Metal substrate structure and method of attaching terminals to a metal substrate structure and semiconductor power module

Abstract

A method for attaching terminals (4) to a metal substrate structure (3) for a semiconductor power module (10) comprises providing at least one terminal (4) and providing a metal substrate structure (3) having a metal top layer (17), a metal bottom layer (19) and an insulating resin layer (18) arranged between the metal top layer (17) and the metal bottom layer (19). The method further comprises coupling the at least one terminal (4) to the metal top layer (17) of the metal substrate structure (3) by laser welding with a laser beam (6).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method of attaching terminals to a metal substrate structure for a semiconductor power module with an insulating resin sheet. The present disclosure also relates to a semiconductor power module for a semiconductor device. The present disclosure also relates to a corresponding metal substrate structure. BACKGROUND

[0002] Conventional insulating metal substrates form low power and medium power semiconductor packaging technologies with both low insulation requirements and low thermal resistance requirements. Terminals are prepared on the insulating metal substrate and need to be reliably connected on the insulating metal substrate. SUMMARY

[0003] Embodiments of the present disclosure relate to a method for attaching terminals to a metal substrate structure, which can contribute to a cost-saving metal substrate structure for a semiconductor power module, which is able to work reliably even in high-voltage power module applications. Further embodiments of the present disclosure relate to a corresponding metal substrate structure and a semiconductor power module for a semiconductor device.

[0004] According to embodiments, a method for attaching terminals to a metal substrate structure for a semiconductor power module comprises providing at least one terminal and providing a metal substrate structure having a metal top layer, a metal bottom layer and an insulating resin layer arranged between the metal top layer and the metal bottom layer. The metal top layer is provided and made of one piece having at least one protrusion with a given local reinforcement thickness of up to 2.0 mm thicker than an adjacent area of the metal top layer. The protrusion is formed at a position on a top surface of the metal top layer configured to be coupled to the at least one terminal. The method further comprises coupling the at least one terminal to the protrusion of the metal top layer of the metal substrate structure by laser welding with a laser beam.

[0005] Due to the described method, a soldered joint connection can be achieved on the insulating metal substrate, which can contribute to a stable and reliable work of the semiconductor power module even in high-voltage power module applications. The method contributes to a firm attachment of the terminals on the insulating metal substrate by laser welding. The intentionally formed protrusion is able to protect the resin layer from heat and can be integrated with a circuit metallization having a locally greater thickness at the position of the terminal leg. The protrusion provides a longer thermal path between the welding position and the resin layer and a stronger lateral heat spreading in the substrate metallization and on the mechanical reinforcement of the substrate.

[0006] It is recognized in connection with the present disclosure that conventional insulated metal substrates enable low power and medium power semiconductor packaging technologies with both low insulation requirements and low thermal resistance requirements. For low reliability requirements, the terminals can be soldered or glued on the substrate, for example. Typically, soldering provides better reliability, but the soldering process can be critical to the substrate structure. In view of this conventional setup of the insulated metal substrate, the corresponding terminals are connected to the top metallization using a soldering technology to provide a typical soldered connection, which can be critical to the stable process on the substrate and the resin insulation sheet material underneath the metallization. The soldering process can cause damage to the substrate structure, in particular ultrasonic soldering, due to friction and pressure between the terminal pins and the substrate, providing a strong impact of thermal and mechanical stress combined with heat on the substrate structure. Here, the resin sheet material is strongly endangered by deformation and crack formation. In the application of ultrasonic soldering of the terminal pins on the circuit metallization of the insulated metal substrate, the corresponding failure modes have to be considered.

[0007] By using the described method for manufacturing the metal substrate structure, the above-mentioned adverse effects due to the laser soldering process can be counteracted. The risk of crack formation or damage in the resin layer can be reduced, and a stable semiconductor power module can be achieved, which is able to work reliably even in high voltage power module applications in the voltage range of, for example, 0.5 kV up to 10.0 kV. One or more terminals can be soldered directly to the metal top layer, for example, to form a direct copper-to-copper contact. As an alternative to the direct contact, additional spacer elements can be located between the bottom surfaces of the terminals facing each other and the upper or top surface of the metal top layer.

[0008] The resin layer forms a dielectric layer and can be realized as a prepreg sheet assembled between two metal plates forming the metal top layer and the metal bottom layer on the top and bottom. Such a metallized sheet or plate is bonded to the insulator of the dielectric resin layer by a lamination process, for example. The desired metallization structure of the metal top layer can then be completed by steps of a subsequent masking process and etching process to locally remove the conductive metal, resulting in the final metallization structure. Alternatively, the top metallization structure can be formed by cutting or stamping, for example, before forming the finished metal substrate structure.

[0009] Alternatively, the resin layer can be formed by molding. For such a molded dielectric layer, the molding substance realizes a pumpable substance with predetermined material properties. The pumpable substance is a liquid or viscous raw material of the resin layer to be formed. For example, the molding substance is an epoxy resin and / or a ceramic-based liquid. Alternatively or additionally, the raw material of the dielectric layer can be a thermoset or thermoplastic resin material, such as polyamide, PBT, PET. Alternatively or additionally, the raw material of the dielectric layer can comprise inorganic fillers to obtain improved thermal conductivity and / or GTE adjustment with respect to the metal top layer and / or the metal bottom layer. For example, the molded dielectric layer comprises a resin-based dielectric material with ceramic filler material, such as AI2O3, AIN, BN, Si3N4 or SiO2. For example, the dielectric layer is an epoxy resin with filler. The dielectric layer can also be based on other materials suitable for transfer molding, injection molding or compression molding or other applicable molding techniques, such as bismaleimides, cyanate esters, polyimides and / or silicones. Alternatively or additionally, the dielectric layer can comprise a ceramic material and / or a wet-molded material or a material combination of two or more of the above-mentioned components.

[0010] The alignment of the metal top layer and the metal bottom layer with a predetermined distance between each other will essentially predetermine the subsequent thickness of the molded dielectric layer. For example, the thickness is defined along a stacking direction of the metal substrate structure which can assume a z-direction. However, for proper positioning of the metal pattern with respect to the x- and y-directions, the alignment can also be done in the perpendicular x- and y-directions. For example, the alignment can be achieved by placing the metal top layer onto a release film or a spacer or another fixture, for example a mold groove of a molding tool. This enables a precise positioning of the metallization structure of the provided metal top layer with respect to the metal bottom layer and can be useful, for example, if the metal top layer comprises separate metal pads due to different operating potentials. In case of lamination, the thickness of the resin layer is given by the thickness and behavior of the lamination layer.

[0011] According to embodiments of the method, the at least one terminal is provided with one or more coatings which partially or completely cover a predetermined surface of the respective terminal. The terminal can comprise an anti-reflective coating on a top surface which is configured to face the incident laser beam during laser welding. By means of an anti-reflective coating, for example arranged on the top side of the terminal pin, the irradiation efficiency of the laser beam can be improved. Alternatively or additionally, the terminal can comprise a coating on a bottom surface which is configured to face the metal top layer of the metal substrate structure during laser welding, the coating being made of a noble metal, such as silver or gold, for example, for preventing oxidation or for improving the laser welding process.

[0012] According to a further embodiment of the method, laser parameters of the laser beam can be given to beneficially influence the laser welding. Thus, the laser beam or the corresponding laser source for the laser welding can be configured to provide a power of 300 W to 3000 W. Alternatively or additionally, the laser beam or the laser source for the laser welding can be configured to provide a travel speed of 1 mm / s to 200 mm / s directed along a top surface of the at least one terminal facing the incident laser beam. Thus, the welding does not necessarily have to be performed at only one point of limitation and the laser spot of the laser beam providing the welding process can be moved with the above-mentioned speed to provide a bonded connection over a defined area.

[0013] The laser beam can further be configured to oscillate at a predetermined frequency. Thus, the laser spot position can oscillate or wobble at a frequency of up to 2 kHz to beneficially influence the welding process.

[0014] According to a further embodiment of the method, the step of coupling the at least one terminal to the metal substrate structure by laser welding comprises aligning the terminal and the metal substrate structure relative to each other such that a top surface of the metal top layer facing each other is in contact with a bottom surface of the terminal. The method further comprises laser welding the terminal with the laser beam such that a welded joint between the terminal and the metal substrate structure is formed and the at least one terminal and the metal top layer are firmly bonded.

[0015] According to a further embodiment of the method, the terminal and the metal substrate structure are aligned relative to each other with a predetermined distance therebetween defining a gap of no more than 500 pm between the top surface of the metal top layer facing each other and the bottom surface of the terminal. The terminal is laser welded with the laser beam such that the terminal is locally melted and a welded joint between the terminal and the metal substrate structure is formed by dripping or flowing or deforming of the melted metal portion (held by surface tension) and the at least one terminal and the metal top layer are firmly bonded. Using such a configuration can improve the positioning of the terminal and a thermal protection of the insulated metal substrate structure is achieved by forming a small gap of a few hundred micrometers between the metal top layer and the terminal. The terminal can comprise an L-shape having a terminal body and a terminal leg which can be held in place while the laser welding bonded connection is provided by a dripping or deformed portion of the molten material from the terminal leg.

[0016] It is recognized in connection with the present disclosure that, although less critical compared to ultrasonic welding, the laser welding process of copper terminals on the circuit metallization of a metal substrate structure formed by a metal top layer beneficially comprises features for minimizing the thermal impact on the thermally sensitive resin sheet or resin layer. In one aspect, the thermal impact on the resin layer can be reduced by protective features reducing the heat flow into the resin layer. In another aspect, additionally or alternatively, the impact can be reduced by features making the thermal effort required to achieve the laser welded terminal bond lower.

[0017] In addition, separate spacer elements can form predetermined protrusions on the surface of the metal top layer, such as copper foil or copper sheet or copper block, etc.

[0018] According to another embodiment, the method comprises providing a metal spacer element configured to form a protrusion for at least one terminal and coupling the metal spacer element to the metal top layer of the metal substrate structure. The method further comprises coupling the at least one terminal to the metal spacer element by laser welding with a laser beam such that a welded joint is formed between the terminal and the metal spacer element and the at least one terminal and the metal spacer element are firmly joined. The metal spacer element can be provided in the form of a metal block or spring having a thickness of, for example, 0.5 mm up to 2.0 mm. The thickness relates to the dimension in the stacking direction of the metal substrate structure and the at least one terminal and can also represent the height of the protrusion extending above the adjacent top surface of the metal top layer.

[0019] Implementing an additional metal block or spring on the top surface of the metal substrate structure at the location where the terminal leg is joined by laser welding helps to protect the resin layer from heat. The metal block or spring can be joined to the circuitry metallization or the metal top layer by welding, gluing, sintering or any other suitable joining method.

[0020] According to another embodiment of the method, the metal spacer element is provided with a coating layer on its top surface configured to face the bottom surface of the at least one terminal during laser welding. The metal spacer element can be fully or partially coated with a noble metal, such as silver or gold or nickel or other metals, at its top surface for improving the joining process with the terminal. Alternatively or additionally, the metal spacer element can be fully or partially coated with a noble metal at its bottom surface for improving the joining process with the metal top layer.

[0021] According to another embodiment of the method, the at least one terminal comprises a terminal leg configured to be coupled with the metal top layer and comprises a structure prepared for improving laser welding. Such a welding structure can be achieved by a thinned area, a slot, a groove and / or a recess in the terminal leg. Alternatively or additionally, the entire terminal leg can be formed thinner than the body of the terminal. For example, the thickness of the thinned terminal leg can range between 0.3 to 0.8 times the thickness of the terminal body.

[0022] Such a specific terminal structure can beneficially influence the laser welding process and can help to reduce the energy impact of the laser irradiation of the heating power or laser beam on the terminal leg. Thus, one option is to partially or completely reduce the thickness of the terminal leg. The entire terminal leg or at least the welding area of the terminal leg can be made thinner than the adjacent sections, such as the vertical body section of the terminal. Alternatively, the terminal leg can be locally thinner, for example by implementing one or more grooves, recesses and / or slots in the terminal leg.

[0023] The welding process is performed on such thinner sections, so that due to the lower amount of metal to be melted and the reduced lateral heat dissipation, the laser energy required to achieve a laser welded connection can be reduced.

[0024] Implementing holes or slots in the terminal leg can achieve a direct irradiation interface, in particular at the edge of the hole or slot between the substrate metallization formed by the metal top layer and the terminal leg, so that only a small amount of metal has to be melted to achieve a laser welded joint connection. In addition, lateral heat spreading in the terminal leg can be prevented or reduced by the holes, slots or grooves.

[0025] The terminal leg can be welded to the metal top layer or the metal spacer element so that the welded connection comprises multiple small local spots on the terminal leg to reduce the heat impact during laser welding with sufficient cooling pauses between the individual welding spot preparations. Here, the total heat energy can not be reduced, but the heat energy of each spot and the pauses in the process favor a sufficient heat dissipation so that the resin layer temperature rise is smaller. Furthermore, the terminal leg can be specifically designed to beneficially influence the formation of multiple welding locations due to, for example, the preparation of holes, slots and / or grooves for welding.

[0026] According to a further embodiment of the method, the step of providing a metal substrate structure comprises providing a metal top layer, providing a metal bottom layer and providing a dielectric material in the form of a shaped mass. The method further comprises aligning the metal top layer and the metal bottom layer relative to each other with a predetermined distance therebetween and introducing the provided shaped mass between the aligned metal top layer and the metal bottom layer, thereby forming the insulating resin layer by shaping, for example by injection molding, compression molding and / or transfer molding.

[0027] Furthermore, according to an embodiment of the method, the step of coupling at least one terminal to the metal top layer by laser welding can be completed before the metal top layer is coupled to the resin layer and / or the metal bottom layer. Thus, the welded connection of the terminal to the metal top layer can be completed first, and then the metal top layer is coupled to the dielectric resin layer and / or the metal bottom layer. In other words, the coupling of the metal top layer to the resin layer and / or the metal bottom layer is performed after the coupling of the terminal to the metal top layer by welding. Thus, mechanical stresses due to the coupling of the terminal and / or thermal stresses due to the laser welding are far away from the resin layer and help to avoid cracks or other damages of the resin layer.

[0028] By using the described manufacturing or attachment methods, the disadvantages of using a laser welding process can be counteracted. Thus, the risk of creating cracks or damages can be reduced, a stable semiconductor power module can be achieved, and the semiconductor power module can be reliably operated. For example, one or more terminals can be directly welded to the surface of the metal top layer to form a direct copper-to-copper contact. Alternatively, there can be a spacer element located between the bottom surface of the terminals facing each other and the upper or top surface of the metal top layer.

[0029] Finally, it is pointed out that all proposed features and methods can be used individually or in combination of two or more.

[0030] According to an embodiment, a metal substrate structure for a semiconductor power module comprises a metal top layer, a metal bottom layer, and an insulating resin layer arranged between the metal top layer and the metal bottom layer coupled with both the metal top layer and the metal bottom layer. The metal substrate structure further comprises at least one terminal coupled to the metal top layer by laser welding.

[0031] The at least one terminal can comprise an anti-reflection coating on a top surface of a terminal leg configured to face an incident laser beam during laser welding and / or a coating on a bottom surface of the terminal leg configured to face the metal top layer of the metal substrate structure during laser welding.

[0032] According to another embodiment, the metal substrate structure comprises a metal spacer element configured to form a protrusion for the at least one terminal and coupled to the metal top layer. The metal spacer element is further coupled to the at least one terminal by laser welding with a laser beam such that a welded joint is formed between the terminal and the metal spacer element, and the at least one terminal and the metal spacer element are firmly bonded. Such a protrusion can be formed from a separate element on the metal top layer and / or can be formed integral with the metal top layer.

[0033] According to embodiments, a semiconductor power module for a semiconductor device comprises an embodiment of the described metal substrate structure, and the semiconductor power module is electrically interconnected with at least one terminal of the metal substrate structure. The semiconductor power module can further comprise a heat sink coupled with the metal bottom layer of the metal substrate structure to dissipate heat during operation of the semiconductor power module. Thus, the semiconductor power module can comprise a separate heat sink. Alternatively or additionally, the metal bottom layer of the metal substrate structure can itself be used as a heat sink, and can be configured to comprise ribs or protrusions on the bottom side with respect to the stacking direction, for example to provide beneficial heat dissipation. The metal bottom layer can further be used as a substrate of the semiconductor power module. The semiconductor power module comprising the metal substrate structure can further be partially or completely encapsulated by a resin or dielectric gel prepared by molding or potting. The terminals can be used as power terminals or auxiliary terminals, for example for signal wiring.

[0034] Furthermore, the semiconductor power module can comprise two or more embodiments of the above-described metal substrate structure. The electronic device can comprise a chip, an integrated circuit, and / or other discrete devices.

[0035] Since the described metal substrate structure can be manufactured by embodiments of the described methods, and since the described semiconductor power module comprises embodiments of the metal substrate structure, the described features and characteristics with respect to the metal substrate structure and the semiconductor power module are also disclosed with respect to the methods, and vice versa. Thus, the present disclosure comprises several aspects, wherein each feature described with respect to one of the aspects is also disclosed herein with respect to another aspect, even if the respective feature is not explicitly mentioned in the context of a particular aspect.

[0036] The present disclosure relates to laser welding of power terminals and auxiliary terminals on an insulated metal substrate or insulated metal substrate, but also to laser welding on substrate structures based on alternative metal substrate structure technologies, like punched and formed metal substrate structures. For example, the insulated metal substrate comprises a relatively thick metal base or bottom layer made of, for example, aluminum and / or copper. The insulated metal substrate further comprises an insulating sheet based on a resin material forming a resin layer, and a circuit metallization forming a metal top layer made of aluminum and / or copper. The resin material for the insulating sheet is typically a thermosetting resin containing thermally conductive inorganic filler material. The filler material is mainly composed of ceramic particles made of aluminum nitride (AIN), silicon nitride (Si3N4), boron nitride (BN), or aluminum oxide (AI2O3) or silicon oxide (SiO2). The resin insulating layer can have a thickness of 100 pm to 200 pm, and the circuit metallization of the metal top layer can have a thickness of 150 pm to 500 pm.

[0037] The terminals can be made of copper or copper alloys as main terminals and / or auxiliary terminals, and are laser-welded to the circuit metallization of an insulating metal substrate. Due to the laser welding, the top surface of the terminal leads is irradiated by a laser beam, resulting in intense localized heating. The controlled localized melting of the terminal lead material and the substrate surface produces a very reliable connection. Depending on the type and material of the terminals, the terminal leads can have a thickness from 0.5 mm to 2.0 mm. To improve the welding process or for protection (e.g., against oxidation), the top surface of the substrate and / or the terminal leads can be coated with a metal layer, such as a metal layer made of nickel, silver, and / or gold.

[0038] Given that laser welding is used to securely bond terminals to a top metal layer or optional metal spacer element, the heat effect must be considered when welding terminal leads to a circuit-covered metal substrate. However, the laser welding process generates heat effects that can locally melt the terminal leads, and additional measures and / or features can be used to prevent or counteract damage to the resin layer during welding. One or more of the following features can be used to improve the thermal condition during laser welding by improving the protection of the resin layer or reducing the overall heat:

[0039] • A locally thicker substrate with metallization is used at the terminal pin locations to locally and mechanically strengthen the substrate and reduce the thermal impact on the resin sheet.

[0040] • An additional sheet is mounted to the substrate surface at the terminal location to locally and mechanically reinforce the substrate and reduce the thermal impact on the resin sheet.

[0041] • One or more coatings on the terminals and / or substrate, such as those with noble metals or other metals like nickel, to prevent oxidation and achieve more efficient bonding.

[0042] • The terminals have an anti-reflective coating to prevent laser reflection and enable more efficient soldering with reduced power.

[0043] • Thin terminal leads (full or partial) are used to achieve more efficient soldering with reduced power, resulting in less material needing to be melted.

[0044] • The slots or holes located on the terminal leads are welded at their edges to concentrate the temperature locally (avoiding lateral diffusion).

[0045] • The gap between the terminal lead and the substrate surface during the soldering process

[0046] • Multiple local laser welding connections.

[0047] These options can be used individually, or two or more of them can be combined.

[0048] For example, the proposed process of laser welding of terminal pins to an insulated metal substrate has great potential in significantly reducing mechanical impact on the resin insulation sheet compared to ultrasonic welding. In addition, the heat impact of the laser welding process can be reduced by applying one or more of the proposed features. A successful welding process can be achieved without damaging the thermally and pressure sensitive resin layer, making the use of this cost-efficient substrate technology interesting. Such an attachment or manufacturing method for metal substrate structures is interesting for high power modules and even higher voltage classes of modules. When replacing the ceramic substrate under the traditional standard setup with an insulated metal substrate welded to the base plate, the costs can be significantly reduced. On the one hand the material costs can be reduced, on the other hand several process steps are removed from the process flow, such as the bonding process between the substrate and the base plate in a power module assembly. However, the described method also allows for the manufacturing of metal substrate structures and semiconductor power modules that can be applied to a wide variety of products, especially low voltage industrial and automotive products. BRIEF DESCRIPTION OF DRAWINGS

[0049] The exemplary embodiments are explained hereinafter with the help of schematic drawings and reference numerals. The drawings show:

[0050] Figure 1 is a side view of an embodiment of a method for attaching a terminal to a metal substrate structure of a semiconductor power module;

[0051] Figure 2 is a side view of another embodiment of a method for attaching a terminal to a metal substrate structure of a semiconductor power module using a wafer;

[0052] Figures 3-4 are side views of embodiments of a terminal for attachment to a metal substrate structure, respectively;

[0053] Figures 5-8 are top views of embodiments of a terminal pin of a terminal, respectively;

[0054] Figure 9 is a flow chart of a method for attaching an embodiment of a terminal to a metal substrate structure.

[0055] The drawings provide further understanding. It is to be understood that the embodiments shown in the drawings are schematic representations and are not necessarily drawn to scale. Identical reference numerals indicate elements or components with the same function. Descriptions thereof are not repeated for each subsequent drawing as long as the function of the elements or components corresponds to each other in different drawings. For the sake of clarity, elements can not present corresponding reference numerals in all drawings. DETAILED DESCRIPTION

[0056] Figure 1A side view of an embodiment of method steps for attaching a terminal 4 to a metal substrate structure 3 of a semiconductor power module 10 for a semiconductor device is shown. The semiconductor power module 10 comprises a metal substrate structure 3 having a metal top layer 17, a metal bottom layer 19 and an insulating resin layer 18 arranged between the metal top layer 17 and the metal bottom layer 19. The electronic device can comprise, for example, a chip and a power semiconductor device.

[0057] The semiconductor power module 10 further comprises a heat sink 1 having a rib structure which is coupled with the metal substrate structure 3 by a bonding layer 2 and / or a thermal interface material layer. With regard to the shown stacking direction A, the terminal 4 will be coupled to the metal top layer 17 and below, the heat sink 1 is coupled with the metal bottom layer 19 via the bonding layer 2.

[0058] In this regard, terms like "above", "below", "top", "upper" and "bottom" refer to the orientation or direction with regard to the stacking direction A as shown in the drawings. Thus, the height or thickness of the described elements is related to the stacking direction A, while the lateral directions B and C are oriented perpendicular to the stacking direction A (see Figures 1-8 ).

[0059] The thickness of the insulating resin layer 18 can be, for example, between 100 pm and 200 pm. The thickness of the circuit metallization formed by the metal top layer 17 can be between 150 pm and 500 pm. The thickness of the metal bottom layer 19 of the substrate can be between 2 mm and 3 mm and can also be configured to dissipate heat from the metal substrate structure 3 and the semiconductor power module 10. The resin layer 18 can comprise an epoxy resin material, but can also comprise other types of resin, like thermoset or thermoplastic resin. The resin layer 18 can be formed as a resin sheet or prepreg sheet assembled or laminated between the two metal layers 17, 19. Alternatively or additionally, the metal substrate structure 3 comprises a resin layer 18 formed by molding, for example by injection molding, transfer molding or compression molding. The resin of the resin layer can contain inorganic fillers, ceramic materials, for example AIN, Si3N4, BN, AI2O3 or SiO2. The metal bottom layer 19 can be made of or comprise copper and / or aluminum and / or corresponding alloys. The circuit metallization formed by the metal top layer 17 can be made of or comprise copper and / or aluminum and / or corresponding alloys. Furthermore, the metal top layer 17 can be partially or completely coated and the corresponding circuit metallization coating can be made of or comprise nickel and / or gold and / or silver and / or other metals.

[0060] The steps of the method for attaching the terminal 4 to the metal substrate structure 3 can follow as Figure 9the flowchart shown. Thus, according to Figure 1 In the embodiment shown, in step S1 at least one terminal 4 is provided. The terminal 4 is provided comprising an anti-reflection coating 5 on its top surface 41.

[0061] In step S2 a metal substrate structure 3 is provided having a metal top layer 17, a metal bottom layer 19 and an insulating resin layer 18 arranged therebetween.

[0062] In optional step S3 an additional metal spacer element 7 can be provided to form a protrusion for the terminal 4 on the top surface 171 of the metal top layer 17 (see Figure 2 ). The spacer element 7 is joined to the top metallization at the terminal position.

[0063] In another step S4 the terminal 4 is coupled to the metal top layer 17 of the metal substrate structure 3 by laser welding with a laser beam 6 such that a weld joint 16 is formed between the terminal 4 and the metal top layer 17 and the terminal 4 and the metal top layer 17 are firmly joined. The anti-reflection coating 5 partially or completely covers the top surface 41 of the terminal 4 facing the incoming laser beam 6 improving the laser welding process.

[0064] With respect to the side view as shown in Figure 3 and Figure 4 The terminal 4 can be provided comprising an L-shape. Thus, the terminal 4 comprises a terminal body 13 and a terminal leg 12 made of one piece or separate pieces. The terminal leg 12 is configured to be coupled with the metal top layer 17 and can be provided comprising a structure ready for laser welding having one or more of a thinned area (see Figure 3 ) and / or a slot, a groove 20 and / or a recess 15 (see Figures 4-8 ). Such a structure can be a real opening or only a recess and / or a thinned portion.

[0065] Such a modification of the terminal leg 12 can contribute to improve the laser welding process and the attachment of the terminal to the metal substrate structure 3. Furthermore, thermal stress affecting the resin layer 18 is reduced. The terminal leg 12 can have a fully reduced thickness or comprise a welding area having a reduced thickness smaller than the thickness of the vertical terminal body 13 of the terminal 4. Alternatively or additionally, one or more grooves 20 or other local recesses 15 can beneficially influence the laser welding process performed on the bottom of such recessed openings (see Figures 4-8 ). This also applies to the implementation of holes or slots, the laser welding can be performed on the edge of such holes or slots 20, for example directly at the interface between the terminal leg 12 and the metallization. The laser welding process can also be performed on multiple small local spots on the terminal leg 12 as Figure 5 and Figure 6The same can also apply to the thinned terminal leg 12, thereby forming a plurality of local solder spots.

[0066] The terminal 4 can be made of or comprise copper and / or a copper alloy and can implement a main terminal or an auxiliary terminal for electrically connecting to an electronic device of the semiconductor power module 10. With respect to the stacking direction A, the terminal leg 12 can comprise a thickness of 1 mm, 1.5 mm or 2 mm. The terminal leg 12 can be partially or completely thinned to comprise a thickness of 0.5 mm or less. Thus, the terminal leg 12 can comprise a thickness of between 0.5 mm and 2 mm. If a local thinned portion is present, this local thinned portion can have a thickness of at least 0.25 mm. Furthermore, the terminal 4 can comprise a terminal coating layer 9 which partially or completely covers the bottom surface 42 of the terminal leg 12. The terminal coating layer 9 can beneficially influence the laser soldering process and can be made of or comprise nickel, gold, silver and / or other metals. Such a coating can also be used in combination with the additional metal spacer element 7 (see Figure 2 ) for attaching the terminal 4.

[0067] If such an additional spacer is provided, the method for attaching the terminal 4 comprises coupling the metal spacer element 7 to the metal top layer 17 of the metal substrate structure 3 and coupling the terminal 4 to the metal spacer element 7 by laser soldering with the laser beam 6 such that a solder joint 16 is formed between the terminal 4 and the metal spacer element 7 and the terminal 4 and the metal spacer element 7 are firmly joined.

[0068] The metal spacer element 7 is arranged between the circuit metallization of the metal top layer 17 and the terminal 4, for example in the form of a metal block or a spring structure, such that the laser soldering process can also be improved and the resin layer 18 is protected. The metal spacer element 7 can have a thickness of 0.5 mm up to 2.0 mm. The metal spacer element 7 can be manufactured, for example, via a punching tool. As an alternative or in addition to the separate metal spacer element 7, the circuit metallization of the metal top layer 17 itself can comprise a locally enhanced thickness which is intentionally formed to have a height of not more than 2.0 mm with respect to the stacking direction A and the adjacent areas of the metal top layer 17. Such a protrusion is formed at the location of the metal top layer 17 where the terminal 4 is attached.

[0069] The metal spacer element 7 can be made of or comprise copper and / or a copper alloy. A spacer coating layer 8 can be arranged on the upper or top surface 71 of the metal spacer element 7 which partially or completely covers the top surface 71. Alternatively or in addition, there can be a coating on the bottom surface of the spacer element 7.

[0070] The spacer coating can be made of or include nickel, gold, silver and / or other metals. The metal spacer element 7 can be connected to the top surface 171 of the metal top layer 17 by welding, sintering, gluing and / or other applicable joining methods.

[0071] Furthermore, the laser welding process can be configured to provide specific parameters to beneficially influence the formation of the one or more welded joints 16. Thus, the laser power of the laser beam 6 can be between 300 W and 3000 W. The speed of the laser spot of the laser beam 6 on the top surface 41 of the terminal 4 can be between 1 mm / s and 200 mm / s. The oscillation frequency for providing the oscillating laser spot can be 2 kHz or less. Such an oscillation can present an oscillation of the irradiation spot position to prevent too strong local heating and can occur in addition to the above-described laser movement.

[0072] Furthermore, the provision for attaching the terminal 4 to the metal substrate structure 3 can be configured to prepare a direct contact between the terminal 4 and the metal top layer 17 or the metal spacer element 7. Alternatively, in terms of the stacking direction, the joining between the above-mentioned joining partners is set with a predetermined gap of no more than 500 pm. This predetermined gap can enable a further beneficial configuration to improve the positioning of the terminal 4 and to protect the insulated metal substrate structure 3 from heat. The laser welding joining connection is provided by the dripping and / or deformation of the molten material of the terminal leg 12, which is held in place.

[0073] The described embodiments of the method for attaching a terminal and / or for manufacturing a metal substrate structure 3 with one or more attached terminals 4 can reduce the risk of forming cracks or damages in the resin layer. Thus, due to this method, a stable semiconductor power module 10 can be achieved, which can reliably work even in high voltage power module applications in the voltage range of, for example, 0.5 kV up to 10.0 kV.

[0074] The described Figures 1-9 The illustrated embodiments represent exemplary embodiments of improved metal substrate structures 3, semiconductor power modules 10 and methods of manufacturing thereof; thus, they do not constitute a complete list of all embodiments. For example, the actual arrangements and methods can differ from the illustrated embodiments in terms of the metal substrate structure 3 and the semiconductor power module 10.

[0075] Reference signs

[0076] 1 heat sink

[0077] 2 bonding layer

[0078] 3 metal substrate structure

[0079] 4 terminal

[0080] 41 top surface of the terminal

[0081] 42 bottom surface of the terminal

[0082] 5 anti-reflection coating

[0083] 6 laser beam

[0084] 7 metal spacer element

[0085] 71 top surface of the metal spacer element

[0086] 8 spacer coating

[0087] 9 terminal coating

[0088] 10 semiconductor power module

[0089] 11 bonding layer

[0090] 12 terminal leg

[0091] 13 terminal body

[0092] 14 leg structure

[0093] 15 recess

[0094] 16 solder joint

[0095] 17 metal top layer

[0096] 171 top surface of the metal top layer

[0097] 18 resin layer

[0098] 19 metal bottom layer

[0099] 20 slot / groove

[0100] A stacking direction

[0101] B lateral direction

[0102] C lateral direction

[0103] S (i) step of a method for manufacturing a metal substrate structure for a semiconductor power module

Claims

1. A method for attaching a terminal (4) to a metal substrate structure (3) for a semiconductor power module (10), comprising: - Provide at least one terminal (4). - A metal substrate structure (3) is provided, the metal substrate structure having a metal top layer (17), a metal bottom layer (19), and an insulating resin layer (18) disposed between the metal top layer (17) and the metal bottom layer (19), wherein the metal top layer (17) is made of a single piece having at least one protrusion having a given local reinforcement thickness, the given local reinforcement thickness being 0.5 mm to 2.0 mm thicker than the adjacent region of the metal top layer (17) and formed on the top surface (171) of the metal top layer (17) at a location configured to be coupled to the at least one terminal (4), and - The at least one terminal (4) is connected to the protrusion of the metal top layer (17) of the metal substrate structure (3) by laser welding using a laser beam (6).

2. The method according to claim 1, wherein, At least one of the metal substrate structure (3) and the at least one terminal (4) is provided with a structure prepared for laser welding, the structure having at least one of a thinned region, slot, groove (20), hole, coating layer (5, 8, 9), opening and recess (15), such that the process of connecting the at least one terminal (4) to the metal top layer (17) of the metal substrate structure (3) by laser welding is controlled to form at least one weld joint (16) and to minimize the thermal impact on the insulating resin layer (18).

3. The method according to claim 1 or 2, wherein, The step of providing at least one terminal (4) includes: The at least one terminal (4) is provided, the at least one terminal having at least one of the following: an anti-reflective coating (5) located on a top surface (41) configured to face the incident laser beam (6) during laser welding; and a coating (9) located on a bottom surface (42) configured to face the metal top layer (17) of the metal substrate structure (3) during laser welding.

4. The method according to claim 1 or 2, wherein, The step of connecting at least one terminal (4) to the metal substrate structure (3) by laser welding includes: - Align the terminal (4) and the metal substrate structure (3) relative to each other such that the top surface (171) of the metal top layer (17) and the bottom surface (42) of the terminal (4) are facing each other in contact, and - The terminal (4) is laser welded using the laser beam (6) to form a weld joint (16) between the terminal (4) and the metal substrate structure (3), and the at least one terminal (4) and the metal top layer (17) are firmly bonded together.

5. The method according to claim 1 or 2, wherein, The step of connecting at least one terminal (4) to the metal substrate structure (3) by laser welding includes: - The terminal (4) and the metal substrate structure (3) are aligned relative to each other and have a predetermined distance between them, and a gap of no more than 500 μm is defined between the top surface (171) of the metal top layer (17) facing each other and the bottom surface (42) of the terminal (4), and - The terminal (4) is laser welded using the laser beam, causing the terminal (4) to partially melt, and a weld joint (16) is formed between the terminal (4) and the metal substrate structure (3) by the dripping, flowing or deforming of the molten terminal material, and the at least one terminal (4) and the metal top layer (17) are firmly bonded together.

6. The method according to claim 1 or 2, comprising: - Provide a metal spacer element (7) configured to form a protrusion for the at least one terminal (4), - Connect the metal spacer element (7) to the metal top layer (17) of the metal substrate structure (3), and - The at least one terminal (4) is connected to the metal spacer element (7) by laser welding using a laser beam (6), such that a weld joint (16) is formed between the terminal (4) and the metal spacer element (7), and the at least one terminal (4) and the metal spacer element (7) are firmly bonded together.

7. The method according to claim 6, wherein, The step of providing the metal spacer element (7) includes: The metal spacer element (7) is provided having: a coating layer (8) on a top surface (71) of a bottom surface (42) configured to face the at least one terminal (4) during laser welding; and / or a coating layer on a bottom surface configured to face the top surface (171) of the metal top layer (17) during laser welding.

8. The method according to claim 6, wherein, The metal spacer element (7) is provided in the form of either a block or a spring, and has a thickness of 0.5 mm to 2.0 mm with respect to the stacking direction (A) of the metal substrate structure (3) and the at least one terminal (4).

9. The method according to claim 6, wherein, The metal spacer element (7) is connected to the metal top layer (17) by at least one of welding, sintering and gluing.

10. The method according to claim 6, wherein, The step of providing at least one terminal (4) includes: The at least one terminal (4) is provided, the at least one terminal having a terminal foot (12) configured to be connected to the metal top layer (17), wherein the terminal foot (12) includes a structure prepared for laser welding, the structure having at least one of a thinning region, a slot, a groove (20), a hole, an opening, and a recess (15).

11. The method according to claim 10, wherein, The laser welding is performed in the thinning region and / or in the groove (20) and / or in the recess (15) and / or on the edge of the hole and / or on the edge of the slot.

12. A semiconductor power module (10), comprising: - A metal substrate structure (3) having a metal top layer (17), a metal bottom layer (19), and an insulating resin layer (18) connecting the metal top layer (17) and the metal bottom layer (19) to the metal top layer and the metal bottom layer, wherein the metal top layer (17) is made of an integral piece having at least one protrusion, the at least one protrusion having a given local reinforcement thickness, the given local reinforcement thickness being 0.5 mm to 2.0 mm thicker than the adjacent area of ​​the metal top layer (17) and formed at a certain position on the top surface (171) of the metal top layer (17), and - At least one terminal (4), which is connected to a protrusion of the metal top layer (17) by laser welding.

13. The semiconductor power module (10) according to claim 12, wherein, The at least one terminal (4) includes at least one of the following: an anti-reflective coating (5) located on a top surface (41) configured to face the incident laser beam (6) during laser welding; and a coating (9) located on a bottom surface (42) configured to face the metal top layer (17) of the metal substrate structure (3) during laser welding.

14. The semiconductor power module (10) according to claim 12 or 13, comprising: A metal spacer element (7) is configured to form a protrusion for the at least one terminal (4), be coupled to the metal top layer (17), and be coupled to the at least one terminal (4) by laser welding using a laser beam (6), such that a welded joint (16) is formed between the terminal (4) and the metal spacer element (7), and the at least one terminal (4) and the metal spacer element (7) are firmly bonded together.

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