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April 1999

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From:
"Hinners, Hans - LYPME" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 20 Apr 1999 14:15:40 -0400
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Hi All,

I have a mystery on my hands and I hope somebody out in cyberland can help.

We have a 10 layer board made out of 1 oz. FR-4 material. Tg = 140 degrees C
which is intermittently showing negative copper etchback during the
electroless process (using Atotech chemistry) but, only on a few layers.

For instance, layers 2,4, and 6 have negative etchback but layers 1,3,5,7-10
are fine.  This etchback feature is not apparent in the (plasma) desmear
coupon, the process in-between being drilled and electroless copper plating.
The only distinguishing feature of these layers is that they are all thermal
layers (which are mostly solid copper).  I'm at a loss to explain how the
layers being solid relates to their etch characteristics but it's the only
thing that jumps out as being unique.  To make it even more confusing
another thermal layer came out okay, layer 9.

We have also seen this on a 17 layer board where a thermal layer has
negative etchback but everything else is okay.

E-mail me directly and I will send you two jpegs of my cross-sections (only
200k!) so you can see what I am talking about.

Anybody seen this before?  Suggestions?   Comments?  Questions?

Thanks a bunch!

Hans

Air Force Material Command - We keep them flying!
~~~~~~~~
Hans M. Hinners                                 WR-ALC/LYPME Bldg. 640
Materials Engineer                                      380 Second Street,
Suite 104
Manufacturing Eng. Sec.                         Robins AFB GA 31098-1638
912-926-1970 (Voice) 468 - 1970 (DSN)   912-926-7974 (Fax)
[log in to unmask]

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