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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