you may need legs... Dave... missing legs are not good...(you may need
re-qual too...pricy either way)...
                                    jk

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of David D. Hillman
Sent: Wednesday, October 20, 2004 9:59 AM
To: [log in to unmask]
Subject: Re: [TN] Picture of LCCC Solder Joints...


The laminate on this is indeed FR4 (minimum Tg 140C) thus there's a huge
CTE mismatch which the solder joint can't accommodate very well! This case
was from a test board (not an actual assembly) but I wouldn't combine BT or
Polyimide laminate materials with LCC style components - ya just can't
revise physics! I have observed the use of controlled CTE laminate
structures (like a Copper Invar Copper core construction) successfully with
LCCs but I view that configuration as an expensive solution for not
understanding design basics. LCC's were the first type of components which
exposed the issue of using the solder joint as both the mechanical and
electrical connection to the pwa - some lessons are just learned the hard
way.

Dave



                      Joyce Koo
                      <[log in to unmask]        To:       [log in to unmask]
                      com>                     cc:
                      Sent by: TechNet         Subject:  Re: [TN] Picture of
LCCC Solder Joints...
                      <[log in to unmask]>


                      10/20/2004 08:45
                      AM
                      Please respond to
                      jkoo






I bet the orginal assembly is qualified using polyimide board (x-y CTE
mismatch is not much), but someone in the later stage changed to FR4
without
knowing the impact...
Are you using FR4?  No answer required...(you can take a "fifth").
                               jk (1.59 cents)

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Steve Gregory
Sent: Tuesday, October 19, 2004 7:32 PM
To: [log in to unmask]
Subject: [TN] Picture of LCCC Solder Joints...


Hi All!

Dave Hillman so kindly sent me a picture of some LCCC solder joints after
thermal cycling
after 500 thermal cycles of -55C to +125C (per IPC-9701 guidelines).
Needless to say it has failed! (CAUTION! Parental discretion is advised
before
viewing!) Go to:

_http://www.stevezeva.homestead.com_ (http://www.stevezeva.homestead.com)

Look at: "LCCC after thermal cycling"

I build assemblies using LCCC's here, 32-pins or lower...mostly radar
stuff...been putting them on assemblies for as long as I've been  here.
Don't know
exactly why our customer still uses them, maybe that's the  only package
they
can get the devices in...and maybe the smaller packages don't  have the
same
CTE mismatch problems.

There is a company that makes compliant SMT leads that can be attached to
LCCC components, and I think that they have a service that will do that for
you.
 It's Interplex NAS, go to:

_http://www.interplexnas.com/index.asp_
(http://www.interplexnas.com/index.asp)

If you absolutely have to use LCCC's, and they're bigger than 32-pins, you
might check them out.

-Steve Gregory-

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