One the subject of vias
This is very precise
To have coverage we suppose
Is all very nice
But in the event
That copper concerns
The end use environment
Will dictate if it burns
Thank you Dewey......................................
John Burke
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE)
Sent: Wednesday, March 07, 2007 10:03 AM
To: [log in to unmask]
Subject: Re: [TN] immersion silver and exposed copper in small vias
Leave no pun unattended
Nor critical via untented
Other concerns do not diminish
Be aware of any surface finish
On the issue of exposure
What's left is closure
Now that we have covered the prose and cons of copper exposure, I agree
with you that it is applicable for all final surface finishes with the
exception of a properly applied minimum thickness of gold.
Dewey
-----Original Message-----
From: Barmuta, Michael [mailto:[log in to unmask]]
Sent: Wednesday, March 07, 2007 10:31 AM
To: Whittaker, Dewey (EHCOE); TechNet E-Mail Forum
Subject: RE: [TN] immersion silver and exposed copper in small vias
Well Honey, not just a Fluke but repeatable for others.
Regarding Direct Corrosion, the oxides formed on the surface of the
copper form an inert non-reactive barrier that help protect it from
further attack. From a Galvanic Corrosion standpoint, copper is more
noble on the electromotive series than tin or tin lead and about the
same as nickel.
This not to say you will never have a problem with copper. However it
has been my experience that if a reactant/contaminant comes in contact
with a PCA and is strong enough to result in a corrosive nature it
doesn't make a difference if you have copper, tin, tin/lead or nickel.
Also remember if using electroplated gold over electroplated nickel over
copper you are not protected from a galvanic problem. It fact it could
be worse with three different metals with exposed edges all with
different electromotive potentials. Just ask the guys etching gold
electroplated PCB's.
I understand your concerns but I don't believe the copper would be any
worse than most other metals being used in PCB construction. As I said
below when the copper was exposed to very corrosive mixed flowing gases
we did not see any deterioration. In fact the stainless steel support
system in the test chamber should more attack and corrosion than the
test vehicles.
Regards
Michael Barmuta
Staff Engineer
Fluke Corp.
Everett WA
425-446-6076
-----Original Message-----
From: Whittaker, Dewey (EHCOE) [mailto:[log in to unmask]]
Sent: Wednesday, March 07, 2007 8:40 AM
To: TechNet E-Mail Forum; Barmuta, Michael
Subject: RE: [TN] immersion silver and exposed copper in small vias
Are these repeatable results or just a Fluke?
Thanks for the input. I agree that exposed copper itself is not a
concern, but I have always been concerned of the what, where and when of
potential contaminant deposition and the subsequent results when exposed
to the end use environment, not to mention the processing environment
during manufacture.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Barmuta, Michael
Sent: Wednesday, March 07, 2007 8:54 AM
To: [log in to unmask]
Subject: Re: [TN] immersion silver and exposed copper in small vias
Hi Lee: Just to substantiate yours, Werners, Waynes and others comments,
exposed copper is not a reliability issue. Agreed that any trapped
chemistries in holes can definably be a problem but that is true even if
the final finish is not copper.
When OSP's were coming on the scene in the late eighties/early nineties
we ran extensive testing with IBM Endicott on exposed copper boards.
Included is the testing protocol was electromigration, humidity cycling
and environmental exposure using MFG (mixed flowing gas).
Based on the type of MFG test that is run, it can be very aggressive.
The MFG test exposes the electronic assembly to controlled
concentrations of corrosive gases in a chamber. This simulates X years
of field service based on the number of hours of chamber time the test
is run. We ran the MFG Type-H test for 420 hours which correlates to 10
years of heavy industrial environments such as pulp/paper mills,
waste/water treatment plants, chemical refineries, etc. Bottom line we
found no performance or reliability differences between the copper and
HASL control assemblies.
We've built literally millions of test and measurement instruments over
the last 15-20 years as exposed copper boards. These are used in every
environment imaginable all over the world. We do not see any issues with
the exposed copper from our field service centers.
Regards
Michael Barmuta
Staff Engineer\
Fluke Corp.
Everett WA
425-446-6076
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lee parker
Sent: Wednesday, March 07, 2007 6:41 AM
To: [log in to unmask]
Subject: Re: [TN] immersion silver and exposed copper in small vias
Copper does not corrode in the since that iron does. Copper is a near
noble
element that behaves more like aluminum; it forms a passivative layer
that
penetrates only a few microns into the material. Think of aerial copper
wire
(so called open wire) used by the phone companies for many years. Where
I
live, the aerial copper wire that was installed in the early 20s is
still in
place and functions as well as it did 90 years ago.
Best regards
Lee
J. Lee Parker, Ph.D.
JLP Consultants LLC
804 779 3389
----- Original Message -----
From: "Hogg, Blair K." <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, March 06, 2007 4:43 PM
Subject: Re: [TN] immersion silver and exposed copper in small vias
I guess I'll have to replace all that corroded copper pipe in my house
with the plastic kind....
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Tuesday, March 06, 2007 4:24 PM
To: [log in to unmask]
Subject: Re: [TN] immersion silver and exposed copper in small vias
Or the Statue of Liberty...
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ian Hanna
Sent: Tuesday, March 06, 2007 3:26 PM
To: [log in to unmask]
Subject: Re: [TN] immersion silver and exposed copper in small vias
That's why they build church roofs out of it I suppose...
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kevin Glidden
Sent: Tuesday, March 06, 2007 4:20 PM
To: [log in to unmask]
Subject: Re: [TN] immersion silver and exposed copper in small vias
Is this really true? I have only been at this around 7 yrs, but
everything I was ever taught says exposed Cu is not allowed for risk of
corrosion.
-----Original Message-----
From: Wayne Thayer [mailto:[log in to unmask]]
Sent: Tuesday, March 06, 2007 3:52 PM
To: [log in to unmask]
Subject: Re: [TN] immersion silver and exposed copper in small vias
And what's wrong with exposed copper? You certainly aren't going to try
and solder down there, are you? Copper does not corrode quickly, and if
its going to be in a corrosive environment, you're going to have to
conformal coat anyway!
The silver is put on boards only to extend the solderability lifetime of
the bare copper, not as a protectant to prevent opens due to corrosion.
This is not a reliability issue at all.
Wayne Thayer
>>> [log in to unmask] 3/6/2007 12:10:08 pm >>>
Hi Fran
The amount of mask intruding into the hole will depend on the
application method. Our curtain coat operation can cause the mask (circa
1-2 microns) to penetrate about 1/3rd into the hole from both sides but
it has not affected the silver taking on the remaining surface. Is the
mask too thick at the hole entrance to prevent the plating solution
getting good access?
You may also need to confirm by micro section what your customer thinks
he is seeing. Is the mask covering all the hole surface? Hope this
helps.
Regards
Alistair
Alistair F Murray MICT
Technical Manager
Artetch Circuits Limited
England UK
Direct Dial: 01903-712931
www.artetch.co.uk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Fran Juliot
Sent: 06 March 2007 15:58
To: [log in to unmask]
Subject: [TN] immersion silver and exposed copper in small vias
Our customer is questioning what they feel is exposed copper in 8 mil
vias holes on silver boards. We feel there is mask residue in the holes
which does not allow silver to take. These are holes that are allowed
to be plugged. Has anyone else ran into this issue with thier customers
and do you have the same look or are your small vias covered with silver
all the way through the via?
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