Process for producing particles and articles having engineered physical properties and for coating an object, as well as resulting particles and articles

The invention relates to a process of producing particles and articles with physical properties designed and covering an object, as well as to particles and resulting articles.

More specifically, the invention relates to a process for designing intrinsic properties, of particles and of producing articles with physical properties designed, manufactured by particle consolidation and to coatings formed from particles, in particular to the production of articles and coatings designed for to have preselected thermal conductivity and thermal expansion coefficients that correspond to those of the materials to which these articles and coating are attached.

According to Lacce's "Mixing Rules", the intrinsic physical properties (for example, thermal conductivity, coefficient of thermal expansion) of a heterogeneous article, composed of at least two well-mixed materials, tend to vary approximately linearly with the volume ratio of a material. , compared to the volume of the other material. For example, a heterogeneous article, composed of a mixture: 5D / 50, in volume percent, of a material having a low coefficient of thermal expansion and another material having a high coefficient of thermal expansion is expected to have a coefficient of thermal expansion that is the average of the coefficients of expansion of the two materials.

In a known process for manufacturing heterogeneous articles, a mixture of two metal powders, which have different thermal conductivities and different thermal expansion coefficients, is compacted and sintered to produce the article. The article has a projected coefficient of thermal expansion, which roughly corresponds to the coefficient of thermal expansion of an object to which the article is designed to be attached and a projected conductivity.

A process is also known which produces a metal matrix with particles of another metal, dispersed, with a low coefficient of expansion (ferrous) to obtain a composite with a coefficient of expansion much lower than of the matrix, the particles of the first material being from Ni-Fe, in a certain proportion, these particles can be partially covered with copper and bonded by diffusion, in a continuous matrix, for example - by pressing and heating, the copper coating could be made by the electroless process ”, the particles can be of micron size, the composite material thus obtained can be included in a substrate with a predetermined expansion coefficient with copper matrix, attached to a semiconductor device, (US 4894293)

Also known is a process for making diamond abrasive particles, coated with a metal compound or metal carbide chemically bonded to the diamond particles, (US 4063907), a process for making thermally conductive particles, such as coated aluminum nitride. copper, embedded in polymeric resin to create a heat-conductive heat dissipation adhesive for integrated circuits (US 5288769), a process that produces a mass of electroconductive particles of Co, Ni, Fe or their alloys coated with carbide, boride or silicon and turned into a resin matrix (US 4218507), a process that produces micronized metal or ceramic particles coated with Ag, Au, Cu, Ni, Fe, Co, Al, etc. or combinations thereof, for example: W-carbide coated with Cu, Ni, Al, or V and a matrix: ceramic - metal of such particles consolidated by pressure and / or heat in inert or reducing atmosphere, (US 5184662) ,

EN 117240 Bl a process that makes a hard body, partially sintered, with ceramic particles coated with Fe or Al alloy (US Pat. No. 5118342), a process that produces abrasive particles of silicon carbide coated with a layer of nitride or metal carbide , deposited in a vapor state (US 4505720), as well as a process which 50 makes diamond particles coated with a surface of silicon carbide by plasma or catalytic deposition, the particles thus coated can be deposited on a substrate on which a metallic alloy is bonded to which they are metallurgically bonded, then being coated by the substrate alloy, for example - by electrolytic growth of the alloy coating around the particles, (US 5277940). 55

The problem that arises consists in finding a process for the realization of particles with physical properties designed by covering particles of a material with one or two materials that allow a maximum variety of combinations of such component materials and the production of articles and of coatings with projected physical properties, in a wide variety. 60

The process according to the invention solves this problem, by a succession of coating phases of a particle made of a first material with a second material, so that the ratio between the volume of the coating and the volume of the particle is essentially equal to a certain volume fraction. The first and second materials and the volume fraction are chosen so that the coated particle has at least a certain intrinsic property 65 which is in accordance with the intrinsic properties of the first and second materials. The first material is, for example, tungsten, molybdenum, graphite, silicon carbide or diamond. The second material is, for example, copper. By this process, a coated particle is manufactured which has one or more intrinsically designed properties (such as thermal conductivity or thermal expansion coefficient) 70 that are different from the intrinsic properties of the first or second materials.

In another aspect, the invention provides a process for manufacturing an article of coated particles. A plurality of coated particles (possibly mixed with other particles) are consolidated so that all the particles are joined together to form an article. The article as a whole has a certain volume fraction, depending on the volumes of the second material in the composition of the coated particles relative to the volumes of the first material in the composition of the coated particles. Preferred embodiments include the following characteristics: the first material, the second material, and the volume fraction are chosen to design the article so that it has a certain intrinsic property, which is in accordance with the intrinsic properties of the first and the second the second material. In particular, the intrinsically designed properties of the coated particles have a high degree of uniformity and isotropy in the article, because each particle is uniformly coated and because the distribution of different materials is not random and there is no separation between different materials in 85 articles. In one embodiment, the article is designed to have a coefficient of thermal expansion, which essentially corresponds to that of an object to which the article is to be attached. The article is also designed to have the desired thermal conductivity. The coated particles are consolidated by compacting and sintering in solid phase or liquid phase. Sintering causes the second material to form bonds between adjacent particles.

In another aspect of the invention, there is represented a process for manufacturing an article of a plurality of particles, which includes a first material and a matrix material, which includes a second material which reacts with the first material. . A pre-coating is formed on the surfaces of the particles. The particles and matrix material are consolidated to make the particles and matrix material merged into one article. Pre-coating the particle surfaces prevents the first and second materials from reacting with each other.

In another aspect, the invention shows the coating of an object with a layer of coated particles.

The coated particles are placed in a liquid and the object is coated with a coating that includes the plurality of particles that have been placed in the liquid. The coating has a certain volume fraction, according to the volume of the second material in each coated particle relative to the volume of the first material.

In another aspect, the invention provides a method for coating an object with particles including a first material, a second material. The particles are placed in the liquid and the object is coated with a coating that includes the particles and the second material. The coating has a certain volume fraction, representing the volume of the second material, in the mentioned coating, relative to the volume of the first material in the coating. The first material, the second material and the volume fraction are chosen so that the coating has at least a certain physical property, for example - thermal conductivity or coefficient of thermal expansion (as opposed to mechanical properties such as tensile strength) . The chosen physical property, of the coating, depends on the physical properties of both the first and the second material.

In another aspect, the invention presents a process for the manufacture of an article, by compacting the coated particles at a certain density and shape.

The compacted particles are joined together to form an article, without increasing the density of the compacted particles and without substantially changing the chosen shape of the article. That is, the particles are compacted to about "total density" (a density at which the compacted particles have a porosity that does not provide interconnected passes that pass from one side of the article to the other). Then the compacted article is sintered. Because the article has full density, sintering does not increase the density of the article or change its shape. The density of the article and thus the final dimensions of the article can be strictly controlled during compaction.

In another aspect, the invention provides the manufacture of an article of particles, in a controlled manner, to make the article of a certain density. The particles, of which at least some include a first material and have surfaces on which a coating is formed, which includes a second material, are consolidated which leads to their union to form the chosen density article. The first and second materials are chosen such that the article has a certain intrinsic property, and the density is so chosen that the intrinsic property presents the behavior designed as a function of temperature. For example, the degree of linearity of the coefficient of thermal expansion of an article consisting of consolidated particles depends on the density of the article. By selecting and controlling the density of the article, the behavior of the coefficient of thermal expansion, as a function of temperature, is controlled and, in general, the choice of the coefficient of thermal expansion is refined.

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In another aspect, the invention provides the manufacture of an article of particles, the article having two or more portions having inherently different properties. A first plurality of particles includes at least one material and a second plurality of particles includes at least one other material. The first plurality of particles and the second plurality of particles are consolidated to merge the first plurality of particles together, to form a first portion (for example a layer) of an article and the second plurality of particles is joined. to form the second part of the article; the particles disposed near the interface between the first and second article portions are joined. The first and second portions of the article present certain intrinsic, different properties - depending on the compositions (and volume fractions) of the particles. For example, the first and second portions may have different coefficients of thermal expansion, and the article may be directly linked between two objects having different coefficients of thermal expansion that correspond to the coefficients of thermal expansion of the two portions. There is a single border (placed at the interface between the two portions of the article) at which there is a mismatch of thermal expansion and not a series of such grace arranged between the consecutive layers of the different articles. The bonds between the particles tend to absorb the demand of the thermal expansion and consequently the cracking or delamination at the joint between two portions is avoided.

The invention presents the advantage that it allows the realization of a wide variety of articles and coatings with physical properties, designed, obtained according to the process according to the invention.

The invention is further illustrated in connection with FIG. 1 ... 12, which represents:

FIG. 1 is a cross-section of a coated particle according to the invention;

FIG. 2, the consolidation of the coated particles of fig. 1, by compaction;

FIG. 3, a coated particle layer of FIG. 1, plated on a surface of an article;

FIG. 4, electronic housing including a flat surface structurally and thermally combined, made from coated particles of fig. 1, and guide frames made of coated particles of fig. 1;

FIG. 5, graph showing the expansion of an article as a function of temperature at densities of 90%, 95% and 100%;

FIG. 6, the consolidation of two distinct layers of coated particles from fig. 1 through tapping;

FIG. 7, an electronic hydride housing, used to include integrated circuits, which is made of coated particles of FIG. 1;

FIG. 8, electronic housing having a low temperature ceramic layer which is heated being disposed on a flat surface, structurally and thermally combined, pre-fabricated, made of coated particles of fig. 1;

FIG. 9, the compression mode of a high power semiconductor including a semiconductor device which is compressed at the interface with a heat distributor consisting of coated particles of FIG. 1;

FIG. 10 is a cross-section of a coated particle according to the invention, the particle having a thin interface pre-coating;

FIG. 11, coated particles according to FIG. 10 which are electrolytically co-deposited on an article together with the matrix material;

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FIG. 12, pre-coated particles that are electrolytically co-deposited on an article together with the matrix material.

According to the invention and the figures, in particular Figs. 1, the particle 12, which may have a diameter of several microns, and which includes a metal element a metal alloy, or a non-metal is covered with a cover 14 of a metal element, a a metal alloy or non-metal is coated with a coating 14 of a metal member, a metal alloy or a non-metal, to form the coated particle 10. The coated particle 10 has intrinsically designed physical properties (for example thermal conductivity or thermal expansion coefficient) and / or intrinsically designed mechanical properties (for example tensile strength). The intrinsic physical properties (excluding the intrinsic mechanical properties) of the coated particle 10 tend to behave according to Lacce's Rule of Mixtures, according to which the intrinsic physical properties vary approximately linearly with respect to the ratio of the coverage volume 14 to the volume of the particle 12. The mechanical properties may vary non-linearly with the ratio of the coverage volume 14 to the volume of the particle 12.

The coating 14 is applied adherently to particles 12, for example by non-electrical deposition "electroless" (a technique presented below). The intrinsic properties of the coated particle 10 are designed by controlling the volume fraction of the coating 14 relative to the particles 12, which can be achieved in two ways: by controlling the size of the particle 12, or by controlling the thickness of the coating 14. Particle 12 includes, for example, elemental tungsten, coating 14 includes elemental copper, and the volume fraction of copper to tungsten is 27% to 73%. Copper has a high thermal conductivity of approximately 391 W / mx K. (Watts per meter-Kelvin degree) and a relatively high coefficient of thermal expansion, about 17.5 ppm / ° C (parts per million per degree centigrade) in a temperature range from 25 ° C to 400 ° C, while tungsten has a relatively low thermal conductivity of about 164W / mx K and a low thermal expansion coefficient of about 4, 5 ppm / ° C in a temperature range from 25 ° C to 400 ° C .

The copper-coated tungsten particle 10 has a thermal conductivity of approximately 226W / m.gr.K at 25 ° C (intermediate between high thermal conductivity of copper and low thermal conductivity of tungsten] and a projected coefficient of thermal expansion of about 8, 2 ppm / ° C (intermediate between the low thermal expansion coefficient of tungsten and the high thermal expansion coefficient of copper] in a temperature range from 25 ° C to 400 ° C.

Referring to FIG. 2, a mold 16 is included, which includes the punch 18 and the shape 20, which is used to reinforce coated particles 10 in an article 22 by pressing, (coated particles 10 having properties designed as described in connection with FIG. 1). . The compacted article 22 is sintered in the solid phase (at a temperature below the melting point of the particles and the melting point of the particle coatings) or alternatively it is sintered in the liquid phase at a temperature above the melting point of the coatings but below the melting point of the particles. ). Sintering leads to particle bonding to provide a heterogeneous article. Particle coating thus serves as a "matrix material" (a material that holds the particles together, forming the article). Article 22 has intrinsically designed physical properties (for example thermal conductivity and / or coefficient of

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230 thermal expansion) and / or intrinsically designed mechanical properties (eg tensile strength) that correspond to those of the coated particles 10 of which the article is manufactured. The intrinsically designed properties of coated particles 10 are present with a high degree of uniformity and isotropy in Article 22, because each particle 10 is uniformly coated and because there is no random distribution of different materials or separation between different materials within Article 22.

Thus, the intrinsic properties of article 22 are designed at the particle level rather than at the article level. The article is, for example, a thermal and structural surface for electronic housings, the thermal and structural surface being designed to have a coefficient of thermal expansion corresponding to that of the object to which it is attached and designed to have a high thermal conductivity. According to the invention, in connection with FIG. 4, the copper-coated tungsten particles, for example, having a tungsten copper volume fraction of 27% to 73%, are compacted at a press of 16 to 200 t / square inch of surface to achieve total density ( above about 90% density), then the compacted coated particles are sintered in a solid state in a hydrogen atmosphere at 1950 degrees Farenheit for about an hour and a half. Not only that the coated particles 10 can be reinforced in an article as described above, but the coated particles can also be coated on the object as a coating. Referring to FIG. 3, a coating 28 of the coated particles 10 having projected properties is shown. The coating 28 is coated on a surface of a metal article, of a metallic or non-metallic alloy 30 through the cladding mask 29. Article 30 may alternatively be an article which is itself composed of particles coated by any of the technical variants presented. During coating, coated particles, for example - copper-coated tungsten particles having a tungsten copper volume fraction of 27% ... 73%, are placed in a liquid and the coating is formed on an article, e.g. - Beryllium, by one of the plating techniques discussed in detail below. Thus, it is possible to increase coverage directly on an article without having to create a link between the coverage and the article. The coating 28 has intrinsically designed physical properties (for example, thermal conductivity, coefficient of thermal expansion) and / or designed intrinsic mechanical properties (for example tensile strength) that correspond to those of the coated particles from which the coating is manufactured. The intrinsically designed properties of the coated particles exhibit a high degree of uniformity and isotropy in the coating 28, because each particle is uniformly coated and because there is no random distribution of the different materials or segregation between the different materials in the coating 28. Thus, the intrinsic properties of the coating 28 they are more designed at the particle level than at the coating level. The plating technique described above may also be implanted where the coating 28 does not include coated particles but consists of a mixture of different particles selected from two different materials in a suitable volume fraction. in FIG. 4 shows an electronic housing 32 which includes semiconductor devices 34 mounted on a substrate 35, the substrate 35 itself being supported by a flat thermal structural surface 36 formed by coated particles. Semiconductor devices 34

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EN 117240 Bl are for example high-power switches in solid state (such as those included in the circuit of an electric motor vehicle) and produces substantial amounts of heat during operation. Substrate 35, to which the semiconductor devices 34 are attached by an adhesive bond, diffusion bond, hard or soft weld, or bonding with hard fusible material, is formed of a material chosen to have a thermal expansion coefficient corresponding to approximately that of of the semiconductor devices 34 as known in the art, to facilitate the binding of the semiconductor devices 34 to the substrate 35. The structural surface 36 is made, according to the present invention, of coated particles. The particle material, the coating material and the volume fraction of the coating material relative to the particle material are chosen so that the structural surface 36 has a high thermal conductivity (to allow it to function as a heat distributor and a thermal plane) and yet has a coefficient of thermal expansion which essentially corresponds to the coefficient of thermal expansion of the substrate 35. Both the thermal conductivity and the coefficient of thermal expansion are very uniform and isotropic on the structural surface 36. Substrate 35 is formed, for example, of aluminum nitride having a coefficient of thermal expansion of about 4.4 ppm / ° C in the range 25 ° C up to at 4 ° C. The structural surface 36 is made of copper-coated graphite particles having a volume fraction of copper to graphite of 24% - 76%. This volume fraction provides a thermal conductivity of approximately 325 W / mx K, and a thermal expansion coefficient of about 4.3 ppm / ° C to 400 ° C), which corresponds closely to that of the aluminum nitride substrate 35. The copper matrix material provides good tensile strength (an intrinsic mechanical property) of the structural surface 36. Alternatively, the structural surface 36 is made of copper coated diamond particles having a volume fraction of copper to diamond of 20% to 80%. This volume fraction provides a thermal conductivity of approximately 781 W / mx K and a thermal expansion coefficient of about 4.8 ppm / ° C (from 25 ° C to 400 ° C). Alternatively, substrate 35 is made of beryllium oxide (BeO) having a coefficient of thermal expansion of about 7.6 ppm / ° C, (25 ° C to 400 ° C). The structural surface 36 is made of copper-coated graphite particles having a volume fraction of copper to graphite from 42% to 58%. This volume provides a thermal conductivity of approximately 380 W / mx K and a thermal expansion coefficient of approximately 7.6 ppm / ° C, from 25 ° C to 400 ° C) which corresponds closely to that of beryllium oxide in the substrate. 35. Alternatively, the structural surface 36 is composed of copper-coated diamond particles having a volume fraction of copper to diamond of 37% to 63%. This volume provides a thermal conductivity of about 698 W / mx K and a coefficient of thermal expansion of about 7.6 ppm ° C (from 25 ° C to 400 ° C). Alternatively, the structural base surface 36 is composed of copper-coated tungsten particles having a volume fraction of copper to tungsten of about 27% to 73%. This volume fraction leads to a thermal conductivity of approximately 226 W / mxK and a coefficient of thermal expansion of approximately 8.2 ppm / ° C, (from 25 ° C to 400 ° C). The structural surface 36 is attached to the substrate 35 in the following manner. A thin layer of coated particles is first co-deposited on the lower surface of

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320 of the substrate 35 as shown in FIG. 3, according to the techniques described below, then the structural surface 36, which is compacted in the manner described above in connection with FIG. 2) but not yet sintered, it is placed in contact with the plated surface of the substrate 35. The structure is then sintered to make the substrate 35 and the structural surface 36 to merge into a single structure. Alternatively, the structural surface 36 is bonded to the plated substrate 35 by bonding with brass, hard or soft solder, diffusion, or adhesive bonding. The guide frames 38 to which the semiconductor devices 34 are attached via connecting wires 40 carrying electrical signals to the ground, supply and output to and from the semiconductor devices 34 are also made of coated particles according to the invention, having a coefficient of thermal expansion. corresponding essentially to the coefficient of thermal expansion of the substrate 35. Substrate 35 is formed, for example, of beryllium oxide (BeO) having a coefficient of thermal expansion of about 7.6 ppm / ° C (from 25 ° C to 400 ° C) and the guide frames 38 are made of particles of copper-coated nickel 42 (nickel 42 being a nickel alloy) having a copper volume fraction of nickel 42 from 20% to 80%, a thermal conductivity of approximately 86.78 W / m · K and a thermal expansion coefficient from about 8.1 ppm ° C (from 25 ° C to 40 ° C). It should be noted that the copper-coated nickel 42 must not have a thermal conductivity as high as that of the copper-coated graphite used on the structural surface 36 because the guide frames 38 are not designed to perform a heat distribution function. Alternatively, however, the guide frames 38 may be manufactured from the same types of coated particles from which the structural surface 36 is manufactured. The guide frames 38 are plated, by means of a plating table, directly on the upper surface of the substrate 35, according to the techniques described previously in connection with FIG. 3. In one embodiment, the guide frames 38 are sintered to achieve a desired density. Even with the energy levels, the thermal densities and the high operating frequencies characteristic of the new electronic technologies and the large and rapid temperature changes that generally occur during the operation of the semiconductor devices 34, breaks and exfoliation are not likely to occur at the joints between the substrate 35 and the guide frames 38 and between the substrate 35 and the structural surface 36 due to the uniformity and isotropy of the thermal conductivities and thermal expansion coefficients of the structural surface 36 and of the guide frames 38.

The overall location structure 32 therefore has a long service life. Not only that the inherently designed properties of the articles manufactured according to the techniques described above depend on the materials chosen for the particles and the coatings of the particles and on the basis of the volume fraction of the coating material relative to the material from which the particles are formed, but in addition the behavior of the intrinsic properties of such articles as a function of temperature (for example the degree of linearity of the coefficient of thermal expansion as a function of temperature) is affected by the densities of the articles. Thus, by controlling the density of such an article, the behavior of the thermal expansion coefficient of the article as a function of temperature can be made to approximate the thermal expansion coefficient of a ceramic material (which behaves nonlinearly with respect to temperature) in the critical process temperature ranges . Figure 5 illustrates the projected thermal expansion in

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RO 117240 Bl parts per million as a function of temperature, for articles made of copper-coated tungsten particles having a volume fraction of copper at tungsten from 27% to 73% (15% copper to 85% by weight) at densities of approximately 100% (theoretical density), 95% and 90% and for two ceramic materials (BeO and AI₂A₃) with which the expansion behavior of the article can be made to correspond within the critical process temperature limits by choosing the appropriate density. It should be noted that the degree to which the article expands (for example - the value of the coefficient of thermal expansion) decreases with decreasing density. The behavior of the thermal expansion coefficient (or the behavior of other properties such as thermal conductivity) can thus be chosen as a function of temperature, and in general the physical properties can thus be further refined, by choosing the density at which the article is manufactured. It should be noted that the properties of articles made from uncoated particles can also be controlled by choosing the densities at which the articles are manufactured.

The following are variants of the process for coating the particles and coating the articles with coated particles.

Referring to FIG. 1, the coating 14 is coated on particles 12 using any suitable "electroless" (self-catalytic) non-electric plating process. The particles to be coated are placed in an electroless bath "containing an aqueous solution of metal ions, one or more reducing chemical agents, a catalyst, one or more complexing agents and one or more bath stabilizers. The metal ions are autocatodically or chemically reduced to the metal by the reducing agent or agents, the reducing agent or agents acting as electron donors and the metal ions acting as electron acceptors. The catalyst accelerates the "electroless" reaction. The complexing agent or agents are used to control the pH of the solution and to control the amount of free metal ions available in the solution. Stabilizers provide as catalytic inhibitors to delay the spontaneous potential decomposition of the bath. In one embodiment, the particles to be coated are for example graphite, diamond or silicon carbide particles, the copper ions are provided by aqueous copper sulphate, the reducing agent is formaldehyde, the catalyst is palladium, the complexing agent is one or more of: sodium and potassium double tartrate, EDTA, (ethylenediaminetetraacetic), ammonium hydroxide, pyridium-3-sulfonic acid and / or potassium tartrate and the stabilizer is one or more of: thiodiglycolic acid, MBT, (methylenbistiocyanate), thiourea, cyanide, sodium and / or vanadium oxide. The "electroless" coating creates either a mechanical or a chemical bond between the coating 14 and the particle 12. The bond will, in general (but not always), be mechanical if the coating 14 or particle 12 are non-metallic and will be generally chemical if both the coating 14 and particle 12 are metallic.

Alternative particle coating processes include electrolytic plating, ion bombardment and spraying. Referring to FIG. 10, in some embodiments, wherein the coating 14 would only form a mechanical bond with the particle 12 if the coating 14 were "electroless" directly onto the particle 12, the particle 12 is pre-coated with an extremely thin layer 68 (the thickness, in figures, is exaggerated) by pre-coating material and then plated with coating 14. The pre-coating (an interface coating) 68 binds strongly to the particle 12 and the coating 14, creating a strong, hard to break, chemically bonded coated particle 10.

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For example, if the particle 12 is graphite or diamond and the coating 14 is copper, the coating 14 will form a mechanical bond with the graphite or diamond if the coating 14 is directly coated on graphite or diamond. Instead, a pre-coating 68 with a metal such as chromium or a cobalt-tungsten alloy, having a thickness in the range of 200 to several thousand Angstroms, is first coated on particle 12, the pre-coating 68 forming an adherent compound with particle 12 at the interface between the pre-coating 68 and particle 12.

Then the coating 14 is plated on the chromium or cobalttungsten 68 pre-coating, the pre-coating 68 forming a metallurgical bond with the coating 14. The pre-coating does not substantially affect the thermal conductivity or the thermal expansion coefficient of the coated particle 10 due to the fact that - The coating is extremely thin. In one embodiment, a small, controlled amount of a palladium or boron catalyst is co-deposited with a cobalt-tungsten coating material, the catalyst serving to accelerate the "electroless" reaction by which a copper coating 14 is placed on a 68 cobalt-tungsten pre-coating. A pre-coating is also used where the coating 14 reacts, corrodes or is destructive to particle 12 or vice versa, for example, if particle 12 is graphite or diamond or the coating 14 is aluminum, highly reactive aluminum will dissolve graphite or the diamond if the coating 14 were directly placed on the particle 12. instead a thin layer 68 of a metal such as chromium or cobalt-tungsten is first coated on particle 12 and then the coating 14 is deposited on the pre-coating 68 to form the coated particle 10. The pre-coating 68 forms a bond with particle 12 made of graphite or diamond, thus protecting particle 12 from the aluminum matrix material. Thus, the pre-coating 68 makes it possible to manufacture articles of coated particles when the particles and their coatings tend to react with each other. Pre-coating 68 also makes it possible to mix coated particles with a thin layer of pre-coating (but without coating 14) in a molten alloy, when the particles and the alloy would otherwise tend to react with each other. For example, graphite particles coated with a thin layer of cobalt - tungsten pre-coating are added to a vacuum aluminum alloy and the alloy containing particles is molded under pressure or extruded into a reticular (or near-reticular) article which in one embodiment is used as a thermal product for electronic devices (for example, a heat distributor and a thermal surface). The cobalt-tungsten pre-coating forms an adhesive bond with graphite particles and forms a metallurgical bond with the aluminum alloy. The volume fraction of the particles relative to the alloy (the particles consisting of up to about 50% by volume) is chosen to make the resulting article have physical properties designed as: thermal conductivity and coefficient of thermal expansion, alternatively, the pre-coated particles they are added to the alloy to mechanically strengthen the resulting article or to affect its weight.

The following are variants of the plating process for articles with coated particle coatings.

According to FIG. 3, an article 30 is coated with a coating 28 of coated particles 10 (article 30 being, for example, a guide frame). If Article 30 is a metal or metal alloy, the coating 28 is electronically placed directly on the article

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RO 117240 Bl by a technique described below. If Article 30 is non - conductive (de

455 however, article 30 is first coated with a thin coating of conductive material, as a matrix material with which the coated particles 10 are coated, using the electroless plating (autocatalytic - the technique described above in connection with particle coating). . The "electroless" bath includes an aqueous solution containing metal ions, one or more chemical reducing agents and one or more 460 many bath stabilizers, as mentioned. The metal ions are autocatalytically or chemically reduced by the reducing agent or agents, which causes the metal to be deposited on article 30. alternatively, the particles (either uncoated, pre-coated or coated) are placed in the aqueous solution and the metal coated particles are simultaneously plated on Article 30. Because the electroless plating is slower than

465 electrolytic plating, the coated particles 10 are electrolytically plated on the thin conductive layer (using the technique described below) as soon as the thin conductive layer is formed, thus forming the coating 28. Referring to FIG. 11, the coating 28 is plated on the conductive article 30 (or on a non-conductive metalized article with a thin conductive layer as described above) by using co-deposition

470 electrolyte of coated particles 10 and the matrix material from which coats 14 of coated particles 10 are formed, in article 30. whereas coated particles 10 (for example, graphite particles 12 coated with a thin coating 68 of chromium or cobalt interface) tungsten over which the copper coating is deposited 14) are plated on article 30, the matrix material is simultaneously plated on

475 the coated particles to fill the gaps between the coated particles, thus forming the coating 28.

Referring to FIG. 12, in an alternative electrolytic plating process, the matrix material and the particles 12 (which are coated with a pre-coating 68 as described above but are not yet coated with the matrix material) are co480 deposited on article 30. whereas the particles 12 are coated on article 30 the particles are simultaneously coated with the matrix material to form the coating 28. For example, the particles 12 are made of graphite, the matrix material is copper and the pre-coating material is a metal such as chromium or cobalt-tungsten. Alternatively, the coating 28 is formed on article 30 by ion bombardment or spraying 485 of the coated particles 10 on the article. The coating 28 is then sintered, after which the coating 28 presents its intrinsically chosen property or properties.

Further embodiments of particles and articles according to the invention result from the fact that there are numerous materials from which particles 12 and coating 14 of FIG. 1. Particles 12 may be made up for example of tungsten, 490 molybdenum, graphite, silicon carbide, diamond, nickel 42, KOVAR (Co - Ni - Fe alloy with 20 ... 40% Co) or a ceramic material and coating 14 it can be made of copper or aluminum for example. The coating may even be non-metallic, (for example - a glass, oxide, ceramic, resin, polymer, or other organic substance such as silicone), if the coating material is capable of melting to form the bond between particles 495 and if not the coating material , nor does the material from which the particles are formed melt at a lower temperature than that at which the coated articles are heated to cause the non-metallic coatings to melt together. The particles can be coated with such non-metallic coating by placing the particles in one

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500 slurry of the non-metallic material and then removing the particles from the slurry, the particles being sized so that when the coated particles are removed from the sludge they have a chosen volume fraction of coverage, relative to the particle material. The coated particles are then consolidated and / or heated, leading to the vitrification or melting of the coatings. Graphite and diamond are good materials for forming particles 12 when the manufactured article or coating must have a low coefficient of thermal expansion and a high thermal conductivity, because these materials not only have a low coefficient of thermal expansion (such as tungsten and molybdenum. ), but also relatively high thermal conductivity (as opposed to tungsten and molybdenum). Consequently, these materials have the advantage that they do not have the undesirable side effect of reducing the thermal conductivity of the coated particles and articles and of the coated particles. Where the article or coating manufactured must have a coefficient of thermal expansion that corresponds to that of a silicon semiconductor or an integrated circuit device to which the article or coating is directly linked (silica having a coefficient of thermal expansion of about 4, 2 ppm / ° C, the article or coating including, for example, copper coated diamond particles having a volume fraction of copper to diamond of about 20% to 80% or graphite particles of copper coated having a volume fraction of copper to graphite of about 24% to 76%.

It is possible to design many intrinsic properties, other than the thermal conductivity or the coefficient of thermal expansion. For example, the electrical conductivity of an article may be designed in combination with the design of other intrinsic properties. Thus, in one embodiment, the choice between the use of graphite particles that are electrically conductive) and diamond particles (which are electrical insulators) is based on the desired electrical conductivity of the article. Referring to FIG. 2, the particles 10 do not have to consist entirely of coated particles. Alternatively, a mixture of coated particles combined with other particles (for example, copper-coated tungsten particles combined with copper particles) can be well mixed then compacted to form an article 22 having intrinsic properties that are a function of fractions by volume of all the materials in the mixture, article 22 presenting the intrinsic isotropic properties. Alternatively, the coated particles are combined with materials having one or more intrinsic anisotropic properties, causing the article to exhibit one or more anisotropic properties as well. For example, coated particles are mixed with crystalline materials having properties that differ in different directions, the crystalline materials being mixed with coated particles in such a way that the crystalline materials tend to be oriented in a common direction. In another example, the coated particles are mixed with carbon fibers, the carbon fibers having to be oriented in a common direction. Carbon fibers provide a tensile strength that varies with direction. Alternative techniques for the manufacture of coated particles include metal injection molding, hot isostatic pressing (hipping), cold isostatic pressing (cipping), hot or cold isostatic forging, hot or cold rolling (which densifies the bound coated particles) and molding under pressure. If the coated particles 22 are compacted, they have a level 2 or level 3 or unknown porosity (a porosity that does not provide interconnected passes passing from one part of the article to the other) and the sintering process does not increase the density or not

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545 changes the shape of the article. The density of the article and thus the final dimensions of the article can be carefully controlled during pressing. It is especially practical to compact at full density when the particles include certain non-metals such as graphite because, for example, copper-coated graphite particles can be compacted to the total density at a relatively low pressure, from 60 to 80 t / square inch. When 550 particles are made of a metal or metal alloy (whether the particles are coated with a metal or not coated), pressures of about 80 to 200 tonnes per square inch are generally required for compacting full-density particles. Referring to FIG. 6, there is shown a molding press device 16, consisting of a punch 18 and a mold 20, which is used to tie two

555 distinct layers 24 and 26 of the particles by pressing to provide an article 25 having intrinsic properties that vary from layer to layer. Layers 24 and 26 consist of particles composed of different materials or having different volume fractions of the materials from which the particles are formed. Particles are not necessarily coated particles. The particles are inserted into the mold 20 in layers 24 and 26,

560 compacted to a certain density chosen to give intrinsic temperature-dependent properties (e.g., thermal conductivity and thermal expansion coefficient) as discussed in connection with FIG. 5 and sintered in a hydrogen atmosphere for about half an hour. Sintering causes the particles of layers 24 and 26 to bind to the interface between the two layers, to result

565 a unique, stratified article. For example, layer 24 includes copper-coated tungsten particles having a tungsten copper volume fraction of 27% to 73% and layer 26 includes elemental copper particles. The layer 24, after pressing, has a thermal conductivity of about 225.78 W / m gr.K and a thermal expansion coefficient of about 8.28 ppm / ° C. The layer 26, after compaction has a

570 a thermal conductivity of about 390 W / m K and a coefficient of thermal expansion about 18.04ppm / ° C. The stratified article 25 is directly connected between two objects having different thermal expansion coefficients that correspond to the thermal expansion coefficients of layers 24 and 26. For example, layer 24 is bonded to a beryllium ceramic and layer 26 is diffused through an absorbent medium.

575 heat, from copper.

Alternatively, layer 24 includes copper-coated diamond having a volume fraction of copper to diamond of 20% to 80% and layer 26 consists of copper-coated graphite having a volume fraction of copper to graphite of 24% to. 76%. After pressing, a silicon mold is bonded to a part of article 25 that corresponds to the layer 2480. Layer 24 has a thermal conductivity of approximately 78 W / m • K and a coefficient of thermal expansion of about 4.8 ppm / ° C between 25 ° C and 400 ° C, which essentially corresponds to the coefficient of thermal expansion of the silicon mold . Layer 24 is alternatively designated to be bonded to a beryllium oxide substrate, layer 24 having a diamond copper volume fraction of 37% to 585 63%, a thermal conductivity of approximately 698 W / mx K and a coefficient of thermal expansion of approximately 7.6 ppm / ° C, (25 ° C - 400 ° C), which essentially corresponds to the coefficient of thermal expansion of the beryllium oxide substrate.

Thus, the stratified article 25 is directly connected between two objects having different coefficients of thermal expansion. The boundary between different expansion coefficients

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590 The thermal element is located in the stratified article 25, more than at one or more interfaces between article surfaces and other devices. Moreover, there is a single border (located between the two layers of the stratified article, individually, 25), where the non-bearing of the thermal expansion coefficients is manifested, instead of a series of such borders located between the consecutive layers of the non-similar articles. Because the copper bonds between the particles are elastic and malleable, the copper bonds tend to absorb the stress of thermal expansion and consequently there are no breaks or exfoliation at the joint between the two layers. Moreover, because the bonds are elastic and because all the bonds are made of the same material (all are copper-copper bonds), the bonds tend to absorb such stresses and the article consequently does not tend to bend or undulate with large temperature changes. In another embodiment there are more than two layers of an article 25 and consequently there is more than one internal boundary at which there is a mismatch of the thermal expansion coefficients. The nonporting at each border is less than the nonporting that occurs when a single border in the stratified article 25. Referring to fig. 7, a hybrid electronic housing 72 is shown having sides 48, base 46 and lid 50, which is used as a housing for semiconductor integrated circuits and other electronic devices.

The hydride electronic housings are generally made of a nickel-iron alloy known as KOVAR, which has a coefficient of thermal expansion that is approximately equal to that of the glass insulators used to insulate the feeders 44 of the device from the KOVAR conductive housing. The application of the invention to the manufacture of the hybrid housing 72 depends on whether the conventional glass insulation is used to insulate the supplies 44 or whether alternative insulation is used. If a conventional glass insulation is used then the object is the manufacture of a hybrid housing having a coefficient of thermal expansion which essentially corresponds to that for KOVAR but having a higher thermal conductivity than that for KOVAR. For example, the hybrid housing can be made of iron-coated graphite particles having a graphite iron volume fraction of 26% to 74%, a thermal expansion coefficient of about 3.2 ppm / ° C at 25 ° C - 400 ° C, corresponding essentially to that of KOVAR and a thermal conductivity of about 295 W / mx K, which is higher than the thermal conductivity of KOVAR (about 11 W / mx K).

If a low-temperature ceramic glass is replaced by glass as a supply insulation, 44, then the hydraulic housing 72 is made, for example, of copper-coated graphite particles having a graphite copper volume fraction of 3% to 61%. This volume fraction provides a thermal conductivity of approximately 279 W / mx K and a thermal expansion coefficient of approximately 6.9 ppm / ° C, (between 25 ° C - 400 ° C), which is designed to correspond essentially the coefficient of thermal expansion of the ceramic glass material used to insulate the supplies 72. The coefficient of thermal expansion is very uniform in the hybrid electronic housing 72. Since the base 46 and the sides 48 of the hybrid electronic housing 72 can be manufactured cross-linked together as a single piece, compared to a KOVAR housing where the base 46 and sides 48 are generally processed separately from large pieces of KOVAR material), the housing 72 can be manufactured without the cost of processing or

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EN 117240 Weld the base 46 and the sides 48 together, although the cover 50 must be bonded to the sides 48 by soldering after the integrated circuits have been placed inside the housing. Referring to FIG. 8, an electronic casing 52 having a set of integrated circuits 54 is mounted on a low temperature ceramic glass substrate 56 placed on a thermal structural base surface 58. The structural surface 58 is made of copper-coated graphite particles having a volume fraction of copper to graphite from 39% to 61%. This volume fraction ensures a high thermal conductivity of approximately 379W / mx K, with high tensile strength and a coefficient of thermal expansion of approximately 6.9 ppm / ° C, (between 25 ° C - 400 ° C), which essentially corresponds to the coefficient of thermal expansion of the ceramic substrate. The coefficient of thermal expansion is very uniform and isotropic on the structural surface 58. The copper-coated graphite particles from which the structural surface 58 is manufactured are compacted at a density chosen to match the expansion behavior of the structural surface 58 with that of the substrate. ceramic 56. Then the coated particles are sintered. A raw-form ceramic substrate 56 (a ceramic substrate that has not yet been heated) is then deposited as a layer on the structural surface 58, after which the raw-form ceramic substrate 56 is heated. The ceramic substrate 56 has a heating temperature below the temperature at which the structural surface 58 is sintered in the solid phase. Consequently, when the ceramic substrate 56 is heated after being placed on the structural surface 58, the coatings of the particles on the structural surface do not melt. The pre-fabricated structural surface 58 ensures high manufacturing efficiency, providing a structural platform on which thin, fragile, ceramic and / or glass layers can be manipulated during the process, without breaking. Referring to FIG. 9, a high power semiconductor compression module 60 is provided which includes a silicon semiconductor device approximately the size of one half dollar or one silver dollar and having a thermal expansion coefficient of approximately 4.3 ppm / ° C. The semiconductor device 62 is coupled by compression to approximately 5000 pounds with a heat distributor 64 consisting of copper-coated graphite particles according to the invention. The semiconductor device 62 has an interior surface of molybdenum, having a low coefficient of thermal expansion, which is fixed to a heat distributor 66 of aluminum (which is not made of particles). The heat distributor 64, having a graphite copper volume fraction of 24% to 76%, is designed to have a high thermal conductivity of 379 W / mx K, and a coefficient of thermal expansion of 4.3 ppm / ° C (between 25 ° C - 400 ° C), which essentially corresponds to the thermal expansion coefficient of the semiconductor device 62, the thermal expansion coefficient being very uniform in the heat distributor 64. Designing the heat expansion coefficient of the heat distributor 64 extends the life of the semiconductor device 62 by preventing the formation of grooves in the semiconductor device 62 by compressing the heat distributor 64 with the interface, which could create a short circuit.

Those skilled in the art can use in many ways and can make many modifications to and from the specific embodiments described, without departing from the meaning of the invention. For example, the principles of the invention can be applied to other fields as weapons

EN 117240 Blast of fire or armament, to ensure that the cartridges and projectiles have the same coefficient of thermal expansion as the pipe from which they are drawn, which can be lined with ceramic material.

claims