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July 1998

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Subject:
Intermetallic Phase: BGA soldering on Immersion Nickel Gold PCB
From:
Joseph Furrer <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Fri, 31 Jul 1998 09:08:45 +0200
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Dear TechNet forum member
Does any one has experience with the Intermetallic layer build between
Immersion Gold/Nickel and Tin Lead eutectic ? The Nickel (4-6 microns)
applied on the PCB surface contains 6-8% Phosphorus. The Goldflash is
0.08 microns thick.
We observed a 0.5 to 2 micron thick intermetallic layer between Nickel
and the Tin Lead Ball after Reflow soldering . It seems not to be the
well known Ni3Sn4 phase, because it is to thick and irregulary. Gold
could not be detected as well (SEM-Analysis). The reliability of the BGA
joints seems to be in a straight correlation to this brittle
intermetallic layer.

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