JPH10163263A - Mounting structure for multichip module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a multichip module having a plurality of chip components mounted from sinking due to its own weight caused by the crush of a BGA solder ball, and to prevent a chip component from coming into contact with the wiring pattern of a mother board and short-circuiting, on the occasion of mounting the multichip module on the mother board using BGA solder balls. SOLUTION: Under the condition of mounting a multichip module MCM having chip components 2, 3 mounted on a board 1, on a mother board 5 by BGA solder balls 4, the chip component 3 is in contact with a mounting pad 6b as a dummy pad formed on the mother board 5. It becomes unnecessary to provide a clearance between the chip component 3 and the mother board 5, and it becomes possible to reduce the height of the mounting construction and to prevent the short circuit of the chip component 3 with wirings 6 on the mother board 5. it becomes unnecessary to increase the diameter of the BGA solder balls 4 more than needed to secure a clearance, and to use BGA solder balls containing metal cores, so it becomes possible to realize the size reduction of the mounting construction and the facilitation of constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-chip module in which chip components are mounted on a substrate, and more particularly, to a multi-chip module of this type which is mounted on a BGA (ball grid grid).
Array: The mounting structure of a multi-chip module for mounting on a motherboard using Ball Grid Array.

[0002]

2. Description of the Related Art Conventionally, as a multi-chip module of this type, for example, as described in Japanese Patent Application Laid-Open No. 6-163634, a solder bump is formed on a bare chip of a semiconductor element, and this solder bump is formed on a substrate. There has been proposed a technique for mounting a bare chip by connecting to a pad of a provided wiring pattern. Also, chip components such as capacitors and resistors are mounted by a solder reflow method or the like. In order to eliminate the need for cleaning the flux at this time, Ma
te'96 (2nd Symposium “Microjoining and Assemb
The technology proposed by Shimada et al., entitled "Leadless Bear Chip Mounting Technology and Application to MCM-L", pp.193-196 of "ly Technology in Electronics" is there. As a technique for mounting such a multichip module on a motherboard such as a printed wiring board, for example, a configuration shown in FIG. 4 has been proposed.

FIG. 4 is a view showing an example of the multi-chip module MCM in which an electrode pad 6a is formed on a surface of a mother board 5 by a part of a wiring 6, and a multi-chip module MCM to be mounted is mounted on a substrate 1 such as a bare chip 2, a resistor and a capacitor. A chip component 3 is mounted, a BGA solder ball 4 is formed on the surface of the substrate 1, and a BGA solder ball 4 is formed by a face-down method with the surface of the multi-chip module MCM facing the motherboard 5.
The structure is such that the solder balls 4 are connected to the electrode pads 6a. Here, when the multi-chip module MCM is mounted on the motherboard 5, the chip components 3 mounted on the board 1 do not hinder the mounting by the BGA solder balls 4, or the chip components 3 are mounted on the motherboard 5. The BGA solder balls 4 are used to prevent an electrical short circuit from being caused by contacting other parts of the wiring 6.
Is formed so that its diameter is larger than the thickness of the chip component 3.

[0004]

In such a conventional mounting structure of a multi-chip module, the diameter of the BGA solder ball 4 is formed larger than the thickness of the chip component 3; In consideration of sinking due to melting of the solder ball 4, the diameter of the BGA solder ball 4 is formed to be large with some margin, and the plane size of the electrode pad 6a of the motherboard 5 is correspondingly formed to be large. Thereby, the multi-chip module MC
When mounting M on motherboard 5, BGA solder balls 4
Is melted, the chip component 3 is connected to the wiring 6 of the motherboard 5.
Can be prevented from being short-circuited due to contact with the wire. In this case, applying the technology described in the above-mentioned document “Mate'96”, a solder ball having a metal core inside is used as a BGA solder ball. A structure is used in which the core functions as a pillar to prevent chip components on the multichip module facing the motherboard from contacting the motherboard.

However, in the technique of increasing the diameter of a BGA solder ball, it is necessary to increase the area occupied by one BGA solder ball and to increase the distance between adjacent BGA solder balls. When the number of external terminals is increased in accordance with the sophistication of the module, the pitch of the external terminals is narrowed, which is a design constraint in miniaturizing the multi-chip module substrate.
In the technology using solder balls having a metal core,
Compared to a ball containing only solder, there is a problem that the cost of the ball is increased and the connection gas yield and reliability are not stable due to the residual gas during the ball production. By the way, both technologies assume that the chip components on the multi-chip module do not contact the motherboard, so the height of the solder ball is not only the height of the chip components but also the contact of the chip components with the motherboard. This is a value obtained by adding a clearance to be ensured, and as a result, there is a problem that the height when the multi-chip module is mounted on the motherboard cannot be kept low.

SUMMARY OF THE INVENTION An object of the present invention is to provide a mounting structure of a multi-chip module and a multi-chip module capable of increasing the mounting density and improving the reliability without reducing the degree of freedom in designing each substrate. Is to provide.

[0007]

The present invention provides a multi-chip module having a plurality of chip components mounted on a substrate.
In a mounting structure that is mounted in a state where it is electrically connected to the wiring pattern provided on the motherboard by BGA solder balls, a part of the wiring pattern is formed on the mounting surface of the motherboard at a position corresponding to the chip component mounted on the multi-chip module The mounting pad is provided. In this case, the BGA solder balls of the multi-chip module are heated and melted when the multi-chip module is mounted on the motherboard, and the chip components contact the mounting pads on the motherboard in a state where the multi-chip module sinks by its own weight. It is configured to be in a state.

In the present invention, the mounting pad is configured as a dummy pad that is not electrically connected to the wiring pattern. Alternatively, the mounting pad is configured as a connection pad that is electrically connected to the wiring pattern, and is configured to be connected to the abutted chip component using an electrically conductive material. Further, the mounting pad may be configured as a die pad integrally formed with a thermal via formed through the motherboard, and the contacted chip components may be connected with at least a thermally conductive material.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of the first embodiment of the present invention. In FIG. 1, required wirings are formed on the front and back surfaces of a multi-chip module substrate 1 (hereinafter, module substrate) formed of ceramics or the like, and pads of the wirings are used to form semiconductor elements. A bare chip 2 is mounted on the module substrate 1 by a flip chip method. Chip components 3 such as resistors and capacitors are mounted on the substrate 1 by a solder reflow method or the like. A BGA solder ball 4 is formed on a pad formed by the wiring in a peripheral portion on the back surface of the module substrate 1, whereby the multi-chip module M
A CM has been formed.

On the other hand, the multi-chip module MCM
Is mounted on the motherboard printed wiring board 5 (hereinafter, referred to as
In the motherboard, wirings 6 of a required pattern are formed on the surface of the insulating substrate, and a part of the wirings 6 is formed as electrode pads 6a corresponding to the BGA solder balls 4 of the multi-chip module MCM. . Further, on the surface of the motherboard 5, a portion corresponding to the chip component on the side facing the motherboard among the chip components 3 mounted on the module substrate 1 of the multi-chip module MCM corresponds to the chip component. A mounting pad 6b having a planar dimension is formed by utilizing a part of the wiring 6. In this embodiment, the mounting pad 6b
Are configured as dummy pads that are not electrically connected to the electrode pads 6a.

The multi-chip module MC
By connecting the M BGA solder balls 4 to the electrode pads 6a of the motherboard 5, the multi-chip module MC
M is mounted, but in this case, BGA
While the solder balls 4 are melted to enable connection to the electrode pads 6a, the melting causes sinking in the multi-chip module MCM. Due to this sinking, the chip component 3 of the multi-chip module MCM comes into contact with the dummy pad 6b of the motherboard 5, and the sinking of the multi-chip module MCM is stopped at this position, and the mounting is completed. At this time, the chip component 3 is in contact with the dummy pad 6b of the motherboard 5, but since the dummy pad 6b does not constitute any electric circuit, the chip component 3 is electrically connected to the other portion of the wiring 6 of the motherboard 5. There is no short circuit. Accordingly, it is not necessary to secure a clearance between the chip component 2 and the motherboard 5, and the height of the multi-chip module mounting structure can be reduced, and the thickness can be reduced.

FIG. 2 is a sectional view showing a second embodiment of the present invention. In the figure, parts equivalent to those of the first embodiment are denoted by the same reference numerals. In this embodiment, the first
In this embodiment, the mounting pad formed as a dummy pad is positively configured as a connection pad 6c that forms a required circuit with another wiring pattern.
That is, the mounting pad 6c is formed as a part of the wiring 6 formed on the motherboard 5, and the mounting pad 6c is formed.
Before the multichip module MCM is mounted, a connection material 7 having the same melting point as the BGA solder balls 4 is supplied by coating or plating or the like.

Therefore, the multi-chip module MC
When M is mounted on the motherboard 5 in the same manner as in the first embodiment, the connection material 7 on the mounting pads 6c is melted simultaneously with the BGA solder balls 4 by heating at that time. And the first
When the multi-chip module MCM sinks under its own weight and the chip component 3 of the multi-chip module comes into contact with the mounting pad 6c as in the embodiment of FIG. 7 and then cooled, whereby the chip component 3 is connected to the mounting pad 6c. Thus, the chip component 3 can be electrically connected to the wiring 6 of the motherboard 5 via the mounting pad 6c, and a required circuit configuration can be realized.

FIG. 3 is a sectional view showing a third embodiment of the present invention. Also in the figure, parts equivalent to those in the first embodiment are denoted by the same reference numerals. In this embodiment, the mounting pad 6d is configured as a heat sink. That is, a thermal via hole 8 penetrating in the thickness direction of the substrate is formed on the motherboard 5, and a die pad 6 d is formed at a position corresponding to the thermal via hole 8 as a mounting pad using a part of the wiring 6. . And
A die attach resin 9 having thermal conductivity for obtaining at least thermal connection is supplied on the die pad 6d in advance.

Therefore, the multi-chip module MC
When M is mounted on the motherboard 5 in the same manner as in the first embodiment, the heating at that time melts the die attach resin 9 on the die pad 6d simultaneously with the BGA solder balls 4 and sinks due to the weight of the multi-chip module MCM. The surface of the chip component, in this case, the bare chip 2 of the semiconductor element is brought into contact with the die attach resin 9. And
After cooling, the bare chip 2 is connected to the die pad 6 d by the die attach resin 9 by additional heat according to the characteristics of the die attach resin 9. Thereby, the heat generated in the bare chip 2 is thermally and electrically connected to the thermal via hole 8 via the die pad 6d, and the heat generated during the operation of the bare chip 3 is radiated to the back side of the motherboard 5 through the thermal via hole 8. In addition, a heat dissipation structure can be obtained. Note that if the die pad 6d is connected to a predetermined potential, for example, a ground potential via the wiring 6, and a resin having thermal conductivity and electrical conductivity is used as the die attach resin 9, the above-described thermal connection can be achieved. At the same time, the bare chip can be electrically grounded.

[0016]

As described above, according to the mounting structure of the multi-chip module of the present invention, when the multi-chip module having the BGA solder balls as the external terminals is mounted on the motherboard, the chip components on the multi-chip module are mounted. Is in contact with the mounting pads on the motherboard, so that the height of the mounting structure can be reduced, the BGA solder ball does not need to be made larger than necessary, and the metal core is not included. Therefore, it is not necessary to use BGA solder balls, and the mounting structure can be reduced in size and the configuration can be simplified. In addition, by configuring the pad to which the chip component abuts as a connection pad and a die pad for a thermal via hole, electrical connection and heat dissipation measures to the chip component can be achieved, thereby simplifying the electrical wiring structure, or dissipating heat. The effect of realizing a mounting structure having excellent characteristics is also obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a mounting structure of a multichip module according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a mounting structure of a multichip module according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a mounting structure of a multichip module according to a third embodiment of the present invention.

FIG. 4 is a sectional view showing an example of a mounting structure of a conventional multi-chip module.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Multi-chip module board 2 Bare chip 3 Chip component 4 BGA solder ball 5 Motherboard 6 Wiring 6a Mounting pad (Dummy pad) 6b Mounting pad (Connecting pad) 6c Mounting pad (Die pad) 7 Connection material 8 Thermal via hole 9 Die attach resin

Claims (5)

[Claims] In a structure for mounting a multi-chip module having a plurality of chip components mounted on a substrate in a state where the multi-chip module is electrically connected to a wiring pattern provided on a mother board by BGA solder balls, a mounting surface of the mother board is provided. And a mounting pad formed by a part of the wiring pattern at a position corresponding to a chip component mounted on the multi-chip module. 2. The BGA solder balls of the multi-chip module are heated and melted when the multi-chip module is mounted on a motherboard, and the chip components are mounted on the motherboard in a state where the multi-chip module sinks by its own weight. The mounting structure of the multi-chip module according to claim 1, wherein the mounting structure is in a state of being in contact with the pad. 3. The mounting structure of a multi-chip module according to claim 2, wherein the mounting pad is a dummy pad that is not electrically connected to the wiring pattern. 4. The multi-chip module according to claim 2, wherein the mounting pad is configured as a connection pad electrically connected to the wiring pattern, and is connected to the abutted chip component by an electrically conductive material. Mounting structure. 5. The mounting pad according to claim 2, wherein the mounting pad is formed as a die pad integrally formed with a thermal via formed through the motherboard, and the abutted chip components are connected by at least a thermally conductive material. 4 is a mounting structure of the multichip module.