hi,
so maybe eric found a way to keep the intermetallic from oxidizing.
phil
-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Tuesday, November 13, 2001 10:07 AM
To: [log in to unmask]
Subject: Re: [TN] Intermetallic Layers
Dave,
Right on! That is our experience also. That's one reason Lucent has an
internal specification for surface finishes. This specification lists
exceptions to industrial specs like IPC. We are not comfortable with a
"minimum coverage" spec for SnPb HASL because we've had many experiences
where 50 microinches or less of solder has caused severe soldering
problems. The failure have almost always been linked to oxidized
copper-tin intermetallic. Boards with thin solder (i.e., exposed and
oxidized copper-tin intermetallic) have successfully been re-used by
re-hasling with agressive water-soluble-fusing fluids which removes the
oxide and allows fress SnPb to "stick" to the IMC.
Regards,
George
George M. Wenger (908)-546-4531 [log in to unmask]
Celiant Corporation
40 Technology Drive
Warren, New Jersey 07059
-----Original Message-----
From: David Hillman [mailto:[log in to unmask]]
Sent: Tuesday, November 13, 2001 12:25 PM
To: [log in to unmask]
Subject: Re: [TN] Intermetallic Layers
Hi Eric! Sorry but I humbly disagree. There is an abundance of published
industry data which shows that oxidized Sn/Cu intermetallic is one of
the
more unsolderable surfaces encountered on an assembly. Problems with
poor
plated thru hole fill due to "weak knees" (thin solder causes the Sn/Cu
intermetallic at the hole rim to become oxidized) and thin HASL coatings
are just two examples of everyday industry solderability issues
associated
with Sn/Cu IMCs. What type of flux did you use in your testing? Very
aggressive flux chemistries will allow the soldering of Sn/Cu IMCs but a
fair majority of the industry is moving away from these types of flux
formulations. With all that being said, without the Sn/Cu IMC we would
have
no solder joints so it is a critical part of a solder joint.
Dave Hillman
Rockwell Collins
[log in to unmask]
Eric Dawson <[log in to unmask]>@ipc.org> on 11/12/2001 07:49:56 AM
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
To: [log in to unmask]
cc:
Subject: [TN] Intermetallic Layers
Hi All,
I notice that a few new references have been made to the above subject
and
thought I would share some of my early work with you.
In my first post as a graduate, I researched the causes of dewetting on
circuit boards. I came across a solution, the make-up of which I have
since
lost, which dissolved the tin lead alloy but left the two intermetallic
layers.
I produced a number of one inch square coupons which I soldered using
63/37
alloy, RMA flux and a Tri Moore Rotary Dip Tester.
These were divided into three categories:
1 Control
2 Remove tin lead and re test in the Rotary Dip.
3 Remove tin lead, Several hours steam ageing and re test.
Microsections showed that I had taken off the alloy successfully and
left
the IMC.s.
All of the re tested coupons soldered successfully, including the steam
aged
ones.
This was some years ago so I cannot remember the etchant nor the hours
and
conditions in the steam ageing equipment. I do remember that the IMC
soldered very well so I am always dubious when somebody blames the
intermetallic for poor soldering.
I seem to be alone in my faith that the IMC solders but this was the
result
of my very own work and I stand by it.
Regards
Eric Dawson, Defender of the IMC.
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