getting rid of gold on pcb

[[email protected]]

We have boards that inadvertently ended up with hard gold finish. As a
result we have 50 microinches of gold causing all kinds of headaches
at assembly.
We asked to have the extra gold stripped off but I was told it was not
possible.
Is there no way to dissolve the gold off? Otherwise we have to get
another batch made and they're expensive.
Mercury bath? Hot cyanide? Microtome? Have an immersion silver finish
over the gold!!! Argghgghgh anything!!

 

[John Larkin]

We have boards that inadvertently ended up with hard gold finish. As a
result we have 50 microinches of gold causing all kinds of headaches
at assembly.
We asked to have the extra gold stripped off but I was told it was not
possible.
Is there no way to dissolve the gold off? Otherwise we have to get
another batch made and they're expensive.
Mercury bath? Hot cyanide? Microtome? Have an immersion silver finish
over the gold!!! Argghgghgh anything!!

50 microinches is a lot. But you could have them hot-dip solder coated
and releveled, which would dissolve the gold and replace with solder.
That might work, but then the gold usually has nickel underneath...

What's the problem with the gold?

John

 

[[email protected]]

50 microinches is a lot. But you could have them hot-dip solder coated
and releveled, which would dissolve the gold and replace with solder.
That might work, but then the gold usually has nickel underneath...

What's the problem with the gold?

John

Hi John,
It's causing a lot of embrittlement as the gold dissolves in the
solder. As it is a 100 mil thick board with 12 plane layers and 6
signal layers, the board sits in the heat soak stage for a long time,
causing more gold to get dissolved.
The boards barely pass visual inspection of the solder joints, and
some 0402 ans 0201 parts just pop off easily.
The few bare boards we have left we want to somehow get them to work.
I'm trying to get the PCB fab to put immersion silver over the gold
but I haven't heard back from them. Perhaps they died laughing.
I like the solder idea, do you mean some sort of HASL ?? Or some sort
of wave process?
It's an unusual request I know.

 

[John Larkin]

Hi John,
It's causing a lot of embrittlement as the gold dissolves in the
solder. As it is a 100 mil thick board with 12 plane layers and 6
signal layers, the board sits in the heat soak stage for a long time,
causing more gold to get dissolved.

What does one of those babies cost?

The boards barely pass visual inspection of the solder joints, and
some 0402 ans 0201 parts just pop off easily.
The few bare boards we have left we want to somehow get them to work.
I'm trying to get the PCB fab to put immersion silver over the gold
but I haven't heard back from them. Perhaps they died laughing.
I like the solder idea, do you mean some sort of HASL ?? Or some sort
of wave process?

I was thinking of trying the regular HASL pass. I know that thin, like
10 uin, gold just dissolves in solder without much effect, and the
solder seems to stick to whatever's underneath, nickel usually.

John

 

[TT_Man]

What does one of those babies cost?


I was thinking of trying the regular HASL pass. I know that thin, like
10 uin, gold just dissolves in solder without much effect, and the
solder seems to stick to whatever's underneath, nickel usually.

John

I would have thought the same..... going through HASL should remove the
gold. Maybe you need to do it a couple of times..... not sure what the fab
plant will say about having their solder contaminated with gold though. But
doesn't the molten gold float on top of the solder?

 

[John Larkin]

I would have thought the same..... going through HASL should remove the
gold. Maybe you need to do it a couple of times..... not sure what the fab
plant will say about having their solder contaminated with gold though. But
doesn't the molten gold float on top of the solder?

It should dissolve nicely. At high gold concentrations, the
intermetallic is nasty brittle stuff, but diluted enough, the gold
shouldn't matter. I have no idea how long it might take to dissolve 50
uin of gold.

John

 

[[email protected]]

It should dissolve nicely. At high gold concentrations, the
intermetallic is nasty brittle stuff, but diluted enough, the gold
shouldn't matter. I have no idea how long it might take to dissolve 50
uin of gold.

John

Maybe I'll ask our assembly guys to put solder paste on the board and
reflow it, then send the boards to the PCB shop to do a HASL? Is that
the process with the hot-air knife and it'll blow away the excess
solder? Oh well look, it's Friday night already.
I'm off to pickle what few neurons I have left!

 

[GoldIntermetallicEmbrittlement]

It should dissolve nicely. At high gold concentrations, the
intermetallic is nasty brittle stuff, but diluted enough, the gold
shouldn't matter. I have no idea how long it might take to dissolve 50
uin of gold.

You're an idiot. The dissolution of the Gold is a BAD thing, dumbass.

It causes embrittlement, and no, after it gets above a certain amount,
it does not go away!

You should get a clue, before you spew.

 

[Robert Baer]

On Fri, 12 Oct 2007 11:35:02 -0700, in sci.electronics.design


I'd try Brasso, don't know what the US equivalent is.
http://en.wikipedia.org/wiki/Brasso


Martin

Brasso has been available in the US for at least 50 years...and is
still available.

 

[John Larkin]

You're an idiot. The dissolution of the Gold is a BAD thing, dumbass.

It causes embrittlement, and no, after it gets above a certain amount,
it does not go away!

You should get a clue, before you spew.

Maybe you'd like to start over, and make a little bit of sense next
time.

John

 

[D from BC]

We have boards that inadvertently ended up with hard gold finish. As a
result we have 50 microinches of gold causing all kinds of headaches
at assembly.
We asked to have the extra gold stripped off but I was told it was not
possible.
Is there no way to dissolve the gold off? Otherwise we have to get
another batch made and they're expensive.
Mercury bath? Hot cyanide? Microtome? Have an immersion silver finish
over the gold!!! Argghgghgh anything!!

I have no experience in this area so I'll just rattle off the wacky
ideas:

1) Sandblasting (copper microspheres?)
2) Planar (as with lumbar)
3) Wet abrasive and lapping (mirror polishing)
4) Air blasting at 1063C (Au melting point)
(Cu melts at 1083C and Ni at 1455C..but PCB will burn)
5) EDM engraving
6) 3:1 HCL:HNO3 etching
7) Chlorine gas etching or Chlorine in solution


D from BC

 

[Robert Baer]

I would have thought the same..... going through HASL should remove the
gold. Maybe you need to do it a couple of times..... not sure what the fab
plant will say about having their solder contaminated with gold though. But
doesn't the molten gold float on top of the solder?

Gold will alloy slightly - around 2% if i remember correctly.

 

[Robert Baer]

I have no experience in this area so I'll just rattle off the wacky
ideas:

1) Sandblasting (copper microspheres?)
2) Planar (as with lumbar)
3) Wet abrasive and lapping (mirror polishing)
4) Air blasting at 1063C (Au melting point)
(Cu melts at 1083C and Ni at 1455C..but PCB will burn)
5) EDM engraving
6) 3:1 HCL:HNO3 etching
7) Chlorine gas etching or Chlorine in solution


D from BC

....and do not forget environmentally and people friendly Mercury as well
as acidic Cyanides...

 

[D from BC]

...and do not forget environmentally and people friendly Mercury as well
as acidic Cyanides...

Wouldn't chlorine would be the choice toxin. If it gets loose, it's
heavier than air and will find something to react with. It's far from
being an inert gas and isn't found naturally in it's elemental form.
I'm guessing the resulting chlorine compounds are going to be more
friendly than mercury compounds or cyanide just sitting around not
reacting with objects.

If chlorine etching is used on the gold..it should be checked out what
temperature should be used.
The colder the temperature...the less reaction to copper.
D from BC

 

[John Larkin]

I have no experience in this area so I'll just rattle off the wacky
ideas:

1) Sandblasting (copper microspheres?)
2) Planar (as with lumbar)
3) Wet abrasive and lapping (mirror polishing)
4) Air blasting at 1063C (Au melting point)
(Cu melts at 1083C and Ni at 1455C..but PCB will burn)
5) EDM engraving
6) 3:1 HCL:HNO3 etching
7) Chlorine gas etching or Chlorine in solution


D from BC

You could probably rub the gold off with a scotchbrite pad and
household cleanser.

John

 

[Martin Griffith]

On Fri, 12 Oct 2007 11:35:02 -0700, in sci.electronics.design

We have boards that inadvertently ended up with hard gold finish. As a
result we have 50 microinches of gold causing all kinds of headaches
at assembly.
We asked to have the extra gold stripped off but I was told it was not
possible.
Is there no way to dissolve the gold off? Otherwise we have to get
another batch made and they're expensive.
Mercury bath? Hot cyanide? Microtome? Have an immersion silver finish
over the gold!!! Argghgghgh anything!!

I'd try Brasso, don't know what the US equivalent is.
http://en.wikipedia.org/wiki/Brasso


Martin

 

[John Larkin]

I'd try Brasso, don't know what the US equivalent is.
http://en.wikipedia.org/wiki/Brasso

The US equivalent is Brasso.

John

 

[D from BC]

You could probably rub the gold off with a scotchbrite pad and
household cleanser.

John

Yup.. Does sound like that'll work and perhaps worth a try..

Gold is a relatively soft metal. Using a pad that is just harder than
the gold but softer than the copper (or plating on copper) will help
reduce wear on the copper.
I know scotchbrite scuffs copper which means something in the
scotchbrite is harder than copper..

Household cleansers (ex Javex) contain chlorine compounds but I don't
know if that will react with gold.. (I'm not a chemist!)
However chlorine gas will. How fast..I dunno..

It's interesting, it takes only 1% chlorine to saturate water. Max
solubility is at 9.6C.. Anymore and it gases.
This can be a good thing too. I suspect chlorine has much more
reactivity with gold at 9.6C temp than with copper..
So.. chilled water saturated with chlorine and etch the board is my
guess... I have no idea if that'll work..but seems like a start.

Joke...Perhaps you could just plop the pcbs in a chlorinated public
swimming pool for a few days..
(I dunno if that'll work..)
D from BC

 

[GoldIntermetallicEmbrittlement]

You could probably rub the gold off with a scotchbrite pad and
household cleanser.

Will your stupidity ever cease?

 

[GoldIntermetallicEmbrittlement]

I'd try Brasso, don't know what the US equivalent is.
http://en.wikipedia.org/wiki/Brasso


Martin

I find it nearly unbelievable some of the horseshit you uneducated
twits spew.