Semiconductor Modules

Abstract

A half-bridge power module (1) comprises: a substrate (2), the substrate comprising an internal load track (11), two intermediate load tracks (12, 14) and two external load tracks (10, 13), wherein an external terminal is mounted on one of the intermediate load tracks (12, 14), an external terminal (3, 4) is mounted on one of the external load tracks (10, 13), and an external terminal (5) is mounted on the internal load track (11); wherein semiconductor switches (101, 102, 105, 106) are mounted on the external load tracks (10, 13) and are electrically connected to the intermediate load tracks (12); and semiconductor switches (103, 104, 107, 108) are mounted on the intermediate load tracks (12, 14) and are electrically connected to the internal load tracks (11).

Description

Background Art

[0001] Semiconductor power modules are widely used in industry. For example, such power modules can be used for controlled switching of large currents and can be used in power converters (such as inverters) to convert DC to AC and vice versa, or for conversion between different voltages or AC frequencies. Such inverters are used in motor controllers, or in interfaces between power generation or storage or distribution networks.

[0002] Semiconductor power modules are designed to meet two main characteristics: high power conversion efficiency and high power density. Factors such as lifetime, cost and quality are also considered. In order to achieve high power density, high-performance wide bandgap semiconductors such as silicon carbide (SiC) semiconductor switches can be used because they generally outperform standard silicon-based semiconductor switches, i.e., insulated gate bipolar transistors (IGBTs). From a thermal and electrical perspective, SiC devices place high demands on the design of power modules. Wide bandgap semiconductors (e.g., SiC semiconductor switches) have the characteristic of very fast switching, which means that the transition from conduction mode to blocking mode takes only a few nanoseconds.

[0003] When such semiconductor power modules are used, the fast switching in the electronic circuits together with the stray inductances lead to voltage overshoots. These voltage overshoots increase switching losses and can cause EMI radiation through oscillations. Due to the high current gradients during switching, the stray / parasitic inductance of the entire assembly needs to be as small as possible.

[0004] SiC MOSFETs are used as semiconductor switches in applications where the highest efficiency is required in a small build volume. SiC MOSFETs exhibit both fast switching speeds and low on-resistance. Since SiC wafers are expensive to manufacture and it is difficult to produce components with an acceptably low amount of crystal defects under current manufacturing processes, the die is typically very small (e.g. 5-25mm 2 ). This keeps yield losses low but limits the total current that can be passed through the SiC semiconductor switch. To achieve high output power, several of these small semiconductor switches (such as MOSFETs) need to be operated in parallel. In applications such as automotive power conversion, using multiple semiconductor switches in parallel takes up space within the semiconductor power module, potentially resulting in a larger module. However, space resources within vehicles are limited and increasing the size of the module is not usually an option. Therefore, it would be a huge advantage if an innovative design of the layout could simultaneously meet the requirements of multiple semiconductor switches in parallel, balanced (symmetrical) operation, low stray inductance, and a small overall layout size. Summary of the invention

[0005] It is therefore an object of the present invention to provide a power module capable of exhibiting simultaneous switching and balanced operation of a plurality of semiconductor switches in parallel, lower stray inductance, and more stable and efficient operation than currently available power modules.

[0006] According to a first aspect of the present invention, the above and other objects are achieved by proposing a power module providing a half-bridge, the power module comprising: at least one substrate comprising an internal load track, two intermediate load tracks and two external load tracks, wherein the internal load track is elongated and can substantially extend through at least one substrate along a first direction; wherein, at one end of the power module along the first direction, an external terminal is mounted on at least one of the intermediate load tracks; wherein an external terminal is mounted on at least one of the external load tracks, and an external terminal is mounted on the internal load track; wherein an external terminal is mounted at the other end of the power module opposite to the external terminal mounted on at least one of the intermediate load tracks along the first direction; wherein a semiconductor switch is mounted on the external load track and electrically connected to the intermediate load track; and wherein a semiconductor switch is mounted on the intermediate load track and electrically connected to the internal load track.

[0007] The substrate may include an insulating substrate having conductive tracks for forming the circuits required to be attached to the insulating substrate. A suitable substrate may be a DBC (direct bonded copper) substrate formed by two conductive copper layers on either side of an insulating ceramic layer. Other suitable substrates may include DBA (direct bonded aluminum) or other substrates known in the art.

[0008] The term "track" is used herein to designate a circuit track that is formed by a metal layer forming part of a substrate and is insulated from other tracks by gaps. The term "load track" is used herein to designate a track that is suitable for carrying a large current (e.g., supplied by an electrical load powered by a power module). Suitable for high current may be a combination of track width and track thickness, thereby forming a large cross-sectional area, thereby allowing a large current to pass without excessive heating.

[0009] The term "semiconductor switch" is used herein to include any of a number of known semiconductor switching devices. Examples of such devices are thyristors, JFETs, IGBTs and MOSFETs, which may be based on conventional silicon technology or wide bandgap technology such as silicon carbide (SiC).

[0010] The term "mounting" is used herein to refer to the permanent connection of a device to a track, and may include an electrically conductive connection. Such connection methods include soldering, brazing and sintering.

[0011] The term "electrically connected to" is used herein to refer to the connection of a portion of a device to a remote track or other device. Traditionally, this form of connection is made using metal wire bonds, including aluminum. However, other metals such as copper may also be used. The term also covers the use of ribbon or ribbon bonds, braided tape, and the use of solid metal structures such as clips or busbars.

[0012] The layout of the load traces may be symmetrical about a line extending along the first direction.

[0013] In one embodiment of the power module of the present invention, each intermediate load trace may include: a first slender arm, which extends along a first direction, between the external load trace and the internal load trace relative to a second direction at right angles to the first direction; and a second slender arm, which extends along the first direction, between the external load trace and the edge of the substrate relative to the second direction, wherein at least one semiconductor switch can be mounted on the external load trace, and the at least one semiconductor switch is electrically connected to the second slender arm of one of the intermediate load traces.

[0014] Additionally or alternatively, the internal load track may include: a third slender arm, which extends along the first direction, relative to the second direction, between the first intermediate load track and the edge of the substrate; and a fourth slender arm, which extends along the first direction, relative to the second direction, between the second intermediate load track and the edge of the substrate, wherein at least one semiconductor switch can be mounted on the intermediate load track and electrically connected to the slender arm of the internal load track.

[0015] In a particularly preferred embodiment, the power module may comprise a gate contact pad, which is positioned centrally of the group of semiconductor switches, and wherein the gate connection may extend radially from the gate contact pad to the semiconductor switches.

[0016] In another preferred embodiment, the external gate contact terminal may be placed on an outer surface of the power module and extend substantially perpendicularly to the substrate plane. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only and therefore they do not limit the present invention. In the drawings:

[0018] Figure 1 A perspective view showing a first embodiment of a power module of the present invention;

[0019] Figure 2 Shows the formation Figure 1 A plan view of an embodiment of a substrate 2 of a portion of a power module 1 is shown;

[0020] Figure 3 Shows the formation Figure 1 A plan view of an alternative embodiment of a substrate 2 of a portion of a power module 1 is shown;

[0021] Figure 4 A plan view showing another embodiment of a substrate of a power module 1 of the present invention;

[0022] Figure 5 A plan view showing another embodiment of a substrate of a power module 1 of the present invention;

[0023] Figure 6 Shows the Figure 5 Improvements to the layout shown; and

[0024] Figure 7 Shows the Figure 4 Improvements to the layout shown. DETAILED DESCRIPTION

[0025] To illustrate the preferred embodiments of the present invention, reference will now be made in detail to the accompanying drawings, in which Figure 1 A first embodiment of a power module 1 of the present invention is shown in . The power module 1 shown comprises a substrate 2 which is within the body of the power module. The power module 1 is designed to provide a half-bridge circuit, and therefore three DC power terminals 3, 4, 5 and two AC power terminals 6, 7 are provided at opposite ends of the package. In this embodiment, the substrate 2 and the circuit connected to the substrate 2 and the internal parts of the power terminals 3, 4, 5, 6, 7 are encapsulated in a molding compound 22. There may be alternative embodiments in which the substrate is attached to a base plate and / or mounted in a frame, which is subsequently filled with silicone gel and covered with a lid. In addition, several substrates may be mounted in a single package to provide a power module comprising several half-bridges.

[0026] Figure 2 Shows the formation Figure 1 An embodiment of a substrate 2 of a portion of a power module 1 is shown. The substrate may be, for example, a DCB (direct copper bonding) substrate, which includes a central ceramic layer that acts as an insulator and is covered with copper layers on both sides. In some embodiments, the lower copper layer remains intact, while the upper copper layer is etched to form a large number of separate conductive channels that form the desired circuit. Components such as semiconductor switches are mounted to the channels.

[0027] exist Figure 2In the embodiment shown, there is an inner load track 11, two intermediate load tracks 12, 14 and two outer load tracks 10, 13. The inner load track 11 is elongated and extends substantially through the substrate 2 in a first direction 8. The AC terminals 6, 7 are mounted on the intermediate load tracks 12, 14 in the first direction 8, at one end of the power module. The DC terminals 3, 4, 5 are mounted on the outer load tracks 10, 13 and the inner load track 11. The DC terminals 3, 4, 5 are mounted on the other end of the power module opposite the AC terminals 6, 7. Semiconductor switches 101, 102, 105, 106 are mounted on the outer load tracks 10, 13 and are electrically connected to the intermediate load tracks 12, 14 by wire bonds, and semiconductor switches 103, 104, 107, 108 are mounted on the intermediate load tracks 12, 14 and are electrically connected to the inner load track 11 by wire bonds. In this embodiment, the semiconductor switches include SiC (Silicon Carbide) MOSFETs. Other types of semiconductor switches, such as IGBTs, may also be used. Each of the semiconductor switch groups may be composed of two or more semiconductor chips.

[0028] Figure 2 The illustrated embodiment is symmetrical about a line 23 extending in the first direction 8 .

[0029] Figure 3 Shows the formation Figure 1 An alternative embodiment of a base plate 2 of a portion of a power module 1 is shown.

[0030] A significant difference between the two embodiments is that here the intermediate load tracks 12, 14 comprise extension arms partially surrounding the outer load tracks 10, 13, the extension arms allowing an alternative route for wire bonds to the intermediate load tracks for semiconductor switches mounted on the outer load tracks. Each intermediate load track 12, 14 comprises a first elongated arm 15 and a second elongated arm 16, the first elongated arm 15 extending in a first direction 8, relative to a second direction 9 at right angles to the first direction 8, between the outer load tracks 10, 13 and the inner load track 11; the second elongated arm 16 extending in the first direction 8, relative to the second direction 9, between the outer load tracks 10, 13 and the edge of the substrate 2. In addition, the inner load track 11 comprises a third elongated arm 17 and a fourth elongated arm 18, the third elongated arm 17 extending in the first direction 8, relative to the second direction 9, between the first intermediate load track 12 and the edge of the substrate 2; the fourth elongated arm 18 extending in the first direction 8, relative to the second direction 9, between the second intermediate load track 14 and the edge of the substrate 2. These arms extending from the inner load tracks allow the semiconductor switches 101, 105 mounted on the intermediate load tracks 12, 14 to have alternative routes for the wire bonds connecting them to the inner load tracks.

[0031] Arms extending from the inner load track pass under the AC terminals 6, 7 but do not make electrical contact with them.

[0032] Figure 4 Another embodiment of the substrate of the power module 1 of the present invention is shown. Here, the layout is topologically similar to Figure 3 In this embodiment, the gate contact pad 19 is positioned centrally within the group of semiconductor switches 101-102, 103-104, 105-106, 107-108, and the gate connection between the gate contact pad and the gate connection on the top surface of each semiconductor switch extends radially from the gate contact pad 19 to the semiconductor switches 101-108.

[0033] Figure 5 Another embodiment of the substrate of the power module 1 of the present invention is shown. Here, the layout of the tracks is similar to Figure 2 Layout of the trace shown.

[0034] Figure 6 Shows the Figure 5 Improvements to the layout shown in Figure 6 In FIG. 1 , slots 301 and 302 are added in the load track 11 for current shaping so as to balance the commutation paths of the chips 107, 108 and 104. Such current slots can be used to equalize the current path lengths between different chips.

[0035] Figure 7 Shows the Figure 4 A similar improvement to the layout shown. Figure 6 As shown, current shaping slots 301 , 302 are also added to the load track 11 .

Claims

1. A power module (1) providing a half-bridge, the power module comprising: At least one substrate (2), the at least one substrate (2) comprising an inner load track (11), two intermediate load tracks (12, 14) and two outer load tracks (10, 13), wherein the inner load track (11) is elongated and extends through the at least one substrate (2) in a first direction (8); Wherein, along the first direction (8), at one end of the power module, an external terminal (6, 7) is mounted on at least one of the intermediate load tracks (12, 14); wherein an external terminal (3, 4) is mounted on at least one of the external load tracks (10, 13), and an external terminal (5) is mounted on the internal load track (11); wherein, along the first direction (8), an external terminal (3, 4, 5) is installed at the other end of the power module facing the external terminal (6, 7) installed on at least one of the intermediate load tracks; wherein a semiconductor switch (101, 102, 105, 106) is mounted on the external load track (10, 13), and the semiconductor switch (101, 102, 105, 106) is electrically connected to the intermediate load track (12); and wherein a semiconductor switch (103, 104, 107, 108) is mounted on the intermediate load track (12, 14), and the semiconductor switch (103, 104, 107, 108) is electrically connected to the internal load track (11), Each intermediate load track (12, 14) comprises: a first slender arm (15), the first slender arm (15) extending along the first direction (8), between the outer load track (10, 13) and the inner load track (11) relative to a second direction (9) at right angles to the first direction (8); and a second slender arm (16), the second slender arm (16) extending along the first direction (8), between the outer load track (10, 13) and an edge of the substrate (2) relative to the second direction (9); The inner load track (11) comprises: a third slender arm (17), the third slender arm (17) extending along the first direction (8) and between the first intermediate load track (12) and the edge of the substrate (2) relative to the second direction (9); and a fourth slender arm (18), the fourth slender arm (18) extending along the first direction (8) and between the second intermediate load track (14) and the edge of the substrate (2) relative to the second direction (9); wherein at least one semiconductor switch (101, 105) is mounted on the outer load track (10, 13), and the at least one semiconductor switch (101, 105) is electrically connected to a second elongated arm (16) of one of the intermediate load tracks (12, 14); and Therein, at least one semiconductor switch (103, 107) is mounted on the intermediate load track (12, 14), and the at least one semiconductor switch (103, 107) is electrically connected to the elongated arm (17, 18) of the inner load track (11).

2. The power module according to claim 1, wherein: The layout of the load tracks (10, 11, 12, 13, 14) is symmetrical about a line extending along the first direction (8).

3. The power module according to claim 1 or 2, wherein: A gate contact pad (19) is positioned centrally of a group of semiconductor switches (101-102, 103-104, 105-106, 107-108), and wherein a gate connection extends radially from the gate contact pad (19) to the semiconductor switches (101-108).

4. The power module according to claim 1 or 2, wherein: One or more external gate contact terminals (20) are placed on the external surface of the power module, and the one or more external gate contact terminals (20) extend perpendicularly to the plane of the substrate (2).

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