In my experience microvoids associated with leadframe soldering to PCB pads
are often associated with minor organic contamination of the leadframe
surface prior to leadframe plating.  This has been shown to result in
significant decreased drop test performance in hand-held electronics.

Based upon readings from a few sources it appears that microvoids associated
with Immersion Silver are due to high organic level in a thick Ag deposit.
Cookson/Enthone provides an interesting presentation on their AlphaStar
ImmAg with a relatively thin deposit with low organic content (approx 1 -6
%, vs. a competitor level reported to be 22%).  In my past experience with
fluoroborate-based immersion Sn that produced a tin deposit about 0.2
micrometers thick, I never saw microvoids, but I did see degraded
solderability with time and temp due to the thin deposit and tin consumption
with the creation of Sn-Cu IMCs.  While I have no direct experience with
this Enthone tin, the presentation shows it to be quite environmentally
robust even with a deposit about the same thickness.


Best regards,
Leo

Leo M. Higgins III, Ph.D.
Vice President, Technical Operations
ASAT, Inc.
3755 Capital of Texas Highway, Suite 100
Austin, Texas     78704

office phone   512-383-4593
mobile           512-423-2002
[log in to unmask]
www.asat.com



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Werner Engelmaier
Sent: Tuesday, May 16, 2006 4:05 PM
To: [log in to unmask]
Subject: Re: [TN] Question about ENIG and other surface finishing


Hi Kerry,
Here are pics of micro-voids.



Werner

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