Semiconductor power conversion apparatus and method of manufacturing the same

A bus bar has a lead portion and a bus bar portion which are integrally shaped. The lead portion is provided in such a shape that branches from the bus bar portion. A part of the lead portion forms a connection part directly electrically connected with a transistor electrode and a diode electrode by a connecting material such as solder. The thickness of the lead portion including the connection part is made smaller than the thickness of the bus bar portion. Accordingly, such an interconnection structure can be provided in which the electrode of the semiconductor device and the bus bar are electrically directly connected with each other and thermal stress at the connection part therebetween can be relieved.

TECHNICAL FIELD

The present invention relates to a semiconductor power conversion apparatus and a method of manufacturing the same, and more particularly to a semiconductor power conversion apparatus having a structure in which a bus bar and a semiconductor device are directly connected with each other, and a method of manufacturing the same.

BACKGROUND ART

In a power conversion apparatus such as an inverter integrated into a motor, the electrodes of semiconductor devices included in the power conversion apparatus are electrically connected with other circuit components using a bus bar, as disclosed in Japanese Patent Laying-Open Nos. 2006-262664, 2004-364427, 2004-040877, 2005-261035, and 2006-074918.

In particular, Japanese Patent Laying-Open No. 2006-262664 discloses a power conversion apparatus suitable for motor drive of a hybrid vehicle, in which the top and bottom surfaces of such a structure as an inverter including semiconductor devices and bus bars are laminated with insulating films so that a plurality of semiconductor devices and circuits are collectively insulated. In particular, in a structure disclosed in Japanese Patent Laying-Open No. 2006-262664, electrodes of semiconductor devices and bus bars are directly connected with each other without bonding wire. Japanese Patent Laying-Open No. 2004-364427 discloses that bus bars are connected to both surfaces of a semiconductor device in order to establish electrical connection.

However, in the structure in which an electrode of a semiconductor device and a bus bar are directly connected with each other as disclosed in Japanese Patent Laying-Open Nos. 2006-262664 and 2004-364427, the bus bar is thermally expanded due to a temperature rise resulting from current passing or heat from the semiconductor device, so that thermal stress acts on a connection portion. Considering that a temperature rise is relatively large in an inverter having a bus bar connected to a plurality of semiconductor devices and that size reduction is demanded for a high-power, power conversion apparatus typically applied to a vehicle, such an interconnection structure is requested that can stably secure electrical connection between an electrode of a semiconductor device and a bus bar even at a temperature rise.

DISCLOSURE OF THE INVENTION

The present invention is made in order to solve such a problem. An object of the present invention is to provide a semiconductor power conversion apparatus having an interconnection structure that electrically directly connects an electrode of a semiconductor device and a bus bar with each other and can connect them stably even at a temperature rise, and a method of manufacturing the same.

A semiconductor power conversion apparatus in accordance with the present invention includes a semiconductor device for performing power conversion and a bus bar for electrically connecting an electrode of the semiconductor device and a circuit component external to the semiconductor device with each other. The bus bar is configured to include a connection section with the electrode and a non-connection section with the electrode that are integrally shaped and to have a thermal stress relief mechanism for relieving thermal stress acting on a connection part with the electrode formed of a part of the connection section.

According to the semiconductor power conversion apparatus described above, the integrally shaped bus bar allows the electrode of the semiconductor device and the bus bar to be electrically directly connected with each other. In addition, the amount of thermal expansion of the bus bar at the connection part can be reduced and therefore the thermal stress acting on the connection part can be relieved, so that the bus bar and the electrode can be connected stably even at a temperature rise.

Preferably, the connection section is formed such that at least the thickness of the connection part is smaller than that of the non-connection section, thereby forming the thermal stress relief mechanism.

Because of such a configuration, the amount of thermal expansion of the connection part with the electrode at a temperature rise is reduced, so that the thermal stress acting on the connection part can be reduced.

Preferably, the connection section has a part shaped to be displaceable in response to thermal stress acting on the connection part, as the thermal stress relief mechanism, in at least a part of a non-connection part with the electrode.

Because of such a configuration, the thermal stress acting on the connection part with the electrode can be released by displacement of the connection section at a temperature rise, so that the thermal stress acting on the connection part can be relieved.

Alternatively, preferably, the connection section has a part having a shape thinner than a thickness of the non-connection section and shaped to be displaceable in response to thermal stress acting on the connection part, in at least a part of a non-connection part with the electrode, thereby forming the thermal stress relief mechanism.

Because of such a configuration, the amount of thermal expansion of the connection part with the electrode at a temperature rise can be reduced, and in addition, the thermal stress acting on the connection part with the electrode can be released by displacement of the connection part, so that the thermal stress acting on the connection part can be relieved.

Preferably, the non-connection section has an electrical connection portion with the circuit component, and the connection section is shaped to branch from the non-connection section.

Therefore, the above-noted bus bar can be realized without complicating the shape.

Further preferably, the semiconductor power conversion apparatus further includes a fixed post for attaching the non-connection section and a circuit board mounted on the fixed post with the non-connection section interposed. The fixed post is formed of an insulating material. The non-connection section has a protrusion portion provided integrally with the non-connection section on that surface opposite to a surface having the fixed post attached thereon. The circuit board has a mounting hole having the protrusion portion fitted therein and a conductive portion. The conductive portion is configured such that electrical connection is established between the non-connection section and a circuit component on the circuit board by connecting the protrusion portion to the mounting hole.

According to the semiconductor power conversion apparatus as described above, provision of the protrusion portion on the bus bar facilitates alignment in the operation of mounting the circuit board, thereby improving the operability. As a result, throughput per unit time can be increased, so that the manufacturing costs can be reduced.

Alternatively, preferably, the bus bar includes first and second protection coats. The first protection coat is formed by covering a surface of a non-connection part with the electrode with an insulating material. The second protection coat is formed by heat-curing an insulating material coated on a surface of the connection part with the electrode in a state of being connected with the electrode.

Further preferably, the bus bar further includes a protection coat formed by heat-curing an insulating material coated on the surfaces of the connection section and the non-connection section in a state of being connected with the electrode.

According to the semiconductor power conversion apparatus described above, the volume that requires insulating protection for the semiconductor device and the connection part of the bus bar is reduced by avoiding the use of wire bonding. Accordingly, while the amount of insulating material for use is reduced, the connection part can be protected properly in view of both strength and insulation.

Preferably, the semiconductor device is configured such that current between first and second current electrodes is controlled according to a potential or current of a control electrode. The bus bar then electrically connects the control electrode with the circuit component. Alternatively, the bus bar electrically connects one of the first and second current electrodes with the circuit component.

According to the semiconductor power conversion apparatus described above, the thermal stress of the connection part is reduced and a disconnection failure is prevented for both the control electrode (typically, gate) and the current electrode (typically, collector and emitter) of a semiconductor device. In addition, the electrode of the semiconductor device and the bus bar can electrically directly be connected with each other without bonding wire.

Preferably, the bus bar is electrically connected with electrodes of a plurality of the semiconductor devices in common.

According to the semiconductor power conversion apparatus described above, the thermal stress of the connection part is reduced and a disconnection failure is prevented for the bus bar connected to a plurality of semiconductor devices and having its temperature easily increased. In addition, the electrode of the semiconductor device and the bus bar can electrically directly be connected with each other without bonding wire.

A method of manufacturing a semiconductor power conversion apparatus in accordance with the present invention includes first and second processes. In the first process, a bus bar is electrically connected with an electrode of a semiconductor device. The bus bar is configured to include a connection section with the electrode of the semiconductor device and a non-connection section with the electrode that are integrally shaped, and the connection section has a thermal stress relief mechanism for relieving thermal stress acting on a connection part with the electrode. In the second process, an insulating protection coat is formed at least for the connection part of the bus bar with the electrode formed through the first process.

According to the method of manufacturing a semiconductor power conversion apparatus described above, the integrally shaped bus bar allows the electrode of the semiconductor device and the bus bar to be electrically directly connected with each other. In addition, the amount of thermal expansion of the bus bar at the connection part can be reduced and therefore the thermal stress acting on the connection part can be relieved. As a result, a disconnection failure between the semiconductor device and the bus bar can be prevented.

Further preferably, prior to the first process, a protection coat is provided which is formed by covering with an insulating material a surface of a non-connection part with the electrode of the bus bar. The second process includes a first sub-process of coating with an insulating material a surface of the connection part with the electrode in a state of being connected with the electrode, and a second sub-process of forming the insulating protection coat by heat-curing a coating formed through the first sub-process. Further preferably, in the first sub-process, the surface of the connection part is coated with an insulating material by spraying a sol-like insulating resin.

Preferably, the second process includes a first sub-process of charging a gel-like insulating material for soaking the semiconductor device and the bus bar, a second sub-process of exhausting and recovering the insulating material so that a coating of the insulating material is left on the surfaces of the connection section and the non-connection section of the bus bar, and a third sub-process of heat-curing the coating of the insulating material formed through the second sub-process thereby forming the insulating protection coat.

According to the method of manufacturing a semiconductor power conversion apparatus as described above, the volume that requires insulating protection for the semiconductor device and the connection part of the bus bar is reduced. As a result, while the amount of insulating material for use is reduced, the connection part can be protected properly in view of strength and insulation.

Alternatively, preferably, in the first process, the non-connection section is attached to a fixed post formed of an insulating material. The method of manufacturing a semiconductor power conversion apparatus further includes a third process of mounting a circuit board on the fixed post with the non-connection section interposed. Then, the third process includes first and second sub-processes. In the first sub-process, a protrusion portion provided integrally with the non-connection section on that surface opposite to a surface of the non-connection section having the fixed post attached thereon is fitted into a mounting hole provided in the circuit board. In the second sub-process, the protrusion portion is connected with a conductive portion provided on a side surface of the mounting hole and electrically connected to a circuit component on the circuit board, whereby the conductive portion and the protrusion portion are electrically connected with each other.

According to the method of manufacturing a semiconductor power conversion apparatus as described above, alignment at a time of mounting a circuit board becomes easy and the operability of the third process is improved. As a result, throughput per unit time can be increased, so that the manufacturing costs can be reduced.

Therefore, according to a semiconductor power conversion apparatus and a method of manufacturing the same in accordance with the present invention, an electrode of a semiconductor device and a bus bar can electrically directly be connected with each other, and in addition, they can be connected stably even at a temperature rise,

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, an embodiment of the present invention will be described in detail with reference to the drawings. It is noted that the same or corresponding parts in the figures are denoted with the same reference characters and a description thereof will not basically be repeated.

FIG. 1is an electrical circuit diagram illustrating an exemplary configuration of a semiconductor power conversion apparatus in accordance with an embodiment of the present invention.

Referring toFIG. 1, an inverter100shown as a typical example of a semiconductor power conversion apparatus in accordance with an embodiment of the present invention is a power conversion apparatus performing electric power conversion between DC voltage of a DC power supply20and AC voltage of each phase of a rotating electric machine M1. A smoothing capacitor30for removing a ripple component of DC voltage is connected to the DC voltage side of inverter100.

DC power supply20is formed of a chargeable power storage device such as a battery or an electric double layer capacitor. The positive electrode of DC power supply20is connected to a positive-side cable21. On the other hand, the negative electrode of DC power supply20is connected to a negative-side cable22equivalent to a ground line.

Rotating electric machine M1formed of a three-phase AC synchronous motor, a three-phase induction motor or the like receives AC power from inverter100to generate a rotational driving force. Rotating electric machine M1is also used as a power generator. Electric power generated during deceleration (regeneration) is converted into DC voltage by inverter100and smoothed by smoothing capacitor30for use in charging DC power supply20.

Inverter100is a three-phase inverter including power semiconductor switching devices Q1-Q6. Although in the embodiment of the present invention the power semiconductor switching device is formed, for example, of an IGBT (Insulated Gate Bipolar Transistor), any other power semiconductor switching device such as a bipolar transistor or a MOS transistor may be used. In the following, the power semiconductor switching device is also referred to as a transistor.

Inverter100is comprised of a U-phase arm102, a V-phase arm104, and a W-phase arm106connected in parallel between a positive electrode bus bar170and a negative electrode bus bar171. U-phase arm102is comprised of transistors Q1, Q2connected in series between positive electrode bus bar170and negative electrode bus bar171. Similarly, V-phase arm104is comprised of transistors Q3, Q4connected in series between positive electrode bus bar170and negative electrode bus bar171, and W-phase arm106is comprised of transistors Q5, Q6connected in series between positive electrode bus bar170and negative electrode bus bar171.

Positive electrode bus bar170and negative electrode bus bar171are electrically connected with positive side cable21and negative side cable22, respectively, through a connection terminal60.

In each phase arm, the connection point between the transistor in the upper arm and the transistor in the lower arm connected in series is electrically connected with each phase end of each phase coil of rotating electric machine M1. Specifically, the connection points of U-phase arm102, V-phase arm104, and W-phase arm106are electrically connected with the respective one ends of a U-phase coil, a V-phase coil, and a W-phase coil by output bus bars174,176, and178, respectively, through a connection terminal70. The other ends of the phase coils of rotating electric machine M1are electrically connected with each other at a neutral point N1.

Passing current of transistors Q1-Q6is taken out as each phase current by output bus bars172,174,176and transmitted to each phase coil of rotating electric machine M1. A current sensor118is provided for output bus bars172,174,176to send the detected each phase current to a control circuit40.

Drive control circuits DC1-DC6are provided respectively corresponding to transistors Q1-Q6. Drive control circuits DC1-DC6control the on/off of the corresponding transistors Q1-Q6in response to respective switching control signals S1-S6generated by a signal generation circuit50. Furthermore, anti-parallel diodes D1-D6are provided in parallel with transistors Q1-Q6, respectively, for allowing reverse current to pass through.

Control circuit40controls an operation of semiconductor power conversion apparatus (inverter)100. Specifically, control circuit40receives a torque command value of rotating electric machine M1, each phase current value, and an input voltage to inverter100(i.e. an output voltage of DC power supply20) to calculate an applied voltage to each phase coil of rotating electric machine M1based on well-known PWM (Pulse Width Modulation) control and output the calculation result to signal generation circuit50.

Signal generation circuit50receives the voltage calculation result for each phase coil from control circuit40to generate switching control signals S1-S6that are PWM control signals for controlling the on/off of transistors Q1-Q6. Switching control signals S1-S6are sent to drive control circuits DC1-DC6, respectively.

It is noted that a converter (not shown) for DC voltage conversion may additionally be arranged on the side of DC power supply20away from smoothing capacitor30. In such a configuration, by controlling the operation of the converter, DC voltage of inverter100can be controlled variably such that AC voltage amplitude applied to rotating electric machine M1attains the optimum level according to the operation region of rotating electric machine M1. Specifically, control circuit40receives the aforementioned torque command value and motor rotational speed to calculate the optimum value (target value) of DC voltage (input voltage) of inverter100. Control circuit40then generates a control signal for specifying a switching operation of the converter which is necessary to realize this input voltage.

FIG. 2is an electrical circuit diagram illustrating a bus bar connection to a semiconductor device in each arm.

Referring toFIG. 2, in each arm, a transistor Q (transistors Q1-Q6or a collective designation of transistors in the not-shown converter) typically formed of IGBT and a diode D (reverse parallel diodes D1-D6or a collective designation of diodes in the not-shown converter) are provided each as a “semiconductor device.”

Transistor Q has current electrodes (main electrodes)150,152and a control electrode154as electrodes and is configured such that passing current between current electrodes150and152is controlled according to a potential or current at control electrode154.

Control electrode154corresponds to a gate in IGBT and a MOS transistor and corresponds to a base in a bipolar transistor. Current electrode150,152correspond to a collector and an emitter in IGBT and a bipolar transistor and correspond to a drain and a source in a MOS transistor. Diode D has an anode (positive electrode)162and a cathode (negative electrode)164as electrodes.

For example, transistor Q has a vertical transistor structure in which current electrodes150,152are formed on the respective opposing surfaces (main electrode surfaces) of a semiconductor chip. Then, control electrode154is formed on either one of the main electrode surfaces. Control electrode154has its potential or current driven by a drive control circuit DC (a collective designation of drive control circuits DC1-DC6). Signal wiring (not shown) electrically connecting sensors and circuits provided for drive control circuit DC and the transistors is also provided in parallel with the drive wiring (not shown). The above-noted drive wiring and signal wiring is formed of a bus bar200c.

The current electrode of transistor Q (also referred to as the transistor electrode hereinafter)150and the cathode of diode D (also referred to as the diode electrode hereinafter)164are connected with a bus bar200a. Anode162of diode D is the electrode in common with current electrode152of transistor Q (also referred to as common electrode152hereinafter) and is connected with a bus bar200b. Each of bus bars200a,200bcorresponds to one of positive electrode bus bar170, negative electrode bus bar171, and output bus bars172,174,176shown inFIG. 1.

In other words, each electrode of the semiconductor device (transistor Q and diode D) is electrically connected to a circuit component external to the semiconductor device, specifically, positive side cable21(the positive electrode of the DC power supply), negative side cable22(the negative electrode of the DC power supply), each phase coil wiring of rotating electric machine M1, drive control circuit DC, or the like, through bus bar200a,200b, or200cformed of a conductor such as copper or aluminum. In the following, bus bar200cis also referred to as a “signal line bus bar” as distinguished from bus bars200a,200bthrough which current associated with power conversion passes.

FIG. 3is a plan view illustrating a connection structure between the semiconductor devices and the bus bars.FIG. 3corresponds to a top view of inverter100mounted on a cooling plate300.

Referring toFIG. 3, each of semiconductor chips302arranged on cooling plate300has transistor Q and diode D shown inFIG. 2.

Transistor electrode150and diode electrode164are provided each as a device top-side electrode and electrically connected with bus bar200a. Bus bar200aincludes a bus bar portion205aand a lead portion210a. Of bus bar200a, bus bar portion205acorresponds to a “non-connection section with the electrode” in the present invention and lead portion210acorresponds to a “connection section with the electrode” in the present invention. Bus bar portion205aextends in the up and down direction on the drawing sheet and is supported by a fixed post310formed of an insulating material.

Referring toFIG. 4that is a cross-sectional view taken along IV-IV inFIG. 3, bus bar portion205a(thickness t1) is supported by fixed post310and is electrically connected to a circuit component external to the semiconductor device as described above through a connection member320corresponding to connection terminal60or70shown inFIG. 1. Although not shown, fixed post310is fixed to cooling plate300by a fastening member such as a bolt or by adhesion.

Referring toFIG. 3again, lead portion210ais formed integrally with bus bar portion205aand is provided to branch from bus bar portion205asuch that it extends in the right and left direction on the drawing sheet. Connection parts215awith transistor electrode150and diode electrode164are provided at part of lead portion210a. That area of bus bar portion205aand lead portion210aexcluding connection part215a, namely, the hatched area inFIG. 3of bus bar200ahas an insulating coat501formed by covering the surface with an insulating material such as an insulating film.

Referring toFIG. 5that is a cross-sectional view taken along V-V inFIG. 3, bus bar200ahaving lead portion210aand bus bar portion205ais formed by integrally press-forming a metal such as copper or aluminum such that a thickness t2of lead portion210aincluding connection part215ais smaller than a thickness t1of bus bar portion205a(t2<t1) and that lead portion210abranches from bus bar portion205a.

Furthermore, lead portion210ais press-formed such that connection part215ais opposed to transistor electrode150and diode electrode164and that the other part is bent as appropriate away from the semiconductor devices. Connection parts215aare electrically directly connected with transistor electrode150and diode electrode164by a connecting material160such as solder without using bonding wire.

Thickness t2of lead portion210aincluding connection part215ais determined by a thickness limit that does not cause a break with application of current, in view of the amount of passing current, and by a formation limit in press-forming. Thickness t2is reduced, for example, to the order of 0.1 mm or so.

In this manner, of bus bar200a, at least connection part215awith the electrode of the semiconductor device (transistor Q or diode D) is reduced in thickness, so that the amount of thermal expansion at the connection part at a temperature rise can be reduced and the acting thermal stress can be reduced, even in a structure in which the electrodes of semiconductor devices and the bus bars are electrically directly connected with each other using the integrally shaped bus bar200awithout bonding wire. In other words, a “thermal stress relief mechanism” in the present invention can be formed by reducing the thickness of at least connection part215aof lead portion210.

Referring toFIG. 3again, common electrode152is provided as a device lower-side electrode and is electrically connected with bus bar200b. Bus bar200bis configured similarly to bus bar200aand includes a bus bar portion205band a lead portion210b. Bus bar portion205bextends in the up and down direction on the drawing sheet and is supported by fixed post310formed of an insulating material, similarly to bus bar portion205a. Bus bar portion205bis also electrically connected with a circuit component external to the semiconductor device as described above, through connection member320corresponding to connection terminal60or70shown inFIG. 1, on fixed post310.

Referring toFIG. 6that is a cross-sectional view taken along VI-VI inFIG. 3, bus bar200bis also provided similarly to bus bar200asuch that thickness t2of lead portion210bincluding connection part215bis smaller than thickness t1of bus bar portion205b(t2<t1) and that lead portion210bbranches from bus bar portion205b. Bus bar200bis also fabricated similarly to bus bar200aby integrally press-forming a metal such as copper or aluminum.

Lead portion210bis press-formed such that connection part215bis opposed to common electrode152and the other part is bent as appropriate away from the semiconductor devices. Connection part215bis directly electrically connected with common electrode152by connecting material160such as solder without using bonding wire.

Therefore, at least connection part215bof bus bar200bis also reduced in thickness, so that the amount of thermal expansion at the connection part at a temperature rise can be reduced and the acting thermal stress can be relieved, even in a structure in which the electrodes of semiconductor devices and the bus bar are electrically directly connected with each other without bonding wire.

Referring toFIG. 3again, control electrode154is electrically connected with signal line bus bar200c. Signal line bus bar200cis fabricated by integrally press-forming a metal such as copper or aluminum, similarly to bus bars200a,200b, and includes the integrally shaped bus bar portion205cand lead portion210c. Bus bar portion205cextends in the up and down direction on the drawing sheet and is fixed with attached to a fixed post330formed of an insulating material. Lead portion210cis provided in such a shape that branches from bus bar portion205b. A part of lead portion210cforms connection part215cthat is directly connected with control electrode154.

Since signal line bus bar200cis provided as drive wiring for control electrode154or signal wiring transmitting sensor outputs etc. as described above, a plurality of signal line bus bars200care arranged in parallel. The respective bus bar portions205cof these independent signal line bus bars200care electrically insulated from each other by an insulating film or the like and arranged in a stack. In that part of lead portion210cexcluding connection part215c, insulating coat501is formed by covering the surface with an insulating material such as an insulating film.

As shown inFIG. 7, a circuit board400equipped with circuit components such as drive control circuit DC is mounted on the main body of inverter100using fixed post330. Circuit board400is attached to fixed post330with signal line bus bar200cinterposed. Then, the circuit component such as drive control circuit DC on circuit board400is electrically connected with the semiconductor device by each signal line bus bar200c.

Circuit board400is provided with a mounting hole410. Furthermore, a conductive path420is formed between a circuit component on circuit board400and mounting hole410by forming a wiring pattern. In other words, mounting hole410additionally serves as a terminal for connecting the above-noted circuit component with the outside.

In the region VII inFIG. 5, a cross section taken along V-V inFIG. 3is shown with circuit board400being mounted.

Fixed post330supporting bus bar portion205cof signal line bus bar200cis fixed to cooling plate300by a fastening member305such as a bolt or by adhesion. A protrusion portion220for being fitted into mounting hole410of circuit board400is provided on the surface opposite to that surface having bus bar portion205cattached to fixed post330. Protrusion portion220is a conductor portion integrally formed with bus bar portion205c. In other words, protrusion portion220can also be fabricated by press-forming.

On a side surface of mounting hole410of circuit board400, a conductive connection portion415is formed which is electrically continuous from conductive path420(FIG. 7). Therefore, an electrical contact is formed between protrusion portion220and conductive connection portion415by fitting protrusion portion220of signal line bus bar200cinto mounting hole410of circuit board400and then performing resistance pressure welding or ultrasonic/laser bonding, so that a circuit component such as drive control circuit DC on circuit board400and signal line bus bar200ccan electrically be connected with each other.

Signal line bus bar200cis also provided such that the thickness of lead portion210cincluding connection part215cis smaller than the thickness of bus bar portion205band that lead portion210bbranches from bus bar portion205b, similarly to bus bars200a,200b.

Therefore, at least connection part215cof bus bar200cis also reduced in thickness, so that the amount of thermal expansion at the connection part at a temperature rise can be reduced and the acting thermal stress can be relieved, even in a structure in which the control electrodes of semiconductor devices and the bus bar are electrically directly connected with each other without bonding wire.

Therefore, even for connection part215cwith control electrode154, thermal stress acting on the connection part at a temperature rise due to heat from any other circuit component can be relieved because of the bus bar connection structure similar to the one for transistor electrode150, common electrode152, and diode electrode164.

As described above, for each of bus bars200a,200band signal line bus bar200c, bus bar portions205a,205b,205cand lead portions210a,210b,210cincluding connection parts215a,215b,215care integrally shaped and connection parts215a,215b,215care directly connected with the electrodes of semiconductor devices by jointing material160, thereby eliminating the need for wire bonding and reducing the manufacturing costs.

In addition, lead portions210a,210b,210care reduced in thickness so that at least connection parts215a,215b,215care reduced in thickness. Therefore, the amount of thermal expansion at the connection parts at a temperature rise is reduced and the acting thermal stress is relieved, resulting in an interconnection structure that allows them to connect each other stably even at a temperature rise. As a result, in a high power and compact power conversion apparatus typically applied to a vehicle, even when the bus bar and the electrode are directly connected with each other without bonding wire, their connection is stable at a temperature rise, thereby preventing disconnection.

FIG. 8shows a process of manufacturing the semiconductor power conversion apparatus in accordance with an embodiment of the present invention, more specifically, an assembly process thereof.

Referring toFIG. 8, in the semiconductor power conversion apparatus in accordance with the present embodiment, in process P100, electrical connection is established by connecting a semiconductor devices formed on each semiconductor chip302on cooling plate300with bus bars200a-200cdescribed above.

Then, upon completion of the bus bar connection operation in process P100, an insulating protection coat forming operation for ensuring insulation of connection parts215a,215b,215cis performed in process P200.

Then, upon completion of the insulating protection coat forming operation in process P200, an operation of mounting circuit board400shown inFIG. 7is performed in process P300.

As shown inFIG. 9, process P300includes sub-processes P310and P320. In sub-process P310, as shown inFIG. 5, protrusion portion220of signal line bus bar200cis fitted into mounting hole410of circuit board400. In sub-process P320, pressure welding or laser or ultrasonic bonding is performed at the concave and convex side surfaces that are fitted together in sub-process P310, so that an electrical contact can be secured between signal line bus bar200cand mounting hole410also serving as a terminal of a circuit component such as drive control circuit DC.

In this manner, signal line bus bar200cis provided with protrusion portion220to be mounted on circuit board400, so that alignment becomes easier in the operation of mounting circuit board400, thereby improving the operability. Accordingly, the throughput per unit time in the circuit board mounting operation (process P300) can be increased, thereby reducing the manufacturing costs of the semiconductor power conversion apparatus.

Next, the insulating protection coat forming operation in process P200will be described in detail.

FIG. 10shows a first example of the insulating protection coat forming process.

As shown inFIG. 11, connection part215a,215b,215cof each bus bar200a,200b,200crequires insulation since an insulating coat (reference numeral501inFIG. 3) such as an insulating film has not yet been formed. In sub-process P210, each connection part is coated with an insulating material500. For example, by spraying a sol-like insulating material (typically, a thermosetting resin such as silicone), a part that requires insulation can be coated locally with insulating material500.

Referring toFIG. 10again, in sub-process P220, the insulating material coated on the surfaces of connection parts215a,215b,215cis subjected to heat treatment using a furnace or the like. As a result, as shown inFIG. 12, the insulating material is cured to form an insulating protection coat510on the surfaces of connection parts215a,215b,215c.

As a result, insulation of connection parts215a,215b,215cis secured, and in addition, the curing treatment improves the mechanical connection strength between the bus bar and the electrode.

FIG. 13shows a second example of the insulating protection coat forming process.

In sub-process P250, as shown inFIG. 14, a gel storage container610is attached to surround that part of the semiconductor device which is connected with the bus bar. Gel storage container610is provided with a gel inlet620and a gel outlet625.

In sub-process P260, the gel-like insulating material (typically, thermosetting resin)600sucked through a filter640by a pump630is supplied from gel inlet620into gel storage container610. Accordingly, the semiconductor devices and the bus bars are soaked as a whole in gel-like insulating material600.

In the subsequent sub-process P270, gel-like insulating material600in gel storage container610is exhausted from gel outlet625. The exhausted gel-like insulating material600is recovered and reused. After exhaustion of gel-like insulating material600, a coating of gel-like insulating material600adheres on the surfaces of the bus bars and the semiconductor devices.

In sub-process P280, gel-like insulating material600in the form of a coating is subjected to a heat curing treatment using a furnace or the like. As a result, as shown inFIG. 15, the insulating material is cured to form an insulating protection coat650on the surface of the semiconductor devices and the bus bars as a whole, including the surfaces of connection parts215a,215b,215c. In addition, the curing treatment provides insulation and also improves mechanical connection strength between the bus bar and the electrode.

According to the insulating protection coat forming process in the second example shown inFIG. 13, it is not necessary to form an insulating coat from an insulating film or the like, for that part other than connection parts215a,215b,215cof bus bars200a,200b,200c, prior to the bus bar connecting process (process P100). In other words, after the integrally shaped bus bars200a,200b,200care fabricated with a bare material such as copper, aluminum, or brass that is not insulated, bus bars200a,200b,200ccan be insulated and protected as a whole including connection parts215a,215b,215cthrough the insulating protection coat forming process (P250-P280) after completion of the bus bar connecting process (process P100). Thus, the manufacturing costs of the bus bar can be reduced. In addition, gel-like insulating material600other than the one adhering on the surfaces of the semiconductor devices and the bus bars can be recovered and reused, thereby reducing the costs of the insulating material.

In particular, in the semiconductor power conversion apparatus in accordance with the present embodiment, a bus bar connection structure can be realized without using wire bonding, so that the volume (spatial extent) of the connection parts that can be insulated and protected can significantly be reduced. Therefore, since an insulating coat is formed locally only at a surface portion of the connection part, insulation can be secured even with the reduced amount of insulating material usage. In addition, since the insulating protection coat is formed through the curing treatment, the mechanical connection strength can also be secured.

In a structure in which bus bars and semiconductor devices are electrically connected through wire bonding, the entire bonding wire needs to be insulated from the surroundings. Thus, in general, insulation is provided for a large volume by providing a housing so as to surround the semiconductor devices and the bus bars and then filling the housing with a gel-like insulating material. By contrast, in the semiconductor power conversion apparatus in accordance with the present embodiment, the improvement of the bus bar connection structure can significantly reduce the amount of insulating material for use and reduce the manufacturing costs.

Although in the foregoing description lead portions210a,210b,210cof bus bars200a,200b,200care reduced in thickness, the lead portion may be structured as shown inFIG. 16as a modification in order to relieve thermal stress at the connection part between the electrode and the bus bar.

As can be understood from comparison betweenFIG. 16andFIG. 5, in the bus bar in accordance with the modification, loose parts250are provided as appropriate at non-connection parts with electrodes, of lead portions210a,210cof bus bars200a,200c. Loose part250may be formed by bending or presswork. Provision of loose part250ensures that lead portion210acan be displaced in the direction in which lead portion210aextends, in response to thermal stress acting on connection parts215a,215c, whereby thermal stress at the connection part between an electrode and a bus bar can be relieved even with a uniform thickness of the entire bus bar without reducing the thickness of lead portion210a. In short, the “thermal stress relief mechanism” in the present invention can also be formed with such loose part250.

Furthermore, as shown inFIG. 17, the structures inFIG. 5andFIG. 16can be combined. Specifically, loose parts250may be provided for lead portions210a,210ceach having the reduced thickness. As a result, the effect of relieving thermal stress can be enhanced. It is hereby confirmed that the similar modification may also be applied to bus bar200b, although not shown inFIG. 16andFIG. 17. InFIG. 16andFIG. 17, the bus bar structure may be formed such that the lead portion is provided with a part shaped to be displaced in response to thermal stress acting on the connection part, in a manner different from loose part250.

The embodiment disclosed herein should be understood as being illustrative rather than being (imitative in all respects. The scope of the present invention is shown not by the foregoing description but by the claims and equivalents to the claims and all modifications with the scope of the claims are intended to be embraced.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a semiconductor power conversion apparatus having a structure in which an electrode of a semiconductor device is electrically connected with another circuit component through a bus bar.