Michael,
If you are experiencing brittle solder joint failures at and interface (e.g., "Black Pad" type failures) then you will most likely see higher levels of P at the interface than in the bulk ENi because there are two processes that concentrate the P. During the ENIG process the immerson gold process replaces Ni atoms with gold atoms thus increasing the amount of P at the gold/nickel interface. Then you solder the ENIG and the gold disolves in the solder and you consume a little more nickel during the formation of nickel-tin intermetallic thus concentrating the P again. The brittle failures that occur happen at an interface and when you examine the two surfaces of the brittle fracture you usually find higher levels of P then in the bulk. The best way to determine the P content in the bulk nickel is cross section a good solder joint and do SEM/EDX in the bulk of the nickel plating.
-----Original Message-----
From: Creswick, Steven [mailto:[log in to unmask]]
Sent: Fri 7/25/2003 11:11 AM
To: [log in to unmask]
Cc:
Subject: Re: [TN] % Phosphorus In Nickel deposit
Michael,
It was my understanding the low to mid-phosphorus nickels (3-6%, 6-9%) were better for soldering, whereas high-phos (9-12%) nickels were better for corrosion resisitance.
In either case, won't the solder at the solder/nickel interface always be 'high' in phos, with the potential for bad intermetallics being present.
However, I defer to the plating guru's of the forum.
Steve Creswick - Gentex Corp
-----Original Message-----
From: Michael Forrester [mailto:[log in to unmask]]
Sent: Friday, July 25, 2003 10:19 AM
To: [log in to unmask]
Subject: [TN] % Phosphorus In Nickel deposit
Is there a specification for the % phosphorous in the nickel deposit for
electroless
Nickel/Immersion Gold for surface mount pads on PWBs? We are seeing as
high as 14% and are also seeing solder joint failures at the nickel
interface on
BGAs w/18mil balls. Is there an industry standard for phosphorous content?
If there is no industry standard, any ideas of what the spec should be?
Thank you.
Best Regards,
Mike Forrester
LeCroy Corp.
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