# Patent

## Title
Package-on-package system with through vias and method of manufacture thereof

## Abstract

A method of manufacture of a package-on-package system includes: providing a package substrate; attaching a semiconductor die to the package substrate; forming an encapsulant around the semiconductor die to have a bottom exposed surface coplanar with a bottom surface of the package substrate and to have a top exposed surface with through openings extending therefrom through the bottom exposed surface; and creating through vias by applying solder into the through openings.

## Background
TECHNICAL FIELD
The present invention relates generally to semiconductor package system, and more particularly to a stackable package-on-package system for multi-chip modules.
BACKGROUND ART
As new generations of electrical consumer products are developed there is a growing need to improve the functionality, performance, reliability, and manufacturing robustness of semiconductor packages. Additionally, new handheld consumer electronic devices such as cell phones and new laptop computers are increasingly designed to present a low-profile. This design trend imposes severe limitations on the thickness of individual electronic components.
System requirements for consumer electronics have motivated the implementation of integrated circuit packages incorporating several semiconductor dies or “chips”. Such multi-chip packages may be realized by connecting multiple semiconductor dies on a single package substrate.
Alternatively, the Package-in-Package (PiP) approach for packaging multi-chip modules involves first mounting a semiconductor die on a package substrate with interconnects, forming an Internal Stacking Module (ISM). This package module can be tested individually prior to assembly into a multi-chip package. Thus the PiP approach provides a means of pre-testing package sub-assemblies (i.e., internal stacking modules), enabling the assembly of complex multi-chip packages using “known good packages.” This modular approach for assembling multi-chip packages reduces overall yield loss.
Yet another implementation of a multi-chip package is termed “Package-on-Package” (PoP). In this approach, one monolithic package is stacked on top of another package using standard interconnects for routing signals between the two packages.
One drawback of existing PiP or PoP packages is that they do not provide sufficient versatility and reliability for integration into larger multi-chip packages. Thus, a need still remains for internal stacking module and/or package-on-package systems with increased interconnection capabilities and reduced overall thickness while improving its reliability.
More specifically, there is a need to reduce the cost of PiP and PoP systems and to reduce warping of the modules during fabrication to facilitate integration into larger multi-chip package modules. In view of yield loss due to package warping it is increasingly critical that answers be found to these problems.
In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Additionally, the need to reduce costs, improve efficiencies and performance, and meet competitive pressures adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.
DISCLOSURE OF THE INVENTION
The present invention provides a method of manufacture of a package-on-package system including: providing a package substrate; attaching a semiconductor die to the package substrate; forming an encapsulant around the semiconductor die to have a bottom exposed surface coplanar with a bottom surface of the package substrate and to have a top exposed surface with through openings extending therefrom through the bottom exposed surface; and creating through vias by applying solder into the through openings.
Furthermore, the present invention provides a package-on-package system including: a package substrate; a semiconductor die attached to the package substrate; an encapsulant surrounding at least portions of the package substrate and the semiconductor die, the encapsulant having a bottom exposed surface coplanar with the bottom surface of the package substrate and a top exposed surface; and through vias extending from the top exposed surface to a bottom exposed surface of the encapsulant.
Certain embodiments of the invention have other steps or elements in addition to or in place of those mentioned above. The steps or element will become apparent to those skilled in the art from a reading of the following detailed description when taken with reference to the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a bottom view of a package-on-package system in one embodiment of the present invention.
FIG. 2 is a bottom view of the package-on-package system in an alternate embodiment of the present invention.
FIG. 3 is a cross-sectional view of the package-on-package system taken along line 3-3 shown in FIG. 1.
FIG. 4 is a top view of a package substrate assembly incorporating the package substrate of FIG. 3.
FIG. 5 is a top view of a package substrate assembly incorporating a package substrate in an alternate embodiment of the present invention.
FIG. 6 is a bottom view of a package-on-package system in an alternate embodiment of the present invention.
FIG. 7 is a cross-sectional view of the package-on-package system taken along line 7-7 shown in FIG. 6.
FIG. 8 is a top view of a package substrate assembly incorporating the substrate connections shown in FIG. 6.
FIG. 9 is a cross-section of a package substrate in the package substrate assembly 800 shown in FIG. 8.
FIG. 10 is a bottom view of a package-on-package system in an alternate embodiment of the present invention.
FIG. 11 is a top view of a package substrate incorporating the substrate connections and the dummy patterns used in the package-on-package system shown in FIG. 10.
FIG. 12 is a cross section of a mold used in the initial stages of the fabrication of the package-on-package system.
FIG. 13 is a cross-section of the package-on-package system of FIG. 3 following molding of the encapsulant;
FIG. 14 is a cross-section of the package-on-package system of FIG. 7 following molding of the encapsulant.
FIG. 15 is a mechanical device used to form the through vias in one embodiment of the invention.
FIG. 16 is the package-on-package system of FIG. 3 at the end of the fabrication process following the formation of the through vias and the external interconnects.
FIG. 17 is the package-on-package system of FIG. 6 at the end of the fabrication process following the formation of the through vias and the external interconnects.
FIG. 18 is a flow chart of a method of manufacture of a package-on-package system in a further embodiment of the present invention.



BEST MODE FOR CARRYING OUT THE INVENTION
The following embodiments are described in sufficient detail to enable those skilled in the art to make and use the invention. It is to be understood that other embodiments would be evident based on the present disclosure, and that system, process, or mechanical changes may be made without departing from the scope of the present invention.
In the following description, numerous specific details are given to provide a thorough understanding of the invention. However, it will be apparent that the invention may be practiced without these specific details. In order to avoid obscuring the present invention, some well-known circuits, system configurations, and process steps are not disclosed in detail.
The drawings showing embodiments of the system are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown exaggerated in the drawing FIGs. Similarly, although the views in the drawings for ease of description generally show similar orientations, this depiction in the FIGs. is arbitrary for the most part. Generally, the invention can be operated in any orientation.
The same numbers are used in all the drawing FIGs. to relate to the same elements. The embodiments have been numbered first embodiment, second embodiment, etc. as a matter of descriptive convenience and are not intended to have any other significance or provide limitations for the present invention.
For expository purposes, the term “horizontal” as used herein is defined as a plane parallel to the plane or surface of the semiconductor die, regardless of its orientation. The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms, such as “above”, “below”, “bottom”, “top”, “side” (as in “sidewall”), “higher”, “lower”, “upper”, “over”, and “under”, are defined with respect to the horizontal plane, as shown in the figures. The term “on” means that there is direct contact among elements.
The term “processing” as used herein includes deposition of material or photoresist, patterning, exposure, development, etching, cleaning, and/or removal of the material or photoresist as required in forming a described structure.
Referring now to FIG. 1, therein is shown a bottom view of a package-on-package system 100 in one embodiment of the present invention. The package-on-package system 100 includes two types of external connections 102: substrate connections 104 and through vias 106.
The substrate connections 104 provide an electrical path through a package substrate 108. The through vias 106 are located entirely within an encapsulant 110, providing electrical connections through the package-on-package system 100.
The package substrate 108 includes tie bars 112 extending to edges 114 of the package-on-package system 100. In one embodiment of the invention, some of the tie bars 112 are configured with an offset 116 from each other.
Referring now to FIG. 2, therein is shown a bottom view of the package-on-package system 200 in an alternate embodiment of the present invention. Similar to the package-on-package system 100, the package-on-package system 200 includes two types of external connections 202: substrate connections 204 and through vias 206.
The substrate connections 204 provide an electrical path through a package substrate 208. The package substrate 208 has a rectangular shape that extends from an end edge 212 to an opposite edge 214 of the package-on-package system 200. An encapsulant 210 surrounds portions of the package substrate 208.
Referring now to FIG. 3, therein is shown a cross-sectional view of the package-on-package system 100 taken along line 3-3 shown in FIG. 1. A semiconductor die 302 is attached to the package substrate 108 using an adhesive 304. Electrical interconnects 306 provide connectivity between the semiconductor die 302 and the substrate connections 104. The electrical interconnects 306 may be implemented using bond wires as shown in FIG. 3.
The through vias 106 extend vertically through a thickness 308 of the package-on-package system 100 providing electrical connections through the package-on-package system 100. The encapsulant 110 has a bottom exposed surface 310 coplanar with a bottom surface 312 of the package substrate 108 and has a top exposed surface 314. The through vias 106 extend from the top exposed surface 314 to the bottom exposed surface 310 of the encapsulant 110.
The through vias 106 may be employed to provide interconnectivity between external components mounted above and below the package-on-package system 100. External interconnects 316 provide connectivity to the next system level.
It has been discovered that the package-on-package system 100 can be implemented using the package substrate 108 which is minimally larger than the semiconductor die 302, reducing the overall cost of the package-on-package system 100.
Additionally the package-on-package system 100 is less susceptible to warping as a result of the fabrication process. Therefore it may easily be integrated as part of a larger multi-chip module. The package-on-package system 100 may be electrically tested and classified as good known package (GKP) prior to integration into a larger module, increasing the overall reliability of a multi-chip module.
Thus, it has been discovered that the package-on-package system 100 of the present invention furnishes important and heretofore unknown and unavailable solutions, capabilities, and functional aspects for implementing a low-cost modular package that can be stacked into a multi-level package.
Referring now to FIG. 4, therein is shown a top view of a package substrate assembly 400 incorporating the package substrate 108 of FIG. 3. The package substrate assembly 400 incorporates multiple repetitions of the package substrate 108 held together by a frame 402 using the tie bars 112. The package substrate assembly 400 is used in the fabrication of the package-on-package system 100.
Referring now to FIG. 5, therein is shown a top view of a package substrate assembly 500 incorporating the package substrate 208 in an alternate embodiment of the present invention. The package substrate assembly 500 incorporates multiple repetitions of the package substrate 208 held together by a frame 502. The package substrate assembly 500 is used in the fabrication of the package-on-package system 200.
Referring now to FIG. 6, therein is shown a bottom view of a package-on-package system 600 in an alternate embodiment of the present invention. The package-on-package system 600 includes two types of external connections 602: substrate connections 604 and through vias 606. The substrate connections 604 provide an electrical path between external elements (not shown) and a semiconductor die (not shown). The through vias 606 extend vertically through a thickness (not shown) of an encapsulant 608, providing electrical connections between the top and bottom surface of the package-on-package system 600.
Referring now to FIG. 7, therein is shown a cross-sectional view of the package-on-package system 600 taken along line 7-7 shown in FIG. 6. A semiconductor die 702 is attached to the substrate connections 604 using an adhesive 704. Electrical interconnects 706 provide connectivity between the semiconductor die 702 and the substrate connections 604. The electrical interconnects 706 may be implemented using bond wires as shown in FIG. 7.
The encapsulant 608 surrounds at least portions of the semiconductor die 702, the substrate connections 604, the electrical interconnects 706, and the through vias 606. The encapsulant 608 has a bottom exposed surface 710 coplanar with a bottom surface 712 of the substrate connections 604 and has a top exposed surface 714. The through vias 606 extend from the top exposed surface 714 to the bottom exposed surface 710 of the encapsulant 608.
The through vias 606 may be employed to provide interconnectivity between external components mounted above and below the package-on-package system 600. External interconnects 716 provide connectivity to the next system level.
It has been discovered that the package-on-package system 600 can be implemented using the substrate connections 604 with a layout footprint minimally larger than the semiconductor die 702, reducing the overall cost of the package-on-package system 600. Additionally the package-on-package system 600 is less susceptible to warping as a result of the fabrication process.
Thus, it has been discovered that the package-on-package system 600 of the present invention furnishes important and heretofore unknown and unavailable solutions, capabilities, and functional aspects for implementing a low-cost modular package that can be stacked into a multi-level package.
Referring now to FIG. 8, therein is shown a top view of a package substrate assembly 800 incorporating the substrate connections 604 shown in FIG. 6. The package substrate assembly 800 incorporates multiple repetitions of the layout for the substrate connections 604 used in each package-on-package system 600. The substrate connections 604 are supported by a package carrier 802. In this embodiment of the invention, the package carrier 802 is a sacrificial plate such as a copper plate.
Referring now to FIG. 9, therein is shown a cross-section of a package substrate 900 in the package substrate assembly 800 shown in FIG. 8. At the initial stages of the fabrication process of the package-on-package system 600, each package substrate 900 includes the package carrier 802 and the substrate connections 604. In one embodiment of the invention, the package carrier 802 is a copper plate, and the substrate connections 604 are plated metal traces.
Referring now to FIG. 10, therein is shown a bottom view of a package-on-package system 1000 in an alternate embodiment of the present invention. The package-on-package system 1000 includes two types of external connections 1002 accessible through its bottom surface: substrate connections 1004 and through vias 1006. The substrate connections 1004 provide an electrical path between external elements and a semiconductor die (not shown). The through vias 1006 extend entirely through the encapsulant 1008, providing electrical connections between the top and bottom surface of the package-on-package system 1000.
The embodiment of the invention shown in FIG. 10 includes dummy patterns 1010 made using the same materials as the substrate connections 1004. The dummy patterns 1010 are features that are used during the fabrication process to facilitate the planarization process for the substrate connections 1004 and to reduce warping of the package-on-package system 1000.
Referring now to FIG. 11, therein is shown a top view of a package substrate 1100 incorporating the substrate connections 1004 and the dummy patterns 1010 used in the package-on-package system 1000 shown in FIG. 10. The package carrier in the package substrate 1100 is not shown for clarity.
Referring now to FIG. 12, therein is shown a cross section of a mold 1200 used in the initial stages of the fabrication of the package-on-package system 100. At this stage of the process, the semiconductor die 302 is already attached to the package substrate 108 and connected to it using the electrical interconnects 306. The package substrate 108 rests on top of a bottom mold plate 1202. A top mold plate 1204 covers the package substrate 108, the semiconductor die 302, and the electrical interconnects 306.
The openings for the through vias 106 are defined by pins 1206 extending through a molding cavity 1208 defined by the top mold plate 1204 and the bottom mold plate 1202. The encapsulant (not shown) is injected through an injection port 1210 into the cavity 1208.
Referring now to FIG. 13, therein is shown a cross-section of the package-on-package system 100 of FIG. 3 following molding of the encapsulant 110. The pins 1206 shown in FIG. 12 define through openings 1302 extending through the encapsulant 110. The through openings 1302 are molds for the through vias 106 (not shown).
The encapsulant 110 has the bottom exposed surface 310 coplanar with the bottom surface 312 of the package substrate 108 and has the top exposed surface 314. The through openings 1302 extend from the top exposed surface 314 to the bottom exposed surface 310 of the encapsulant 110.
Referring now to FIG. 14, therein is shown a cross-section of the package-on-package system 600 of FIG. 7 following molding of the encapsulant 608. The pins 1206 shown in FIG. 12 define through openings 1402 extending through the encapsulant 608. The through openings 1402 are molds for the through vias 606 (not shown). The package carrier 802 of FIG. 8 is dissolved following the formation of the encapsulant 608.
The encapsulant 608 has the bottom exposed surface 710 coplanar with the bottom surface 712 of the substrate connections 604 and has a top exposed surface 714. The through openings 1402 extend from the top exposed surface 714 to the bottom exposed surface 710 of the encapsulant 608.
Referring now to FIG. 15, therein is shown a mechanical device 1500 used to form the through vias 106 in one embodiment of the invention. In this step of the fabrication process for the package-on-package system 100, the structure of FIG. 13 is placed between a support plate 1502 and a stencil plate 1504 of the mechanical device 1500. The through openings 1302, previously defined by the molding of the encapsulant 110, are aligned to openings 1506 in the stencil plate 1504.
The through vias 106 are formed by applying solder 1508 into the through openings 1302 using a wedge 1510. Vertical pressure on the wedge 1510 ensures filling of the through openings 1302. A non-stick material 1512 on the support plate 1502 prevents sticking of the through vias 106.
Referring now to FIG. 16, therein is shown the package-on-package system 100 of FIG. 3 at the end of the fabrication process following the formation of the through vias 106 and the external interconnects 316.
Referring now to FIG. 17, therein is shown the package-on-package system 600 of FIG. 6 at the end of the fabrication process following the formation of the through vias 606 and the external interconnects 716.
Referring now to FIG. 18, therein is shown a flow chart of a method 1800 of manufacture of a package-on-package system 100 in a further embodiment of the present invention. The method 1800 includes: providing a package substrate in a block 1802; attaching a semiconductor die to the package substrate in a block 1804; forming an encapsulant around the semiconductor die to have a bottom exposed surface coplanar with a bottom surface of the package substrate and to have a top exposed surface with through openings extending therefrom through the bottom exposed surface in a block 1806; and, creating through vias by applying solder into the through openings in a block 1808.
The resulting method, process, apparatus, device, product, and/or system is straightforward, cost-effective, uncomplicated, highly versatile, accurate, sensitive, and effective, and can be implemented by adapting known components for ready, efficient, and economical manufacturing, application, and utilization.
Another important aspect of the present invention is that it valuably supports and services the historical trend of reducing costs, simplifying systems, and increasing performance.
These and other valuable aspects of the present invention consequently further the state of the technology to at least the next level.
While the invention has been described in conjunction with a specific best mode, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the aforegoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the scope of the included claims. All matters hithertofore set forth herein or shown in the accompanying drawings are to be interpreted in an illustrative and non-limiting sense.

## Claims

1. A method of manufacture of a package-on-package system comprising:
providing a package substrate;
attaching a semiconductor die to the package substrate;
providing the package substrate includes forming the package substrate incorporating tie bars extending to edges of the package-on-package system;
forming an encapsulant around the semiconductor die to have a bottom exposed surface coplanar with a bottom surface of the package substrate and to have a top exposed surface with through openings extending therefrom through the bottom exposed surface;
forming the encapsulant includes creating through openings located on one side of the tie bars; and
creating through vias by applying solder into the through openings.

2. A method of manufacture of a package-on-package system comprising:
providing a package substrate with substrate connections;
attaching a semiconductor die to the package substrate;
providing the package substrate includes forming the package substrate incorporating tie bars extending to edges of the package-on-package system;
connecting the semiconductor die to the substrate connections in the package substrate using electrical interconnects;
molding an encapsulant around the semiconductor die using a mold with pins to have a bottom exposed surface coplanar with a bottom surface of the package substrate and to have a top exposed surface, wherein the pins define through openings extending from the top exposed surface through the bottom exposed surface; the molding an encapsulant includes creating through openings located on either side of the tie bars; and
creating through vias by applying solder through a stencil plate with openings aligned to the through openings.

3. A package-on-package system comprising:
a package substrate;
a semiconductor die attached to the package substrate;
the package substrate includes tie bars extending to edges of the package-on-package system;
an encapsulant surrounding at least portions of the package substrate and the semiconductor die, the encapsulant having a bottom exposed surface coplanar with the bottom surface of the package substrate and a top exposed surface; and
through vias extending from the top exposed surface to a bottom exposed surface of the encapsulant, the through vias being located on one side of the tie bars.

4. The system as claimed in claim 3 further comprising:
substrate connections defined in the package substrate;
electrical interconnects for connecting the semiconductor die to the substrate connections in the package substrate; and

wherein:
the encapsulant is a molding compound.

5. The system as claimed in claim 4 wherein:
the package substrate includes an offset between the tie bars; and
the through vias are located on either side of the tie bars.