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June 1998

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Subject:
From:
"Singleton, Vern" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 30 Jun 1998 15:42:06 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (163 lines)
Come on, guys!  All "I" said was the launch failure was due to a "Bad
solderjoint".  I never said anything about the actual mechanism, what
type component, leadfinish or any other metric and/or
mechanism---because I don't know.  All I want is the "best joint
possible" for any product type.  That means getting good,wetted
side/heel fillets for all leaded SMT devices.


-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, June 30, 1998 3:07 PM
To: [log in to unmask]; [log in to unmask]; [log in to unmask]
Cc: [log in to unmask]; [log in to unmask]; [log in to unmask];
[log in to unmask]
Subject: Re: Pramod Patel/solder joint reliability


Hi Mark & Vern,
It definitely is news to me, "that the China Launch problems were due to

a lack of side/toe filleting". Failure at launch can only mean one of
two
things: (1) the solder joint was never properly made (wetted), or (2)
inappropriate flight-hardware testing prior to launch accummulated too
much
fatigue damage (micro/macro-cracks) to withstand the mechanical loads
during
launch (see Hubble, Magellan, Gallileo). In neither case, would the
presence
of side/toe filleting made a signficant difference.
Side fillets will defintely increase the peeling stress required due to
the
forces necessary to rip through them; that does not however equate to a
more
reliable solder joint in the long-term. If you have inadequately wetted
solder
joints, however, solder and toe fillets will likely prolong the time at
which
an infant mortality failure will occur in the short-term.
The decision makers for "Missile, Launch Vehicle, wartime avionics/sonar
and/or Spacecraft" should properly educate themselves as to what and
what not
solder joints can do. #1 issue: get away from large ceramic components
on
FR-4, #2 issue: qual testing should not be done on flight-hardware.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask]

In a message dated 6/30/98 10:38:55, [log in to unmask] wrote:

>I suggest you fellas do some more homework before drawing to Mark's
>conclusion, as one "can always make the statement that proper wetting
>makes for better peel strengths", independent of which surfaces you are
>discussing. Side fillets(PROPERLY wetted) make a VERY SIGNIFICANT
>difference in peel strengths of properly formed gull-wing and/or J-Lead
>products.  The issue is not the raw peel strength itself, but the
>long-term reliability of the joints continuously under
thermo-mechanical
>stress. That is where the side-fillets become essential to long-term
>reliability of our systems.
>
>Bottomline, do YOU want to be responsible for Missile, Launch Vehicle,
>wartime avionics/sonar and/or Spacecraft failures due to simple
>solderjoint issues??
>
>I firmly believe you all are playing with fire in downplaying the
>importance of "side-fillets" to long-term solderjoint reliability.
>
>You likely missed or ignored the "multi-millions" lost on the China
>launch due to a simple solderjoint failure(??)
>
>----Original Message-----
>From: Kwoka, Mark [mailto:[log in to unmask]]
>Sent: Tuesday, June 30, 1998 10:47 AM
>To: [log in to unmask]
>Cc: [log in to unmask]; [log in to unmask];
>[log in to unmask]; [log in to unmask]; [log in to unmask]; Kwoka,
>Mark
>Subject: RE: RE: Need Pramod Patel's email address and/or telephone #
>
> Werner,
> Thanks for the clarification. Your second and fifth points are what I
was
>after. I infer that if inadequate wetting of the lead to the board
> land is infact present, then the "lead peeling test" will indicate
lower
>"peeling forces" than would be obtained from identical leads
> that were "adequately wetted". Also,  side fillets are not important
if
>adequate lead wetting is exhibited.
> Regards,
>   Mark
>       -----Original Message-----
>       From:   [log in to unmask] [SMTP:[log in to unmask]]
>       Sent:   Wednesday, June 17, 1998 4:33 PM
>       To:     Kwoka, Mark
>       Cc:     [log in to unmask]; [log in to unmask];
>[log in to unmask]; [log in to unmask]; [log in to unmask]
>       Subject:        Re: RE: Need Pramod Patel's email address and/or
>telephone #
>
>       Hi Mark,
>       First, there is no such thing as a 'lead pull test;' while you
are of course
>       pulling on the lead, what you are doing to the solder joint is
peeling it-
the
>       proper reference is a lead peeling test. Some of your notions
about solder
>       joint strength result directly from the false mental picture
resulting from
>       the words 'tensile pull'.
>       Second, the solder joint strength, as determined by a lead
peeling test, has
>       no bearing on the reliabilty of the solder joint, provided the
peeling test
>       does not reveal inadequate wetting.
>       Third, in a peeling test you always need to observe the whole
peel-load
>       history for the whole peeling process; with a 1T or larger heel
fillet, the
>       largest load will be at the initial portion of peeling through
the heel
>       fillet, with lower loads subsequently depending on whether or
not (at to
what
>       extent) side fillets are present.
>       Fourth, the fracture surface of the peeled solder joints give
typically more
>       infrmation than do the peel-load histories, because the ONLY
realy important
>       finding is whether or not adequate wetting has taken place.
>       Fifth, the reliability in actual use does to a large extent
depend on the
heel
>       fillet and the 'bottom flat' wetting; if the foot length is <3W,
than also
on
>       the presence of a toe fillet, because short feet 'rock' during
thermal
>       cycling. Side fillets are less important, unless you have
wetting problems.
>
>       Werner Engelmaier

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