JP2765236B2 - Radiation fins with improved thermal conductivity and lifetime - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a radiating fin, and more particularly to a radiating fin that is lightweight and has enhanced thermal conductivity.

[0002]

2. Description of the Related Art FIG. 11 is a perspective view of a conventional semiconductor storage device. The semiconductor storage device 1 includes a substrate 4 on which the semiconductor element 3 is mounted, and a package 5 which supports the substrate 4 from below and has a space for accommodating the semiconductor element 3.
And. A lid 6 is attached to the package 5 from below. The lead wire 21 is electrically connected to the semiconductor element 3.

In recent years, the amount of heat generated by the semiconductor element 3 has been increasing due to the increase in speed, capacity, and frequency of ICs. In the apparatus shown in FIG. 11, this heat is sufficiently dissipated to the outside. Can not do. Therefore, various demands have been increased for a radiation fin for dissipating generated heat to the outside of the semiconductor storage device 1. The characteristics required for this kind of heat radiation fins are good heat conduction and light weight.

FIG. 12 is a cross-sectional view of a conventional semiconductor storage device provided with heat radiation fins. The semiconductor storage device shown in FIG. 12 is different from the semiconductor storage device shown in FIG.
Is attached. The substrate 4 is formed of a Mb-W composite material or a Cu-W composite material. The package 5 is formed of alumina. The lid 6 is made of Kovar (29% Ni-1).
7% Co-Fe). The radiation fins 2 are formed of an aluminum alloy in consideration of lightness. The heat radiation fins 2 are fixed by screws 7 provided on the back surface of the substrate 4.
It is attached to the back surface of the substrate 4.

FIG. 13 is a cross-sectional view of a conventional small semiconductor storage device provided with a radiation fin. The conventional example shown in FIG. 13 is the same as the conventional example shown in FIG. 12 except for the following points. Corresponding portions bear the same reference numbers, and description thereof will not be repeated.

Since it is necessary to reduce the size, the radiation fins 2
Of the blade 2a project upward. The radiation fins 2 and the substrate 4 are adhered by an adhesive 8 containing a filler having good heat conductivity.

[0007] The conventional semiconductor storage device provided with the radiation fin is configured as described above, and has the following problems. That is, in the method of connecting the radiation fins 2 and the substrate 4 with the screws 7 shown in FIG. 12, the contact area between the radiation fins 2 and the substrate 4 cannot be sufficiently increased, resulting in insufficient heat radiation. Was. On the other hand, in the method of connecting the radiation fins 2 and the substrate 4 with the adhesive 8 shown in FIG. 13, the heat conduction of the adhesive 8 was poor, and the heat dissipation was insufficient. In the case of the semiconductor storage device shown in FIG. 13, the package side (the substrate 4 formed of the Mb-W composite material or the Cu-W composite material and the package 5 formed of alumina) and the radiation fins 2 (made of aluminum) The thermal expansion coefficient after connection (normally -50 ° C).
(150 ° C., 300 cycles), peeling and the like occurred on the connection surface, which was a problem in use.

In order to solve such problems, the present inventors have separately developed a substrate for mounting a semiconductor element (Japanese Patent Laid-Open No. Sho 59-21032), a Mo-Cu composite material or a W-Cu composite material. Was diverted to a radiation fin. The coefficient of thermal expansion of this Mo—Cu composite or W—Cu composite is close to that of alumina or Kovar. Therefore, when these composite materials are used for radiation fins,
Even if a thermal cycle test is performed, the above-described problem of peeling does not occur. In addition, the Mo—Cu composite material and the W—Cu composite material have excellent thermal characteristics as radiation fins. Among them, Mo-Cu having a relatively small specific gravity
The composite material (specific gravity: 9 to 10 g / cc) is currently in practical use as a lightweight heat radiation fin.

[0009] However, this Mo-Cu composite material also
Since it is heavier than aluminum (specific gravity: 2.7 g / cc) conventionally used as a heat radiation fin, it is too heavy when applied to a large-sized heat radiation fin for a large semiconductor chip which has been recently demanded. was there.

Therefore, as a solution, referring to FIG. 14, a connecting portion 9 for connecting the radiating fin 2 formed of aluminum and the package 5 formed of alumina is provided.
The connecting portion 9 and the radiation fin 2 are made of a Mo-Cu composite material.
Are bonded with solder 22 (lead-tin, lead-tin alloy, etc.) and used.

[0011]

However, FIG.
As shown in FIG. 2, aluminum, which is a material forming the radiation fins 2, is easily oxidized, and its surface is usually covered with a thin oxide film. Therefore, it is necessary to perform plating (usually, nickel plating, then nickel plating) on the surface of the aluminum in order to make the wettability of the solder poor and to join with the solder. In addition, molybdenum present on the joint surface of the Mo—Cu composite material, which is a constituent material of the connection part 9, deteriorates the wettability with the solder material. Therefore, in order to join with solder, it was necessary to plate the joint surface of the Mo—Cu composite material with nickel plating or the like. further,
When both are connected by solder, there is a problem that a certain amount of holes are generated inside the solder layer, and these holes hinder heat conduction. Further, the thermal conductivity of the solder material is low, and this solder material also has a problem that the thermal conductivity is hindered.

Referring to FIG. 14, the joined product of fin 2 and connecting portion 9 made by the above-described method is made of nickel or nickel + after soldering in order to impart corrosion resistance.
It had to be plated with gold or the like. However, it is difficult to plate a product in which such various materials are mixed, because the reactivities of the materials to chemicals are different.

An object of the present invention is to provide a radiation fin in which a fin and a connecting portion are firmly connected.

[0014]

SUMMARY OF THE INVENTION The present invention relates to a radiating fin which is attached to a semiconductor storage device for storing a semiconductor element and radiates heat generated from the semiconductor element to the outside. The heat radiation fins include a fin formed of an aluminum alloy, Mo-Cu, Cu-W, and A.
It is formed of a composite material selected from the group consisting of l-Si, and includes a connection portion for connecting the fin and the semiconductor storage device. The fin and the connection portion are in close contact with each other by friction pressure welding at their interface.

[0015]

The radiation fin according to the present invention is lightweight because the fin uses an aluminum alloy. Also, Mo
Since the connection portion formed of a composite material selected from the group consisting of -Cu, Cu-W and Al-Si and the fin are friction-welded at their interface and are in close contact with each other, they are made of metal. It is firmly connected by bonding.

Mo--Cu, Cu--W and Al--Si all have good thermal conductivity, and at the interface between the fin and the connection, there is a member such as solder that reduces the thermal conductivity. As a result, the obtained radiating fins have good thermal conductivity.

Further, Mo-Cu, Cu-W and Al-
Since the difference in the coefficient of thermal expansion between the connection portion formed of the composite material selected from the group consisting of Si and the material constituting the package is small, no thermal strain occurs at the interface between the package and the connection portion. That is, the radiation fin and the package are firmly connected, and the life thereof is extended.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 is a perspective view of a radiation fin according to an embodiment of the present invention. The radiation fins 13 are attached to a substrate on which the semiconductor element is mounted, and dissipate heat generated from the semiconductor element to the outside. Heat radiation fins 13
Includes a fin 2 formed of an aluminum alloy and a connecting portion 9. The connection portion 9 is formed of a composite material formed of Mo-Cu, Cu-W, or Al-Si. The fin 2 and the connecting portion 9 are in close contact with each other by friction pressure welding at their interface. Fins 2 that are in close contact with each other by friction welding
And the connecting portion 9 are connected to each other at their interface by metal bonding.

FIG. 2 is a cross-sectional view of the semiconductor storage device to which the heat radiation fins according to the embodiment are attached.

The semiconductor storage device 1 includes a substrate 4 on which the semiconductor element 3 is mounted, and a package 5 which supports the substrate 4 from below and has a space for accommodating the semiconductor element 3.
And. A lid 6 is attached to the package 5 from below. Lead 21 is electrically coupled to semiconductor element 3.

The radiating fins 13 in which the connecting portions 9 and the fins 2 are connected by metal bonding are used to bond the connecting portions 9 and the substrate 4 to each other with a heat conductive adhesive (epoxy resin + Ag). Fixed to

The substrate 4 is made of an Mb-W composite material or Cu-W
It is formed of a composite material. The package 5 is formed of alumina. The lid 6 is made of Kovar (29% Ni-17% Co-
Fe).

Table 1 shows the measurement results of the thermal expansion coefficient and the thermal conductivity of the Cu-W alloy used for the connecting portion 9. In this table, the thermal expansion coefficients of Al ₂ O ₃ , Si, GaAs and the like are also shown.

[0025]

[Table 1]

As is apparent from Table 1, when Cu is added in an amount of 2 to 30% by weight in the Cu-W alloy, there is no difference in the thermal expansion coefficient between the Cu-W alloy and Al ₂ O ₃ .

Table 2 shows the measurement results of the thermal expansion coefficient and the thermal conductivity of the Mo—Cu alloy used in the connection portion 9 according to another embodiment of the present invention.

[0028]

[Table 2]

Referring to these tables, Mo-Cu and Cu-W alloys have good thermal conductivity. Further, since no member such as solder that reduces the thermal conductivity is interposed at the interface between the fin 2 and the connecting portion 9, the obtained heat dissipating fin 13 has good thermal conductivity.

The connecting portion 9 made of Mo-Cu or Cu-W alloy and the material (Cu-
W, Al ₂ O _3, etc.), the thermal expansion does not occur at the interface between the package 1 and the connecting portion 9. That is, the radiation fins 13 and the package 5 are firmly connected, and the life of the semiconductor storage device is extended.

FIG. 3 is a cross-sectional view of a semiconductor storage device to which heat radiation fins are attached according to another embodiment of the present invention.

FIG. 3A is a perspective view of a semiconductor storage device provided with a radiation fin, and FIG. 3B is a cross-sectional view taken along line BB in FIG. 3A.

Referring to these figures, semiconductor storage device 1
Has a package 5 (made of alumina) for accommodating the semiconductor element 3. Package 5 includes
A lid 6 (formed of Kovar) is attached from below. Lead wire 21 is electrically connected to semiconductor element 3. The radiating fins 13 are connected to the fins 2 (made of an aluminum alloy) whose wings 2 a extend upward and the connecting portions 9.
Consists of The connection part 9 is formed of Mo-Cu, Cu-W, or an Al-Si alloy. The connecting portion 9 and the fin 2 are friction-welded at the interface between them and are in close contact with each other. Both are connected by a metal bond. Heat radiating fin 13 in which connecting portion 9 and fin 2 are connected by metal bonding
Is fixed to the package 5 by bonding the connecting portion 9 and the package 5 with a heat conductive adhesive (epoxy resin + Ag). Since the difference in the coefficient of thermal expansion between the connection portion 9 and the package 5 is small, no thermal distortion occurs at the interface between the package 5 and the connection portion 9. Even in such an embodiment, the radiation fins 13 and the package 1 are firmly connected, and the life thereof is extended.

FIG. 4 is a schematic view showing a process of manufacturing the heat radiation fin shown in FIG. Referring to FIG.
0 is M which is to be the connection portion 9 of the radiation fin 13 shown in FIG.
An o-Cu composite material, 11 is aluminum to be the fin 2. The Mo-Cu composite material 10 and the aluminum 11 are joined by a friction welding method in which the connecting surfaces of the two are rotated in opposite directions while applying pressure.

Aluminum 11 and Mo-Cu composite 10
In the friction welding, the properties (hardness, toughness, etc.) of both materials are significantly different, so that appropriate joining conditions must be set in order to obtain stable joining strength.

Aluminum 11 and Mo-Cu composite 10
When the two are rotated in opposite directions while applying pressure while aligning the connection surfaces with the aluminum oxide film 12, the aluminum oxide film 12 is discharged to the outside at the connection surface with reference to FIG. This will be described in more detail later with reference to the drawings.

Referring to FIG. 4C, when the Mo-Cu composite material 10 and the aluminum 11 are cut, a heat radiation fin 13 in which the fin 2 and the connecting portion 9 are joined is obtained.

According to this method, complete bonding without voids at the bonding interface can be obtained. Also according to this method,
Both can be joined without forming a solid solution layer of aluminum and copper with low thermal conductivity at the joint interface. As a result, a radiation fin having good heat conduction is obtained. Further, according to the radiation fins 13 thus produced, since there are no various metals such as solder, the plating process after the connection is also facilitated.

In order to obtain a sufficient bonding strength, it is necessary to eliminate the oxide film present on the aluminum bonding surface. In consideration of this point, the shape, rotation speed and pressure of the bonding surface are set. There is a need.

Next, under various conditions, aluminum and M
The result of performing friction welding with the o-Cu composite material will be described. Example 1 FIGS. 5A to 5E are views showing a state of friction welding between aluminum and a Mo—Cu composite material in a case where a bonding surface is a flat surface. It is a picture of the situation. In the figure, 10 is Mo-Cu.
11 is aluminum, and 12 is an aluminum oxide film formed on the surface of the aluminum 11. Referring to these figures, when the joining surface is a flat surface,
The deformation at the time of joining occurs on the aluminum 11 side because the toughness of the Mo—Cu composite material 10 is higher than that of the aluminum 11. The bonding conditions were aluminum oxide film 1
It is necessary to select a pressure contact condition sufficient to discharge 2 from the joining surface 30 to the outside. The bonding strength (Kg / mm ² ) in each state was determined by preparing a sample having the shape shown in FIG. The results are summarized in Table 3.

[0041]

[Table 3]

Embodiment 2 FIGS. 6A to 6E show the tip angle α of the Mo—Cu composite material.
11 and Mo-C when is 120 °
FIG. 4 is a view showing friction welding with the u-composite material 10 and showing a state of deformation with time. The bonding strength (Kg / mm ² ) in each state is shown in FIG.
It was determined by preparing a sample having the shape shown in (b). The results are summarized in Table 4.

[0043]

[Table 4]

According to this embodiment, the Mo—Cu composite material 1
Since the leading end of O has a convex conical shape, the pressure welding starts from a small area at the center of the end surface of the aluminum 11 and the aluminum oxide film 12 is easily discharged from the joint surface. Therefore, deformation of the aluminum 11 at the time of pressing can be reduced, and the bonding strength can be improved. Example 3 FIGS. 7A to 7D show the effect of the shape of the bonding surface on the bonding strength. The tip angles of the Mo—Cu composite material were set to 180 ° (plane), 160 °, and 120 °. , 80 °, are cross-sectional views of the joint structure obtained when the angle is changed to 80 °. The result
Table 5 summarizes the results.

[0045]

[Table 5]

As is clear from Table 5, the bonding strength can be improved by forming an angle at the tip of the Mo—Cu composite material. The bonding strength (Kg / mm ² ) is 1
If it is about 0 kg, it can sufficiently withstand use. Fourth Embodiment In the case of the first embodiment, at the time of friction welding, A
When l is used, Al is softened by frictional heat, and it becomes difficult to apply a sufficient pressure to the joining portion, and the joining strength may decrease. In this embodiment, the area of the bonding surface of CuW and CuMo, which has high hardness and low thermal deformation at the time of friction welding with Al, is made smaller than that of Al.
1 can be prevented, the force applied at the time of pressing can be maintained, and sufficient bonding strength can be obtained after pressing.

That is, as shown in FIG. 15, the shape of the CuMo material 10 to be joined to the aluminum 11 is reduced only at the joining portion, and under the same conditions as in the first embodiment,
It was friction-welded with the Al material. The results are summarized in Table 6.

[0048]

[Table 6]

By comparing Table 6 and Table 3, it can be seen that in the case of the present embodiment, the bonding strength is significantly improved. Example 5 A combined product obtained by friction-welding the Mo-Cu composite material 10 and aluminum 11 shown in FIG. 9 and the Mo-Cu composite material shown in FIG.
The thermal conductivity of the composite (prior art) formed by connecting the composite material 10 and the aluminum 11 with the solder 22 was compared. Five samples were prepared for each, and the heat conduction was measured. The method of measuring heat conduction is by the laser flash method.
The measurement was performed from the Mo—Cu composite material side 10. Table 7 shows the results.

[0050]

[Table 7]

As is clear from Table 7, the joint formed by friction-welding the Mo-Cu composite material 10 and the aluminum 11 has a significantly higher thermal conductivity than the joint formed by the solder 22. .

In the above embodiment, the connection portion is made of Mo-
The case where a Cu alloy or a Cu-W alloy is used has been exemplified, but the present invention is not limited to this, and the same effects as those of the embodiment can be obtained even if an Au-Si alloy is used.

Although the above embodiment has exemplified the case where aluminum is used for the fins, the present invention is not limited to this, and it is an Al alloy (for example, an Al-Si alloy) to which other elements are added. You may.

Further, in the present invention, in order to form a stronger skeleton of W or Mo, it is permissible to add an iron group element of 20% by weight or less. By the addition of the iron group element, the sinterability of W and Mo is also promoted.

The present invention has been summarized as follows. (1) The heat radiation fin according to claim 1, wherein the Mo-Cu composite material has a Cu content of 2 to 3.
0% by weight.

(2) The heat radiation fin according to the claim, wherein the specific gravity of the Mo—Cu composite material is 9 to 10 g.
/ Cc.

(3) The heat radiation fin according to the present invention, wherein the Mo—Cu composite material or the W—Cu composite material contains an iron group element.

(4) The heat radiation fin according to the above (3), wherein the content of the iron group element is 20% by weight or less.

(5) The heat-dissipating fin according to the present invention, wherein the W-Cu composite material has a Cu content of 2 to 2.
30% by weight.

(6) The heat radiation fin according to the present invention, wherein the interface between the fin and the connection portion is a plane.

(7) The heat-dissipating fin according to the present invention, wherein at the interface between the fin and the connecting portion, the tip of the connecting portion has a conical shape that enters the fin. .

(8) The heat radiation fin according to the above (7), wherein a tip angle of the conical shape is 160 ° or less.

(9) The heat radiation fin according to the present invention, wherein the Al alloy contains PureAl.

(10) The heat radiation fin according to the present invention, wherein the Al alloy includes an Al—Si alloy.

[0065]

As described above, the radiation fin according to the present invention is lightweight because the fin is made of an aluminum alloy. Further, Mo-Cu, Cu-W and A
The connecting portion formed of a composite material selected from the group consisting of l-Si and the fin are friction-welded at their interface and are in close contact with each other, so that both are firmly bonded by metal bonding. .

Further, Mo-Cu, Cu-W, Al-S
i has good thermal conductivity, and since there is no intervening member such as solder at the interface between the fin and the connection portion, the radiation fin obtained has a high thermal conductivity. It will be good.

Further, Mo-Cu, Cu-W and Al
Since the difference in the coefficient of thermal expansion between the connection portion formed of the composite material selected from the group consisting of -Si and the material constituting the package is small, no thermal strain occurs at the interface between the package and the connection portion. As a result, the radiation fin and the package are firmly connected, and the life thereof is extended.

[Brief description of the drawings]

FIG. 1 is a perspective view of a radiation fin according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a semiconductor storage device provided with a radiation fin according to the present invention.

FIG. 3 is a perspective view (a) and a cross-sectional view (b) of a semiconductor storage device provided with a radiation fin according to another embodiment of the present invention.

FIG. 4 is a schematic view illustrating a manufacturing process of a heat radiation fin according to the present invention.

FIG. 5 is a cross-sectional view illustrating a manufacturing process of the radiation fin according to one embodiment of the present invention.

FIG. 6 is a cross-sectional view illustrating a manufacturing process of a radiation fin according to another embodiment of the present invention.

FIG. 7 is a cross-sectional view of a joint structure obtained by examining the effect of the shape of the joint surface on the joint strength and obtained when the tip angle of the Mo—Cu composite material is changed.

FIG. 8 is a view showing a structure of a sample for measuring a bonding strength of the heat radiation fin according to the present invention.

FIG. 9 is a perspective view of a sample for measuring the heat conduction of the radiation fin according to the present invention.

FIG. 10 is a perspective view of a sample for measuring heat conduction of a conventional radiating fin in which a Mo—Cu composite material and aluminum are joined by solder.

FIG. 11 is a perspective view of a conventional semiconductor storage device.

FIG. 12 is a cross-sectional view of a conventional semiconductor storage device provided with a radiation fin.

FIG. 13 is a cross-sectional view of another conventional example of a semiconductor storage device provided with a radiation fin.

FIG. 14 is a cross-sectional view of still another conventional example of a semiconductor storage device provided with a radiation fin.

FIG. 15 is a cross-sectional view showing a step of manufacturing a heat radiation fin according to still another embodiment of the present invention.

[Explanation of symbols]

 2 Fin 9 Connecting part 13 Heat radiation fin

Claims (1)

(57) [Claims] 1. A radiating fin attached to a substrate for mounting a semiconductor element and dissipating heat generated from the semiconductor element to the outside, the fin being made of an aluminum alloy, a Mo-Cu, W- And a connecting portion formed of a composite material selected from the group consisting of Cu and Al-Si, for connecting the fin and the substrate, wherein the fin and the connecting portion have friction at their interface. A heat dissipating fin with improved thermal conductivity and life that is pressed and adhered.