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December 2006

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From:
"Wenger, George M." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wenger, George M.
Date:
Fri, 15 Dec 2006 16:49:34 -0500
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I echo your comment about this not being an immersion sil
Denny,



I echo your comment about this not being an immersion silver problem.

We've seen these types of defects, fortunately very infrequently, and

they are usually associated with imaging issues.  If there is an

appropriate amount of copper  in the PTH's the amount of copper consumed

during a replacement reaction that deposits only a few microinches of

silver should not etch enough copper to cause the ring voids.



Regards,

George

George M. Wenger

Andrew Corporation Wireless Network Solutions

Senior Principal FMA / Reliability Engineer

40 Technology Drive, Warren, NJ 07059

(908) 546-4531 [Office]  (732) 309-8964 [Cell]



-----Original Message-----

From: TechNet [mailto:[log in to unmask]] On Behalf Of Dennis Fritz

Sent: Friday, December 15, 2006 3:38 PM

To: [log in to unmask]

Subject: Re: [TN] How does this happen?



In a message dated 12/15/2006 8:59:36 A.M. Eastern Standard Time,

[log in to unmask] writes:



Another  possibility is that the single panel was reworked through

immersion  silver.  Immersion silver is notorious for etching copper as

it  plates.  I've seen it lift narrow traces right off the substrate.

The  voids probably just correspond to naturally low areas of copper

plating,  whether from PTH or electrolytic copper.





**************************

I still vote for an imaging problem and rework (maybe more than once) at

that step.  There is nearly breakout of the surface pad at the 2:00

position of

the holes.  I am 99.9% sure this is NOT an immersion silver  problem -

first,

the fine trace is OK,  and second, the small hole appears  fine.  Any

silver

attack problem is usually associated with an  electrochemical cell set

up

between large copper and small copper areas (fine  traces).  These sort

of

"electrochemical cells" have been shown for years -  such as where 0.5

ounce inner

layers in holes are recessively etched, compared  to adjacent 2 ounce

inner

layers in MLB holes.



Denny Fritz

MacDermid, Inc.



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