JPH11112173A - Mounting structure member of electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a mounting structure member and a connecting method of an electronic apparatus of high reliability in which thermal and mechanical stress of a semiconductor package is relieved, and heat is effectively dissipated with thermal conduction system. SOLUTION: A mother board 10A is arranged above a cabinet of an electronic apparatus to be mounted and connected with an inner circuit of a printed wiring board 1A by using lead wires 8. The printed wiring board 1A is so wholly turned over that flip chips 3 are positioned below the printed wiring board 1A. The flip chips 3 are directly bonded to a heat dissipating plate 12 of high thermal conductivity which is collectively built in an integrity with a metal plate 14 below the cabinet, interposing thermally conductive sheets 11 stuck on the backside of the flip chips 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting structure of an electronic device, and more particularly to a mounting structure of an electronic device such as a portable electronic device such as a sub-notebook personal computer using a semiconductor integrated circuit stored in a flip-chip type semiconductor package. .

[Detailed description of the invention]

2. Description of the Related Art In recent technical trends of electronic devices, particularly in portable electronic devices represented by sub-notebook personal computers, there is an active movement to mount a high-speed and high-performance microprocessor in an ultra-small and thin size casing. There is a demand for a mounting structure that is more cost effective.

To meet these demands, a printed wiring board surface has a fine thin-film multilayer wiring layer made of an insulator and a conductor having a low dielectric constant, and a plurality of flip chips including a microprocessor are provided on the thin-film multilayer wiring layer. 2. Description of the Related Art A semiconductor package technology for mounting a semiconductor integrated circuit (hereinafter, flip chip) stored in a semiconductor package has been developed.

Referring to FIG. 6, which is a cross-sectional view of a mounting structure of a conventional electronic device of this type, the mounting structure of the conventional electronic device has a wiring pad on a back surface and a thin-film multilayer wiring layer 2 on a front surface. A plurality of flip chips 3 mounted on the thin-film multilayer wiring layer 2 via metal bumps 4, a mother board 10 having wiring pads on the front and back surfaces, and a printed wiring board 1. A metal bump 20 for joining a wiring pad on the back surface side of the motherboard 10 to a wiring pad on the front surface side of the motherboard 10;
The heat conductive sheet 11 stuck on the back side, the aluminum plate 21 in the upper part of the housing, and the high heat conductive heat radiating plate 12 bonded to the aluminum plate 21 and stuck on the top of the heat conductive sheet 11 Prepare.

Next, the operation of a conventional mounting structure for electronic equipment will be described with reference to FIG. 6. First, as a method of connecting a semiconductor package to a motherboard 10, wiring pads on the back side of the printed wiring board 1 are used. And a wiring pad on the front side of the motherboard 10 via a metal bump 20 to join a well-known BGA (Ball Grid Array).
y) method is adopted.

Further, in a recent mounting technique in which a plurality of flip chips 3 are mounted at a high density, there is a problem of heat due to an increase in heat generation density per unit area. As shown in the figure, a heat conductive sheet 11 is stuck on the back side of the flip chip 3, and an aluminum plate 21 at the top of the housing is further placed on the heat conductive sheet 11.
And a heat-dissipating plate 12 having a high thermal conductivity joined to the heat-dissipating plate.

Further, although not shown, examples of mounting a radiating fin, a microfan, a heat pipe, or the like directly bonded to the flip chip back surface in addition to the illustrated radiating plate 12 have been reported as the radiating structure. .

The above-mentioned conventional electronic device mounting structure has a structural problem that stress concentrates on the metal bumps 4 joining the thin-film multilayer wiring layer 2 and the flip chip 3.

As described above, the electrode pads on the element surface side of the flip chip 3 are rigidly connected to the wiring pads of the thin-film multilayer wiring layer 2 by the metal bumps 4, and the connection pads on the lower surface of the printed wiring board 1 are connected to the metal bumps. The connection pad 20 is rigidly connected to the connection pads of the motherboard 10.

On the other hand, since the heat radiating plate 12 is rigidly joined to the back surface of the flip chip 3, in this structure, thermal and mechanical stress concentrates on the joint of the metal bump 4, and excessive stress is applied. Is easily applied.

Further, since the structure is such that heat is diffused to the aluminum plate 21 at the upper part of the housing, the keyboard surface temperature rises because the keyboard 15 is provided on the aluminum plate at the upper part of the housing as shown in the figure.

[0012]

In the above-mentioned conventional electronic device mounting structure, the electrode pads on the element surface side of the flip chip are rigidly joined to the wiring pads of the thin-film multilayer wiring layer by metal bumps, and the printed wiring is further provided. The connection pads on the lower surface of the board are bonded to the connection pads of the motherboard and rigid by metal bumps, and the heat sink is rigidly bonded to the back side of the flip chip. There is a drawback that stress concentrates on the metal bump to be joined, which causes a reduction in reliability.

In addition, since the structure is such that heat is diffused to the aluminum plate on the upper part of the housing, there is a disadvantage that the surface temperature of the keyboard provided on the aluminum plate rises.

An object of the present invention is to solve the above-mentioned drawbacks and to be applicable to an ultra-thin size such as a portable electronic device. An object of the present invention is to provide a mounting structure of an electronic device in which a cause of deterioration is eliminated.

[0015]

A mounting structure for an electronic device according to the present invention is bonded via a metal bump to a thin-film multilayer wiring layer composed of an insulator and a conductor having a low dielectric constant formed on the surface as an internal circuit. A printed wiring board mounted with a semiconductor integrated circuit (hereinafter, flip chip) stored in a plurality of lip-chip type semiconductor packages; a motherboard for interfacing the internal circuit and the external circuit of the printed wiring board; In a mounting structure of an electronic device provided with a radiator plate for radiating heat generated by a circuit, the motherboard is disposed above a housing of the electronic device to be mounted, and the internal circuit of the printed wiring board is mechanically flexible. Electrically connected, flip the flip-chip together with the printed circuit board so that the flip chip is below the printed circuit board. It is characterized in that directly joined to the heat radiating plate of the integrated high thermal conductivity and the housing bottom of the metal plate via the pasted thermally conductive sheet in a flip-chip backside.

[0016]

Next, an embodiment of the present invention will be described with reference to FIG.
Referring to FIG. 1 also shown in a cross-sectional view with common reference characters / numerals attached to the same components as those of FIG. 1, the mounting structure of the electronic apparatus of the present embodiment shown in FIG. There is a metal bump 4 on the thin-film multilayer wiring layer 2
, A plurality of flip chips 3 mounted by bonding via a heat conductive sheet 11, a heat conductive sheet 11 bonded to the back side of the flip chip 3, and a heat conductive plate bonded to a lower portion of the heat conductive sheet 11 12 and a plurality of external input / output pins 5 for wiring connection,
A printed wiring board 1A having a through-hole 16 into which a thin film multilayer wiring layer 2 common to the conventional one is formed, and a lead wire 8 fitted to each of the input / output pins 5 for electrical / mechanical connection U-shaped connection fitting 6 for performing
A socket 7 having a connection terminal 9 for making an electrical connection between the lead wire 8 and the motherboard 10A, a motherboard 10A having a wiring through hole arranged at the top of the housing and having the connection terminal 9 fitted therein, And an aluminum plate 14 at the lower part of the housing to which the heat sink 12 is joined.

Next, the functional operation of the present embodiment will be described with reference to FIG. 1. First, in order to efficiently radiate the heat generated from the flip chip 3, there is provided a mounting plate disposed at the lowermost position with the heat radiating plate 12 as a base. Adopted structure. As shown in the figure, the semiconductor package is turned upside down so that the back side of the flip chip 3 is on the lower side, and the external input / output pins 5 of the semiconductor package are connected by means of stress relaxation, which will be described later. Since a large heat radiating plate 12 made of a copper plate having a large heat transfer area, a high thermal conductivity, and a low cost can be joined to the rear surface side, a heat radiating ratio of 80% or more is radiated as described below. This makes it possible to realize a mounting structure for performing the operation.

Regarding the determination of the heat radiating structure, in the above-described conventional mounting structure, several types of heat radiating plates having different materials such as aluminum and copper and sizes related to the heat transfer area are joined to the back surface of the flip chip 3. As a result, it became clear that, of the total heat generation, heat having a heat radiation ratio of about 40% to 80% or more passed through the heat radiating plate. In the other heat dissipation paths, the heat dissipation rate from the metal bumps 4 to the printed wiring board 1 was about 15%, and the heat dissipation rate from the side of the flip chip 3 to the surrounding air was about 5%. Therefore, it has been found that an overwhelming heat radiation effect can be obtained by optimizing the mounting structure that radiates heat from the back surface of the flip chip 3.

Further, in the mounting structure based on the motherboard 10 as in the conventional mounting structure, when the large and inevitably heavy heat sink 12 is mounted as in the present embodiment, the metal bumps of the flip chip 3 are mounted. A load due to gravity is applied to the joint of No. 4, which causes a reduction in reliability. Therefore, by disposing the heat radiating plate 12 at the lowermost portion as in the present embodiment, such a factor of reducing reliability is eliminated.

In addition, the structure in which heat is dissipated to the aluminum plate at the bottom of the housing can suppress a rise in keyboard surface temperature.

Next, in order to alleviate thermal and mechanical stress, a method of mounting the semiconductor package (flip chip 3) upside down and an electrical connection method between the printed wiring board 1 and the motherboard 10A using lead wires are employed. .

First, in the former method of mounting the semiconductor package upside down, the flip chip 3 is turned upside down and connected to the lower heat sink, so that the junction of the flip chip 3 due to the gravity of the heat sink as in the prior art is used. There is no load on the system.

Next, the latter connection method using a lead wire is different from the conventional BGA method using a metal bump 20 in that a connection method is provided with a mechanical degree of freedom using an extremely thin lead wire 8. As a result, excessive stress on the metal bumps 4 is reduced, and the reliability is improved by several steps as compared with the conventional structure.

Next, the structure of the external input / output pins 5 connected to the lower surface of the printed wiring board 1 and the connection method thereof are schematically illustrated in a state where the external input / output pins 5 are separated from the printed wiring board 1 and a state where the external input / output pins 5 are joined. 2A and 2B shown in cross-sectional views
Referring to FIG. 3, the external input / output pin 5 is
And an insertion portion 52 for electrically connecting to an external input / output through hole 16 provided in the printed wiring board 1.
And a stopper 51 for adjusting the insertion position.

In the example of this embodiment, the printed wiring board 1
Size is 50 × 50mm, number of external input / output pins is about 30
The pin 0 and the external input / output pin arrangement are 2.54 mm grid area arrangement. Recently, in such a package specification, connection by the BGA method described in the related art is often used. However, in the pin insertion method of the present embodiment, the plating finish dimension of the through hole 16 in the printed wiring board 1 is reduced. The external input / output pin insertion part 52 is finished to be larger than the outer diameter by about 50 microns, and all the pins are collectively joined by mechanical pressing as shown in the figure, and at the same time, the position is adjusted by the stopper 51. Thereafter, a conductive resin 53 is filled in order to improve the flatness of the through hole 16 and the reliability of connection with the thin-film multilayer wiring layer 2.

From the above, it is not necessary to use metal bump formation and connection-related devices as in the conventional BGA method.
It can be said that it is a very superior mounting method in terms of cost, for example, because it is possible to easily perform the batch joining, so that it can be assembled in a short time.

Next, referring to FIG. 3 which is an enlarged cross-sectional view schematically showing a state in which the inverted semiconductor package (flip chip 3) is connected to the motherboard 10A, first, at the top of the figure. The configuration of the socket 7 connected to the through hole 40 in the motherboard 10A through the connection terminal 9 will be described. The socket 7 includes a connection terminal 9, a U-shaped connection fitting 6, a connection terminal and a U-shaped connection. It is composed of a lead wire 8 for electrically connecting a connection fitting, and a plastic case 71.

The case 71 has a groove 72 for fixing the connection terminal and a groove 73 for temporarily storing the lead wire 8.
And a groove 74 for temporarily storing the U-shaped connection fitting 6.
Are provided.

As described above, the connection terminal 9 uses a relatively wide and general insertion type metal alloy pin having an arrangement pitch of 2.54 mm. In addition, it has a socket fixing portion 91 for fixing to the groove 72 of the case. In order to increase the mounting density of the motherboard 10, it is effective to use surface-mount type connection terminals.

Next, FIG. 4 shows the structure of the U-shaped connection fitting 6.
Referring to (A), this U-shaped connection fitting 6 has a thin plate L
The L-shaped plate end portion 60 is reversely bent so as to be larger than the outer diameter of the spherical portion 50 at the end of the external input / output pin 5, and four L-shaped plates are formed so as to form a split groove 61. By incorporating the letter-shaped thin plate into the base plate 62, the spherical portion 50 of the external input / output pin 5 can be wrapped so as to be surely electrically connected using the spring effect.

Next, referring to FIG. 4B, which shows a method of connecting and assembling a lead wire 8 for electrically connecting the connection terminal 9 and the U-shaped fitting 6, the lead wire 8 can be used. It is desirable that the wire diameter is as short as possible and the wire diameter is extremely thin. The lead wire 8 is connected by caulking and fixing the lead wire connection portion 92 of the connection terminal 9 and also caulking and fixing the lead wire connection portion 63 of one U-shaped connection fitting 6, and then connecting the connection terminal 9 to the socket. 7
The lead wire 8 is housed in the groove 73, and the U-shaped connection metal fitting 6 is housed so that the U-shaped connection metal fitting 6 does not fall when the flip chip 3 is turned upside down.

Flip chip 3 to motherboard 10A
After the flip chip 3 is turned upside down so that the back side of the flip chip 3 is on the lower side, the spherical portion 30 at the tip of the external input / output pin 5 is aligned with the U-shaped connection metal fitting 6 and is collectively pressed by mechanical pressing. Join and assemble.

Next, the final connection state between the semiconductor package (flip chip 3) connected to the motherboard 10A and the heat radiating plate 12 is enlarged and schematically shown in a sectional view in FIG.
Referring to FIG. 3, first, in the state shown in FIG.
The U-shaped connection fitting 6 is detached from the socket 7 at the same time as the entire semiconductor package is moved downward from this state as shown in the figure. Further, the temporarily accommodated lead wire 8 also extends downward by an arbitrary length, and is joined where the back surface of the flip chip 3 comes into contact with the surface of the heat sink 12. It should be noted that it is very important for the lead wires 8 in this connected state to have a mechanical degree of freedom as shown in FIG.

[0034]

As described above, in the electronic device mounting structure of the present invention, the motherboard is arranged on the upper part of the housing of the electronic device to be mounted so that the internal circuit of the printed wiring board is mechanically flexible. Electrically connected, flip the flip-chip together with the printed circuit board so that the flip chip is below the printed circuit board, and directly connect the flip chip to a high heat conductive heat sink integrated with the metal plate at the bottom of the housing Therefore, in order to meet the demand for ultra-thin and small-sized portable devices such as sub-notebook personal computers, it is possible to solve the problem of heat and stress, and to expect low cost, highly reliable and excellent effects.

First, since the semiconductor package is turned upside down and the flip chip back side is directly joined to a heat radiator having high thermal conductivity, a large amount of heat can be efficiently radiated by heat conduction.

Also, since heat is efficiently released from the aluminum plate at the bottom of the housing to the entire housing, there is an effect that a rise in temperature of the keyboard surface or the like can be suppressed.

Further, by electrically connecting the semiconductor package and the mother board with a lead wire with a mechanical degree of freedom, the stress on the metal bump at the flip-chip junction is reduced, and the problems of distortion and breakage are solved. This has the effect.

Further, there is an effect that a metal bump forming and connection-related device such as a BGA method is not required, and a batch joining method using a pressing force can reduce costs such as shortening an assembling time.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a mounting structure of an electronic device of the present invention.

FIG. 2 is a cross-sectional view showing a configuration and a connection method of external input / output pins of FIG.

FIG. 3 is a cross-sectional view illustrating details of a method of connecting the electronic device of the present embodiment.

FIG. 4 is a cross-sectional view showing a configuration and a connection method of the U-shaped connection fitting of FIG. 3;

FIG. 5 is a cross-sectional view illustrating a final connection state of the electronic device connection method according to the present embodiment.

FIG. 6 is a cross-sectional view illustrating an example of a mounting structure of a conventional electronic device. It is a block diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1A Printed wiring board 2 Thin-film multilayer wiring layer 3 Flip chip 4, 20 Metal bump 5 External input / output pin 6 U-shaped connection metal fitting 7 Socket 8 Lead wire 9 Connection terminal 10, 10A Motherboard 11 Thermal conductive sheet 12 Heat sink 14, 21 Aluminum plate 15 Keyboard 16, 40 Through hole 50 Spherical part 51 Stopper 52 Insertion part 53 Conductive resin 60 L-shaped tip 61 Split groove 62 Base plate 63, 92 Lead wire connection part 71 Case 72, 73, 74 Groove 91 Socket fixing part

Claims (5)

[Claims] 1. A semiconductor integrated circuit housed in a plurality of lip-chip type semiconductor packages by bonding via a metal bump onto a thin-film multilayer wiring layer made of an insulator and a conductor having a low dielectric constant formed on the surface as an internal circuit. (Hereinafter referred to as a flip chip) mounted electronic device including a printed wiring board, a motherboard for interfacing the internal circuit and the external circuit of the printed wiring board, and a heat radiating plate for radiating heat generated in the internal circuit. In the structure, the motherboard is arranged on an upper part of a housing of the electronic device to be mounted, and electrically connected to the internal circuit of the printed wiring board in a mechanically flexible state, wherein the flip chip is provided on the printed wiring board. The printed circuit board is turned over so as to be on the lower side, and the flip chip is attached to the back side of the flip chip. Mounting structure of an electronic device, characterized in that the bonded directly to the housing bottom of the metal plate high thermal conductivity the heat radiating plate integrated with via. 2. The printed wiring board has input / output pins for connection of the internal circuit, and the motherboard has a through-hole connected to the interface wiring, and a connection fitted into the through-hole. 2. A socket having a terminal and a connection fitting connected to the connection terminal by a lead wire and fitted to the input / output pin is joined to a lower surface of the motherboard.
The mounting structure of the electronic device described in the above. 3. The input / output pin has one end formed in a spherical shape, and the other end formed into a rod shape so as to be mechanically pressed into a through hole provided in the printed wiring board, inserted at once, and joined. 2. The mounting structure for an electronic device according to claim 1, wherein a stopper is provided at a boundary between the spherical portion and the printed wiring board at a predetermined position. 4. The connection terminal according to claim 2, wherein the connection terminal is a rod-shaped pin having a sharp end at one end so as to fit into the through hole of the motherboard, and having the other end connected to the lead wire. Electronic device mounting structure. 5. The connecting metal fitting is formed by reverse bending a tip of four L-shaped plates obtained by bending a thin plate into an L shape so as to be larger than an outer diameter of the spherical portion of the input / output pin. 3. The mounting structure for an electronic device according to claim 2, wherein the mounting structure is joined to the base plate so as to form a groove.