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Sender:	TechNet <[log in to unmask]>
Subject:	Intermetallic Phase: BGA soldering on Immersion Nickel Gold PCB
From:	Joseph Furrer <[log in to unmask]>
Date:	Fri, 31 Jul 1998 09:08:45 +0200
Content-Type:	multipart/mixed; boundary="------------998A96B36E11709166B1B198"
Organization:	Ascom Hasler AG Switzerland
Reply-To:	"TechNet E-Mail Forum." <[log in to unmask]>, Joseph Furrer <[log in to unmask]>
Parts/Attachments:	text/plain (610 bytes) , vcard.vcf (194 bytes)

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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