Power semiconductor module and method of forming same

Abstract

The present invention relates to a method for connecting a terminal (24) to a substrate (12) to form a power semiconductor module (10) by using ultrasonic welding. The terminal (24) includes a first connection region (28) located on a terminal leg (26). The first connection region (28) is adapted to connect the terminal (24) to the substrate (12). The terminal (24) further includes a second connection region (32), which is located on the terminal leg (26) opposite the first connection region (28). The substrate (12) includes a third connection region (30) adapted to connect to the first connection region (28) of the terminal (12). The method includes the steps of a) contacting the first connection region (28) with the third connection region (30), b) using an ultrasonic welding tool (38) to act on the second connection region (32) to connect the terminal (24) to the substrate (12), and after performing step c), performing a smoothing step to smooth the second connection region (32). After step c), the method further includes step d) of connecting at least one electrical connection to the second connection region (32).

Description

[Technical Field]

[0001] Technical Field The present invention relates to a method for forming a power semiconductor module, and more particularly to welding terminals to a substrate during the formation of a power semiconductor module.The present invention also relates to a semi-finished power semiconductor module.The present invention further relates to a power semiconductor module. [Background technology]

[0002] Background technology Power semiconductor modules in general are widely known in the art. There are a variety of connection techniques for connecting terminals to conductive structures such as substrates or substrate metallization.

[0003] Welding, such as ultrasonic welding (USW), also known as ultrasonic welding, is a known technique for connecting terminals to substrate metallization that can be used to manufacture reliable, high-temperature power electronics modules. In particular, ultrasonic welding is widely used to join copper terminals to ceramic substrates that have copper metallization.

[0004] After the welding step is performed, preferably by applying a welding force to the upper surface of the terminal leg, the force of the welding tool imparts a knurled pattern to this surface.

[0005] Alternatively, it is known to use laser welding to join the terminals to the substrate or substrate metallization, however, a consideration with this technique is the risk of forming brittle intermetallic phases when connecting dissimilar materials.

[0006] DE 102014104496 A1 describes an apparatus and a method for connecting connection elements of a power semiconductor module to conductor tracks by welding. The apparatus includes an abutment for placement of a substrate. The abutment has a first partial abutment and a second partial abutment. The first partial abutment has a resistance of 50 kN / mm 2~300kN / mm 2 The second partial contact portion is a metal formed body having an elastic modulus of 10 N / mm 2 ~500N / mm 2 The elastic molding has an elastic modulus of . The lower element rests on the second partial abutment. The apparatus further includes a holding device for fixing the lower element to the abutment, a sonotrode, and a positioning device for positioning the connecting element relative to the substrate.

[0007] US2011 / 058342A1 discloses a semiconductor device having a multilayer frame obtained by stacking multiple lead frames each having an electronic component mounted thereon and sealing the stack with resin. The interlayer distance between the lead frame on which the electronic component is mounted and another lead frame on which another electronic component is mounted is shorter than the distance from the surface of the lead frame to the top surface of the electronic component.

[0008] JP2015146393A describes forming a lower-layer ultrasonic bond by ultrasonically bonding a lower-layer bonding wire to a bonded member (electrode or wiring pattern). Furthermore, an upper-layer ultrasonic bond is formed by ultrasonically bonding an upper-layer bonding wire superimposed on the lower-layer ultrasonic bond. By cutting the upper-layer bonding wire, a notch is formed downstream of the upper-layer ultrasonic bond in the wiring direction. At this time, a support is provided below the notch to support the notch from below.

[0009] As described above, the prior art still has room for improvement, particularly in terms of reliably connecting terminals to a substrate without applying excessive force during the process of forming a power semiconductor module. Summary of the Invention [Problem to be solved by the invention]

[0010] Summary of the Invention It is therefore an object of the present invention to provide a solution for at least partially overcoming at least one of the disadvantages of the prior art, in particular to provide a solution for providing a high-quality arrangement for a power semiconductor module by reliably connecting the terminals to the substrate without applying undue force. [Means for solving the problem]

[0011] These objects are at least partly solved by a method for connecting terminals to a substrate to form a power semiconductor module having the features of independent claim 1. These objects are further solved at least partly by a semi-finished power semiconductor module having the features of independent claim 6, by a power semiconductor module having the features of independent claim 7 and by a method for forming a power semiconductor module having the features of independent claim 8. Advantageous embodiments are set out in the dependent claims, the further description and the accompanying drawings. The described embodiments, alone or in any combination with the respective embodiments, may provide the features of the invention, unless expressly excluded.

[0012] A method for connecting a terminal to a substrate to form a power semiconductor module by using ultrasonic welding is described. The terminal comprises a first connection region located on a terminal leg. The first connection region is adapted to connect the terminal to the substrate. The terminal further comprises a second connection region, the second connection region being located on the terminal leg opposite the first connection region. The substrate comprises a third connection region adapted to be connected to the first connection region of the terminal. The method comprises: a) contacting a first connection region with a third connection region; b) connecting the terminal to the substrate by acting on the second connection region with an ultrasonic welding tool; c) after performing step b), smoothing the second connection region by performing a smoothing step; After step c), the method further comprises: d) connecting at least one electrical connection to the second connection region.

[0013] Such a method offers significant advantages over prior art solutions, particularly with respect to providing high quality placement by reliably and securely connecting the terminals to the substrate or substrate metallization.

[0014] The present invention thus refers to a method for connecting terminals to a substrate to form a power semiconductor module, which method is therefore suitable and intended to be performed during the manufacture of a power semiconductor module, and in particular deals with connecting terminals to a substrate and thereby in particular to a substrate metallization.

[0015] Connection, in the sense of the present invention, is understood to mean thereby mechanically and electrically connecting the terminal to the substrate or substrate metallization.

[0016] The terminal may have a generally L-shaped configuration, the lower portion of which is connected to the substrate at its first connection area, such as a welding area. The terminal, in the sense of the present invention, may have a thickness of 600 μm or more, illustratively 1000 μm or more, and a width of 2 mm or more. Furthermore, the connection area, such as a welding area, may have dimensions of 2 mm x 2 mm or more. The cross section of the terminal may be rectangular, and the angle between two parts of the L-shape aligned in different orientations may be a right angle or an angle greater than 90°.

[0017] In contrast to terminals, typical parameters for wire bonds include a diameter of 400 μm or less and a connection area, such as a weld area of ​​0.5 mm by 1 mm or less. The angle between the connection area and the adjacent portion may be oblique, for example, much greater than 90 degrees, and the cross section may be circular.

[0018] Furthermore, for ribbons, as opposed to terminals, typical parameters include a thickness of 300 μm or less, a width of 2 mm or more, and a connection area, such as a weld area of ​​0.5 mm x 2 mm or less. The angle between the connection area and the adjacent portion may be oblique, e.g., much greater than 90 degrees, and the cross section may be rectangular.

[0019] The power semiconductor module may have features known in the art, for example, a power semiconductor module to be manufactured may include a metallization provided on a ceramic substrate, the metallization adapted to electrically connect terminals to be connected to the metallization with the respective power semiconductor devices.

[0020] Also disposed on the substrate metallization are power semiconductor devices, also referred to as chips. Such power semiconductor devices may generally be formed as known in the art and may each comprise, among other things, a transistor or switch, such as a MOSFET and / or an IGBT, and / or a plurality of power semiconductor devices may comprise a diode. The power semiconductor devices may each be interconnected and thus in electrical contact, e.g., galvanic contact, with the metallization.

[0021] The substrate can generally be formed from a main layer, which is a ceramic main layer, and from an upper metallization and a lower metallization. For example, the substrate can be an Al / AlN / Al substrate, thus having an AlN main layer and an aluminum upper metallization and a lower metallization. This allows for high cycling reliability and does not cause problems with silver ion migration. However, copper metallization may be preferred as the upper metallization and / or the lower metallization.

[0022] With respect to the terminals and metallization to be connected to one another, it is provided that the terminals have a first connection area and the substrate or substrate metallization respectively has a third connection area.

[0023] Thus, the first connection area is the area of ​​the terminal that is intended to be connected to the substrate metallization, and correspondingly, the third connection area is the area of ​​the substrate or substrate metallization that is intended to be connected to the terminal.

[0024] In fact, it is known that highly advanced designs of power semiconductor modules require welding of terminals to the substrate, particularly welding of the first connection region to the third connection region. For example, it is known to connect copper-based terminals to aluminum metallization on ceramic substrates. Furthermore, it may be necessary to connect hard copper terminals, such as CuNiSi press-pin auxiliary terminals, to ceramic substrates with copper metallization. Regardless of the material combination used, however, ultrasonic welding is the preferred option for connecting terminals to the substrate. This may be due to the fact that such techniques are known for connecting terminals to substrates to form reliable, high-temperature power electronics modules. In particular, ultrasonic welding is widely used, for example, to join copper terminals to ceramic substrates with copper metallization.

[0025] It is further specified that the terminal has a second connection region located on the terminal leg opposite the first connection region, such that the second connection region can be adapted to receive the force of a welding tool for applying welding energy to the terminal or the terminal leg, respectively.

[0026] With regard to the method of connecting the terminals to the substrate or substrate metallization, respectively, it is further provided that the method comprises the following steps:

[0027] First, according to step a) of the method, the method comprises contacting the first connection region with the third connection region. According to this step, the terminal is thereby positioned in its final position, for example to be connected to the substrate metallization. This step can be realized, for example, manually or automatically, for example by an automatic positioning device.

[0028] Further, according to step b) of the method, the method includes connecting the terminal to the substrate by acting on the second connection region with a welding tool, which may generally be performed as known in the art by using conventional ultrasonic welding, for example, by using a sonotrode and / or by applying welding energy to the terminal legs.

[0029] In particular, when the terminal is in its final position, i.e., the position where the terminal is to be connected to the substrate, after performing step a), a welding tool, such as a sonotrode, is provided and positioned and manipulated so that welding energy is applied to the terminal leg in the second connection region, which is mostly located above the terminal leg.

[0030] The welding parameters used may be selected in an appropriate manner and may correspond to those used in the prior art. Generally, the welding parameters may depend on the material of the terminal, the material of the substrate, or the substrate metallization, respectively, and therefore may not depend on the materials of the first, second, and third connection regions. Furthermore, the thickness of the terminal legs may affect the welding parameters and, therefore, the distance between the first and third connection regions.

[0031] However, using ultrasonic welding as a connection technique can have disadvantages, particularly when the second connection region is to be used to connect a further electrical connection, such as a wire bond connection, to the second connection region. In this regard, it has been found that, particularly with ultrasonic welding, the surface used to apply the welding energy by the welding tool is relatively rough. More specifically, the knurling pattern of the welding tool, such as a sonotrode, can deform the second connection region and thereby, in particular, the upper surface of the terminal leg.

[0032] In such circumstances, it has been found that the second connection area after carrying out the welding step is deformed so that a kind of knurling pattern is applied to the surface of the terminal or terminal leg.

[0033] Furthermore, according to the method described herein, method step c) provides that the method comprises a further step of smoothing the third connection region by performing a smoothing step.

[0034] The smoothing of the surface can be performed immediately after the welding step or as a separate process step. Furthermore, the smoothing can be achieved by using one step or, in particular, by using subsequent steps. Thus, after step c), the second connection region is smoother than the second connection region before step c).

[0035] In particular, this step may provide significant advantages over prior art techniques that connect the terminals to the substrate by ultrasonic welding.

[0036] In particular, by smoothing the surface of the terminal leg, and thereby the second connection region, any rough surfaces, such as knurled structures, can be removed. Instead, the surface becomes smooth. It has now been found that smoothing the second connection region, and thereby in most cases the upper surface of the terminal leg, can result in extremely good properties for providing a further step of connecting an electrical connection to the second connection region, and thereby, in particular, to the upper surface of the terminal leg.

[0037] This step therefore allows the second connection area to be designed to secure electrical connections, such as wire bonds, to the second connection area, which may allow further parts of the electrical circuit of the power semiconductor module to be connected to the terminals. For example, it may be provided to secure wire bonds to the second connection area, which connect the terminals to the power semiconductor devices of the electrical circuit. This step may be realized by a welding step, which may be a step performed after the welding step for connecting the terminals to the substrate.

[0038] Therefore, the method avoids the commonly occurring effects of ultrasonic welding that cause degradation of the properties of the terminal leg structure, and in particular the structure of the second connection region, when a further welding step is performed, for example, to connect a wire bond in the second connection region. In other words, the upper surface of the leg, after, for example, ultrasonic welding, is not, or very rarely, prepared for a further joining step to join the electrical connection.

[0039] In contrast to this commonly occurring effect, the present invention allows the surface that comes into contact with the welding tool when connecting the terminal to the conductive structure by ultrasonic or laser welding to have a structure that is sufficiently suitable to allow a further electrical contact to be made to this area, which may be realised to connect the terminal to a further component of an electrical circuit, such as, for example, a power semiconductor device in particular.

[0040] This may enable extremely high quality bonds between the terminals and electrical connections, such as wire bonds, to be achieved.

[0041] The respective surfaces can therefore be connected very reliably, which can enable a high working capacity of the power semiconductor module and can prevent breakages due to poor quality connections.

[0042] Apart from this, the power semiconductor module can function with high safety due to a stable and reliable connection between the terminals and the substrate or substrate metallization.

[0043] The above-mentioned advantages further allow for significant improvements in the design and packaging of the manufactured power semiconductor module, in that the terminals themselves can be used to connect to the power semiconductor devices. As a result, the substrate surface, such as the surface of the metallization, can be optimized by achieving greater design freedom, in that electrical connections connected to the metallization according to the prior art can now be connected to terminals on the smoothed surface. As a result, the area obtained on the metallization can be used to arrange more power semiconductor devices, allowing the power semiconductor module to operate with particularly excellent performance and efficiency.

[0044] Thus, the present invention provides a solution to a problem during the manufacturing of power semiconductor modules where the design of a power module package having a given footprint is a trade-off between the area of ​​substrate metallization required for the power semiconductor device and the area of ​​substrate metallization required for additional components such as wire bonds, terminals, space for processing margins, etc.

[0045] Thus, it can be seen that the methods described herein offer significant advantages over prior art solutions for forming power semiconductor modules.

[0046] For this reason, the present invention also relates to a method of forming a power semiconductor module, including a method of connecting terminals to a substrate, and reference is made to the method of connecting terminals to a substrate for respective features and advantages.

[0047] Thus, this method of forming a power semiconductor module may further include providing the power semiconductor devices, internal and / or external electrical connections, and protection means, such as one or more mold bodies and / or housings, as is generally known in the prior art.

[0048] According to the above description, the method described herein, such as the manufacturing process of a power semiconductor module, after step c), further comprises: d) connecting at least one electrical connection to the second connection region.

[0049] This takes advantage of the fact that, in particular, after smoothing the terminal leg or the second connection area, the electrical connection can be reliably connected to the second connection area, which in turn can achieve long-term stability of the electrical connection and, in addition, can improve the efficiency of the power semiconductor module.

[0050] In this regard, the above-mentioned advantages are particularly effective when step d) includes welding a wire bond to the second connection region. The wire bond may be formed from a material selected from the group consisting of, for example, copper, aluminum, and alloys containing at least one of these metals.

[0051] Additionally, a wire bond or other electrical connection secured to the second connection region may connect the terminal leg to the power semiconductor device.

[0052] With regard to the smoothing step, smoothing is generally achieved if the degree of smoothness increases, such that this degree of smoothness is higher after step c) compared to the state before step c).

[0053] It may be preferable that step c) is performed by, and thus includes, a material removal step. Thus, according to this embodiment, it may be provided that, for example, a knurled structure formed on the second connection region can be removed by removing material. This step makes it possible to provide a particularly smooth surface, so that the above-mentioned advantages can be particularly effectively realized. Furthermore, this embodiment can be particularly reliably realized when the terminal legs have an appropriate thickness.

[0054] According to the above description, this method step can be performed, for example, when the terminal or the terminal leg, respectively, is formed from a material having a relatively high hardness. Thus, for example, this embodiment can be implemented in at least the terminal leg or the second connection region in combination with a terminal formed from a copper alloy such as CuNiSi, but these examples are not intended to be limiting.

[0055] Generally, the specific steps for carrying out the method can be selected according to specific needs. As a non-limiting example, it can be specified that the material removal step includes at least one process selected from the group consisting of grinding, polishing, planarizing, and shearing. In particular, it has been found that these examples can provide a very smooth surface and can be sufficiently applicable to, for example, the terminal leg materials described above. Furthermore, these methods result in a surface that can be suitably used to connect wire bonds, for example, by welding.

[0056] It may be further specified that step c) includes applying at least one of pressure and heat to the second connection region. Thus, this embodiment includes a pressure-based smoothing step and / or a heat-based smoothing step. This embodiment may also result in a very smooth surface. This may be implemented, in particular, in combination with a similarly soft material and / or in combination with a material having a low melting point. Thus, for example, this embodiment may be implemented in combination with a terminal formed of copper, such as soft-annealed copper, at least in the terminal leg or second connection region.

[0057] This step may be performed, for example, by using a pressure application tool acting on the second connection region, or in conjunction with a heat application tool acting on the connection region, or with both tools or a combination of these tools.

[0058] It may further be provided that the terminal, at least in its terminal leg and therefore in the second connection region, is made from a material selected from the group consisting of copper, such as soft annealed copper, or a copper alloy, such as Cu-NiSi.

[0059] These materials combine excellent electronic properties with good processability. Terminals made from these materials therefore exhibit excellent operating conditions, thereby enabling the power semiconductor module to function very efficiently. Apart from this, the second connection region can have a very smooth surface, for example by using the method described above.

[0060] For further advantages and technical features of the method, reference is made to the semi-finished product, the power semiconductor module, the method for forming the power semiconductor module, the figures and further description.

[0061] Furthermore, a semi-finished product of a power semiconductor module is described, which is formed from a terminal and a substrate, and therefore particularly includes the terminal and the substrate. The terminal includes a first connection region located on a terminal leg. The first connection region is adapted to connect the terminal to the substrate. The terminal further includes a second connection region. The second connection region is located on the terminal leg opposite the first connection region. The substrate includes a third connection region adapted to be connected to the first connection region of the terminal. The first connection region is connected to the third connection region. The second connection region has a smoothed surface. An electrical connection is connected to the second connection region.

[0062] Such semi-finished products allow significant advantages over prior art solutions, especially in the process of forming power semiconductor modules.

[0063] In this regard, in particular, the feature that the second connection region has a smoothed surface may provide a significant advantage over prior art in which the terminal is connected to the substrate by ultrasonic welding.

[0064] In particular, by smoothing the surface of the terminal leg and thus the second connection area, any rough surfaces, such as knurled structures, that appear during ultrasonic welding can be eliminated, resulting in a smooth surface that has better properties for the subsequent welding step and therefore for connecting further electrical connections to the second connection area.

[0065] For this purpose, an electrical connection is connected to the second connection area. For example, it may be provided that a wire bond or a plurality of wire bonds are connected to the second connection area.

[0066] With regard to the smoothed surface, it may be preferred that the surface of the second connection region has a surface roughness Ra in the range of ≦400 μm, in particular ≦300 μm, such as ≦200 μm. The surface roughness Ra may be understood as the arithmetic mean value of a particularly filtered roughness profile determined from the deviation around a centerline within an evaluation length and may be determined by scanning electron microscopy.

[0067] With respect to the terminals, it may be specified that they may comprise one or more of a collector terminal, an emitter terminal and an auxiliary terminal.

[0068] This step therefore enables the surface that was in contact with the welding tool when connecting the terminal to the conductive structure by ultrasonic welding to have a structure that is sufficiently suitable to allow a further electrical contact to be made later to this area, which may be realised for connecting the terminal to a further component of an electrical circuit, for example, in particular a power semiconductor device.

[0069] This may enable very high quality bonds, such as wire bonds, to be achieved between the terminals and the electrical connections.

[0070] The respective surfaces can therefore be connected very reliably, which can enable a high workability of the power semiconductor module and can avoid breakages due to poor quality connections.

[0071] Apart from this, the power semiconductor module can function with high safety due to a stable and reliable connection between the terminals and the substrate or substrate metallization.

[0072] Furthermore, the semi-finished product may make it possible to manufacture power semiconductor modules that can function with particularly high performance and efficiency.

[0073] For further advantages and technical features of the semi-finished product, reference is made to the method, the power semiconductor module, the figures and further description.

[0074] A power semiconductor module is further described. The power semiconductor module is formed from a semi-finished product as described in the further description. It can be further specified that the power semiconductor module includes the semi-finished product as described above and can further have features that are essentially known in the art for power semiconductor modules, such as power semiconductor devices. For example, the power semiconductor module can include an IGBT.

[0075] Such a power semiconductor module may offer significant advantages over the prior art, particularly when electrical connections are made to the second connection areas, and it may be provided in particular that wire bonds are welded to the second connection areas.

[0076] In summary, the connection to the second connection surface of the electrical connector, such as a wire bond, can be formed by achieving a high quality connection, which can result in high working stability and excellent long-term stability of the module.

[0077] Furthermore, the power semiconductor module can function with particularly high efficiency. For further advantages and technical features of the power semiconductor module, reference is made to the semi-finished product, the method, the figures and further description.

[0078] BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. Individual features disclosed in the embodiments may, alone or in combination, constitute aspects of the invention. Features of various embodiments may be carried over from one embodiment to another. [Brief explanation of the drawings]

[0079] [Figure 1] 1 is a cross-sectional side view of a power semiconductor module according to the present invention; [Figure 2] 10 is a side cross-sectional view showing a welding step for connecting a terminal to a substrate by a welding tool. [Figure 3] 10 is a cross-sectional side view of a semi-finished product for forming a power semiconductor module after a smoothing step for smoothing the terminals. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0080] Description of the embodiment 1 shows a power semiconductor module 10. The power semiconductor module 10 includes a substrate 12 with a lower metallization 14 and an upper metallization 16. The lower metallization 14 may be connected to the substrate 12 or its main layer 13, respectively, by a solder layer 18, and may be connected on the opposite side to a bottom plate, not shown in these figures. Furthermore, the upper metallization 16 may be connected to the substrate main layer 13 by yet another solder layer 20.

[0081] Additionally, a power semiconductor device 22 is provided on the left-hand portion of the top metallization 16. The power semiconductor device or devices 22 provided therein may generally be formed as known in the art and may, inter alia, each comprise a transistor or switch, such as a MOSFET and / or an IGBT, and / or the power semiconductor devices 22 may comprise a diode.

[0082] Separate from the power semiconductor device 22, a terminal 24 is shown provided on the right-hand portion of the top metallization 16. The terminal 24 may be, for example, an emitter terminal, a collector terminal or an auxiliary terminal.

[0083] Terminal 24 is further shown to include a terminal leg 26 connected to substrate 12 or its top metallization 16. In this regard, terminal 24 is shown to include a first connection region 28 located on terminal leg 26. In this case, first connection region 28 is connected to substrate 12 or its top metallization 16. Substrate 12 has a third connection region 30 at top metallization 16. Third connection region 30 is further connected to first connection region 28 of terminal 14.

[0084] Terminal 24 is further defined as having terminal leg 26 with second connection region 32 located on the opposite side of terminal leg 26 from first connection region 28. A further electrical connection is disposed in second connection region 32. More specifically, wire bond 34 is shown secured, in particular welded, to second connection region 32.

[0085] Wire bonds 34 provide electrical connections from terminals 24 to power semiconductor devices 22 .

[0086] Additionally, it can be seen that the second connection region 32 has a smoothed surface, a feature that allows for a durable and effective connection of an electrical connection or wire bond 34 to the second connection region 32.

[0087] This feature is explained in more detail in Figures 2 and 3. In this regard, Figures 2 and 3 illustrate a method of connecting terminals 24 to substrate 12. This method results in, among other things, a semi-finished product 36 of power semiconductor module 10, which can then be used in the process of forming power semiconductor module 10.

[0088] In this regard, Figure 2 illustrates the state of terminal 24 after an ultrasonic welding step has been performed to connect terminal 24 to substrate 12. Due to the knurling structure of welding tool 38, it can be seen that second connection region 32 of terminal leg 26 also has a knurling structure 40.

[0089] However, in this state, further electrical connections cannot be properly connected to the second connection area 32. The invention therefore proposes to smooth the second connection area 32 after the welding step.

[0090] This is shown in more detail in Figure 3. According to Figure 3, it is shown that the second connection region 32 is smoothed, thereby providing the second connection region 32 with a very smooth surface. The smoothing of the second connection region 32 may be achieved, for example, by using a smoothing tool 42 with a flat surface 44 that acts on the second connection region 32 with heat and / or pressure, preferably with both heat and pressure, as shown in Figure 3. Alternatively or additionally, it may be provided that the smoothing of the second connection region 32 may be achieved by a material removal step, such as grinding.

[0091] 3 is sufficient to allow electrical connections, such as wire bonds 34 shown in FIG. 1, to be connected to the second connection areas 32. In the state shown in FIG.

[0092] This allows for durable, long-term, stable connections for the wire bonds 34 , which in turn allows for high effective performance of the power semiconductor module 10 .

[0093] While the invention has been illustrated and described in detail in the accompanying drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary, and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the accompanying drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. [Explanation of symbols]

[0094] 10 Power Semiconductor Module 12 PCB 13 Main layer 14 Metallic coating 16 Metallic coating 18 solder layer 20 solder layer 22 Power Semiconductor Devices 24 terminals 26 terminal leg 28 First Connection Area 30 Third Connection Area 32 Second Connection Area 34 Wirebond 36 Semi-finished products 38 Welding Tools 40 Structure 42 Smoothing tool 44 Surface

Claims

1. 1. A method for connecting terminals (24) to a substrate (12) to form a power semiconductor module (10) by using ultrasonic welding, comprising: The terminal (24) has an L-shape in a side cross-sectional view, The L-shaped shape has a lower portion that is closer to the substrate (12) and an upper portion that is farther from the substrate (12), the lower portion and the upper portion are aligned in different orientations, and the angle between the lower portion and the upper portion is a right angle or an angle greater than 90°; The lower portion of the terminal (24) constitutes a terminal leg (26), The terminal (24) includes a first connection area (28) located on the terminal leg (26); The terminal (24) further comprises a second connection region (32) located on the terminal leg (26) opposite the first connection region (28); The substrate (12) includes a third connection region (30), and the method comprises: a) contacting said first connection region (28) with said third connection region (30); b) connecting the terminal (24) to the substrate (12) by acting on the second connection region (32) with an ultrasonic welding tool (38); c) after performing step b), smoothing the second connection region (32) by performing a smoothing step; d) after performing step c), connecting at least one electrical connection to said second connection region (32).

2. 2. The method of claim 1, wherein step d) comprises welding a wire bond (34) to the second connection region (32).

3. The method of claim 1 or 2, wherein step c) comprises a material removal step.

4. The method of claim 3 , wherein the material removal step comprises at least one of grinding, polishing, planarizing, and shearing.

5. The method of any one of claims 1 to 4, wherein step c) comprises applying at least one of pressure and heat to the second connection region (32).

6. A method of forming a power semiconductor module (10), said method comprising the method of any one of claims 1 to 5.

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