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December 1999

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Subject:
From:
David Hillman <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 21 Dec 1999 13:39:20 -0600
Content-Type:
text/plain
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text/plain (172 lines)
Hi Michael! Answers can be found below:

1) Is Collins performing Au or Al wire bonding on Pd? Let us know, if you
could, when/where the results will be published.

*** Collins is conducting Au wire bonding and not Al wire bonding (due to use
environment concerns). We should be publishing our current wirebond/Chip On
Board test efforts sometime in late 2000 - possibly at the next IPC Surface
Finish conference (that assumes I can get all of the failure and statistical
analysis done in the next few months - there are some very neat Pd/wirebond
interactions showing up). We will also have some data on immersion Ag,
electroless Au, and immersion Au wirebonding included in the study data.

2) You cited some relevant work on intermetallics published in 1969. Are you
concerned that more up to date studies haven't been performed or published?
In particular, more up to date work on current plating/metallization/solder
alloy combinations found in newer and proposed board designs. [maybe no one
wants to commit research money to possibly obsolete lead-bearing solders!]

*** As Bill Hampshire pointed out, the neat thing about metallurgical studies is
that the data is relevant forever providing the good testing protocol was
followed (that doesn't mean the data set can be applied haphazardly!). The Bader
study has been shown to be very reliable by a number of different sources over a
span of several years. I quite happily reproduced Bader's testing with some Pd
wire in a solder pot so I believe his data set from some first hand experience
(or maybe I was using Steve's Math 101 and got lucky (Sorry Steve!) :) ).

Pb-Sn solder metallurgy may not be as sexy as sol-gels or thin film physics,
but a lot of folks sure do depend on mechanically and electrically reliable
solder joints!

*** With the push for Pb free solder systems I think the field of solder
metallurgy is going to get a whole lot more "interesting"!

Happy Holidays!
Dave Hillman
Rockwell Collins
[log in to unmask]




"Alderete, Michael" <[log in to unmask]> on 12/15/99 05:13:44 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to
      "Alderete, Michael" <[log in to unmask]>

To:   [log in to unmask]
cc:

Subject:  Re: [TN] Ni/Pd/Au



Dave-

Thanks for sharing the Ni/Pd/Au finishes info. Many of us hunger for real
data on Au/solder interactions, as well as actual experiences with alternate
finshes [Imm tin, Ni/Pd/Au, etc.], as we ponder the risks of moving away
from HASL.

I had a few questions-

1) Is Collins performing Au or Al wire bonding on Pd? Let us know, if you
could, when/where the results will be published.

2) You cited some relevant work on intermetallics published in 1969. Are you
concerned that more up to date studies haven't been performed or published?
In particular, more up to date work on currrent plating/metallization/solder
alloy combinations found in newer and proposed board designs. [maybe no one
wants to commit research money to possibly obsolete lead-bearing solders!]

Pb-Sn solder metallurgy may not be as sexy as sol-gels or thin film physics,
but a lot of folks sure do depend on mechanically and electrically reliable
solder joints!

Best Regards,

Michael Alderete
Aerojet


Dave Hillman wrote...
------------------------------

Date:    Thu, 9 Dec 1999 18:11:36 -0600
From:    David Hillman <[log in to unmask]>
Subject: Re: Ni/Pd/Au

Hi TechNet! I can fill in some holes on the Ni/Pd/Au clarify some of the
questions:

1.   Intermetallics

Some work done by the NCMS consortia and here at Rockwell Collins has shown
that
there is a number of intermetallic phases possible but the Pd3Sn
intermetallic
phase is brittle and causes solder joint embrittlement similar to the Au4Sn
intermetallic phase. The way to avoid the formation of the Pd3Sn was to keep
the
Pd thickness in the 9-12 microinch range. Per Bader's work ("Dissolution of
Au,
Ag, Pd, Pt, Cu, and Ni in Molten Tin Lead Solder", December 1969 Welding
Research Supplement) Pd is slow to diffuse into molten solder so the
soldering
process time becomes a critical parameter to allow the Pd to diffuse into
the
solder and not form the Pd3Sn phase.

2.   Rework cycles

We haven't seen any problems provided the initial solder process was done
properly and the rework process has proper process controls. It seems to be
comparable to tin/lead rework at least up to 3 reworks (if you need more
than
that something is wrong!:).

3.   Gold embrittlement

The gold layer on the Pd I am familiar with is an immersion gold which is
only
3-5 microinches thick - not enough to cause embrittlement problems. This
gold
layer does two things: (1) it improves wirebonding values by 2-3 grams pull
force in comparison to just a Pd/Ni finish; (2) it protects the Pd surface.
Pd
is a very cool element and is used in many process as a initiator or
"getter. Pd
is used to seed laminate thru holes prior to copper plating and you can find
Pd
in your catalytic converter on your car. By putting gold over the Pd surface
you
eliminate any Pd surface interactions with the environment. Seems like
overkill
to put one noble metal on another noble metal but the properties of Pd are
the
reason. Collins has a large wirebond study nearly finished up which includes
the
Ni/Pd/Au and we'll be publishing some neat stuff sometime in late 2000.

4.   Fine pitch or BGA components

The Ni/Pd/Au finish is just as flat as immersion tin or immersion silver or
immersion gold so it works for both fine pitch and BGAs.

5.   Pressfit

Sorry but I haven't played in this area yet. Hey Paul K. - haven't you done
some
stuff with Pd and pressfit?

Well, hope that helps.

Dave Hillman
Rockwell Collins
[log in to unmask]

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