It has been documented that the two rows of pads on the perimeter of the
die have the largest stresses than any other joints on a BGA package. This
is due to the local CTE mismatch due to the die attach. The optimal BGA
package design would thus remove those pads (or not attach joints to them)
to reduce the maximum joint stresses the package would see during thermal
cycling. Ground planes and Heat xfer planes to remove heat from the die
sometimes take precedence over joint stress considerations though.

-ejr


Eric J. Roulo
Santa Clara University
Mechanical Engineering

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