JPH11233697A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the radiation performance of FET with suppressing the manufacturing cost from increasing. SOLUTION: This device comprises a mount 15 with a pellet 11 connected through an Au foil 18, a stem 20 connected the mount through a solder zone 32, a spacer 24 fixed to the outside of the mount 15 of the stem 20 through the solder zone 32, a gate lead 27 and a drain lead 28 fixed to the spacer 42 by Ag braze to electrically connect to the pellet 11 through wires 34, and a hermetically sealed cap 38. The stem 20 is made of Cu, the mount 15 is made of CuW with an Au plating film 17 formed on an Ni plating film 16, and the stem 20 is covered with an Ni plating film 22. Thus it is possible to reduce the manufacturing cost with ensuring a high heat radiating performance by the Cu stem and relax the stresses between the pellet and the stem by the CuW mount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to an improvement in a heat dissipation structure, for example, to a technique effective for use in a field effect transistor for high frequency power amplification.

[0002]

2. Description of the Related Art In recent years, UH has been widely used as communication equipment.
There are mobile telephones such as mobile telephones and automobile telephones using F-band electromagnetic waves. A high-frequency power amplifying field-effect transistor (hereinafter, referred to as a high-frequency power amplifying unit) is provided in a high-frequency power amplifying unit of a wireless relay station that relays these mobile telephones by electromagnetic waves.
It is called FET. ) Is used.

As a conventional FET used in a high-frequency power amplification unit of a radio relay station, a semiconductor pellet (hereinafter, referred to as a pellet) in which an amplification circuit including an FET element is built, a stem to which the pellet is fixed, One comprising a spacer fixed to the outside of the stem pellet, a gate lead and a drain lead fixed to the spacer and electrically connected to the pellet by a wire, and a cap hermetically sealing the pellet and the wire. is there.

In this FET, the heat generated by the pellet is radiated to the motherboard of the high-frequency power amplification unit of the radio relay station via the stem. Therefore, a technique for improving the heat radiation performance of the stem by forming the stem using a copper-tungsten alloy (hereinafter, referred to as CuW) having good thermal conductivity and electric conductivity and a thermal expansion coefficient close to that of the material of the pellet. Has been proposed. Further, in order to enhance the heat radiation performance, it is conceivable to form a base in the center of the stem made of CuW and fix the pellet on the base.

[0005] The following example describes a technique for improving heat dissipation performance by using a material having good thermal conductivity such as CuW in a semiconductor device. That is, Japanese Patent Application Laid-Open No. 8-222668 proposes a ceramic package having a CuW radiator plate or a Cu radiator fin on the back surface of a chip. JP-A-61-76148 proposes a ceramic package having a heat radiating plate made of CuW on the back surface of a chip. JP-A-61-16553
Japanese Patent Application Laid-Open Publication No. H11-216, proposes a ceramic package having a heat radiating plate or heat radiating fin made of CuW on the back surface of a chip. Japanese Patent Application Laid-Open No. 61-117855 proposes a ceramic PGA type package having a heat radiating plate made of a copper-molybdenum alloy or an aluminum heat radiating fin on the back surface of a chip. Japanese Patent Application Laid-Open No. Hei 8-306684 proposes a resin-sealed package in which a radiator plate is formed of CuW and Cu.

[0006]

However, in an FET in which the stem is formed of CuW and the base is formed on the stem, not only is CuW expensive but also hard and brittle CuW requires a cutting process. The inventor has found that there is a problem of an increase in cost.

An object of the present invention is to provide a semiconductor device capable of improving heat radiation performance while suppressing an increase in manufacturing cost.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0009]

The outline of a typical invention among the inventions disclosed in the present application is as follows.

That is, a semiconductor pellet in which an electric circuit including a semiconductor element is built, a stem to which the semiconductor pellet is fixed, a spacer fixed to the outside of the semiconductor pellet of the stem, and a semiconductor pellet fixed to the spacer. What is claimed is: 1. A semiconductor device comprising: an electrically connected lead; and a sealing body in which a semiconductor pellet and a part of the lead are sealed, wherein the semiconductor pellet is fixed to a mount, and the mount is attached to the stem by a wax. It is characterized by being attached.

According to the above-described means, as a material for forming the stem, a material having good heat conductivity and electric conductivity, capable of being subjected to press working, and being inexpensive can be used. In addition, the manufacturing cost can be reduced while ensuring high heat radiation performance. Then, by configuring the mount so as to reduce the residual stress between the semiconductor pellet and the stem, it is possible to prevent a failure such as damage to the semiconductor pellet due to the residual stress. In addition, since the mount is smaller than the stem and can be formed in a flat plate shape, an increase in manufacturing cost can be suppressed even when an expensive material is used.

[0012]

FIG. 1 is a side sectional view showing an FET according to an embodiment of the present invention. FIG. 2 et seq. Are explanatory diagrams showing a method of manufacturing an FET according to an embodiment of the present invention.

In the present embodiment, the semiconductor device according to the present invention is configured as an FET. This FET10
Is a pellet 11 in which an electric circuit including a semiconductor element is formed by using a silicon substrate;
8, a mount 15 mechanically and electrically connected by a gold-silicon eutectic layer formed from 8, a stem 20 mechanically and electrically connected to the mount 15 by a soldering portion 32, and a mount of the stem 20. Spacer 24 mechanically connected to the outside of solder 15 by soldering portion 32
A gate lead 27 and a drain lead 28 fixed to the spacer 24 by silver wax 26 and electrically connected to the pellet 11 by an aluminum wire 34, respectively, a pellet 11, a part of the gate lead 27, and a drain lead 28. And a cap 38 hermetically sealed in cooperation with the spacer 24.

The stem 20 has good thermal conductivity and electrical conductivity, can be pressed, and is manufactured using copper, which is a low-cost material. Therefore, the production cost of the stem 20 can be reduced while securing high heat radiation performance. The mount 15 is manufactured using CuW, which is a material having good thermal conductivity and electrical conductivity and a thermal expansion coefficient similar to that of silicon. Therefore, since the mount 15 can reduce the residual stress between the pellet 11 and the stem 20, it is possible to prevent an obstacle such as damage to the pellet 11 due to the residual stress. In addition, since the mount 15 is smaller than the stem 20 and can be formed in a flat plate shape, an increase in manufacturing cost can be suppressed even when CuW, which is a material more expensive than copper, is used.

A gold plating film 17 is applied on a nickel plating film 16 on the surface of the mount 15, and a nickel plating film 22 is applied on a surface of the stem 20. Therefore, the soldered portions 32 are securely bonded to the surfaces of the mount 15 and the stem 20, respectively. Since the soldering portion 32 has flexibility, the stress due to the difference in thermal expansion coefficient between the mount 15 and the stem 20 is absorbed, and the stress due to the difference in thermal expansion coefficient between the pellet 11 and the stem 20 is used. Can be prevented from being damaged.

Next, a method of manufacturing an FET according to an embodiment of the present invention and its operational effects will be described with reference to FIGS. Then, this description clarifies the details of the configuration of the FET.

FIG. 2 shows a pellet bonding step in which the pellet is bonded to the mount.

The pellet 11 is made of silicon (Si), which is an example of a semiconductor material, and is formed in a rectangular plate shape as shown in FIG. 2 to form an electric circuit including an FET element. ing. A gate electrode pad 12 and a drain electrode pad 13 are formed on one principal surface (hereinafter, referred to as an upper surface) of the pellet 11, and a source electrode pad 14 is entirely formed on a lower surface.

The mount 15 is made of CuW, as shown in FIG.
Is formed in a rectangular plate shape somewhat similar to the pellet 11 as shown in FIG. CuW is a material having excellent thermal conductivity and electrical conductivity and having a thermal expansion coefficient close to that of silicon as a constituent material of the pellet 11. Since CuW has a hard and brittle property, it is difficult to press work. However, since the mount 15 has a simple rectangular plate shape, even if CuW is used, it can be manufactured without using complicated cutting. CuW is expensive, but the mount 15 is
Since it is only formed to be larger than 1, Cu
Since the amount of W used is suppressed to a small amount, an increase in manufacturing cost can be suppressed.

As shown in FIG. 2B, a nickel plating film 16 and a gold plating film 17 are applied to the surface of the mount 15. That is, the nickel plating film 16 for securing the surface plating property is mounted on the mount 1.
After being deposited on the entire surface of No. 5, a gold plating film 17 is deposited to facilitate the formation of a gold-silicon eutectic layer. Here, since the mount 15 has a smaller surface area than the stem, the amount of gold used can be reduced and the manufacturing cost can be reduced.

Incidentally, since the mount 15 has a simple rectangular flat plate shape, the gold plating film 17 can be partially applied, and the amount of gold used can be further reduced by performing the partial plating. Can be. When the gold plating film 17 is applied only to the mounting surface (hereinafter, referred to as the upper surface) of the pellet 11, a silver plating film may be applied to the lower surface.

The pellet 11 is bonded to the mount 15 configured as described above via the gold foil 18.
A pellet mount assembly 19 is manufactured. That is, when the pellet 11 is pressed via the gold foil 18 onto the mount 15 heated to about 450 ° C. by the heat block (not shown), the source electrode pad 14 formed on the lower surface of the gold foil 18 and the pellet 11 is pressed. Between gold and
Since a silicon eutectic layer (not shown) is formed, the pellet 11 is mechanically and electrically connected to the mount 15. At this time, since the gold plating film 17 is applied to the upper surface of the mount 15, the gold foil 18 is attached to the mount 1.
5 is securely fixed. Since gold is excellent in heat conductivity and electric conductivity, the pellet 11 is in a state in which the mount 11 is connected to the mount 15 with good heat conductivity and electric conductivity.

FIG. 3 shows the soldering process in which the pellet mount assembly and the leaded spacer are soldered to the stem.

The stem 20 is made of copper and formed in a rectangular plate shape as shown in FIG. 3, and the length of the short side is set to be sufficiently longer than the short side of the mount 15. I have. A pair of mounting portions 21, 21 is formed in a U-shaped notch at both ends on the long side of the stem 20.
The surface of the stem 20 is coated with a nickel plating film 22 for improving solderability.

Copper is a low-cost material having excellent heat conductivity and electric conductivity. In addition, since copper is easy to press, the stem 20 and the mounting portion 21 can be integrally formed by press, and can be manufactured at low cost. However, since the coefficient of thermal expansion of copper is about five times the coefficient of thermal expansion of silicon, when the pellet 11 is directly bonded to the stem 20, cracks may occur in the pellet 11 due to stress due to the difference in coefficient of thermal expansion. .

The spacer 24 of the leaded spacer 23 is made of alumina ceramic and is formed in a substantially square frame plate shape as shown in FIG. The outer diameter of the spacer 24 is set substantially equal to the length of the short side of the stem 20, and the inner diameter is set to be longer than the length of the long side of the mount 15. Metalized 2 on both end faces of spacer 24
5 (see FIGS. 1 and 4) are respectively formed,
A silver solder (silver solder, Cu-Zn-) is formed on the metallization 25 formed on one end surface (hereinafter referred to as an upper surface).
It is a hard wax mainly composed of an Ag-based alloy. ) 26 are fixed to each other.

On both silver waxes 26, 26, a gate lead 27 and a drain lead 28 formed in a rectangular plate shape.
Is silver soldering. As a constituent material of the gate lead 27 and the drain lead 28, Kovar material or 42 alloy (42% nickel iron alloy)
For example, a refractory metal that does not soften even at a high temperature of about 850 ° C. for silver brazing is used. A nickel plating film 29 and a gold plating film 30 (see FIGS. 1 and 4) are applied to the surfaces of the gate lead 27 and the drain lead 28. That is, after the nickel plating film 29 for ensuring the surface plating property is applied to the entire surface, the gold plating film 3 for improving the silver brazing property and the bonding property is used.
0 has been deposited.

The leaded spacer 23 and the pellet mount assembly 19 configured as described above are soldered to the stem 20 configured as described above, which is a kind of brazing. That is, the stem 20 is mounted on a heat block (not shown) heated to about 350 ° C., and the upper surface of the stem 20 has a substantially square solder foil 31 slightly larger than the outer diameter of the spacer 24. Is placed. Subsequently, the leaded spacer 23 and the pellet mount assembly 19 are
It is placed concentrically on and rubbed. Since the soldering portion 32 is formed by this soldering, the spacer 2
4 is mechanically connected to the stem 20, and the mount 15 is mechanically and electrically connected to the stem 20.

At this time, since the nickel plating film 22 is applied to the surface of the stem 20, the soldered portion 32 is securely bonded to the stem 20. Further, since the metallization 25 is attached to the spacer 24, the soldering portion 32
Is securely bonded to the spacer 24. Therefore, the leaded spacer 23 is firmly fixed to the stem 20. Since the gold plating film 17 is applied to the surface of the mount 15, the soldered portion 32 is securely bonded to the mount 15. Therefore, the mount 15 is
To be in a state of being firmly fixed.

Here, since only the nickel plating film 21 is applied to the stem 20, the manufacturing cost can be reduced as compared with the case where an expensive gold plating film is applied. However, if a gold plating film is applied on the nickel plating film 22, the adhesive strength with the soldered portion 32 can be further increased. Even in the case of using gold, since the stem 20 is formed in a flat plate shape, it is possible to adopt a partial plating process. It is possible to reduce the cost and suppress an increase in cost. Also, by reducing the amount of gold, which is a noble metal, by the partial plating process, it is not necessary to reduce the thickness of the gold plating film, so that an increase in high-frequency loss due to the reduction in the thickness of the gold plating film can be avoided. it can.

The pellet mount assembly, leaded spacer and stem assembly (hereinafter referred to as a stem assembly) 33 manufactured as described above includes a wire 34 made of aluminum in FIG. Bonded as shown. That is, in a state where the stem assembly 33 is held on a bonding stage (not shown),
The aluminum wire 35 inserted through the wedge 36 is first bonded to the gate electrode pad 12 of the pellet 11, and then the silver solder 26 to which the gate lead 27 is fixed is attached.
Is subjected to a second bonding. Similarly, the first bonding is performed to the drain electrode pad 13, and then the second bonding is performed to the drain lead 28. Incidentally, a plurality of wires 34 are respectively bridged on the gate side and the drain side.

As shown in FIG. 5, a cap 38 is attached to and fixed to the assembly (hereinafter, referred to as a wire assembly) 37 which has been wire-bonded as described above. That is, as shown in FIG. 5, a sealer 39 is welded to the lower surface of the opening end of a cap 38 formed of alumina ceramic and formed in a substantially square dish shape substantially the same as the outer shape of the spacer 24. . The cap 38 is placed on the wire assembly 37 with the sealer 39 in contact with the upper surface of the leaded spacer 23, and is heated through a sealing furnace (not shown). Heated and melted sealer 3
When 9 is cooled and solidified, the sealing portion 40 is formed, so that the spacer 23 with the lead and the cap 38 are sealed, and the hermetic sealing body 41 is formed.

The pellet 11 is placed inside the hermetically sealed body 41.
The mount 15, the wires 34, a part of the gate lead 27, and a part of the drain lead 28 are in a hermetically sealed state. As described above, the FET 10 shown in FIG. 5B and FIG. 1 is manufactured.

Next, the heat radiation effect and effect of the FET 10 manufactured as described above and configured as described above will be described.

For example, when the FET 10 is mounted on the motherboard of the high-frequency power amplifier unit of the wireless relay station, the stem 20 of the FET 10 is brought into contact with the mounting surface of the motherboard, and the mounting portions 21 are screwed. .
The heat generated by the pellet 11 due to the operation of the FET 10 is radiated to the motherboard via the mount 15 and the stem 20. At this time, since the mount 15 and the stem 20 are formed of CuW and copper, respectively, having good thermal conductivity, the heat generated from the pellet 11 is efficiently transmitted to the motherboard via the mount 15 and the stem 20. The heat is effectively dissipated.

Here, since the pellet 11 is mounted on the upper surface of the mount 15 protruding from the stem 20, the heat generated from the pellet 11 is diffused and propagated from the entire lower surface of the pellet 11 to the entire mount 15. Fifteen
Is transmitted to the stem 20 from the entire lower surface thereof and diffused to the entire stem 20, and the heat radiation efficiency becomes extremely good.

The mount 15 to which the pellet 11 is fixed is made of CuW having a thermal expansion coefficient similar to that of silicon.
No stress due to the difference in thermal expansion coefficient is generated between the two. Therefore, the risk that the pellet 11 is damaged by the stress can be avoided.

On the other hand, although the difference in thermal expansion coefficient between CuW forming the mount 15 and copper forming the stem 20 is large, the mount 15 and the stem 20 are mechanically separated by a soldering portion 32 having flexibility. Because of the connection, the stress caused by the difference in the coefficient of thermal expansion between the two can be absorbed by the flexibility of the soldered portion 32. Therefore, since the stress due to the difference in the thermal expansion coefficient between the mount 15 and the stem 20 does not act on the pellet 11 fixed to the mount 15, the pellet 11 can be prevented from being damaged by the stress. .

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and can be variously modified without departing from the gist thereof. Needless to say.

For example, the mount is not limited to using CuW, and when the size of the pellet is small, annealed (full annealing) copper or silver (which is cheaper than CuW) may be used. However, when the electric resistance does not matter, molybdenum (Mo) may be used. Since copper, silver, molybdenum, and the like are press-processable materials, the manufacturing cost can be further reduced.

The gold plating film can be replaced with a silver plating film depending on the use environment of the FET (semiconductor device).

The spacer is not limited to being formed of alumina ceramic, but may be formed of other ceramics, or an insulating material such as resin. When the spacer is formed of a resin, the lead can be mechanically connected to the spacer by soldering.

The sealing of the pellets and wires is not limited to the hermetic sealing structure, but may be a resin sealing structure by a potting molding method or a transfer molding method.

In the above description, the field of use in which the invention made mainly by the present inventor was used as the background
Although the description has been given of the case where the present invention is applied to the manufacturing technique of the present invention, the present invention is not limited to this.

[0045]

The effects obtained by typical aspects of the invention disclosed in the present application will be briefly described as follows.

By fixing the semiconductor pellet to a mount and brazing the mount to a stem, the material for forming the stem has good thermal conductivity and electric conductivity and can be pressed. Since a low-cost material can be used, manufacturing cost can be reduced while high heat radiation performance is ensured. Then, by configuring the mount so as to reduce the residual stress between the semiconductor pellet and the stem, it is possible to prevent a failure such as damage to the semiconductor pellet due to the residual stress.
In addition, since the mount is smaller than the stem and can be formed in a flat plate shape, an increase in manufacturing cost can be suppressed even when an expensive material is used.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an FET according to an embodiment of the present invention.

FIGS. 2A and 2B show a pellet bonding step in a method for manufacturing an FET according to an embodiment of the present invention, wherein FIG.
Is an exploded perspective view, and (b) is a side sectional view after bonding.

FIG. 3 is an exploded perspective view showing the same soldering step.

FIG. 4 also shows a wire bonding step,
(A) is a perspective view, (b) is a partially cut side view after wire bonding.

FIG. 5 also shows a step of forming a hermetically sealed body,
(A) is an exploded perspective view, (b) is a perspective view after formation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... FET (semiconductor device), 11 ... Pellet (semiconductor pellet), 12 ... Gate electrode pad, 13 ... Drain electrode pad, 14 ... Source electrode pad, 15 ... Mount, 16 ... Nickel plating film, 17 ... Gold Plating film, 18 ... Gold leaf, 19 ... Pellet mount assembly, 2
0: stem, 21: mounting part, 22: nickel plating film, 23: spacer with lead, 24: spacer, 25
... metallized, 26 ... silver wax, 27 ... gate lead, 28
... Drain lead, 29 ... Nickel plating film, 30 ...
Gold plating film, 31: solder foil, 32: soldering part, 33
... Stem assembly, 34 ... Wire, 35 ... Aluminum wire, 36 ... Wedge, 37 ... Wire assembly, 38 ... Cap, 39 ... Sealer, 40 ... Sealing part, 41 ... Airtight sealing body.

Claims (10)

[Claims] 1. A semiconductor pellet in which an electric circuit including a semiconductor element is formed, a stem to which the semiconductor pellet is fixed, a spacer fixed to the outside of the semiconductor pellet of the stem, and a semiconductor pellet fixed to the spacer. What is claimed is: 1. A semiconductor device comprising: an electrically connected lead; and a sealing body sealing a part of the semiconductor pellet and the lead, wherein the semiconductor pellet is fixed to a mount, and the mount is attached to the stem by a wax. A semiconductor device characterized by being attached. 2. A plating film is applied to each of the brazing surfaces of the stem and the mount, and the material of the plating film on the stem side is formed of a metal material that is more base than the material of the plating film on the mount side. The semiconductor device according to claim 1, wherein 3. The semiconductor device according to claim 2, wherein the stem side is a nickel plating film, and the mount side is a gold plating film. 4. The semiconductor device according to claim 1, wherein the mount is formed of a material having a smaller coefficient of thermal expansion than the stem. 5. The semiconductor device according to claim 1, wherein the stem is formed of copper, and the mount is formed of a copper-tungsten alloy. 6. The semiconductor device according to claim 1, wherein said semiconductor pellet is brazed to said mount.
Or the semiconductor device according to 5. 7. The semiconductor device according to claim 1, wherein the spacer is brazed to the stem. 8. The semiconductor device according to claim 1, wherein the mount is annealed more than the stem. 9. The method according to claim 1, wherein the mount to which the semiconductor pellet is fixed is pressed onto the stem via a brazing material and brazed. Manufacturing method of a semiconductor device. 10. The method according to claim 9, wherein the spacer is pressed together with the mount onto a brazing material on the stem and brazed.