The ability for water to diffuse out of the package is a key factor.
Generally speaking the thinner packages have greater moisture stress
resistance (MSL), if all other factors are the same.  Here the packages you
present have mixed variables.  I believe that the possible, small, negative
MSL impact that may occur going from 44 to 64 leads is much less than the
likely, strong, positive MSL impact expected going from a 4.5mm thick
package to a 1mm  package.

Numerous other factors are important (size of leadframe die attach pad,
size/thickness of die, Ag on the die attach pad, leadframe thickness, choice
of mold compound, etc.

Best regards,
Leo



Leo M. Higgins III, Ph.D.
Director of Applications Engineering
ASAT, Inc.
3755 Capital of Texas Highway, Suite 100
Austin, TX     78704

ph.  512-383-4593
fax. 512-383-1504

-----Original Message-----
From: Genny Gibbard [mailto:[log in to unmask]]
Sent: Friday, October 08, 2004 1:20 PM
To: [log in to unmask]
Subject: [TN] Moisture sensitivity


Just a question for interest sake.  Are there any general correlations
between package size, and lead numbers, and moisture sensitivity that can be
made?
For instance, do you think a 17.5mm square 44 lead 4.5mm thick package would
have less or more moisture sensitivity than a 16mm square 64 lead  1 mm
thick package.  The IC's have different functions.

Gut feeling, I think the 64 lead would have more sensitivity.  It is
smaller, with more and finer pitch outside connections.  As dimensions get
smaller, I think the danger of moisture doing damage goes up.  Also, since
there are more leads I feel that there are more locations that possibly
moisture could get in, as the potential for seal breaks is probably greater
at interfaces between plastic and metal?

Am I out to lunch in my general reasoning?

Just thought I would spice up Friday.

To all those Canadians out there, enjoy your turkey and pumpkin pie this
weekend.

Genny Gibbard (mailto:[log in to unmask])

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