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January 2006

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Tue, 10 Jan 2006 12:46:04 -0600
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Hi, Dr. Gil
It depends on the service environment the assembly is expected to see.
Usually the LGA soldered directly to the pads on the PWB is not able to
withstand as many cycles to failure as the same package mounted with
Pb90/Sn10 balls or interposer pins, which will help provide stress
relief to accomodate the differences in thermal expansion between the
PWB and the LGA package.
So, it depends on the application and the material properties of the PWB
and the component. A device that will see relatively little temperature
cycling and little other shock or stresses may do very well with the LGA
soldered directly to the PWB. On the other hand, if the assembly is
going to see severe thermal cycling, you may wish to attach it with Pb90
balls or some other compliant pin technology to extend the time to
failure of the solder joints. You would need to qualify this by building
prototypes and cycling over time under the same conditions (or
worst-case conditions) in order to determine mean time to failure.
(My apologies to Doug Pauls for using the trademark phrase "it depends"
twice without permission.)

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Zilber Gil
Sent: Tuesday, January 10, 2006 11:56 AM
To: [log in to unmask]
Subject: [TN] LGA Package reliability

Hello all,



As more and more devices are coming in a LGA packaging format I am
wondering regarding the reliability of the interconnect. I did not found
a clear opinion and definite results in papers dealing with this issue.
More of that, some companies sending the package as "BGA ready" (meant
that you put later on a BGA solder balls) while other recommends to
direct assemble the device. Even more confusing is the fact that some of
the pads are rectangle while others are round.

Does someone have more data regarding the reliability and process for
this packaging type (assuming a device size of 15x15 mm)?



Thanks and happy New Year,



Dr. Gil Zilber

Elta system Ltd.




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