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March 2007

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Subject:
From:
"Barmuta, Michael" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Barmuta, Michael
Date:
Wed, 7 Mar 2007 07:53:37 -0800
Content-Type:
text/plain
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text/plain (312 lines)
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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