US Patent 10157884 3D die stacking structure with fine pitches

A package includes package includes a first package component including a first plurality of electrical connectors at a top surface of the first package component, and a second plurality of electrical connectors longer than the first plurality of electrical connectors at the top surface of the first package component. A first device die is over the first package component and bonded to the first plurality of electrical connectors. A second package component is overlying the first package component and the first device die. The second package component includes a third plurality of electrical connectors at a bottom surface of the second package component. The third plurality of electrical connectors is bonded to the second plurality of electrical connectors. A fourth plurality of electrical connectors is at a bottom surface of the second package. The second and the fourth plurality of electrical connectors comprise non-solder metallic materials.