Inge,
It doesn't appear that the nickel is diffusing into the solder much more
than what I have normally noted.  The surface of the copper appears to
be rough with small cracks in it.  The nickel has moved into them and
then formed an IMC.  I would suggest that the small islands of nickel
noted in the micrograph are areas where the nickel has migrated into
cracks that are not visible in the cross section (either above or below
where the cut was made).

mark

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, August 20, 2008 6:00 AM
To: [log in to unmask]
Subject: Re: [TN] Diffuse topic

Mornin' Inge!

Got your picture up! Go to:

http://stevezeva.homestead.com/files/Nickel_Diffusion.jpg

Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Wednesday, August 20, 2008 5:08 AM
To: [log in to unmask]
Subject: [TN] Diffuse topic

Investigation of coax Kovar/glass feed thrues soldered to nickel plated
metal bodies gave, that nickel from the feed thrue's barrel nickel
plating diffused as much as 38 micrometers (!)into the tin from the
tin/lead solder during the vapour phase soldering. Nickel had diffused
from both the feedthrue and the package.  How is that possible? Thought
polish smear gave false picture, but the analyst claims that what you
see is true nickel diffusion and nickel/tin IMCs. I'll ask dr Gregory
for help with a photo for  you all. The sample you will see is exposed
more than normal to an etchant to prove that smear is not the
case..start from the bottom shows nickel (black), nickel IMCs (greyish)
and topmost tin (bright). There is nearly no lead present.

Inge

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