Solderability performance and pull strength don't necessarily correlate.
You can have gool solderability on an Alloy 42 lead and still have a
lower pull strength than a poorly soldered copper lead. Because the
copper lead forms an intermetallic layer, the bond strength is higher
than with alloy 42. Did you ever notice that when you pull an Alloy 42
lead by hand, its pretty easy and you're left with a fairly smooth
interface while for a copper lead, the force required is slightly higher
and you're left with a rough interface. This doesn't mean you don't get
a good solder joint with Alloy 42.

Sincerely,

Paul Terranova

DIGITAL's Analytical and Environmental Test Services Lab
Phone: 508-467-3109
FAX: 508-467-6796
[log in to unmask]

        -----Original Message-----
        From:   Tom Monico [SMTP:[log in to unmask]]
        Sent:   Wednesday, February 18, 1998 2:16 PM
        To:     [log in to unmask]
        Subject:        [TN] Solderability od alloy 42

        Hi all,
         
        We've noticed different solderability performance of alloy 42
TSOP lead frames vs. copper 194 lead frames on an electroless
nickel/immersion gold SMT finish. Alloy 42 exhibits reduced
solderability at lower reflow temperatures. However, even at 218 degrees
C, the alloy 42 lead frame still does not yield the bond pull strength
of the copper lead frame.
         
        Any comments or observations would be greatly appreciated.
         
        Tom Monico
        MicroVia, Inc. 
         

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