Underfill structure for semiconductor packages and methods of forming the same
A method for forming an underfill structure and semiconductor packages including the underfill structure are disclosed. In an embodiment, the semiconductor package may include a package including an integrated circuit die; an interposer bonded to the integrated circuit die by a plurality of die connectors; and an encapsulant surrounding the integrated circuit die. The semiconductor package may further include a package substrate bonded to the interposer by a plurality of conductive connectors; a first underfill between the package and the package substrate, the first underfill having a first coefficient of thermal expansion (CTE); and a second underfill surrounding the first underfill, the second underfill having a second CTE less than the first CTE.
1. A device comprising:
a package comprising:
an integrated circuit die;
an interposer bonded to the integrated circuit die by a plurality of die connectors; and
an encapsulant surrounding the integrated circuit die;
a package substrate bonded to the interposer by a plurality of conductive connectors;
a first underfill between the package and the package substrate, the first underfill having a first coefficient of thermal expansion (CTE), wherein a first width of the first underfill extending along a surface of the package is greater than a second width of the first underfill extending along a surface of the package substrate; and
a second underfill surrounding the first underfill, the second underfill having a second CTE less than the first CTE, wherein the second underfill is in direct contact with the encapsulant.
2. The device of claim 1 , wherein the first underfill tapers from the package toward the package substrate.
3. The device of claim 2 , wherein the second underfill tapers from the package substrate toward the package.
4. The device of claim 1 , wherein the first underfill is in contact with the interposer and spaced apart from the encapsulant.
5. The device of claim 1 , wherein the second underfill is in contact with the package and spaced apart from the conductive connectors.
6. The device of claim 1 , wherein the first underfill has a greater flowability than the second underfill.
7. The device of claim 1 , wherein a third width of the second underfill proximal the package substrate is greater than a fourth width of the second underfill distal the package substrate, the third width and the fourth width being measured between opposite sidewalls of the second underfill.
8. 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, wherein a width of the first underfill along the interposer is greater than a width of the first underfill along the package substrate; and
depositing a second underfill surrounding the first underfill, the second underfill having a lower coefficient of thermal expansion (CTE) than the first underfill, the second underfill having a first sidewall contacting the first underfill, the second underfill having a second sidewall opposite the first sidewall, the second sidewall extending from a sidewall of the interposer to a surface of the package substrate.
9. The method of claim 8 , wherein forming the first underfill comprises flowing a first underfill material between the interposer and the package substrate.
10. The method of claim 8 , wherein the first underfill is cured before forming the second underfill.
11. The method of claim 8 , wherein the first underfill and the second underfill are cured simultaneously.
12. The method of claim 8 , further comprising exposing surfaces of the interposer and the package substrate to a plasma before forming the first underfill.
13. The method of claim 8 , wherein the second underfill has a higher concentration of silicon by weight than the first underfill.
14. The method of claim 8 , wherein the second underfill has a CTE lower than a CTE of the first underfill.
15. A device comprising:
a package substrate;
an interposer attached to the package substrate by a plurality of conductive connectors;
a first underfill extending from the package substrate to the interposer, the first underfill surrounding the plurality of conductive connectors, wherein a first width of the first underfill adjacent the interposer is greater than a second width of the first underfill adjacent the package substrate; and
a second underfill surrounding the first underfill, the second underfill having a different material composition than the first underfill, the second underfill extending from the package substrate to a topmost extent, the topmost extent of the second underfill being disposed above a topmost surface of the first underfill.
16. The device of claim 15 , further comprising:
a die attached to the interposer; and
an encapsulant surrounding the die.
17. The device of claim 16 , further comprising a lid over the package substrate, the interposer, the die, and the encapsulant, wherein a thermal interface material extends from the lid to the encapsulant and the die.
18. The device of claim 17 , wherein the lid is attached to the package substrate by a first adhesive.
19. The device of claim 17 , wherein the lid is attached to a ring by a first adhesive, wherein the ring encircles the encapsulant, the die, and the interposer, wherein the ring is attached to the package substrate by a second adhesive.
20. The device of claim 15 , wherein the second underfill has a lower coefficient of thermal expansion (CTE) than the first underfill.