I agree with your approach; it is a good practice.
Our customers ARE the DoD types on the nuclear missile, land warrior, and various other military avionics and space projects, and they are indeed, VERY conservative, I can guarantee you that! And rightly so.
I have a very strong negative feeling about the use of bismuth in any high-reliability soldering application, to be honest. One simply cannot ensure there is never more than is intended, and the total mix is always anybody’s guess.
From: Dennis Fritz [mailto:[log in to unmask]]
Sent: Friday, July 24, 2015 9:07 AM
To: Stadem, Richard D.; [log in to unmask]
Subject: Re: [TN] Dave is famous!
Dean, I think we are in violent agreement. You said "any Pb-free
solder on the replacement part termination is less than 1% or 2% of the final
solder joint" and I said "carefully de-soldered and care used
to remove as much Pb-free solder as possible"
I am sure on the NASA/DoD repair work done on by the military, the component was removed carefully and the solder wicked from the original joint . Then, the 2M repair procedure wets the attachment site with eutectic and that is wicked off. Finally, the good component is attached with eutectic.
My analogy is double dipping component leads to replace either gold or pure tin finish with eutectic.
I am open to further discussion of Pb-free finishes containing bismuth, and being reworked with eutectic. I know Hillman and others have said it is fine - not enough bismuth left to intermetallic with Pb for low melting/weak intermetallics. BUT, is anyone reworking lead-free bismuth with eutectic on a daily basis? DoD types are VERY conservative.
Denny Fritz
-----Original Message-----
From: Stadem, Richard D. <[log in to unmask]<mailto:[log in to unmask]>>
To: TechNet E-Mail Forum <[log in to unmask]<mailto:[log in to unmask]>>; Dennis Fritz <[log in to unmask]<mailto:[log in to unmask]>>
Sent: Fri, Jul 24, 2015 7:39 am
Subject: RE: [TN] Dave is famous!
I agree with you Denny, but I would change that to say, so long as any Pb-free
solder on the replacement part termination is less than 1% or 2% of the final
solder joint. That way you never need worry about the non-homogenous lead-rich
areas in the final solder joint, which Dave has taught us is what leads to
issues and typically only occurs in BGA or CSP ball solder joints.
Otherwise,
component termination SOLDER finishes that are lead-free are (usually) fully
compatible with Sn63 solder from either an assembly or rework standpoint, except
for possibly the tin-whisker issue that could affect the portion of the
termination NOT soldered with lead solder. Of course, this does not apply to any
non-solder termination finish, such as gold, which we know should be removed
prior to assembly.
Regarding Famous Dave, I would go so far as to simply
state his contributions to the electronics industry are so prevalent (and so
well-presented) that I consider him to be part of an elite group that includes
pioneers with names such as Englemaier, Lau, Hwang, Shangguan, Handwerker,
Pecht, Liu, Fjelstad, Turbini and a few others whose work has greatly
contributed to reliability in electronics, especially in the face of
RoHS.
Dean
-----Original Message-----
From: TechNet
[mailto:[log in to unmask]<mailto:[log in to unmask]>] On Behalf Of Dennis Fritz
Sent: Thursday, July 23,
2015 8:10 PM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Dave is famous!
Thanks
Dave, from the other members of the NASA/DoD consortium, for sharing the fame.
The first two rounds of the NASA testing included some rework, especially
the Round Two. There, the military, focused on the Navy 2M repair group, wanted
to know what reliability effect occurs if Pb-free solder is repaired with
eutectic. So far, Defense has allowed only eutectic solder at their repair
stations because typical DoD repair technicians have little practical way of
determining whether the assemblies are Pb-free (mostly from COTS) or is they are
assembled with original eutectic solder. There are no XRF machines on ships and
very few at depots.
So, if boards are carefully de-soldered and care used
to remove as much Pb-free solder as possible, and eutectic is used to solder in
new components - is there reliability loss?
The answer - very little
reliability is lost, so long as the repair is done carefully and to specified
procedure.
Denny Fritz
-----Original Message-----
From: David
Hillman <[log in to unmask]<mailto:[log in to unmask]>>
To: TechNet
<[log in to unmask]<mailto:[log in to unmask]>>
Sent: Thu, Jul 23, 2015 6:36 pm
Subject: Re: [TN] Dave is
famous!
Hi Drew - thanks for the kind words. The Technet community gets the
same credit for all of the great support and communication of information
sources that makes our jobs easier. Here is the web link to the investigation I
think Phil and Jim
were
discussing:
http://teerm.nasa.gov/nasa_dodleadfreeelectronics_proj2.htm
The
NASA
DoD Phase 2 was a great consortium project with lots of hard working folks doing
cool things.
Dave
On Thu, Jul 23, 2015 at 3:30 PM, Drew meyer
<[log in to unmask]<mailto:[log in to unmask]>> wrote:
> Gentlemen. Thanks for the notification
of
Dave's work!
>
> Thank you Dave for all your input through Technet
and
published data. You
> help all of us face the issues of PCB manufacturing
at
one time or
> another. Thanks for all the hard earned knowledge
shared!
>
>
Drew
>
> -----Original Message-----
> From: TechNet
[mailto:[log in to unmask]<mailto:[log in to unmask]>]
On Behalf Of Ed Popielarski
> Sent: Thursday, July
23, 2015 12:26 PM
> To:
[log in to unmask]<mailto:[log in to unmask]>
> Subject: [TN] Dave is famous!
>
>
Dave Hillman was
mentioned in a widely distributed article
today!
>
>
http://www.circuitinsight.com/programs/51504.html
>
> "I would
like to point
out that the consortium for the aerospace and
> military people,
which our good
friend, Dave Hillman has produced some of
> the best, most
comprehensive test
data... Dave, if we're wrong, please
> contact us. But the
point is this is the
only known published data
> comparing un-repaired boards
with repaired boards
that I know of."
>
> Ed Popielarski
> Engineering
Manager
>
>
[cid:[log in to unmask]<mailto:[log in to unmask]>]
>
970 NE
21st Ct.
> Oak Harbor, Wa. 98277
>
>
Ph: 360-675-1322
> Fx: 206-624-0695
>
Cl: 949-581-6601
>
>
>
> "It's one kind of victory to slay a
beast,
move a mountain, and
> cross a chasm, but it's another kind altogether
to
realize that the beast,
> the mountain, and the chasm were of your
own
design."
>
>
https://maps.google.com/maps/myplaces?hl=en&ll=48.315753,-122.643578&spn=0.011188,0.033023&ctz=420&t=m&z=16&iwloc=A
>
>
>
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