# Patent

## Title
Redistribution film for IC package

## Abstract

A redistribution film for IC package is disclosed, which comprises a top redistribution layer configured on top of a bottom redistribution layer. The top redistribution layer is fabricated following PCB design rule, and the bottom redistribution layer is fabricated following IC design rule. Further, the interface between the top redistribution layer and the bottom redistribution layer is optionally made roughed to increase bonding forces therebetween.

## Background
BACKGROUND
Technical Field
The present invention relates to a redistribution film for IC package, especially relates to a film composed of double redistribution layers where a top redistribution layer is made and configured on top of a bottom redistribution layer. The top redistribution layer is fabricated following PCB design rule and the bottom redistribution layer is fabricated following IC design rule.
Description of Related Art
FIG. 1A shows a prior art substrate for IC package
FIG. 1A shows a prior art substrate for IC package disclosed in US2014/0102777A1 which has an embedded silicon interposer 20. The silicon interposer 20 has four lateral sides 206. A molding compound 22 wraps the silicon interposer 20 around the four lateral sides 206. A plurality of via metal 200 is made through the silicon interposer 20. An insulation liner 201 is made between the through via 200 and the silicon interposer 20 for an electrical insulation there-between. A top redistribution layer 21 is made on top of the silicon interposer 20 with a plurality of metal pad 210 exposed on top. The plurality of metal pad 210 on top is provided for accommodating an IC chip (not shown) to mount. A circuit built-up layer 25 is made on bottom of the silicon interposer 20 with a plurality of metal pad 220 configured on bottom. A plurality of solder ball 24 is configured and each solder ball 24 is configured on bottom of a corresponding bottom metal pad 220.
FIG. 1B shows a reversed view of FIG. 1A. FIG. 1B is made to present the prior art of FIG. 1A in a position similar to a package substrate of the present invention to facilitate a comparison there between. FIG. 1B shows an up-down view of FIG. 1A. The top solder ball 24 is configured for mounting the package substrate onto a mother board (not shown). The bottom metal pad 210 is configured for a chip or chips to mount.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A ̃1B show a prior art substrate for IC package.
FIGS. 2A ̃2I show a fabricating process for a first embodiment according to the present invention.
FIGS. 3A ̃3I show a fabricating process for a second embodiment according to the present invention.
FIGS. 4A ̃4N show a fabricating process for a third embodiment according to the present invention.



DETAILED DESCRIPTION OF THE INVENTION
FIGS. 2A ̃2I Show a Fabricating Process for a First Embodiment According to the Present Invention.
FIG. 2A shows: preparing a temporary carrier; applying a release layer 31 on top of the temporary carrier; and applying a seed layer 32 on top of the release layer 31.
FIG. 2B shows: applying a patterned photoresist PR on top of the seed layer 32.
FIG. 2C shows: forming a patterned bottom metal pad 341.
FIG. 2D shows: stripping the photoresist 33; and leaving a plurality of bottom metal pad 341.
FIG. 2E shows: forming a bottom redistribution layer RDL1, at least one redistribution circuit 342 is included in the RDL1, the redistribution circuit 342 is made using the bottom metal pad 341 as a start point according to IC design rule or equivalent; forming a plurality of first top metal pad 343 on top of the bottom redistribution layer RDL1. A plurality of dielectric layer 351, 352 is intervened among the circuit 341, 342, 343 according to conventional IC fabricating processes. The circuit 341, 342, 343 are collectively called redistribution circuit.
FIG. 2F shows: forming a top redistribution layer RDL2 according to conventional PCB fabricating processes or equivalent on top of the bottom redistribution layer RDL1; forming a plurality of second top metal pad 443 on top of the top redistribution layer RDL2; at least one redistribution circuit 442 is included and is made using the first top metal pad 343 as a start point. The redistribution 442 is electrically coupled to the second top metal pad 443. The circuit 443, 442 are collectively called redistribution circuit. Dielectric layers 451, 452, 453 are intervened among the redistribution circuit 443, 442. The dielectric material for PCB fabricating process can be one of polyimide (PI), prepreg (PP) or benzocyclobutene (BCB).
FIG. 2G shows: planting a plurality of solder ball 38, each is planted on top of a corresponding second top metal pad 443.
FIG. 2H shows: removing the temporary carrier; and removing the seed layer 32 from bottom of the bottom redistribution layer RDL1; and mounting at least a chip 391 on bottom of the bottom metal pad 341. Underfill 392 is configured in a space between the chip 391 and the metal pad 341.
FIG. 2I shows: a single unit IC package singulated from the product of FIG. 2H.
FIG. 3A ̃3I Fabricating Process for a Second Embodiment According to the Present Invention.
FIGS. 3A ̃3D are the same as FIGS. 2A ̃2D, for simplification, the description to FIGS. 3A ̃3D is omitted.
FIG. 3E shows: a plurality of recess 382 is made on top of a top dielectric layer of the bottom redistribution layer RDL1. The recess 382 is made to enhance the roughness of the top surface of the bottom redistribution layer RDL1. The increased roughness enhances bonding force to a layer formed on top of the bottom redistribution layer RDL1 in a later fabricating process.
FIGS. 3F ̃3I are Similar to FIGS. 2F ̃2I, We Describe Again as Follows:
FIG. 3F shows: forming a top redistribution layer RDL2 according to conventional PCB fabricating processes or equivalent on top of the bottom redistribution layer RDL1; forming a plurality of second top metal pad 443 on top of the top redistribution layer RDL2; at least one redistribution circuit 442 is included and is made using the first top metal pad 343 as a start point. The redistribution 442 is electrically coupled to the second top metal pad 443. The circuit 443, 442 are collectively called redistribution circuit. Dielectric layers 451, 452, 453 are intervened among the redistribution circuit 443, 442. The dielectric material for PCB fabricating process can be one of polyimide (PI), prepreg (PP) or benzocyclobutene (BCB).
FIG. 3G shows: planting a plurality of solder ball 38, each is planted on top of a corresponding second top metal pad 443.
FIG. 3H shows: removing the temporary carrier; and removing the seed layer 32 from bottom of the bottom redistribution layer RDL1; and mounting at least a chip 391 on bottom of the bottom metal pad 341. Underfill 392 is configured in a space between the chip 391 and the metal pad 341.
FIG. 3I shows: a single unit IC package singulated from the product of FIG. 3H.
FIG. 3I is a single unit of IC package with a roughed interface between top redistribution layer RDL2 and bottom redistribution layer RDL1. The roughness is caused by the plurality of recess 382.
FIG. 4A ̃4M Fabricating Process for a Third Embodiment According to the Present Invention.
FIGS. 4A ̃4E are the same as FIGS. 2A ̃2E, for simplification, the description to FIGS. 4A ̃4E is omitted.
FIG. 4F ̃4J shows: a plurality of recess 382 is made on a top dielectric layer of the bottom redistribution layer RDL1. The plurality of recess 382 is made to enhance the roughness of the top surface of the bottom redistribution layer RDL1. The increased roughness enhances bonding force to a layer formed on top of the bottom redistribution layer RDL1 in a later fabricating process.
FIG. 4F shows: applying a first patterned photoresist PR1 on top of the bottom redistribution layer RDL1 and exposing partial top surface of the bottom redistribution layer RDL1.
FIG. 4G shows: applying a seed layer 42 on top of the first photoresist PR1 and on the exposed top surface of the bottom redistribution layer RDL1.
FIG. 4H shows: applying a second patterned photoresist PR2 on top of the seed layer 42; forming a plurality of trench 45 to expose the seed layer 42 on a bottom of each corresponding trench 45.
FIG. 4I shows: forming a metal bump 46 in each corresponding trench 45 using the seed layer 42 as a start point.
FIG. 4J shows: stripping the second photoresist PR2; stripping the seed layer 42; stripping the first photoresist PR1; and leaving a plurality of metal bump 46 on top of a top dielectric layer of the bottom redistribution layer RDL1.
FIGS. 4K ̃4N are the same as FIGS. 2F ̃2I, we describe again as follows:
FIG. 4K shows: forming a top redistribution layer RDL2 according to conventional PCB fabricating processes or equivalent on top of the bottom redistribution layer RDL1; forming a plurality of second top metal pad 443 on top of the top redistribution layer RDL2; at least one redistribution circuit 442 is included and is made using the first top metal pad 343 as a start point. The redistribution 442 is electrically coupled to the second top metal pad 443. The circuit 443, 442 are collectively called redistribution circuit. Dielectric layers 451, 452, 453 are intervened among the redistribution circuit 443, 442. The dielectric material for PCB fabricating process can be one of polyimide (PI), prepreg (PP) or benzocyclobutene (BCB).
FIG. 4L shows: planting a plurality of solder ball 38, each is planted on top of a corresponding second top metal pad 443.
FIG. 4M shows: removing the temporary carrier; and removing the seed layer 32 from bottom of the bottom redistribution layer RDL1; and mounting at least a chip 391 on bottom of the bottom metal pad 341. Underfill 392 is configured in a space between the chip 391 and the metal pad 341.
FIG. 4N shows: a single unit IC package singulated from the product of FIG. 4M.
FIG. 4N is a single unit of IC package with a roughed interface between top redistribution layer RDL2 and bottom redistribution layer RDL1. The roughness is caused by the plurality of metal bump 46.
While several embodiments have been described by way of example, it will be apparent to those skilled in the art that various modifications may be configured without departs from the spirit of the present invention. Such modifications are all within the scope of the present invention, as defined by the appended claims.

## Claims

1. A fabricating process for a redistribution film for IC package, the process comprising:
applying a release layer on top of a temporary carrier;
applying a seed layer on top of the release layer;
applying a first patterned photoresist on top of the seed layer;
forming a plurality of bottom metal pads over the seed layer and in the first patterned photoresist;
stripping the first patterned photoresist;
forming a bottom redistribution layer, layer by layer, according to IC design rule and using the plurality of bottom metal pads as a start point, the bottom redistribution layer including
a plurality of first conductive layers, wherein a top first conductive layer among the plurality of first conductive layers includes a plurality of first top metal pads exposed on a top surface of the bottom redistribution layer, and
a plurality of first conductive vias coupling the plurality of first conductive layers to each other and to the plurality of bottom metal pads; and

after said forming the bottom redistribution layer, forming a top redistribution layer, layer by layer, according to PCB design rule, directly on top of the bottom redistribution layer and using the plurality of first top metal pads as a start point, the top redistribution layer including
a plurality of second conductive layers, wherein a top second conductive layer among the plurality of second conductive layers includes a plurality of second top metal pads exposed on a top surface of the top redistribution layer, and
a plurality of second conductive vias coupling the plurality of second conductive layers to each other and to the plurality of first top metal pads,

wherein, in a thickness direction in which the top redistribution layer is stacked on the bottom redistribution layer, a thickness of each of the plurality of second conductive layers is greater than a thickness of each of the plurality of first conductive layers.

2. A fabricating process for a redistribution film for IC package as claimed in claim 1, further comprising:
planting a plurality of solder balls, each configured on a top surface of a corresponding second top metal pad among the plurality of second top metal pads.

3. A fabricating process for a redistribution film for IC package as claimed in claim 2, further comprising:
removing the temporary carrier;
removing the seed layer;
mounting at least one chip on bottom of the bottom metal pads; and
singulating to produce a plurality of IC package units.

4. A fabricating process for a redistribution film for IC package as claimed in claim 1, further comprising:
forming a plurality of recesses on a top surface of a top dielectric layer of the bottom redistribution layer before the top redistribution layer is formed.

5. A fabricating process for a redistribution film for IC package as claimed in claim 4, further comprising:
planting a plurality of solder balls, each configured on a top surface of a corresponding second top metal pad among the plurality of second top metal pads.

6. A fabricating process for a redistribution film for IC package as claimed in claim 5, further comprising:
removing the temporary carrier;
removing the seed layer;
mounting at least one chip on bottom of the bottom metal pads; and
singulating to produce a plurality of IC package units.

7. A fabricating process for a redistribution film for IC package as claimed in claim 1, further comprising:
forming a plurality of bumps on top of the bottom redistribution layer before the top redistribution layer is formed.

8. A fabricating process for a redistribution film for IC package as claimed in claim 1, further comprising, before the top redistribution layer is formed:
applying a second patterned photoresist on a top dielectric layer of the bottom redistribution layer while exposing a portion of the top dielectric layer of the bottom redistribution layer;
applying a further seed layer on top of the second patterned photoresist and on the exposed portion of the top dielectric layer of the bottom redistribution layer;
applying a third patterned photoresist on top of the further seed layer, the third patterned photoresist including a plurality of trenches to expose the further seed layer on a bottom of each trench among the plurality of trenches;
forming a plurality of metal bumps, each in a corresponding trench among the plurality of trenches, using the further seed layer as a start point;
stripping the second and third patterned photoresists and the seed layer while leaving the plurality of metal bumps on top of the top dielectric layer of the bottom redistribution layer, wherein the top redistribution layer is formed on top of the plurality of metal bumps and the bottom redistribution layer.

9. A fabricating process for a redistribution film for IC package as claim in claim 8, further comprising:
planting a plurality of solder balls, each configured on a top surface of a corresponding second top metal pad among the plurality of second top metal pads.

10. A fabricating process for a redistribution film for IC package as claim in claim 9, further comprising:
removing the temporary carrier;
removing the seed layer;
mounting at least one chip on bottom of the bottom metal pads; and
singulating to produce a plurality of IC package units.

11. A fabricating process for a redistribution film for IC package as claimed in claim 8, further comprising, after said stripping the second and third patterned photoresists and the seed layer:
forming a dielectric layer over the bottom redistribution layer and the plurality of metal bumps,
wherein
the plurality of first top metal pads of the bottom redistribution layer, bottom conductive features of the top redistribution layer, and the plurality of metal bumps are embedded in the dielectric layer,
the bottom conductive features of the top redistribution layer are in direct electrical and physical contact with the corresponding first top metal pads of the bottom redistribution layer, and
top surfaces of the plurality of metal bumps are below a top surface of the dielectric layer.

12. A redistribution film for IC package, the redistribution film comprising:
a bottom redistribution layer fabricated according to IC design rule, the bottom redistribution layer having a plurality of bottom metal pads and a plurality of first top metal pads, wherein a density of the plurality of bottom metal pads is higher than a density of the plurality of first top metal pads;
a top redistribution layer fabricated according to PCB design rule, the top redistribution layer configured on top of the bottom redistribution layer and having a plurality of second top metal pads, wherein the density of the plurality of first top metal pads is higher than a density of the plurality of second top metal pads;
a plurality of bumps configured on a top surface of the bottom redistribution layer; and
a dielectric layer over the top surface of the bottom redistribution layer,
wherein
the plurality of first top metal pads of the bottom redistribution layer, bottom conductive features of the top redistribution layer, and the plurality of bumps are embedded in the dielectric layer,
the bottom conductive features of the top redistribution layer are in direct electrical and physical contact with the corresponding first top metal pads of the bottom redistribution layer,
top surfaces of the plurality of bumps are below a top surface of the dielectric layer,
the bottom redistribution layer includes
a plurality of first conductive layers, wherein a topmost first conductive layer among the plurality of first conductive layers includes the plurality of first top metal pads, and
a plurality of first conductive vias coupling the plurality of first conductive layers to each other and to the plurality of bottom metal pads,

the top redistribution layer includes
a plurality of second conductive layers, wherein a topmost second conductive layer among the plurality of second conductive layers includes the plurality of second top metal pads, and
a plurality of second conductive vias coupling the plurality of second conductive layers to each other and to the plurality of first top metal pads, and

in a thickness direction in which the top redistribution layer is stacked on top of the bottom redistribution layer, the dielectric layer is (a) below the plurality of second conductive layers of the top redistribution layer and (b) above the plurality of first conductive vias of the bottom redistribution layer.

13. The redistribution film for IC package of claim 12, wherein
in the thickness direction in which the top redistribution layer is stacked on the bottom redistribution layer, a thickness of each of the plurality of second conductive layers is greater than a thickness of each of the plurality of first conductive layers.

14. The redistribution film for IC package of claim 12, wherein
each of the plurality of metal bumps has
a bottom surface covered from below by a dielectric material of the bottom redistribution layer,
the top surface covered from above by the dielectric layer, and
side surfaces connecting the bottom surface to the top surface, and covered by the dielectric layer which extends around the metal bump.

15. The redistribution film for IC package of claim 14, wherein
in the thickness direction in which the top redistribution layer is stacked on top of the bottom redistribution layer, a height of each of the plurality of metal bumps is higher than a height of each of the plurality of first top metal pads of the bottom redistribution layer.

16. The redistribution film for IC package of claim 15, wherein
in the thickness direction in which the top redistribution layer is stacked on top of the bottom redistribution layer, the plurality of metal bumps are (a) below the plurality of second conductive layers of the top redistribution layer and (b) above the plurality of first conductive vias of the bottom redistribution layer.

17. The redistribution film for IC package of claim 16, wherein
the bottom conductive features of the top redistribution layer are lowermost second conductive vias among the plurality of second conductive vias of the top redistribution layer.

18. The redistribution film for IC package of claim 12, wherein
in the thickness direction in which the top redistribution layer is stacked on top of the bottom redistribution layer, the plurality of metal bumps are (a) below the plurality of second conductive layers of the top redistribution layer and (b) above the plurality of first conductive vias of the bottom redistribution layer.