Underfill Structure for Semiconductor Packages and Methods of Forming the Same

A method comprising:

• attaching a die to a first surface of an interposer;
• encapsulating the die with an encapsulant;
• forming a plurality of conductive connectors on a second surface of the interposer, the second surface being opposite the first surface;
• bonding the interposer to a package substrate through the conductive connectors;
• depositing a first underfill between the interposer and the package substrate and around the conductive connectors;
• and
• depositing a second underfill surrounding the first underfill, the second underfill having a lower coefficient of thermal expansion (CTE) than the first underfill.

A device comprising:

• a first package comprising:
• a first integrated circuit die;
• an encapsulant around the first integrated circuit die;
• and
• a redistribution layer over the encapsulant and the first integrated circuit die;
• a plurality of functional connectors;
• a second package bonded to the first package by the plurality of functional connectors, wherein the functional connectors and the redistribution layer electrically connect a second integrated circuit die of the second package to the first integrated circuit die;
• a first underfill between the first package and the second package, the first underfill surrounding the plurality of functional connectors;
• a second underfill surrounding the first underfill, the second underfill having a different material composition than the first underfill, wherein a topmost extent of the second underfill is disposed above a topmost surface of the first underfill.