DE112020003541T5 - power semiconductor module - Google Patents

Abstract

The invention relates to a method for connecting a connection (22) to a substrate (12) in order to form a power semiconductor module (10), the connection (22) having a first connection region (28) which is formed from a first material, and the substrate (12) having a second bonding region (30) formed from a second material, the first material having a first hardness and the second material having a second hardness, the first hardness being different than the second hardness , wherein such a first connection area (28) or such a second connection area (30) which has a higher hardness forms a connection partner area, and such a first connection area (28) or such a second connection area (30) which has a lower hardness , forming a connection base portion, and wherein the terminal (22) is bonded to the substrate (12) by using ultrasonic welding or Laser welding is joined, characterized in that prior to joining the terminal (22) to the substrate (12), the method includes the step of providing a bonding layer (32) having a surface sub-layer formed of a material having a hardness which corresponds to the hardness of the connection partner area, wherein the connection layer (32) is provided on the connection base area and wherein the surface part layer faces the connection partner area.

Description

technical field

The present invention relates to a method for forming a power semiconductor module. The present invention also relates to a power semiconductor module. The present invention relates in particular to a power semiconductor module which has an improved connection of a connection to a substrate metallization.

State of the art

Power semiconductor modules are well known in the art. There are various connection techniques to connect a connection to an electrically conductive structure, such as a substrate or a substrate metallization.

Ultrasonic Welding (USW) is a well-known technique for connecting a lead to a substrate metallization that can be used for a high-reliability, high-temperature power electronics module. In particular, ultrasonic welding for joining terminals made of copper to a ceramic substrate having copper plating is commonly used. This is mainly due to the fact that both a copper termination and copper plating are annealed copper that has a low hardness, such as in the range of about 50 Vickers hardness.

However, it is also known per se that advanced designs of power semiconductor modules require welding of different materials, e.g. a copper terminal with an aluminum metallization of a ceramic substrate, or a hard copper terminal, such as a press pin auxiliary terminal made of CuNiSi, with a ceramic substrate having a copper metallization . When using ultrasonic welding to join dissimilar materials, the harder material is likely to push into the softer material or deform the softer material.

As an alternative, it is known per se to use laser welding to join a terminal to a substrate or substrate metallization. However, when considering this technique, there is a risk of formation of brittle intermetallic phases when dissimilar materials are joined.

There is therefore potential for improvement with regard to connecting different materials, in particular when considering connecting connections to substrate metallizations of substrates.

JP2009302579 describes that a front electrode of a semiconductor chip and a lead frame are made of the same material, and the tip end portion of the lead frame is processed into a convex shape, and respective surface films of the semiconductor chip and the lead frame face each other. By performing ultrasonic vibration while applying pressure, the same metal formed on the outermost surface diffuses into each other, and direct metal bonding can be performed without using solder. Therefore, the focus is on a connection between a semiconductor chip and a lead frame. A reference to connecting a terminal to an electrically conductive structure is not described.

However, this step is in no way comparable to attaching a lead to a substrate as it is an entirely different process. In this respect, according to the prior art, max. 100 mW is applied to the semiconductor electrode in the case of wire bonding, and in contrast, in ultrasonic welding of terminals up to the kW range is applied.

JP 2008042039 A describes that a wiring member is divided into two parts of an electrode plate acting as a heat spreader and a lead frame, and the electrode plate is soldered to the main surface of the semiconductor chip in a state not bonded to the lead frame. Then the bonding end of the lead frame is placed over the extension extending laterally from the peripheral edge of the electrode plate and heated locally by laser welding, electron beam welding, etc.

JP 2012 039018 A describes that a surface of a connection portion to be connected to a wiring pattern of a lead is curved into a convex shape before ultrasonic bonding and the convex surface is directed to the wiring pattern. The ultrasonic wave applicator is pressed against the surface opposite to the convex surface to apply ultrasonic waves, thereby ultrasonically bonding the lead and the wiring structure.

CN 104241209 relates to a particular power module for an outdoor power supply, which includes a lead frame, a control chip, a thermistor, a power chip, a diode and a metal wire as a dedicated power integral mo dul includes. The heat dissipation substrate is arranged on the bottom of the case. The thermistor, power chip and diode are soldered to the substrate. The power chip and diode are connected to the lead frame by ultrasonic bonding, and the lead frame is spread on both sides of the heat dissipation substrate, and the metal wire connects the control chip to the lead frame.

WO 2007/033829 relates to a method for manufacturing a power semiconductor module, wherein a contact between a contact area and a contact element is formed in the form of an ultrasonically welded contact, a sonotrode used for the ultrasonic welding process is also used to assemble the contact areas with contact ends and thereby for assembling contacts with base areas.

JP 2011061105 A describes the following to provide a highly reliable bonding technique that achieves sufficient bonding strength and suppresses pad cracks when a lead terminal is bonded to a pad of a substrate in an ultrasonic manner. A coating layer harder than the pad and the lead terminal is formed on the pad on a metal base and an insulating film. During ultrasonic bonding, an ultrasonic wave is applied to an ultrasonic tool to break the coating layer, and the lead terminal and the pad on both sides of the coating layer are directly bonded to each other by plastic flow.

U.S. 2014/021620 A1 describes that according to embodiments, a power device includes a semiconductor structure having a first surface facing a second surface, a top electrode, and a bottom electrode. The top electrode may include: a first contact layer located on the first surface of the semiconductor structure, and a first bond pad layer located on the first contact layer and formed of a metal containing nickel (Ni). The bottom electrode may include: a second contact layer located under the second surface of the semiconductor structure, and a second bond pad layer located under the second contact layer and formed of a metal containing Ni.

However, the references cited above still leave room for improvement, particularly with regard to connecting, in a gentle and reliable manner, a terminal to a substrate in a power semiconductor module.

Summary of the Invention

It is therefore an object of the invention to provide a solution to at least partially overcome at least one disadvantage of the prior art. In particular, it is an object of the present invention to provide a solution for connecting a terminal to a substrate reliably and gently.

These objects are at least partially achieved by a method for connecting a terminal to a substrate to form a power semiconductor module having the features of independent claim 1. Furthermore, these objects are at least partially achieved by a power semiconductor module having the features of independent claim 13 . Advantageous embodiments are indicated in the dependent claims, in the further description as well as in the figures, whereby the described embodiments alone or in any combination of the respective embodiments can provide a feature of the present invention, unless expressly excluded.

A method is described for connecting a connection to a substrate in order to form a power semiconductor module, the connection having a first connection region which is formed from a first material, and the substrate having a second connection region which is formed from a second material. wherein the first material has a first hardness and wherein the second material has a second hardness, the first hardness differing from the second hardness, such a first connection area or such a second connection area having a higher hardness forming a connection partner area, and such a first connection portion or such a second connection portion having a lower hardness forms a connection base portion, and wherein the terminal is connected to the substrate by using ultrasonic welding or laser welding, characterized in that before the Ve rbonding the terminal to the substrate, the method comprises the step of providing a bonding layer having a surface portion layer formed from a material having a hardness corresponding to the hardness of the bonding partner region, wherein the bonding layer is provided on the bonding base region and wherein the surface sub-layer faces the connection partner area.

Such a method provides considerable advantages over prior art solutions, particularly in terms of reliable reliable and reliable connection of a connection to a substrate or a substrate metallization.

The present invention therefore relates to a method for connecting a terminal to a substrate in order to form a power semiconductor module. The method is therefore suitable and intended to be carried out in the course of producing a power semiconductor module, and deals in detail with connecting a connection to a substrate and thus in particular with substrate metallization.

The terminal may have a generally L-type shape, the lower part of which is connected to the substrate at its first connection portion such as a weld portion. A connection within the meaning of the present invention can have a thickness of greater than or equal to 600 μm, for example greater than or equal to 1000 μm, and a width of greater than or equal to 2 mm. In addition, the joining area, such as the welding area, may have dimensions equal to or larger than 2mm x 2mm. The cross-section of the terminal can be rectangular and the angle between the two differently oriented parts of the L-shape can be right-angled or more than 90°. Also, a port may not be flexible.

Unlike a terminal, typical parameters for wire bonds include a diameter that is less than or equal to 400 µm and a connection area, such as a weld area, that is less than or equal to 0.5 mm x 1 mm. An angle between the connection area and the adjacent part can be oblique, such as much more than 90°, and the cross-section can be circular. In addition, a wire bond can be flexible, i.e. bendable.

Also, with respect to a ribbon as opposed to a terminal, typical parameters include a thickness of 300 µm or less, a width of 2 mm or more, and a joining area such as a weld area that is 0.5 mm x 2 mm or less. An angle between the connection area and the adjacent part can be oblique, such as much more than 90°, and the cross section can be rectangular. In addition, a band can be flexible, i.e. bendable.

A connection within the meaning of the present invention should therefore mean a mechanical and/or electrical connection of the connection to the substrate or the substrate metallization.

In this respect, the power semiconductor module can generally have functionalities as known in the prior art. For example, the power semiconductor module that should be manufactured includes a metallization configured to electrically connect a terminal that should be connected to this metallization to respective power semiconductor devices.

Power semiconductor components are also arranged on the substrate metallization. Such power semiconductor devices may generally be formed as known in the art and may each include transistors or switches, such as MOSFETs and/or IGBTs, and/or the plurality of power semiconductor devices may include diodes, among others. The power semiconductor components can be connected to one another accordingly and can therefore be in electrical contact, such as galvanic contact, with the metallization.

With regard to the terminals and the metallization that should be connected to one another, it is provided that the terminal has a first connection region formed from a first material and that the substrate has a second connection region formed from a second material , wherein the first material has a first hardness and wherein the second material has a second hardness, the first hardness being different than the second hardness.

Therefore, the first connection area is that area of the connection that should be connected to the substrate metallization, and correspondingly the second connection area is that area of the substrate or substrate metallization that should be connected to the connection. In many applications, the first connection area and the second connection area are formed from different materials and therefore have different hardnesses. It may be the case that the first material and thus the material provided at the first connection area has a higher hardness compared to the second material and thus that material provided at the second connection area, or it may be provided that the second material has a higher hardness compared to the first material.

According to the method described, it is provided that such a first connection area or such a second connection area, which has a higher hardness, forms a connection partner area, and such a first connection area or such a second connection region having a lower hardness forms a connection base region.

In fact, it is also known per se that advanced designs of power semiconductor modules require welding of different materials. For example, it is known to connect a copper-based connector to an aluminum metallization of a ceramic substrate. It may also be necessary to connect a hard copper terminal, such as a CuNiSi press-fit auxiliary terminal, to a ceramic substrate that has copper metallization.

Regardless of the particular first and second materials, it is often desirable that the terminal be bonded to the substrate using ultrasonic welding or laser welding. This may be due to the fact that these techniques for connecting a lead to a substrate to form a reliable, high-temperature power electronics module are known per se. In particular, ultrasonic welding for bonding terminals made of copper, for example, to a ceramic substrate having copper plating is commonly used. This is mainly due to the fact that both a copper termination and copper plating are annealed copper that has a low hardness, such as in the range of about 50 Vickers hardness.

However, using these welding techniques can lead to disadvantages, especially in a case where the first material has a different hardness compared to the second material. When using ultrasonic welding to join dissimilar materials, the harder material is likely to push into the softer material or deform and thus damage the softer material.

In order to overcome this disadvantage of the prior art and according to the method described here it is provided that before connecting the terminal to the substrate, a connecting layer is provided which has a surface part layer which is formed from a material which has a hardness which corresponds to the hardness of the connection partner area, wherein the connection layer is provided on the connection base area and the surface layer faces the connection partner area.

With regard to the connection layer, it can be provided that the connection layer can consist of the surface part layer or it can comprise more layers than the surface part layer, as described below. In the case where only one connecting layer is mentioned, provision can be made for this term to describe the surface sub-layer if the connecting layer consists of the surface sub-layer.

The step of providing the connecting layer, as described above, makes it possible for the surfaces that come into contact with the electrically conductive structures using ultrasonic welding or using laser welding when connecting the terminal to have a corresponding hardness, which in particular corresponds to the material of the first Material and the second material, which has the higher hardness, corresponds. A corresponding hardness within the meaning of the present invention should mean in particular the same hardness or the same hardness and a tolerance of +/- 30% with regard to the higher hardness value.

Disadvantages with regard to a different hardness in each case, which can occur according to the prior art, can be avoided in this way.

Therefore, in particular, when using ultrasonic welding or laser welding to join dissimilar materials, it can be avoided that the harder material is likely to be pressed into the softer material or the softer material is deformed. Therefore, the material having the lower hardness can be prevented from being damaged in the joining process.

Again, a very high quality metallurgical bond can be enabled to be achieved at the interface between the first material and the bonding layer or the second material and the bonding layer.

Therefore, highly reliable connection of the respective faces can be achieved, which in turn can enable high workability of the power semiconductor module, which can avoid damage occurring due to inferior connections.

Apart from that, the power semiconductor module can work with a high level of safety due to the stable and reliable connection between the connection and the substrate or the substrate metallization.

Apart from the above, it can also be avoided that the ceramic substrate can break during ultrasonic welding and the metallization gap can be reduced or even short-circuited. This may be because that described method allows a gentle and effective connection technology of the terminal and the substrate.

Provision can be made for the step of providing a connecting layer to include the step of cold gas spraying (CGS). In terms of CGS, this process represents a coating deposition process. Solid powders are accelerated to a high velocity in a supersonic jet of gas. When they hit the material to be coated, they are plastically deformed and adhere to the surface. According to this method, a connecting layer can be applied particularly reliably and adaptively, for example with regard to the thickness and the material used. Apart from that, this method can be carried out independently of the geometry of the respective first and second connection area.

Cold spray can generally be used independently of the first and second materials.

However, as a non-limiting example, it can be envisaged that this embodiment is used in combination of copper and aluminum as the first and second material. In this regard, an Al/AlN/Al substrate is often preferred for high-voltage power modules because it has high cycle reliability and no silver ion migration problem compared with the AMB-Cu/AlN/Cu (ABM: active metal brazed) substrate. However, according to the prior art, it poses a great challenge to weld a copper-based terminal to such a kind of Al/AlN/Al substrate. This may be because aluminum metallization is much softer than copper as the material of the terminal, which can force the copper-based terminal into the aluminum metallization. In addition, in this case the ceramic material of the substrate AIN is very susceptible to cracking.

Therefore, cold spray is a very effective embodiment for providing a bond layer to join copper and aluminum by welding.

Therefore, an additional copper layer can be provided using CGS on the existing aluminum metallization of the substrate within a selected area where the terminal bonding is to take place, i.e. in the second connection area. This copper clad area allows ultrasonic welding or laser welding of the copper termination to the aluminum metallization by protecting the aluminum metallization and the ceramic AlN substrate through the bonding layer.

It can also be envisaged that cold gas spraying can be replaced by other methods, e.g. selective laser melting (SLM), or cold gas spraying of multiple layers, such as with a changed composition of the layers, can be used so that the material gradually changes from Aluminum changes to copper. This is described in more detail below.

Provision can also be made for the step of providing a connecting layer to include the step of metal plating. In this regard, metal plating is a surface coating process in which a metal is deposited on a conductive surface. For example, it includes both electroplating and electroless plating.

Metal plating can generally be used independently of the first and second materials.

However, as a non-limiting example, it can be envisaged that this embodiment is used for connecting press-fit terminals to metallizations of substrates, such as ceramic substrates, in particular aluminum metallizations or in particular copper metallizations.

Press-fit terminals are commonly used for the auxiliary terminals in power module cases because of their high reliability, high-temperature capability, and their simplicity during assembly, such as inverter assembly. However, the press-fit terminal must be a hard copper alloy such as formed from CuNiSi in order to form a metallurgical bond during assembly and to reliably maintain contact even at high operating temperatures. According to the state of the art, the ultrasonic welding of press-fit terminals to a copper metallization presents a great challenge, especially since the bond pads of the auxiliary terminals are typically small and a Cu metallization of the substrate is much softer than the CuNiSi alloy.

The use of plating allows for a very simple manufacturing process and also allows very thin layers to be formed as interconnect layers. In particular, in this embodiment it is possible to provide a bonding layer on the copper metallization, wherein the bonding layer or at least the surface part layer thereof of an alloy such as a NiAg alloy, or of a multi-layer structure having the layer sequence Ni/Au or Ni/Cu, in order to increase the hardness in comparison with the copper plating. This enables providing more friction at the interface during welding, which in turn results in a stable and reliable metallurgical bond.

As indicated above, the present method can be very effective, for example, in a case where a press-fit auxiliary terminal is to be connected to a substrate metallization as an electrically conductive structure, since in this case different materials often have to be welded together. Therefore, the present invention enables forming a high-temperature and high-performance semiconductor module with a press-fit auxiliary welded terminal.

According to the above, it can be provided that the terminal is a press-fit auxiliary terminal. In this regard, a press-fit connector is used to enable a permanent electrical and mechanical connector-PCB connection, it can be made of different materials, which are usually a hard Cu alloy, i.e. CuNiSi, CuSn alloys.

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

This embodiment makes it possible to provide bonding layers that have a large thickness, which can offer advantages in a case where harsh welding conditions should be used and in a case where the power module operates at high power and high temperature.

As a non-binding example, according to this embodiment, a copper plate having a small or large thickness, or a plate made of a copper alloy such as CuNiSi alloy, can be provided on the first connection portion such as the terminal , for example, is sintered at the same time and thus in the same process step of chip attachment. This also allows for both ultrasonic welding of copper terminations to aluminum metallization and further ultrasonic welding of press-fit terminals comprising copper alloy to copper or aluminum metallization.

Provision can therefore be made in particular for the step of providing a connecting layer to include the step of sintering a preformed layer onto the connecting base region. In particular, this step can provide a durable and reliable connection with regard to sintering a preformed layer on the first connecting portion or on the second connecting portion, so that there is no fear that providing a preformed layer as a connecting layer works against the advantages described above.

Provision can also be made for the connection to be connected to the substrate using ultrasonic welding. It has been found that, particularly when using ultrasonic welding, the problem can arise that a comparatively softer material is damaged by the comparatively harder material, or in other words the comparatively harder material is pressed into the comparatively softer material, as described above. Therefore, the advantages described are particularly effective in a case where the terminal is connected to the substrate, and therefore in particular to the substrate metallization, by means of ultrasonic welding.

It can also be provided that the first material comprises a copper alloy and thus in particular a copper alloy with high hardness, such as consists of it, and the second material comprises copper and in particular soft copper, such as consists of it, or that the second material comprises a copper alloy and therefore in particular comprises a high hardness copper alloy, such as consists of, and the first material comprises copper and in particular soft copper, such as consists of. In this regard and in detail, it can be provided that the soft copper is a soft annealed copper having a hardness that is in an example range of 50 to 70 HV, which is in no way limiting, the hardness being according to DIN EN ISO 6507-1 :2018 to 6507-4:2018 can be determined. For example, substrate metallization, such as a ceramic substrate, is often formed by such annealed copper. In addition, and with regard to a high-hardness copper alloy, the latter can have, for example, a hardness in the range of, for example, 120 to 200 HV, which is not limiting. It may include or consist of a SuNiSi alloy, which may, for example, be a material in an auxiliary terminal such as a press-fit terminal.

It can also be provided that the first material comprises aluminum, such as consists of it, and the second material copper comprises, such as consists of, or that the first material comprises, such as consists of copper and the second material comprises, such as consists of aluminum. According to this embodiment, copper and aluminum are again materials that have different hardnesses, and therefore joining these materials using ultrasonic welding or using laser welding may lead to the problems described. Therefore, in this case, again, the present method can be very effective.

Such an embodiment may be present, for example implemented, in high voltage power modules comprising an Al/AIN/AI substrate. Such a substrate may be preferred for a high voltage application because it has high cycle reliability and silver ion migration can be avoided when using active metal brazing (AMB), for example, which is in contrast to a Cu/ceramic/Cu substrate, for example. However, it presents a challenge to weld a copper-based termination to a comparably soft aluminum metallization since the copper material can be pushed into the aluminum metallization as described above.

It can also be provided that the connection layer is formed in such a way that it comprises a layer of a base part layer in addition to the surface part layer, the base part layer being arranged directly adjacent to the connection base area, so that the surface part layer comprises the material of the connection partner area and the base part layer comprises the material of the connection base area includes.

In other words, the surface sub-layer forms the surface of the bonding layer after it has been attached to the bonding base region, i.e. the first or second bonding region having the lower hardness. Therefore, after the bonding layer is attached to the bonding base portion, the partial surface layer faces the bonding partner portion and thus faces the first or second bonding portion having the higher hardness.

Such an arrangement, particularly when it comprises a plurality of more than two layers and therefore more than the base sub-layer and the surface sub-layer, may be referred to as a multi-layer structure or arrangement. You can therefore change its composition directly in a two-layer arrangement or gradually in an arrangement that has more than two layers, such that the first material of the connection is connected to the same material of the connection layer, and correspondingly that the second material of the substrate metallization with is connected to the same material of the connection layer. The material change is therefore in a direction that runs from the connection to the electrically conductive structure.

Such an embodiment can enable a particularly reliable and stable connection of the connection to the substrate. Therefore, the described advantages of the present invention can be particularly pronounced according to this embodiment.

Provision can therefore be made for the connection layer to change its composition continuously from the first material to the second material.

It can also be provided that the connection layer is continuously provided on the substrate metallization and on a main body of the substrate adjacent to the substrate metallization. According to this embodiment, therefore, there is provided a continuous interconnection layer disposed both on the substrate, i.e. on the substrate main body, and on the substrate metallization. This can be done using CGS or SLM, for example. According to this embodiment, the terminal may be at least partially, for example entirely, located in the vicinity of the metallization, and therefore at least partially or entirely on the substrate main body. However, due to the continuous connection layer, a connection for transmitting currents or signals from the connection to the metallization is still possible.

This embodiment enables the terminal to be provided without having a soft layer such as an aluminum layer underneath. This can expand the process window of ultrasonic welding or laser welding. A particularly reliable connection of the connection to the electrically conductive structure can in turn be provided. Therefore, the described advantages of the present invention can be particularly pronounced according to this embodiment.

With regard to further advantages and technical features of the method, reference is made to the power semiconductor module, the figures and the further description.

In addition, a power semiconductor module is described that has a substrate metallization for contacting power semiconductor components and for contacting a terminal, and comprises a terminal for arranging on the substrate metallization, wherein the terminal has a first connection area formed from a first material, and wherein the substrate has a second connection area formed from a second material, wherein the first material has a first hardness and the second material has a second hardness, wherein the first hardness differs from the second hardness, and wherein the terminal is connected with its first connection region to the substrate with its second connection region, such a first Connection area or such a second connection area, which has a higher hardness, forms a connection partner area, and such a first connection area or such a second connection area, which has a lower hardness, forms a connection base area, characterized in that a verb bonding layer is provided between the first bonding region and the second bonding region, the bonding layer having a surface sub-layer formed of a material having a hardness corresponding to the hardness of the bonding partner region, the surface layer facing the bonding partner region.

The terminal is preferably an auxiliary press-fit terminal. Such a terminal is usually made of a high hardness copper alloy such as CuNiSi, while the substrate metallization is usually made of very soft annealed copper. In particular, when such parts are joined by ultrasonic welding or laser welding, it may damage the softer material, i.e., the metallization or the substrate main body, through cracks.

Such a power semiconductor module provides significant advantages over the prior art, which are described in detail in terms of the method. In summary, by providing the connection layer, the power semiconductor module can be manufactured without the risk of damage to the softer material in the course of ultrasonic welding or laser welding. Instead, a very stable and reliable electrical connection can be provided between the connection and the electrically conductive structure, which in turn enables safe, reliable and high-performance operation of the power semiconductor module.

To summarize the above, the present invention solves an important problem of how to weld two dissimilar materials with different hardnesses, which in turn enables an advanced power module design.

With regard to further advantages and technical features of the power semiconductor module, reference is made to the method, the figures and the further description.

character list

These and other aspects of the invention will be apparent from and illustrated by the embodiments described below. Individual features disclosed in the embodiments can represent an aspect of the present invention alone or in combination. Features of the various embodiments may be carried over from one embodiment to another embodiment.

• 1 eine seitliche, teilweise auseinandergezogene Schnittansicht einer ersten Ausführungsform eines Leistungshalbleitermoduls gemäß der Erfindung;
• 2 eine seitliche, teilweise auseinandergezogene Schnittansicht einer zweiten Ausführungsform eines Leistungshalbleitermoduls gemäß der Erfindung; und
• 3 eine seitliche, teilweise auseinandergezogene Schnittansicht einer dritten Ausführungsform eines Leistungshalbleitermoduls gemäß der Erfindung.

Show it:

• 1 a side, partially exploded sectional view of a first embodiment of a power semiconductor module according to the invention;
• 2 a side, partially exploded sectional view of a second embodiment of a power semiconductor module according to the invention; and
• 3 12 is a side, partially exploded sectional view of a third embodiment of a power semiconductor module according to the invention.

Description of Embodiments

1 10 shows a power semiconductor module 10. The power semiconductor module 10 comprises a substrate 12, which has a substrate main body 14, which may be formed from a ceramic, such as aluminum nitride, and a substrate metallization 16, which may be formed from copper, such as an annealed soft copper. having. In addition, the substrate main body 14 is connected to a base plate 18 by means of another copper layer 20, which layer 20 can be described as a bottom metallization. Such a substrate 12 is therefore a Cu/ceramic/Cu substrate or a Cu/AlN/Cu substrate.

The substrate metallization 16 forms an electrically conductive structure and is used, among other things, to connect power semiconductor components, which are not shown per se, to terminals 22, such as a power terminal 24 and an auxiliary terminal 26. The terminals 22 and in particular the auxiliary terminal 26 can consist of a hard copper alloy, such as CuNiSi, are formed.

Each terminal 22 is also shown to include a first connection region 28 formed of a first material and the substrate 12 having a second connection region 30 formed of a second material, the first material having a first hardness and wherein the second material has a second hardness, the first hardness being different than the second hardness.

This is primarily due to the materials described above for the terminals 22 and the substrate metallization 16.

In order to connect the terminals 22 to the substrate 12, i.e. the substrate metallization 16, it is envisaged to use ultrasonic welding or laser welding. Since the respective connection regions 28, 30 are formed from different materials, which can lead to disadvantages due to the welding step, the connections 22 are connected to the substrate 12 with the aid of a connection layer 32.

More precisely, it is provided that the connection 22 and according to the embodiment of FIG 1 specifically, the auxiliary press-fit terminal 26 is bonded to the substrate 12 using ultrasonic welding or laser welding. In this regard, a welding tool 34, such as a sonotrode, is illustrated.

In addition, before connecting the terminal 22 to the substrate 12, the connection layer 32 is provided. The tie layer 32 includes a surface sub-layer, which is the only layer of the tie layer 32 in the figures. The connection layer 32 is formed from a material which has a hardness which corresponds to the hardness of the connection partner area, ie that connection area 28, 30 which has the higher hardness. The bonding layer 32 is provided on the bonding base region, ie each bonding region 28, 30 having the lower hardness and the in 1 the second connecting portion 30 is. Therefore, the material of the connection layer 32 and thus its hardness corresponds to the hardness of the copper alloy of the auxiliary connection 26.

Therefore, the connection layer 32 is provided on the second connection portion 30, the connection layer 32 being formed of a material having a hardness corresponding to the hardness of the first material, i.e., the copper alloy of the auxiliary terminal 26.

The provision of the connecting layer 32 can comprise at least one of the following steps: cold gas spraying, metal plating, and the step of bonding a preformed layer to the second connecting region 30.

In 2 Another embodiment is shown, in comparison with 2 the same or comparable components are defined by the same reference numbers.

According to 2 generally the same applies as in 1 .

However, according to 2 the substrate is an Al/ceramic/AlN substrate, or more specifically, an Al/AlN/Al substrate. It is therefore provided that the power semiconductor module 10 comprises a substrate 12, which has a substrate main body 14, which can be formed from aluminum nitride, and a substrate metallization 16, which can be formed from aluminum. In addition, the substrate main body 14 is connected to a base plate 18 by means of another layer of aluminum as layer 20 and therefore as a lower metallization.

In order to implement an ultrasonic welding of the terminals 22 on the substrate 12, a respective connection layer 32 is therefore again provided on the second connection layer 30. FIG.

However, since the substrate metallization 16 is formed of aluminum, a bonding layer 32 is also provided between the power terminal 24 and the substrate 12 since using ultrasonic welding also the combination of aluminum and copper of the power terminal can cause problems.

The connection layer 32 is provided on the second connection region 30, the connection layer 32 being formed of a material having a hardness corresponding to the hardness of the first material, i.e. the copper alloy of the auxiliary terminal 26 and the copper of the power terminal, respectively.

In 3 Another embodiment is shown, in comparison with 3 the same or comparable components are defined by the same reference numbers.

According to 3 the substrate is comparable to 2 an Al/ceramic/AlN substrate, or more specifically an Al/AlN/Al substrate. It is therefore provided that the power semiconductor module 10 comprises a substrate 12, which has a substrate main body 14, which can be formed from aluminum nitride, and a substrate metallization 16, which can be formed from aluminum. Also, the substrate t main body 14 is connected to a base plate 18 by means of another layer of aluminum as layer 20 and therefore as the lower metallization.

In order to implement an ultrasonic welding of the terminals 22 on the substrate 12, a respective connection layer 32 is therefore again provided on the second connection layer 30. FIG.

However, since the substrate metallization 16 is formed of aluminum, a bonding layer 32 is also provided between the power terminal 24 and the substrate 12 since using ultrasonic welding also the combination of aluminum and copper of the power terminal can cause problems.

The connection layer 32 is provided on the second connection region 30, the connection layer 32 being formed of a material having a hardness corresponding to the hardness of the first material, i.e. the copper alloy of the auxiliary terminal 26 and the copper of the power terminal, respectively.

However, in addition to 2 and 1 contemplated that the interconnect layer 32 would be continuously provided on the metallization 16 and on the substrate main body 14 adjacent to the substrate metallization. This can be implemented using CGS or SLM, for example.

While the invention has been shown and described in detail in the drawings and the foregoing description, such showing and description are intended as an illustration or example and not as a limitation; the invention is not limited to the disclosed embodiments. Other modifications to the disclosed embodiments may be understood and effected by one skilled in the art from practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the term "comprising" does not exclude other elements or steps, and the indefinite article "a/an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not mean that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as a limitation on the scope.

Reference List

10

power semiconductor module

12

substrate

14

main body

16

metallization

18

base plate

20

layer

22

connection

24

power connection

26

auxiliary connection

28

First connection area

30

Second connection area

32

connection layer

34

welding tool

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• JP 2009302579 [0007]
• JP 2008042039 A [0009]
• JP 2012039018 A [0010]
• CN104241209 [0011]
• WO 2007/033829 [0012]
• JP 2011061105 A [0013]
• US2014021620A1 [0014]

Claims (14)

A method for connecting a terminal (22) to a substrate (12) to form a power semiconductor module (10), the terminal (22) having a first connection region (28) formed from a first material, and the substrate ( 12) has a second connection region (30) formed from a second material, the first material having a first hardness and the second material having a second hardness, the first hardness being different from the second hardness, such a first connection area (28) or such a second connection area (30), which has a higher hardness, forms a connection partner area, and such a first connection area (28) or such a second connection area (30), which has 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 i st, characterized in that prior to bonding the terminal (22) to the substrate (12), the method comprises the step of providing a bonding layer (32) having a surface sub-layer formed from a material having a hardness which corresponds to the hardness of the connection partner area, wherein the connection layer (32) is provided on the connection base area and the surface part layer faces the connection partner area. procedure after claim 1 , characterized in that the step of providing a connecting layer (32) comprises the step of cold gas spraying or selective laser melting. Procedure according to one of Claims 1 or 2 , characterized in that the step of providing a bonding layer (32) comprises the step of metal plating. Procedure according to one of Claims 1 until 3 characterized in that the step of providing an interconnection layer (32) comprises the step of bonding a premolded layer to the interconnection base region. procedure after claim 4 characterized in that the step of providing a bonding layer (32) comprises the step of sintering a preformed layer to the bonding base region. Procedure according to one of Claims 1 until 5 characterized in that the terminal (22) is bonded to the substrate (12) using ultrasonic welding. Procedure according to one of Claims 1 until 6 , characterized in that the first material comprises a copper alloy and the second material comprises copper, or in that the first material comprises copper and the second material comprises a copper alloy. Procedure according to one of Claims 1 until 7 , characterized in that the first material comprises aluminum and the second material comprises copper, or in that the first material comprises copper and the second material comprises aluminum. Procedure according to one of Claims 1 until 8th , characterized in that the terminal (22) is a press-fit auxiliary terminal (26). Procedure according to one of Claims 1 until 9 , characterized in that the connection layer (32) is formed in such a way that it comprises a layer of a base part layer in addition to the surface part layer, the base part layer being arranged directly adjacent to the connection base area, so that the surface part layer comprises the material of the connection partner area and the base part layer comprises the material of the Includes connection base area. procedure after claim 10 , characterized in that the connecting layer (32) changes its composition continuously from the first material to the second material. Procedure according to one of Claims 1 until 11 , characterized in that the connection layer (32) is provided continuously on a metallization (16) and on a main body (14) of the substrate (12) adjacent to the metallization (16). Power semiconductor module (10) comprising a substrate metallization (16) for contacting power semiconductor components and for contacting a connection (22), and a connection (22) for arranging on the substrate metallization (16), the connection (22) comprising a first connection area (28) formed from a first material, and wherein the substrate (12) has a second connection region (30) formed from a second material, the first material having a first hardness and the second material having a having a second hardness, the first hardness being different from the second hardness, and the terminal (22) having its first connection be region (28) is connected to the substrate (12) with its second connection area (30), such a first connection area (28) or such a second connection area (30) which has a higher hardness forming a connection partner area, and such first connection area (28) or such a second connection area (30) which has a lower hardness, forms a connection base area, characterized in that a connection layer (32) is provided between the first connection area (28) and the second connection area (30), wherein the connection layer (32) has a surface part layer formed of a material having a hardness corresponding to the hardness of the connection partner area, the surface layer facing the connection partner area. Power semiconductor module (10) after Claim 13 , characterized in that the terminal (22) is a press-fit auxiliary terminal (22).

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