Patent ID: 8455270

Claim:
A process of forming three-dimensional (3D) die comprising the steps of: testing a plurality of wafers by a testing apparatus for die that pass (good die) or fail (bad die) predetermined test criteria; placing a first tested wafer in proximity to a second tested wafer, wherein each of the wafers has a notch for alignment to another wafer; aligning in a wafer stacking apparatus the first and second wafers so as to maximize the number of good die of the first wafer aligned with good die of the second wafer wherein the step of aligning comprises: aligning by a processor device the first and second wafers so that the notches of both wafers are aligned; counting by a processor device the number of good die of the first wafer aligned with good die of the second wafer; rotating by a processor device the first or second wafer a predetermined amount; counting by a processor device the number of good die of the first wafer aligned with good die of the second wafer; repeating the rotating and counting steps until the rotated wafer has been rotated 360 degrees; and choosing by a processor device an orientation of the first and second wafers with the maximum number of good die of the first wafer aligned with good die of the second wafer; bonding the first and second wafers; and dicing the stack of first and second wafers into 3D stacks of good die bonded to good die.