JPH09107050A - Semiconductor device mounting structure - Google Patents

Abstract

(57) Abstract: In a semiconductor device, heat dissipation is improved from the package surface to improve the breakdown resistance. A wettability with the liquid metal 13 is applied to a region of the surface of a metal layer 8 on the stem 3 to be in contact with the liquid metal 13, a surface of a resin 11 covering the semiconductor chip 1, and an inner surface of a metal cap 15. Copper layer 1 which is a metal layer having
After providing 2, the space formed by the metal cap 15 and the stem 3 was filled with the liquid metal 13 and the inert gas 16.

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 mounting an element that requires heat dissipation during operation.

[0002]

2. Description of the Related Art A can package typified by TO-3 as shown in FIG. 5 is widely used for mounting a power semiconductor device which requires reliability. Most of this method is
An electrode 102 electrically insulated and mechanically connected by a sealing low melting point glass 101 such as Kovar or borosilicate glass is formed on a stem 100 made of an alloy containing iron, copper and nickel as a main component. Stem 1 on the back
00, and the pad electrode of the semiconductor chip 1 and the electrode 102 are electrically connected by the wire 103. The chip and the wire 103 are sealed by filling the inert gas 16 with the sealing cap 104 made of the same material as the stem 100 and the stem 100.

[0003]

If excessive power is accidentally applied to this package, the stem 1
The semiconductor chip 1 may be peeled from 00, or the semiconductor chip 1 may be cracked due to the difference in the coefficient of thermal expansion. As described above, the semiconductor chip 1 often locally deteriorates due to heat generation to deteriorate the performance as an element even if the element is not completely destroyed. Of course, it is necessary to avoid inputting an excessive amount of power, but heat is generated from the semiconductor chip 1 on the surface thereof, but heat is radiated only from the back surface of the chip, which is a factor that requires reliability. As a result, it has been desired to improve the fracture resistance from the viewpoint of the package.

[0004]

Means for Solving the Problems As a means for solving the above-mentioned problems, the present invention uses a structure as set forth in the claims. That is, as described in claim 1 as the first means, it has good heat and electric conductivity and at least the "first metal such as mercury and indium which becomes liquid at the operating temperature of the semiconductor chip" on the surface. At least the surface of the second metal on the stem is a metal plate made of "a second metal which is an iron or nickel that does not form an alloy with the first metal or an alloy thereof" in the region to be contacted with the stem. A layer of "a third metal such as gold, silver, copper, tin, and aluminum that has wettability with the first metal" is provided in a region to be contacted with the first metal, and electrically insulated in the stem. A semiconductor element including a transistor having an electrode penetrating through the front and back surfaces, the back surface being adhered to a portion other than the electrode portion on the metal plate, and electrically connected to the metal plate and the electrode is formed. Semiconductor chip And has an epoxy or polyimide resin material that thinly coats and connects the surface of at least the electrically conductive substance on the surface of the semiconductor chip and the surface of the electrical connection portion, A metal cap made of the same material as the metal plate, which has three metal layers and is adhered to the metal plate so as to enclose the semiconductor chip and the resin material and seals the inside. The third metal layer, and the space formed by the stem and the metal cap is filled with a metal that becomes a liquid at the operating temperature of the semiconductor chip, and the first metal such as helium, nitrogen, argon, or xenon. Any one of inert gas or a mixed gas that does not react with the metal is larger than the volume in which the metal expands due to the change in operating temperature of the semiconductor chip and Is obtained by the mounting structure filled volume fraction can be present as bubbles in the metal.

As a second means, as described in claim 2, in the first method, the semiconductor chip 1 having the second metal layer on at least the surface layer of the back surface is bonded face down on the stem. In addition, the mounting structure is such that the gap between the semiconductor chip 1 and the stem and the periphery of the chip are filled and insulated with a resin material while being electrically connected at the same time.

As a third means, as described in claim 3, the first or second means is made of a similar material formed inside the metal cap by being thermally coupled to the metal cap. This is a mounting structure in which one or more protrusions are arranged so as to be close to and not in contact with the semiconductor chip.

[0007]

First, the operation of the present invention will be described. By using the first means, the operation of the semiconductor chip in the cap that does not deteriorate in strength due to contact with mercury or indium by adding a few steps to the conventional mounting method using a can package. A metal that becomes liquid at a temperature can be filled, and heat can be radiated from the surface of the semiconductor chip through the liquid metal by heat conduction, and the heat radiation performance is remarkably improved as compared with the conventional case of using a filling gas such as nitrogen. Further, since the liquid metal is used and a small amount of the bubbles of the inert gas are simultaneously enclosed in the filling of the liquid metal, the pressure applied to the semiconductor chip in order to relieve the pressure in the cap caused by the volume expansion accompanying the temperature rise of the liquid metal. Can be made small and uniform.
Moreover, in particular, when mercury is used as the liquid metal,
It is known that mercury has a very high surface tension. If a small amount of air is taken into the inside as mercury by forming a material that has a wettability or alloys with the area around which mercury contacts, Does not allow air bubbles to come into contact with the outer surface that contacts. By using the material having wettability, the adhesion between the semiconductor chip, the mercury and the metal cap is improved, and the heat transfer efficiency in the heat transfer path from the semiconductor chip to the metal cap via the mercury is improved.

By using the second means, the liquid metal comes into contact with the back surface even when the power semiconductor chip is mounted by using the bump, so that the electrical resistivity is 40% as compared with the material such as the connecting wire. About twice as high, but much larger cross-sectional area (depending on the chip size, about 100 times or more)
Therefore, the electric resistance can be suppressed to be low.

By using the third means, in the first or second means, a protrusion made of a similar material that is thermally coupled to the metal cap is formed inside the metal cap on the semiconductor chip. Since the mounting structure is arranged so as to be close to and not in contact with each other, in the structure of the first means, the thermal conductivity of the protrusion is lower than that of the liquid metal, and the structure is connected to the cap to be cooled, so that the direct heat conduction is improved. In addition, when the chip is installed horizontally, the convection with the liquid metal is promoted between the protrusion on the cooling side and the semiconductor chip on the heat generating side. In the structure according to the second means, the electrical resistance of the liquid metal can be improved without the protrusions exerting stress on the semiconductor chip.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings are deformed for ease of description, and the vertical and horizontal dimensional ratios and the dimensional ratios of respective constituent parts are shown. It does not reflect accurately. Further, the numerical values and materials used in the present embodiment are examples used to realize the embodiment, and the numerical values are not limited to the following, and the materials have the characteristics shown in the claims. It is not limited to the following as long as it is shown.

FIG. 1 is a diagram for explaining the first embodiment of the present invention. Semiconductor elements such as transistors are formed on the surface of the semiconductor chip 1, and these can be connected to the outside from the pad electrodes 2 on the semiconductor chip 1. The surface of 1 is covered with an insulating film. Stem 3 is 3m thick
The base 5 made of copper is joined to a part of the metal made of 42-nickel alloy of m or other alloy having good heat conduction by silver-copper solder 6, and the back surface of the semiconductor chip 1 is in this region. Are joined using lead-tin solder 7. On the other hand, when a material other than iron-nickel alloy or the like is used for the stem 3, when mercury is used as the liquid metal 13 on the surface in the region sealed by the metal cap 15, it is not alloyed with mercury (does not form amalgam). When the metal layer 8 made of iron, nickel or an alloy thereof is formed to a thickness of 1 μm, the stem 3 is not attacked by mercury and the strength does not deteriorate. Further, in the above-mentioned sealing region, a lead 9 made of a package lead wire material typified by a copper-core iron-chromium wire penetrating the stem 3 is insulated and bonded using a low melting point sealing glass 4 such as Kovar glass. . The pad electrode 2 on the semiconductor chip 1 bonded on the base 5 and the lead 9 are connected by a bonding wire 10. The polyimide resin or the epoxy resin 11 is formed to have a minimum thickness necessary to obtain a withstand voltage so as to thinly cover the exposed portion of the conductive material, but if it is too thick, the thermal resistance becomes large and the heat dissipation deteriorates. It is preferable that the element formation region of the semiconductor chip 1 be formed particularly thin or not formed. Further, in order to improve the wettability of the liquid metal 13 with mercury, a 1 μm-thick copper layer 12 is vapor-deposited on the surface of the resin 11, and the gas to be enclosed later is the liquid metal (mercury) 13.
Trapped inside. The copper layer may be gold, silver, tin, lead, etc., but copper is the cheapest of these. Here, the outer surface is treated with nickel plating to prevent contact, and the inner surface is covered with liquid metal (mercury).
A copper layer 12 having wettability with 13 is formed in advance, and an iron metal cap 15 provided with an injection port 14 for injecting the liquid metal (mercury) 13 is resistance-welded so as to cover the above-mentioned sealing region. . After that, liquid metal (mercury) in the sealed space
13 is injected and nitrogen gas is sealed as the inert gas 16 to seal the injection port 14. In this embodiment, the size of each part is almost the same as that of TO-3.
Since the volume inside 5 is approximately 2.2 cm ³ , when the temperature of the liquid metal (mercury) 13 rises from 25 ° C. to 150 ° C., the body expansion coefficient (0.182 × 10 ⁻³ (deg ⁻¹ ) increases the expanded volume). Since it is 5 mm ³ , the above inert gas 16
When 10 mm ^{3 is} injected, the expansion of the liquid metal (mercury) 13 can be absorbed and the deformation of the metal cap 15 and the stem 3 can be prevented. With the above structure, the inner surface of the package is covered with a material having wettability with mercury. Therefore, regardless of the mounting direction of the package, the extremely large surface tension of the liquid metal (mercury) 13 causes the inert gas 16 to form bubbles. As a result, it is possible to prevent the bubbles from coming into contact with the liquid metal (mercury) 13 and particularly contacting the semiconductor chip 1 side to hinder the heat conduction. From the above, liquid metal (as mercury, thermal conductivity: about 8 to 9 (WM
^-1 K ^-1 )) 13 and heat can be dissipated by heat conduction, and the conventional filling gas (as nitrogen, thermal conductivity: about 0.
026 (WM ^-1 K ^-1 )), the heat dissipation is 300
It is significantly more than doubled, and stable heat radiation can be realized regardless of the mounting direction. Further, since the heat medium for heat dissipation is liquid, heat conduction by convection can be expected, and heat dissipation is further improved. In addition, since the semiconductor chip 1 is covered with mercury (liquid metal 13) which is a heavy metal containing almost no radioactive isotope, there is an effect that the radiation resistance is significantly improved.

The second embodiment will be described below. In the second embodiment, the semiconductor chip 1 in the first embodiment is joined to the stem face down using solder bumps, and the gap between the semiconductor chip 1 and the stem and the peripheral edge of the semiconductor chip 1 are made of a resin material. It is a mounting structure that is filled and insulated by using. The second embodiment will be described below with reference to FIG.

The stem 17 is made of a metal plate made of the same material as that of the stem 3 in the first embodiment.
Similarly to the above, a semiconductor layer in which a metal layer 8 that does not alloy with a liquid metal is formed on the surface in a region sealed by the metal cap 15 on the stem 17, and leads 9 penetrating the stem 17 are bonded facedown. The chips 1 are insulated and bonded to the positions corresponding to the pad electrodes by using Kovar glass. The pad electrodes of the semiconductor chip 1 on the stem 17 are bonded on the leads 9 using the bumps 18 of lead-tin solder, so that the semiconductor chip 1 and the stem 1 are joined together.
The space between 7 and the periphery of the semiconductor chip 1 are filled with epoxy resin or polyimide resin 11 to be insulated from the surroundings. Further, in order to improve the wettability with the liquid metal 13 in the above-mentioned sealing region, at least the back surface of the semiconductor chip 1 is
A copper layer 12 of μm is vapor-deposited. The metal cap 15 filled with the liquid metal 13 and the inert gas 16 is sealed to the above structure as in the first embodiment.

According to the above structure, the power semiconductor chip 1
Since the liquid metal 13 comes into contact with the back surface even when the bumps are mounted using the bumps 18, the low electrical efficiency is about 40 times higher than that of a material such as an aluminum wire for connection when mercury is taken as an example, but the cross-sectional area is much larger. Large (depending on the chip size, it is about 1
The electrical resistance can be suppressed to a low level because it can be reduced to about 100 times or more), and not only the on-resistance of the device can be reduced, but also the electrical connection is made by the liquid metal 13, so that a local stress is not generated. Reliability is significantly improved because it does not exist.

Since the non-wetting portion of the liquid metal 13 is also in contact with the liquid metal 13, heat is radiated, and the inert gas 16 to be filled is fixed in the non-wetting region due to the surface tension of the liquid metal 13. Therefore, it is preferable not to form the metal layer (copper layer 12) for improving the wettability in the region 19 which does not hinder the heat radiation, taking the region in FIG. 2 as an example. It can be applied.

The third embodiment will be described below. In the third embodiment, a protrusion made of the same material that is thermally coupled to the metal cap 15 inside the metal cap 15 in the first or second embodiment is close to and in contact with the semiconductor chip 1. This is a mounting structure that is arranged so that it will not be placed. The following description will be made with reference to FIGS. 3 and 4, but the description of the same parts as those in the first and second embodiments will be omitted.

FIG. 3 is an application of the third embodiment to the first embodiment, in which the pillar 2 made of the same material as the metal cap 15 or the stem 3 is provided inside the metal cap 15.
0 is joined by welding, and the surface thereof has a thickness of 1 μm of a thin metal film having wettability with the liquid metal 13, for example, a copper layer 1 against mercury
2 is formed in advance. Although the pillar 20 has a length that does not contact the surface of the semiconductor chip 1, it is preferable that the tip end of the pillar 20 be as close as possible in terms of thermal coupling. As a result, liquid metal with poor thermal conductivity 1
From 3 (8-9 (WM ^-1 K ^{-1 for} mercury)) to the material of the column 20 having good thermal conductivity, the cross-section integral of the column 20 is improved in thermal conductivity, and the effect is to use 42 nickel alloy for the column 20. If so, the thermal conductivity is about 13 (WM ^-1 K ^-1 ), so pillar 2
About 150% per 0 cross section, about 84 (W for pure iron)
Since it is M ⁻¹ K ⁻¹ ), heat dissipation is improved about 10 times. Further, when the semiconductor chip 1 is installed so that its surface is downward and horizontal, the heat generating portion is located below the metal cap 15 on the upper cooling side, and liquid convection is unlikely to occur, but the protrusions are cooling points. Since it is close to the semiconductor chip 1, convection of the liquid metal 13 is promoted and heat dissipation is improved. Since the pillar 20 is not directly mounted, the semiconductor chip 1
No local stress is applied to the same as in the above embodiment.

FIG. 4 is an application of this embodiment to the first embodiment. One end of the semiconductor chip 1 is close to the back surface of the semiconductor chip 1 and a pillar 20 having the same structure as that shown in FIG. 3 is installed. Has been done. In the present embodiment, since the pillar 20 can be used as a conductor, the cross-sectional integral resistance of the pillar 20 is improved by replacing it with the liquid metal 13 having a high resistivity (mercury has a low efficiency of 96 (μΩcm at 20 ° C.)). . As an example, when pure iron is used for the pillar 20, the low efficiency is 9.8 (μΩcm at 20
C.), the cross-sectional area can be reduced to one-tenth, and the electrical resistance of the liquid metal 13 and thus the on-resistance of the device can be further improved without the pillars 20 stressing the semiconductor chip 1.

[0019]

The effects of the present invention are summarized below.
According to the first aspect of the invention, since the liquid metal and a small amount of inert gas are enclosed in the metal package and the liquid metal is brought into contact with the insulated semiconductor chip surface, the heat dissipation from the semiconductor chip surface is remarkably improved. In addition, stable heat radiation can be realized regardless of the mounting direction. Further, since the heat medium for heat dissipation is liquid, heat conduction by convection can be expected, and heat dissipation is further improved. In addition, since the chip is covered with mercury, which is a heavy metal containing almost no radioisotope, it has an effect of significantly improving radiation resistance.

According to the second aspect of the invention, the semiconductor chip is joined to the stem face down using solder bumps, and the gap between the semiconductor chip and the stem and the periphery of the chip are filled and insulated with a resin material. Since the structure is used, in addition to the above effects, even when a power semiconductor chip is mounted using bumps, the liquid metal comes into contact with the back surface. Since the connection cross-sectional area can be made much larger than that of wires, the electrical resistance connecting to the back surface of the chip can be suppressed to a low level, not only the on-resistance of the device can be lowered, but also the electrical connection can be made by liquid metal. Since this is done, no local stress is applied and reliability is significantly improved.

According to the third aspect of the present invention, a metal column having good thermal conductivity and a surface having a wettability with a liquid metal is joined inside the cap of the package, and the chip surface is brought into as close as possible but not contacted. Since the structure is adopted, in addition to the above effects, the drawback of liquid metal having a relatively poor thermal conductivity is remarkably improved, and the heat dissipation is further improved, and further when the surface of the semiconductor chip is installed so as to be downward and horizontal. In the above, since the heat generating portion is located above the upper cooling side cap, liquid convection is unlikely to occur, but since the protrusion serves as a cooling point and is close to the semiconductor chip, convection of liquid metal is promoted to improve heat dissipation. . Furthermore, in addition to the effect of the second embodiment, the disadvantage of liquid metal having a relatively poor resistivity can be remarkably improved, and the on-resistance of the device can be further improved.

[Brief description of the drawings]

FIG. 1 is a sectional view illustrating a first embodiment according to the present invention.

FIG. 2 is a sectional view illustrating a second embodiment according to the present invention.

FIG. 3 is a cross-sectional view illustrating a first application example of the third embodiment according to the present invention.

FIG. 4 is a sectional view for explaining a first application example of the third embodiment according to the present invention.

FIG. 5 is a sectional view illustrating a conventional example of the present invention.

[Explanation of symbols]

 1 Semiconductor Chip 2 Pad Electrode 3 Stem 4 Low Melting Point Sealing Glass 5 Base 6 Silver-Copper Solder 7 Lead-Tin Solder 8 Metal Layer (Second Metal) 9 Lead 10 Bonding Wire 11 Resin (Polyimide Resin or Epoxy Resin) 12 Copper layer (third metal) 13 Liquid metal (first metal) 14 Injection port 15 Metal cap 16 Inert gas 17 Stem 18 Bump 19 Region (region where copper layer 12 is not formed) 20 Pillars

Claims (3)

[Claims] 1. A first metal and an alloy are formed in a region having good heat and electric conductivity and at least in contact with the "first metal which becomes liquid at an operating temperature of a semiconductor chip" on the surface. A second metal that does not have a second metal ", at least the first metal surface of the second metal on the metal plate.
Has a “third metal having wettability with the first metal” layer in a region to be contacted with the metal, and has electrodes that are electrically insulated and penetrate the front and back in the metal plate, A semiconductor chip formed with a semiconductor element including a transistor, the back surface of which is adhered to a portion other than the electrode portion on the plate and which is electrically connected to the metal plate and the electrode; A resin material that thinly coats and insulates the surface of at least the part where the conductive material is exposed and the electrical connection part, and has the third metal layer on the surface of the resin material, and the semiconductor chip and the resin A metal cap made of the same material as the metal plate, which is attached to the metal plate so as to enclose the material and seals the inside, and has the third metal on the inner surface of the metal cap, the metal plate And metal In the space formed by the cap, the first metal has a volume larger than that of the first metal that expands due to a change in operating temperature of the semiconductor chip and that can exist as bubbles in the metal. A mounting structure for a semiconductor device having a space filled with one of helium, nitrogen, argon, xenon, or a mixed gas. 2. The structure according to claim 1, further comprising the semiconductor chip that is face down bonded and electrically connected to the electrode on the metal plate, and the second chip is provided on at least a surface layer of a back surface of the semiconductor chip. And a resin material for filling and insulating the gap between the semiconductor chip and the metal plate and the peripheral edge of the chip. 3. The structure according to claim 1, wherein the metal cap has one or more protrusions made of the same material as the metal cap and having a third metal layer on the surface thereof. A mounting device for a semiconductor device, wherein one end of the protrusion is fixed to the metal cap so as to be thermally coupled, and the other end is arranged so as to be close to and not to contact the semiconductor chip.