[SI-LIST] : backside metal

Tom Zimmerman (zimmerman@fnal.gov)
Fri, 24 Sep 1999 10:26:05 -0700

Matt,

In my experience, if you want a good electrical connection to the
backside
of a die, you must metallize. I've mounted dice that are not metallized
on
the back, and I always get a high resistance connection (Kohms). On one
chip that I designed (in a radhard p++ epi process -- very low
resistivity
substrate), we actually used the substrate to conduct the analog ground
current through the backside to the die pad instead of using bondwires.
In
order to do this, we had to backgrind and backplate with metal. I was
amazed at the incredibly low resistance contact we were able to achieve
-
on the order of a few milliohms from die pad to bulk.

If you have p- wafers (higher resistivity substrate), then I think you
need
to ask if it is of any benefit to ground the backside.

Tom Zimmerman

-----Original Message-----
From: Matt Kaufmann [SMTP:matt@silicon-spice.com]
Sent: Friday, September 10, 1999 1:27 PM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : backside metal

Hello,

Can anyone comment on the necessity of metallizing the backside of the
die
if we want to ground the backside? In other words, if we want to have
an
electrical connection between the package substrate and the backside of
the
die, is backside metallization required or is the presence of
electrically
conductive adhesive sufficient (assuming the die sits on a grounded die
pad)?

Thanks,

Matt

Matt Kaufmann
Senior Packaging Engineer
Silicon Spice Inc.
matt@silicon-spice.com

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