Hi Dave, thanks for the box,
INSERTED FEW NOTES BELOW
-----Original Message-----
From: David Hillman [mailto:[log in to unmask]]
Sent: Friday, 10 December 1999 11:12
To: [log in to unmask]
Subject: Re: [TN] 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.
EXACTLY, CRITICAL IS THE WORD, NOT WORTH THE RISK AND COST IN MY OPINION,
KEEPING THINGS COOL AND FAST CONTRADICTS THIS TOO MUCH
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!:).
YEP, ONCE WET, MULTIPLIES AIN'T A PROBLEM
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.
AS YOU SAID, LAYERS OF NOBLES WITH MINOR GAINS AND MAJOR COSTS
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.
FLAT ISSUE INDEED
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?
YES, I'D AGREE WITH GEORGE ON THIS ONE,
EVEN FROM MY DAYS OF CONSTRUCTING (NO OTHER WORD FOR IT) OAK SWITCH STATORS
AND ROTORS,
IF YOU CAN'T COPE WITH COSTS OF COIN SILVER SOLIDS,
THIS ELABORATE PLATING IS GOOD SUBSTITUTE FOR :
SLIDE/INSERT=FINGER, TOUCH=CLIP/CARBON PILL TOUCH PAD,
PRESSFIT=PINS, ATE=NEEDLES,
HOWEVER, IT IS A PALATIAL APPROACH TO PLATING,
HARDLY JUSTIFIABLE GAINS (MINOR) ON COSTS (MAJOR) TO GO OUTSIDE OF
"STANDARD" NiAu STREAM.
THE PRESSFITS GRIP WORKS ON DAMASCEN LAMINATES CHARACTERS :
THAT IS SEQUENTIAL SOFTER AND HARDER LAYERS WORK IN HIGH TENSILE STRENGTH
UPON THE FLEXED WALL,
NOT MENTIONING THE DURABILITY
SORRY TO BE PERHAPS TOO LACONIC FIRST TIME DARREL ,
BUT IN MORE WORDS SAME RECO > IF YOU SOLDER (SMD's) , stick with NiAu .
LOWER RISKS (WIDER TOLERANCES)ON PRESSFITS WON'T JUSTIFY MUCH HIGHER ONES ON
JOINTS,
NiAu BEING AS IT IS LIKE A FIRE (TOP VERSATILITY IF CONTROLLED, DISASTROUS
IF NOT)
Well, hope that helps. AS WELL, PK
Dave Hillman
Rockwell Collins
[log in to unmask]
Darrel Therriault <[log in to unmask]> on 12/06/99 11:59:13 AM
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
to
Darrel Therriault <[log in to unmask]>
To: [log in to unmask]
cc:
Subject: [TN] Ni/Pd/Au
TechNet,
A PWB supplier is recommending a Ni/Pd/Au finish for .062" and .093" FR-4
PWB
with mixed PTH/SMT components, as well as press fit connectors.
Any comments/guidance, pro or con, regarding :
1. Intermetalics
2. Rework cycles
3. Gold embriddlement
4. Fine pitch or BGA components
5. Pressfit
All info appreciated.
Regards.......DT
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