On Thu, 31 May 2001 18:05:26 EDT, Werner Engelmaier <[log in to unmask]>
wrote:
>Hi Pete and Steve,
>Just to make sure that misinformation does not get disseminated.In a
message
>dated 05/30/2001 23:44:39, [log in to unmask] writes:
>>BGA's, especially CBGA's have given us a real headache, mostly because the
>>assembly process has to be spot on. We're making VME conduction-cooled
>>cards with both PBGA's (35x35mm 1.27mm pitch) and CBGA's (21x21mm 1.27mm
>>pitch), that are used in an avionics box. We had some boards made where
the
>>manufacturing process was OK for the other components but the BGA solder
>>joints looked a little rough for avionics quality standards. They survived
>>initial temperature cycling, but failed very quickly with only gentle,
>>single axis vibration perpendicular to the board surface. The poor joints
>>were blamed and we're working on improving the process with a different
>>board stuffer.
>Vibration failures do not occur in real solder joints, that is solder
joints
>that truly metallurgically bond. Your failures are, I bet, interfacial
>failures of "SJs" that never properly wetted. Most likely bec ause the
CBGAs
>have a larger thermal mass and acted as heat sinks letting the solder balls
>never reach proper reflow conditions.
>
>>From more long-term experience in a previous prison camp, it was LCC's,
>>particularly 20 pin LCC's that showed signs of solder joints cracking
under
>>qualification testing (15g accelerations and thermal cycling from -40 to
>>+125 deg). The problem was improved by putting a pad underneath to lift
>>them off the board surface and using a stepped solder stencil to deposit
10
>>mils paste on the pads for these devices. The higher solder joints gave
>>greater flexibility.
>Nothing new about reducing the strains in solder joints from a given
thermal
>expansion mismatch by making them taller. It is NOT greater "flexibility,"
>but reduced strain.
>
>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], Website: www.engelmaier.com
>
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Continuing the thread on package reliability...
Do any Technetters have experience with a package designated "LPP" (leadless
plastic package), offered by Elantec. A drawing of this device can be found
at <www.elantec.com/pages/apppdf/MDP0046_F.pdf>. It appears very similar
to an LCC, however the die is encapsualted in plastic mold compound. Also,
note that the die is attached to a large thermal pad which is soldered to
the PWB. I have searched this forum's archive and could find no mention of
this package.
I have a copy of Elantec's application notes for this package (pdf format)
which has more detail on the package construction and their manufacturing
process recommendations. Unfortunately, I could not find a link to this
document on their web page. I can email a copy to any interested
Technetters.
I would appreciate if anyone could share their views and experiences with
LPP type devices. Thank you in advance.
Ellsworth D. Berkowitz, P.E.
Paradyne Networks Inc.
727-530-8121 phone
"The opinions expressed above are soley those of the author and do not
necessarily reflect those of Paradyne Networks Inc."
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