Direct bonded copper substrate manufactured using silver sintering

Abstract

The invention is entitled "Direct Bond Copper Substrate Made Using Silver Sintering." The invention discloses a direct bond copper (DBC) substrate comprising: a ceramic sheet; a first leadframe disposed on a first side of the ceramic sheet; a second leadframe disposed on a second side of the ceramic sheet; and a sintered joint between the first leadframe and the ceramic sheet. The ceramic sheet is at least one of an aluminum oxide sheet, an aluminum nitride sheet, a silicon nitride sheet, or a boron nitride sheet. A surface of the ceramic sheet is metallized, and the first leadframe is disposed on the metallized surface of the ceramic sheet. The first leadframe is a conductive metal trace, and the second leadframe is one of a conductive metal trace, a solid metal sheet, a metal foil, or a conductive sheet made of boron nitride, graphite, or carbon.

Description

[0001] Related applications

[0002] This application claims priority and benefit to U.S. Patent Application No. 16 / 744,378, filed January 16, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This specification relates to direct-bonding copper substrates for packaging power devices. Background Technology

[0004] Advanced silicon technology can be used to manufacture modern high-power devices (e.g., silicon power devices such as insulated-gate bipolar transistors (IGBTs), fast recovery diodes (FRDs), etc.) to meet high power requirements. The role of the substrate in power electronics is to provide interconnections between devices to form circuits (like printed circuit boards) and to cool components. High-power devices (e.g., IGBTs, FRDs, etc.) can be packaged in single-sided cooled (SSC) or dual-sided cooled (DSC) power modules. Direct-bonded copper (DBC) substrates are electronic circuit boards on which power devices are mounted in SSC and DSC power modules. DBC substrates are commonly used due to their excellent thermal conductivity, which aids in heat dissipation. DBC substrates consist of a ceramic tile (e.g., alumina) and copper sheets bonded to one or both sides of the substrate via a high-temperature cladding process. With the increasing demands for power module performance, the integrity and reliability of the DBC substrate itself have become crucial. Internal defects (ceramic-copper interface voids, cracks, etc.) that are common in traditional DBC manufacturing processes may now be unacceptable for the good performance of power modules. Summary of the Invention

[0005] A direct-bonded copper (DBC) substrate includes: a ceramic sheet; a first lead frame disposed on a first side of the ceramic sheet; a second lead frame disposed on a second side of the ceramic sheet; and a sintered bonding portion located between the first lead frame and the ceramic sheet.

[0006] In a general aspect, one method includes: applying a sintered precursor material layer to each of a first surface and a second surface of a ceramic sheet; and assembling a precursor assembly for a direct-bonded copper (DBC) substrate by coupling a first lead frame to the sintered precursor material layer on the first surface of the ceramic sheet and a second lead frame to the second surface of the sintered precursor material layer on the second surface of the ceramic sheet, such that the ceramic sheet is disposed between the first lead frame and the second lead frame. The method further includes sintering the first lead frame and the second lead frame to the ceramic sheet to form a sintered-bonded DBC substrate.

[0007] In one aspect, sintering a first lead frame and a second lead frame to a ceramic sheet to form a sintered DBC substrate includes applying a sintering heat treatment to the precursor assembly at a temperature of less than 500°C and a pressure of less than 100 MPa.

[0008] On the other hand, applying the sintering precursor material layer includes metallizing a first surface of the ceramic sheet and applying the sintering precursor material layer to the metallized first surface of the ceramic sheet.

[0009] Details of one or more embodiments are set forth in the accompanying drawings and the following description. Other features will be apparent from the specification and drawings, as well as from the claims. Attached Figure Description

[0010] Figure 1A This is an illustration of a cross-sectional view of an exemplary DBC substrate manufactured using a low-temperature sintering process.

[0011] Figure 1B yes Figure 1A An illustration of a perspective view of a single component of the DBC substrate.

[0012] Figure 2 This is a flowchart illustrating an exemplary method for manufacturing a DBC substrate.

[0013] Figure 3 It is possible Figure 2 An illustration of an exemplary precursor component of a DBC substrate assembled by the method.

[0014] Figure 4 This is an illustration of an exemplary heated pressing fixture for heat and pressure treatment of a precursor assembly for a DBC substrate.

[0015] Figure 5 This is an illustration of an exemplary precursor component of a DBC substrate. Detailed Implementation

[0016] This document discloses direct-bonded copper (DBC) substrates and methods for manufacturing DBC substrates. DBC substrates are intended for use in electronic circuits involving, for example, high-power devices (e.g., silicon power devices such as insulated-gate bipolar transistors (IGBTs), fast recovery diodes (FRDs), etc.). High-power devices can be attached to the DBC substrate and packaged in, for example, single-sided cooled (SSC) or dual-sided cooled (DSC) power modules. The DBC substrate may include a lead frame, i.e., a thin metal frame, which is typically bonded to a ceramic substrate (e.g., an alumina sheet) using a high-temperature bonding process (e.g., copper cladding at temperatures greater than 1000°C).

[0017] The method for manufacturing the DBC substrate described herein involves at least using a bonding process (e.g., sintering) to sinter a combination of leadframes, sintered material layers, and ceramic sheets at low temperatures to avoid defects (e.g., ceramic-copper interface voids, cracks, etc.) that can be caused by direct high-temperature bonding of the leadframes to the ceramic sheets (e.g., copper cladding at temperatures greater than 1000°C).

[0018] According to the principles of this disclosure, in an exemplary DBC substrate, the lead frame is sintered and bonded to a ceramic sheet (e.g., alumina (Al2O3), aluminum nitride (AlN), boron nitride (BN), silicon nitride (SN), etc.) via a low-temperature sintering process through a sintering material layer (e.g., an Ag material layer). The low-temperature sintering process may, for example, involve a sintering temperature of less than about several hundred degrees Celsius (e.g., 500°C).

[0019] Figure 1A A cross-sectional view shows an exemplary DBC substrate manufactured using a low-temperature sintering process. The DBC substrate 100 includes a ceramic sheet 110, a first lead frame 120, and a second lead frame 130. The ceramic sheet 110 may be made of a thermally conductive and electrically insulating material (e.g., Al₂O₃, AlN, BN, SN, etc.). The first lead frame 120 and the second lead frame 130 may be made of a conductive metal or metallic material (e.g., copper). The first lead frame 120 is sintered to a first side 111 of the ceramic sheet via, for example, a sintering bond 142. The second lead frame 130 is sintered to a second side 112 of the ceramic sheet via, for example, a sintering bond 152. Sintered joints 142 and 152 may be made of sintered material (e.g., gold (Au), silver (Ag), copper (Cu) or any mixture thereof) that can bond lead frames 120 and 130 to the ceramic sheet by a sintering process at a temperature (e.g., 500°C or lower) lower than that involved in conventional copper cladding processes manufactured by DBC.

[0020] In an exemplary embodiment, the ceramic sheet 110 may be metallized, i.e., have a surface covered with an intermediate metal or metal layer (e.g., layer 114) that facilitates bonding of the ceramic sheet 110 to sintered materials (e.g., sintered joints 142 and sintered joints 152) disposed on the surface of the ceramic sheet 110. In an exemplary embodiment, the intermediate metal or metal layer may be made of an alloy (e.g., a titanium-nickel-silver (TiNiAg) alloy).

[0021] In an exemplary embodiment, the ceramic sheet 110 may not be metallized, that is, it may not be covered by an intermediate metal or metal layer (e.g., layer 114), and the sintering material may be directly disposed on the surface of the ceramic sheet 110 to form a sintered joint (e.g., sintered joint 142 and sintered joint 152) between the ceramic sheet 110 and the lead frame (e.g., first lead frame 120 and second lead frame 130).

[0022] Figure 1B For example, a perspective view shows individual components of the DBC substrate 100 during manufacturing (e.g., ceramic sheet 110, lead frame 120, and lead frame 130). The first lead frame 120 may be a patterned conductive metal or metal sheet (e.g., a trace), to which one or more power semiconductor devices (not shown) may be attached (e.g., using solder or conductive epoxy) in a device package (e.g., an SSC or DSC power module). In an exemplary embodiment, the lead frame 120 may be patterned (e.g., trace 122) to provide interconnections with one or more attached power semiconductor devices and interconnections between one or more attached power semiconductor devices. A thin metal or metal layer 114 (e.g., TiNiAg) is applied to a first side 111 of the ceramic sheet 110 to facilitate sintering between the ceramic sheet 110 and the lead frame 120. When the lead frame 120 is placed on the ceramic sheet 110, the thin metal or metal layer 114 may have a pattern matching the pattern of the trace 122.

[0023] In an exemplary embodiment, leadframe 130 may be, for example, metal or a metal plate (e.g., a copper plate). Leadframe 130 may be solid metal or a metal plate, or, like leadframe 120, may be a patterned plate (i.e., a trace).

[0024] In an exemplary embodiment, lead frame 120 may be, for example, a copper trace, and lead frame 130 may be a metal foil (e.g., copper foil).

[0025] In an exemplary embodiment, lead frame 120 may be, for example, a copper trace, and lead frame 130 may be a conductive sheet made of graphite or carbon.

[0026] In an exemplary embodiment, lead frame 120 may be, for example, a copper trace, and lead frame 130 may be a conductive sheet made of a thermally conductive material (e.g., a thermally conductive material such as ultrapure BN).

[0027] In an exemplary embodiment, the thickness T1 of the lead frame 120 may be, for example, between about 0.05 mm and about 3.0 mm, and a similar thickness T2 of the lead frame 130 may be, for example, between about 0.05 mm and about 3.0 mm.

[0028] In an exemplary embodiment, lead frame 120 and lead frame 130 may have different thicknesses. For example, the thickness T1 of lead frame 120 may be between about 0.05 mm and about 3.0 mm, and the different thickness T2 of lead frame 130 may be between about 0.1 mm and about 5.0 mm.

[0029] Figure 2 An exemplary method 200 for manufacturing a DBC substrate (e.g., DBC substrate 100) using a low-temperature sintering process, according to the principles of this disclosure, is shown. The low-temperature sintering process may involve sintering at a temperature less than about 500°C.

[0030] The DBC substrate component may include a ceramic sheet, a first lead frame, and a second lead frame. The ceramic sheet may be made of a thermally conductive and electrically insulating material such as alumina (Al₂O₃), BN, SN, or AlN. The first lead frame may, for example, be a copper sheet with a trace pattern. The trace pattern may be formed, for example, from a solid metal sheet (e.g., a copper sheet) by imprinting, micromachining, precision stamping, or cutting (e.g., laser cutting, photo-etching). The second lead frame may, for example, be a solid metal sheet (e.g., a copper sheet). In some embodiments, the second lead frame may also be a copper sheet with a trace pattern.

[0031] Method 200 may include metallizing one or more surfaces of a ceramic sheet (e.g., the top surface on one side and the second side of the ceramic sheet) (210), and applying a sintering precursor material layer to each of a first surface and a second surface of the ceramic sheet (220). In an exemplary embodiment, the first and second surfaces may be metallized surfaces of the ceramic sheet. In another embodiment, the first and second surfaces may be unmetallized surfaces of the ceramic sheet. Whether the first and second surfaces of the ceramic sheet should be metallized may depend on the nature of the sintering precursor material layer used at 220 in method 200.

[0032] The sintering precursor material may, for example, comprise any type of metal or metal particles that can be bonded to the lead frame and ceramic sheet (e.g., ceramic sheet 110). The sintering precursor material may, for example, be an Ag-based sintering material for forming Ag sintered joints. The sintering precursor material may, for example, be a Cu-based sintering material for forming Cu sintered joints.

[0033] In an exemplary embodiment of method 200, the metallized surface 210 may include depositing (e.g., sputtering, evaporation, electroless plating, electroplating, etc.) an intermediate metal or metal alloy layer (e.g., TiNiAg) on ​​the surface of the ceramic sheet. The intermediate metal or metal alloy (e.g., TiNiAg) may facilitate the sintering bonding of the ceramic sheet with the sintering precursor material.

[0034] The layer to which the sintering precursor material 220 is applied may include the application of the sintering precursor material (e.g., Au particles, Ag particles, Cu particles) using wet-state application techniques or dry-state application techniques. Wet-state application techniques may include, for example, screen printing or stencil printing, squeegee coating, spraying, dipping, and fine needle dispensing techniques.

[0035] When employing a wetted state application technique, the sintering precursor material may be, for example, a suspension of metal particles in a solvent and / or surfactant, which is advantageous for wetted state applications. In an exemplary embodiment, the wetted state coating precursor material may comprise metal particles (e.g., Au particles, Ag particles, or Cu particles, or mixtures thereof) combined with a binder (e.g., epoxy resin), dispersant, and diluent or liquid carrier.

[0036] Dry-state application techniques may involve film transfer processes to apply sintered precursor materials as dry films to the surface of suitable ceramic sheets. The dry film can be prepared, for example, by initially depositing (e.g., screen printing or otherwise dispensing) a wetted sintered precursor material onto a temporary substrate or support such as a polymer (e.g., polyethylene terephthalate) tape backing. The sintered precursor material can be applied to the temporary substrate or support in a wetted, flowable state and then heated or otherwise dried to produce a dry film transferable to the appropriate surface of the ceramic sheet.

[0037] Method 200 may further include: assembling a precursor assembly (230) of a DBC substrate by coupling a first lead frame to a sintering precursor material layer applied to a first surface of a ceramic sheet and coupling a second lead frame to a sintering precursor material layer applied to a second surface of a ceramic sheet, such that the ceramic sheet is disposed between the first lead frame and the second lead frame; and sintering the first lead frame and the second lead frame to the ceramic sheet to obtain a sintered bonded DBC substrate (240).

[0038] Figure 3 An exemplary precursor assembly 300 is shown that can be assembled (at stage 240) via method 200. The precursor assembly 300 may include a ceramic sheet, one or more lead frames, and a combination of one or more sintered material layers that can be sintered together at low temperatures using a bonding process (e.g., sintering). For example, the precursor assembly 300 may include a ceramic sheet 110 sandwiched between a first lead frame 120 and a second lead frame 130. In the precursor assembly 300, one or more surfaces of the ceramic sheet 110 may be metallized, for example, by an intermediate metal or metal alloy (e.g., TiNiAg) coating 114. Additionally, a sintered precursor material layer 143 may be interposed between the first lead frame 120 and the ceramic sheet 110, and a sintered precursor material layer 153 may be interposed between the second lead frame 130 and the ceramic sheet 110.

[0039] In method 200, sintering a first lead frame and a second lead frame to a ceramic sheet to obtain a sintered bonded DBC substrate 250 may include applying pressure and heat to a precursor assembly 300, such as a precursor assembly in a heated pressing fixture.

[0040] Figure 4 An exemplary heated pressing jig 400 is shown, which can be used for the heat and pressure treatment of a precursor assembly 300 to sinter a first lead frame and a second lead frame to a ceramic sheet. The heated pressing jig 400 may include a movable press 420 and a heated pressure chamber 410 for holding the precursor assembly 300, the movable press applying pressure (e.g., as shown in the image). Figure 4 (As indicated by arrow 42) is applied to the precursor assembly 300 held in the pressure chamber.

[0041] In an exemplary embodiment, the ceramic sheet 110 in the precursor assembly 300 may be coated with a TiNiAg coating 114. Additionally, the sintering precursor material layers 143 and 153 may be Ag-based sintering materials. The heat and pressure treatment of the precursor assembly 300 in the heated pressing jig 400 during a low-temperature sintering process can cause Ag particles to diffuse or mix between the TiNiAg coating 114 and the sintering precursor material layers (e.g., sintering precursor material layers 143 and 153) to form sintered joints 142 and 152 (located between the ceramic sheet 110 and the lead frames 120 and 130, respectively). Figure 4 In the image, for visual illustrative purposes, the interdiffusion or mixing of Ag particles between the TiNiAg coating and the sintering precursor material layer is demonstrated by the TiNiAg coating 114 and the sintering precursor material layer (e.g., ...). Figure 3 The dashed boundary line 160 between the sintering precursor material layer 143 and the sintering precursor material layer 153 is shown.

[0042] In an exemplary embodiment, the precursor component 300 can undergo Ag sintering thermal and pressure treatment using a sintering temperature between about 200°C and 300°C, and a pressure between about 10 MPa and about 25 MPa.

[0043] In an exemplary embodiment where the sintering precursor material is a Cu-based sintering material, the heat and pressure treatment of the precursor assembly 300 for Cu sintering can be performed using a sintering temperature between about 200°C and about 500°C, and a pressure between about 10 MPa and about 50 MPa. In an exemplary embodiment, the pressure used for Cu sintering may depend on the thickness of the Cu-based sintering material (e.g., layers 143 and 153) in the precursor assembly 300. Thicker Cu-based sintering material layers may require sintering at higher pressures than thinner Cu-based sintering material layers.

[0044] In an exemplary embodiment where the sintering precursor material is a sintering material based on an Ag and Cu mixture, the heat and pressure treatment for sintering the precursor assembly 300 for the Ag and Cu mixture can be performed using a sintering temperature between about 200°C and 500°C, and a pressure between about 5 MPa and about 100 MPa. The pressure used for sintering the Ag and Cu mixture can depend on the thickness of the Ag and Cu mixture sintering precursor material (e.g., layers 143 and 153) in the precursor assembly 300. Thicker precursor material layers may require sintering at higher pressures than thinner precursor material layers.

[0045] In an exemplary embodiment, the sintering precursor material (e.g., layers 143 and 153) in the precursor assembly 300 may be a pressureless sintering material. In such embodiments, the heat and pressure treatment of the precursor assembly 300 may be performed at a pressureless temperature (or at a low pressure, for example, to hold the part in place in the fixture 400) for the pressureless sintering material.

[0046] The low-temperature sintering process of method 200 enables the fabrication of large DBC substrates (e.g., larger than four inches on one side) with minimal or no warping of the DBC components. Exemplary DBC substrates bonded by low-temperature sintering using method 200 may have rectangular panel sizes ranging from about 5” x 7” to about 14” x 14”.

[0047] In an exemplary embodiment, the sintering precursor material (e.g., ...) used for sintering the lead frame to the ceramic sheet Figure 3 One or more of the sintering precursor material layer 143 and sintering precursor material layer 153 may be replaced by a low-temperature bonding material (e.g., lead / lead-free solder, transition liquid phase solder, etc.).

[0048] In an exemplary embodiment, one or more semiconductor device dies may be attached to the leadframe of the DBC substrate prior to low-temperature sintering bonding of the leadframe to the ceramic wafer. The semiconductor device dies (e.g., IGBTs, FRDs, etc.) may be attached using, for example, solder or conductive adhesive or epoxy resin (e.g., attached to leadframe 120).

[0049] Figure 5 A DBC precursor assembly 500 is shown, which can be assembled with a semiconductor device die 510 (e.g., IGBT) and a semiconductor device die 520 (e.g., FRD) attached to a lead frame 120 via method 200 (at stage 240). The precursor assembly 500 may include a ceramic sheet 110 sandwiched between a first lead frame 120 and a second lead frame 130.

[0050] In precursor assembly 500, as in precursor assembly 300, one or more surfaces of ceramic sheet 110 may be metallized, for example, by an intermediate metal or metal alloy (e.g., TiNiAg) coating 114. Additionally, a sintered precursor material layer 143 may be interposed between the first lead frame 120 and the ceramic sheet 110, and a sintered precursor material layer 153 may be interposed between the second lead frame 130 and the ceramic sheet 110.

[0051] Like the precursor assembly 300, the precursor assembly 500 can undergo a low-temperature and pressure sintering process (e.g., in a heated pressing fixture 400) to sinter the lead frame 120 and lead frame 130 to the ceramic sheet 110.

[0052] A method includes: applying a sintering precursor material layer to each of a first surface and a second surface of a ceramic sheet; assembling a precursor assembly for a direct-bonded copper (DBC) substrate by coupling a first lead frame to the sintering precursor material layer on the first surface of the ceramic sheet and coupling a second lead frame to the second surface of the sintering precursor material layer on the second surface of the ceramic sheet, such that the ceramic sheet is disposed between the first lead frame and the second lead frame; and sintering the first lead frame and the second lead frame to the ceramic sheet to form a sintered-bonded DBC substrate.

[0053] In this method, sintering a first lead frame and a second lead frame to a ceramic sheet to form a sintered DBC substrate includes applying a sintering heat treatment to the precursor assembly at a temperature of less than 500°C.

[0054] Sintering bonding involves applying sintering heat and pressure treatment to the precursor assembly at a temperature of less than 500°C and a pressure of less than 100 MPa.

[0055] In this method, applying the sintering precursor material layer includes metallizing a first surface of the ceramic sheet and applying the sintering precursor material layer to the metallized first surface of the ceramic sheet.

[0056] In this method, the ceramic sheet is at least one of an alumina sheet, an aluminum nitride sheet, a silicon nitride sheet, or a boron nitride sheet; the first lead frame includes conductive metal traces; and the second lead frame includes one of conductive metal traces, a solid metal sheet, or a metal foil. In an exemplary embodiment, the second lead frame includes a conductive sheet made of boron nitride, graphite, or carbon.

[0057] In this method, applying a sintering precursor material layer includes applying one of a silver-based sintering material, a copper-based sintering material, a gold-based sintering material, or a combination thereof to at least one surface of a ceramic sheet.

[0058] In this method, assembling a precursor assembly for a direct-bonded copper (DBC) substrate includes coupling at least one semiconductor device die to a first lead frame. In an exemplary embodiment, the method further includes coupling at least one semiconductor device die to the first lead frame prior to sintering bonding to form a sintered-bonded DBC substrate.

[0059] In this method, the thickness of at least one of the first lead frame or the second lead frame is between about 0.05 mm and about 3.0 mm. In an exemplary embodiment, the thickness of the first lead frame is between about 0.05 mm and about 3.0 mm, and the thickness of the second lead frame is between about 0.1 mm and about 5.0 mm.

[0060] It should be understood that in the foregoing description, when an element such as a layer, region, substrate, or component is referred to as being on, connected to, electrically connected to, coupled to, or electrically coupled to another element, the element may be directly on, connected to, or coupled to the other element, or one or more intermediate elements may be present. Conversely, when an element is referred to as being directly on, directly connected to, or directly coupled to another element or layer, no intermediate elements or layers are present. Although the terms "directly on," "directly connected to," or "directly coupled to" may not be used throughout the specific embodiments, elements shown as being directly on, directly connected to, or directly coupled to an element can be referred to in this manner. The claims of this application (if any) may be amended to describe the exemplary relationships described in the specification or shown in the drawings.

[0061] As used in this specification and claims, the singular form may include the plural form unless the context clearly indicates otherwise. In addition to the orientations shown in the figures, spatially relative terms (e.g., above, on, above, below, under, beneath, etc.) are intended to cover different orientations of the device in use or operation. In some embodiments, the relative terms above and below may respectively include vertically above and vertically below. In some embodiments, term proximity may include lateral proximity or horizontal proximity.

[0062] Some implementations may be implemented using various semiconductor processing and / or packaging techniques. Some implementations may be implemented using various types of semiconductor processing techniques associated with a semiconductor substrate, including, but not limited to, silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), silicon carbide (SiC), etc.

[0063] While certain features of the described embodiments have been illustrated herein, many modifications, alternatives, variations, and equivalents will now occur to those skilled in the art. Therefore, it should be understood that the appended claims are intended to cover all such modifications and variations falling within the scope of the embodiments. It should be understood that these modifications and variations are presented by way of example only and not limitation, and various changes in form and detail are possible. Any parts of the apparatus and / or methods described herein can be combined in any way, except for mutually exclusive combinations. The embodiments described herein may include various combinations and / or sub-combinations of the functions, components, and / or features of the different embodiments described.

Claims

1. A method for manufacturing a direct-bonded copper (DBC) substrate, comprising: A sintering precursor material layer is applied to each of the first and second surfaces of the ceramic sheet; By coupling a first lead frame to the sintered precursor material layer on a first surface of the ceramic sheet and coupling a second lead frame to the second surface of the sintered precursor material layer on a second surface of the ceramic sheet, the ceramic sheet is disposed between the first lead frame and the second lead frame, thereby assembling a precursor assembly for direct bonding to a copper substrate. An intermediate metal layer is directly disposed on at least one of the first and second surfaces of a ceramic sheet, between the ceramic sheet and a sintering precursor material layer made of metal particles. The intermediate metal layer is in direct contact with both the ceramic sheet and the sintering precursor material layer, and the intermediate metal layer has a portion that diffuses into the sintering precursor material layer. as well as The first lead frame and the second lead frame are sintered and bonded to the ceramic sheet to form a sintered bonded direct-bonded copper substrate.

2. The method of claim 1, wherein sintering the first lead frame and the second lead frame to the ceramic sheet to form the sintered bonded direct-bonded copper substrate comprises: Sintering heat and pressure treatment are applied to the precursor assembly at a temperature of less than 500°C and a pressure of less than 100 MPa.

3. A direct-bonded copper (DBC) substrate, comprising: Ceramic shards; The first lead frame is disposed on the first side of the ceramic sheet; The second lead frame is disposed on the second side of the ceramic sheet; The sintered joint made of metal particles between the first lead frame and the ceramic sheet; as well as An intermediate metal layer is disposed directly on at least one of the first and second surfaces of the ceramic sheet, between the ceramic sheet and the sintered joint, wherein the intermediate metal layer is in direct contact with both the ceramic sheet and the sintered joint, and wherein the intermediate metal layer has a portion that diffuses into the sintered joint.

4. The direct-bonded copper substrate of claim 3, wherein the surface of the ceramic sheet is metallized to form an intermediate metal layer, and the first lead frame is disposed on the metallized surface of the ceramic sheet.

5. The direct-bonded copper substrate according to claim 3, wherein the ceramic sheet is at least one of an alumina sheet, an aluminum nitride sheet, a silicon nitride sheet, or a boron nitride sheet.

6. The direct bonding copper substrate according to claim 3, wherein the first lead frame is a conductive metal trace.

7. The direct bonding copper substrate according to claim 3, wherein the second lead frame is one of a conductive metal trace, a solid metal sheet, a metal foil, or a conductive sheet made of boron nitride, graphite, or carbon.

8. The direct-bonded copper substrate according to claim 3, wherein the sintered bond comprises a silver-based sintered material, a copper-based sintered material, a gold-based sintered material, or a combination thereof.

9. The direct-bonding copper substrate of claim 3, wherein the thickness of at least one of the first lead frame or the second lead frame is between 0.05 mm and 3.0 mm.

10. The direct-bonding copper substrate of claim 3, wherein the first lead frame has a thickness between 0.05 mm and 3.0 mm, and the second lead frame has a different thickness between 0.1 mm and 5.0 mm.

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