# Patent

## Title
Stacked-type semiconductor package

## Abstract

Corresponding parts to a first path portion in a first signal transmission path to a first semiconductor chip are an interconnection member and a second path portion a second signal transmission path to a second semiconductor chip and are not formed on the first tape. An electric length of the second signal transmission path is allowed to be adjusted independently of the first tape, so that the electric length of the second signal transmission path can be easily made equal to or substantially equal to that of the first signal transmission path.

## Background
BACKGROUND OF THE INVENTION
This invention relates to a stacked-type semiconductor package, and more particularly to a stacked-type DRAM package which has high data rate transfer capability.
To increase memory capacity of a memory device package without making its profile large, there have been employed multiple techniques for stacking a plurality of memory chips into a vertical chip stack. For example, known techniques are disclosed in JP-A H11-220088 and U.S. Pat. No. 6,473,308 B2, which are incorporated herein by reference in its entirety. JP-A H11-220088 provides a stackable chip package of a unique structure, in accordance with which a chip stack can be obtained simply by stacking the same structured packages in turn. U.S. Pat. No. 6,473,308 B2 provides a chip package including a flex circuit which allows multiple chip packages to be easily assembled into a chip stack. However, according to the above prior arts, stacked packages in a chip stack have different electric lengths of data paths.
To solve the problem of the different electric lengths on stacked packages, US 2004/0227222 A1 has disclosed a four-layer substrate or tape comprising four conductive layers, which provides almost the same electric lengths to semiconductor chips mounted on the opposite surfaces of the tape. However, the four-layer tape is more expensive than a two-layer tape of normal one and increases a cost of a staked-type semiconductor package.
Therefore, there is a need for another technique of a staked-type semiconductor package which allows electric lengths of packages to be substantially equal to each other.
SUMMARY OF THE INVENTION
According to an aspect of the present invention, a stacked-type semiconductor package comprises an external connection terminal, a first semiconductor chip, a first tape, an interconnection member, a second semiconductor chip, and a second tape. Mounted on the first tape is the first semiconductor chip, while mounted on the second tape is the second semiconductor chip. The first tape is formed with a common path portion and a first path portion; the common path portion extends from the external connection terminal to a diverging point; and the first path portion extends from the diverging point to the first semiconductor chip. The interconnection member is connected to the diverging point. The second tape is formed with a second path portion which extends from the interconnection member to the second semiconductor chip.
The common path portion and the first path portion constitute a first signal transmission path to the first semiconductor chip, while the common path portion, the interconnection member and the second path portion constitute a second signal transmission path to the second semiconductor chip. Because the common path portion is shared by the first signal transmission path and the second signal transmission path, the corresponding parts to the first path portion are the interconnection member and the second path portion, which are not formed on the first tape. Therefore, an electric length of the second signal transmission path is allowed to be adjusted independently of the first tape, so that the electric length of the second signal transmission path can be easily made equal to or substantially equal to that of the first signal transmission path.
An appreciation of the objectives of the present invention and a more complete understanding of its structure may be had by studying the following description of the preferred embodiment and by referring to the accompanying drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded, perspective view schematically showing a stacked-type semiconductor package according to an embodiment of the present invention, wherein some components including elastomer sheets are not shown for the sake of clarity;
FIG. 2 is a cross-sectional view schematically showing the stacked-type semiconductor package of FIG. 1, wherein some components, especially right-side components are not shown for the sake of clarity;
FIG. 3 is a schematic view showing electric lengths of signal transmission paths; and
FIG. 4 is a cross-sectional view schematically showing a modification of the stacked-type semiconductor package of FIG. 1, wherein three semiconductor chips are stacked in a semiconductor package, and some components, especially right-side components are not shown for the sake of clarity.



DESCRIPTION OF PREFERRED EMBODIMENTS
As shown in FIGS. 1 and 2, a stacked-type semiconductor package according to a embodiment of the present invention comprises a first tape 10, a first semiconductor chip 20, a second tape 30, a second semiconductor chip 40, first solder balls 50a, 50b and second solder balls 60a, 60b, wherein the first solder balls 50a, 50b serve as external connection terminals which are to be connected to an external object such as a printed circuit board of a memory module, and the second solder balls 60a, 60b serve as interconnection terminals for interconnecting semiconductor chips. The illustrated stacked-type semiconductor package is a BGA (ball grid array) package. In this embodiment, the first and the second semiconductor chips 20, 40 are DRAM chips which have the same structure, and the stacked-type semiconductor chip is a stacked-type DRAM package. However, the present invention is not limited thereto and may be applied to another kind of semiconductor chips and another kind of semiconductor package.
The first and the second semiconductor chips 20, 40 shown in FIGS. 1 and 2 have the same structure with center pad configuration. The first semiconductor chip 20 has a plurality of bonding pads which are positioned on a center area of the first semiconductor chip 20. Likewise, the second semiconductor chip 40 has a plurality of bonding pads which are positioned on a center area of the second semiconductor chip 40. In this embodiment, the bonding pads of the first and the second semiconductor chips 20, 40 are lined up in the respective center rows.
The first tape 10 comprises a chip mount section 11 and an outer section 12 positioned outside the chip mount section 11. As apparent from FIGS. 1 and 2, the first semiconductor chip 20 is mounted on the chip mount section 11 through an elastomer sheet 70, which serves as a shock absorber or buffer. The illustrated chip mount section 11 is defined larger than the bottom area of the first semiconductor chip 20 in consideration of the size of the elastomer sheet 70.
The illustrated first tape 10 comprises a first base formed with a plurality of transmission lines 14, 15, each of which comprises a wire and a conductive via, wherein the first base is a polyimide film, and the wire of each transmission line 14, 15 is made of copper. In FIGS. 1 and 2, although only one or two transmission lines 14, 15 are shown for the sake of clarity, the actual first tape 10 has more transmission lines. By forming the wires on the polyimide film, followed by forming a center window 13 therein, the wires of the transmission lines 14, 15 have the respective free ends 14f, 15f. The free ends 14f, 15f are to be bonded to the bonding pads of the first semiconductor chip 20.
The transmission lines 14, 15 are generally formed on a top surface of the first base although parts of the transmission lines 14, 15 reach a bottom surface of the first base, as described in detail afterwards. On the bottom surface except a first predetermined area, a first reference plane 16 is formed. In other words, the first reference plane 16 generally covers the bottom surface but does not cover the first predetermined area. In this embodiment, the first reference plane 16 is made of copper.
The first reference plane 16 is supplied with a referential voltage such as a ground voltage upon its actual use. Together with the first reference plane 16, each of the transmission lines 14, 15 constitutes a microstrip transmission line structure so that each of the transmission lines 14, 15 has high transmission reliability.
The transmission line 14 comprises a ball land 14a, a conductive via 14b, a wire portion 14c, another ball land 14d, and another wire portion 14e. The ball land 14a is formed on the bottom surface of the first base and is positioned within the first predetermined area of the first base so as to be electrically isolated from the first reference plane 16. The conductive via 14b is connected to the ball land 14a and extends to the top surface of the first base. The wire portion 14c extends from the conductive via 14b to the ball land 14d. The wire portion 14e extends from the ball land 14d to the free end 14f. Connected to the ball land 14a is the first solder ball 50a, while connected to the ball land 14d is the second solder ball 60a. The free end 14f is connected to the bonding pad of the first semiconductor chip 20 and is protected by a resin protector 75. The ball land 14a, the conductive via 14b, the wire portion 14c, and the ball land 14d constitute a common path portion which is shared by the first and the second semiconductor chips 20, 40. On the other hand, the wire portion 14e constitutes a first path portion which is used only as a part of a first signal transmission path to the first semiconductor chip. The ball land 14d serves as a diverging point at which the common path portion branches off.
The transmission line 15 comprises a ball land 15a, a conductive via 15b, a wire portion 15c, another ball land 15d, another wire portion 15e and the free end 15f, similar to the ball land 14a, the conductive via 14b, the wire portion 14c, the ball land 14d, the wire portion 14e and the free end 14f of the transmission line 14.
The arrangement of the first solder balls 50a, 50b of the external connection terminals is defined and standardized, for example, by JEDEC (Joint Electron Device Engineering Council). Therefore, the arrangement of the ball lands 14a, 15a is compliant with the definition and standard. On the other hand, the second solder balls 60a, 60b of the interconnection members are not restricted to the standard and definition but may be arranged in accordance with a unique arrangement. Therefore, the ball lands 14d, 15d of the diverging points may be arranged without restriction of the standard and definition.
As apparent from FIG. 1, the ball lands 14d, 15d of the diverging points are positioned on the outer section 12, on which the first semiconductor chip 20 is not mounted. Therefore, the second solder balls 60a, 60b of the interconnection members can be directly positioned on the respective ball lands 14, 15.
The illustrated second tape 30 comprises a second base formed with a plurality of transmission lines 34, 35, each of which comprises a wire and a conductive via, wherein the second base is a polyimide film formed with a center window 33, and the wire of each transmission line 34, 35 is made of copper. In FIGS. 1 and 2, although only one or two transmission lines 34, 35 are shown for the sake of clarity, the actual second tape 30 has more transmission lines.
The transmission lines 34, 35 are generally formed on a top surface of the second base although parts of the transmission lines 34, 35 reach a bottom surface of the second base, as described in detail afterwards. On the bottom surface except a second predetermined area, a second reference plane 36 is formed. In other words, the second reference plane 36 generally covers the bottom surface but does not cover the second predetermined area. In this embodiment, the second reference plane 36 is made of copper.
The second reference plane 36 is supplied with the referential voltage upon its actual use. Together with the second reference plane 36, each of the transmission lines 34, 35 constitutes a microstrip transmission line structure so that each of the transmission lines 34, 35 has high transmission reliability.
The transmission line 34 comprises a ball land 34a, a conductive via 34b, and a wire portion 34c. The ball land 34a is formed on the bottom surface of the second base and is positioned within the second predetermined area of the second base so as to be electrically isolated from the second reference plane 36. The conductive via 34b is connected to the ball land 34a and extends to the top surface of the second base. The wire portion 34c extends from the conductive via 34b into the center window 33 of the second base and has a free end 34d which is bonded to the bonding pad of the second semiconductor chip 40 and is protected by a resin protector 85. Mounted on the ball land 34a is the second solder ball 60a. The transmission line 34 and the second solder ball 60a constitute a second path portion which is used only as a part of a second signal transmission path to the second semiconductor chip.
The transmission line 35 comprises a ball land 35a, a conductive via 35b, a wire portion 35c and a free end 35d, similarly to the ball land 34a, the conductive via 34b, the wire portion 34c and the free end 34d of the transmission line 34.
As apparent from FIGS. 1 and 2, the second semiconductor chip 40 is mounted on the second tape 30 through another elastomer sheet 80 serving as a shock absorber or buffer. On the peripherals of the second semiconductor chip 40, another resin protector 90 is provided, as shown in FIG. 2.
As best shown in FIG. 3, the first path portions (14e, 15e) and the second path portions (34, 60a; 35, 60b) are branched off from the common path portions (14a, 14b, 14c; 15a, 15b, 15c). In this embodiment, the actual lengths of the wire portions 34c, 35c of the second tape 30 are designed equal to the actual lengths of the wire portions 14e, 15e, respectively. Therefore, the electric lengths of the first signal transmission paths from the solder balls 50a, 50b to the first semiconductor chip 20 are substantially equal to the electric length of the second signal transmission paths, respectively.
In the present embodiment, each of the first and the second tapes 10, 30 has a plurality of signal transmission lines, as mentioned above. The signal transmission lines include DQ signal lines and Command/Address (C/A) signal lines. In this embodiment, every DQ signal line has a feature similar to the first or the second signal transmission path, wherein the electric path to the first semiconductor chip 20 is substantially equal to the electric path to the second semiconductor chip 40. On the other hand, the C/A signal lines have not such features because of the signal rate different from that of the DQ line, wherein the electric path to the first semiconductor chip 20 is different from the electric path to the second semiconductor chip 40. However, the C/A signal lines may have a feature similar to the first or the second signal transmission path.
Although the stacked-type semiconductor package according to the above-described embodiment comprises two semiconductor chips 20, 40, the present invention is not limited thereto but may be applied to a stacked-type semiconductor package comprising three or more semiconductor chips. In FIG. 4, there is shown a stacked-type semiconductor package into which three semiconductor chips are stacked. The stacked-type semiconductor package of FIG. 4 comprises additional solder balls 160a, a third tape 130, a third elastomer sheet 180 and a third semiconductor chip 140, in addition to the components of the stacked-type semiconductor package of FIG. 2. The third tape 130 is formed with transmission lines each of which comprises a conductive via 134b and a wire portion 134c. The conductive via 134b is connected to the additional solder ball 160a. The third semiconductor chip 140 is mounted on the third tape 130 through the third elastomer sheet 180 and is connected to the wire portion 134c. The additional solder ball 160a and the transmission line comprised of the conductive via 134b and the wire portion 134c constitute a third path portion which is used only as a part of a third signal transmission path to the third semiconductor chip. The wire portion 134c may have the same length of the wire portion 34c, and the third path portion may have the electric length substantially equal to that of the second path portion.
The preferred embodiments of the present invention will be better understood by those skilled in the art by reference to the above description and figures. The description and preferred embodiments of this invention illustrated in the figures are not to intend to be exhaustive or to limit the invention to the precise form disclosed. They are chosen to describe or to best explain the principles of the invention and its applicable and practical use to thereby enable others skilled in the art to best utilize the invention.
While there has been described what is believed to be the preferred embodiment of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the sprit of the invention, and it is intended to claim all such embodiments that fall within the true scope of the invention.

## Claims

1. A stacked-type semiconductor package comprising:
an external connection terminal;
a first semiconductor chip;
a first tape on which the first semiconductor chip is mounted and which is formed with a common path portion and a first path portion, wherein the common path portion extends from the external connection terminal to a diverging point, and the first path portion extends from the diverging point to the first semiconductor chip;
an interconnection member connected to the diverging point;
a second semiconductor chip;
a second tape on which the second semiconductor chip is mounted and which is formed with a second path portion extending from the interconnection member to the second semiconductor chip, wherein
the first tape comprises a first base which has top and bottom surfaces;
the external connection terminals are arranged on the bottom surface of the first base;
the first tape comprises a chip mount section and an outer section positioned outside the chip mount section;
the chip mount section and the outer section are positioned on the top surface of the first base;
the first semiconductor chip mounted on the chip mount section; and
the diverging point is arranged on the outer section.

2. The stacked-type semiconductor package according to claim 1, wherein the first path portion has an electric length substantially equal to another electric length of the second path portion.

3. The stacked-type semiconductor package according to claim 1, wherein the external connection terminal comprises a solder ball.

4. The stacked-type semiconductor package according to claim 1, wherein the interconnection member comprises a solder ball.

5. The stacked-type semiconductor package according to claim 1, wherein:
on the bottom surface except for a predetermined area, a reference plane for a referential voltage is formed;
the common path portion comprises a connection portion connected to the external terminal, a conductive via connected to the connection portion and a wire portion extending from the conductive via to the diverging point, wherein the connection portion is formed on the bottom surface and is positioned within the predetermined area so as to be electrically isolated from the reference plane, the conductive via is formed in the first base and extends from the bottom surface to the top surface, the wire portion is formed on the top surface;
the first path portion is formed on the top surface of the first base; and
the common path portion and the first path portion together with the reference plane constitute a microstrip transmission line structure.

6. The stacked-type semiconductor package according to claim 5, wherein:
the second tape comprises a second base which has top and bottom surfaces;
on the bottom surface of the second base except for an additional predetermined area of the second base, an additional reference plane for a referential voltage is formed;
the second path portion comprises an additional connection portion connected to the interconnection member, an additional conductive via connected to the additional connection portion and an additional wire portion extending from the additional conductive via to second semiconductor chip, wherein the additional connection portion is formed on the bottom surface of the second base and is positioned within the additional predetermined area so as to be electrically isolated from the additional reference plane, the additional conductive via is formed in the second base and extends from the bottom surface to the top surface of the second base, the additional wire portion is formed on the top surface of the second base; and
the second path portion together with the additional reference plane constitute a microstrip transmission line structure.

7. The stacked-type semiconductor package according to claim 1, comprising a plurality of data signal lines connected to the first and the second semiconductor chips, wherein each of the data signal lines comprises the first path portion, the second path portion and the common path portion.

8. The stacked-type semiconductor package according to claim 1, wherein the first and the second semiconductor chips comprises DRAM chips, respectively.

9. The stacked-type semiconductor package according to claim 1, wherein the first and the second semiconductor chips comprise bonding pads connected to the first and the second path portions, respectively, and each of the bonding pads is positioned on a center area of the first or the second semiconductor chip.

10. The stacked-type semiconductor package according to claim 1, further comprising at least one elastomer sheet interposed between the first semiconductor chip and the first tape and/or between the second semiconductor chip and the second tape.

11. The stacked-type semiconductor package according to claim 1, further comprising an additional interconnection member, a third semiconductor chip and a third tape, wherein:
the third semiconductor chip is mounted on the third tape; and
the third tape is formed with a third path portion extending from the additional interconnection member to the third semiconductor chip.

12. The stacked-type semiconductor package according to claim 11, wherein the third path portion has an electric length substantially equal to another electric length of the second path portion.

13. A stacked-type semiconductor package comprising:
an external connection terminal;
a first semiconductor chip;
a first tape on which the first semiconductor chip is mounted which is formed with a common path portion and a first path portion, wherein the common path portion extends from the external connection terminal to a diverging point, and the first path portion extends from the diverging point to the first semiconductor chip;
an interconnection member connected to the diverging point;
a second semiconductor chip;
a second tape on which the second semiconductor chip is mounted and which is formed with a second path portion extending from the interconnection member to the second semiconductor chip, wherein
the first tape comprises a first base which has top and bottom surfaces;
on the bottom surface except for a predetermined area, a reference plane for a referential voltage is formed;
the common path portion comprises a connection portion connected to the external terminal, a conductive via connected to the connection portion and a wire portion extending from the conductive via to the diverging point, wherein the connection portion is formed on the bottom surface and is positioned within the predetermined area so as to be electrically isolated from the reference plane, the conductive via is formed in the first base and extends from the bottom surface to the top surface, the wire portion is formed on the top surface;
the first path portion is formed on the top surface of the first base; and
the common path portion and the first path portion together with the reference plane constitute a microstrip transmission line structure.