, it becomes poison. I just pour some in a tray or on a
paper towel and discard when im done, i never reuse.

Lemon juice = citric acid
vinegar [Acetic acid] + salt [sodium chloride] =
(HAc +NaCl) ->
HCl [hydrochloric acid] + NaAc [Sodium Acetate?]

Either way they are acid bath cleaners - the HCl would be
the nastier of the two.

Norm

newphreak_16@... wrote:

>
>
> Hi there
> Ive never tried Lemon Juice however i remember i think from Mr.
> Wizard, (remember him?) a good way to clean copper.
> Take some white vinegar, (red wine vinegar also works) and mix in
> some table salt.
>
> This is your copper cleaner. Drop your board into a shallow tray
> with some of this stuff and watch the tarnish vanish. Rinse well with
> water. Get it all off or it will just start to corrode later.
>
> This removes tarnish, but won't pollish, A good pencil eraser may be
> used to burnish the copper traces.
>
>
> A little thing to remember, Being vinegar and salt, one would assume
> that this is a safe substance, and it is... BUT once you use it to
> clean copper, it becomes poison. I just pour some in a tray or on a
> paper towel and discard when im done, i never reuse.
>
>
>
>
>
>
>
>
> Be sure to visit the group home and check for new Bookmarks and files:
> http://groups.yahoo.com/group/Homebrew_PCBs
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
>

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