JP3139383B2 - Cooling device for power semiconductors - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for cooling a power semiconductor used in the field of power electronics. [0002] In recent years, in the field of power electronics, GTO thyristors (gate turn-off thyristo) have been developed.
r), IGBT (insulated gate bipolar transistor)
The progress of power semiconductors (hereinafter simply referred to as “semiconductors”) such as power transistors, which are typified by, is remarkable. These semiconductors are components such as choppers, converters, and inverters that are widely used as control devices and power supply devices for electric motors, and convert or control large power. The semiconductor generates considerable heat due to the internal loss accompanying the switching for the conversion and control of the large power. However, the semiconductor is extremely weak to heat, and the junction temperature is 130 to 150.
Destruction occurs when temperature exceeds ℃. Therefore, cooling these semiconductors to below the allowable temperature is indispensable for securing the operation speed, improving the reliability, or extending the life. On the other hand, a motor control device and a power supply device are generally composed of a plurality of semiconductors, and it is necessary to minimize the temperature difference between the semiconductors in order to operate normally. Furthermore, the proportion of the cooling device in the size and weight of the control device and the power supply device of these electric motors is large, and as the size and performance of the entire device are rapidly increasing, it is strongly required that the cooling device be reduced in size and weight. Have been. Conventionally, a cooling device using a heat sink or a heat pipe has been developed in order to remove heat generated from these semiconductors. For example, a cooling device in which a semiconductor constituting an inverter is mounted on the back surface of a heat sink having cooling fins and the heat sink is forcibly air-cooled by a fan is disclosed in JP-A-3-256562. In this prior art, a cooling air flow is caused to flow in parallel with the heat sink bottom plate, and a plurality of semiconductors are arranged in the cooling air flow direction. Further, as another example, a heat pipe cooling thyristor stack in which a plurality of semiconductors are attached to a heat absorbing side of a heat pipe and secondary cooling is performed by natural air cooling of a fin provided on a heat radiating side is described in 1987, edited by The Japan Society of Mechanical Engineers,
"Cooling Technology for Electronic Equipment", pp. 72-73, '87, published by Hakuhodo Shuppan. [0004] The above prior art has the following problems. In the technique disclosed in Japanese Patent Application Laid-Open No. 3-256562, a plurality of semiconductors are arranged in a direction in which cooling air flows, so that air whose temperature is increased by heat radiation from semiconductors located on the upstream side flows through the semiconductors on the downstream side. As a result, the temperature of the semiconductor on the downstream side becomes higher. In order to prevent this temperature rise, it is necessary to increase the air flow rate, and it is unavoidable to increase the size of the fan and increase the noise. Furthermore, when the degree of integration of semiconductors increases and the amount of heat generation increases, it becomes difficult to reduce the temperature difference between semiconductors to a predetermined value or less. On the other hand, in the cooling method described in "Cooling Technology for Electronic Equipment", edited by the Japan Society of Mechanical Engineers, the temperature difference between semiconductors is almost eliminated, but a heat pipe is interposed between a heat generating portion and a heat radiating portion. In order to increase the cooling capacity, the radiator must be forcibly cooled, and a separate fan such as a fan is required. Therefore, an increase in the size and weight of the device is inevitable. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the conventional cooling technique, and has as its object to provide a small and lightweight power semiconductor cooling device having a small cooling temperature difference between semiconductors. And The present inventors have conducted various experiments and studies to develop a light-weight cooling device capable of uniformly cooling a heat-generating power semiconductor. As a result, the axial flow fan is mounted on the pin fin type heat sink, and the cooling air flows vertically into or out of the substrate from the upper end of the pin fin, and the semiconductor that generates heat is disposed on the peripheral portion of the back surface of the heat sink.
It has been found that the cooling temperature difference between semiconductors is very small, and that the cooling device itself does not need to be increased in size and can be reduced in weight. The present invention has been made based on such findings, and the gist thereof is as follows. In a cooling apparatus, a heat sink provided with a plurality of radiating pin fins which are in close contact with one surface of a substrate and an axial fan having a rotation axis perpendicular to the substrate is mounted near the tip of the radiating pin fins. A power semiconductor cooling device characterized in that a power semiconductor to be cooled is mounted on a surface of a substrate in a temperature T region satisfying the following expression, which is determined in advance, on a surface opposite to the surface provided with the pin fins. . T ≦ 0.7 · (Tmax−Ta) + Ta where: T: A condition opposite to the surface of the heat sink substrate on which the pin fins are provided, under a constant heat flux condition (the heat generation density per unit time becomes uniform). Temperature Tmax of the surface of the substrate in contact with the heater when the axial flow fan is rotated in a steady state with a heater of the same size as the surface of the substrate that generates heat under such conditions) FIG. 1 is a diagram showing an example of a cooling device according to the present invention. Inverter cooling using an IGBT, which is a typical power semiconductor, is shown in FIG. FIG. FIG.
FIG. 2B is a perspective view, and FIG. 2B is a plan view of a surface of the heat sink opposite to the surface provided with the pin fins (hereinafter referred to as the back surface of the substrate). In FIG. 1, a heat sink 1 is of a pin fin type having a large number of pins 3 of rectangular cross section on the surface of a substrate 2 thereof. The inverter element 4 to be cooled is mounted on the back surface of the substrate. In this example, as shown in FIG. 2B, the six IGBTs 4a to 4f, which are the heating elements, are closely bonded to the outer peripheral edge of the back surface of the heat sink substrate by screws (not shown). On the heat sink 1, four axial fans 5a to 5d are fixed in close contact with the tips of the pin fins by screws 6. Each axial fan has a motor 7 and a blade 8 at the center, and cooling air is flown into the heat sink from the outside by the axial fan. The rotating directions of the adjacent axial fans are opposite to each other so that the air flows flowing from the axial fans to the heat sink hardly collide with and interfere with each other. The heat generated by the IGBT moves in the order of the heat sink substrate and the pin fins by heat conduction, is transmitted to the cooling air by heat transfer from the pin fin surface, and flows out to the outer periphery of the heat sink. FIG. 2 shows that the heater shown in FIG. 1 is used to make a heater close to the entire back surface instead of the IGBT using the cooling device composed of the fan and the heat sink. FIG. 4 is a distribution diagram of T-Ta, the difference between the temperature of the back surface of the substrate and the temperature of the atmosphere around the substrate when the substrate is heated under various conditions. From this distribution diagram, it can be seen that the periphery is cooled better than the center of the substrate, and the temperature is low and uniform. This temperature distribution is due to the fact that cooling air is difficult to flow directly under the motor of the axial fan and the temperature is high, and the center of the heat sink also interferes with other parts because the airflow from each fan interferes somewhat. This is presumably because the air at the center of the substrate rises because the air is less likely to flow. From this, it can be seen that when the heating element is placed on the peripheral portion of the heat sink substrate, the cooling effect is high and the temperature difference between the heating elements is reduced. As a result of various experiments and examinations on the position of the substrate suitable for mounting the semiconductor, the temperature T on the back surface of the heat sink was T ≦ 0.7 · (Tmax−T
a) It was confirmed that the region was + Ta. That is, T is a heater having the same size as the surface of the heat sink substrate and having the same size as the surface of the substrate, which is closely attached to the surface of the heat sink substrate opposite to the surface provided with the pin fins. Is the temperature of the substrate surface in contact with the heater when is rotated in a steady state. Tmax is the maximum temperature of the substrate surface in contact with the heater, and Ta is the temperature of the atmosphere around the substrate. The substrate mounting position of the semiconductor is defined as follows.
The reason for setting the area to be (Tmax-Ta) + Ta is as follows. That is, T is 0.7 · (Tmax−Ta) +
When a semiconductor is mounted at a position exceeding Ta, the difference between the temperature of the semiconductor and the temperature of the semiconductor mounted on the outermost peripheral portion of the substrate becomes too large, and the electrical characteristics of the integrated circuit formed on the semiconductor differ from the temperature. It was confirmed that the temperature difference of the semiconductor became equal to or less than a general allowable value. The dotted line shown in FIG.
7 · (Tmax−Ta) + Ta isotherm. In this case, the semiconductor may be mounted on the substrate surface outside the isotherm. FIG. 3 is a diagram showing an example of a state where a semiconductor is mounted in a region where T is 0.7 · (Tmax−Ta) + Ta or less in the case of the temperature distribution shown in FIG. The arrangement of IGBT
FIG. 3A shows an epoch-making effect.
Even if they are arranged radially as in (b), a sufficient effect, that is, an effect that the cooling effect is high and the temperature difference between the heating elements is reduced. If the IGBT whose output has a significant temperature dependency is arranged as described above, effective cooling can be performed, and the IGBT can be effectively cooled.
The normal operation of a power device or the like using the above is guaranteed. The cooling air may flow from the side of the heat sink, be sucked out by the axial fan, and flow out to the outside. At this time, it is preferable that the rotation directions of the axial fans adjacent to each other are opposite to each other. FIGS. 4A and 4B show an example of a cooling device according to the present invention when one axial fan is used. FIG. 4A is a perspective view, and FIG.
Is a view as seen from the back side of the substrate. In FIG.
The heat sink 1 is of a pin fin type having a large number of pins 3 having a rectangular cross section on the surface of a substrate 2. As shown in FIG. 4B, four IGBTs 4a to 4d as heating elements
Is T ≦ 0.7 · (Tmax on the back surface of the heat sink substrate 2.
−Ta) It is tightly joined to the outer peripheral portion of the substrate satisfying + Ta by a screw (not shown). Heat sink 1
, An axial fan 5 is fixed by a screw 6 close to the tip of the fin. Each axial fan has a motor 7 in the center.
And cooling blades 8, and the cooling air is flown into the heat sink from the outside by an axial fan. FIG. 5 shows the temperature of the back surface of the heat sink substrate when the entire back surface is heated under the same heat flux condition instead of the IGBT shown in FIG. 4B using the fan and the heat sink having the structure shown in FIG. Difference from ambient temperature around substrate, TT
The distribution of a is shown. The dotted line in the figure is T = 0.7 · (Tmax−
It is an isotherm of Ta) + Ta. In this temperature distribution, the isothermal lines are substantially concentric, and the IGBTs, which are the four heating elements, are also arranged at the periphery of the heat sink as shown in FIG. Can be made smaller than a predetermined value. The number of semiconductors may be any number as long as the semiconductors can be tightly fixed to the periphery of the substrate. The cross-sectional shape of the pin fin of the heat sink is not limited to a rectangle, but may be a circle, an ellipse, or the like. Note that the use of the pin fin type heat sink in the present invention is superior in heat radiation than in the case of using other fin shapes without directivity of air flow, and is suitable for cooling a power semiconductor having a large calorific value. Because there is. The heat sink is preferably made of a material having a high thermal conductivity, such as aluminum or an alloy thereof. In order to improve the performance of the cooling device according to the present invention, it is desirable that the axial fan be of a high static pressure and large air flow type as long as noise and noise conditions permit. EXAMPLES Example 1 The cooling performance of the cooling device shown in FIG. 1 was examined. The heat sink and the axial fan of the cooling device used were as follows. Heat sink: substrate dimensions: 243 mm x 243 mm x 5 mm Pin fin height: 35 mm Pin fin cross section: 2 mm x 2 mm (rectangular cross section) Pin fin pitch: 4 mm Substrate, fin material: Duralumin (JISA2024) Fan: Axial fan (4 ): External dimensions: 120 mm × 120 mm Input voltage: AC100V Input current: 0.13 A At this time, the fans 5a and 5c in FIG. 1A are clockwise as viewed from above, and 5b and 5d are counterclockwise. , And arranged to flow cooling air into the heat sink. On the back surface of the heat sink substrate, six 118 mm × 60 mm sheet heaters were replaced with T
FIG. 1 that satisfies ≦ 0.7 · (Tmax−Ta) + Ta
Paste at the positions of 4a to 4f shown in FIG.
W, heat is generated at a total of 1800 W, and each fan is input 100
It was rotated at V and cooled. As a result of measuring the temperature between the atmosphere and the surface of the seat heater, the difference between the temperatures was 46.8 ° C. on average and 4 min.
At 5.0 ° C., a maximum of 50.4 ° C., the difference between the maximum and minimum temperatures was only 5.4 ° C. Next, as a comparative example, the same cooling device as described above was used, and the same six sheet heaters were attached to the back surface of the heat sink substrate. FIG. 6 is a view showing the state of attachment of six sheet heaters (4a to 4f). This gives T ≦ 0.7
Affixed over the periphery of the substrate satisfying (Tmax-Ta) + Ta and the center of the substrate not satisfying (Tmax-Ta) + Ta. In the same manner as described above, each heater was heated at 300 W, that is, 1800 W in total, and each fan was rotated at an input of 100 V to perform a cooling test. The temperature difference between the atmosphere and the surface of the seat heater is 54.2 ° C. on average, 45.9 ° C. minimum, and 81.0 ° C. maximum.
1 ° C., and the difference between the maximum temperature and the minimum temperature was 35.2 ° C. Comparing the two, the cooling device of the present invention has improved cooling performance on average by 15% or more in terms of thermal resistance as compared with the comparative example, and the difference between the maximum temperature and the minimum temperature is about 1%.
It can be seen that this is greatly improved to / 7. Example 2 The cooling performance of a cooling device having one axial fan shown in FIG. 4 was examined. The heat sink and the axial fan of the cooling device used were as follows. Substrate dimensions: 120 mm × 120 mm × 3 mm Pin fin height: 22 mm Pin fin diameter: 2 mm (circular cross section) Pin fin pitch: 4 mm Substrate, fin material: pure aluminum (JISA1050) Fan: axial flow fan (1) External dimensions: 120 mm × 120 mm Input voltage: AC 100 V Input current: 0.13 A Four 58 mm × 28 mm sheet heaters are provided on the back surface of the heat sink substrate, and T ≦ 0.7 · (Tmax−Ta) + T
4a-4d shown in FIG. 4 (b) that satisfies a.
The cooling test was performed by rotating the fan at 100 V input. The atmosphere and the surface temperature of the seat heater were measured. The average temperature difference is 46.1 ° C, minimum 42.7 ° C, maximum 52.9 ° C.
And the difference between the maximum temperature and the minimum temperature was only 10.2 ° C. Next, as a comparative example, the same cooling device as described above was used, and four identical sheet heaters were attached to the back surface of the heat sink substrate. FIG. 7 is a view showing a state in which four seat heaters are attached (4a to 4d). This gives T ≦ 0.7
Affixed over the periphery of the substrate satisfying (Tmax-Ta) + Ta and the central portion of the substrate not satisfying (Tmax-Ta) + Ta. As described above, each heater was heated at 130 W, that is, at a total of 490 W, and each fan was rotated at an input of 100 V to perform cooling. As a result, the temperature difference between the atmosphere and the surface of the seat heater was 68.4 ° C. on average and 45. 1 ℃, up to 10
2.9 ° C, the difference between the maximum and minimum temperature is 57.8 ° C
Met. Comparing the two, the cooling device of the present invention has improved cooling performance by an average of 45% or more in terms of thermal resistance as compared with the comparative example, and the difference between the maximum temperature and the minimum temperature is about 1%.
It can be seen that this is greatly improved to / 6. According to the present invention, the cooling capability of the heat sink as a whole can be improved, and at the same time, the cooling can be performed so that the temperature difference between the heat-generating semiconductors becomes very small. The size and weight can be reduced. If the present invention is applied to cooling of a power semiconductor such as an inverter using an IGBT, a semiconductor having a large calorific value can be cooled by simple forced air cooling without increasing the size of a heat sink. It can be said that it greatly contributes to the development of the electronics industry.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of a cooling device of the present invention. FIG. 2 is a diagram showing a temperature distribution on a back surface of a heat sink substrate. FIG. 3 is a diagram showing an example of a semiconductor arrangement of the cooling device of the present invention. FIG. 4 is a diagram showing another example of the cooling device of the present invention. FIG. 5 is a diagram showing a temperature distribution on the back surface of the heat sink substrate. FIG. 6 is a diagram showing an example of a semiconductor arrangement of a conventional cooling device. FIG. 7 is a diagram showing another example of a semiconductor arrangement of a conventional cooling device. [Description of Signs] 1 heat sink 2 heat sink substrate 3 pin fin 4 semiconductor 5 axial fan 7 motor

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05K 7/20 H01L 23/36 H01L 23/467

Claims (1)

(57) [Claims] Cooling in which an axial fan having a rotation axis perpendicular to the substrate is attached to a heat sink provided with a plurality of radiating pin fins which are in close contact with one surface of a substrate and provided upright on the one surface of the substrate. The device is characterized in that a power semiconductor to be cooled is mounted on a surface of the substrate in a temperature T region satisfying the following equation, which is determined in advance, on a surface of the substrate opposite to the surface provided with the heat radiation pin fins. Cooling device for power semiconductors. T ≦ 0.7 · (Tmax−Ta) + Ta where: T: a condition where the heat flux is fixed on the surface of the heat sink substrate opposite to the surface provided with the pin fins (the condition that the heat generation density per unit time becomes uniform) ), The temperature of the substrate surface in contact with the heater when the axial fan is rotated in a steady state with a heater of the same size as the surface of the substrate, which generates heat in close contact, Tmax: the maximum temperature of the substrate surface in contact with the heater Ta: temperature of the atmosphere around the substrate