JP2008042124A - Semiconductor power module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce conductive noise of mainly 30 MHz or lower in a semiconductor power module. <P>SOLUTION: With respect to the semiconductor power module 2, a rectifying circuit 7 and an inverter circuit 8 are packaged integrally, while as in metal base plates 10a and 10b and cooling bodies 5a and 5b, is constituted separated. Furthermore, the cooling bodies 5a and 5b are connected via an impedance element 15 so that the conductive noise having a frequency, of especially 30 MHz or lower, can be reduced efficiently. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for reducing high-frequency leakage current and electromagnetic noise associated with a switching operation in an inverter or uninterruptible power supply (UPS) that performs power conversion by switching a power semiconductor element.

Power conversion devices such as inverters and UPS perform power conversion by switching power semiconductor elements built in a power module at a frequency of several KHz to several tens KHz. An example of the circuit configuration of the power converter is shown in FIG.
FIG. 7 shows a typical circuit connected to a three-phase AC power source 6 as a multi-phase power source. The three-phase AC power source 6 is temporarily connected to a DC power source (DC smoothing in the figure) by a bridge circuit unit 7 composed of diode chips 71 to 76. (Shown as electrolytic capacitor 1).

  By switching the rectified DC power supply 1 with the upper and lower arms alternately by IGBTs (insulated gate bipolar transistors) 81 to 86 as power semiconductor elements, AC power is supplied to the motor 3 as a load to change the motor 3. Drive at frequency. The IGBTs 81 to 86 are connected to freewheeling diodes (FWD) 91 to 96 in antiparallel, and perform an operation of returning the motor current when the IGBT is off.

  Further, the switching of the IGBT is generally performed by a PWM (pulse width modulation) system. Furthermore, the power module applied to the power converter includes an IGBT chip and an FWD chip housed in the module container 2, and heat generated by energization of the power chip passes through the metal base 10 installed on the bottom surface of the module container 2. The cooling body 5 is often configured to be cooled.

FIG. 8 is a cross-sectional view showing the structure of the power module.
Here, circuit patterns 12a and 12b are formed on the surface of the insulating substrate 13, and power chips 71 and 81 are mounted by soldering or the like. The power chip and the circuit pattern are connected by an aluminum wire 111 or the like. The back surface of the insulating substrate 13 is a solid pattern 12c so as to be fixed to the metal base 10 serving as a ground. The metal base 10 provided on the bottom surface of the module is attached to the cooling body 5, and the electrical loss (= heat) generated when the power chip is energized is conducted to the metal base 10 and the cooling body 5 through the insulating substrate 13. To dissipate heat.

  On the other hand, the circuit patterns 12a and 12b and the metal base 10 are electrically insulated by an insulating substrate 13 made of a material such as ceramic. That is, as shown in FIG. 7, the cooling body 5 to which the module 2 is attached is electrically insulated from the electric circuit portions 7 and 8, so as to prevent an electric shock or a ground fault due to contact with the cooling body 5. In addition, the cooling body 5 is grounded (see reference numeral 4 in FIG. 7). Further, the power module 2 is provided with terminals 2 a to 2 d and wired to the capacitor 1, the AC power source 6, and the motor 3 installed outside.

FIG. 9 is a top view showing the internal structure of the power module.
That is, a circuit pattern 12a corresponding to the rectifier circuit unit 7 and a circuit pattern 12b corresponding to the inverter circuit unit are respectively formed on the surface of the insulating substrate 13, and the chips 71 to 76, 81 to 86, and 91 to 96 are The circuit pattern is connected by wiring with solder or aluminum wire 112.

In the configuration as described above, a high dv / dt (voltage change) is generated by switching a power semiconductor element such as an IGBT, and a high-frequency common mode current flows between the ground 4 and the main electric circuits 7 and 8. A phenomenon occurs. This is because the main circuit and the cooling body (ground) are coupled by the capacity of the insulating substrate.
As described above, the electrical circuits 7 and 8 and the ground 4 are insulated from each other by the insulating substrate 13. However, when the high-frequency current flows out, communication failure occurs in the radio installed near the power converter. May occur, or other devices connected to the same power supply device may be adversely affected.

The path of the noise current is indicated by reference numeral 16 in FIG. As the inverter-side power chips 81 to 86 and 91 to 96 are switched, the potential of the inverter circuit unit 8 fluctuates with respect to the ground 4, so that a high-frequency current flows through the ground line, and this current flows to other devices. It may have an adverse effect or be radiated as electromagnetic noise.
FIG. 6 shows an equivalent circuit in this case. In the figure, reference numeral 134 denotes a common mode electromotive force generated by switching of the power chip, and 132 denotes a stray capacitance with respect to the ground of the inverter circuit unit 8, that is, a capacitance of the insulating substrate. Reference numeral 131 denotes a stray capacitance C with respect to the ground on the rectifier circuit unit 7 side, and 133 denotes a stray inductance L existing on the wiring between the rectifier circuit and the inverter circuit.

By the way, as a prior art for the purpose of suppressing the noise current flowing as shown in FIG. 6, for example, as in Patent Document 1, a conductive layer other than the ground electrode, that is, the potential of the main electric circuit is provided in the insulating substrate of the power module. In order to prevent noise current from flowing to the ground line, as in Patent Document 2, for example, the cooling body is not grounded, or an electrode having a small potential fluctuation, for example, a positive electrode or a negative electrode is connected to the cooling body. In some cases, the conduction noise is reduced.
However, in Patent Document 1, since the thickness of the insulating layer film between the main electric circuit and the ground line becomes thin, the stray capacitance between the circuit and the ground increases, and the leakage current to the ground line increases. The problem arises.

  On the other hand, in the case of Patent Document 2, when the cooling body is not grounded, structural considerations for preventing electric shock due to contact with the cooling fins are required. In general, the stray capacitance between the main electric circuit and the ground line is several tens pF to several hundreds pF, whereas the junction capacitance of the switching element is 1000 pF or more. Therefore, the noise electromotive force generated at the time of switching is applied to the former capacitance, and the stray capacitance on the device side can be regarded as a short circuit. Therefore, it cannot be said that the positive and negative lines are stable with respect to the ground line, and may fluctuate similarly to the output terminal.

Therefore, the applicant separates the inverter device 1 into a rectifier module and an inverter module as in Patent Document 3, for example, and each module is provided with a radiator, and between these radiators via an impedance element. A method of reducing noise by connecting is proposed (proposed method).
JP 2000-031325 A JP 2000-260937 A JP 2006-115649 A

However, the proposed method mainly reduces radiated noise at a frequency of 30 MHz or higher, and not only a target different from that for reducing conductive noise at a frequency of 30 MHz or lower, but also a rectifier module and an inverter module. There is a problem that it can be applied only to those separated.
Therefore, an object of the present invention is to make it applicable to a module in which a rectifier circuit and an inverter circuit are integrally formed, and particularly to reduce conduction noise at a frequency of 30 MHz or less.

In order to solve such a problem, according to the first aspect of the present invention, the first metal base insulated from the rectifier circuit unit is provided for the semiconductor module in which the rectifier circuit unit and the inverter circuit unit are integrally packaged. A plate and a second metal base plate insulated from the inverter circuit section are separately provided, and noise is reduced by insulating the first metal base plate and the second metal base plate from each other. Features.
In the invention of claim 1, the first metal base plate and the second metal base plate can be short-circuited via an impedance element (invention of claim 2).

  In the first aspect of the invention, the first cooling body to which the first metal base plate is attached and the second cooling body to which the second metal base plate is attached are separated from each other. (Invention of claim 3). In the invention of claim 3, the first metal base plate or the first cooling body and the second metal base plate or the second cooling body are short-circuited via an impedance element. (Invention of claim 4).

  According to the present invention, in the power module in which the rectifier circuit and the inverter circuit are integrated, it is possible to particularly reduce the conductive noise by separating the cooling base plate of these power circuits. As a result, the noise filter can be reduced or reduced, and there is an advantage that noise can be reduced at a low cost. That is, the power module is often integrated from the viewpoint of cost reduction and space saving, but it can be said that the present invention is effective when applied to such a case.

1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a sectional view of FIG. 1, and FIG. 4 is a top view of FIG.
As shown in FIGS. 1, 2 and 4, the circuit patterns 12a and 12b and the power chips 71 to 76, 81 to 86 and 91 to 96 formed on the surface of the insulating substrate 13 are arranged in the conventional power module. Same as the configuration. Here, the ground pattern on the back surface of the insulating substrate 13 and the metal base portion to which the ground pattern is fixed are divided into a rectifier circuit side 10a and an inverter circuit side 10b, and these are packaged as one power module 2. It is a feature. The ground pattern is divided into 12c and 12d as shown in FIG.
The cooling bodies to which the power modules are attached are also installed as 5a and 5b for the rectifier circuit 7 and the inverter circuit 8, respectively. Between these cooling bodies 5a and 5b, impedances such as ferrite cores and resistors are provided. Element 15 is connected.

As shown in FIG. 4, the rectifier circuit unit 7 and the inverter circuit unit 8 are arranged on the same insulating substrate 13, and the metal base plate is divided into 10a and 10b and packaged. Further, the cooling body 5a to which the metal base 10a on the rectifier circuit 7 side is attached and the cooling body 5b to which the metal base 10b on the inverter circuit 8 side is attached are configured separately. An impedance 15 such as a resistor, a ferrite core, or a soft magnetic material typified by an amorphous metal thin film (amorphous) magnetic material is inserted between the cooling bodies 5a and 5b. One of the cooling bodies 5a and 5b (5a in FIG. 1) is grounded (4) to prevent electric shock.
Here, the impedance 15 may be connected between the divided metal base plates 10a-10b, or may be connected between the divided cooling bodies 5a-5b. Or you may connect between the metal base 10a-cooling body 5b and between the metal base 10b-cooling body 5a.

Further, when the impedance 15 is connected, the temperature immediately below and in the vicinity of the semiconductor elements (diodes, IGBTs) constituting the rectifier circuit and the inverter circuit becomes high due to heat generation of the semiconductor elements. Since the heat generating heat dissipation path is formed in the direction of the semiconductor element → the metal base plate → the cooling body, it is preferable to provide an impedance 15 at a location that does not hinder this.
For example, a resistance element may be soldered to a metal base plate, or a ferrite core or an amorphous magnetic material may be screwed to the cooling body.

The equivalent circuit of FIG. 1 is shown in FIG.
By inserting the impedance 15 as shown in FIG. 1, the noise current indicated by reference numeral 16 in FIG. 5 is suppressed and attenuated, so that the noise can be made smaller than in the conventional case shown in FIG. On the other hand, ferrite or amorphous is an inductance at a low frequency, and can be regarded as a short circuit in terms of direct current. Moreover, since it can be equivalently regarded as a resistance at a high frequency, it has a noise current suppressing effect as described above.

FIG. 3 is a sectional view showing another embodiment of the present invention.
As is clear from comparison with FIG. 1, the case where the insulating substrate 13 of FIG. 1 is separated into a rectifier circuit 13a and an inverter circuit 13b is shown. The cooling bodies are also configured separately as shown in the figure, but if the noise current is not a problem (small), the cooling bodies may be combined into one. Thereby, the effect similar to FIG. 1, FIG. 2 can be anticipated.

Configuration diagram showing an embodiment of the present invention Module cross-sectional view of FIG. Module sectional view showing another embodiment of the present invention Top view of FIG. Equivalent circuit diagram showing noise current path in case of FIG. Equivalent circuit diagram showing conventional noise current path Configuration diagram showing a typical power conversion circuit example Module sectional view of FIG. Top view of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Smoothing capacitor (DC power supply), 2 ... Module container, 2a-2d ... Terminal, 3 ... Motor (load), 4 ... Grounding, 5a, 5b ... Cooling body, 6 ... Three-phase alternating current power supply, 7 ... Rectification circuit part , 71-76, 81-86, 91-96 ... semiconductor chip, 8 ... inverter circuit section, 10a, 10b ... metal base plate, 111, 112 ... wire, 12a, 12b ... circuit pattern, 12c, 12d ... ground pattern, 13, 13a, 13b ... insulating substrate, 131, 132 ... stray capacitance, 133 ... stray inductance, 134 ... common mode electromotive force, 15 ... impedance.

Claims (4)

  A first metal base plate insulated from the rectifier circuit unit and a second metal insulated from the inverter circuit unit for a semiconductor module in which the rectifier circuit unit and the inverter circuit unit are integrally packaged. A semiconductor power module, wherein a base plate is provided separately, and noise is reduced by insulating the first metal base plate and the second metal base plate from each other.   The semiconductor power module according to claim 1, wherein the first metal base plate and the second metal base plate are short-circuited via an impedance element.   2. The semiconductor according to claim 1, wherein a first cooling body to which the first metal base plate is attached and a second cooling body to which the second metal base plate is attached are separated from each other. Power module. 4. The short circuit between the first metal base plate or the first cooling body and the second metal base plate or the second cooling body via an impedance element. The semiconductor power module described in 1.

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