JP2001274321A - High breakdown voltage flat semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase dielectric strength and reduce insulation size in a package by selecting a gas having a better insulation property than a nitrogen gas which has been used in the conventional method, for a gas to be enclosed in the package of a flat semiconductor device for power. SOLUTION: In this flat semiconductor device, an IGBT chip 2 and a diode chip 3 are assembled in combination with collector electrodes 7, insulation partition walls 8 and the like in the sealed flat package 1 comprising an outer case (ceramic) 4 and case electrodes 5, 6; and then an insulation is enclosed in the package. For the insulation gas to be enclosed in the package, a carbon dioxide which has a better insulation property than nitrogen and whose leakage gas has no adverse effect on the surrounding areas is used instead of a nitrogen gas which has been used in the conventional method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high withstand voltage flat semiconductor device for electric power used in the field of power electronics.

[0002]

2. Description of the Related Art First, a power IG applied to an inverter
The structure of the flat semiconductor device for electric power described above will be described with reference to FIGS. 1A and 1B by taking a BT module as an example. In the figure, 1 is a sealed flat package, 2 is an IGBT chip, and 3 is a diode chip. The flat package 1 is a ceramic outer case 4 and is sealed to both upper and lower surfaces with the outer case 4 interposed therebetween. And a case electrode (emitter side) 5 and a case electrode (collector side) 5 made of copper. Here, the IGBT chip 2 and the diode chip 3 are arranged on a plane as shown in the drawing, and a collecting electrode 7 is superposed on each chip, and an insulating partition 8 for holding an assembling position is arranged between the chips. In actual use, the flat package 1 is pressed against an external heat radiator and attached to the case electrodes 5 and 6 so that the heat generated by the chips 2 and 3 is removed from the case electrodes 5 and 6.
To efficiently radiate heat to the outside.

Further, in a flat semiconductor module employing the above-described pressure contact structure, the peripheral region of the power semiconductor chip is not resin-sealed inside the package as in a normal power transistor module. In order to protect the structure from the use environment, an inert gas is sealed as an insulating gas, and a nitrogen gas is used in the conventional apparatus as the sealed gas.

[0004]

By the way, in recent years, high breakdown voltage and large current of power semiconductor devices have been rapidly progressing.
At present, a power IGBT with a withstand voltage of 4.5 to 6 kV has been developed. In this case, the nitrogen gas sealed in the flat package as described above is a gas that does not produce negative ions from the viewpoint of discharge physics, and is an insulating gas that produces other negative ions in a partial discharge phenomenon due to local insulation defects. It is not an advantageous gas in terms of dielectric strength as compared with. In addition, air has a higher dielectric strength than nitrogen gas because it contains oxygen, which causes the formation of negative ions, compared with nitrogen gas.However, it contains active oxygen and has an oxidizing effect. Since the improvement of the dielectric strength is at most about 10%, it is hardly used as an insulating gas for high withstand voltage.

As for the effective ionization coefficient that determines the dielectric strength, the nitrogen gas rapidly increases from a low electric field region as shown by a characteristic line C1 in the characteristic diagram showing the relation between the specific electric field and the ionization coefficient in FIG. Further, the ionization coefficient is large even in a high electric field region. On the other hand, in the assembly structure of the semiconductor device shown in FIG.
This is a creeping insulation for the T chip 2, the diode chip 3 and the insulating partition 8. Particularly, when minute foreign matter such as dust adheres to the surface of these parts, the size of the foreign matter and the relative discharge breakdown voltage shown in FIG. As shown by the relationship characteristic diagram of
The dielectric strength rapidly decreases depending on the size of the foreign matter.

As shown in FIGS. 4 (a) and 4 (b), an insulation structure in which a high voltage lead wire 11 in which a core wire 11a is covered with an insulation jacket 11b is superposed on a ground metal 10 and In the insulating configuration in which the high-voltage conductor 13 is disposed on the ground metal 10 with the insulating dielectric 12 interposed therebetween as shown in FIG. 3C, the difference between the dielectric constant and the electrical conductivity between the gas in the surrounding atmosphere and the dielectric causes , Or a very high electric field concentration occurs at the boundary indicated by P2. In particular, in the wiring structure of FIGS. 4 (a) and 4 (b),
Interface portion P1 where outer sheathed lead wire 11 contacts ground metal 10
, A theoretically infinite electric field is generated. FIG.
In the structure in which the insulating dielectric 12 interposed between the high-voltage conductor 13 and the ground metal 10 is opposed to the high-voltage conductor 13 with a small gas-phase gap P2 as shown in FIG. The electric field concentrated in the phase increases to a value corresponding to the dielectric constant of the insulating dielectric 12 and the gas times the average electric field obtained by dividing the potential difference between the high-voltage conductor 13 and the ground metal 10 by the distance therebetween.

For this reason, when a partial discharge occurs at the above-mentioned boundary portions P1 and P2, this triggers and rapidly progresses to dielectric breakdown of the entire insulating structure. In addition, as shown in FIG.
In a flat semiconductor device in which the GBT chip 2, the diode chip 3, and the insulating partition 8 are integrated and assembled, as shown in FIG. 4, the high voltage portion and the ground metal or the insulating dielectric face each other with a small gap therebetween. Always exists.

For this reason, when nitrogen gas is sealed in the flat package 1 shown in FIG. 1 for a high breakdown voltage flat semiconductor device having a rated voltage of 4.5 to 6 kV class, the nitrogen gas described in FIG. IGBT chip 2,
A high electric field concentration occurs between the diode chip 3 and the case electrode 6 on the collector side and the insulating partition wall 8, causing a very large ionization multiplication in this portion, which triggers a local discharge. Eventually, the road will be destroyed.

Although it is conceivable to enclose a halogen-based gas such as SF ₆ as an insulating gas in the package to improve the dielectric strength, SF ₆ gas is a gas having a high global greenhouse effect. there have been found, gradually it tends to its use is restricted, and when an accident occurs in the semiconductor device, a halogen gas such as SF ₆ is easily decomposed by touching the hot arc, fluorine Ya Hydrofluoric acid and hydrochloric acid, which are chlorine compounds, and their secondary reactants are generated. These are very toxic and can cause adverse effects on the surrounding environment if gas leaks from the package.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has been studied by the inventors on the properties of the gas to be sealed in the package, such as the insulating properties of various gases and the effects of leaked gas on the surrounding environment. Based on the results, instead of the nitrogen gas used conventionally, a gas with better insulation than nitrogen gas was selected to improve the dielectric strength and reduce the insulation size in the package. It is an object of the present invention to provide a breakdown voltage semiconductor device.

[0011]

According to the present invention, a power semiconductor chip is incorporated in a sealed flat package, and an insulating gas is sealed in the package. In the apparatus, carbon dioxide is adopted as the insulating gas. Carbon dioxide has the same ionization coefficient in the low electric field region as nitrogen, but exhibits a lower ionization coefficient than nitrogen in the high electric field region. It is possible to suppress the start of discharge in a portion. Also, regarding the dielectric breakdown voltage in a quasi-equivalent electric field, carbon dioxide is higher than nitrogen, and in a region where pressure (gap length) is low, the dielectric strength is approximately 1.5 times that of nitrogen. As a whole, the dielectric breakdown voltage is increased, and as a result, the dielectric strength can be improved and the insulation dimensions can be reduced as compared with the conventional device using nitrogen as the gas for filling the package.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an embodiment of the present invention, FIG.
As shown in FIG. 1, carbon dioxide is used as an insulating gas to be sealed in the package of the semiconductor device. For this purpose, a gas conduit 9 penetrating through the outer case 4 to the flat package 1 in FIG.
After the module is assembled, the interior of the package is evacuated through the gas conduit 9 to replace the air with carbon dioxide, and then the gas conduit 9 is sealed off.

Here, as shown by the characteristic line C2 in FIG. 2, carbon dioxide has an ionization coefficient equivalent to that of nitrogen in a low electric field region, but has a lower ionization coefficient in a high electric field region than nitrogen. Thus, even if a local electric field concentration portion exists at the boundary portions P1 and P2 in the insulating structure shown in FIGS. 4 (a) to 4 (c), discharge starts at that portion by using carbon dioxide as the surrounding gas. Can be deterred.

FIGS. 5 (a) and 5 (b) show P and P in a quasi-equal electric field.
FIG. 4 is a characteristic diagram showing a relationship between a breakdown voltage ratio of nitrogen and carbon dioxide to d (pressure × gap length), where (a) shows a case where a positive voltage is applied, and (b) shows a case where a negative voltage is applied. Is shown. As can be seen from this characteristic diagram, the dielectric breakdown voltage of carbon dioxide is higher than that of nitrogen in a wide range of Pd, and has a dielectric strength of about 1.5 times in a particularly low Pd region. Thereby, in addition to the effect of suppressing the start of discharge described in FIG.
The dielectric breakdown voltage of the entire insulating system is higher than that of nitrogen, so that a flat semiconductor device can have an improved dielectric strength and a reduced insulating dimension.

[0015]

As described above, according to the present invention, the use of carbon dioxide as a gas to be sealed in the package of a high-voltage, large-capacity flat semiconductor device improves the dielectric strength of the semiconductor device. At the same time, the insulation dimensions can be reduced and the insulation margin can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a flat semiconductor device in which a power IGBT module is implemented. FIG. 1 (a) is a plan view schematically showing an arrangement of IGBTs and diode chips mounted on a package, and FIG. Side view sectional view showing structure

FIG. 2 is a characteristic diagram showing a relation between a normal electric field and an ionization coefficient, which is obtained by comparing nitrogen and carbon dioxide.

FIG. 3 is a characteristic diagram showing a relationship between the size of a foreign substance attached to the surface of a component to which a voltage is applied and a relative breakdown voltage.

FIGS. 4A and 4B are schematic diagrams for explaining local electric field concentration between a ground metal and a high-voltage conductor. FIGS. 4A and 4B are side views of a model in which a sheath lead wire is connected to the ground metal. Figure and cross section, (c) is a side view of the model with an insulating dielectric interposed between the ground metal and the high-voltage conductor

FIG. 5 shows Pd (pressure × gap length) in a quasi-equal electric field,
Characteristic diagram showing the relationship between the breakdown voltage ratio of carbon dioxide to nitrogen

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flat package 2 IGBT chip 3 Diode chip 4 Surrounding case made of ceramics 5, 6 Case electrode 7 Collector electrode 8 Insulating partition 9 Gas conduit

Claims (1)

[Claims] 1. A high-voltage flat semiconductor device for electric power, comprising a power semiconductor chip mounted on a sealed flat package,
A high-withstand-voltage flat semiconductor device characterized in that a power semiconductor chip and a collector electrode are stacked and sandwiched between case electrodes of a package, and carbon dioxide is sealed as an insulating gas in a package in which an insulating gas is sealed. .