US20060125093A1

US20060125093A1 - Multi-chip module having bonding wires and method of fabricating the same

Info

Publication number: US20060125093A1
Application number: US11/353,509
Authority: US
Inventors: In-Ku Kang; Hee-Kook Choi; Sang-Ho An; Sang-Yeop Lee
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2003-07-31
Filing date: 2006-02-13
Publication date: 2006-06-15
Also published as: US20050023674A1; US7030489B2

Abstract

Provided herein are multi-chip modules (MCMs) having bonding wires and fabrication methods thereof. The multi-chip module includes a substrate and a plurality of chips sequentially stacked. At least one top chip, stacked above a lowest chip, has an insulating film that covers the backside thereof. Also, each of the stacked chips has bonding pads formed on the periphery or edges of its upper surface. At least one insulator is interposed between the stacked chips. The insulator exposes the pads on the underlying chip. The pads of the respective chips are connected to a set of interconnections, which are disposed on the substrate. This configuration of stacked chips enables the overall height of the memory module to be reduced because the insulating film prevents the bonding wires from contacting the substrate of the top chips.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent Ser. No. 10/632,700, filed on Jul. 31, 2003, now pending, the contents of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a semiconductor package and a fabrication method thereof and, more particularly, to a multi-chip module having bonding wires and method of fabricating the same.
2. Description of the Related Art
As portable electronic devices become smaller, the dimensions of semiconductor packages in the electronic devices must also be reduced. To help accomplish this, a multi-chip module technique is widely used because it can increase the capacity of the semiconductor package. Multi-chip modules (MCMs) include a plurality of chips, which are stacked.
FIG. 1 is a cross sectional view illustrating a conventional multi-chip module having bonding wires.
Referring to FIG. 1, a bottom chip 3 and a top chip 7 are sequentially stacked on a substrate such as a lead frame or a printed circuit board. The substrate includes a flat body 1 and a first group of interconnections 1 a and a second group of interconnections 1 b formed on a surface of the body 1. The bottom chip 3 is attached and fixed to the body 1 using an adhesive 5, which is interposed between the bottom chip 3 and the body 1. Spacers 9 are interposed between the top chip 7 and the bottom chip 3 in order to separate the top chip 7 from the bottom chip 3. The bottom chip 3 has a plurality of pads 3 a formed on its edges.
The pads 3 a are electrically connected to the first group of interconnections 1 a through a first group of bonding wires 13. In this case, the first group of bonding wires 13 may be in contact with a backside surface of the top chip 7 if the top chip 7 has the same dimension as the bottom chip 3. Thus, the spacers 9 should have a sufficient height to prevent the first group of bonding wires 13 from being in contact with the backside of the top chip 7. In other words, a distance S between the bottom chip 3 and the top chip 7 should be determined in consideration of the height of the first group of bonding wires 13. Accordingly, there is a limitation in reducing the total thickness of the multi-chip module.
Further, the top chip 7 has a plurality of pads 7 a formed on its edges. The pads 7 a are electrically connected to the second group of interconnections 1 b through a second group of bonding wires 15. The space between the bottom chip 3 and the top chip 7 is filled with an insulator 11.
FIG. 2 is a cross sectional view illustrating another conventional multi-chip module having bonding wires.
Referring to FIG. 2, a bottom chip 23 and a top chip 27 are sequentially stacked on a substrate such as a lead frame or a printed circuit board. The substrate has the same configuration as the substrate described in FIG. 1. That is to say, the substrate includes a flat body 21 and a first group of interconnections 21 a and a second group of interconnections 21 b formed on a surface of the body 21. Also, the bottom chip 23 is attached and fixed to the body 21 using an adhesive 25, which is interposed between the bottom chip 23 and the body 21. An insulator 29 is interposed between the chips 23 and 27 in order to separate the top chip 27 from the bottom chip 23. The bottom chip 23 has a plurality of pads 23 a formed on its edges.
The pads 23 a are electrically connected to the first group of interconnections 21 a through a first group of bonding wires 31. In this case, the first group of bonding wires 31 may be in contact with a backside surface of the top chip 27 if the top chip 27 has the same dimension as the bottom chip 23. Thus, the insulator 29 should have a sufficient thickness to prevent the first group of bonding wires 31 from being in contact with the backside of the top chip 27. In other words, a distance S between the bottom chip 23 and the top chip 27 should be determined in consideration of the height of the first group of bonding wires 31. Accordingly, there is a limitation in reducing the total thickness of the multi-chip module.
Further, the top chip 27 has a plurality of pads 27 a formed on its edges. The pads 27 a are electrically connected to the second group of interconnections 21 b through a second group of bonding wires 33.
In the meantime, a multi-chip module is taught in U.S. Pat. No. 6,333,562 B1 to Lin, entitled “Multichip module having stacked chip arrangement”. In addition, U.S. Pat. No. 6,388,313 B1 discloses a multi-chip module having a bottom chip and a top chip, which are sequentially stacked.
According to the aforementioned conventional MCMs, it is difficult to prevent bonding wires connected to the bottom chip from contacting the backside surface of the top chip. Therefore, it is difficult to realize a thin and reliable package module.

SUMMARY OF THE INVENTION

It is therefore a feature of the present invention to provide thin and reliable multi-chip modules (MCMs) having bonding wires.
It is another feature of the invention to provide methods of fabricating these thin and reliable MCMs having bonding wires.
According to an aspect of the invention, a multi-chip module is provided. The multi-chip module comprises a substrate and a plurality of chips sequentially stacked on the substrate. The substrate includes a plurality of interconnections formed on a top surface thereof. The plurality of chips comprises a lowest chip and at least one top chip. Each of the chips has a plurality of pads formed on the periphery or edges of a front surface thereof. In addition, the top chip stacked above the bottom chip each have an insulating tape, which is attached to its backside. An insulator is interposed between the chips. The insulator preferably has a smaller width than the chips to expose the pads. The pads of the lowest chip are electrically connected to a first group of interconnections on the substrate through a first group of bonding wires. Similarly, the pads of additional chips above the lowest chip are electrically connected to additional groups of interconnections through respective groups of bonding wires.
The top chip may have a greater planar area than a lower chip located under it. Alternatively, all the chips may have substantially the same dimensions, and have their edges aligned.
In an embodiment of the invention, the multi-chip module comprises a substrate with a bottom and top chip sequentially stacked on the substrate. The substrate includes first and second groups of interconnections on a top surface thereof. Each of the chips has pads formed on edges of a front surface thereof. In addition, the top chip includes an insulating tape, which is attached to its backside. An insulator is interposed between the top chip and the bottom chip. The insulator preferably has a smaller width than the chips, thereby leaving the pads of the bottom chip exposed. The pads of the bottom chip are electrically connected to the first group of interconnections through a first group of bonding wires. Similarly, the pads of the top chip are electrically connected to the second group of interconnections through a second group of bonding wires.
The substrate may be a lead frame or a printed circuit board. The top chip can have the same dimension as the bottom chip, or, alternatively, the top chip may have a greater planar area than the bottom chip.
According to another aspect of the invention, a fabrication method of a multi-chip module is provided. The method comprises preparing a substrate and mounting a bottom chip on the substrate. The substrate includes first and second groups of interconnections formed on a top surface thereof. The bottom chip is also mounted on the top surface. The bottom chip pads, which are formed on the edges its front surface, are connected through a first group of bonding wires to the first group of interconnections on the substrate. An insulator is then formed on the upper surface of the bottom chip in a manner to leave the pads on its edges exposed. Next, a top chip is mounted on the insulator. The top chip has an insulating tape attached to its backside. Thus, the insulating film may be in contact with the insulator. The top chip also has pads formed on edges its front surface, which are connected through a second group of bonding wires to the second group of interconnections on the substrate.
Conductive bumps may be additionally formed on the pads of the bottom chip prior to connection with the first group of bonding wires. In this case, the first group of bonding wires are connected to the pads through the bumps and are preferably formed using a bump reverse bonding technique.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing embodiments of the present invention in detail with reference to the attached drawings, in which:
FIG. 1 is a cross-sectional view illustrating a conventional multi-chip module;
FIG. 2 is a cross-sectional view illustrating another conventional multi-chip module;
FIG. 3 is a cross-sectional view illustrating a multi-chip module according to an embodiment of the present invention; and
FIGS. 4 to 6 are cross-sectional views for describing a method of fabricating a multi-chip module according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the present invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout the specification.
FIG. 3 is a cross-sectional view illustrating a multi-chip module according to an embodiment of the present invention.
Referring to FIG. 3, a bottom chip 55 and a top chip 63 are sequentially stacked on a substrate 51. The substrate 51 includes a plurality of interconnections formed on a surface of the substrate 51. The substrate 51 may be, for example, a lead frame or a printed circuit board. The interconnections are composed of a first group of interconnections 51 a and a second group of interconnections 51 b. The bottom chip 55 has bonding pads 57 formed on the periphery or edges of its front surface. Also, the top chip 63 has bonding pads 65 formed on the edges of its front surface. In particular, the top chip 63 has a chip substrate 63 a and an insulating film 63 b attached to its backside surface. In addition, the insulating film 63 b can cover the backside surface of the chip substrate 63 a. The insulating film 63 b has a tape-shaped configuration or a sheet-shaped configuration.
An adhesive 53 may be interposed between the bottom chip 55 and the substrate 51. Thus, the bottom chip 55 is fixed to the substrate 51 by the adhesive 53. Also, an insulator 61 is interposed between the bottom chip 55 and the top chip 63. The insulator 61 may have a smaller width than the chips 55 and 63 so that the pads 57 of the bottom chip 55 are exposed. The top chip 63 may have the same dimensions as the bottom chip 55 and fully cover the bottom chip 55, as shown in FIG. 3. Alternatively, the top chip 63 may have a greater planar area than the bottom chip 55. In other words, the top chip 63 may be wider and/or longer than the bottom chip 55.
The pads 57 of the bottom chip 55 are electrically connected to the first group of interconnections 51 a through a first group of bonding wires 59. In this case, the chip substrate 63 a of the top chip 63 is not in direct contact with the first group of bonding wires 59 because of the presence of the insulating film 63 b, even though the insulator 61 is very thin. Therefore, the total height of the stacked chips 55 and 63 can be reduced as compared to the conventional MCMs shown in FIGS. 1 and 2.
Further, conductive bumps 57 a may be additionally formed on the pads 57 of the bottom chip 55. In this case, the first group of bonding wires 59 are electrically connected to the pads 57 through the bumps 57 a and are preferably formed using a bump reverse bonding technique, which is well known in the art. If the first group of bonding wires 59 are formed using the bump reverse bonding technique, the height from a top surface of the pads 57 to the highest portion of the bonding wires 59 can be remarkably reduced. This allows the insulator 61 to become thinner without any contact between the bonding wires 59 and the insulating film 63 b. Accordingly, reliability of a multi-chip module can be improved.
The pads 65 of the top chip 63 are electrically connected to the second group of interconnections 51 b through a second group of bonding wires 67. Bumps 65 a may be additionally stacked on the pads 65 of the top chip 63. In this case, the second group of bonding wires 67 are electrically connected to the pads 65 through the bumps 65 a. The second group of bonding wires 67 may be formed using the above-mentioned bump reverse bonding technique. The stacked chips 55 and 63 as well as the bonding wires 59 and 67 are sealed with an epoxy molding compound (EMC) 69.
A method of fabricating a multi-chip module according to an embodiment of the present invention will now be described with reference to FIGS. 4 to 6.
Referring to FIG. 4, a substrate 51 is first provided that has a plurality of interconnections formed on a surface thereof. Also, the interconnections include a first group of interconnections 51 a and a second group of interconnections 51 b. A bottom chip 55 is mounted on the substrate 51. Adhesive material 53 may be additionally put on the surface of the substrate 51 before mounting the bottom chip 55 on the substrate 51. Accordingly, the bottom chip 55 can be fixed to the substrate 51 by the adhesive 53. The bottom chip 55 has bonding pads 57 formed on the edges of its front surface (top surface).
Referring to FIG. 5, a first group of bonding wires 59 are formed to connect the pads 57 a to the first group of interconnections 51 a. The bonding wires 59 may be formed of gold wires. Conductive bumps 57 a may be additionally formed on the pads 57 before forming the first group of bonding wires 59. In this case, the first bonding wires 59 are electrically connected to the pads 57 through the bumps 57 a and are preferably formed using a bump reverse bonding technique. If the first group of bonding wires 59 are formed using the bump reverse bonding technique, the distance from a top surface of the pads 57 to the highest portion of the bonding wires 59 can be significantly reduced. An insulator 61 is then formed on the bottom chip 55. Preferably, the insulator 61 has a narrower width than the bottom chip, thereby still exposing or uncovering the pads 57 and the bonding wires 59. In other words, the insulator 61 can be preferably formed to fit on a predetermined region on the bottom chip where it will be surrounded by the pads 57.
Referring to FIG. 6, a top chip 63 is mounted on the insulator 61. The top chip 63 includes a chip substrate 63 a and a thin insulating film 63 b attached to its backside surface (bottom surface). Thus, the insulating film 63 b can cover the entire backside surface of the chip substrate 63 a. Accordingly, the insulating film 63 b can be in contact with the insulator 61. The top chip also has bonding pads 65 formed on edges of its front surface (top surface) of the chip substrate 63 a.
The top chip 63 may have the same dimensions as the bottom chip 55 and may be mounted to fully cover the bottom chip 55, as shown in FIG. 6. Alternatively, the top chip 63 may have a greater planar area than the bottom chip 55. In other words, the top chip 63 may be wider and/or longer than the bottom chip 55. In any case, the edges of the top chip 63 are located above the ends of the first group of bonding wires 59 where they are connected to the pads 57 of the bottom chip. Even if the bonding wires are touching the top chip 63, the chip substrate 63 a is not in direct contact with the bonding wires 59 because of the presence of the insulating film 63 b. This results in allowing the thickness of the insulator 61 to be drastically reduced. Accordingly, the total height of the stacked chips 55 and 63 are greatly reduced as compared to the conventional multi-chip module shown in FIGS. 1 and 2.
Further, in the event that the first group of bonding wires 59 are formed using the bump reverse bonding technique as described above, the insulating film 63 b can be altogether prevented from being in contact with the bonding wires 59. In other words, the thickness of the insulator 61 can be even further reduced without any contact between the bonding wires 59 and the insulating film 63 b. As a result, a highly reliable and thin multi-chip module is realizable.
Subsequently, a second group of bonding wires 67 are formed to connect the pads 65 of the top chip 63 to the second group of interconnections 51 b. The second group of bonding wires can be formed using a conventional wire bonding technique (See the dashed line 67 a in FIG. 6). Alternatively, bumps 65 a may be formed on the pads 65 prior to formation of the second group of bonding wires 67. In this case, the second group of bonding wires 67 (the solid line in FIG. 6) may be formed using the bump reverse bonding technique and electrically connect to the pads 65 through the bumps 65 a.
Though not shown in the drawing of FIG. 6, epoxy molding compound (refer to 69 of FIG. 3) is then formed to seal the stacked chips 55 and 63 as well as the bonding wires 59 and 67 (or 67 a).
According to the embodiments described above, the thickness of an insulator interposed between stacked chips can be reduced by employing a thin insulating film that covers the backside surface of the chip substrate of the top chip. Therefore, a reliable and thin multi-chip module can be realized.

Claims

1. A method of fabricating a multi-chip module, the method comprising:

preparing a substrate having first and second groups of interconnections formed on a top surface thereof;

mounting a bottom chip on the top surface, the bottom chip having pads formed thereon;

forming a first group of bonding wires that connect the pads of the bottom chip to the first group of interconnections;

attaching an insulator on an upper surface of the bottom chip, the insulator being surrounded by the pads of the bottom chip; and

mounting a top chip on the insulator, the top chip including a insulating tape attached to a backside thereof, the top chip having pads formed thereon.

2. The method of claim 1 further comprising:

forming a second group of bonding wires that connect the pads of the top chip to the second group of interconnections.

3. The method of claim 1 further comprises providing an adhesive on the substrate before mounting the bottom chip on the substrate, the bottom chip being fixed to the substrate by the adhesive.

4. The method of claim 1 further comprises forming bumps on the pads of the bottom chip before forming the first group of bonding wires, the first group of bonding wires being connected to the bumps on the pads of the bottom chip.

5. The method of claim 4, wherein the first group of bonding wires are formed using a bump reverse bonding technique.

6. The method of claim 1 further comprises forming bumps on the pads of the top chip before forming the second group of bonding wires, the second group of bonding wires being connected to the bumps on the pads of the top chip.

7. The method of claim 1 further comprises forming an epoxy molding compound that encapsulates the bottom chip, the top chip and the bonding wires.

8. The method of claim 1, wherein the pads are formed on edges of the top surfaces of the chips.

9. The method of claim 1, wherein the insulator is attached on a central region of the bottom chip, thereby having a width smaller than the bottom chip and the top chip.