EP2629910A1

EP2629910A1 - Starting material and process for producing a sintered connection

Info

Publication number: EP2629910A1
Application number: EP11713483.3A
Authority: EP
Inventors: Daniel Wolde-Giorgis; Andrea Feiock; Robert Kolb; Thomas Kalich
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2010-10-20
Filing date: 2011-03-29
Publication date: 2013-08-28
Also published as: EP2630267A1; WO2012052191A1; US20130216848A1; US20130251447A1; EP2630267B1; WO2012052192A1

Abstract

The present invention relates to a starting material for producing a sintered connection. In order to avoid the formation of cracks in the joining partners in the case of fluctuating thermal loading, the starting material comprises second particles 20 in addition to metallic first particles 10, wherein the second particles 20 at least proportionately contain a particle core material which has a coefficient of thermal linear expansion α at 20°C which is less than the coefficient of thermal linear expansion α at 20°C of the metal or of the metals of the first particles in metallic form, and wherein the D₅₀ value of the second particles 20 is greater than or equal to half the D₅₀ value of the first particles 10 and less than or equal to two times the D₅₀ value of the first particles 10. In addition, the present invention relates to a corresponding sintered connection 100', to an electronic circuit 70 and also to a process for forming a thermally and/or electrically conductive sintered connection.

Description

description

title

Starting material and method for producing a sintered compound

The invention relates to a sintered compound, a starting material thereof and a process for their preparation, further comprising an electronic circuit containing the sintered compound according to the preamble of the independent claims.

State of the art

Power electronics are used in many areas of technology. Especially in electrical or electronic devices in which large currents flow, the use of power electronics is unavoidable. The currents required in the power electronics lead to a thermal load on the electrical or electronic components contained. Another thermal stress is given by the use of such electrical or electronic devices at operating locations with respect to the room temperature significantly increased and possibly even constantly changing temperature. As examples, control devices in the automotive sector may be mentioned for this purpose, which are arranged directly in the engine compartment.

In particular, many connections between power semiconductors or integrated circuits (IC) with each other and with carrier substrates are already subject to permanent temperature loads of up to 175 degrees Celsius. Usually, a connection of electrical or electronic components - for example, to a carrier substrate - by a connecting layer. As such a bonding layer, solder joints are known.

In most cases, soft solders are used which are based on tin-silver or tin-silver-copper alloys. However, especially at application temperatures close to the melting temperature, such bonding layers show dwindling electrical and mechanical properties that can lead to failure of the assembly.

Lead-containing solder joints can be used at higher temperatures than soft solder joints. However, lead-containing solder joints are severely limited by legal regulations for reasons of environmental protection in terms of their permissible technical applications.

Alternatively, lead-free brazing alloys are available for use at elevated or high temperatures, in particular above 200 degrees Celsius. Lead-free brazing alloys generally have a higher melting point than 200 ° C. When using brazing material to form a bonding layer, however, only a few electrical or electronic components come into consideration as joining partners, which can withstand the high temperatures during the melting of the brazing alloys.

One solution is the low-temperature connection technology (NTV), in which silver-containing sintered compounds can be produced at temperatures substantially lower than the melting temperature. Instead of a solder, a paste is used which contains chemically stabilized silver particles and / or silver compounds. Under the sintering conditions, in particular under temperature and pressure, while the stabilizing constituents are burned out and / or the silver compounds broken, so that the silver particles or released silver atoms come into direct contact with each other and with the material of the joining partners. By interdiffusion and / or diffusion, a high-temperature-stable connection can be formed at already significantly lower temperatures than the melting temperature. Under thermal cycling, however, thermo-mechanical stresses and even cracking in semiconductor devices or even in the carrier substrate occur.

Document DE 102009000192 A1 describes a sintered material for producing a sintered compound, which can be formed as a sintered paste and comprises metallic structural particles provided with an organic coating and non-organically coated metallic and / or ceramic auxiliary particles which do not degas during the sintering process.

Disclosure of the invention

The present invention is a starting material of a sintered compound comprising metal-containing first particles and second particles, in particular wherein the second particles at least partially contain a particle core material whose thermal expansion coefficient α at 20 ° C less than the thermal expansion coefficient α at 20 ° C of the metal or the metals of the first particles in metallic form and / or its thermal expansion coefficient α at 20 ° C <15-10 ^"6 K ^{" 1} and wherein the D ₅₀ value of the second particle is greater than or equal to half the D ₅₀ - value of first particle and less than or equal to twice the D ₅₀ value of the first particle.

The D ₅₀ value is understood to mean the median value of a particle size distribution, in particular of primary particles, in particular according to DIN 53 206, which indicates the particle diameter, in particular primary particle diameter, above and below which the diameter of the half of the particles is in each case and which corresponds to the diameter in which the cumulative distribution reaches the value 0.5. The D ₅₀ value of particles and in particular of mixtures of several different particles, such as first, second, third and / or fourth particles, can be determined in particular by means of electron microscopy, optionally in combination with energy-dispersive X-ray spectroscopy (EDX).

By the addition of second particles, which have a particle core material with a low thermal expansion coefficient, can Advantageously, the thermal expansion coefficient α (CTE, English: Coefficient of Thermal Expansion) of the starting material or the sintered compounds formed therefrom are significantly reduced. Previous experiments show that in this way sintered compounds can be formed, which advantageously has a coefficient of thermal expansion α at 20 ° C in a range of> 3-10 ^"6 K ^{" 1} to <15-10 ^" ⁶ K ^{" 1} , for example> 3 -10 ^"6 K ^{" 1} to <10-10 ^"6 K ^{" 1} , in particular of> 3-10 ^"6 K ^{" 1} to <7-10 ^"6 K ^{" 1} . Sintered compounds with such a low thermal expansion coefficient can not be achieved by the conventionally used silver pastes, which usually have a coefficient of thermal expansion α at 20 ° C by 19.5-10 ^"6 K ^{" 1} , and are of particular interest for the semiconductor technology, since this often joining partner are joined together by means of sintered connections, on the one hand, such as chips, a very low linear expansion coefficient, for example of about 3-10 ^"6 ^{K" 1,} and on the other hand, for example, metallic circuit substrate, a very high linear expansion coefficient, for example of about 16 , 5-10 ^"6 K ^{" 1} , which is one of the main causes of thermal stress cracking. By means of the second particles, the coefficient of thermal expansion can advantageously be set such that this coefficient lies between the coefficients of thermal expansion of the joining partners to be connected via the sintered layer, for example between 16.5-10 ^"6 K ^{" 1} (circuit carrier) and 3-10 ^"6 K ^{". 1} (chip) is located. Thus, thermo-mechanical stresses between the joining partners and the sintered connection, which can lead to crack formation in the joining partners during thermal cycling, can advantageously be significantly reduced. Advantageously, the cost of materials can be reduced by the use of inexpensive second particles.

In the context of the present invention, it has been found that, in order to achieve optimum results, the particle size or particle size distribution of the first and second particles should not deviate too much from each other, since too high a fine fraction of second particles adversely affects the sintering of the first particles and This can affect the stability of the sintered compound, wherein an excessive coarse fraction of second particles can lead to inhomogeneities and, accordingly, to macroscopic fluctuations in the material properties within the sintered compound. Overall, it is thus advantageously possible to form sintered connections with a significantly improved thermomechanical stability under thermal cycling from the starting material according to the invention.

In the context of the present invention, a starting material of a sintered compound can be understood to mean a starting material which is used for producing a sintered compound, in particular for the mechanical and electrical connection of electrical and / or electronic components. The starting material according to the invention can be, for example, a paste, a powder mixture or a sintered material preform body.

In the context of the present invention can be used as the metal, in particular all elements of the alkali metal group, in particular Li, Na, K, Rb, Cs, and alkaline earth metal group, in particular Be, Mg, Ca, Sr, Ba, the transition metal elements, in particular Sc, Y, La, Ti , Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg , the lanthanides and the elements aluminum, gallium, indium, tin, thallium, lead and bismuth are understood.

For the purposes of the present invention, noble metals are understood as meaning the elements silver, gold, platinum, palladium, ruthenium, rhodium, osmium and iridium.

Silicon is understood in the context of the present invention as a semi-metal and not as metal.

In the context of the present invention, adjectives with the ending -containing, such as metal-containing, noble metal, silver and copper-containing, mean that at least one element of the end-containing element group, for example one or more metals or one or more noble metals, or with the suffix -containing element, for example silver or copper, is included. In addition to the elemental shape, in particular the metallic shape, the elements or the element, for example, elemental, ie metallic silver, so are also compounds of Ele- or element, for example silver carbonate, silver oxide and / or silver carboxylates.

In the context of the present invention, metallic can in particular be understood to mean a form in which metallic bonds are present between the atoms of one or more elements, in particular where the atoms form a lattice with freely movable (delocalized) electrons.

In one embodiment, the particulate core material is a chemically inert and physically stable material.

Under a chemically inert material is understood to mean a material which undergoes no chemical reaction with the other materials of the starting material under the sintering conditions.

A physically stable material is understood to be a material which under the sintering conditions has no phase transition, for example from solid to liquid (melting).

In one embodiment, the D ₅₀ value of the second particles is greater than or equal to half the D ₅₀ value of the first particles and less than or equal to 1.5 times the D ₅₀ value of the first particles. In particular, the D ₅₀ value of the second particles may be greater than or equal to 0.75 times the D ₅₀ value of the first particles and less than or equal to the 1.25 times D ₅₀ value of the first particles. Thus, advantageously, the thermomechanical stability of the sintered compound under thermal cycling can be further improved.

The D ₅₀ value of the first particles and / or second particles as well as the third particles explained below may be in the range of, for example,

> 0.01 μηη to <50 μηι, in particular> 0.1 μηη to <10 μηι, for example of

> 1 μηη to <7 μηη, lie. Particles having such a particle size distribution advantageously have a large specific surface area and thus an increased reactivity. Thus, advantageously, the necessary processing temperature and the process time for forming a sintered connection can be kept low. If, for example, first particles with a D ₅₀ value of 3 μm are used, the second particles preferably have a D ₅₀ value in a range of> 1.5 μm to <6 μm (half to double the D ₅₀ value of the first one) Particles), for example, from> 1, 5 μηι to <4.5 microns (half to 1, 5 times D ₅₀ value of the first particles), in particular from> 2.25 microns to <3.75 microns (0.75 - to 1, 25 times D ₅₀ - value of the first particles).

In a further embodiment, the thermal expansion coefficient α of the particle core material at 20 ° C <10 10 ^"6 K ^{" 1} , in particular <7.5-10 ^"6 K ^{" 1} , preferably <5-10 ^"6 K ^{" 1} . Thus, advantageously, the thermal coefficient of linear expansion can be reduced more strongly and / or with a smaller amount of second particles.

In a further embodiment, the particle _{core material} has a thermal conductivity λ _20/5 ο at 20 ° C and 50% air humidity of> 15 Wm ^"1 K ^{" 1} or> 25 Wm ^"1 K ^{" 1} , preferably of> 50 Wm ^"1 K. ^"1 , in particular of> 100 Wm ^{" 1} K ^"1 , on. This is particularly advantageous for increasing the power density of semiconductor chips.

In another embodiment, the particle core material is selected from the group consisting of elemental silicon (Si), silicon oxide (SiO ₂ ), silicon carbide (SiC), aluminum nitride (AIN), silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₃ ), metallic tungsten (W), metallic molybdenum (Mo), metallic chromium (Cr), metallic platinum (Pt), metallic palladium (Pd), boron carbide (BC), beryllium oxide (BeO), boron nitride (BN), preferably elemental silicon and / or silica, silicon carbide, aluminum nitride, silicon nitride, alumina, and combinations thereof. These materials advantageously have a low thermal coefficient of linear expansion, which, as already explained, is advantageous in order to avoid cracking of the joining partners. In addition, during a temperature treatment of the starting material for forming a sintered connection, these materials generally behave chemically inert in an advantageous manner and, in the case of a formed sintered compound, exist in unchanged form within the metal matrix formed. Within the scope of an embodiment, the second particles or at least their particle cores may be formed from such a material. Particular preference is given to elemental silicon and / or silicon dioxide.

For example, the second particles may at least partially contain elemental silicon and / or silica. In particular, the second particles may have a particle core of elemental silicon and / or silicon dioxide, in particular elemental silicon. Elemental silicon and silicon dioxide have an extremely low coefficient of thermal expansion .alpha. (CTE, English: Coefficient of Thermal Expansion) and have therefore proved to be particularly advantageous, inter alia, for reducing the thermal expansion coefficient of the sintered connection. Already by the addition of a small amount, therefore, a greater reduction of the coefficient of thermal expansion of the sintered connection can advantageously be achieved than by other additives. In addition, elemental silicon and silicon dioxide advantageously have low Young's moduli, which may have an advantageous effect on the elasticity of the sintered compound. By reducing the coefficient of thermal expansion of the sintered connection and the good elastic properties, in turn, the thermomechanical stress between the sintered connection and the semiconductor component connected thereto and thus the tendency for the semiconductor component to crack can be significantly reduced. Due to the favorable coefficients of linear expansion and Young's modules of elemental silicon or silicon dioxide advantageously a sintered compound of such a starting material have a lower coefficient of linear expansion at the same or even lower Young's modulus than a similar unfilled sintered compound, in particular which instead of a proportion of second particles a correspondingly larger Share of first particles.

In principle, both amorphous and crystalline, in particular polycrystalline, elemental silicon and / or silicon dioxide can be used. The elemental silicon and / or silicon dioxide can in principle be used in all available degrees of purity. To minimize the material costs, for example, crude silicon, for example, with a purity of> 95%, can be used. In another embodiment, the particulate core material is amorphous elemental silicon and / or amorphous silica. Amorphous elemental silicon and amorphous silica advantageously have a particularly low coefficient of thermal expansion and a low Young's modulus, in particular the elongation coefficient and Young's modulus of amorphous elemental silicon is less than that of crystalline elemental silicon and amorphous silica, respectively, than that of crystalline silica ,

In a preferred embodiment, the particle core material is elemental silicon. Elemental silicon is preferred in the context of the present invention, since both its amorphous form compared to amorphous silica and its crystalline form compared with crystalline silica by a smaller coefficient of linear expansion and a higher electrical conductivity and thermal conductivity is characterized. Through the use of elemental silicon, the coefficient of thermal expansion of the sintered connection can therefore be reduced significantly, in particular while maintaining good elastic properties.

The second particles may in particular each have a particle core with a coating applied thereto. In this case, the particle core is preferably formed from the particle core material, for example from elemental silicon, silicon dioxide, silicon carbide, aluminum nitride, silicon nitride and / or aluminum oxide. In this case, the coating can be formed from a particle coating material that is different from the particle core material. Insofar as the particles are coated, the D ₅₀ value refers to the particle size including the coating.

In a further embodiment, the second particles are spherical, in particular substantially round, for example substantially spherical, particles. The term "essentially" can be understood to mean that slight deviations from the ideal shape, in particular spherical form, for example by up to 15%, are to be avoided by avoiding corners and edges, advantageously overvoltages of stress and thus cracking spots in the composite material can be avoided , Within the scope of a further embodiment, the first particles have a particle core with a first coating applied thereto and / or the second particles have a particle core with a second coating applied thereto.

The first and / or second coating or the later explained third and / or further coating advantageously encloses in each case the particle cores essentially completely, but at least almost completely. As a result, the coatings act on the one hand like a protective jacket, by means of which it can be ensured that the particles and the proportion of the material contained in the respective coating remain chemically stable, which has an advantageous effect on the storage capacity. In addition, such an agglomeration of the particles can be reduced or even avoided. Furthermore, by an in particular metal-containing, in particular metallic, coating, for example on the second, optionally third and optionally fourth particles, the sintering of the coated particles, for example on the first or other particles can be improved.

The coatings preferably assume a significantly lower proportion of the particle volume than the particle cores. This has an advantageous effect on the sintering process and the thermal and electrical properties of the starting material and the sintered compound.

In a further embodiment, the first particles are noble metal and / or copper-containing. As precious metal, silver, gold, platinum and / or palladium are particularly preferred. Preferably, the first particles are silver-containing.

In a further embodiment, the first particles contain in particular at least one metal, in particular at least one noble metal and / or copper, preferably silver, in metallic form and / or at least one organic or inorganic metal compound, in particular noble metal and / or copper compound, preferably silver compound, in particular, which can be converted by a temperature treatment into the metallic form of the at least one underlying metal. The organic or inorganic metal compound may, for example, be selected from the group consisting of silver carbonate, silver oxide, silver lactate, silver stearate and combinations thereof. These compounds may advantageously convert at high temperatures into the underlying metal in metallic form.

In particular, the first particles may have a metal-containing, in particular noble metal and / or copper-containing, for example, silver-containing, particle core.

Within the scope of an embodiment, at least a portion of the first particles has a particle core which contains at least one metal, in particular at least one noble metal and / or copper, preferably silver, in metallic form. For example, at least a portion of the first particles of at least one metal, in particular noble metal and / or copper, preferably silver, may be formed in metallic form.

As part of an alternative or additional embodiment, at least a portion of the first particles on a particle core containing at least one organic or inorganic metal compound, in particular noble metal and / or copper compound, preferably silver compound, in particular which by a thermal treatment in the metallic form of at least an underlying metal is convertible.

Within the scope of a specific embodiment, at least a first part of the first particle has a particle core which contains at least one metal, in particular at least one precious metal and / or copper, preferably silver, in metallic form, at least a second part of the first particle having a particle core containing at least one organic or inorganic metal compound, in particular noble metal and / or copper compound, preferably silver compound, which is convertible by a thermal treatment in the metallic form of the at least one metal of the first part of the first particles.

Alternatively or additionally, the first coating, for example of the first part of the first particles, at least one organic or inorganic metal compound, in particular precious metal and / or copper compound, preferably silver compound, contain, in particular which by a Tempe- in which at least one underlying metal in metallic form is convertible. The organic or inorganic metal compound may in this case also be selected, for example, from the group consisting of silver carbonate, silver oxide, silver lactate, silver stearate and combinations thereof. These compounds may advantageously convert at high temperatures into the underlying metal in metallic form.

Alternatively or additionally, the first coating of the first particles or a further coating applied to the first coating of the first particle may contain a reducing agent by means of which the reduction of one or the organic or inorganic metal compound, in particular noble metal and / or copper compound, preferably silver compound, to the metallic form, for example at a temperature in the range of or optionally below the sintering temperature of the metallic form of the at least one underlying metal, is feasible.

Alternatively or additionally, the second and / or third particles can also have a coating containing such a reducing agent.

The reducing agent content of the starting material is preferably selected such that it is present in a stoichiometric ratio to the proportion of the metal compound, in particular noble metal and / or copper compound, preferably silver compound, in particular to be reduced, contained in the starting material. Thus, advantageously, a very high conversion rate of up to 99% or more can be achieved.

As the reducing agent, for example, at least one alcohol from the group of primary or secondary alcohols and / or at least one amine and / or formic acid and / or at least one fatty acid, in particular isostearic acid, stearic acid, oleic acid, lauric acid or a mixture of different fatty acids can be used.

Overall, such reducing agent-containing first coatings can be applied in a simple manner to the first particles. In addition, the abovementioned reducing agents show in the context of a temperature treatment of the To obtain a sintered compound a particularly good reduction behavior compared to the organic or inorganic metal compounds or noble metal oxides contained in the second coating of the second particles. By reducing agent-containing coatings, the reducing agent can advantageously be distributed very uniformly and finely in total in the starting material. This allows the sintering process within the starting material to be made more uniform and faster. This results in the advantage that a sintered connection produced from the starting material according to the invention can have a very homogeneous sintered structure, in particular with a high thermal and / or electrical conductivity. This effect can be further enhanced by the use of coatings which contain organic or inorganic metal compounds corresponding to the first particles, in particular noble metal and / or copper compounds, preferably silver compounds, and for example are in direct contact with the coatings containing the reducing agent. Advantageously, the temperature at which the organic or inorganic metal compound converts to the underlying metallic form can be lowered. This makes it possible for joining partners advantageously connected via the formed sintered connection, for example electrical and / or electronic components of an electronic circuit, to not be exposed to high temperatures during the formation of the sintered connection. Thus, temperature-sensitive electrical and / or electronic components can be electrically and / or thermally contacted in electronic circuits, which could not be used due to the usual too high process temperatures in the connection production.

The second coating may be metal-containing, in particular noble metal and / or copper-containing, preferably silver-containing. In the context of one embodiment, the second coating contains at least one metal, in particular noble metal and / or copper, preferably silver, in metallic form. In another embodiment, the second coating contains at least one metal as an organic or inorganic metal compound, in particular noble metal and / or copper compound, preferably silver compound, in particular which by a thermal treatment in the metallic form, in particular of the at least one underlying metal, in particular first par is convertible. The organic or inorganic metal compound may in this case also be selected, for example, from the group consisting of silver carbonate, silver oxide, silver lactate, silver stearate and combinations thereof. These compounds may advantageously convert at high temperatures into the underlying metal in metallic form.

Alternatively or additionally, the second coating or a further coating applied to the second coating may contain a reducing agent, by means of which the reduction of one or the organic or inorganic metal compound, in particular noble metal and / or copper compound, preferably silver compound, in particular of the metal / metals the first particle, the metallic form, for example at a temperature in the range of or optionally below the sintering temperature of the metallic form of the at least one underlying metal, in particular the first particles, is feasible.

In a further embodiment, the second coating contains at least one metal which is selected from the group consisting of silver, platinum, palladium, gold, tin and combinations thereof. Preferably, the second coating contains at least one of the metals of the first particles. In particular, the second coating may contain the same metals as the first particles, for example silver. Thus, advantageously, the adhesion of the second particles in the starting material can be improved. Since the layer thickness of the coating is preferably smaller than the radius of the particle cores, their thermal expansion coefficient influences the sintering compound less than the coefficient of linear expansion of the particle core material. In order to further minimize the coefficient of linear expansion of the sintered material, however, it may be advantageous to use platinum and / or palladium in the coating material.

Furthermore, the starting material may comprise third particles. The third particles may also have a particle core and optionally a third coating applied to the particle core. The third coating may be metal-containing, in particular precious metal and / or copper-containing, preferably silver-containing. In the context of one embodiment, the third coating contains at least one metal, in particular noble metal and / or copper, preferably silver, in metallic form. In another embodiment, the third coating contains at least one metal as an organic or inorganic metal compound, in particular noble metal and / or copper compound, preferably silver compound, in particular which by a temperature treatment in the metallic form, in particular of the at least one underlying metal, in particular first particle, is convertible. The organic or inorganic metal compound may also hereby be selected, for example, from the group consisting of silver carbonate, silver oxide, silver lactate, silver stearate and combinations thereof. These compounds may advantageously convert at high temperatures into the underlying metal in metallic form.

Alternatively or additionally, the third coating or a further coating applied to the third coating may contain a reducing agent, by means of which the reduction of one or the organic or inorganic metal compound, in particular noble metal and / or copper compound, preferably silver compound, in particular of the metal / metals the first particle, the metallic form, for example at a temperature in the range of or optionally below the sintering temperature of the metallic form of the at least one underlying metal, in particular the first particles, is feasible.

In another embodiment, the third coating includes at least one metal selected from the group consisting of silver, platinum, palladium, gold, and combinations thereof. Preferably, the third coating contains at least one of the metals of the first particles. In particular, the third coating may contain the same metals as the first particles, for example silver. Thus, advantageously, the adhesion of the third particles in the starting material can be improved. Since the layer thickness of the coating is preferably smaller than the radius of the particle cores, their thermal expansion coefficient influences the sintering compound less than the coefficient of linear expansion of the particle core material. In order to further minimize the coefficient of linear expansion of the sintered material, however, it may be advantageous to use platinum and / or palladium in the coating material. Preferably, the third particles contain at least proportionally at least one metal, for example tin, in particular in metallic form, which by means of a temperature treatment, in particular in the range of or optionally below the sintering temperature of the metallic form of the metal / metals of the first particles, an alloy with the or the metals of the first particles is formed, in particular which has a lower melting point than the one or more metals of the first particles in metallic form. In particular, the particle cores of the third particle may be formed therefrom. Thus, advantageously, the processing temperature for forming the sintered connection can be further reduced. Furthermore, the alloys may be present as ductile phases within the formed sintered structure, whereby the formed sintered compounds are less susceptible to thermal and / or mechanical stresses, in particular changing loads. Furthermore, tin, for example, has a low melting point, so that when a temperature treatment of the starting material, the particles of tin melt prematurely and cause a cohesive contact of all particles contained in the starting material. This advantageously favors the diffusion processes occurring during the sintering process.

In a further embodiment, the starting material, based on the total weight of the constituents, comprises> 5% by weight, in particular> 10% by weight, for example> 20% by weight or> 25% by weight, of second particles, in particular wherein the sum of the constituents of the starting material gives 100% by weight. With such an amount of second particles, a significant reduction of the thermal expansion coefficient of the sintered compound, in particular based on a corresponding sintered compound, which comprises a further part of first particles instead of the second particles, can be achieved.

In a further embodiment, the starting material comprises, based on the total weight of the constituents, <60% by weight, in particular <50% by weight, of second particles, in particular wherein the sum of the constituents of the starting material gives 100% by weight. With such an amount of second particles in the starting material, it is advantageously possible to produce a well-bonded or adherent sintered layer. Insofar as the starting material still has third particles, the starting material comprises, based on the total weight of the constituents, in total second and third particles <60% by weight, in particular <50% by weight, in particular wherein the sum of the constituents of the starting material 100 wt .-% results.

Within the scope of a further embodiment, the starting material comprises, based on the total weight of the constituents,> 5% by weight or> 10% by weight to <60% by weight, in particular> 10% by weight or> 20% by weight. % or> 25% by weight to <50% by weight, of second particles or second and third particles in total, in particular wherein the sum of the constituents of the starting material gives 100% by weight.

In a further embodiment, the starting material comprises, based on the total weight of the constituents, from> 25 wt .-% to <80 wt .-% of the first particles, in particular wherein the sum of the constituents of the starting material 100 wt .-% results.

Furthermore, the starting material may comprise at least one solvent. For example, the starting material, based on the total weight of the ingredients,> 5 wt .-% or> 10 wt .-% to <25 wt .-%, in particular> 10 wt .-% to <20 wt .-%, of Solvents, in particular wherein the sum of the constituents of the starting material 100 wt .-% results.

Furthermore, the starting material may comprise at least one or more additives, for example reducing and / or oxidizing agents.

For example, the starting material may comprise> 25 wt.% To <80 wt.% Of first particles and> 5 wt.% To <60 wt.% Of second particles or of second and third particles in total, in particular the sum of the constituents of the starting material gives 100% by weight. Furthermore, the starting material may comprise> 5% by weight to <25% by weight of solvents and / or> 0.1% by weight to <10% by weight of additives, in particular where the sum of the constituents of the starting material is 100% % By weight. The starting material is preferably provided as a paste. The viscosity of the paste is significantly adjustable by the admixed solvent. Likewise, it is advantageous to provide the starting material in the form of a tablet or as a shaped body, in particular as a flat shaped body. In this case, the paste-like starting material is placed in a mold or applied to a film. Subsequently, the solvent is expelled by means of a temperature treatment from the starting material. Here, in particular, a solvent can be provided which can be expelled without residue even at a temperature in the range of or below the sintering temperature of the starting material. The starting material formed in this way can also be manufactured as a major benefit, which is then cut into small application-specific shaped bodies.

In principle, the first, the second, the third and the further coatings of the first, second and / or third particles contained in the starting material can be carried out by means of known coating methods. These can be taken from known technical literature. By way of example, mention may be made of chemical and physical coating methods, such as, for example, chemical or physical vapor deposition.

With regard to further features and advantages of the starting material according to the invention, reference is hereby explicitly made to the explanations in connection with the use according to the invention, the sintered compound according to the invention, the electronic circuit according to the invention, the method according to the invention and the figures.

Another object of the present invention is the use of elemental silicon, silicon oxide, silicon carbide, aluminum nitride, silicon nitride, aluminum oxide, metallic tungsten, metallic molybdenum, metallic chromium, metallic platinum, metallic palladium, boron carbide, beryllium oxide, boron nitride and combinations to reduce the thermal expansion coefficient α of a starting material of a sintered compound or a sintered compound, in particular in a sintering paste, a sintering powder or a Sintermaterialvorformkörper. With regard to further features and advantages of the use according to the invention, reference is hereby explicitly made to the explanations in connection with the starting material according to the invention, the sintered compound according to the invention, the electronic circuit according to the invention, the method according to the invention and the figures.

Another object of the present invention is a sintered compound of a starting material according to the invention.

Previous experiments show that a sintered bond formed from such a starting material advantageously has a thermal expansion coefficient α at 20 ° C in a range of> 3-10 ^"6 K ^{" 1} to <15-10 ^"6 K ^{" 1} , for example> 3-10 ^"6 K ^{" 1} to <10-10 ^"6 K ^{" 1} , in particular of> 3-10 ^"6 K ^{" 1} to <7-10 ^"6 K ^{" 1} . Sintered compounds with such a low thermal expansion coefficient can not be achieved by the conventionally used silver pastes, which usually have a coefficient of thermal expansion α at 20 ° C by 19.5-10 ^"6 K ^{" 1} , and are of particular interest for the semiconductor technology, since this often joining partner are joined together by means of sintered connections, on the one hand, such as chips, a very low linear expansion coefficient, for example of about 3-10 ^"6 ^{K" 1,} and on the other hand, for example, metallic circuit substrate, a very high linear expansion coefficient, for example of about 16 , 5-10 ^"6 K ^{" 1} , which is one of the main causes of thermal stress cracking. By means of the second particles, the coefficient of thermal expansion can advantageously be set such that this coefficient lies between the coefficients of thermal expansion of the joining partners to be connected via the sintered layer, for example between 16.5-10 ^"6 K ^{" 1} (circuit carrier) and 3-10 ^"6 K ^{". 1} (chip) is located. Thus, thermo-mechanical stresses between the joining partners and the sintered connection, which can lead to crack formation in the joining partners during thermal cycling, can advantageously be significantly reduced. The sintered compound formed from the starting material according to the invention can also advantageously a relatively high thermal conductivity, measured at 20 ° C and 50% humidity, of

> 100 Wm ^"1 K ^{" 1} . This is in particular to increase the performance density of semiconductor chips advantageous. In particular, the addition of elemental silicon, the cracking can be well countered, since elemental silicon has a particularly advantageous effect on the elasticity of the sintered compound due to its low Young's modulus. In addition, the sintered compounds according to the invention can advantageously achieve an electrical conductivity which is only slightly lower than that of pure silver.

Preferably, the proportion of second particles is adjusted such that the coefficient of thermal expansion a _{s of} the sintered compound layer at 20 ° C is less than or equal to the thermal expansion coefficient a _F i of a first (connected by the sintered connection) joining partner at 20 ° C and greater than or equal to the thermal Linear expansion coefficient a _{F2 of} a second (connected by means of the sintered connection) joining partner at 20 ° C.

In the context of one embodiment, the proportion of second particles in the starting material is adjusted such that the thermal expansion coefficient a _s of the sintered connection respectively of the central portion of the sintered compound ranges: a _F2 + 0.2 (a _F ra _F2) ^ a _s ^ a _F2 + 0.8 (a _F ra _F2), in particular a _F2 + 0.25 (a _F ra _F2) ^ a ^ a _s 0.75 + _F2 (a _F ra _F2) is located, wherein a _F i is the coefficient of linear expansion of a first joining partner and a _F _{2 is} the coefficient of linear expansion of a second joining partner and a _F i> a _F2 . Thus, advantageously, cracking under thermal cycling can be significantly reduced.

Within the scope of a preferred embodiment, the proportion of second particles in the sintered compound increases stepwise or continuously from one boundary layer to a first joining partner having a greater coefficient of linear expansion in the direction of a boundary layer with a second joining partner having a smaller thermal coefficient of linear expansion, or vice versa Particles in the sintered compound gradually or continuously from a boundary layer with a first joining partner with a smaller coefficient of linear expansion in the direction of a boundary layer with a joining partner with a larger thermal expansion coefficient. Thus, advantageously, the differences between the thermal expansion coefficients between each other contact the boundary layers and thus the cracking under thermal cycling are particularly advantageous minimized. Such a gradient can be produced, for example, by applying a plurality of sintered paste layers with a sinking or increasing proportion of second particles, for example by a printing process.

With regard to further features and advantages of the electronic circuit according to the invention, reference is hereby explicitly made to the explanations in connection with the starting material according to the invention, the sintered compound according to the invention, the use according to the invention, the method according to the invention and the figures.

Another object of the present invention is an electronic circuit with a sintered connection according to the invention.

With regard to further features and advantages of the electronic circuit according to the invention, reference is hereby explicitly made to the explanations in connection with the starting material according to the invention, the sintered compound according to the invention, the method according to the invention and the figures.

The invention further relates to a method for forming a thermally and / or electrically conductive sintered compound. The starting point here is a starting material according to the invention.

The starting material can be brought between two joining partners. Preferred joining partners are electrical and / or electronic components with contact points, which are brought into direct physical contact with the starting material.

Preferably, the proportion of second particles is set such that the thermal expansion coefficient a _{s of} the sintered compound layer at 20 ° C is less than or equal to the coefficient of thermal expansion a _F i of a first joining partner at 20 ° C and greater than or equal to the thermal expansion coefficient a _F 2 of a second Joining partner at 20 ° C is. In one embodiment, the proportion of second particles is adjusted such that the coefficient of thermal expansion a _{s of} the sintered compound or of the middle region of the sintered compound is in a range: a _F 2 ⁺ 0.2- (a _F i-a _F 2) ^ a _s ^ a _F2 + 0.8- (a _F ra _F2 ), in particular a _F2 + 0.25- (a _F ra _F2 ) ^ a _s ^ a _F2 + 0.75- (a _F ra _F2 ), where a _F i is the coefficient of linear expansion of a first joining partner and a _F _{2 is} the coefficient of linear expansion of a second joining partner and a _F i> a _F2 . Thus, advantageously, cracking under thermal cycling can be significantly reduced.

Within the scope of a preferred embodiment, the proportion of second particles in the sintered compound increases stepwise or continuously from one boundary layer to a first joining partner having a greater coefficient of linear expansion in the direction of a boundary layer with a second joining partner having a smaller thermal coefficient of linear expansion, or vice versa Particles in the sintered compound gradually or continuously from a boundary layer with a first joining partner with a smaller coefficient of linear expansion in the direction of a boundary layer with a joining partner with a larger thermal expansion coefficient. Thus, advantageously, the differences between the thermal expansion coefficients between contacting boundary layers and thus the cracking under thermal cycling can be minimized particularly advantageous.

Such a gradient can be produced, for example, by applying a plurality of sintered paste layers with decreasing or increasing proportion of second and / or third particles, for example by a printing process. Here, the starting material can be applied in the form of a printing paste, for example by means of screen or stencil printing on the contact points. Likewise, the order is possible through injection or dispensing.

Another possibility remains to arrange the starting material as a shaped body between the joining partners.

Subsequently, the sintered compound is formed by a temperature treatment of the starting material. For example, a processing temperature of <400 ° C, preferably from

<300 ° C, in particular of <250 ° C, are provided. Optionally, this is done under pressure to improve the sintering process. As process pressure, a pressure <10 MPa is provided, preferably <4 MPa or even

<1, 6 MPa, more preferably <0.8 MPa. Insofar as the reducing agent was not used stoichiometrically, but in excess, excess reducing agent can be completely burned out under the condition of sufficient oxygen supply, for example under an air atmosphere. Bonding partners with contact points made of a noble metal, for example gold, silver or an alloy of gold or silver, are preferably provided.

In an alternative possibility of the method according to the invention, the sintered compound is formed in vacuo and / or under a nitrogen atmosphere. Since in this case excess reducing agent can not be burned, a starting material is to be provided in which the proportion of the starting material, in particular to be reduced, organic or inorganic metal compound in the second coating to the proportion of the reducing agent in the starting tool in a stoichiometric ratio. During the temperature treatment, the reducing agent is therefore completely used up. In addition, the organic or inorganic metal compound is completely converted to the metallic form. Advantageously, joining partners with a non-noble-metal-containing contact point, which is made of copper, for example, may also be provided in this process alternative. Thus, cost-effective electrical and / or electronic components can be used.

With regard to further features and advantages of the method according to the invention, reference is hereby explicitly made to the explanations in connection with the starting material according to the invention, the use according to the invention, the sintered connection according to the invention, the electronic circuit according to the invention and the figures.

Drawings and examples Further advantages and advantageous embodiments of the subject invention are illustrated by the drawings and explained in the following description. It should be noted that the drawings have only descriptive character and are not intended to limit the invention in any way. Show it

Fig. 1 is a schematic plan view of particles of an inventive

Starting material of a sintered compound according to a first embodiment, which comprises first and second particles;

Fig. 2 is a schematic plan view of particles of an inventive

Starting material of a sintered compound according to a second embodiment, which comprises first, second and third particles;

4a-f schematic cross sections through embodiments of first particles;

5a-e schematic cross-sections through embodiments of second particles;

Fig. 6a, b are schematic cross-sections through embodiments of third particles;

7 shows a schematic cross section through a first embodiment of the invention electronic circuit;

8 shows a schematic cross section through a second embodiment of the invention electronic circuit. and

9 shows a schematic cross section through a sintering furnace in the production of a sintered connection or electronic circuit according to the invention.

In the figures, the same components and components with the same function with the same reference numerals.

FIG. 1 schematically shows first particles 10 and second particles 20, which in a first embodiment are provided in a starting material according to the invention of a sintered connection. FIG. 1 illustrates that the first 10 and second 20 particles are substantially the same size. Preferably, the first 10 and second 20 particles have a particle size distribution which is as similar as possible. In particular, the D ₅₀ value of the second particle 20 is greater than or equal to half the D ₅₀ value of the first particles 10 and Such a relation of the particle size distribution of the first 10 and second 20 particles has proved to be particularly advantageous since a higher fines content of second particles have an adverse effect on the sintering of the first particles can, wherein a higher coarse fraction of second particles can lead to large inhomogeneities and, accordingly, to macroscopic variations in the material properties within the sintered compound.

FIG. 2 schematically shows first 10, second 20 and third 30 particles which, in a second embodiment, are provided in a starting material according to the invention of a sintered connection. In the embodiment shown, these are also substantially the same size and have a similar particle size distribution.

In the context of the embodiments illustrated in FIGS. 1 and 2, the starting material may comprise metal-containing, first particles 10 of one or more configurations shown in FIGS. 3 a to 3 f. By way of example, the first particles 10 may be noble-metal and / or copper-containing, in particular silver-containing, particles. For easier understanding, the figures are explained below on the basis of silver-containing first particles 10.

FIG. 3 a shows a first particle 10, which is formed from silver in metallic form.

FIG. 3b shows a first particle 10 which is formed from an organic or inorganic silver compound, for example silver carbonate (Ag ₂ C0 ₃ ) and / or silver oxide (Ag ₂ O, AgO), which can be converted into metallic silver by a temperature treatment.

FIG. 3c shows a first particle 10, which has a particle core 1 1 of silver in metallic form and a first coating 12 made of an organic or inorganic silver compound, for example silver carbonate and / or silver oxide, applied thereon, which can be converted into metallic silver by a temperature treatment is. FIG. 3d shows a first particle 10, which has a particle core 1 1 of silver in metallic form and a first coating 12 made of an organic or inorganic silver compound, for example silver carbonate and / or silver oxide, applied thereon Silver is convertible. In addition, the particle 10 shown in FIG. 3d has a further coating 13 applied to the first coating 12, which contains a reducing agent, for example a fatty acid, by means of which the reduction of the organic or inorganic silver compound to metallic silver can be carried out.

FIG. 3 e shows a first particle 10 which has a particle core 1 1 made of silver in metallic form and a first coating 12 containing a reducing agent, for example fatty acid, wherein the reducing agent is used to reduce an organic or inorganic silver compound, for example silver carbonate and / or silver oxide, to metallic silver is feasible. The organic or inorganic silver compound may be part of another first 10, second 20 or third 30 particles.

FIG. 3f shows a first particle 10 which has a particle core 1 1 made of an organic or inorganic silver compound, for example silver carbonate and / or silver oxide, which can be converted into metallic silver by a temperature treatment. Moreover, the first particle 10 has a first coating 12 applied to the particle core 11, which contains a reducing agent, for example fatty acid, by means of which the reduction of the organic or inorganic silver compound to metallic silver of metallic silver can be carried out.

FIG. 4 a shows a second particle 20 whose particle core is formed from a material which has a low thermal coefficient of linear expansion α at 20 ° C. of <10 10 ^-6 K ^-1 , in particular of 10 10 ^-6 K ^-1 . These may be, for example, elemental silicon, silicon oxide, silicon carbide, aluminum nitride, silicon nitride, aluminum oxide, metallic tungsten, metallic molybdenum, metallic chromium, metallic platinum, metallic palladium, boron carbide, beryllium oxide and / or boron nitride. In addition, these materials advantageously also have a good thermal conductivity A ₂ o _/ so at 20 ° C and 50% humidity of> 50 Wm ^"1 K ^" \, in particular of> 100 Wm ^" ¹ K ^{" 1} , which is particularly advantageous for increasing the power density of semiconductor chips.

Figure 4b shows a second particle 20, which comprises a particle core 21 of a material having a low coefficient of thermal expansion α at 20 ° C of <10 10 ^"6 ^{K" 1,} in particular <10 10 ^"6 K ^'1. In this case, a second coating 22 of silver, platinum or palladium in metallic form is applied to the particle core 21.

FIG. 4c shows a second particle 20 which has a particle core 21 made of a material with a low thermal coefficient of linear expansion α at 20 ° C. of <10 10 ^-6 K ^-1 , in particular of <10 10 ^-6 K ^-1 . In addition, the particle 20 has a second coating 22 of an organic or inorganic silver compound, for example silver carbonate and / or silver oxide, applied to the particle core, which is convertible into metallic silver by a temperature treatment.

FIG. 4 d shows a second particle 20, which has a particle core 21 made of a material with a low thermal expansion coefficient α and a second coating 22 applied thereto, which contains a reducing agent, for example fatty acid, by means of which the reduction of an organic or inorganic silver compound, for example, silver carbonate and / or silver oxide, which is part of another first 10, second 20 or third 30 particle, to metallic silver is feasible.

FIG. 4 e shows a second particle 20, which has a particle core 21 made of a material with a low thermal expansion coefficient and a second coating 22 made of an organic or inorganic silver compound, for example silver carbonate and / or silver oxide, applied thereto Silver is convertible. Moreover, the particle 20 shown in FIG. 4e has a further coating 23 applied to the second coating 22, which contains a reducing agent, for example a fatty acid, by means of which the reduction of the organic or inorganic silver compound to metallic silver can be carried out. FIG. 5a shows a third particle 30 which contains a metal, for example tin, which forms an alloy with silver by means of a temperature treatment and / or has a lower melting point than metallic silver.

FIG. 5b shows a third particle 30, which has a particle core 31 made of a metal, for example tin, which forms an alloy with silver by means of a temperature treatment and / or has a lower melting point than metallic silver. In addition, the third particle shown in FIG. 5b has a third coating 32, applied to the particle core 31, of an organic or inorganic silver compound, for example silver carbonate and / or silver oxide, which can be converted into metallic silver by a temperature treatment.

FIG. 6 shows a first embodiment of an electronic circuit 70, which has a substrate 65 with at least one contact point 66. By means of a sintered connection 100 'produced from a starting material 100 according to the invention, the contact point 66 of the substrate 65 is connected to a contact point 61 of a chip 60.

FIG. 7 shows a second embodiment of an electronic circuit 70, which has a first substrate 65 with at least one contact point 66. By a first sintered connection 100, which is produced from a starting material 100 according to the invention, the first contact point 66 of the first substrate 65 is connected to a first contact point 61 of a chip 60. A second contact point 61 'of the chip 60 is in turn connected to a contact point 66' of a second substrate 65 'by a second sintered connection 100, which is also produced from the starting material 100 according to the invention.

FIG. 8 shows a sintering furnace 80 and an electronic circuit 70 arranged in a process chamber 90 of the sintering furnace 80. The electronic circuit 70 has a substrate 65 with at least one first contact point 66 made of copper. On the substrate 65, a chip 60 is arranged with at least one second contact point 61 made of a silver alloy. Between the at least first contact point 66 made of copper and the at least second contact point 61 made of the silver alloy is an inventive starting material 100 as a paste applied. The starting material 100 contains proportionally a mixture of first 10 and second 20 particles according to the figures 1 to 4e.

In order to form a sintered connection 100 'between the at least first contact point 66 of the substrate 65 and the at least second contact point 61 of the chip 60, the electronic circuit 70 is subjected to a temperature treatment with the starting material 100 contained. To carry out the temperature treatment, the sintering furnace 80 contains a heating device within the process space 90. In the process space 90, for example, there is a vacuum or a protective gas atmosphere during the temperature treatment of the starting material 100.

The starting material 100 is applied, for example, as a paste in which the first 10 and second 20 particles and optionally the third particles 30 are present in dispersed form.

As a result of the temperature treatment of the electronic circuit 70, 100 physical and / or chemical reaction processes are triggered in the starting material. In this case, optionally contained reducing agent, for example a fatty acid, with an organic or inorganic silver compound, for example silver carbonate and / or silver oxide, already react at a temperature in the range or optionally below the sintering temperature of silver to metallic silver. By the above-described embodiments of the silver compounds containing particles, thereby a largely complete conversion into silver can be achieved.

The metal-containing first particles 10 sinter into an electrically conductive sintered structure. The second particles or their particle cores behave inertly. The coatings 12, 13, 22, 23, 31, 32 explained in connection with FIGS. 3 c to 5 b can assist sintering within the sintered structure. The elementary material of the second particles 20 is after the formation of the sintered compound 100 'finely distributed within the metallic silver matrix of the sintered structure 100' before. In addition, third particles 30 can also be sintered in the silver matrix according to FIGS. 5a and 5b. The third particles 30, for example tin, optionally contained in the starting material 100 as a mixture with the first and second particles 10 and 20, melt prematurely during the temperature treatment and support a material contact of all the particles 10, 20, 30 contained in the starting material 100. In addition, the third particles 30 may form alloys with the constituents of the first 10 particles and optionally particle coatings 12, 13, 22, 32. These alloys are then present as ductile phases within the silver matrix formed in the sintered structure.

Likewise, contacting of the first and second contact points 61, 66 of the substrate or the chip 65 takes place by means of the formed sintered connection 100 '. Contacting of the first contact point 66 made of copper during the temperature treatment without corrosion phenomena is possible because the contacting takes place under vacuum or in a protective gas atmosphere he follows. As a result, a non-noble material, such as copper, for example, remains free of oxidation products even during the temperature treatment for forming the sintered connection 100 '.

Claims

claims

1 . Starting material (100) of a sintered compound (100 '), comprising

- Metal-containing first particles (10) and

second particles (20),

characterized in that

the second particles (20) at least partially contain a particle core material (21) whose thermal expansion coefficient α at 20 ° C is less than the thermal expansion coefficient α at 20 ° C of the metal or the metals of the first particles (10) in metallic form,

and

wherein the D ₅₀ value of the second particles (20) is greater than or equal to half the D ₅₀ value of the first particles (10) and less than or equal to twice the D ₅₀ value of the first particles (10).

2. Starting material according to claim 1, wherein the thermal expansion coefficient α of the particle core material (21) at 20 ° C <10 10 ^"6 K ^{" 1} , in particular <7.5-10 ^"6 K ^{" 1} , preferably <5-10 ^{". 6} K ^"1 , is.

3. Starting material according to claim 1 or 2, wherein the D ₅₀ value of the second particle (20) is greater than or equal to half the D ₅₀ value of the first particle and less than or equal to 1, 5 times the D ₅₀ value of the first particle (10).

4. Starting material according to one of claims 1 to 3, wherein the particle core material (21) has a thermal conductivity A ₂ o / so at 20 ° C and 50% air humidity of> 15 Wm ^"1 K ^{" 1} or> 25 Wm ^"1 K ^" , preferably of> 50 Wm ^"1 K ^" ¹ , in particular of> 100 Wm ^"1 K ^{" 1} .

5. Starting material according to one of claims 1 to 4, wherein the particle core material (21) is a chemically inert and physically stable material.

6. Starting material according to one of claims 1 to 5, wherein the particle core material (21) is selected from the group consisting of elemental silicon, silicon oxide, silicon carbide, aluminum nitride, silicon nitride, aluminum oxide, metallic tungsten, metallic molybdenum, metallic chromium, metallic platinum, metallic Palladium, boron carbide, beryllium oxide, boron nitride and combinations, in particular elemental silicon, silicon dioxide, silicon carbide, aluminum nitride, silicon nitride, aluminum oxide, metallic molybdenum, metallic chromium, metallic platinum, metallic palladium and combinations thereof.

7. Starting material according to one of claims 1 to 6, wherein the particle core material (21) is elemental silicon and / or silicon dioxide, in particular amorphous elemental silicon and / or amorphous silicon dioxide.

8. Starting material according to one of claims 1 to 7, wherein the second particles (20) have a particle core (21) with a second coating applied thereto (22), wherein the second coating (22) comprises at least one metal which is selected from the group consisting of silver, platinum, palladium, gold, tin and combinations thereof.

9. Starting material according to one of claims 1 to 8, wherein the second particles (20) are spherical, in particular substantially round, for example, substantially spherical, particles.

10. Starting material according to one of claims 1 to 9, wherein the first particles (10) precious metal and / or copper-containing, in particular silver, are, in particular wherein the first particles (10) at least one metal, in particular at least one noble metal and / or copper , in particular silver, in metallic form and / or at least one organic or inorganic metal compound, in particular precious metal and / or copper compound, in particular silver compound, in particular wherein the organic or inorganic metal compound by thermal treatment in the at least one underlying metal in metallic form is convertible.

1 1. Starting material according to one of claims 1 to 10, wherein the first particles (10) have a particle core (1 1) with a first coating applied thereto (12).

12. Starting material according to one of claims 1 to 1 1, wherein the starting material (100), based on the total weight of the constituents,

> 5 wt .-%, in particular> 10 wt .-%, for example> 20 wt .-% or

> 25 wt .-%, and / or <60 wt .-%, in particular <50 wt .-%, of second particles (20) and> 25 wt .-% to <80 wt .-% of first particles (10 ).

13. sintered connection (100 ') of a starting material according to one of claims 1 to 12.

14. sintered connection (100 ') according to claim 13, wherein the proportion of second particles (20) is set such that the coefficient of thermal expansion a _{s of} the sintered compound (100') or the central region of the sintered compound (100 ') in a range: a _F2 + 0.2- (a _F i-a _F 2) ^ a _F 2 ⁺ 0.8- (a _F i-a _F2 ), where a _F i is the linear expansion coefficient of the first joining partner (65) and a _{F2 is} the coefficient of linear expansion of the second joining partner and a _F i> a _F2 ,

in particular wherein the proportion of second particles (20) in the sintered compound (100 ') stepwise or continuously from a boundary layer (66) with the first joining partner (65) with the larger coefficient of linear expansion a _F i towards a boundary layer (61) with the second joining partner (60) increases with the smaller thermal expansion coefficient.

15. An electronic circuit (70) with a sintered connection (100 ') according to claim 13 or 14.

16. A method for forming a thermally and / or electrically conductive sintered connection (100 '), wherein a starting material (100) of the sintered connection (100') is provided according to one of claims 1 to 12, comprising the following steps:

- Providing the starting material (100) - Forming the sintered connection (100 ') by a temperature treatment of the starting material (100).