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Date: | Tue, 25 Aug 1998 08:03:32 -0600 |
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I have seen some papers indicating effect of certain halides on
intermetallic growth rates.
-----Original Message-----
From: Phillip E. Hinton [SMTP:[log in to unmask]]
Sent: Saturday, August 22, 1998 12:43 PM
To: [log in to unmask]
Subject: Re: [TN] BGA'S IN SPACE
Kelly,
I believe that you must have been in a hurry when you grouped
electromigration, "intermetallic growth" and dendritic growth in a
single
category, but so much misinformation is being passed around about
intermetallics, I feel it necessary to add a correction.
You said that "intermetallic" growth and electromigration and
dendritic growth
are the same and caused by the presence of moisture. "Intermetallic
growth"
is caused by the diffusion between two metals in contact with each
other to
form compounds of those metals, and is not in any way related to the
other two
growth mechanisms, and the presence of moisture is not a causitive
nor an
inhibitor. Increasing temperature when the two metal are in contact
will
increase the intermetallic growth rate and the intermetallic gets
thicker, but
does not produce metallic shorts between conductors or BGA lands.
Another slight change in the information about "whiskers". Whiskers
are made
up of a single crystals that mainly grow from thin coatings or
platings of
pure tin or nearly pure tin coated/plated and where the
coating/plating is in
compression. It can happen with Sn96, Sn99, but much less likely
with Sn63.
Fusion of the coating helps, but is not a whisker eliminator.
Whisker
formation is most likely when the temperature is near 60 degrees C.
and
moisture of the enviornment is elevated.
Phil HInton
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