Method and device of pop stacking for preventing bridging of interposer solder balls

A method of package-on-package (POP) stacking comprising:

• providing a first semiconductor package, the first semiconductor package having a first body, and a plurality of first solder balls disposed on an upper surface of the first body;
• providing a second semiconductor package, the second semiconductor package having a second body, and a plurality of second solder balls disposed on a bottom surface of the second body;
• performing a pick-and-drop positioning process, comprising disposing the second semiconductor package onto the first semiconductor package so as to move the second solder balls towards the first solder balls;
• and
• performing a reflow soldering process on the first body and the second body, the reflow soldering process comprising using a stand-off mechanism to control a minimum vertical gap between the first body and the second body and heating the first solder balls and the second solder balls to solder the first solder balls and the second solder balls to each other and form a plurality of interposer solder balls, each of the plurality of interposer solder balls having a height substantially equal to the minimum vertical gap and a cross sectional width less than a pitch between two adjacent interposer solder balls of the plurality of interposer solder balls.