Connecting material for connecting overlapping components of power electronic devices

Abstract

Connecting material (230) between overlapping components (210, 220) for connecting overlapping components (210, 220) of a power electronic device, wherein the connecting material (230) comprises: a mixture of composite particles (100), wherein each of the composite particles (100) has a core-shell structure with a core (102) and a shell (104) surrounding the core (102), wherein the core (102) is made of a copper-based material and the shell (104) is made of a low melting point material whose melting temperature or solidus temperature is below that of the copper-based material, wherein the copper-based core material comprises more than 96 wt.% copper, wherein the mixture of composite particles (100) contains a first particle fraction (106) with a first mean particle size and a second particle fraction (108) with a second mean particle size, and where the first mean particle size is at least one order of magnitude larger than the second mean particle size, the shell material is low-melting-point indium with a melting temperature of 156 °C, wherein in each composite particle the core makes up 50 to 90 wt% of the composite particle and the shell makes up 10 to 50 wt% of the composite particle, wherein a layer of the bonding material (230) is arranged between the overlapping components (210, 220) by applying the layer of the bonding material (230) to a first surface (212) of the first component (210) by spray coating.

Description

INTRODUCTION

[0001] The present disclosure relates to electronic devices and in particular to materials and methods for joining overlapping components of electronic devices.

[0002] An electronic component consists of several active and passive electronic components interconnected to form an electronic circuit, often mounted on a substrate or chip made of semiconductor material. When the electronic components are located on the same substrate, the resulting component is called an integrated circuit (IC). In practice, such electronic components are often assembled into a package containing several interconnected electrically conductive and electrically insulating layers, which may be configured to connect the electronic components to an external environment and / or dissipate heat from the electronic components.During assembly, the electronic components and the electrically conductive and electrically insulating layers can be mechanically joined together in the form of a vertical stack using an adhesive or electrically conductive bonding material.

[0003] The components of electronic enclosures are often relatively sensitive to heat. Therefore, when assembling an electronic enclosure, it is generally desirable to use joining materials that can effectively and efficiently form robust mechanical connections between such components at relatively low processing temperatures.

[0004] JP 2020 - 40 074 A describes a first core-shell powder consisting of a copper core and a tin outer layer, with a copper content of 25 to 55% by mass and a tin content of 75 to 45% by mass. The average particle diameter is between 0.5 µm and 2 µm. A second core-shell powder also consists of a copper core and a tin outer layer, with the same mass fractions of copper and tin, but with an average particle diameter of 5 µm to 10 µm. The mixing ratio of the two powders is adjustable.

[0005] US 2003 / 0006066A1 describes a conductive composition for filling vias to create reliable vertical connections (Z-connections). The vias can be either coated or uncoated prior to filling. A method for manufacturing high-density electronic packages using this technology is also described.

[0006] WO 2010 / 032 841 A1 describes a conductive filler with oxidation resistance that can be easily sintered, a conductive paste with excellent storage stability in air that forms a conductive layer with high conductivity, and an article with such a conductive layer. The conductive filler is characterized by the following: It contains copper filler with an average aggregate particle size of 0.5–20 µm, copper nanoparticles with an average aggregate particle size of 50–200 nm, and an aliphatic carboxylic acid. Furthermore, the filler contains 5–50 parts by weight of copper nanoparticles per 100 parts by weight of copper filler and 1–15 parts by weight of aliphatic carboxylic acid per 100 parts by weight of the total amount of copper filler and copper nanoparticles.

[0007] EP 1 827 066 A2 describes how electrical conductors and layers are formed by exposing conductor formulations consisting of metal particles or metal precursors or mixtures thereof, typically in the form of ink or paste, to an electrically activated reducing gas at a sufficient temperature and for a sufficient duration to cause sintering. SUMMARY

[0008] The object of the invention is to realize an effective and reliable connection between the overlapping components of a power electronic device at low temperatures without subjecting the components to thermal stress. This object is achieved by the subject matter according to claim 1. Further developments are described in the dependent claims.

[0009] A bonding material for connecting overlapping components of a power electronic device is disclosed. The bonding material can comprise a mixture of composite particles. Each of the composite particles can have a core-shell structure with a core and a shell surrounding the core. The core can be made of a copper-based material, and the shell of a low-melting-point material whose melting or solidus temperature is lower than that of the copper-based material. The mixture of composite particles can contain a first particle fraction with a first mean particle size and a second particle fraction with a second mean particle size. The first mean particle size can be at least one order of magnitude larger than the second mean particle size.

[0010] The copper-based core material can consist of more than 96% copper by weight. The low-melting-point shell material can have a melting point or solidus temperature in the range of 200°C to 300°C.

[0011] The low-melting-point material of the shell may contain at least one of the following materials: tin, indium, zinc, phosphorus, copper(I) phosphide or an alloy of copper and one or more elemental metals or non-metals.

[0012] The bonding material may contain a binder, a dispersant, or a solvent. In this case, the mixture of bonding particles can make up 70 to 95% of the bonding material.

[0013] In each composite particle, the core can make up 50 to 90 wt% of the composite particle and the shell 10 to 50 wt% of the composite particle.

[0014] The first mean particle size can range from 1 micrometer to 30 micrometers, and the second mean particle size can range from 10 nanometers to 100 nanometers.

[0015] The first particle fraction can make up 60% to 80% of the mixture of composite particles by volume, and the second particle fraction can make up 20% to 40% of the mixture of composite particles by volume.

[0016] A method for joining overlapping components of a power electronic device is disclosed. In the method, a volume of bonding material can be arranged between opposing surfaces of at least partially overlapping first and second components. The bonding material can contain a mixture of composite particles, each of which has a core-shell structure comprising a core and a shell surrounding the core. The volume of bonding material can be heated to a sintering temperature in the range of 200°C to 300°C to form a continuous liquid phase between the first and second components, which wets the opposing surfaces of the first and second components. The continuous liquid phase can solidify into a bond that joins the first and second components along their opposing surfaces.The core of each composite particle can consist of a copper-based material, and the shell of each composite particle can consist of a low-melting-point material whose melting or solidus temperature is lower than that of the copper-based material. The mixture of composite particles can contain a first particle fraction with a first mean particle size and a second particle fraction with a second mean particle size. The first mean particle size can be at least one order of magnitude larger than the second mean particle size.

[0017] When the volume of the bonding material is heated to the sintering temperature, at least some of the low-melting-point material of the shells of the bonded particles can melt.

[0018] The low-melting material of the shells of the composite particles may contain at least one of the following materials: tin, indium, zinc, phosphorus, copper(I) phosphide or an alloy of copper and one or more elemental metals or non-metals.

[0019] When the volume of the compound material is heated to the sintering temperature, intermetallic compounds can form within the continuous liquid phase through chemical reaction between the copper-based material of the cores and the low-melting-point material of the shells of the composite particles. In embodiments, the low-melting-point material of the shells of the composite particles can contain tin, and in this case, the intermetallic compounds can comprise Cu6Sn5 and / or Cu3Sn.

[0020] The solid compound formed along the opposing surfaces of the first and second components can have a composite structure comprising a continuous copper matrix phase and a particle phase embedded within the continuous matrix phase. The particle phase can include intermetallic compounds formed within the continuous liquid phase by chemical reactions between the copper-based core material and the low-melting-point shell material of the composite particles.

[0021] The volume of the bonding material can be heated to the sintering temperature by convection, conduction, radiative heating, resistance heating, electromagnetic induction or plasma heating.

[0022] A protective gas can be applied to the volume of the joining material when the volume of the joining material is heated to the sintering temperature. In this case, the protective gas can consist of at least one of the elements helium, argon, nitrogen, hydrogen, or carbon monoxide.

[0023] No pressure may be exerted on the volume of the joining material during the formation of the continuous liquid phase or during the formation of the solid bond.

[0024] The joining material may contain a solvent. In this case, before heating the volume of the joining material to the sintering temperature, the volume of the joining material can be heated to an initial temperature in the range of 100°C to 180°C in order to remove at least some of the solvent from the joining material.

[0025] The first component can comprise a power semiconductor chip and the second component a thermally and electrically conductive copper substrate.

[0026] Another method for joining overlapping components of a power electronic device is disclosed. In this method, a layer of bonding material can be applied to a substrate. The bonding material can contain a mixture of composite particles. Each of the composite particles can have a core-shell structure comprising a core and a shell surrounding the core. A component can be positioned in an at least partially overlapping relationship to the substrate such that at least a portion of the bonding material layer is located between a first surface of the substrate and an opposing second surface of the component.The layer of compound material can be heated to a sintering temperature in the range of 200°C to 300°C to form a continuous liquid phase between the substrate and the component, wetting the opposing first and second surfaces of the substrate and the component. This continuous liquid phase can solidify into a bond that joins the component and the substrate along their opposing first and second surfaces. The core of each compound particle can be made of a copper-based material, and the shell of each compound particle can be made of a low-melting-point material whose melting or solidus temperature is lower than that of the copper-based material. The mixture of compound particles can contain a first particle fraction with a first medium particle size and a second particle fraction with a second medium particle size.The first mean particle size can be at least one order of magnitude larger than the second mean particle size.

[0027] The layer of bonding material can be applied to the first surface of the substrate with a thickness ranging from 10 micrometers to 100 micrometers.

[0028] The above summary is not intended to represent every possible embodiment or aspect of the present disclosure. Rather, the preceding summary is intended to illustrate some of the novel aspects and features disclosed herein. The features and advantages mentioned above, as well as other features and advantages of the present disclosure, will be readily apparent from the following detailed description of representative embodiments and modes of carrying out the present disclosure in conjunction with the accompanying drawings and claims. BRIEF DESCRIPTION OF THE FIGURES

[0029] Illustrative embodiments are described below in conjunction with the accompanying figures, where identical designations denote identical elements and where: Fig. Figure 1 is a schematic side cross-sectional view of a power electronic device comprising a power semiconductor chip mounted on a stack of interconnected electrically conductive and electrically insulating layers and physically connected to them by a thermally and electrically conductive solid connection; Fig. Figure 2 is a schematic representation of a cross-section of a mixture of composite particles that may be contained in a bonding material used to form the thermally and electrically conductive solid bond of Fig. 1 is used; Fig. Figure 3 is a schematic side cross-sectional view of two overlapping components of a power electronic device, wherein a layer of a compound material comprising a mixture of composite particles of Fig. 2 contains, is arranged before joining between opposing surfaces of the components; and Fig. Figure 4 is a schematic side cross-sectional view of the overlapping components of Fig. 3, after the components have been joined together along their opposite surfaces by forming a thermally and electrically conductive solid bond between them, the formation of the solid bond being achieved by mixing composite particles in the layer of the joining material of Fig. 3 is subjected to a liquid phase sintering process.

[0030] The present disclosure is open to modifications and alternative forms, representative embodiments of which are illustrated by way of example in the drawings and described in detail below. The inventive aspects of this disclosure are not limited to the particular forms disclosed. Rather, the present disclosure is intended to cover modifications, equivalents, combinations, and alternatives that fall within the scope of the disclosure as defined by the appended claims. DETAILED DESCRIPTION

[0031] The bonding material presented here consists of a mixture of composite particles that enables the formation of robust, thermally and electrically conductive, solid connections between adjacent, overlapping components of electronic devices at relatively low process temperatures (e.g., less than 300 °C). Furthermore, the bonding material presented here contains no relatively expensive metals (e.g., silver) and can be used to form tight, solid connections without applying compressive forces at the joint. Each of the composite particles in the bonding material presented here has a core-shell structure defined by a core and a shell surrounding the core.The core consists of a copper-based material, and the shell is made of a material with a relatively low melting point and / or solidus temperature compared to that of the copper-based core material and can be referred to here as a "low-melting-point material." When joining two overlapping components, a volume of the bonding material is injected between the opposing surfaces of the components and heated to a sintering temperature. This results in the formation of a continuous liquid phase of molten material that extends between and wets the opposing surfaces of the components to be joined. The continuous liquid phase then solidifies into a dense, solid bond that joins the components along their opposing surfaces.

[0032] The mixture of composite particles in the bonding material presented here consists of a first particle fraction with a first mean particle size and a second particle fraction with a second mean particle size, the first mean particle size being several orders of magnitude larger than the second mean particle size. Formulating the bonding material with two particle fractions exhibiting significantly different mean particle sizes (compared to particle mixtures consisting of relatively similar-sized particles without discernible particle fractions) enables the formation of relatively dense, solid bonds in a relatively short time without the application of compressive forces at the bonding point.

[0033] The interconnect material presented here can be used to mechanically and optionally electrically connect a variety of overlapping components of electronic devices along their opposing surfaces. For example, the interconnect material disclosed here can be used to connect overlapping electrically insulating layers and / or electrically conductive layers, and can be used to connect active electronic components (e.g., semiconductor devices, integrated circuits, and / or electromechanical devices) to such layers. The following description specifically describes the interconnect material for use in conjunction with power electronic devices, but it is not limited to such use, as those familiar with the subject will recognize.The terms "copper-based material" and "copper material" used here refer to materials that consist primarily of copper (Cu), meaning that copper is the largest single component of the material by weight. This can include materials containing more than 50% copper by weight as well as those containing less than 50% copper by weight, as long as copper is the largest single component.

[0034] The term "metal" used here refers to elemental metals as well as metal alloys that contain a combination of an elemental metal and one or more metallic or non-metallic alloying elements.

[0035] The terms "melting temperature" or "melting point" used here refer to the temperature (a-point) at which a solid material becomes liquid at atmospheric pressure. The terms "solidus temperature" or "solidus point" used here refer to the highest temperature (a-point) at which a material is completely solid; at temperatures above the solidus temperature, the material is at least partially liquid.

[0036] The term "sintering" refers to a process in which adjacent surfaces of metal-containing solid particles are fused together by heating. The term "liquid-phase sintering" refers to a form of sintering in which a liquid phase forms during heating, coexisting with the solid particles.

[0037] As used here, the term "approximately" means that a number designated as "approximately" is the given number plus or minus 1-10% of that given number.

[0038] As used herein, the term “essentially” refers to a large extent or a high degree, e.g., “essentially everything” may refer to at least about 90%, at least about 95%, at least about 99%, and preferably at least 99.9%.

[0039] Fig. Figure 1 is a schematic representation of a power electronic device 10 containing an active electronic component in the form of a power semiconductor chip 12 mounted on a stack 14 of interconnected electrically conductive and electrically insulating layers. The power semiconductor chip 12 can be a bipolar transistor, an insulated-gate bipolar transistor (IGBT), a metal-oxide-semiconductor field-effect transistor (MOSFET), a thyristor, or a diode. The stack 14 of interconnected electrically conductive and electrically insulating layers can be configured to electrically connect the semiconductor chip 12 to an external circuit (not shown) and / or to electrically connect or isolate the semiconductor chip 12 from one or more additional components of the power electronic device 10. In the Fig. In the embodiment shown in Figure 1, the stack 14 of interconnected electrically conductive and electrically insulating layers comprises a base plate 16 and an electrically insulating substrate 18, which is mounted on the base plate 16 and physically connected to it by forming a first fixed connection 20. The semiconductor chip 12 is located on top of the stack 14 and is mounted on the substrate 18 and physically connected to it by forming a second fixed connection 22.

[0040] The base plate 16 provides mechanical support to the components of the power electronic device 10 located above it and can be connected to an underlying heat sink (not shown) to facilitate heat dissipation from the power electronic device 10 during its operation. The base plate 16 defines a mounting surface 24 on which the substrate 18 is mounted and can be made of a metal and / or ceramic material exhibiting high thermal conductivity and a low coefficient of thermal expansion.

[0041] The electrically insulating substrate 18 mechanically supports the semiconductor chip 12 and can electrically isolate the semiconductor chip 12 from other electrical or electronic components of the power electronics device 10. The substrate 18 has a first main surface 26 facing the base plate 16 and an opposite second main surface 28 facing away from the base plate 16 and towards the semiconductor chip 12. The substrate 18 is mounted on the mounting surface 24 of the base plate 16 via the first fixed connection 20 and is physically attached to it, the first fixed connection 20 extending as a continuous layer between the mounting surface 24 of the base plate 16 and the opposite first main surface 26 of the substrate 18.In embodiments, the substrate 18 can have a composite structure in the form of a metallized ceramic substrate with a ceramic intermediate layer 30, which lies between a first and a second metal layer 32, 34 on opposite first and second sides and is directly connected to them. In such a case, as in . Fig. As shown in Figure 1, the first main surface 26 of the substrate 18 is defined by the first metal layer 32, which is arranged on the first side of the ceramic interlayer 30, and the second main surface 28 of the substrate 18 can be defined by the second metal layer 34, which is arranged on the second side of the ceramic interlayer 30. The ceramic interlayer 30 can consist of a ceramic material, e.g., aluminum oxide (Al₂O₃), aluminum nitride (AlN), beryllium oxide (BeO), and / or silicon nitride (Si₃N₄), and the first and second metal layers 32, 34 can consist of copper (Cu), copper oxide (CuO), and / or aluminum (Al). In certain cases, the metallized ceramic substrate may be in the form of a directly bonded copper substrate (DBC), a directly bonded aluminum substrate (DBA), or a ceramic substrate with active metal brazing (AMB).

[0042] The power semiconductor chip 12 is mounted on and physically attached to the second main surface 28 of the substrate 18 via the second solid connection 22, the second solid connection 22 extending as a continuous layer between the second main surface 28 of the substrate 18 and an opposite surface 36 of the semiconductor chip 12. The first and second solid connections 20, 22 are formed between adjacent, overlapping components of the power electronic device 10 (i.e., between the base plate 16 and the substrate 18 and between the substrate 18 and the semiconductor chip 12) using a bonding material comprising a mixture of composite particles 100 (see Fig. 2) Each of the composite particles has a core-shell structure with a core 102 and a shell 104 surrounding the core 102.

[0043] The core 102 of each of the composite particles consists of a copper-based material and is configured to impart high thermal and electrical conductivity to the resulting solid compounds 20, 22. In embodiments, the copper-based material of the core 102 can comprise more than 96% copper by weight, preferably more than 98% copper, and more preferably more than 99.9% copper. Pure elemental copper (Cu) has a melting point of about 1084°C at 1 atm, a thermal conductivity of about 394 W / mK at 20°C, and an electrical conductivity in the range of about 100.0% to about 101.5% IACS at 20°C.

[0044] The shell 104 of each composite particle is formulated to facilitate the liquid-phase sintering of the mixture of composite particles 100 and may consist of a material having a relatively low melting point and / or a relatively low solidus temperature compared to the copper-based material of the core 102. As such, the shell 104 material may be referred to as a “low-melting-point material”. Shell 104 can be made, for example, of tin (Sn) with a melting point of approximately 231°C at 1 atm, indium (In) with a melting point of approximately 156°C at 1 atm, zinc (Zn) with a melting point of approximately 419°C at 1 atm, phosphorus (P) with a melting point of approximately 44°C at 1 atm, copper(I) phosphide (Cu3P) with a melting point of approximately 900°C at 1 atm, and / or an alloy of tin (Sn) and / or an alloy of copper (Cu) and one or more elemental metals or nonmetals (e.g.,, Sn-Cu, Sn-Zn, Sn-Zn-Cu, Sn-Cu-Ag, Sn-In, Sn-Zn-In, Sn-Ag, Sn-In-Ag, Sn-Sb, Sn-Ag-Sb, Sn-Cu-Ni, Sn-Ag-Zn-Cu, and / or Sn-Bi). The melting point and / or solidus temperature of the material of the shell 104 is preferably below 300 °C and particularly preferably below 250 °C.

[0045] In each composite particle, the core 102 can constitute 50% to 90% of the composite particle by weight, and the shell 104 can constitute 10% to 50% of the composite particle by weight. The shell 104 of each composite particle can completely encapsulate the core 102 and have a thickness over the core 102 ranging from one (1) nanometer to one (1) micrometer.

[0046] As in Fig. As shown in Figure 2, the mixture of composite particles 100 contains two particle fractions: a first particle fraction 106 with a first mean particle size and a second particle fraction 108 with a second mean particle size that is smaller than the first mean particle size of the first particle fraction 106. In certain embodiments, the first mean particle size of the first particle fraction 106 can be an order of magnitude larger than the second mean particle size of the second particle fraction 108. For example, the first mean particle size of the first particle fraction 106 can be greater than or equal to ten (10) times and less than or equal to one hundred (100) times larger than the second mean particle size of the second particle fraction 108.The first particle fraction 106 can constitute, by volume, 60% to 80% or, more preferably, 65% to 75% of the mixture of composite particles 100, and the second particle fraction 108 can constitute, by volume, 20% to 40% or, more preferably, 25% to 35% of the mixture of composite particles 100. The first particle fraction 106 can have a first mean particle size in the range of 1 micrometer to 30 micrometers, and the second particle fraction 108 can have a second mean particle size in the range of 10 nanometers to 100 nanometers.

[0047] The first particle fraction 106 can be substantially free of composite particles with a particle diameter of less than 10 nanometers and substantially free of composite particles with a particle diameter of more than 10 micrometers. Simultaneously, the second particle fraction 108 can be substantially free of composite particles with a particle diameter of less than one (1) nanometer and substantially free of composite particles with a particle diameter of more than one (1) micrometer. Thus, the first particle fraction 106 can have a first particle size distribution in the range of 10 nanometers to 10 micrometers, and the second particle fraction 108 can have a second particle size distribution in the range of one (1) nanometer to one (1) micrometer. In some embodiments, the first particle size distribution of the first particle fraction 106 can partially overlap with the second particle size distribution of the second particle fraction 108.In other embodiments, the first particle size distribution of the first particle fraction 106 cannot overlap with the second particle size distribution of the second particle fraction 108.

[0048] The bonding material may contain one or more additives, which may, for example, be configured to facilitate the application of the bonding material to a surface of one of the components of the power electronic device 10 before assembly, or to facilitate the formation of the bonding material into a pre-formed film or foil that can be positioned between overlapping components of the power electronic device 10 before assembly. Thus, in addition to the mixture of bonding particles 100, the bonding material may contain a binder, a dispersant, and / or a solvent.

[0049] In embodiments in which the bonding material contains one or more additives, the mixture of bonding particles 100 can constitute 70 to 95% of the bonding material by weight.

[0050] If present, the binder may be a polymeric binder and be present in the compound material at a concentration of 5 to 30% by weight. The dispersant may consist of fish oil and be present at a concentration of 1 to 10% by weight. The solvent may consist of Texanol or Terpineol and be present in the compound material at a concentration of 1 to 10% by weight.

[0051] The Fig. 3 and Fig. Figure 4 illustrates the steps of a method for producing a thermally and electrically conductive connection 200 between overlapping first and second components 210, 220 of a power electronic device. As shown in Figure 4. Fig.As best illustrated in Figure 3, the first and second components 210, 220 to be joined can be positioned in an at least partially overlapping, spaced-apart relationship, and a volume or layer of bonding material 230 can be positioned between opposing first and second surfaces 212, 222 of the first and second components 210, 220. As described above, the layer of bonding material 230 contains the mixture of composite particles 100 and may contain one or more additives. The layer of bonding material 230 can be positioned between the first and second components 210, 220 by applying the layer of bonding material 230 to the first surface 212 of the first component 210, for example, by printing, screen printing, roller coating, extrusion, or spray coating.Alternatively, the layer of bonding material 230 can be preformed in the form of a thin film or foil, which is placed on the first surface 212 of the first component 210. The layer of bonding material 230 can have a thickness in the range of 10 micrometers to 100 micrometers. The second component 220 is positioned on the first surface 212 of the first component 210 above the layer of bonding material 230, so that the layer of bonding material 230 lies between the opposing first and second surfaces 212, 222 of the first and second components 210, 220.

[0052] In embodiments where the layer of the bonding material 230 contains an additive, the layer of the bonding material 230 can be preheated at a relatively low temperature in the range of 100°C to 180°C in order to remove at least some of the additive and / or to modify the chemical and / or mechanical properties of the layer of the bonding material 230 in a manner desirable for storage or transport. In some embodiments, the layer of the bonding material 230 can be preheated after the layer of the bonding material 230 has been positioned on the first surface 212 of the first component 210, but before the second component 220 is positioned on the first surface 212 of the first component 210 above the layer of the bonding material 230.

[0053] After the layer of bonding material 230 has been positioned between the opposing first and second surfaces 212, 222 of the first and second components 210, 220 and optionally preheated, the layer of bonding material 230 can be heated to a sintering temperature to initiate the liquid-phase sintering of the mixture of composite particles 100 contained therein. The sintering temperature is a temperature above the solidus temperature of the shell material 104 and below the melting temperature of the core material 102. The sintering temperature thus depends on the chemical composition of the shell 104 and the chemical composition of the core 102. The sintering temperature can be a temperature above the melting temperature of the shell material 104. The sintering temperature can be a temperature below the solidus temperature of the core material 102.The chemical compositions of the core 102 and the shell 104 are formulated such that a sintering temperature of less than 300 °C is possible, ensuring that the first and second components 210, 220, which are joined together, remain at a sufficiently low temperature that does not impair the physical integrity of the components 210, 220 during the entire liquid-phase sintering process. In embodiments, the liquid-phase sintering of the mixture of composite particles 100 in the layer of bonding material 230 can be carried out by heating the layer of bonding material 230 to a sintering temperature in the range of 200 °C to 300 °C for a duration of 1–5 minutes.

[0054] Without being bound to the theory, it is assumed that during liquid-phase sintering, a continuous liquid phase forms in the layer of compound material 230, which wets the surfaces of the composite particles 100 and also wets the opposing first and second surfaces 212, 222 of the first and second components 210, 220 that are joined together. The formation of the continuous liquid phase in the layer of compound material 230 can allow the composite particles 100 to move relative to each other, leading to a solidification of the composite particles 100 and a densification of the layer of compound material 230. During liquid-phase sintering, the core material 102 can react with the shell material 104 to form one or more intermetallic phases within the layer of compound material 230.These intermetallic phases may have melting points and / or solidus temperatures above the sintering temperature and precipitate as intermetallic particles in the liquid phase during liquid-phase sintering. The solidification of the continuous liquid phase leads to the formation of a relatively dense solid compound 200, which bonds the first and second components 210, 220 along their opposing first and second surfaces 212, 222.

[0055] The formation of intermetallic phases with relatively high melting points and / or high solidus temperatures during the sintering process can lead to the formation of a solid compound 200 that does not melt or deform when reheated to the same sintering temperature. For example, in embodiments where the core material 102 comprises copper and the shell material 104 comprises tin, intermetallic phases of Cu6Sn5 (mp of about 415°C) and / or Cu3Sn (mp of about 640°C) can form within the continuous liquid phase during the sintering process. With the bonding material described here, components of power electronic devices can be joined at relatively low sintering temperatures (e.g., less than 300°C) by forming robust, thermally resistant solid bonds that can subsequently withstand the relatively high operating temperatures of power electronic devices (e.g.,can withstand temperatures of 200 °C or more).

[0056] The resulting solid compound 200 can have a composite structure comprising a continuous matrix phase and one or more particulate phases dispersed and embedded within the matrix phase. The continuous matrix phase can consist of essentially the same material as the core 102, i.e., the continuous matrix phase can comprise a copper-based material. The one or more particulate phases can comprise particles of the same material as that of the shell 104 and / or particles of one or more intermetallic compounds formed as a result of chemical reactions between the material of the core 102 and the material of the shell 104 during the sintering process. The resulting solid compound 200 can have a porosity of less than 20% and preferably less than 5%.

[0057] The layer of compound material 230 can be heated during liquid phase sintering by one or more of the following heating processes: convection, conduction, radiative heating (e.g. infrared and / or laser heating), resistance or Joule heating, electromagnetic induction and / or plasma heating.

[0058] The liquid-phase sintering process can be carried out, for example, in an inert gas environment or under reducing gases to prevent chemical reactions between the composite particle material 100 and the environment during the sintering process. In this case, the layer of the bonding material 230 can be exposed to a protective gas during liquid-phase sintering. Examples of protective gases are helium, argon, nitrogen, hydrogen, and / or carbon monoxide.

[0059] The bonding material presented here can be used to create robust, thermally and electrically conductive, solid connections between adjacent, overlapping components of a wide variety of high-performance electronic devices at relatively low processing temperatures. These and other advantages will be readily apparent to those skilled in the art in light of the foregoing disclosure.

[0060] While some of the best modes and other embodiments have been described in detail, there are various alternative designs and embodiments for realizing the present teachings defined in the appended claims. The person skilled in the art will recognize that modifications can be made to the disclosed embodiments without affecting the scope of the present disclosure. Furthermore, the present concepts expressly include combinations and subcombinations of the described elements and features. The detailed description and the drawings are supporting and descriptive of the present teaching, the scope of which is defined exclusively by the claims.

Claims

[1] Connecting material (230) between overlapping components (210, 220) for connecting overlapping components (210, 220) of a power electronic device, the connecting material (230) comprising: a mixture of composite particles (100), wherein each of the composite particles (100) has a core-shell structure with a core (102) and a shell (104) surrounding the core (102), wherein the core (102) is made of a copper-based material and the shell (104) is made of a low melting point material whose melting temperature or solidus temperature is lower than that of the copper-based material, wherein the copper-based core material comprises more than 96 wt% copper, wherein the mixture of composite particles (100) contains a first particle fraction (106) having a first average particle size and a second particle fraction (108) having a second average particle size, and wherein the first mean particle size is at least one order of magnitude larger than the second mean particle size, wherein the material of the low melting point shell is indium with a melting temperature of 156 °C, wherein in each composite particle the core constitutes 50 to 90 wt.% of the composite particle and the shell constitutes 10 to 50 wt.% of the composite particle, wherein a layer of the bonding material (230) is arranged between the overlapping components (210, 220) by spray coating the layer of the bonding material (230) onto a first surface (212) of the first component (210). [2] The bonding material (230) of claim 1, wherein the first average particle size is in a range of 1 micrometer to 30 micrometers and wherein the second average particle size is in a range of 10 nanometers to 100 nanometers. [3] The bonding material (230) of claim 1, wherein the first particle fraction constitutes 60% to 80% by volume of the mixture of composite particles and wherein the second particle fraction constitutes 20% to 40% by volume of the mixture of composite particles.

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