Power semiconductor modules

Abstract

The present invention relates to a method for connecting a terminal (22) to a substrate (12) to form a power semiconductor module (10), wherein the terminal (22) has a first connection area (28) formed of a first material, and wherein the substrate (12) has a second connection area (30) formed of a second material, wherein the first material has a first hardness, and wherein the second material has a second hardness, wherein the first hardness is different from the second hardness, wherein such first connection area (28) or second connection area (30) with a higher hardness forms a connection mating area, and the first connection area (28) or second connection area (30) with a lower hardness forms a connection base area, and wherein the terminal (22) is connected to the substrate (12) by using ultrasonic welding or laser welding, characterized in that, before connecting the terminal (22) to the substrate (12), the method comprises the step of providing a connection layer (32) having a surface sublayer formed of a material having a hardness corresponding to the hardness of the connection mating area, wherein the connection layer (32) is arranged on the connection base area, and wherein the surface sublayer faces the connection mating area.

Description

Technical Field

[0001] The present invention relates to a method of forming a power semiconductor module. The present invention also relates to a power semiconductor module. In particular, the present invention relates to a power semiconductor module having an improved connection of terminals to a substrate metallization layer. Background Art

[0002] Power semiconductor modules are generally well known in the art. For connecting the terminals to an electrically conductive structure such as a substrate or a substrate metallization, respectively, there are different connection techniques.

[0003] Ultrasonic welding (USW) is a known technique for connecting terminals to substrate metallization layers, which can be used for high reliability and high temperature power electronic modules. In particular, ultrasonic welding is widely used to connect terminals made of copper to ceramic substrates with copper metallization layers. This is mainly due to the fact that both the copper terminals and the copper metallization layers are annealed copper with low hardness (e.g., in the range of about 50 Vickers hardness).

[0004] However, it is well known that advanced designs of power semiconductor modules require welding of different materials, such as copper terminals to aluminum metallization of ceramic substrates, or hard copper terminals (e.g., press-pin assisted terminals made of CuNiSi) to ceramic substrates with copper metallization layers. When ultrasonic welding is used to join different materials, the harder material is likely to be pressed into or deform the softer material.

[0005] As an alternative, it is known to use laser welding to connect the terminals to the substrate or the substrate metallization, respectively. However, when considering this technology, there is a risk of forming brittle intermetallic phases when connecting different materials.

[0006] Therefore, there may be room for improvement in connecting dissimilar materials, especially when considering connecting the terminals to the substrate metallization layer of the substrate.

[0007] JP 2009302579 describes that the front electrode of the semiconductor chip and the lead frame are made of the same material, and the tip portion of the lead frame is processed into a convex shape, and the corresponding surface films of the semiconductor chip and the lead frame face each other. By performing ultrasonic vibration while applying pressure, the same metals formed on the outermost surface diffuse with each other, and metal bonding can be performed directly without using solder. Therefore, the connection of the semiconductor chip to the lead frame becomes the focus. There is no description of the tip for connecting the terminal to the conductive structure.

[0008] However, this step is completely different from the fixing of the terminals to the substrate, since it is a completely different process. In this respect, according to the prior art, a maximum of 100 mW is applied in the case of wire bonding on semiconductor electrodes, and in contrast, in the case of ultrasonic welding of terminals, the range of up to kW is applied.

[0009] JP 2008042039 A describes that a wiring member is divided into two parts, an electrode plate used as a heat sink and a lead frame, and the electrode plate is soldered to the main surface of a semiconductor chip in a state where it is not bonded to the lead frame. Then, the bonded end of the lead frame is superimposed on an extension extending laterally from the periphery of the electrode plate, and locally heated by laser welding, electron beam welding, etc.

[0010] JP 2012039018 A describes that one surface of a connection portion to be bonded to a wiring pattern of a lead is bent into a convex shape before ultrasonic bonding with the convex surface facing the wiring pattern. An ultrasonic applying device is pressed against the surface opposite to the convex surface to apply ultrasonic waves, thereby ultrasonically bonding the lead and the wiring pattern.

[0011] CN 104241209 relates to a dedicated power supply module for outdoor power supply, which as a dedicated power supply integrated module includes a lead frame, a control chip, a thermistor, a power chip, a diode, and a metal wire. A heat dissipation substrate is located at the bottom of the package. The thermistor, the power chip and the diode are welded on the substrate. The power chip and the diode are connected to the lead frame by ultrasonic bonding, and the lead frame is distributed on both sides of the heat dissipation substrate, and the metal wire connects the control chip to the lead frame.

[0012] WO 2007 / 033829 relates to a method for producing a power semiconductor module, in which a contact in the form of an ultrasonic welding contact is produced between a contact region and a contact element, a sonotrode used for the ultrasonic welding process also being used to assemble the contact region with the contact end and thus the contact part with the base region.

[0013] JP 2011061105 A describes a high reliability connection technology for providing sufficient connection strength and suppressing pad breakage when ultrasonically connecting a lead terminal to a pad of a substrate, as described below. A coating harder than the pad and the lead terminal is formed on the pad on the metal base and the insulating film. During ultrasonic connection, ultrasonic waves are applied to an ultrasonic tool to break the plating layer, and both the lead terminal and the pad on both sides of the plating layer are directly connected to each other by plastic flow.

[0014] US 2014 / 021620 A1 describes a power device according to an embodiment, comprising a semiconductor structure having a first surface facing a second surface, an upper electrode, and a lower electrode. The upper electrode may include a first contact layer on the first surface of the semiconductor structure and a first bonding pad layer formed of a metal containing nickel (Ni) on the first contact layer. The lower electrode may include a second contact layer below the second surface of the semiconductor structure and a second bonding pad layer formed of a metal containing Ni below the second contact layer.

[0015] However, the above cited references still leave room for improvement, particularly in terms of connecting terminals to substrates in power semiconductor modules in a gentle and reliable manner. Summary of the invention

[0016] Therefore, it is an object of the present invention to provide a solution that at least partially overcomes at least one disadvantage of the prior art. In particular, it is an object of the present invention to provide a solution for reliably and gently connecting a terminal to a substrate.

[0017] These objects are solved at least in part by a method for connecting terminals to a substrate to form a power semiconductor module, the method having the features of independent claim 1. These objects are also solved at least in part by a power semiconductor module having the features of independent claim 13. Advantageous embodiments are given in the dependent claims, in the further description, and in the drawings, wherein the described embodiments may provide features of the invention alone or in any combination of the individual embodiments, as long as this is not explicitly excluded.

[0018] A method for connecting a terminal to a substrate to form a power semiconductor module is described, wherein the terminal has a first connection area formed by a first material, and wherein the substrate has a second connection area formed by a second material, wherein the first material has a first hardness, and wherein the second material has a second hardness, wherein the first hardness is different from the second hardness, wherein such first connection area or second connection area with higher hardness forms a connection mating area, and such first connection area or second connection area with lower hardness forms a connection base area, and wherein the terminal is connected to the substrate by using ultrasonic welding or laser welding, characterized in that before connecting the terminal to the substrate, the method includes the step of providing a connection layer, which has a surface sublayer formed by a material having a hardness corresponding to the hardness of the connection mating area, wherein the connection layer is arranged on the connection base area, and wherein the surface sublayer faces the connection mating area.

[0019] This approach offers significant advantages compared to prior art solutions, in particular with regard to reliable and secure connection of the terminals to the substrate or substrate metallization layer, respectively.

[0020] The present invention therefore relates to a method of connecting a terminal to a substrate to form a power semiconductor module. The method is therefore suitable and intended for execution in a process for producing a power semiconductor module and in detail relates to connecting the terminal to the substrate and thus in particular to the substrate metallization layer.

[0021] The terminal may generally have an L-shaped form, the lower part of which is connected to the substrate via its first connection area (e.g., a welding area). The terminal in the sense of the present invention may have a thickness equal to or greater than 600 μm (e.g., equal to or greater than 1000 μm) and a width equal to or greater than 2 mm. In addition, the connection area (e.g., welding area) may have a size equal to or greater than 2 mm×2 mm. The cross-section of the terminal may be rectangular, and the angle between the two differently oriented parts of the L-shape may be at right angles or greater than 90°. In addition, the terminal may be non-flexible.

[0022] Typical parameters of the wire bond include a diameter equal to or less than 400 μm and a connection area (e.g., soldering area) equal to or less than 0.5 mm x 1 mm compared to the terminal. The angle between the connection area and the adjacent portion can be oblique (e.g., much greater than 90°), and the cross-section can be circular. In addition, the wire bond can be flexible (i.e., bendable).

[0023] In addition, with respect to the strip relative to the terminal, typical parameters include a thickness equal to or less than 300 μm, a width equal to or greater than 2 mm, and a connection area (e.g., soldering area) equal to or less than 0.5 mm x 2 mm. The angle between the connection area and the adjacent portion may be oblique (e.g., much greater than 90°), and the cross-section may be rectangular. In addition, the strip may be flexible (i.e., bendable).

[0024] Connecting in the sense of the present invention shall therefore mean mechanically and / or electrically connecting the terminals to the substrate or substrate metallization, respectively.

[0025] In this regard, generally, the power semiconductor module may have functions known in the art.For example, the power semiconductor module to be produced comprises a metallization layer adapted to electrically connect terminals to be connected to the metallization layer with respective power semiconductor devices.

[0026] Also located on the substrate metallization layer are power semiconductor devices. Such power semiconductor devices can generally be formed as known in the art and can respectively include, in particular, transistors or switches (e.g., MOSFETs and / or IGBTs) and / or multiple power semiconductor devices can include diodes. The power semiconductor devices can be respectively interconnected and can therefore be in electrical contact (e.g., galvanic contact) with the metallization layer.

[0027] With respect to the terminals and metallization layers that should be connected to each other, it is provided that the terminals have a first connection area formed by a first material and the substrate has a second connection area formed by a second material, wherein the first material has a first hardness and wherein the second material has a second hardness, wherein the first hardness is different from the second hardness.

[0028] Thus, the first connection area is the area of ​​the terminal intended to be connected to the substrate metallization layer, and correspondingly, the second connection area is the area of ​​the substrate or the substrate metallization layer, respectively, intended to be connected to the terminal. In many applications, it is the case that the first connection area and the second connection area are formed of different materials and therefore have different hardnesses. It may be the case that the first material, i.e. the material provided in the first connection area, has a higher hardness than the second material, i.e. the material provided in the second connection area, or it may be provided that the second material has a higher hardness than the first material.

[0029] According to the described method, provision is made for such first connection region or second connection region having a higher hardness to form a connection fitting region and such first connection region or second connection region having a lower hardness to form a connection base region.

[0030] In fact, it is also known that advanced designs of power semiconductor modules require welding of different materials. For example, it is known to connect copper-based terminals to the aluminum metallization layer of a ceramic substrate. In addition, it may be necessary to connect hard copper terminals (e.g., CuNiSi pressure pin auxiliary terminals) on a ceramic substrate with a copper metallization layer.

[0031] Independent of the specific first and second materials, it is often desirable to connect the terminal to the substrate by using ultrasonic welding or laser welding. This may be due to the fact that techniques are known for connecting the terminal to the substrate to form reliable and high temperature power electronic modules. In particular, ultrasonic welding is widely used to connect, for example, terminals made of copper to a ceramic substrate having a copper metallization layer. This is mainly because the copper terminal and the copper metallization layer are both annealed copper with a low hardness (e.g., in the range of about 50 Vickers hardness).

[0032] However, using these welding techniques can result in disadvantages, particularly where the first material has a different hardness than the second material. When ultrasonic welding is used to join dissimilar materials, the harder material is likely to be pressed into the softer material or deform the softer material thereby damaging it.

[0033] In order to overcome this disadvantage of the prior art and according to the method described herein, it is provided that before connecting the terminal to the substrate, a connecting layer is provided, which has a surface sublayer formed by a material whose hardness corresponds to the hardness of the connection mating area, wherein the connecting layer is arranged on the connection base area and wherein the surface layer faces the connection mating area.

[0034] With respect to the connection layer, it may be specified that the connection layer may consist of a surface sublayer, or it may include more layers than a surface sublayer, as described below. In the case of the connection layer alone, in the case where the connection layer consists of a surface sublayer, it may be specified that the term describes the surface sublayer.

[0035] This step of providing the connection layer as described above allows the surface that is contacted when the terminal is connected to the conductive structure by ultrasonic welding or by laser welding to have a corresponding hardness, which corresponds in particular to the material with the higher hardness of the first material and the second material. In the sense of the present invention, corresponding hardness shall in particular mean the same hardness or having the same hardness and a tolerance of + / -30% relative to the higher hardness value.

[0036] Thus, the disadvantages which can occur according to the prior art in relation to correspondingly different hardnesses can be avoided.

[0037] Thus, in particular, it can be avoided that when different materials are connected using ultrasonic welding or laser welding, the harder material is easily pressed into the softer material or deforms the softer material. Thus, it can be prevented that the material with the lower hardness is damaged during the connection process.

[0038] This, in turn, may allow a very high quality metallurgical bond to be achieved at the interface between the first material and the connecting layer or the second material and the connecting layer.

[0039] Thus, a very reliable connection of the individual surfaces may be achieved, which in turn may allow a high operating capacity of the power semiconductor module (damages due to poor-quality bonds may be avoided).

[0040] In addition, the power semiconductor module can be operated with high safety due to the stable and reliable connection between the terminals and the substrate or the substrate metallization layer, respectively.

[0041] In addition to this, possible cracking of the ceramic substrate during ultrasonic welding can be avoided and the metallization gap can be reduced or even shortened. This is possible because the described method allows a gentle and effective connection technology of the terminal and the substrate.

[0042] It can be provided that the step of providing the connecting layer comprises a step of cold gas spraying (CGS). With CGS, this process is a coating deposition method. Solid powder is accelerated to high speed in a supersonic gas jet. During the impact with the material to be coated, it undergoes plastic deformation and adheres to the surface. According to this method, a particularly reliable and adaptive connecting layer can be applied, for example with regard to thickness and the material used. In addition to this, the method can be carried out independently of the geometry of the respective first and second connecting regions.

[0043] Cold air spraying can generally be used independently of the first material and the second material.

[0044] However, as a non-limiting example, it may be provided that this embodiment is used in combination with copper and aluminum as the first and second materials. In this regard, an Al / AlN / Al substrate is generally preferred for high voltage power modules because it has high cycle reliability and does not present silver ion migration issues compared to active metal brazed Cu / AIN / Cu substrates. However, according to the prior art, it is very challenging to weld copper-based terminals on such Al / AlN / Al substrates. This may be due to the fact that the aluminum metallization layer is much softer than copper as the terminal material, so the copper-based terminals may be pressed into the aluminum metallization layer. In addition, in this case, the ceramic material AlN of the substrate is easily cracked.

[0045] Therefore, cold gas spraying is a very effective embodiment for providing a connecting layer to join copper and aluminum by welding.

[0046] Thus, an additional copper layer can be provided by CGS on the existing aluminum metallization layer of the substrate in the selective area where the terminal bonding will be performed (i.e., the second connection area). By protecting the aluminum metallization layer and the ceramic AlN substrate with the connection layer, this copper plated area enables ultrasonic welding or laser welding of copper terminals on the aluminum metallization layer.

[0047] It can also be provided that cold gas spraying can be exchanged by other methods, for example, selective laser melting (SLM) of multiple layers or cold gas spraying of multiple layers can be used or when, for example, the composition of the layers is changed, so that the material gradually changes from aluminum to copper. This will be described in more detail below.

[0048] It can also be provided that the step of providing the connection layer includes a step of metal plating. In this regard, metal plating is a surface coating process in which a metal is deposited on a conductive surface. It includes, for example, electroplating and chemical plating.

[0049] The metal coating can generally be used independently of the first material and the second material.

[0050] However, as a non-limiting example, it may be provided that this embodiment is used to connect a press-fit terminal to a metallization layer of a substrate (eg a metallization layer of a ceramic substrate, in particular an aluminum metallization layer or in particular a copper metallization layer).

[0051] Press-fit terminals are widely used as auxiliary terminals in power module packaging due to their high reliability during assembly (e.g., inverter assembly), high temperature resistance, and simplicity. However, press-fit terminals must be hard copper alloys (e.g., made of CuNiSi) to form metallurgical bonds during assembly and maintain reliable contact even at high operating temperatures. According to the prior art, ultrasonic welding of press-fit terminals on copper metallization layers is very challenging, especially when the bonding feet of the auxiliary terminals are usually small and the copper metallization layer of the substrate is much softer than the CuNiSi alloy.

[0052] The use of a plating layer allows a very simple production process and further allows the formation of a very thin layer as a connecting layer. In particular, in the present embodiment, a connecting layer can be provided on the copper metallization layer, wherein the connecting layer or at least its surface sublayer is formed by an alloy (such as a NiAg alloy) or a multilayer structure with a layer sequence Ni / Au or Ni / Cu to increase the hardness relative to the copper metallization layer. This allows a stronger friction force to be provided at the interface during welding, thereby forming a stable and reliable metallurgical bond.

[0053] As described above, the present method can be very effective, for example, in the case where the press-fit auxiliary terminal should be connected to the substrate metallization layer as a conductive structure, because in this case different materials usually have to be welded together. Therefore, the present invention allows the formation of high-temperature and high-power semiconductor modules with welded auxiliary press-fit terminals.

[0054] According to the above, the terminal can be specified as an auxiliary press-fit terminal. In this regard, the press-fit terminal is used to achieve permanent electrical and mechanical terminal to PCB connection, which can be made of different materials (usually made of hard copper alloy, i.e. CuNiSi, CuSn alloy).

[0055] It can also be provided that the step of providing the connection layer comprises the step of bonding a preformed layer to the connection base region. This can be done, for example, by sintering.

[0056] This embodiment allows providing a connection layer with a large thickness, which may prove advantageous in cases where harsh soldering conditions should be used and in cases where the power module is operated at high powers and temperatures.

[0057] As a non-binding example, according to the present embodiment it can be provided that, for example, at the same time and therefore in the same process step of the chip attachment, a copper plate or a plate made of a copper alloy (e.g., a CuNiSi alloy) with a smaller or larger thickness is sintered on the first connection area (e.g., on the terminal). This also enables both ultrasonic welding of copper terminals on aluminum metallization layers and ultrasonic welding of press-fit terminals comprising copper alloys on copper or aluminum metallization layers.

[0058] It can therefore be specifically provided that the step of providing the connection layer comprises the step of sintering a preformed layer onto the connection base region. In particular with regard to sintering the preformed layer onto the first connection region or the second connection region, this step can provide a durable and reliable connection, so that there is no risk that the above advantages are offset by providing a preformed layer as the connection layer.

[0059] It can also be provided that the terminal is connected to the substrate by using ultrasonic welding. It has been found that, in particular by using ultrasonic welding, problems may arise according to which relatively soft material is damaged by relatively hard material, or in other words, relatively hard material is pressed into relatively soft material, as described above. Therefore, the advantages described are particularly valid in the case of connecting the terminal to the substrate (and therefore, in particular to the substrate metallization layer) by ultrasonic welding.

[0060] It can also be provided that the first material comprises, for example, a copper alloy (and therefore, in particular a high-hardness copper alloy) (e.g., consists of a copper alloy, and therefore, in particular a high-hardness copper alloy) and the second material comprises, for example, copper (and therefore, in particular soft copper) (e.g., consists of copper, and therefore, in particular soft copper), or that the second material comprises, for example, a copper alloy (and therefore, in particular a high-hardness copper alloy) (e.g., consists of a copper alloy, and therefore, in particular a high-hardness copper alloy) and the first material comprises, for example, copper (and in particular soft copper) (e.g., consists of copper, and therefore, in particular soft copper). In this regard and in more detail, it can be provided that the soft copper is a soft annealed copper with a hardness in the exemplary, but not limiting, range of 50-70 HV, wherein the hardness can be determined according to DIN EN ISO 6507-1:2018 to 6507-4:2018. For example, a substrate metallization layer of a ceramic substrate is usually formed of such a soft annealed copper. In addition, with respect to the high-hardness copper alloy, the latter can, for example, have an exemplary, but not limiting, hardness of 120-200 HV. It may include or consist of a CuNiSi alloy, which may be the material in an auxiliary terminal (eg, a press-fit terminal), for example.

[0061] It can also be provided that the first material includes aluminum (e.g., consists of aluminum) and the second material includes copper (e.g., consists of copper), or the first material includes copper (e.g., consists of copper) and the second material includes aluminum (e.g., consists of aluminum). Again according to the present embodiment, copper and aluminum are materials with different hardnesses, and therefore connecting these materials by ultrasonic welding or laser welding may cause problems as described above. Therefore, also in this case, the present method may be very effective.

[0062] Such an embodiment may exist, for example, in a high voltage power module including an Al / AlN / Al substrate. Such a substrate may be preferred for high voltage applications because it has high cycle reliability and can avoid silver ion migration when using active metal brazing (AMB), for example, as opposed to a copper / ceramic / copper substrate. However, soldering copper-based terminals to relatively soft aluminum metallization layers is challenging because the copper material may be pressed into the aluminum metallization layer as described above.

[0063] It can also be provided that the connecting layer is formed to include a base sublayer in addition to the surface sublayer, wherein the base sublayer is placed directly adjacent to the connecting base area so that the surface sublayer includes the material of the connecting fitting area and the base sublayer includes the material of the connecting base area.

[0064] In other words, the surface sublayer forms the surface of the connection layer after it has been attached to the connection base area (i.e., to the first or second connection area with lower hardness). Thus, after the connection layer has been attached to the connection base area, the surface sublayer faces the connection mating area and thus faces the first or second connection area with higher hardness.

[0065] Such an arrangement, in particular in the case of a multilayer with more than two layers and thus with more than a base sublayer and a surface sublayer, can also be referred to as a multilayer structure or a multilayer arrangement, respectively. Thus, the composition can be changed directly in a two-layer arrangement or gradually in an arrangement with more than two layers, so that a first material of the terminal is connected to the same material of the connection layer and, correspondingly, a second material of the substrate metallization layer is connected to the same material of the connection layer. Thus, the material change exists in the direction proceeding from the terminal to the conductive structure.

[0066] Such an embodiment may allow a particularly reliable and stable connection of the terminal to the substrate.Thus, the advantages of the invention described may be particularly pronounced according to this embodiment.

[0067] It can therefore be provided that the connecting layer changes its composition continuously from a first material to a second material.

[0068] It can also be provided that the connection layer is continuously arranged on the substrate metallization layer and on the body of the substrate adjacent to the substrate metallization layer. Therefore, according to this embodiment, a continuous connection layer is provided, which is located both on the substrate (i.e., on the substrate body) and on the substrate metallization layer. This can be performed, for example, by CGS or SLM. According to this embodiment, the terminal can be at least partially (e.g., completely) located next to the metallization layer and therefore at least partially or completely located on the substrate body. However, due to the continuous connection layer, a connection for transmitting a current or a signal from the terminal to the metallization layer is still feasible.

[0069] This embodiment allows providing a terminal without a soft layer (e.g., an aluminum layer) underneath. This can broaden the process window for ultrasonic welding or laser welding. Furthermore, a particularly reliable connection of the terminal to the conductive structure can be provided. Therefore, the advantages of the invention described can be particularly significant according to this embodiment.

[0070] For further advantages and technical features of the method, see the power semiconductor module, the drawings, and the further description.

[0071] A power semiconductor module is further described, comprising a substrate metallization layer for contacting a power semiconductor device and for contacting a terminal, and comprising a terminal for being placed on the substrate metallization layer, wherein the terminal has a first connection area formed by a first material, and wherein the substrate has a second connection area formed by a second material, wherein the first material has a first hardness, and wherein the second material has a second hardness, wherein the first hardness is different from the second hardness, and wherein the terminal is connected to the substrate via its first connection area and via the second connection area of ​​the substrate, wherein such first connection area or second connection area with higher hardness forms a connection mating area, and such first connection area or second connection area with lower hardness forms a connection base area, characterized in that the connection layer is arranged between the first connection area and the second connection area, wherein the connection layer has a surface sublayer, which is formed by a material with a hardness corresponding to the hardness of the connection mating area, wherein the surface layer faces the connection mating area.

[0072] The terminal is preferably an auxiliary press-fit terminal. Such a terminal is usually made of a high-hardness copper alloy (e.g., CuNiSi), while the substrate metallization layer is usually made of very soft annealed copper. In particular, when connecting these components by ultrasonic welding or laser welding, the softer material, i.e., the metallization layer or the substrate body, may be damaged due to cracking.

[0073] Such a power semiconductor module provides significant advantages over the prior art, which are described in detail for the present method. In summary, by providing a connection layer, a power semiconductor module can be produced without the risk of damaging the softer material during ultrasonic welding or laser welding. Instead, a very stable, reliable electrical connection can be provided between the terminal and the conductive structure, thereby allowing a safe, reliable, and high-performance operating behavior of the power semiconductor module.

[0074] In summary, the present invention solves an important goal, namely how to weld two different materials of different hardness together to allow for advanced power module design.

[0075] For further advantages and technical features of the power semiconductor module, see the method, the drawings, and the further description. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] These and other aspects of the present invention will become apparent from the embodiments described below and will be explained with reference to the following. Each feature disclosed in the embodiments constitutes an aspect of the present invention alone or in combination. Features of different embodiments can be transferred from one embodiment to another.

[0077] In the attached picture:

[0078] Figure 1 shows a partially exploded cross-sectional side view of a first embodiment of a power semiconductor module according to the invention;

[0079] Figure 2 shows a partially exploded cross-sectional side view of a second embodiment of a power semiconductor module according to the invention; and

[0080] Figure 3 A partially exploded sectional side view of a third exemplary embodiment of a power semiconductor module according to the invention is shown. DETAILED DESCRIPTION

[0081] Figure 1 A power semiconductor module 10 is shown. The power semiconductor module 10 comprises a substrate 12 having a substrate body 14 formed of ceramic (e.g., aluminum nitride) and a substrate metallization layer 16, which can be formed of copper (e.g., annealed soft copper). In addition, the substrate body 14 is connected to a bottom plate 18 via a further copper layer 20, wherein the layer 20 can be described as a bottom metallization layer. Thus, such a substrate 12 is a Cu / ceramic / Cu substrate or a Cu / AlN / Cu substrate, respectively.

[0082] The substrate metallization 16 forms an electrically conductive structure and serves in particular to connect power semiconductor devices, likewise not shown, with terminals 22 such as power terminals 24 and auxiliary terminals 26. The terminals 22 (and in particular the auxiliary terminals 26) may be formed of a hard copper alloy (e.g. CuNiSi).

[0083] It is further shown that each terminal 22 includes a first connection region 28 formed of a first material and the substrate 12 has a second connection region 30 formed of a second material, wherein the first material has a first hardness and wherein the second material has a second hardness, wherein the first hardness is different from the second hardness.

[0084] This is primarily due to the aforementioned materials used for the terminals 22 and the substrate metallization 16 .

[0085] Ultrasonic welding or laser welding is provided for connecting the terminal 22 to the substrate 12 (i.e., the substrate metallization layer 16). Since the respective connection areas 28, 30 are formed of different materials, which may lead to disadvantages due to the welding step, the terminal 22 is connected to the substrate 12 via the connection layer 32.

[0086] In more detail, it is provided that the terminal 22 (and according to Figure 1 1 and 12. In this regard, a welding tool 34, such as an ultrasonic welding electrode, is shown.

[0087] Further, before the terminal 22 is connected to the substrate 12, a connection layer 32 is provided. The connection layer 32 has a surface sublayer, which is the only layer of the connection layer 32 in the figure. The connection layer 32 is formed of a material having a hardness corresponding to the hardness of the connection mating area (i.e., the connection area 28, 30 having a higher hardness). The connection layer 32 is provided in the connection base area (i.e., the connection area 28, 30 having a lower hardness, Figure 1 In the embodiment, the area with lower hardness is on the second connection area 30). Therefore, the material of the connection layer 32 and therefore its hardness corresponds to the hardness of the copper alloy of the auxiliary terminal 26.

[0088] Therefore, the connection layer 32 is provided on the second connection region 30 , wherein the connection layer 32 is formed of a material having a hardness corresponding to the hardness of the first material (ie, the copper alloy of the auxiliary terminal 26 ).

[0089] The provision of the connection layer 32 may include at least one of cold gas spraying, metal plating, and bonding a preformed layer to the second connection region 30 .

[0090] exist Figure 2 In another embodiment, Figure 2Compared to the above, the same or corresponding components are defined by the same reference numerals.

[0091] according to Figure 2 ,and Figure 1 Compared to, the same usually applies.

[0092] However, according to Figure 2 , the substrate is an Al / ceramic / AlN substrate, or in more detail an Al / AlN / Al substrate. Therefore, it is provided that the power semiconductor module 10 comprises a substrate 12, the substrate 12 having a substrate body 14 which can be formed of aluminum nitride and a substrate metallization layer 16, which can be formed of aluminum. Furthermore, the substrate body 14 is connected to the bottom plate 18 via another aluminum layer as layer 20 and thus as a bottom metallization layer.

[0093] Therefore, in order to realize ultrasonic welding of the terminal 22 to the substrate 12 , a corresponding connection layer 32 is again provided on the second connection layer 30 .

[0094] However, since the substrate metallization layer 16 is formed of aluminum, the connection layer 32 is also provided between the power terminal 24 and the substrate 12 by using ultrasonic welding, and furthermore, the combination of aluminum and copper of the power terminal may also cause problems.

[0095] The connection layer 32 is provided on the second connection region 30 , wherein the connection layer 32 is formed of a material having a hardness corresponding to the hardness of the first material (ie, the copper alloy of the auxiliary terminal 26 or the copper of the power terminal).

[0096] exist Figure 3 In another embodiment, Figure 3 Compared to the above, identical or comparable components are defined by the same reference numerals.

[0097] according to Figure 3 ,and Figure 2 In contrast, the substrate is an Al / ceramic / AlN substrate, or in more detail an Al / AlN / Al substrate. Therefore, it is provided that the power semiconductor module 10 comprises a substrate 12 having a substrate body 14 which may be formed of aluminum nitride and a substrate metallization layer 16 which may be formed of aluminum. Furthermore, the substrate body 14 is connected to a base plate 18 via another aluminum layer as layer 20 and thus as a bottom metallization layer.

[0098] Therefore, in order to realize ultrasonic welding of the terminal 22 to the substrate 12 , a corresponding connection layer 32 is again provided on the second connection layer 30 .

[0099] However, since the substrate metallization layer 16 is formed of aluminum, a connection layer 32 is also provided between the power terminal 24 and the substrate 12 , and since ultrasonic welding is used, the combination of aluminum and copper of the power terminal may also cause problems.

[0100] The connection layer 32 is provided on the second connection region 30 , wherein the connection layer 32 is formed of a material having a hardness corresponding to the hardness of the first material (ie, the copper alloy of the auxiliary terminal 26 or the copper of the power terminal, respectively).

[0101] However, in addition to Figure 1 and Figure 2 Furthermore, it is provided that the connection layer 32 is arranged continuously on the metallization layer 16 and continuously on the substrate body 14 adjacent to the substrate metallization layer. This can be realized, for example, by means of CGS or SLM.

[0102] Although the invention has been described and illustrated in detail in the drawings and the foregoing description, such description and illustration should be considered illustrative or exemplary rather than restrictive; the invention is not limited to the disclosed embodiments. Other variations of the embodiments to be disclosed may be understood and implemented by those skilled in the art in practicing the claimed invention through a study of the drawings, the present 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 fact that certain measures are listed 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.

[0103] Reference Symbols List

[0104] 10 Power semiconductor modules

[0105] 12 substrate

[0106] 14 Main Body

[0107] 16 Metallization layer

[0108] 18 Base Plate

[0109] 20th floor

[0110] 22 terminals

[0111] 24 Power Terminals

[0112] 26 Auxiliary terminals

[0113] 28 First connection area

[0114] 30 Second connection area

[0115] 32 Connection Layer

[0116] 34 Welding tools

Claims

1. A method of connecting a terminal (22) to a substrate (12) to form a power semiconductor module (10), in, The terminal (22) has a first connection area (28) formed of a first material, and wherein the substrate (12) has a second connection area (30) formed of a second material, wherein the first material has a first hardness, and wherein the second material has a second hardness, wherein the first hardness is different from the second hardness, wherein such first connection area (28) or second connection area (30) having a higher hardness forms a connection mating area, and such first connection area (28) or second connection area (30) having a lower hardness forms a connection base area, and wherein the terminal (22) is connected to the substrate (12) by using ultrasonic welding or laser welding. 12), characterized in that, before connecting the terminal (22) to the substrate (12), the method includes the step of providing a connection layer (32), the connection layer having a surface sublayer formed by a material having a hardness corresponding to the hardness of the connection matching area, wherein the connection layer (32) is arranged on the connection base area, and wherein the surface sublayer faces the connection matching area, wherein the connection layer (32) is formed to include a base sublayer in addition to the surface sublayer, wherein the base sublayer is placed directly adjacent to the connection base area, so that the surface sublayer includes the material of the connection matching area and the base sublayer includes the material of the connection base area.

2. The method according to claim 1, It is characterized in that The step of providing the connecting layer (32) comprises the step of cold gas spraying or selective laser melting.

3. The method according to any one of claims 1 or 2, It is characterized in that The step of providing a connection layer (32) includes a step of metal plating.

4. The method according to any one of claims 1 or 2, It is characterized in that The step of providing a connecting layer (32) comprises the step of bonding a preformed layer to the connecting base region.

5. The method according to claim 4, It is characterized in that The step of providing a connection layer (32) comprises the step of sintering a preformed layer onto the connection base region.

6. The method according to any one of claims 1 or 2, It is characterized in that The terminal (22) is connected to the substrate (12) by using ultrasonic welding.

7. The method according to any one of claims 1 or 2, It is characterized in that The first material comprises a copper alloy and the second material comprises copper, or characterized in that The first material includes copper and the second material includes a copper alloy.

8. The method according to any one of claims 1 or 2, It is characterized in that The first material comprises aluminum and the second material comprises copper, or characterized in that The first material includes copper and the second material includes aluminum.

9. The method according to any one of claims 1 or 2, It is characterized in that The terminal (22) is a press-fit auxiliary terminal (26).

10. The method according to claim 1, It is characterized in that The connecting layer (32) changes its composition continuously from the first material to the second material.

11. The method according to any one of claims 1 or 2, It is characterized in that The connecting layer (32) is disposed continuously on the metallization layer (16) and is disposed continuously on the body (14) of the substrate (12) adjacent to the metallization layer (16).

12. A power semiconductor module (10), comprising a substrate metallization layer (16) for contacting a power semiconductor device and for contacting a terminal (22), and comprising a terminal (22) for being placed on the substrate metallization layer (16), in, The terminal (22) has a first connection area (28) formed of a first material, and wherein the substrate (12) has a second connection area (30) formed of a second material, wherein the first material has a first hardness, and wherein the second material has a second hardness, wherein the first hardness is different from the second hardness, and wherein the terminal (22) is connected to the substrate via its first connection area (28) and via the second connection area (30) of the substrate (12), wherein such first connection area (28) or second connection area (30) having a higher hardness forms a connection mating area, and such first connection area (28) having a lower hardness forms a connection mating area. The first connection area (28) or the second connection area (30) forms a connection base area, characterized in that a connection layer (32) is arranged between the first connection area (28) and the second connection area (30), wherein the connection layer (32) has a surface sublayer, and the surface sublayer is formed by a material having a hardness corresponding to the hardness of the connection matching area, wherein the surface sublayer faces the connection matching area, wherein the connection layer (32) also includes a base sublayer, and the base sublayer is placed directly adjacent to the connection base area, and wherein the surface sublayer includes the material of the connection matching area and the base sublayer includes the material of the connection base area.

13. The power semiconductor module (10) according to claim 12, It is characterized in that The terminal (22) is a press-fit auxiliary terminal (22).

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