----------

Greetings and Salutations J. Fjelstad,

What are typical thata JA and thata JC values for the Tessera microBGA (tm) 
packages?  I'm mainly wondering if this design could be used for conduction 
cooled applications.  Also, is this reduction it stress technique only 
limited to micro?  What about 1 and 1.27 mm designs?  We are not a big user 
of BGA but we can get backed into a corner with design trade-offs.

Thank You,
Kevin Thorson
Loral Defense Systems - Eagan
[log in to unmask]
 ----------
From: TechNet-request
To: TechNet
Subject: Re: Protection of BGA Solder Joints
Date: Saturday, February 17, 1996 12:27AM

Hello Roger,

Hitachi is a licensee of the Tessera microBGA (tm) package and is developing
their capability for volume manufacture at this time. One unique ability of
the Tessera technology is to decouple the mismatch in coeffiecients of
thermal exapansion between the silicon and the FR-4 by means of a patented
compliant interposer. Recently completed finite element modelling performed
by Tessera shows a near 20x reduction in stress in the solder ball joints
using this technology. Should you desire more information please feel free 
to
contact me and I will provide you with contacts in Japan working the 
project.

Regards,
J. Fjelstad