hi,
i tend to look on the dark side of life. hasn't everyone seen copper corrode in a marine environment? why tempt murphy if you know your product will be in a 'harsh' environment unless you have performed some tests to determine how long it will survive?
phil
-----Original Message-----
From: Yehuda Weisz [mailto:[log in to unmask]]
Sent: Sunday, April 29, 2001 3:32 PM
To: [log in to unmask]
Subject: Re: [TN] Fw: Reliability of exposed copper
Hi Steve,
You see - that's exactly what I mean. Copper is very corrosion resistant,
however we are coating it with so many corrosion resistant finishings. I am
quite certain that someone examined this issue at least once.
I was asked by Susan - What exactly am I talking about, so here goes:
I am talking about the bad things that might happen to an isolated trace or
the PTH in several holes that are only copper plated. The environment can
vary from room to harsh.
The trigger to this "weird" question is a discussion that we've held
regarding tented via holes for BGA. We need to tent the via holes near the
BGA to avoid the entrapment of soldeballs inside the via holes. Everywhere
it is recommended that if the via holes are tented - they should be tented
on both sides (we are working with dry film soldermask, that's why we are
tenting and not plugging).
Then came our QA people and said "Oh no.....you have now a via hole inside
that is copper plated and protected only by a thin (2 mil) plastic film on
both sides. What will happen if this film is damaged and some flux or other
contaminant gets inside the hole?"
I sort of agreed with them but on the other side - the copper oxide is
acting as a kind of a barrier that protects the copper after the initial
surface attack. That is why we have so many copper objects that live almost
forever (telegraph wires for example).
Again, I am quite certain that we didn't invent anything new here and these
discussions were held (in one form or the other) in other corners of the
globe too. So, I want to find some of these discussions and if any work was
done to check who's right - these reports I am interested in.
I'll be very gratefull for any inputs.
Best regards,
Yehuda
----- Original Message -----
From: Stephen R. Gregory <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, April 29, 2001 7:09 PM
Subject: Re: [TN] Fw: Reliability of exposed copper
> Hi Yehuda!
>
> Here's an article discussing OSP's and includes discussion about OSP and
> press-fit interconnects, which essentially is bare copper. Go to:
>
> http://img.cmpnet.com/assembly/db_area/archives/top100/pdf/9905enthone.pdf
>
> Bare copper is not a problem, the copper will oxidise to a certain point,
and
> the oxidation acts as a barrier to prevent further oxidation...you can't
> solder to oxidized copper, but it won't deteriorate further. There are
> environments that could cause problems though (salty, humid, hot,
> environments for example), but then you would want to conformally these
> assemblies anyway, whether OSP coated or otherwise finished...
>
> One of the best examples of copper robustness is the statue of liberty,
> entirely made of copper, withstood the elements (acid rain included) for
> 100-years before requiring restoration. Another example is the telegraph
> lines that were strung across the US in the 1800's...non-insulated copper
> wire that survive even today...
>
> -Steve Gregory-
>
>
>
> << Hi All,
> I am sending this question again, in case somebody does have a relevant
> input. I suppose that over time, this issue must have been discussed or
> examined in the industry or in the military standard committees.
>
> Thanks,
> Yehuda
>
> ----- Original Message -----
> From: Yehuda Weisz
> To: IPC TechNet
> Sent: Sunday, April 15, 2001 9:26 PM
> Subject: Reliability of exposed copper
>
>
> Hi Technetters,
> I hope that you got over Easter and its bunnies easily and I would like
to
> ask a small question.
>
> Does anyone of you remember any study regarding the reliability of
exposed
> copper (such as in a unprotected PCB - no soldermask and no solder) in
> different environmental conditions?
>
> Best regards,
> Yehuda
> >>
>
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