Mechanical effects of copper through-vias in a 3D die-stacked module

Mechanical effects of copper through-vias formed in silicon dies in a three dimensional module, in which four bare-dies with copper through-vias are vertically stacked and electrically connected through the copper-vias and metal bumps, were numerically and experimentally studied. To examine the mechanical effects caused by the existence of the copper through-vias in a rigid silicon-chip, a series of stress analyses, related simple mechanical tests, and reliability tests were carried out. All these results show that the copper through-via has unique effects on the stress distribution caused by thermal mismatch and on the interconnection reliability in the 3D die-stacked module. In particular, it was found that the developed micro copper through-via is reliable because the stress distribution due to thermal load is close to the hydrostatic pressure condition, and enhances chip-to-chip interconnection reliability because the copper-via restrains the plastic deformation of a gold bump during temperature cycling.