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Motorola developed
the first plastic ball grid array packages for
computer and portable electronics applications,
and similar packaging concepts are now being used
by all of the major semiconductor suppliers.
Ball Grid
Array (BGA) packaging technology offers many advantages
over more conventional fine pitch surface mount
(e.g. Quad Flat Packs (QFPs)) and Pin Grid Array
(PGA) technologies.
These benefits
include:
- The ability to reduce
component size, cost, and weight.
- Obtain higher I/O count
for a given substrate area.
- Better electrical performance
can be achieved.
- Extension to multi-chip
modules is easier.
Most importantly, manufacturing
is simplified due to reduced problems in co-planarity
(no leads), placement (self-centering on reflow),
paste printing (solder bridging between leads),
and handling (no bent leads), resulting in overall
higher assembly yield.
Although well established
for use in computing, consumer electronics, and
other applications, the automotive industry has
been slower to adopt BGA technology due to solder
joint reliability concerns in the more adverse
under-the-hood thermal cycling environment. For
example, Delphi-Delco Electronics has shown the
reliability of early BGA package designs was inferior
to that of QFPs for automotive range thermal cycles.
DaimlerChrysler has developed a 35 mm multi-chip
plastic ball grid array package that is now in
volume production for under-the-hood applications.
However, in order to meet reliability goals, a
thicker substrate was required for the BGA inter-poser
board, and only the outermost two rows of solder
balls in the large BGA component are being used
for I/O during operation.
Example of well formed
solder ball
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Example of poorly formed
solder ball
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For future generation products,
smaller BGA packages are being proposed to further
reduce the total printed wiring board area covered
by the BGA components and to reduce the BGA substrate
cost. Such packages will most likely utilize thinner
inter-poser substrates and require the use of
underfill encapsulation to insure thermal cycling
reliability.
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Preliminary
Microscopy Cross-section
(27mm solder
balls)
(click to
enlarge)
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In this project,
the under-the-hood reliability of smaller
BGA packages will be examined through experimentation
and modeling. The major goal will be to
develop a fundamental knowledge on the interaction
of BGA design, size, and underfill on package
manufacturing and reliability in the automotive
environment.
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Finite Element Results
Plastic Strains for Temperature
Dependant Creep/Plasticity Model
(click to
enlarge)
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Auburn CAVE
All Rights Reserved
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