Molding compound supported RDL for IC package

1. A molding compound supported redistribution layer (RDL) structure for an integrated circuit (IC) package, the RDL structure comprising:

a molding compound having opposite topmost and bottommost surfaces, and extending continuously from the topmost surface to the bottommost surface;

a plurality of metal pillars, each extending through the molding compound and having

a top end protruded above the topmost surface of the molding compound, and

a bottom end protruded below the bottommost surface of the molding compound;

a bottom RDL on bottom of the molding compound and having

a plurality of first bottom metal pads, and

a plurality of first top metal pads;

a plurality of solder balls, each over the top end of a corresponding metal pillar among the plurality of metal pillars; and

a chip mounted on the plurality of first bottom metal pads,

wherein

each solder ball among the plurality of solder balls covers a top face of the top end of the corresponding metal pillar, and extends around and covers a peripheral side face of the top end of the corresponding metal pillar,

a density of the plurality of first bottom metal pads is higher than a density of the plurality of first top metal pads,

the bottom end of each metal pillar among the plurality of metal pillars is electrically coupled to a corresponding first top metal pad among the plurality of first top metal pads, and

in a thickness direction of the RDL structure, the bottom RDL is arranged between the chip and the plurality of metal pillars.

2. A molding compound supported RDL structure as claimed in claim 1 , further comprising:

a top protection layer between (i) each solder ball among the plurality of solder balls and (ii) the top end of the corresponding metal pillar among the plurality of metal pillars,

wherein the top protection layer is in direct contact with and covers the top face and the peripheral side face of the top end of the corresponding metal pillar.

3. A molding compound supported RDL structure as claimed in claim 2 , wherein the top protection layer is selected from the group consisting of Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG) and Organic Solderability Preservatives (OSP).

4. A molding compound supported RDL structure as claimed in claim 2 , further comprising:

a bottom protection layer configured on bottom of a corresponding first bottom metal pad among the plurality of first bottom metal pads.

5. A molding compound supported RDL structure as claimed in claim 4 , wherein the bottom protection layer is selected from the group consisting of ENEPIG and OSP.

6. A molding compound supported RDL structure as claimed in claim 1 , wherein:

each solder ball among the plurality of solder balls is in direct contact with the top face and the peripheral side face of the top end of the corresponding metal pillar among the plurality of metal pillars.

7. A molding compound supported RDL structure as claimed in claim 6 , further comprising:

a bottom protection layer configured on bottom of a corresponding first bottom metal pad among the plurality of first bottom metal pads.

8. A molding compound supported RDL structure as claimed in claim 7 , wherein the bottom protection layer is selected from the group consisting of ENEPIG and OSP.

9. A molding compound supported RDL structure as claimed in claim 1 , wherein an entirety of the chip is below the bottom RDL and the molding compound.

10. A molding compound supported RDL structure as claimed in claim 1 , wherein the plurality of solder balls are in direct contact with the topmost surface of the molding compound.

11. A molding compound supported RDL structure as claimed in claim 1 , wherein the molding compound is free of semiconductor material embedded therein.

12. A molding compound supported redistribution layer (RDL) structure for an integrated circuit (IC) package, the RDL structure comprising:

a molding compound having opposite topmost and bottommost surfaces, and extending continuously from the topmost surface to the bottommost surface;

a plurality of metal pillars, each extending through the molding compound and having

a top surface coplanar with the topmost surface of the molding compound, and

a bottom end protruded below the bottommost surface of the molding compound; and

a bottom RDL configured on bottom of the molding compound and having

a plurality of first bottom metal pads, and

a plurality of first top metal pads,

wherein

a density of the plurality of first bottom metal pads is higher than a density of the plurality of first top metal pads,

the bottom end of each metal pillar among the plurality of metal pillars is electrically coupled to a corresponding first top metal pad among the plurality of first top metal pads,

the bottom RDL further comprises a topmost dielectric layer in direct contact with the bottommost surface of the molding compound,

the plurality of first top metal pads and the bottom end of each metal pillar among the plurality of metal pillars are embedded in the topmost dielectric layer, and

the plurality of metal pillars do not extend through the topmost dielectric layer.

13. A molding compound supported RDL structure as claimed in claim 12 , further comprising:

a top RDL configured on top of the molding compound and having

a plurality of second bottom metal pads on top of the plurality of metal pillars, and

a plurality of second top metal pads,

wherein

a density of the plurality of second bottom metal pads is higher than a density of the plurality of second top metal pads; and

the top surface of each metal pillar among the plurality of metal pillars is electrically coupled to a corresponding second bottom metal pad among the plurality of second bottom metal pads.

14. A molding compound supported RDL structure as claimed in claim 13 , further comprising:

a plurality of solder balls, each configured on top of a corresponding second top metal pad among the plurality of second top metal pads.

15. A molding compound supported RDL structure as claimed in claim 12 , further comprising:

a bottom protection layer configured on bottom of a corresponding first bottom metal pad among the plurality of first bottom metal pads.

16. A molding compound supported RDL structure as claimed in claim 15 , wherein the bottom protection layer is selected from the group consisting of ENEPIG and OSP.

17. A molding compound supported RDL structure as claimed in claim 12 , further comprising:

a chip mounted on the plurality of first bottom metal pads,

wherein an entirety of the chip is below the bottom RDL and the molding compound.

18. A molding compound supported RDL structure as claimed in claim 12 , wherein the molding compound is free of semiconductor material embedded therein.

19. A fabricating process for a molding compound supported redistribution layer (RDL) structure for an integrated circuit (IC) package, the fabricating process comprising:

applying a release layer on top of a temporary carrier;

applying a bottom seed layer on top of the releasing layer;

applying a first patterned photo resist on top of the bottom seed layer;

forming a plurality of patterned first bottom metal pads;

stripping the first patterned photo resist;

stripping the bottom seed layer between the plurality of first bottom metal pads;

forming a bottom RDL using the plurality of first bottom metal pads as a starting point, the bottom RDL having a plurality of first top metal pads;

forming a first top dielectric layer with a plurality of openings, each exposing a top of a corresponding first top metal pad among the plurality of first top metal pads;

applying a top seed layer on top of the first top dielectric layer and the plurality of first top metal pads;

forming a second patterned photo resist on top of the top seed layer;

forming, in the second patterned photo resist, a plurality of metal pillars, each on top of a corresponding first top metal pad among the plurality of first top metal pads;

stripping the second patterned photo resist;

stripping the top seed layer between the plurality of metal pillars;

applying a molding compound to encapsulate the plurality of metal pillars, wherein each metal pillar among the plurality of metal pillars extends through the molding compound and has a bottom end protruded below the molding compound;

thinning the molding compound from top to expose top ends of the plurality of metal pillars;

planting a plurality of solder balls, each over the top end of a corresponding metal pillar among the plurality of metal pillars; and

mounting a chip on the plurality of first bottom metal pads,

wherein

the molding compound has opposite topmost and bottommost surfaces, and extends continuously from the topmost surface to the bottommost surface,

the top ends of the plurality of metal pillars protrude above the topmost surface of the molding compound,

the bottom ends of the plurality of metal pillars protrude below the bottommost surface of the molding compound,

each solder ball among the plurality of solder balls covers a top face of the top end of the corresponding metal pillar, and extends around and covers a peripheral side face of the top end of the corresponding metal pillar,

a density of the plurality of first bottom metal pads is higher than a density of the plurality of first top metal pads,

the bottom end of each metal pillar among the plurality of metal pillars is electrically coupled to a corresponding first top metal pad among the plurality of first top metal pads, and

in a thickness direction of the RDL structure, the bottom RDL is arranged between the chip and the plurality of metal pillars.

20. A fabricating process for a molding compound supported RDL structure as claimed in claim 19 , further comprising:

before said planting the plurality of solder balls, forming a protection layer bracketing the exposed top end of each metal pillar among the plurality of metal pillars, wherein the top protection layer is in direct contact with and covers the top face and the peripheral side face of the top end of the corresponding metal pillar;

removing the temporary carrier; and

removing the bottom seed layer from bottom of each first bottom metal pad among the plurality of first bottom metal pads.

21. A fabricating process for a molding compound supported RDL structure as claimed in claim 20 , further comprising:

forming a bottom protection layer on bottom of a corresponding first bottom metal pad among the plurality of first bottom metal pads.

22. A fabricating process for a molding compound supported RDL structure as claimed in claim 19 , further comprising:

before said planting the plurality of solder balls, forming a protection layer bracketing the exposed top end of each metal pillar among the plurality of metal pillars;

wherein, in said planting the plurality of solder balls, the top protection layer is cleaned out by soldering flux and heat and each of the plurality of solder balls is in direct contact with the top face and the peripheral side face of the top end of the corresponding metal pillar among the plurality of metal pillars;

removing the temporary carrier; and

removing the bottom seed layer from bottom of each first bottom metal pad among the plurality of first bottom metal pads.

23. A fabricating process for a molding compound supported RDL structure as claimed in claim 22 , further comprising:

forming a bottom protection layer on bottom of a corresponding first bottom metal pad among the plurality of first bottom metal pads.