AT395002B - CERAMIC MATERIAL WITH LOW DIELECTRICITY CONSTANT - Google Patents

Description

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AT 395 002 B

The speed of transmission of an electrical signal along a transmission line is limited by the dielectric constant of the insulating material surrounding the conductor. For high speed transmission of signals into and out of the integrated circuit device, which is in a ceramic package, the dielectric constant of the ceramic should Material as low as possible. Multi-layer aluminum oxide substrates are often used for the production of ceramic packages. The dielectric constant of these ceramics is typically 9 to 10 when measuring at 1 MHz. Substitution of organic components can reduce the dielectric constant to 3 to 5. A disadvantage of using organic components, such as various epoxy materials, is that these materials undergo thermal degradation even at relatively low temperatures and that they are not leakproof. Such materials are also poor heat conductors and excessive temperature rise can occur in the integrated circuit packages. An object of the present invention is to manufacture a ceramic material with a low dielectric constant so that high-speed transmission of signals into and out of the integrated circuit contained in a ceramic package containing the ceramic material of the present invention can be obtained. The present invention is a low dielectric constant ceramic material comprising a foamed metal oxide and sinterable material. A foamed metal oxide is a metal oxide whose particles have an internal structure that consists of hollow cells or pores with thin walls. The combination of walls and cells or pores is referred to in the description and in the claims as an internal foam structure. Preferably, the foamed metal oxide particles have a surface area greater than about 15 m 2 / g and the metal oxide is preferably aluminum oxide. The sinterable material is preferably a glass that can be sintered at a temperature between 800 ° and 1100 ° C. The ceramic material of the invention can be used to produce a sintered ceramic insulation material having a dielectric constant of less than 6 when measured at 1 MHz. The present invention is a ceramic material consisting of a foamed metal oxide made of sinterable material. The inside of the foamed metal oxide particle consists of thin-walled hollow cells or pores. The combination of walls and cells or pores is referred to as an internal foam structure, and metal oxides having such an internal foam structure are referred to as foamed metal oxides. Such foamed metal oxide particles preferably have a high surface area index, typically 15 m 2 / g to 50 m 2 / g. There are several methods for making such foamed metal oxides. One method is described in the Walsh article entitled Ultrafine Metal Oxides by Decomposition of Salts in a Flame, UltrafineParticles (John Wilev & Sons 19631), and in U.S. Patent No. 3,161,463 and U.S. Patent No. 3,172,753 A method of making foamed alumina is disclosed in a PhD thesis by Renato Ciminelli entitled "SvnthesisofaluminafromAlfNO ^ .g ^ ObvtheEvanorativeDecomnositionofSolutionProcess" (Pennsylvania State University, University Park, PA, December 1983) U.S. Patent No. 4,970,062 entitled "High Surface Area Metal Oxide Foams and Method of Producing the Same." Jordan et al., assigned to Cabot Corporation of Waltham, MA. The teaching of the six references cited is discussed here incorporated by reference According to the method of making foamed metal oxides disclosed in U.S. Patent No. 4937062, a solution or slurry of a decomposable saline solution is introduced into a gas of high temperature and high kinetic energy. The solution is kinetically atomized into fine droplets by the gas. The high temperature and high kinetic energy of the gas ensure that the solution is atomized and heated extremely quickly. The droplets thus formed evaporate, leaving a viscous dehydrated salt that breaks down into oxide particles. The interior of the oxide particles consists of thin walls that delimit hollow cells or pores; this combination of walls and cells / pores is referred to throughout the description and in the claims as a foam structure. The oxide foam particles of this invention have a large surface area index. More specifically, the process for producing large surface area metal oxide foam particles comprises the steps of: atomizing a decomposable metal salt solution with a high temperature and high kinetic energy gas and holding the salt droplets thereby formed in the high temperature gas until the droplets dehydrate, foam and solidify as metal oxide particles will. Initially, the process requires rapid heating of the atomized solution. This rapid heating is accomplished by initially contacting the solution with a high temperature atomizing gas, ensuring that the droplets are small by kinetic atomization, and ensuring that there is a large initial velocity difference between the droplets and the hot gas. In the preferred embodiment, fine droplets of the metal salt solution become -2-55 by kinetic atomization

AT 395 002 B of the metal salt solution formed with a gas of high temperature and high speed. When the metal salt solution is introduced into the high speed gas as a coherent liquid stream or as large drops, the high shear and turbulence of the high speed gas atomize the metal salt solution into fine droplets. The gas, which can be generated by burning a fuel or by a plasma arc, S has a velocity of at least 0.2 Mach at the time of importing the metal salt feed solution.

In the following examples, the high speed gas is formed by burning natural gas with either air or with oxygen-nitrogen mixtures. The temperature of the atomizing gas when the feed solution is blown in is at least 700K to ensure that the equilibrated temperature thereof after formation of the foam particles, i.e. H. the temperature of the gas after atomization and decomposition without the 10 additional application »heat through the furnace walls or otherwise is at least 400 K. The salt, the nitrate,

Sulphates or chlorides and other easily hydrolyzable salts of the metal, is first dissolved in a solvent of either water or alcohol. If chlorides are used, some of the metal in the solution should be in the form of an oxide or hydroxide complex rather than a simple ion. The metals include any metal that is oxidizable from a solution of its inorganic salts in a flame environment, such as aluminum, titanium, zirconium, etc. For the purpose of the present patent application, the term “solution” includes simple solutions, dispersions and slurries .

Following atomization in the burner section of the reactor, the mixture of the hot atomizing gas and the droplets of metal salt feed solution run into the reaction section of the main reactor. In the larger reaction section, the water or other solvent evaporates, leaving a viscous salt that foams when the remaining water and salt decomposition gases evaporate. The high temperature of the atomizing gas and the rapid mixing between the droplets and the hot gas, the high relative speed between the gas and the feed solution contribute to the high heating rate experienced by the atomized droplet

All of the heat is preferably supplied to the hot gas before the metal salt feed solution is injected. Any thermal energy added to the gas after the droplets are formed will not be as effective in achieving a rapid rise in particle temperature. Configurations in which the metal salt feed solution contains fuel and the hot atomization gas is oxygen-rich, or the metal salt feed solution contains an oxidizer and the hot atomization gas is fuel-rich, or where some of the heat is brought from an external source to the reaction section are less desirable. 30 worth seeing In such configurations, a higher temperature in the reaction section of the reactor will be required to achieve the same properties as particles that are formed when all heat is evolved in the atomizing gas before contact with the metal salt feed solution.

Once the oxide particles are formed, the temperature of the particles and atomizing gas is reduced and the particles are collected. The temperature can be quickly reduced by adding a quenching liquid such as water, or can be slowly reduced by applying heat to the Environment is dissipated. The particles can be maintained at one or more intermediate temperatures for specified periods by adding the quench liquid in more than one step. After cooling to the appropriate temperature, the particles can be collected by conventional means such as fiber filters or cyclones. When the particles are collected, they can contain a small amount of undecomposed salt, or they can contain the hydrated metal oxide, or they can partially consist of the metal oxide in the amorphous phase. The particles can be calcined to complete the conversion of the salt to the oxide or to change the metal oxide phase. This talcination can be done by any of the methods known in the art, e.g. B. fixed bed, fluidized bed or rotary kiln. 45 The individual foam particles can be as small as 0.1 micron or as large as 30 micron. These

Metal oxide particles have a high specific surface area and consist of thin walls that delimit hollow cells or pores. The walls can be as thin as 50 angstroms, but more often they are about 100 to 200 angstroms thick. The typical size of the pores or cells is 0.1 micron, but can be between 0.01 micron and 2.0 micron. A typical particle will contain many such cells. A minority of the particles can be individual hollow spheres. The high surface area foam particles of the present invention are useful in a variety of applications including catalyst supports, polymer fillers and abrasive materials.

Sinterable materials that are useful in making the ceramic materials of the invention include, or are not limited to, one or more of the following, but are not limited to: silicates, borosilicate glass, oxides that are sinterable at low temperature, and leaded compounds such as lead oxide and lead silicates, and preferably the sinterable material Glass that can be sintered at a temperature between 800 ° C and 1100 ° C. -3-

AT 395 002 B

The ceramic material according to the invention consists of a mixture * in percent by weight - of 1 to 50% by weight of metal oxide and 50 to 99% of sinterable material. Ceramic material according to the invention can be produced by a variety of methods. In general, powdered sinterable material is combined with foamed metal oxide powder, the resulting powder mixture is processed into a green structure, and the green structure is sintered to form a dense structure with closed pores. This leads to a ceramic material that is dense, strong and has a low dielectric constant.

More specifically, the ceramic material of the present invention can be made by mixing a foamed metal oxide powder and a powdered sinterable material with a binder such as polyvinyl alcohol dissolved in water and spray dried to form a free flowing powder that typically contains 2 to 4% by weight of binder resulting spray dried powder can be molded in a die, the binder removed by heating to a low temperature, and the ceramic material by heating to a temperature sufficient to sinter the ceramic material, usually to a temperature greater than 850 ° C, to be compressed.

Another method of producing ceramic material according to the invention is to produce a green structure by forming a slip containing the powdered sinterable material, the foamed metal oxide powder and a water-soluble binder, pouring the resulting slip into a mold, such as a plaster mold. The slip is allowed to dry in the mold, the resulting dried structure is removed from the mold and sintered to form a dense ceramic structure that has closed porosity.

A third method of making the ceramic material of the invention is to form a green structure by extruding a mixture of a powdered sinterable material, a foamed metal oxide and a suitable binder, such as methyl cellulose dissolved in water, through a suitable heated extrusion die.

In a fourth embodiment, a green structure is made by injecting a mixture of powdered sinterable material, foamed metal oxide and binder into a heated tool.

Other processing methods, such as screen printing, powder rolling or film casting, can be used to form green ceramic structures, which when fired form ceramic structures that are dense, have low dielectric constants, and closed porosity due to the void areas formed due to the use of a foamed metal oxide will have.

For a further explanation of the methods described above, see W. D. Kingery, “Introduction to Ceramics,” first edition, pp. 33-71 (John Wiley & Sons 1960).

To produce single-layer or multi-layer ceramic packages, one method of forming the green structure is to use green plates made by film casting or a Doctorblade process as described in Examples 1-4. First, a slurry is mixed by mixing together sinterable material that makes up 30 to 95 percent by weight of the slip, foamed metal oxide that makes up 10-90 percent of the slip, a binder that makes up 2-30 percent by weight of the slip Plasticizer which makes up 2-30% by weight of the slip, a solvent which makes up 15-70% of the slip, and a dispersant which makes up 0.1 to 2% of the slip. Preferably, the foamed metal oxide is calcined to reduce the surface area of the foamed metal oxide to 15-50, but it is not calcined so far that the cells in the internal structure break down.

Synthetic resins such as polyvinyl alcohol, polyvinyl butyral and polymethyl methacrylate can be used as binders to optimize slip formation so that it can be cast. Dioctyl phthalate and butyl benzyl phthalate are commonly used as plasticizers. Toluene, trichloroethane, methanol, methyl ethyl ketone and the like can be used as the solvent. Fish oil, phosphate esters and the like can be used as dispersants to aid in dispersing the powder mixture in the slip. Mixing is typically done in ball mills using suitable grinding media that are compatible with the composition so as not to contaminate the powder mixture. It is common to mix the powders with the solvent and dispersant in the mill jar to break up agglomerated particles and then add the binder and plasticizer to form the finished slip. The resulting slip is then applied to a carrier structure as a uniform film, by means of a "doctor blade", which has an adjustable means for controlling the film thickness, or by curtain coating. The carrier structure can be a metal foil or a tape, a Mylar or polyester foil, or a glass plate.

After drying, the green plate is processed for use in the formation of ceramic packages. This additional processing may include circuit board printing using metal-containing inks, punching and filling through holes with metal inks, punching cavities to position a semiconductor mold in the finished structure, and laminating the green sheets to form the desired structure. The metallization inks can contain noble metals or non-noble metal powders. The green structure is sintered in air, in a neutral atmosphere or in a reducing atmosphere, depending - -4-

AT 395 002 B ity of the metallization used to form the conductor pattern. For example, a reducing atmosphere is required when using molybdenum or tungsten to prevent oxidation.

For further explanation regarding the production of green films by casting or "doctor blading" see U.S. Patent No. 2,966,719; U.S. Patent No. 3,698,923 and U. S. Patent No. 3,998,917. The teachings of the patents mentioned are incorporated herein by reference.

In order to explain the invention in more detail, the following examples are provided. However, it should be understood that the examples are included for illustration and are not intended to limit the scope of the invention as set forth in the claims.

The following test methods were used to analyze the ceramic material made by the methods of the following examples.

Dielectric constant:

The dielectric constant of the ceramic materials was measured according to ASTM method D150-81. Electrodes were attached to both sides of the sintered material with silver filled polymer paste (from ESL Inc. of King of Prussia PA) that cured at 120 ° C for 15 minutes. The capacitance and tan δ were measured using the Hewlett Packard Company's HP4192A impedance analyzer, which is equipped with a tweezer-like sample fixation. The basic capacitance was set to zero before the measurement, but the edge capacitance was corrected according to the method described in the ASTM method.

Flexural strength:

The flexural strength was determined by performing a three point flexural strength test as described in ASTM method C158-84.

Density:

The apparent density, density and surface pores of the sintered ceramic materials were determined according to ASTM Test Method No. C373-72.

Example 1:

Glass masses with the product number P-941 were obtained from Pemco Products from Mobay Chemical Co. of Baltimore MD. The glass mass consisted of 3.3% by weight CaO, 16.1% MgO, 19.6% AljOj and 61% SiOj. The glass mass was ground to an average particle size of about 2.7 µm. Foamed alumina powders were obtained from Cabot Corporation of Billerica, MA.

The foamed alumina powder was prepared using the method described in US Patent No. 4937062 entitled "High Surface Area Metal Oxide Forms and Method of Producing the Same" by Jordan et al. (filed March 7, 1988). Residence time of the mixture of the high temperature gas and the alumina particles was 37.5 msec and the mean temperature in the reactor was higher than 1750 ° C. The type of reactor used was like that used in Examples 1-4 of the aforementioned Jordan et al. U.S. patent application. has been used. The reactor had metal walls that were cooled and the solution injection nozzle formed a coherent stream. Therefore, the mixture of high-kinetic, high-temperature atomizing gas and particles was cooled as it passed through the reactor. The average temperature in the reaction section was determined by measuring the amount of nitrogen adsorbed per gram of oxide at 77 K and a pressure of 0.1 atmosphere. The resulting foamed alumina powder had a surface area of 20 rvP '/ g and consisted primarily of a-alumina with trace amounts of S-alumina, as determined by X-ray diffraction. For the film casting, 270 g of pre-ground P-941 glass powder and 30 g of the foamed alumina powder were ball-milled in a mixed solvent containing 115 g of trichloroethane, 111 g of ethanol and 0.8 g of WITCAMINE PA-78B surfactant from Witco Chemical Corporation from Newark, NJ. After 16 hours in the ball mill, 30.5 g of BUTVAR® B79 binder from Monsanto Co. of St. Louis MO, 18.0 g of SANTICIZER® 160 plasticizer from Monsanto Co, 1.2 g of UCON2000® plasticizer from Union Carbide Corporation of Danbury, CT, was added to the mixture of glass and foamed alumina and further ball milled for 6 hours. A paint-like slip was separated from the milling media, vented in a vacuum to remove trapped air bubbles from the material.

The viscosity was 13000 cps as measured on a Brookfield viscometer using the # 6 spindle at 20 RPM. The slip was then poured onto a polyester backing sheet through a doctor blade with a 0.040 inch (1.016 mm) gap. Dried film, called green film, was die cut to give 12.7 mm (1/2 inch) diameter disks. Three of these disks were pressed at 3000 psi (20 MPa) pressure -5-

AT 395 002 B laminated at a temperature of 60 ° C. The three laminates were sintered »at 920 ° C in air. The physical properties are given in the table.

Example 2:

As a control, a ceramic material was made as before, except that a standard non-foamed alumina was used in place of the foamed alumina. The slip for the film casting was thus produced in the same way as in Example 1. 270 g of pre-ground P-941 powder, 30 g of standard aluminum oxide A152 from Alcoa Co from Pittsburgh PA, 117 g of trichloroethane, 107 g of methanol, 1, were placed in a ball mill. 62 g of UCON 2000® plasticizer and 0.9 g of WITCO 934 surfactant from Witco Chemical Co. of Newark, NJ mixed. The viscosity of the slip was 2700 cps. Three 12.7 mm (1/2 inch) diameter disks were laminated together as before and fired in air at 920 ° C. The physical properties of the sintered ceramic material are given in the table.

Example 3:

Green bodies were made following the procedure in Example 1 except that the ceramic formulation contained 20% by weight foamed alumina, which is twice as much foamed alumina as in Example 1, and the laminated disks were made at the higher temperature of 980 ° C burned. The physical properties of the resulting ceramic material are given in the table.

Example 4:

As in Example 3, a ceramic material was made using 20% by weight foamed alumina powder. However, the glass used was specially made and contained 1.4% by weight PbO, 413% S1O2, 11.1% MgO, 3 , 4% CaO, 27.0% B2O3 and 13.5% A ^ Og. Which was sinterable at a lower temperature than the glass used in Example 3 due to the addition of B2O3. The physical properties of the resulting ceramic material are given in the table.

table

Properties Example 1 Example 2 Example 3 Example 4 Dielectric constant 4.5 63 43 4.2 tan δ 0.0020 0.0012 0.0024 0.0004 Flexural strength kpsi 18 ± 4 - 8.9 ± 1.3 18.7 ± 4.5 MPa 127 + 28 63 ± 9 133 ± 32 Apparent density g / cm ^ 2.50 2.80 2.53 2.11 Density ("bulk density") g / cm ^ 230 2.80 1.76 2 , 11 surface pores ("apparent porosity") (%) 0 0 30.4 0

From the data obtained from Examples 1 and 2, as shown in the table, it can be concluded that the use of foamed alumina powder in a ceramic material results in a ceramic material that has a lower dielectric constant than ceramic material that is only non- contains standard foamed alumina.

Example 3 shows that the addition of too much foamed alumina to the ceramic material results in a structure with a high apparent open porosity, resulting in a material that is not dense while still creating a ceramic material with a low dielectric constant.

However, Example 4 shows that dense, solid ceramic material can be made even though a large amount of foamed alumina is used when the glass matrix is sinterable at a low temperature. In Example 4, B2O3 was added to the glass composition, which lowered the sintering temperature of the material.

From the flexural strength data, it can be determined that the use of foamed alumina in a ceramic material results in a ceramic material that has a mechanical strength comparable to or higher than that of quartz glass. The mechanical strength of a ceramic material containing foamed alumina is small - than the mechanical strength of a ceramic material containing standard non-foamed alumina

Although the present invention has been described in terms of certain embodiments, it is not so limited and it should be understood that variations and modifications that are apparent to those skilled in the art can be made without departing from the spirit and scope of the invention removed is -6-

Claims (19)

AT 395 002 B PATENT CLAIMS 1. Ceramic material, characterized in that it comprises foamed metal oxide and sinterable material. 2. Ceramic material according to claim 1, characterized in that the sinterable material is a glass which is sinterable at a temperature between 800 ° and 1100 ° C. 3. Ceramic material according to claim 1, characterized in that the sinterable material is a compound selected from the group consisting of silicates, borosilicate glass, oxides which are sinterable at a temperature between 800 ° and 1100 ° C, lead oxides and lead silicates. 4. Ceramic material according to claim 1, characterized in that the foamed metal oxide has a surface area of more than 15 m2 / g. 5. Ceramic material according to claim 1, characterized in that the foamed metal oxide is foamed aluminum oxide. 6. Ceramic material according to claim 1, characterized in that the foamed metal oxide is calcined foamed aluminum oxide 7. Green structure, characterized in that it comprises foamed metal oxide and sinterable material 8. Green structure according to claim 7, characterized in that the sinterable material is a glass which is sinterable at a temperature between 800 ° and 1100 ° C. 9. Green structure according to claim 7, characterized in that the sinterable material is a compound selected from the group consisting of silicates, borosilicate glass, oxides which are sinterable at a temperature between 800 ° and 1100 ° C, lead oxides and lead silicates. 10. Green structure according to claim 7, characterized in that the foamed metal oxide has a surface area of more than 15 nr / g. 11. Green structure according to claim 7, characterized in that the foamed metal oxide is foamed aluminum oxide 12. Green structure according to claim 7, characterized in that the foamed metal oxide is calcined foamed aluminum oxide 13. Green structure according to claim 7, characterized in that it further contains one or more plasticizers. 14. Gestertertes ceramic material, characterized in that it was made from foamed metal oxide and sinterable material. 15. Sintered ceramic material according to claim 14, characterized in that the sinterable material was a glass which is sinterable at a temperature between 800 ° and 1100 ° C. 16. Sintered ceramic material according to claim 14, characterized in that the sinterable material was a compound selected from the group consisting of silicates, borosilicate glass, oxides which are sinterable at a temperature between 800 ° and 1100 ° C, lead oxides and lead silicates. -7- AT 395 002 B 17. Sintered ceramic material according to claim 14, characterized in that the foamed metal oxide had a surface area of more than 15 m ^ / g. 18. Sintered ceramic material according to claim 14, characterized in that the foamed metal oxide was foamed aluminum oxide. 19. Sintered ceramic material according to claim 14, characterized in that the foamed metal oxide was calcined foamed aluminum oxide. -8th-