JP2004221381A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which is provided with a thermal conduction restricting means to enhance the junction reliability. <P>SOLUTION: The semiconductor device has a plurality of kinds of semiconductor elements 11, 12 having a different heat resistance and a circuit substrate 15 mounting the semiconductor elements 11, 12, and the thermal conduction restricting means is provided to connect with the semiconductor element 11 which is higher in the heat resistance out of the semiconductor elements 11, 12. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor device having a semiconductor element, for example, a semiconductor device having a semiconductor element such as a transistor or a diode for driving a motor.
[0002]
[Prior art]
2. Description of the Related Art In recent years, switching semiconductor elements for power circuits such as IGBTs (insulated gate bipolar transistors) and MOSFETs have increased heat generation with higher performance and higher functionality, and have caused heat-related problems. FIG. 5 shows a package structure of a conventional semiconductor device.
[0003]
FIG. 5 shows a TO220 package used for a semiconductor element package of a transistor or a diode. 1A is a transistor, 1B is a diode, 2 is a high-temperature solder represented by SnAgCu solder, Pb solder, AuSn solder, and the like. Is a heat diffusion plate (copper), 4 is a metal wire (aluminum or gold), 5 is a metal lead, 6 is an epoxy resin, 7 is a secondary circuit board, 8 is a wiring pattern on a circuit board, 9 is solder, and 10 is heat radiation. It is a board.
[0004]
The TO220 package configured as described above will be described below.
[0005]
First, the semiconductor element 1 of the transistor 1A and the diode 1B is connected to the heat diffusion plate 3 by the high-temperature solder 2. Next, the metal wire 4 is used to electrically connect between the transistor 1A and the diode 1B and between the semiconductor element 1 and the metal lead 5. In addition, usually, the metal wire 4 uses an aluminum wire or a gold wire. For example, when the metal wire 4 is made of aluminum, since the electrode of the semiconductor element 1 is formed of aluminum, ultrasonic energy is applied between the aluminum on the surface of the electrode and the aluminum of the metal wire 4 at room temperature. When pressed while pressing, the oxide film on each aluminum surface is removed, and bonding is obtained. The metal wire 4 is routed to the metal lead 5 plated with nickel on copper, and joined to the metal lead 5 by a wedge bonding method.
[0006]
Then, for the purpose of physical protection and reliability improvement of the semiconductor element 1 and the metal wire 4, the semiconductor element 1, the metal wire 4 and the heat diffusion plate 3 are covered by using a transfer molding technique or an injection molding technique. Sealing with resin 6 is performed. Through these steps, an electronic component called "TO-220" formed by the semiconductor element 1, the high-temperature solder 2, the heat diffusion plate 3, the metal wires 4, the metal leads 5, and the epoxy resin 6 is completed.
[0007]
Next, with the metal lead 5 inserted into the insertion hole of the secondary circuit board 7, the electronic component “TO-220” is placed on the secondary circuit board 7 and the entire secondary circuit board 7 is dipped. Then, the metal leads 5 and the wiring pattern 8 on the circuit board on the secondary circuit board 7 are electrically and physically joined by the solder 9.
[0008]
By the way, in the above-described configuration, the surface temperature of the semiconductor element 1 is limited in use temperature by the glass transition temperature Tg which is a material property value of the epoxy resin 6. Therefore, in order to enhance heat dissipation and lower the temperature of the semiconductor element, there is an effort to improve the heat generated from the semiconductor element 1 by improving the heat conduction from the heat diffusion plate 3 and the epoxy resin 6 to the heat dissipation plate 10. There were many.
[0009]
For example, a method described in Patent Literature 1 is generally known as a method for improving heat dissipation of a semiconductor element without using an epoxy resin. This method is characterized in that the heat sink is formed of the same material as the package substrate.
[0010]
[Patent Document 1]
JP-A-01-151257 (page 2-3, FIG. 1)
[0011]
[Problems to be solved by the invention]
However, in the structure of Patent Document 1 described above, the temperature of the semiconductor element is well transmitted to the package substrate, and the temperature of the package substrate rises. As a result, the temperature of the lead frame rises due to heat conduction from the package substrate. For this reason, there has been a problem in that the reliability of the joint due to a rise in temperature is reduced in the solder joint where the lead frame and the external circuit board are electrically and physically joined.
[0012]
The present invention has been made in order to solve the above-described problems, and has as its object to provide a semiconductor device provided with a heat conduction suppressing unit and having improved junction reliability.
[0013]
[Means for Solving the Problems]
In order to achieve this object, the present invention has a plurality of types of semiconductor elements having different heat resistances, and a circuit board on which these semiconductor elements are mounted, and a semiconductor element having a higher heat resistance among the semiconductor elements. Is provided with a heat conduction suppressing means.
[0014]
Thereby, heat conduction inside the semiconductor device can be suppressed, and a semiconductor device with improved junction reliability can be obtained.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and description thereof will be omitted.
[0016]
FIG. 1 shows a semiconductor device according to a first embodiment of the present invention, in which two semiconductor elements having different heat resistance characteristics, a SiC semiconductor element 11 and a Si semiconductor element 12, are mounted together. The feature of the SiC semiconductor element 11 is that it has high heat resistance that operates even at 400 ° C., and realizes lower loss than the Si semiconductor element 12. The Si semiconductor element 12 has low heat resistance and is limited to use at 150 ° C. or lower. Thus, when semiconductor elements having different characteristics are mounted in the same package, it is necessary to change the heat conduction suppressing means depending on the heat resistance temperature.
[0017]
FIG. 2 shows an example of the heat conduction suppressing means. The semiconductor element 13 is used for switching a driving current to a driving device such as a motor, and is a driving semiconductor element that generates heat and requires heat radiation treatment, and includes a transistor and a diode. The protruding electrode 14 is formed on the semiconductor element 13. The projecting electrode 14 is joined to the semiconductor element 13 by heating a metal ball (not shown) at 100 to 300 ° C. and applying an ultrasonic wave of 60 kHz. Then, the metal wiring on the circuit board 15 is again bonded to the metal by heat and ultrasonic waves, and the bonding is performed electrically and physically. At this time, by changing the shape of the protruding electrode 14 to 0.3 mmφ to 1.0 mmφ, the flow of electricity and heat can be suppressed. That is, the heat flowing from the bump electrode 14 is suppressed by the shape, for example, the size of the bump electrode 14.
[0018]
In this state, the metal wires 16 are joined. The metal wire 16 is formed of aluminum or gold, and is formed on the semiconductor element 13 and the metal lead 17 by the above-described aluminum wire wedge bonding method or gold wire ball bonding method. At this time, heat conduction can be suppressed by changing the shape of the metal wire 16, for example, the wire diameter.
[0019]
Further, the circuit board 15 has a reduced-pressure space 18 in the circuit board, an insulating material 19, and a metal case 20. In this state, the circuit board 15 is put into a reduced-pressure atmosphere, and the metal case 20 is pressed to complete a package. When the package is returned to the atmospheric state, since the pressure inside the metal case 20 is reduced, the adhesion between the metal case 20 and the circuit board 15 is maintained. That is, since the gap between the semiconductor element 13 and the circuit board 15 becomes the decompression space 21, the transmission by heat radiation is reduced.
[0020]
The metal lead 17 is connected to a wiring pattern 24 on a secondary circuit board 23 by a solder 25 via a heat radiating plate 22 serving as a heat radiating means.
[0021]
When the semiconductor device is a transistor, there are three or more metal leads 17. One is electrically connected to the lower electrode of the semiconductor element 13 and corresponds to the middle metal lead 17 in FIG. The remaining two metal leads are joined to two electrodes on the upper part of the semiconductor element 13 and correspond to the left and right metal leads 17 in FIG.
[0022]
Here, the flow of heat when the semiconductor element 13 is in a driving state will be described.
The semiconductor element 13 is a switch element that turns on and off a voltage of 100 V to 1500 V. In this switching operation, a loss occurs. In a normal semiconductor device such as an IGBT, heat loss is 10% of applied power. Heat is generated from the entire semiconductor element 13 that is performing an electrical switching operation, and is generated as long as the switching operation is performed. Therefore, unless the heat generated from the conversion loss of electricity is properly processed, the semiconductor element 13 It leads to malfunction and destruction.
[0023]
However, since the solder 25 joint is weak to heat, it is not desirable to flow heat as much as possible. Therefore, a configuration is adopted in which the periphery of the semiconductor element 13 is placed in the reduced-pressure space 21 to block heat radiation to the outside. At this time, the temperature rise of the semiconductor element 13 itself becomes a problem. However, when Si is used for the semiconductor element 13, the upper limit is 120 ° C. to 200 ° C., and when SiC is used, the upper limit is 300 ° C. to 400 ° C. Since the decompression space 21 has the same effect as a thermos, the flow of heat from the circuit board 15 to the metal leads 17 is suppressed, and the heat gradient between the heat of the semiconductor element 13 and the metal leads 17 increases. The same effect can be obtained by the reduced pressure space 18 in the circuit board. In this case, the effect can be further enhanced by providing the decompressed space 18 in the circuit board in the portion where the semiconductor element 13 is mounted.
[0024]
Further, in order to suppress a rise in the temperature of the solder 25 joining portion on the secondary circuit board 23, the heat sink 22 is caulked to the metal lead 17. As a result, the heat transmitted from the circuit board 15 is conducted to the metal leads 17, a part of the heat is radiated into the air by the heat radiating plate 22, and the rest is transferred to the solder 25 joint. The solder 25 joint is designed so that the maximum temperature is 80 ° C. to 125 ° C., although it differs depending on the shape to be joined, the substrate material, the semiconductor driving conditions, and the like.
[0025]
Thus, by providing the semiconductor element 13 with the heat conduction suppressing means, the influence of heat on the surroundings is reduced. As a result, as shown in FIG. 1, two semiconductor elements having different characteristics, that is, a SiC semiconductor element 11 and a Si semiconductor element 12, are mounted together. That is, the SiC semiconductor element 11 having high heat resistance is joined to the circuit board 15 via the protruding electrode 14 to enhance the heat insulation effect on the same circuit board 15, and the Si semiconductor element 12 having low heat resistance is provided with the heat dissipation means. The entire surface of the lower electrode is joined to the circuit board 15 to improve heat dissipation. With such a structure, semiconductors having different heat resistance can be mounted in the same package.
[0026]
Another example of the heat conduction suppressing means is shown in FIG. In FIG. 3, reference numeral 26 denotes a metal contact portion, and reference numeral 27 denotes a metal lead pressing portion, which is applicable when a large current is used, switching loss of the semiconductor element 13 is large, and heat generation is large. Since the entire surface of the lower electrode of the semiconductor element 13 is joined to the circuit board 15, the allowable current value can be increased, so that a large current can flow. However, since the heat conduction is improved, the heat insulating effect is obtained by the reduced pressure space 18 in the circuit board in the circuit board 15. When the temperature of the semiconductor element 13 becomes 200 ° C. to 400 ° C., the joining by the aluminum wire or the gold wire used at 200 ° C. or lower shown in FIG. 2 is caused by the softening of the metal or the increase of the metal diffusion into the semiconductor element 13. Can no longer be used. For this reason, the semiconductor element 13 is pressed between the circuit board 15 and the metal lead pressing portion 27 by being pressed by the metal lead pressing portion 27. Molybdenum is applied to the contact portion of the metal lead pressing portion 27 so as to withstand a temperature of 200 ° C to 400 ° C. This allows the joint to move even when thermal stress is applied, so that the stress can be released.
[0027]
As described above, by changing the electrical connection between the semiconductor element and the circuit board to the conventional wiring wire and using the protruding electrode and the metal piece, the stray inductance and the conduction resistance can be reduced, and the device can be reduced. The overall size can also be reduced. Further, by disposing the metal piece and the semiconductor element with an insulating resin material and integrating the circuit board, the insulating resin material, and the heat radiating member, heat dissipation from the semiconductor element can be increased as compared with the conventional case. .
[0028]
By applying gold plating to the electrodes of the semiconductor element and the protruding electrodes, it is possible to perform solder joining even when these materials are made of aluminum. In addition, by providing the barrier metal directly below the electrodes of the semiconductor element, it is not necessary to apply gold plating to the semiconductor elements, particularly the electrodes, and by providing a protective material on the side surfaces of the semiconductor elements, Thus, damage to the semiconductor element can be prevented.
[0029]
FIG. 4 shows a semiconductor device according to a second embodiment of the present invention, showing a structure in which two semiconductor elements having different characteristics, a SiC semiconductor element 11 and a Si semiconductor element 12, are mounted in the same package. ing. The SiC semiconductor element 11 having high heat resistance is stacked on the Si semiconductor element 12 via the bump electrode 14. At this time, the temperature difference between the SiC semiconductor element 11 and the Si semiconductor element 12 can be suppressed by changing the cross-sectional area of the bump electrode 14. With this structure, a plurality of chips can be mounted in a small area, and the location for stacking can be determined by heat resistance.
[0030]
In the case where a plurality of semiconductor elements are stacked, by connecting the stacked semiconductor elements with the protruding electrodes, stray inductance and conduction resistance can be reduced.
[0031]
Note that heat transfer is determined by the heat transfer coefficient and shape, which are physical properties of the material. The ease and difficulty of the flow of heat is generally defined by the thermal resistance R (° C./W). The meaning of thermal resistance is the same as that of electrical resistance. When a temperature difference (° C) is generated with respect to the amount of heat (W) given to a certain shape, it indicates the characteristics of the object. When it is high, it has the effect of suppressing heat. In order to increase the thermal resistance, it is necessary to select a material having a low thermal conductivity, a shape in which heat does not easily flow (for example, a small cross-sectional area in which heat flows, a long path in which heat flows, etc.), and other substances (such as air and There is a method in which the area radiating heat to water is small, and the amount of other substances radiating heat is small (for example, vacuum insulation). Devising the shape of the protruding electrode or the metal wire described in the embodiment means increasing this thermal resistance, and by devising something other than the shape, the same effect can be obtained even if the thermal resistance is increased. .
[0032]
【The invention's effect】
As described above, according to the present invention, a semiconductor device having a plurality of types of semiconductor elements having different heat resistances and a circuit board on which these semiconductor elements are mounted, and a semiconductor element having a higher heat resistance among the semiconductor elements. By providing the heat conduction suppressing means in the connection, the effects of heat radiation and heat insulation can be mounted inside the same package, and the size can be reduced by a stacked structure as compared with the device configuration. Therefore, it is possible to provide a package in which the Si semiconductor and the SiC semiconductor can be mounted together.
[Brief description of the drawings]
FIG. 1 is a diagram showing a semiconductor device according to a first embodiment of the present invention; FIG. 2 is a diagram illustrating a heat conduction suppressing unit; FIG. 3 is a diagram illustrating a heat conduction suppressing unit; FIG. FIG. 5 is a view showing a semiconductor device according to a second embodiment of the present invention. FIG. 5 is a view showing a conventional package structure of a semiconductor element.
DESCRIPTION OF SYMBOLS 11 SiC semiconductor element 12 Si semiconductor element 14 Protruding electrode 15 Circuit board 16 Metal wire 17 Metal lead 18 Reduced pressure space in circuit board 20 Metal case 22 Heat sink 23 Secondary circuit board

Claims (9)

It has a plurality of types of semiconductor elements having different heat resistances, and a circuit board on which these semiconductor elements are mounted, and includes a heat conduction suppressing means in a connection portion for mounting a semiconductor element having a higher heat resistance among the semiconductor elements. A semiconductor device, comprising: 2. The semiconductor device according to claim 1, wherein the plurality of types of semiconductor elements are a Si semiconductor element and a SiC semiconductor element. 3. The semiconductor device according to claim 1, wherein a case is provided as a means for suppressing heat conduction, wherein a reduced pressure space is provided around the semiconductor element. The semiconductor device according to any one of claims 1 to 3, wherein a reduced pressure space in the substrate, which is a reduced pressure space, is provided in a portion of the circuit board on which the semiconductor element is mounted as the heat conduction suppressing means. 5. The method according to claim 1, wherein a protruding electrode for joining the semiconductor element and the circuit board is provided as the heat conduction suppressing means, and the shape of the protruding electrode is determined according to the amount of heat conduction. Semiconductor device. The heat conduction suppressing means is provided with a metal wire for joining the semiconductor element and the circuit board, and a shape of the metal wire is determined according to a heat conduction amount. Semiconductor device. The semiconductor device according to claim 3, wherein the bonding between the semiconductor element and the circuit board is performed by applying pressure. 8. The semiconductor device according to claim 1, further comprising a lead for joining the circuit board and the secondary circuit board, wherein the lead is provided with a heat radiating unit. 9. The semiconductor device according to claim 1, wherein a heat radiation promoting means is provided for connecting a semiconductor element having a lower heat resistance among the semiconductor elements.

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