EP1343600B1 - Method for making thin films in metal/ceramic composite - Google Patents

Abstract

Process for manufacturing composite metal/ceramic thin films, consisting of: a) preparing a suspension (S) in an organic solvent starting from a substantially homogenous mixture of ceramic reinforcements, metallic particles, a binder, a plasticizer and a dispersant, the metallic particles constituting at least 5% by weight of the suspension; b) tape casting the suspension to form a thin film, and then de-binding said thin film; c) densifying the de-binded thin film in a furnace.

Description

Field of the invention

The invention relates to a method for manufacturing thin metal / ceramic composite films, in which the ceramic reinforcements are homogeneously distributed in the metal matrix.

The invention finds applications in all fields using metal / ceramic composite substrates or films and, in particular, in the field of the manufacture of electronic components intended, for example, in the field of automotive or automotive aeronautics.

State of the art

Conventionally, the metal films are made by a rolling process. However, this rolling method does not make it possible to obtain a homogeneous distribution of the ceramic reinforcements in the metal matrix; it is therefore not suitable for the manufacture of metal / ceramic composite films. In addition, beyond a certain concentration of ceramic powder, the residual stresses, caused by rolling, lead to cracking of the film.

Other processes used for the manufacture of metal / ceramic composite films are the pressing, injection and extrusion processes. However, none of these processes makes it possible to obtain films with an excellent surface state. In addition, these methods become expensive, since the thickness of the film must be less than one millimeter.

In addition, there are tape casting methods that make it possible to produce thin films. Such methods are described in the following articles: ALCOCK J., DESCRIBE S., Tape casting, a flexible approach to surface engineering, Materials world, 13-14, February (2000); BÖHNLEIN-MAUß J., SIGMUND W., WEGNER G., MEYER W.H., HEßEL F., SEITZ K, ROOSEN A., The function in the casting of alumina, Advanced Materials, vol. 4, No. 2, 73-81 (1992); MORENO R., The role of slip additives in tape casting technology: I-Solvents and dispersants, American Ceramic Society Bulletin, vol. 71, No. 10, 1,521-1,531 (1992); MORENO R., The role of slip additives in tape casting technology: Part II-Blinders and Plasticizers, American Ceramic Society Bulletin, vol. 71, No. 11, 1647-1657 (1992) and in US-5,002,710 and US-5,473,008.

However, it is not possible to find, in all of these works related to casting tape, a device (bench + suspension) for casting strips of metal / ceramic composite material.

Presentation of the invention

The purpose of the invention is precisely to remedy the thin film manufacturing processes described above. To this end, it proposes a method for manufacturing thin metal / ceramic composite films using a strip casting method.

1. a) préparer une suspension (S) dans un solvant organique à partir d'un mélange sensiblement homogène de renforts céramiques, de particules métalliques, d'un liant, d'un plastifiant, et d'un dispersant, les particules métalliques constituant au moins 5 %, en masse, de la suspension ;
2. b) effectuer un coulage en bande de la suspension pour former un film mince, puis effectuer un déliantage de ce film mince ;
3. c) réaliser la densification du film mince délianté, dans un four.

More specifically, the invention relates to a method for manufacturing thin metal / ceramic composite films comprising:

1. a) preparing a suspension (S) in an organic solvent from a substantially homogeneous mixture of ceramic reinforcements, metal particles, a binder, a plasticizer, and a dispersant, the metal particles constituting at least 5%, by weight, of the suspension;
2. b) casting a slurry of the slurry to form a thin film, then debinding this thin film;
3. c) densification of the delaminated thin film in an oven.

The band casting technique is used to orient and control the distribution of ceramic reinforcements.

In other words, the process described according to the invention makes it possible to manufacture metal / ceramic composite films with an orientation of the ceramic particles in the plane of the film, in particular for highly anisotropic particles, such as fibers and platelets. This improves some properties of the composite in the plane of the film, such as decreasing the thermal coefficient of expansion and increasing the thermal conductivity.

Advantageously, the suspension has a viscosity of between 0.5 and 3 Pa.s.

• au moins une poudre métallique et au moins un renfort céramique constituant environ 30 à 60 % du volume total de la suspension ;
• un solvant organique constituant environ 15 à 45 % du volume de la suspension ;
• un liant et un plastifiant constituant environ 30 à 70 % du volume de la suspension ;
• un dispersant représentant environ 0,1 à 2 % de la masse des poudres céramique et métallique ; et
• des additifs représentant environ 0,01 à 2 % de la masse des poudres métallique et céramique.

Preferably, the suspension is produced by mixing:

• at least one metal powder and at least one ceramic reinforcement constituting approximately 30 to 60% of the total volume of the suspension;
• an organic solvent constituting approximately 15 to 45% of the volume of the suspension;
• a binder and a plasticizer constituting about 30 to 70% of the volume of the suspension;
• a dispersant representing about 0.1 to 2% of the mass of ceramic and metallic powders; and
• additives representing about 0.01 to 2% of the mass of metal and ceramic powders.

According to one embodiment of the invention, the dispersant is a phosphoric ester, a polyacrylate, a sulfonate, a perfluorate or a carbon chain acid of 2 to 30 carbon atoms.

According to the invention, the metal powder may be a powder of copper, aluminum, silver, gold, nickel, titanium, chromium, zinc or an alloy of two or more of these materials . The ceramic reinforcement may be a powder and / or a short fiber (that is to say a fiber whose length varies between 1 and 500 μm) of graphite, carbides, nitrides or oxides.

According to a variant of the invention, the densification of the film consists of sintering the film in an oven.

According to another variant of the invention, the densification of the film consists of hot rolling and annealing of the film.

• à broyer en jarre ou par attrition les poudres métalliques et les renforts céramiques avec le solvant et le dispersant ; et
• à ajouter et à mélanger à cette substance un liant et un plastifiant.
  L'invention a trait en outre à un procédé de préparation de pièces en composite à structure stratifiée dans lequel on forme plusieurs films minces (films « en cru ») par les étapes a) et b) décrites plus haut, puis on empile lesdits films minces et on soumet l'empilement à une thermocompression.
  De préférence, les films minces empilés ont des compositions différentes.

Preferably, the preparation of the suspension consists of:

• grinding jars or attrition metal powders and ceramic reinforcements with the solvent and the dispersant; and
• to add and mix with this substance a binder and a plasticizer.
  The invention furthermore relates to a process for the preparation of laminated structure composite parts in which several thin films ("green" films) are formed by steps a) and b) described above, and then said films are stacked thin and the stack is subjected to thermocompression.
  Preferably, the stacked thin films have different compositions.

Brief description of the figures

• Figure 1 shows schematically the step of preparing the suspension from metal particles and ceramic reinforcements;
• Figure 2 schematically shows the strip casting step of the slurry to form a thin film; and
• Figures 3A and 3B show two embodiments of the densification step of the film in a furnace.

Detailed description of embodiments

The invention relates to a method for manufacturing thin metal / ceramic composite films.

This process consists in preparing a suspension, also called "slip", comprising a substantially homogeneous mixture of ceramic reinforcements and metal particles.

These metal particles and ceramic reinforcements are chosen, respectively, in the form of one or more metal powder (s) and one or more ceramic reinforcement (s). These powders and short fibers are mixed with an organic solvent, a dispersant, a binder and a plasticizer.

• les poudres métalliques et les renforts céramiques représentent 30 à 60 % du volume total de matière sèche de la suspension (c'est-à-dire de l'ensemble du volume occupé par le liant, le plastifiant, le dispersant et les poudres métallique et céramique) ;
• le solvant représente 15 à 45 % du volume total de matière sèche ;
• le liant et le plastifiant représentent 30 à 70 % du volume de matière sèche ;
• le dispersant représente entre 0, 01 et 2 % de la masse des poudres métallique et des renforts céramiques ;
• d'autres additifs sont ajoutés, tels que des agents de décollement et/ou des agents mouillants, qui représentent entre 0,01 et 2 % de la masse des poudres métallique et céramique.

The proportion of these different elements is as follows:

• the metal powders and the ceramic reinforcements represent 30 to 60% of the total volume of dry matter of the suspension (that is to say of the whole volume occupied by the binder, the plasticizer, the dispersant and the metal powders and ceramic);
• the solvent represents 15 to 45% of the total volume of dry matter;
• the binder and the plasticizer represent 30 to 70% of the volume of dry matter;
• the dispersant represents between 0.01 and 2% of the mass of metal powders and ceramic reinforcements;
• other additives are added, such as release agents and / or wetting agents, which represent between 0.01 and 2% of the mass of metallic and ceramic powders.

In Figure 1, there is shown this first step of the method of the invention, namely the step of preparing the suspension.

This step of preparation of the suspension S consists, first of all, in a grinding jar, or attrition, metal and ceramic powders with the solvent and the dispersant. This grinding step is carried out by means of an attritor mill (represented by reference 1 in FIG. 1) or by a jar crusher.

The assembly thus obtained is then mixed with binders and plasticizers, using a mixer, referenced 2.

The metal powder (s) intended to form the metal matrix of the suspension may be, for example, a powder of copper, aluminum or silver. gold, nickel, titanium, chromium, zinc or an alloy of two or more of these metals.

The ceramic reinforcement (s) intended to form the ceramic reinforcements of this suspension may be, for example, a powder or a short graphite fiber, or a powder or a short fiber based on carbides, such as silicon carbide, nitrides, such as aluminum nitride, or oxides, such as silica or zirconium tungstate.

The ceramic reinforcements may be in the form of fibers or platelets or substantially spherical grains, with a diameter of between about 0.1 microns and 100 microns.

The fibers are generally short fibers with a diameter of 10 nm to 10 μm, and a length of 100 nm to 10 mm.

These ceramic reinforcements may be coated with a layer of metallic material, such as cobalt, nickel, silver or gold. In this case, the thickness of the metal coating is at least 0.01 μm. This coating can be achieved by immersing the ceramic reinforcements in an electrolytic bath. This coating has the advantage of improving the densification of the material during the densification step of the film, and in particular when this densification consists of sintering because it makes it possible to increase the metal / ceramic interface.

The suspension used according to the invention is a suspension or organic system.

Thus, the solvent used to make this suspension S is an organic solvent, generally chosen from ketones, alcohols and mixtures thereof.

The dispersant used to produce this suspension serves to ensure the homogeneity and stability of the suspension by developing repulsion between ceramic reinforcements and metal particles.

In other words, the dispersant ensures good stability and good dispersion of the particles together. The dispersant makes it possible, after drying, to obtain a homogeneous and compact strip.

This dispersant is chosen from surfactants, macromolecules, such as fish oil, phosphoric esters, polyacrylates, sulphonates, perfluorates and carbon chain acids having from 2 to 30 carbon atoms, for example oxalic acid and stearic acid.

The binder used to make this suspension has the role of ensuring the cohesion of the strip (or film), after evaporation of the solvent. This binder is generally a non-water-soluble compound chosen from polyalcohols, vinyl compounds, such as polyvinyl butyral and acrylic compounds and mixtures thereof.

The plasticizer used in this suspension has the role of ensuring a great flexibility, a great fluidity, to the band; this flexibility is necessary during the casting strip of the suspension and, later, during the handling of the band. This plasticizer may be, for example, a polyethylene glycol or dibutyl phthalate.

In other words, the suspension also contains a plasticizer which makes it possible to obtain a strip, or thin film, in flexible raw material and sufficiently strong to be handled. Indeed, the report binder / plasticizer makes it possible to adjust the mechanical cohesion of the strip and its flexibility. These strips can therefore be stacked and thermocompressed so as to produce stacks of bands of different compositions. This solution is not possible with the methods of the prior art.

Note, moreover, that the system, the suspension implemented according to the invention, does not require lubricant.

Figure 2 shows schematically the second step of the method of the invention, that is to say the strip casting step of the suspension. Indeed, the suspension S made during the first step is cast on a casting bench 3 so as to form a band B, also called thin film. The strip casting consists of casting the suspension S on a support which may be, for example, a steel strip 8 or a polymer wire, referenced 5 in FIG. 2. In order to allow easy casting of the suspension, this suspension must have a viscosity of the order of 0.5 to 3 Pa.s.

The casting of the suspension is obtained by the relative movement between a shoe 6 of the casting bench and the support 5. The shoe 6 comprises knives 7, whose height is adjustable. Thus, the thickness of the film can be modified by changing the height between these knives 7 and the support 5. It is thus possible, thanks to this band casting, a very regular film thickness.

When the suspension S has been cast in the form of a strip B, it travels inside a dryer 4, under a controlled atmosphere, in order to eliminate organic compounds. This step is called debinding. More specifically, thermal debinding consists in slowly heating the strip of material in a controlled atmosphere, in an oven or dryer 4 in order to remove the organic compounds contained mainly binder and plasticizer. For example, the heating rate in the dryer is of the order of 0.2 to 2 ° C / min between 100 ° C and 500 ° C.

Figures 3A and 3B show two different embodiments of the third step of the method of the invention, that is to say the densification step of the film.

This densification step consists of evaporating the solvent and drying the thin film obtained after debinding.

This step of densification of the film has the role of evaporating the solvent. It can be carried out, for example, in two different ways: the film can be densified by sintering in a passage furnace or in a batch oven, or by hot rolling, using a rolling mill and an annealing furnace.

The first variant, shown in FIG. 3A, shows that the film B, obtained after debinding, is cut into plates P1 to Pn. These plates are introduced into an oven, referenced 9, under a controlled atmosphere. This oven can be a furnace or a batch oven. Densification by sintering is carried out under a controlled atmosphere, or under a reducing atmosphere, for example hydrogen, hydrogenated nitrogen, argon or hydrogenated argon, so as to avoid the oxidation of the material.

The sintering temperature depends on the particle size and the nature of the metal powders and ceramic reinforcements. For example, for a copper metal powder, the temperature is between 700 ° C and 1080 ° C; for aluminum, the temperature is between 450 ° C and 650 ° C.

The second variant of the densification step is shown in FIG. 3B. In this variant, the film B is introduced into a rolling mill 10, placed in an annealing furnace 11. The film B is then hot rolled in the furnace 11 under a controlled atmosphere. The cutting of the film B in plates P1, P2,... Is carried out at the outlet of the annealing furnace 11.

This mode of densification by hot rolling and annealing of the film makes it possible to improve the densification of the material under the action of pressure and temperature. This variant is therefore particularly well suited to metal / ceramic composites which are poorly densified by natural sintering and composites made of ductile metals, such as copper, aluminum or gold.

Claims (13)

1. Method of manufacturing thin metal/ceramic composite films, characterised in that it involves:

   a) preparing a suspension (S) in an organic solvent using a substantially homogenous mix of ceramic reinforcements for metal particles, a binder, a plasticizer and a dispersing agent, the metal particles making up at least 5% of the mass of the suspension;

   b) pouring the suspension (6) in a strip so as to form a thin film (B), then debinding this thin film;

   c) densifying the debinded thin film in a furnace.
2. Method according to claim 1, characterised in that the suspension (S) has a viscosity of between 0.5 and 3 Pa.S.
3. Method according to claim 1 or 2, characterised in that the suspension (S) is made by mixing:

   - at least one type of metal powder and at least one ceramic reinforcement, together making up around 30% - 60% of the total volume of the suspension;

   - an organic solvent making up around 15% - 45% of the volume of the suspension;

   - a binder and a plasticizer making up around 30% - 70% of the volume of the suspension;

   - a dispersing agent equal to around 0.1% - 2% of the mass of the ceramic reinforcements and metal powders; and

   - additives equal to around 0.01% - 2% of the mass of the ceramic reinforcements and metal powders.
4. Method according to any one of the claims from 1 to 3, wherein the binder is a non-water-soluble compound chosen from among polyalcohols, vinyl compounds, acrylic compounds and their mixes.
5. Method according to any one of the claims from 1 to 4, wherein the organic solvent is chosen from among ketones, alcohols and their mixes.
6. Method according to any one of the claims from 1 to 5, wherein the dispersing agent is chosen from among surface active agents, macromolecules such as fish oil, phosphoric esters, polyacrylates, sulphonates, perfluorates and carbon chain acids of 2 to 30 carbon atoms.
7. Method according to any one of the claims from 3 to 6, characterised in that the metal powder consists of powder of copper, aluminium, silver, gold, nickel, titanium, chromium, zinc or an alloy of two or more of these materials.
8. Method according to any one of the claims from 3 to 7, characterised in that the ceramic reinforcement consists of powder and/or short fibres of graphite, carbide, nitride or oxide.
9. Method according to any one of the claims from 1 to 8, characterised in that the densification of the film involves fritting the film in a furnace.
10. Method according to any one of the claims from 1 to 8, characterised in that the densification of the film involves hot rolling and annealing the film.
11. Method according to any one of the claims from 3 to 10, characterised in that the preparation of the suspension involves:

    - grinding the metal and ceramic powders in a jar or by attrition together with the solvent and the dispersing agent; then

    - adding a binder and a plasticizer to the substance and mixing them in.
12. Method for preparing a composite piece with a laminated structure wherein several thin films are formed according to steps a) and b) of claim 1, said thin films are stacked, and the stack is subjected to thermocompression.
13. Method according to claim 12, wherein the thin films have different compositions.

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