Yuan Li:
It may well be attributed to several items: first, most TBGA's use
polyimides whereas very few of the PBGA's would. Next is the use of a
power/ground ring in the typical TBGA, as opposed to the discrete
power/ground etches or at best power and ground planes. The CTE mismatch
of this ground ring, being a horizontal laminar system (as opposed to a
compressive vertical structure) would increase the residual stresses at
the ball attach. Finally, it is likely that the staircase construction
of the TBGA has mismatched CTE's in it (induced by slight variations in
the sequntial application of the layers), and these mismatches result in
stresses being manifest at the package body and the ball attach.
> Bill Davis, Ph.D.
> Diamond Multimedia Systems
> Senior Scientist
> Tel. 408.325.7868
> Cell. 408.888.5650
> e-mail: [log in to unmask]
>
>
-----Original Message-----
From: LI YUAN [mailto:[log in to unmask]]
Sent: Wednesday, May 12, 1999 12:12 PM
To: [log in to unmask]
Subject: [TN] BGA Solder joint reliability
Dear BGA Reliabilty Experts:
I have done FEM simulations for BGAs and have found some results I
cannot
explain. Hope you can enlighten me on it.
I modeled BT-based BGAs and tape-based BGAs (both cavity up) under
0-100C
1 cycle per hour condition. For BT BGAs, with the same die size, the
larger the package, the better the mean fatigue life. This phenomina may
be attributed to die/package ratio, the bigger the die/package ratio,
the
worse the fatigue life. However, for tape BGAs (tape substrate is much
thinner than BT substrate), the result is the opposite. With the same
die
size, the larger the package, the worse the fatigue life.
Can someone explain why the difference between BT and Tape BGAs?
Best regards,
Yuan Li
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