JP7481109B2 - Power Module - Google Patents

Description

The present invention relates to a power module.

Electric and hybrid vehicles are equipped with a motor as the vehicle's power source, and a power conversion device is provided to control the power supplied to this motor. The power conversion device includes a power module with built-in power semiconductor elements, a drive circuit that drives the power module, a control circuit that controls them, and a capacitor for smoothing the current.

Power modules generate large amounts of heat due to power conversion losses, so if the temperature rises, the performance of the power module decreases and there is a risk that its useful life will also be shortened. To prevent the effects of this heat, various technological developments have been made regarding highly efficient cooling technologies.

As one of the cooling technologies for power modules, a direct cooling structure in which the heat dissipation base of the circuit body housing the power semiconductor elements is placed inside the refrigerant flow path provides high cooling performance. In addition, a double-sided direct cooling structure that cools the circuit body from both the front and back also has high cooling performance and has been put to practical use.

For example, Patent Document 1 describes providing a flow path cover that faces the heat dissipation base of the circuit body and forms a flow path for the refrigerant, and laser welding the edge of the flow path cover to the heat dissipation base.

Since a refrigerant flows through the flow paths of a power module, internal pressure is generated. This internal pressure places high stress on the welded parts, and if there is an internal defect in the welded part, the strength around the defect will be insufficient, and weld cracks will progress to the surface, making it impossible to ensure airtightness and watertightness. In particular, weld cracks will progress quickly if an external force is applied to them. From the perspective of product quality, it is necessary to completely eliminate weld cracks.

JP 2019-68533 A

The welded joint between the flow passage cover and the heat dissipation base was prone to weld cracks, and internal defects in the welds could impair the airtightness of the flow passage.

The power module of the present invention includes a circuit body, and a flow path cover fixed to an outer periphery of a heat dissipation base of the circuit body by a weld and forming a flow path space between the circuit body and the heat dissipation base through which a refrigerant flows, the distance from the outer periphery of the flow path cover to the center of the weld is greater than the plate thickness of the flow path cover, and the weld is made of an aluminum alloy having a Mg content of 0.2 to 2.0% (mass%, the same applies below) and a Si content of 0.2 to 0.6% .
The power module of the present invention includes a plurality of circuit bodies, an intermediate frame that connects the plurality of circuit bodies and is fixed to a heat dissipation base of the circuit bodies at a second welded portion, and a flow path cover that is fixed to an outer periphery of the intermediate frame at a first welded portion and forms a flow path space between the intermediate frame and the heat dissipation base through which a refrigerant flows, wherein a distance from an outer periphery end of the flow path cover to a center of the first welded portion is greater than a plate thickness of the flow path cover, a relationship between a distance Ls from an inner periphery end of the intermediate frame to the center of the second welded portion and a plate thickness Ts of the intermediate frame is 0<Ls/Ts<3.0, and a composition of the first welded portion is formed of an aluminum alloy having a Mg content of 0.2 to 2.0% (mass%, the same applies below).

The present invention makes it possible to prevent weld cracks in the welded parts and maintain the airtightness of the flow path.

FIG. 2 is a cross-sectional view of the power module according to the first embodiment. 5 is a cross-sectional view of the vicinity of a welded portion between a flow passage cover and a heat dissipation base in the first embodiment. FIG. FIG. 2 is a diagram for explaining the effect of the ratio of the welding position and the plate thickness on the weld crack susceptibility. FIG. 4 is a diagram showing the shape of a weld bead of a welded portion. FIG. 2 is a top view of the power module according to the first embodiment. FIG. 11 is a cross-sectional view of a power module according to a second embodiment. FIG. 11 is a cross-sectional view of the vicinity of a welded portion of a power module according to a second embodiment. FIG. 11 is a top view of a power module according to a second embodiment. FIG. 11 is a cross-sectional view of the vicinity of a welded portion in a modified example of the second embodiment.

Embodiments of the present invention will be described below with reference to the drawings. The following description and drawings are examples for explaining the present invention, and some parts have been omitted or simplified as appropriate for clarity of explanation. The present invention can also be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

The position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc., in order to facilitate understanding of the invention. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[First embodiment]
FIG. 1 is a cross-sectional view of a power module 100 according to the first embodiment.
As shown in FIG. 1, a circuit body 120 of a power module 100 incorporates two power semiconductor elements 100-a and 100-b.

The two power semiconductor elements 100-a, 100-b are bonded on both sides to conductive substrates 102-a, 102-b by first adhesive resins 101-a, 101-b. The conductive substrates 102-a, 102-b are joined to cooling substrates 110-a, 110-b, which have a multi-layer structure, by second adhesive resins 103-a, 103-b. The cooling substrates 110-a, 110-b are formed by laminating conductive layers 104-a, 104-b, insulating layers 105-a, 105-b, and heat dissipation bases 106-a, 106-b, with the heat dissipation bases 106-a, 106-b being arranged on the outside.

The circuit body 120 is constructed by sealing the power semiconductor elements 100-a, 100-b, conductive substrates 102-a, 102-b, cooling substrates 110-a, 110-b, etc. with resin (not shown).

A number of cooling pin fins 107-a, 107-b are joined to the heat dissipation bases 106-a, 106-b facing outward. In addition, flow path covers 202-a, 202-b are installed to cover the cooling pin fins 107-a, 107-b of the heat dissipation bases 106-a, 106-b. The flow path covers 202-a, 202-b are fixed to the outer periphery of the heat dissipation bases 106-a, 106-b with first welds 301-a, 301-b, and form flow path spaces 203-a, 203-b through which the refrigerant flows between the heat dissipation bases 106-a, 106-b.

In the power module 100 configured as described above, heat generated from the power semiconductor elements 100-a, 100-b is conducted to the cooling pin fins 107-a, 107-b, and the refrigerant flows through the flow passage spaces 203-a, 203-b, thereby cooling the heat of the power semiconductor elements 100-a, 100-b. Note that, although the power module 100 with a double-sided direct cooling structure is shown in this embodiment, a power module with a single-sided direct cooling structure may also be used.

FIG. 2 is a cross-sectional view of the first welded portion 301-a and its vicinity.
2, the flow passage cover 202-a and the heat dissipation base 106-a are joined by laser welding at a first welded portion 301-a. As described later, the distance from the outer peripheral end 202-e of the flow passage cover 202-a to the center position of the first welded portion 301-a is denoted by Ld, and the plate thickness of the flow passage cover 202-a is denoted by Td.

Next, we will explain the composition of the materials used for the heat dissipation base 106-a and the flow path cover 202-a. The same applies to the heat dissipation base 106-b and the flow path cover 202-b.

The heat dissipation base 106-a and the flow path cover 202-a use an aluminum alloy with the same composition. Specifically, an aluminum alloy plate material is used that has an Mg content of 0.2-2.0% (mass%, the same applies below), a Si content of 0.2-0.6%, a Cu content of 0.2% or less, a Mn content of 1.5% or less, and a total content of other alloying elements of 0.5% or less.

The reason why the compositional components of the aluminum alloy are specified as above is that they were selected to prevent cracks during laser welding. This is the result of conducting laser welding experiments on aluminum alloys with different compositional components and analyzing the correlation between the differences in compositional components and laser welding cracking susceptibility (ease of cracking). Specifically, if the Mg content is 0.2% or less, the strength of the aluminum alloy is insufficient, and if it exceeds 2.0%, the occurrence rate of cracks increases sharply under the same welding conditions. Furthermore, as the Mg content increases, the ratio and size of voids that occur in the first welded part 301-a due to the intense evaporation of Mg during laser welding also increases sharply, and the water pressure of the refrigerant in the flow path increases the risk of refrigerant leakage.

The reason why the Si content is specified as 0.2-0.6% is that a certain amount of alloying elements must be added to improve the strength of the aluminum alloy. The Si content has the effect of improving the fluidity of the molten pool during welding, and also allows the formation of a eutectic structure during the solidification of the molten pool, which has a certain effect on reducing weld cracks. However, if the Si content exceeds 0.6%, the cracking sensitivity increases.

Cu is an element that generally promotes cracking, but it is necessary to add a small amount to improve corrosion resistance and strength. In this embodiment, the Cu content is 0.2% or less.

Mn is an alloying element that is often used in aluminum alloys because it has the effect of preventing deterioration of toughness and corrosion resistance, and has a particularly excellent hardening effect. However, in the case of laser welding, if the Mn content is 1.5% or more, the occurrence rate of weld cracks increases, so in this embodiment, it is set to 1.5% or less.

In this embodiment, the heat dissipation base 106-a and the flow path cover 202-a are made of materials having the same composition, no additives are used during welding, and the composition of the weld metal (metal of the first welded part 301-a) formed after welding is the same as that of the heat dissipation base 106-a and the flow path cover 202-a. That is, the composition of the first welded part 301-a is Mg content 0.2 to 2.0%, Si content 0.2 to 0.6%, Cu content 0.2% or less, Mn content 1.5% or less, other alloy element content flow rate 0.5% or less in total, and the remainder Al. Even if the heat dissipation base 106-a and the flow path cover 202-a are made of materials having a different composition from the above, as long as the composition of at least the first welded part 301-a is the same as the above, weld cracks can be prevented.

The aluminum alloy composition as described above is the composition with the lowest susceptibility to weld cracking for the weld structure described below. If the rigidity of the structure is improved by changing the weld structure, the requirements for the range of compositional components described above will be somewhat broader. In particular, elements other than Mg may be adjusted depending on the weld structure. Therefore, the composition of the first welded part 301-a welded in this embodiment has a Mg content of 0.2 to 2.0%, which is the minimum required condition for preventing laser weld cracking.

Next, the plate thickness Td and the welding structure of the passage cover 202-a will be described with reference to FIG.
In this embodiment, the flow passage cover 202-a uses a plate material with a plate thickness Td of 1.0 mm or more and 3.0 mm or less. This is because a plate thickness of 1.0 mm or more is necessary due to the requirements for the overall structural strength and rigidity. If the plate thickness is 3.0 mm or more, the entire power module 100 becomes larger, and the amount of heat input used in laser welding must also increase. As a result, the weld is more likely to crack and the deformation of the welded part becomes larger.

The welding conditions for laser welding in the above-mentioned material composition and welded structure vary depending on the plate thickness of the flow path cover 202-a, but are as follows when the plate thickness Td of the flow path cover 202-a is 1.0 mm or more and 3.0 mm or less. The laser wavelength is 1.0 μm or more, the laser output is 1.0 kW to 4.0 kW, the welding speed is 2.0 m/min to 20 m/min, and the shielding gas is Ar or N2. In this embodiment, an infrared laser with a wavelength of 1.0 μm or more is used, but a green laser with a wavelength of 500 μm to 550 μm or a blue laser with a wavelength of 300 μm to 400 μm may also be used.

After determining the thickness Td of the flow path cover 202-a, the welding position is determined. That is, the distance Ld from the outer peripheral end 202-e of the flow path cover 202-a shown in FIG. 2 to the laser irradiation position (the center position of the first welded portion 301-a) is determined so that the ratio to the thickness Td of the flow path cover 202-a is Ld/Td>1.0.

3 is a diagram for explaining the influence of the ratio of the welding position and the plate thickness on the weld crack susceptibility, in which the horizontal axis indicates Ld/Td and the vertical axis indicates the crack susceptibility.
The laser welding crack susceptibility experiment used aluminum plate test pieces with different plate thicknesses. For each aluminum plate test piece with different plate thicknesses, bead-on-plate welding capable of penetrating the plate material was performed under welding conditions of constant laser output and welding speed while changing the distance of the laser irradiation position from the outer peripheral end 202-e of the test piece. After welding, the occurrence of cracks in the center of the weld bead was evaluated. The crack susceptibility can be quantitatively evaluated from the length of the crack.

Figure 3 shows the relationship between Ld/Td and the crack susceptibility (coefficient of susceptibility to cracking) based on the length of the weld crack. As shown in Figure 3, as Ld/Td increases, the laser sensitivity decreases. That is, for a given plate thickness Td, if the position of the first welded portion 301-a is increased in distance from the outer peripheral end 202-e of the plate material, the material between the first welded portion 301-a and the outer peripheral end 202-e has a certain deformation capacity. In this case, the degree of restraint on the first welded portion 301-a decreases, and the tensile stress applied to the first welded portion 301-a decreases, preventing weld cracks. In particular, when Ld/Td is 1.0 or more, the tensile stress decreases rapidly, and it has been confirmed that good welding without cracks can be performed in this embodiment.

The reason why the ratio of distance Ld to plate thickness Td was set to Ld/Td > 1.0 is that experiments have demonstrated a correlation between laser weld cracking susceptibility and Ld/Td, as shown in Figure 3.

FIG. 4 is a diagram showing the shape of the weld bead of the first welded portion 301-a.
The ratio of the weld bead width W of the first welded portion 301-a to the plate thickness Td is 0.3<W/Td<1.0. This is because a certain weld bead width W is necessary to ensure the strength of the first welded portion 301-a, and also because welding deformation and stress increase when the weld bead width W exceeds Td.

FIG. 5 is a top view of the power module 100 in this embodiment.
The flow path cover 202-a is approximately 250-300 mm long and 40-100 mm wide, and is fixed to the heat dissipation base 106-a (see FIG. 1) by first welded parts 301-a all around. The three dotted rectangular frames 109 in the figure each indicate an area including a plurality of power semiconductor elements. The cross-sectional view taken along line A-A is shown in FIG. 1.

[Second embodiment]
FIG. 6 is a cross-sectional view of a power module 200 according to the second embodiment.
A power module 200 in the second embodiment shown in Fig. 6 differs from the power module 100 in the first embodiment shown in Fig. 1 in that intermediate frames 201-a, 201-b are provided to connect a plurality of circuit bodies 120. The same parts as those in the first embodiment shown in Fig. 1 are given the same reference numerals and their description will be omitted.

In this embodiment, the heat dissipation bases 106-a, 106-b of the circuit body 120 are fixed to the intermediate frames 201-a, 201-b at the second welded parts 302-a, 302-b. Furthermore, the flow path covers 202-a, 202-b are fixed to the outer periphery of the intermediate frames 201-a, 201-b at the first welded parts 301-a, 301-b. The flow path covers 202-a, 202-b form flow path spaces 203-a, 203-b through which the refrigerant flows between the heat dissipation bases 106-a, 106-b. In this embodiment, unlike the first embodiment, the flow path covers 202-a, 202-b are not directly welded to the heat dissipation bases 106-a, 106-b. Furthermore, by providing the intermediate frames 201-a, 201-b, the heat dissipation bases 106-a, 106-b and the flow path covers 202-a, 202-b are not directly welded, so there is little deformation due to heat, etc., and the flow path covers 202-a, 202-b are less likely to crack.

The circuit body 120 is constructed by sealing the power semiconductor elements 100-a, 100-b, conductive substrates 102-a, 102-b, cooling substrates 110-a, 110-b, etc. with resin (not shown). Note that, although this embodiment shows a power module 200 with a double-sided direct cooling structure, a power module with a single-sided direct cooling structure may also be used.

FIG. 7 is a cross-sectional view of the vicinity of a welded portion of a power module 200 according to the second embodiment.
The welding of the flow passage cover 202-a and the intermediate frame 201-a is the same as that of the first embodiment shown in Fig. 2. That is, the ratio of the distance Ld from the outer peripheral end 202-e of the flow passage cover 202-a to the laser irradiation position (the center position of the first welded portion 301-a) to the plate thickness Td of the flow passage cover 202-a is Ld/Td>1.0. This is a ratio necessary to prevent weld cracks, as in the first embodiment.

The second welded portion 302-a that connects the heat dissipation base 106-a and the intermediate frame 201-a is the inner peripheral edge of the intermediate frame 201-a. In other words, the welded joint is a fillet joint. If the distance from the inner peripheral edge of the intermediate frame 201-a to the center of the second welded portion 302-a is Ls (see Figure 9), then the ratio of the distance Ls to the plate thickness Ts of the intermediate frame 201-a is Ls/Ts = 0.

FIG. 8 is a top view of the power module 200 in this embodiment.
In this example, three circuit bodies 120 are connected by an intermediate frame 201-a. The heat dissipation base 106-a (see FIG. 6) of each circuit body 120 is fixed to the intermediate frame 201-a at a second welded portion 302-a. The second welded portion 302-a is the entire outer periphery of the heat dissipation base 106-a of the circuit body 120. The flow path cover 202-a is fixed to the intermediate frame 201-a at its entire outer periphery by a first welded portion 301-a. The cross-sectional view of the line B-B is shown in FIG. 6.

(Modification)
FIG. 9 is a cross-sectional view of the vicinity of a welded portion in a modified example of the second embodiment.
The welding of the flow passage cover 202-a and the intermediate frame 201-a is the same as that of the first embodiment shown in Fig. 2. That is, the ratio of the distance Ld from the outer peripheral end 202-e of the flow passage cover 202-a to the laser irradiation position (the center position of the first welded portion 301-a) to the plate thickness Td of the flow passage cover 202-a is Ld/Td>1.0. This is a ratio necessary to prevent weld cracks, as in the first embodiment.

The distance Ls from the inner peripheral end 201-e of the intermediate frame 201-a to the center of the second welded portion 302-a is set so as to satisfy the condition 0 < Ls/Ts < 3.0 with respect to the plate thickness Ts of the intermediate frame 201-a. The reason for setting Ld/Ts to 3.0 or less is to make the size of the power module 200 and the flow path as small as possible.

In the power module 200 of the second embodiment, the first welded portion 301-a is made of an aluminum alloy with a Mg content of 0.2 to 2.0% (mass %, the same applies below). The second welded portion 302-a is made of an aluminum alloy with a Mg content of 0.2 to 2.0%. The heat dissipation bases 106-a, 106-b, the intermediate frames 201-a, 201-b, and the flow path covers 202-a, 202-b are made of an aluminum alloy with a Mg content of 0.2 to 2.0%, a Si content of 0.2 to 0.6%, a Cu content of 0.2% or less, and a Mn content of 1.5% or less. By using such a composition, weld cracks can be prevented.

According to the embodiment described above, the following advantageous effects can be obtained.
(1) The power module 100 includes a circuit body 120 and flow path covers 202-a, 202-b that are fixed to the outer periphery of the heat dissipation bases 106-a, 106-b of the circuit body 120 by first welds 301-a, 301-b and form flow path spaces 203-a, 203-b through which a refrigerant flows between the heat dissipation bases 106-a, 106-b, and the distance from the outer periphery end 202-e of the flow path covers 202-a, 202-b to the center of the first welds 301-a, 301-b is greater than the plate thickness Td of the flow path covers 202-a, 202-b, and the composition of the first welds 301-a, 301-b is formed of an aluminum alloy with a Mg content of 0.2 to 2.0% (mass %, the same applies below). This prevents weld cracks in the welds and maintains the airtightness of the flow paths.

(2) The power module 200 includes a plurality of circuit bodies 120, intermediate frames 201-a, 201-b that connect the plurality of circuit bodies 120 and are fixed to the heat dissipation bases 106-a, 106-b of the circuit bodies 120 by second welding parts 302-a, 302-b, and flow path covers 202-a, 202-b that are fixed to the outer periphery of the intermediate frames 201-a, 201-b by first welding parts 301-a, 301-b and form flow path spaces 203-a, 203-b through which a refrigerant flows between the flow path covers 202-a, The distance from the outer peripheral end 202-e of the intermediate frame 201-a, 201-b to the center of the first welded portion 301-a, 301-b is greater than the plate thickness of the flow path cover 202-a, 202-b, and the relationship between the distance Ls from the inner peripheral end 201-e of the intermediate frame 201-a, 201-b to the center of the second welded portion 302-a, 302-b and the plate thickness Ts of the intermediate frame 201-a, 201-b is 0<Ls/Ts<3.0, and the composition of the first welded portion 301-a, 301-b is formed from an aluminum alloy with a Mg content of 0.2 to 2.0% (mass %, the same below). This prevents weld cracks in the welded portion and maintains the airtightness of the flow path.

The present invention is not limited to the above-described embodiment, and other forms that are conceivable within the scope of the technical concept of the present invention are also included within the scope of the present invention, so long as they do not impair the characteristics of the present invention. In addition, the above-described embodiment may be combined with modified examples.

100, 200... Power module, 100-a, 100-b... Power semiconductor element, 101-a, 101-b... First adhesive resin, 102-a, 102-b... Conductive substrate, 103-a, 103-b... Second adhesive resin, 104-a, 104-b... Conductive layer, 105-a, 105-b... Insulating layer, 106-a, 106-b... Heat dissipation base, 107-a, 10 7-b...cooling pin fins, 110-a, 110-b...cooling substrate, 120...circuit body, 201-a, 201-b...intermediate frame, 201-e...inner peripheral end, 202-a, 202-b...flow path cover, 202-e...outer peripheral end, 203-a, 203-b...flow path space, 301-a, 301-b...first welded part, 302-a, 302-b...second welded part.

Claims (5)

A circuit body;
a flow path cover that is fixed to an outer periphery of the heat dissipation base of the circuit body by a welding portion and that forms a flow path space through which a refrigerant flows between the flow path cover and the heat dissipation base,
A distance from an outer peripheral end of the flow passage cover to a center of the welded portion is greater than a plate thickness of the flow passage cover,
The power module is formed from an aluminum alloy having a composition of the welded portion with a Mg content of 0.2 to 2.0% (mass %, the same applies below) and a Si content of 0.2 to 0.6% . 2. The power module according to claim 1,
The heat dissipation base and the flow path cover are made of an aluminum alloy having a composition including an Mg content of 0.2 to 2.0%, an Si content of 0.2 to 0.6%, a Cu content of 0.2% or less, and an Mn content of 1.5% or less. A plurality of circuit bodies;
an intermediate frame that connects the plurality of circuit bodies and is fixed to the heat dissipation bases of the circuit bodies by second welded portions;
a flow path cover that is fixed to an outer periphery of the intermediate frame by a first welded portion and that forms a flow path space through which a refrigerant flows between the intermediate frame and the heat dissipation base,
A distance from an outer peripheral end of the flow passage cover to a center of the first welded portion is greater than a plate thickness of the flow passage cover,
A relationship between a distance Ls from an inner peripheral end of the intermediate frame to a center of the second welded portion and a plate thickness Ts of the intermediate frame is 0<Ls/Ts<3.0,
The power module is formed from an aluminum alloy having a composition of the first welded portion with a Mg content of 0.2 to 2.0% (mass %, the same applies below). 4. The power module according to claim 3 ,
The power module is formed from an aluminum alloy having a composition of the second welded portion with a Mg content of 0.2 to 2.0%. 4. The power module according to claim 3 ,
The heat dissipation base, the intermediate frame, and the flow path cover are made of an aluminum alloy having a Mg content of 0.2 to 2.0%, a Si content of 0.2 to 0.6%, a Cu content of 0.2% or less, and a Mn content of 1.5% or less.