Package-on-package structures and methods for forming the same

A package comprising:

• a bottom package comprising:
• a package component comprising:
• a first conductive feature at a top surface of the package component;
• and
• a second conductive feature at a bottom surface of the package component, wherein the first conductive feature is electrically coupled to the second conductive feature;
• a partial metal ball having a rounded bottom surface in contact with a top surface of the first conductive feature, and the partial metal ball has a top surface recessing toward a center of the partial metal ball;
• a die over and bonded to the package component;
• a top package over the bottom package;
• and
• a solder region bonding the partial metal ball to the top package.

A package comprising:

• a bottom package comprising:
• a package component comprising:
• a top surface;
• and
• a metal pad at the top surface of the package component;
• a partial metal ball over and electrically coupling to the metal pad;
• and
• a die over and bonded to the package component;
• and
• a solder region over and joined to the partial metal ball.