WO1988003087A1

WO1988003087A1 - Ceramic-glass-metal composite

Info

Publication number: WO1988003087A1
Application number: PCT/US1987/002471
Authority: WO
Inventors: Narendra N. Singhdeo; Deepak Mahulikar; Sheldon H. Butt
Original assignee: Olin Corporation
Priority date: 1986-10-30
Filing date: 1987-10-01
Publication date: 1988-05-05
Also published as: JPH02500907A; AU1046788A; CN87107196A; EP0341246A4; KR880701635A; EP0341246A1

Abstract

Engineering ceramic product formed of a ceramic-glass-metal composite being strong, durable, formable into complex shapes and having improved thermal conductivity. Metal elements can be embedded into the composite to enable simplified fabrication of devices such as a semiconductor packaging. Specifically, a semiconductor casing (22) comprises a base component (24) and lid component (28) both formed of a ceramic-glass-metal composite material (26) of this invention. The composite material comprises ceramic particles, a glassy phase for adhering the ceramic particles together, and metallic particles dispersed discontinuously throughout the composite. A metallic lead frame (30) is embedded into the base component (24). A sealing glass (32), such as a solder glass from the group consisting of borosilicate, soda-lime-silica, lead-silicate and lead-zinc-borate, bonds the base component (24) to the lid component (28).

Description

CERAMIC-GLASS-METAL COMPOSITE While the invention is subject to a wide range of applications, it is especially suited for use as a fabricating component for semiconductor chips individually or in groups. The invention discloses the bonding together of ceramic particles to form a coherent composite with desired properties which may be specifically tailored for specific applications in the packaging of electronic components, artificial body parts, grinding wheels, engine parts, and ceramic engines, to name a few.

In the past, glass-ceramic composites have been formed by one-step processes into complex shapes. This technique proved effective for many applications. However, as the final product had a more complex shape, the higher pressure required to form the composite within the mold resulted in the molten glass between the ceramic particles being squeezed out^'and interlocking of ceramic particles. The result is a retardation of further flow so that the densification and shaping of the composite to the desired final configuration requires more pressure or may not be possible. The present invention overcomes this problem by combining metallic particles with the ceramic particles and glass to enhance the flow of the composite within the mold.

The composite may be formed of a combination of materials such that it is either electrically conductive or non-electrically conductive. Also, the coefficient of thermal expansion may be regulated in accordance with the requirements of the speci-fic application. A composite having a low coefficient of thermal expansion, while being non-electrically conductive, is particularly useful in the electronics industry. Presently, low expansivity materials are widely used in the microelectronic industry as substrate materials for semiconductor packages, hybrid circuit packages and chip carriers. These materials are particularly useful when the coefficient of thermal expansion (CTE) of the substrate is critical, i.e. when silicon chips or low expansivity leadless chip carriers are mounted directly to the substrate.

Alumina ceramics are presently the most widely used substrate material. There is a moderate mismatch between the coefficients of thermal expansion of alumina and the silicon chip. This mismatch does not usually generate unacceptably high stresses on a chip mounted to an alumina substrate when they are subjected to thermal cycling. This degree of CTE mismatch is usually acceptable even when the chip sizes are relatively large or when the chip is rigidly adhered to the substrate. Alumina ceramics are particularly attractive since they are less costly than most other low expansivity substrate materials.

However, there are a number of drawbacks to alumina ceramics made in the conventional way such as poor tolerance control, poor thermal conductivity, i.e. in the range of about 10 to about 20 watts per meter kelvin, and manufacturing capabilities limiting alumina substrate areas to less than about 50 sq. in.

Conventional ceramic products, and ceramic substrates in particular, may be manufactured in accordance with the following procedure. Powders of alumina or other ceramic materials are mixed together with glass powders and organics. In the conventional "green tape" or "cold press" processes, the organics are two phase mixtures consisting of a solvent, such as terpineol, and a solute, such as polymethylmethacrylate. This particular solvent-solute mixture is exemplary and other organic mixtures may be used in their place. The organic mixture forms a paste or slurry when mixed with the mixture of glass and ceramic powders. The solute:solvent ratio and the type of organic mixture, is selected in accordance with the paste rheology desired for the particular application, i.e. the "green tape" or the "cold press" process. In the green tape process, a controlled amount of slurry is placed between two sheets of plastic. The slurry, sandwiched between the plastic sheets, is passed through a rolling mill to attain a consistent thickness. The sheets of material are then cut or punched into desired shapes for firing. In the cold press process, the glass and ceramic powders are mixed with a lower percentage of solvent, as compared with the green tape process. The mixture of glass, ceramic and organics is then pressed into a desired shape and fired.

The organics, in either process, are volatilized at substantially lower temperatures than the firing or processing temperature of the ceramic bodies or ceramic substrates. The solvents usually evaporate at temperatures below about 100°C and the solutes evaporate at temperatures below about 450°C. The loss of the solute and solvent leaves pores in the green tape or cold pressed body. At the peak firing temperatures (approximately 1600°C for the conventional ceramics or approximately 900°C for the low fired ceramics). the glassy phase melts, a certain amount of sintering of the alumina particles occurs, and there is a resulting densification of the bodies. The fired substrates, being devoid of any connected 5 pores, produce a hermetic substrate that allows an extremely limited quantity of gaseous penetration (< 1 x 10 —8cc He/sec). The latter characteristics of the fired substrates make them^'particularly suitable for fabricating hermetically sealed,

10 semiconductor enclosures.

The densification, however, causes a great deal of shrinkage, amounting to as much as 17% in the linear dimension. It is thus unrealistic to economically produce finished parts which have

15 better than about _ 1% tolerance in the linear dimension. Therefore, dimensional tolerances for the standard fired ceramic substrates is typically quoted by ceramic manufacturers to be +1%. Tighter dimensional tolerances are considerably more

20. expensive so as to offset the yield loss.

The electronic industry is seeking higher levels of automation in their factories. The automatic machines are generally capable of positioning parts, such as the previously described

25 substrates, to a much tighter tolerance than _+l% of the linear dimension of the part. In fact, the tolerance of the ceramic part is, in most cases, the limiting factor in attaining the desired level of automation.

30 The present invention provides a unique method of manufacturing structures of ceramic-glass-metal to their final configuration in a one-step process by conventional means at temperatures well below the firing temperature of either the conventional

35 ceramics, i.e. about 1600°C, or even "low fired ceramics", i.e. about 900°C. The present process also imparts unique properties to the manufactured product because organics are not necessarily required in the manufacturing process.

The present invention is also directed to components and methods of producing components for radically improving the CERDIP technology. Currently, the CERDIP technology utilizes a ceramic base and lid. A ^"sealant, usually a solder glass, seals the package at a relatively low temperature, ie. about 470°C. A metallic leadframe resides in the sealant. The strength of the CERDIP seal depends on the strength of the glass sealant, the length and width of the seal, the presence of pores or other discontinuities and eventually the nature of the bond between the glass and the metallic leadframe. Usually, the glass is the weakest component of the CERDIP package. The adhesion between the leadframe and the glass sealant is relatively poor in most package designs. If the seals are subjected to significant mechanical or ther o-mechanical loading, the seal can readily fail. Under similar conditions, a more expensive, ceramic side brazed package, utilizing a metallic seal, would remain intact. The CERDIP designs are modified to compensate for their inherent weakness. They have a larger seal area as compared to a side brazed package of the same size. The result is a die cavity of reduced width as compared with that of the side brazed package. In instances where the size of the space to accommodate the package is limited, larger chips which cannot be fit within the reduced sized die cavity of a CERDIP, require mounting in a more expensive side brazed ceramic package. The present invention can overcome this problem by separating the leadframe from the interior of the glass seal.

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The leadframe can be firmly affixed to the base or lid of the package in the manner of the side brazed package. The resulting superior package does not transmit stress into the seal from flexure of the leads which routinely occurs during the handling of the package. At the same time, the size of the die cavity may be enlarged so that the package competes

^~ in reliability with the sidebrazed package but at a much lower cost. The present invention is also suitable for fabricating multi-layer packages, such as pin grid arrays and sidebrazed packages.

Throughout the world, fine ceramics are considered to be one of the most important basic materials for the 1990^fs and the 21st century.

This expectation is based on the following factors. First of all, fine ceramics are expected to play an important role as a new basic material in developing and advancing such frontier industries as electronics, information technology, bio-technology, medical electronics, etc. The future of these industries depends on the development of new materials. They demand materials which have greater capability than any currently available material in resisting heat, corrosion, radioactivity, etc. They also demand new functional materials which show advanced performance in chemical, optical and electromagnetic functions. Fine ceramics are considered to be the materials which ca fulfill these requirements and, hence, act as one of the key materials which will support the anticipated development of these frontier industries. Secondly, the excellent qualities of fine ceramics are expected to help existing industries improve the quality of their products. A ceramic engine for the car industry is just one example. Clearly, fine ceramics are expected to present great opportunity for currently depressed basic materials industries to revitalize themselves by becoming a supplier of fine ceramics. Thirdly, fine ceramics are considered to be important from the view of each countries national economic security. Every country is concerned about conserving its natural resources including oil and precious metals.

Consequently, the development of a ceramic engine is eagerly awaited in order to conserve oil. The development of ceramics as a substitute for such precious metals as nickel, cobalt and chromium is similarly desired.

Presently, the main areas of application are electromagnetic and mechanical components.- The former is called electro-ceramics and includes IC packages, electrical condensers, thermistors and variable resistors.

Mechanical and heat-resistance ceramics are called engineering ceramics and are conventionally used in applications such as Gas turbines, turbo-charge turbines and ceramic engines. Informational electronics is one of the main areas where ceramics can be applied and where functional ceramics have already been used. Structural ceramics have been less widely applied in practice. However, they are expected to play an important role in improving the efficiency of energy uses in motor vehicles, industrial machinery and so on. Structural ceramics, also known as engineering ceramics, with their excellent mechanical and thermal capabilities are considered to be very important for the future. In addition, functional ceramics such as electrical ceramics and optical cera ics are expected to grow faster than ever in the wake of miniaturization and envelopment of new devices in the electronics industry. Bio-ceramics, such as those being used in artificial teeth and replacement joints, are also beginning to show rapid growth and will be spurred by the advancement of medical technology.

The innovative features of the present invention enable the composite to be effectively used in many areas of the growing ceramics industry. Even when the composite contains a large percentage of ceramic particles, it can now be die formed to a complex, final shape at moderate pressures and temperatures. The key to this discovery is the addition of a low concentration of metal or metal alloy particles which greatly reduces the range of forming pressures. In the past, the required high pressures primarily permitted only the forming of relatively non-complex configurations. With the metal or metal alloy particle additive, complex configurations with a tight tolerance are possible because the composite, at the processing temperature, flows quite readily. The forming technology is somewhat similar to that involved in injection molding of plastics. Presently, ceramic products having a complex shape are difficult to manufacture because of factors including the shrinkage and the hardness of ceramics. Once the ceramic product is formed to the general, final shape, a it is very time-consuming and expensive to machine it into the final design.

Even with this design limitation, ceramic materials have been employed in many products which take advantage of their high strength, chemical durability and light weight. For example, ceramics have been incorporated in engines, artificial limbs, and cutting tools to name just a few. It is a problem underlying the present invention to manufacture electronic packaging for components incorporating a ceramic-glass-metal composite whose physical characteristics can be tailored to provide specific mechanical, electrical, thermal, and chemical properties by judicious choice.

It is an advantage of the present invention to provide electronic packaging for components incorporating a composite and a method of forming the composite which obviates one or more of the limitations and disadvantages of the described prior arrangements.

It is a further advantage of the present invention to provide electronic packaging for components incorporating a composite and a method of forming the composite which provides a substrate having good flexure strength.

It is a still further advantage of the present invention to provide electronic packaging for components incorporating a composite and a method of forming the composite which can produce parts with a tight tolerance.

It is another advantage of the present invention to provide electronic packaging for components incorporating a composite and a method of forming the composite which can be fired at a low temperature.

It is yet another advantage of the present invention to provide electronic packaging for components incorporating a composite and a method of forming the composite which can be inexpensively processed. It is a still further advantage of the present invention to embed a metallic element into a component formed of a ceramic-metal-glass composite.

It is a yet further advantage of the present invention to provide electronic packaging for components incorporating a leadframe embedded into a ceramic substrate formed of a ceramic-metal-glass composite.

It is still another advantage of the present invention to provide electronic packaging for components incorporating a multi-layer device fabricated from a ceramic-glass-metal composite having metallic elements embedded into the composite at desired locations.

It is a further advantage of the present invention that engineering ceramic products formed of a ceramic-glass-metal composite which can be molded into complex shapes are provided. Accordingly, there has been provided components and the process of forming the components for housing semiconductor devices. The components are formed of a unique ceramic-glass-metal composite material comprising ceramic particles, metallic particles dispersed throughout the composite and a glassy phase for adhering the ceramic and metallic particles together. The composite may be formed, in a single step, by conventional processes such as hot forging and hot pressing in a mold to enable simplified fabrication of semiconductor packaging. Metallic elements can be embedded into the composite during the hot pressing step. The invention is particularly adaptable to form CERDIP*s, hybrid packages, circuit boards and multilayer devices. Also, there has been provided engineering ceramic products formed of a ceramic-glass-metal composite. These products are strong, durable, formable into complex shapes and have improved thermal conductivity. They include rotors, engine blocks, replacement for body parts, and grinding wheels to name a few. The ceramic-glass-metal composite includ^'es cerramic particles, a glass for adhering the ceramic particles together and metallic particles to enhance the flow characteristics at a processing temperature.

The invention and further developments of the invention are now elucidated by means of the preferred embodiments in the drawings. DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a prior art CERDIP package.

Figure 2 illustrates a prior art substrate having a leadframe glass bonded thereto. Figure 3A illustrates a CERDIP package in accordance with the present invention.

Figure 3B illustrates a cross-sectional view through the ceramic-glass-metal substrate of Figure 3A having the leadframe embedded therein. Figure 4 illustrates a CERDIP package having metal coupons in the base and lid cavities in accordance with the present invention.

Figure 5 illustrates a substrate of the ceramic-glass-metal composite in accordance with the present invention.

Figure 6A illustrates a layer of the ceramic-glass-metal composite with an opening extending therethrough.

Figure 6B is a view through section B-B of Figure 6A. Figure 7A illustrates a layer of the ceramic-glass-metal composite with an opening extending therethrough.

Figure 7B is a view through section B-B of Figure 7A.

- Figure 8 illustrates the components of a multilayer device prior to hot pressing.

Figure 9 illustrates the components of a multilayer device subsequent to hot pressing. Figure 10 illustrates a semiconductor casing including a heat sink.

Figure 11 illustrates a semiconductor casing formed of a ceramic-glass-metal composite in accordance with the present invention. Figure 12 illustrates a semiconductor casing of a ceramic-glass-metal composite including a ceramic. lid.

Figure 13 illustrates a semiconductor casing formed of a ceramic-glass-metal composite and including a metal lid.

Figure 14 illustrates a semiconductor device similar to the embodiment of Figure 12 but without a heat sink.

Figure 15 illustrates a semiconductor casing formed of a body of the ceramic-glass-metal composite and including a cup shape member which acts as a surface to bond the semiconductor device to as well as a heat sink.

Figures 16A-16E illustrate the series of steps for forming a multilayer, ceramic-glass-metal circuit structure in accordance with the present invention.

Figure 17 is a perspective view of a ceramic rotor for a turbo-charge turbine. Figure 18 is a perspective view of a hip and leg bone prosthesis. Figure 19 is a perspective view of a ceramic engine.

Figure 20 is a perspective view of a grinding wheel.

Figure 21 is a perspective view of a ceramic engine block.

The present invention particularly relates to a composite formed of a mixture of ceramic and metal particles bound together by a glass. The composite can be formed into any desired shape by techniques such as hot forging and hot pressing at a processing temperature where the selected glass is at least soft and preferably in the fluid condition. The resulting shaped composite is particularly adaptable, for example, to form substrates for semiconductor devices, hybrid packages, multilayer packages or rigid, printed circuit boards.

The invention involves mixing together appropriate proportions of at least three different types of materials to provide selected properties. One of the materials is a ceramic powder which is present in a volume percent range selected according to the desired physical property requirements such as the mechanical, electrical, thermal and chemical properties. Typically, ceramics are known for their physical characteristics including high strength, low ductility, high dielectric constant, low coefficient of thermal expansion and chemical nonreactivity. The second material is a glass which forms a matrix for binding the ceramic and metallic particles together. Since glass is relatively fragile, it is typically provided at such a proportion so as to prevent a significant reduction of the composite strength, primarily provided by the ceramic particles. The glass is selected to be chemically reactive with the ceramic particles as well as with the third material, metal or alloy particles. The third material is comprised of metal or alloy particles which are dispersed throughout the composite. The metal or alloy particles enable the ceramic particles to shift position, while the composite is being pressed into a desired shape at the processing temperature, with less applied pressure as compared to a ceramic-glass slurry alone. In addition, the metal particles improve the thermal conductivity of the composite. The metal particles are preferably soft and ductile. It is believed that they tend to mold onto the adjacently disposed surfaces between adjacent ceramic ^"particles so that the ceramic particles can slide over each other during the forming process without being damaged. It is believed that the metal particles substantially reduce the occurrence of interlocking between ceramic particles thereby reducing the pressure necessary for forming the final shapes. The resulting composite is particularly useful in that it may be readily formed by a one step process into a complex, final shape having a very tight tolerance.

The ceramic material typically comprises particles selected for their physical characteristics. The specific ceramic may be selected from the group consisting of AL₂0-., SiC, BeO, Ti0₂, Zr0₂, MgO, A1N, Si₃N₄, BN and mixtures thereof. The present invention is not limited to these ceramics and may incorporate any desired ceramic or mixture of ceramics. The ceramic particles are present in a range of from about 20 to about 80 volume percent of the final fired composite and in a preferred range of from about 40 to about 65 volume percent. The ceramic particles can have any desired shape and have an average diameter of over about 1 micron, preferably, between about 1 to about 200 microns and most preferably, between about 40 to about 100 microns. The factors considered in selecting the desired ceramic include its dielectric constant, its coefficient of thermal expansion, its strength and chemical durability.

Conventionally, ceramics have been chosen for their high temperature capabilities since their melting point is at a temperature between about 1300° to about 2500°C. However, the present invention may not require the high temperature capabilities since the ceramic particles are bonded together in a glassy matrix which may have a relatively low softening temperature as compared to that of the ceramic. It is also within the terms of present invention to choose glasses which can be frabricated into components that are stable at very high temperatures.

A second component of the composite comprises a glassy phase having any desired composition in accordance with the properties required by the final composite. The glassy phase functions to bind the ceramic and metallic particles together within a matrix of the glass. An important characteristic is that the glass preferably is chemically reactive with both the ceramic and metallic particles. Also, it may be important that the glass has physical characteristics such as good chemical durability, high strength, an acceptable dielectric constant, and a softening point in a selected temperature range. Suitable glasses may be selected from the group consisting of silicate, borosilicate, phosphate, zinc-borosilicate, soda-lime-silica, lead-silicate, lead-zinc-borate glasses, however, any desired glass may be utilized. They may include phosphate glass systems c having high coefficients of thermal expansion and relatively low temperature softening points. In addition, a vitreous or devitrified glass may be selected.

A preferred example of a useful glass which 0 provides thermosetting properties suitable for application in an electronic environment is a devitrified, solder glass. This glass is a PbO-ZnO-B_jO, type glass and has a nominal composition of about 10 wt. % B, .025 wt. % A, 8.5 wt. % Si, .04 wt. % Ti, .01 wt. % Fe, 8.5 wt. % Zn, 12.5 wt. % Zr, .25 wt. % Hf, 2.0 wt. % Ba and the balance Pb. All elements are- reported as wt. % of corresponding oxide. After the glass is liquid, it is held at a temperature of about 500°C for about 0 10 minutes. The glass, upon solidification, then devitrifies. At that point, it will not re elt until it reaches a temperature of about 650°C. The glass is present in a range of from about 15 to about 50 volume percent of the fired composite and in a preferred range of from about 20 to about 40 volume percent. The glass is preferably selected with a softening temperature of from about 300° to about 1300°C. The processing temperature is selected so that the glass is at least above its 0 softening point and preferably is in the liquid state.

A thermosetting composite may be formed by mixing the ceramic and metal particles with a glass that devitrifies above a certain temperature. 5 First, the composite is preferably, formed at a processing temperature where the glass is in a liquid condition. The composite may then be held in an oven at approximately the processing temperature for a sufficient period so that it has a devitrified structure when it solidifies. When the glass is in the crystalline state, it is usually much stronger than in the vitreous state. A composite of this nature, i.e. ceramic and metal particles mixed with a devitrified glass, may be characterized as a thermosetting material. The latter characteristic is imparted because the remelting temperature is considerably higher than the original processing temperature.

For example, a devitrifiable solder glass, CVIII manufactured by Owens Illinois Co., becomes liquid at a processing temperature of about 470°C. This glass as previously described is a PbO-ZnO-B2θ, type glass and has a nominal composition of about 10 wt. % B, .025 wt. % A, 8.5 wt. % Si, .04 wt. % Ti, .01 wt. % Fe, 8.5 wt. % Zn, 12.5 wt. % Zr, .25 wt. % Hf, 2.0 wt. % Ba and the balance Pb. All elements are reported as wt. % of corresponding oxide. After the glass is liquid, it is held at a temperature of about 500"C for about 10 minutes so that upon solidification it has a devitrified structure. At that point, it will not remelt until it reaches a temperature of about 650°C. The thermosetting characteristics of the devitrified glasses are particularly advantageous because they allow the final product to be used in a higher temperature environment than the original processing temperature.

The third component of the composite comprises metallic particles which preferably are ductile at the processing temperature. The metallic particles are provided for their ability to reduce significantly the pressure necessary to densify the final composite product. It is believed that they mold about the surfaces of the ceramic particles when they are pressed between the ceramic particles during the processing procedures, thereby reducing or eliminating interlocking of the ceramic particles so as to reduce processing pressures. For example, the usual processing includes heating the mixture of ceramic particles with the metallic particles and the glass to the processing temperature where the metal particles are soft and ductile but not molten. The resulting composite slurry may be formed, i.e. in a mold. As the ceramic-glass-metal slurry flows into the shape of the mold, the ceramic particles are pressed against each other. The glassy phase is squeezed out from between adjacent ceramic particles providing points of contact. Without the presence of the metallic particles, the ceramic particles would remain in contact and could lock in position thereby retarding the ability of the slurry to flow. The ease of flowability is required for densification and shaping of the composite to the desired final configuration. Any loss of flowability becomes increasingly significant as the final shape becomes more complex.

A unique aspect of the present invention is the addition of metallic particles into the composite to significantly affect the flowability of the composite slurry. The metallic particles act sort of as a lubricant to enable the ceramic particles to slide over each other. It is believed that some of the metallic particles move into the interstices between adjacent ceramic particles and mold onto the ceramic particles at the points of contact which could interlock. It is believed that the metallic particles, being squeezed by the ceramic particles moving towards each other, adhere to the ceramic particles and then deform. This deformation enables the slurry containing the ceramic particles to move and flow, i.e. in a mold, while preventing damage to the ceramic particles. The metallic particles may be constituted of any metal or alloy which does not melt at the processing temperature of the composite. Preferably, the metals and alloys are selected from the group consisting of aluminum, copper, iron, silver, gold, stainless steel and alloys thereof. Preferably, the selected metals and alloys are ductile at the processing temperature. Since any metal or alloy is ductile slightly below its melting temperature and below its solidus, respectively, a suitably selected processing temperature enables the use of any metal or alloy which will be ductile at the latter temperature. In the case where the metal or alloy is not ductile enough at the processing temperature, added pressure may be applied during the forming process to provide the required deformation. The metal or metal alloy particles preferably have an average diameter between about .01 to about 50 microns. The final, fired composite may either contain the metallic particles dispersed continuously or discontinuously throughout the composite. Even in the case where the metallic particles are dispersed continuously, they do not form a matrix and are primarily subject to localized sintering. When the particles are dispersed continuously, the product would be classified as electrically conductive and when the particles are dispersed discontinuously the product would typically be classified as an insulator. The metallic particles are present in the composite in an effective amount up to about 45 vol. % of the fired composite to enhance the flow characteristics of the composite at the processing temperature. Preferably, the metallic particles make up from about 5 to about 45 vol. % of the composite.

For applications where the composite is preferably classified as an insulator such as for electronic packaging components, the metallic particles are preferably provided in a volume percent so that they are discontinuously dispersed throughout the fired composite. Preferably, the metal or metal alloy particles in this instance make up less than about 25 volume percent of the final, fired composite. More preferably, the metal particles make up. less than about 15 volume percent of the fired composite. Limiting the volume percent of metallic particles within these ranges is believed to prevent the formation of a continuous metal path in the final, fired composite.

The final composite, even with discontinuously dispersed metallic particles _r exhibits improved thermal conductivity as compared with a composite formed with only ceramic particles bonded together with a glassy matrix. It is particularly surprising that the final composite having dispersed metallic particles has increased thermal conductivity since there is no corresponding increase in electrical conductivity. The reason for this unusual characteristic is not fully understood.

For application where the composite is preferably classified as electrically conductive, the metallic particles are preferably provided in a volume percent so that they are continuously dispersed throughout the fired composite. Preferably, the metal or metal alloy particles in this instance make up more than about 25 volume percent of the final, fired composite. More preferably, the metal or metal alloy particles make up from about 30 to about 45 volume percent of the fired composite. Limiting the volume percent of ' the metallic particles within these ranges is believed to promote the formation of a continuous metal path in the final, fired composite thereby providing good electrical conductivity as well as thermal conductivity. Such an electrically conductive composite is believed to have wide application in areas outside the electronic packaging field such as in engineered composites and electronic composites where electrical conductivity is desired.

The process of forming the composite of the present invention includes providing three primary components; ceramic particles, metallic particles and a glass. The process may be accomplished by different techniques depending on the specific materials selected. For example, the ceramic particles may first be mixed with relatively ductile metal particles. Next, glass particles for bonding the ceramic particles together are added to the mixture. The mixture is heated to the processing temperature preferably corresponding to the temperature at which the glass particles are liquid and at least to their softening temperature. This preferably provides a semi-solid slurry of molten glass with solid metal and ceramic particles dispersed therein. Then, the composite preferably as a semi-solid slurry can be formed by conventional processes such as hot forging or hot pressing in a mold to any desired shape. With hot pressing, the mixture is preferably compacted at a pressure of from about 500 pounds per square inch (psi) to about 300 x 10 psi. The lowest usable pressure is believed to be that which enables the metallic particles-, adhered between adjacent ceramic particles, to^' deform. This depends on the ductility of the metal or alloy^"at the processing temperature. In the event that the metal is not ductile enough at the processing temperature, a higher pressure may be used to deform the metal particles.

Finally, the mixture is cooled to solidify the glass and bind the composite into a final devitrified shape. A conventional parting agent, such as boron nitride, may be provided on the mold walls to enhance the removal of the pressed product from the mold. Preferably, the parting agent does not stick to either the mold walls or the pres.sed body. However, the primary consideration is that the parting agent does not stick to the mold walls. An important advantage of the present invention is that the pressed composite is very dense and has a final shape that very closely corresponds to that of the mold.

The present invention can produce parts with much tighter tolerance, and a more complex shape than ceramic manufacturing processes currently available in the industry. This significant advantage is primarily due to the following reasons. Firstly, the starting materials do not necessarily contain any constituents, such as organics, which are lost during the actual process of fabrication. These losses can result in undue shrinkage. Secondly, the metal particles enable the ceramic particles to better flow over each other during processing. Another important advantage is that the firing temperature may be substantially lower than the range of temperatures at which ceramic materials are now fired. Processing at a lower temperature inherently decreases the processing cost as compared to any known process.

The fabrication process may include conventional steps including hot pressing and hot forging. Hot pressing can be carried out directly on the mixture of powders or on cold compacts. Depending on the glass, however, the hot pressing may require oxidizing atmospheres. For example, a solder glass such as PbO-ZnO-B-O-. requires an oxidizing atmosphere to prevent a change in the state of the glass.

Additional improvements in both thermal and mechanical properties can be obtained by using devitrified glasses in the composite. For electronic packaging, a devitrified glass enables the package to be formed at a significantly lower temperature than the temperature at which the package can operate.

An exemplary process follows. About 45 vol. % of a devitrifying glass (Owens Illinois CVIII) in fine particulate form (-325,90% mesh) was mixed with about 45 vol. % of fine particulate Al-0₃ (-120 mesh) and about 10 vol. % of fine atomized aluminum metal powder (-325 mesh). The resulting mixture was cold compacted at about 50 x 10 psi. The cold compacts were then hot pressed into 1-1/4" dia. 0.1" thick discs at a temperature of about 470°C and under a pressure of about 25 x 10 psi. The discs were then placed in an oven and kept at a temperature of about 500°C for about 10 minutes so that the final structure was devitrified.

An example of a ceramic-glass-metal composite formed of a vitreous glass follows.

About 45 vol. % of a vitreous glass (Corning 7052) in a fine particulate form (-325, 90% mesh) can^' be mixed with about 45 vol. % of fine particulate Al₂0₃ (-120 mesh) and about 10 vol. % of fine atomized iron metal powder (-325 mesh) .

The resulting mixture can be cold compacted at about 50 x 10 psi. The cold compacts can then be hot pressed into disc at a temperature of about

3 1220°C and under a pressure of about 25 x 10 psi pressure. The disc can then be solidified into a final structure that is vitreous. The resultant disc are thought to be very dense, and have a thermal expansion of about 70 x 10 in./in./°C.

The ceramic-glass-metal composite may also be constituted so as to be electrically conductive. An example of this type of structure is provided. About 15 vol. % of a vitreous glass (Corning 7052) in fine, particulate form (-325, 90% mesh) may be mixed with about 40 vol. % of fine atomized iron metal powder (-325 mesh) and the remainder of fine particulate Al-O^ (-120 mesh) . The resulting mixture can be cold compacted at about 50x10 psi.

The cold compacts can then be hot pressed into discs at a temperature of about 1220°C and under a

3 pressure of about 25x10 psi pressure. The discs can then be solidified into final structures that are vitreous. The resultant discs are thought to be very dense, have a thermal expansion of about

The composite described hereinbefore is particularly suitable for applications relating to semiconductor packaging. A first preferred embodiment is directed to CERDIP package wherein the unique composite of the present invention is substituted for the ceramic base and lid of the prior art as illustrated in Figure 1. The prior art package 8 typically included a ceramic base 10 and lid 12 with a leadframe 14 disposed therebetween. The leadframe is first bonded with a sealing glass 16 to the base component 10. The glass 16 bonding the leadframe to substrate 10 protrudes above the upper surface of the leadframe as illustrated in Figure 2. Then, the device 18 is bonded to the surface of the base using a conventional sealing material. Next, the device is electrically connected to the leads with bonding wires 20. A preform 21 of the sealing glass may be disposed between the leadframe and the lid 12.

Finally, the lid 12 is stacked on the glass preform and the base 10. The structure is then subjected to a temperature and pressure to hermetically seal the package. A potential weakness of the prior art CERDIP packages becomes evident in Figure 1. The sealing glass disposed between the base and lid, has the leadframe embedded therein. Therefore, the glass and the glass bonding sites, on either side of the leadframe, are subject to high stress from flexure of the leadframe. The leadframe is usually subjected to this type of flexure during the handling and installation of the package.

With the advent of the ceramic-glass-metal composite of this invention, ceramic shapes can be formed at relatively low temperatures, i.e. below about 500°C. This is particularly useful in fabricating semiconductor packages where because of the tremendous volume cost savings i.e. a critical issue. Since a low temperature can be used to form the ceramic-glass-metal composite, the mold has a longer working life and lower energy requirements are needed. However, a vitreous, low temperature glass for the glassy phase may result in the formed composite being subject to deterioration from exposure to high operating temperatures. The solution to this potential problem may be to form the^' glassy matrix from a devitrified glass as explained hereinbefore.

An important aspect of the present invention is the ability to embed metallic elements into the composite. This can be accomplished in a single step during the forming of the composite into a final shape. The metallic element is preferably formed of any metal or alloy which is thermally compatible with the glassy phase in the composite. If the metallic element does not adhere to the glassy phase, it may be appropriate to place an adherent coating on the surface of the metallic element to accomplish the same purpose. Examples of suitable metals include the group consisting of nickel, copper, aluminum^', iron, gold, silver and alloys thereof.

Applying this technology to the fabrication of electronic packaging results in strong, inexpensive, rapidly manufactured packages which can have a large number of configurations. For example, this technique may be utilized to embed a leadframe into a substrate during the hot forming step in the manufacture of a CERDIP. The result is a leadframe embedded directly into the ceramic-glass-metal composite, rather than into the glass sealant as in a conventional CERDIP. This new structure eliminates one of the significant weaknesses of the CERDIP structure, i.e. the breaking of the glass seal fo leadframe flexure. Referring to Figure 3, there is illustrated a semiconductor casing 22. The base component 24 and lid component 28 are both formed of a ceramic-glass-metal composite material 26 of this invention. The composite material comprises ceramic particles, a glassy phase for adhering the ceramic particles together, and metallic particles dispersed discontinuously throughout the composite. A metallic leadframe 30 is embedded into the base component 24. A sealing glass 32, such as a solder glass from the group consisting of borosilicate, soda-lime-silica, ,lead-silicate and lead-zinc-borate, bonds the base component 24 to the lid component 28.

The ceramic-glass-metal composite material 26 may be constituted in accordance with the principles set forth earlier in this specification. For example, the ceramic particles comprise about 20 to about 80 vol. percent of the final composite and preferably about 40 to about 65 vol. percent of the composite. The ceramic particles are selected in a range of from about 1 to about 200 microns in size. The metal particles comprise an effective amount up to about 25 vol. percent and preferably an effective amount up to about 15 vol. percent of the composite for enhancing the flow characteristics of the composite at the processing temperature. The latter temperature is selected to preferably be above the glass softening temperature of the glass, which bonds the composite together, and more preferably at or above the temperture at which the glass becomes liquid. Moreover, the bonding time and temperature of the sealing glass 32 is selected so that the glass in the composite does not become soft enough for the lid and base to significantly deform. In addition the metallic particles are about .01 to about 50 microns in size. The metallic particles have a melting temperature above the processing temperature which has been selected for enhancing the flow characteristics of said composite. The metallic particles are selected so as not to be molten at the processing temperature for forming the composite. The glass for adhering the composite together is selected from the group consisting of vitreous and devitrified glass.^"

By using devitrified glasses as the matrix of the composite, additional improvement in thermal and mechanical properties of the CERDIP package disclosed herein can be obtained. Specifically, devitrified glass results in improved thermal conductivity and mechanical properties of the composites.

A semiconductor casing 22, as illustrated in Figure 3, may be fabricated with the following steps. A base component 24 and a lid component 28 can be manufactured by first cold compacting the ceramic-glass-metal mixture with an organic binder, such as polymethyl etacrylate (PMMA) and polyvinylalcohol (PVA) , to the appropriate dimensions and shapes. The components can then be fired to a temperature of less than about 400°C to burn off the organic binder. Then, as illustrated in Figure 3B, a metallic leadframe 30 is placed on the top surface of the base component and hot pressed at a temperature where the glass is soft and at a pressure up to about 300 x 10 psi so that the top surface of the leadframe remains exposed and the glass consolidates and fills in the voids left by the burning out of the organics. The leadframe is preferably formed of any metal or alloy which is thermally compatible with the glassy phase in the composite. Also, the leadframe material is preferably bondable to the glassy phase of the composite as. well as the sealing glass 32. If the metallic leadframe itself does not adhere to the glassy phase, it may be appropriate to place an adherent coating on the surface of the metallic leadframe to accomplish the same purpose. Examples of suitable leadframe metals include nickel, copper, aluminum, iron, gold, silver and alloys thereof. However, the present invention is not limited to these metals or alloys and includes any metal or alloy which will function as required. Typically, a semiconductor device 34 may be attached to the base component using a conventional bonding material, such as, gold-silicon attach alloys or solder. Next, the device 34 may be wire bonded to the ends of the leadframe. Then a preform of sealing glass 32 may be disposed between the base component 24 and- the lid component 28. The package is then heated to the softening temperature of sealing glass 32 and pressed together. Next, the package is cooled to solidify the sealing glass 32 and form a hermetic seal.

The semiconductor casing of the type illustrated in Figure 3 has unique advantages over the the prior art CERDIP's. For example, the pressing of the leadframe into in the base component will result in significantly better lead coplanarity. This may improve the speed of ultrasonic wire bonders since the bonding operation of the lead wires between the leadframe and the chips may be significantly faster. Also, the shiny glass between the lead tips as shown in Figure 2, has been substantially eliminated. This is because the leadframe 30 is now affixed into the ceramic-glass-metal base component 24 as illustrated in Figure 3B. The advantage is a significant increase in the efficiency of the vision recognition system and a corresponding increase in the productivity of the wire bonding operation. Currently, vision recognition systems are utilized to automatically locate the lead tips of the leadframe attached to the CERDIP part. The systems often mistake the intervening glass for the lead tip as the reflectivity of the glass is equal to or better than the aluminum on the lead tip. Since the vision recognition system operates on a gray scale of contrast, the problem causes serious malfunctioning of the vision recognition systems. The current solution is to keep the glass at a much lower level as compared to the lead tips. This may be accomplished by tighter process control but often recognition error remains and the rejected work has to be completed in a manual machine. The present process can provide a dark ceramic, adjacent the aluminized or metallized lead, which provides excellent contrast. Referring to Figure 4, there is illustrated another embodiment of an electronic package 31 which includes metallic plates 33 and 34 embedded in the inside cavities of the lid and base components 28^* and 26', respectively. This package 31 may be manufactured in a similar manner to that described above with reference to the embodiment illustrated in Figure 3. The components illustrated in Figure 4 which are essentially the same as those illustrated in Figure 3 have the same reference numeral with a prime. The metallic plates reduce the "soft error" probability as the metallic materials usually contain a significantly lower quantity of naturally present radioactive elements as compared to conventional ceramics. Radioactive elements are responsible for soft errors which are a significant problem for semiconductor memories. Conventional ceramic manufacturers resort to expensive materials to reduce the radioactivity of the ceramic parts. The present invention overcomes this problem by embedding a metallic plate 33 into the cavity of the ceramic composite lid 28* as shown in Figure 4. This metallic plate is preferably formed of any metal or alloy which is thermally compatible with the glass matrix of the composite. Also, the metallic material is preferably bondable to the glassy phase of the composite. If the metal itself does not adhere to the glassy phase, it may be appropriate to place an adherent coating, such as a plating on the surface of the metal to accomplish the same purpose. Examples of suitable metallic material includes nickel, copper, aluminum, iron, gold, silver and alloys thereof. It is also within the terms of the present invention to place a metallic plate 34 in the cavity of the base plate, which in conjunction with the metallic plate 33 in the lid, will provide electromagnetic shielding. The metallic plate disposed in the cavity of the base has the same selection requirements as specified for the plate in the lid. The CERDIP parts, manufactured with metal plates, have an additional advantage as compared to parts produced by conventional methods. The die attach cavity metallization may be accomplished by electroplating a much smaller thickness of as compared to the conventional method of thick film application in the die cavity. In a conventional thick film application method, a thickness of as high as about 600 to about 700 micro-inches of gold is applied. This thickness results from the sintering process. The fired gold layer has a porosity as a result of the sintering process. The gold paste contains as its main ingredients powders of gold and glass. These powders are contained in an organic base consisting of a solute phase and a solvent phase to provide the appropriate rheology for the application of paste. The porous nature of the sintered gold also necessitates thicker layers to safeguard against process problems at die attach, i.e. the unknown extent of porosity is and cannot be properly controlled. During the firing process, the glassy flux chemically bonds with the substrate. The bond between the glass and the gold, however, is mechanical in nature. The glassy phase and gold interweave and form numerous mechanical locks. The extra amount of gold used to form such a bond is special for this application and not necessary in electroplating gold to a metal plate.

The electroplated layer of gold on the metallic plate or coupon, i.e. base plate 34, need not be any thicker than about 50 to about 60 micro-inches to accomplish the same objective. As gold constitutes a significant portion of the cost of a CERDIP, ie. about 40%, a reduction in gold usage by as much as 90% would dramatically reduce the cost of the part.

The present invention is not limited to CERDIP's but also includes other design configurations, such as CERQUADS. This is similar to a CERDIP except that the leads extend from all four sides of the package. In the past this was not feasible with ceramic packages because of the impact of the lead flexure on the seal.

Another embodiment of the present invention is directed to the production of multi-layer packages as shown in Figures 5 through 10. In Figure 5 a first layer of cold pressed ceramic-glass-metal composite 40, in accordance with the principles described hereinbefore, is illustrated. In Figures 6A and 6B, a second layer of cold pressed ceramic-glass-metal composite 42, preferably of the same material as used to form layer 40, is illustrated. In Figures 7A and 7B, a third layer of cold pressed ceramic-glass-metal composite 44, preferably of the same material as used to form layer 42, is illustrated. Metallic elements in various configurations as desired may be added at different locations and assembled in accordance with the specific requirements of the component being fabricated. For example, in Figure 8 a leadframe component 46 is disposed about layers 40' and 42'. Components which are essentially the same as those illustrated in another Figure have the same reference numeral primed. Also, a metallic element 48 is placed on the surface of the first layer 40'. Further a metallic seal ring 50 is placed on the top surface of the third layer 44'.

The structure 49, formed by these ceramic-glass-metal components in conjunction with the metallic elements 48 and 50, is then hot pressed to embed the leadframe 46 and the seal ring 50 into the composite bodies 47 to form the structure 54 illustrated in Figure 9. This Figure 9 is not to the same scale as Figure 8. The hot pressing may be done at a processing temperature dependent upon the selection of the glass for the glassy matrix of the composite. The metallic element 49 may be electroplated with a layer of gold to enhance the bonding of a semiconductor die thereto. The die may be attached within the cavity and wire bonded to the ends of the leads 51.

Finally, a metallic cover (not shown) can be sealed to the seal ring 50.

The metal used in forming the hermetically sealed component, or any other similar device, may be surface coated in a variety of ways. For example, the metal may be gold plated. A typical processsing temperature of about 470°C for borosilicate solder glasses would not degrade the quality of such a plating. Also, the metal could be selectively plated, e.g., the bond tips 31 and the exposed portions of the leadframe can be gold plated. The metal area in contact with the composite may be nickel plated to improve the adhesion between the glass and the metal. Portions of the metal inserts 48 or 50 could be plated after embedding into the composite. It is also within the terms of the present invention to plate with any desired metal or metal alloy as required by the specific requirements of the material system and the application of the product. Further, composite metal inserts 48 or 50 wherein the cladding is the desired coating can be used if appropriate.

Referring to the embodiment illustrated in the Figure 10, there is shown a a package 59 which is similar to the CERDIP type package of Figure 9 with the addition of a heat sink 60 and a top cover 62. The package 59 may be classified as a leadless ceramic chip carrier. This embodiment takes advantage of the ability to bond a metal structure into the composite. The metal structure is selected in accordance with the principles discussed regarding the metallic elements 33 and 34 of Figure 4. The heat sink 60 has an upper section 68 having a peripheral shape being substantially the same as cavity 65 in the composite body 66 and extending into cavity 65. The heat sink 60 also has a lower section 69, larger than the upper section 68 which extends to an outer surface 67 of the composite body 66. The heat sink 60 has the dual function of removing heat generated by die 63 and providing a surface 61 to which the die 63 can be bonded. Again the surface 61 can be gold plated as discussed hereinbefore. The top cover 62, may be fabricated of any desired metal or alloy, such as those selected for the leadframe 46, and can bonded to the seal ring 50' using conventional techniques such as soldering and brazing.

Referring to the embodiment of Figure 11, there is shown a package 70, similar to that of Figure 10, except that the external leads 72 are brazed or welded to the leadframe 73 embedded in the ceramic body 74. The added fins 71 on the heat sink 60' are optional. Moreover, the metal heat sink 60' itself is optional^' and provided to improve thermal performance although it may be omitted, if desired. The heat sink 60* is preferably formed of a high conductivity metal or alloy, such as, for example, one being selected from the group consisting of copper, aluminum, gold,, silver, nickel, iron and alloys thereof, which is compatible with the ceramic-glass-metal composite material used to form the ceramic body 74. The metal lid 62' is preferably soldered, brazed or welded to the metal seal ring 50" embedded in the composite body 74.

Referring to the embodiment illustrated in Figure 12, there is shown a package 80 which is similar to the package 59 of Figure 10. The difference between package 59 and package 80 resides in the seal ring 50' and metal cap 62 having been replaced with a ceramic-glass-metal composite cover 82 and a sealing glass 84. Again, the heat sink 60" is optional and may be omitted. if desired. The embedded internal leads 88 may, if desired, be fabricated from a material of relatively low thermal conductivity since the lead and leadframe do not provide a significant contribution to the thermal performance. The leads 90 may also be fabricated from a relatively .low conductivity material. Since both the leadframe 88 and the leads 90 are formed from a solid metal, the leads 90 may be attached to the leadframe 88 by spot welding rather than gold alloy brazing to gold metallization as is typically done in the multilayer packages. This, may provide a significant cost advantage.

Referring to the embodiment of Figure 13, there is illustrated a package 100 which provides a high quality replacement for a CERDIP package. The ceramic-glass-metal component 102 forms the body of the package. A leadframe 104 is embedded in the body 102. Leads 90' may be affixed to the leadframe 88' by any conventional technique such as brazing or by spot welding. A metal seal ring 50' ^*' is also embedded into the top surface 110 of the component 102. The seal ring 50^rf'has a gold coating 112 disposed on its upper surface. Also, a gold coating 114 is provided on the ends of leadframe 88' to enhance the bonding of bonding wires from a chip. Finally, a conventional lid 62' ^rι is provided to be sealed to the seal ring by any conventional means such as soldering.

Referring to the embodiment of Figure 14, there is illustrated a package 120 which is similar to that illustrated in Figure 13. However, to reduce the cost of the package, the metal top 62' ^•' and gold coating 112 are replaced with a ceramic lid 82* bonded directly to a ceramic-glass-metal component 102' with a solder glass 84'. Referring to the embodiment of Figure 15, there is illustrated a package or semiconductor casing 130 which is provided with a unique heat sink that has superior thermal performance. The package 130 includes a body component 131 having a cavity 133 adapted to receive a semiconductor device 135. A leadframe 134 is also embedded into the body component 131 with lead ends 139 extending into the cavity for wire bonding to the semiconductor device 135. A cup shaped component 132 is molded into the ceramic-glass-metal component 131 so that the surface 137 of the cup becomes the die mounting surface. A flange 136, extending substantially perpendicular from sidewalls 142 of the component 132, becomes a portion of the bottom surface of the casing 130. In effect, the flange 136 becomes a heat .sink. The flange 136 may also include folded up end sections 138 which extend substantially perpendicular to the flange 136 and up the sides of the package. However, it is within the terms of the present invention to delete the end sections 138. If desired, a metallic element 140, such as a high conductivity material like copper, may be affixed to the bottom of the package to bridge from one portion of the flange 136 to the other portion of the flange and further improve the heat sink capabiliites of the flange. Also, the sidewall 142 of the drawn section of the cup 132 may be provided with a plurality of ports 144 through which the ceramic-glass-metal mixture flows in order to fill the cavity. To provide maximum thermal performance, the flange cup is preferably selected of a high thermal conductivity material, such as copper. The thickness of the cup may be maximized without failure of the bond between the ceramic-glass-metal composite and the metallic cup due to mismatch in the coefficients of thermal expansion. A sealing lid, not shown, may be attached onto the top surface 146. The lid may be formed of any desired material such as metal, glazed metal or a ceramic and bonded in accordance with the techniques described with regards to the embodiments illustrated in Figures 12, 13 and 14, i.e. with a sealing glass, with a seal ring and a gold-tin solder or with a solder glass.

The ceramic-glass-metal composites, as described herein, are particularly useful to fabricate multi-layer, ceramic-glass-metal substrates which can contain electrical conductor patterns between adjacent pairs of a plurality of ceramic-glass-metal substrates. The manufacturing ^"steps of a typical unit will now be described. The assembly begins with a substrate 150, as illustrated in Figure 16A, preferably formed by the process of consolidating a mixture of the ceramic-glass-metal composite with an organic binder, such as PMMA . Note that any number of through-holes 152 are provided as required. These through-holes 152 are of any desired diameter and are typically in the range of about 5 to 20 mils. The size of the through-holes 152 does not make up part of the invention and they may be larger or smaller as required. The holes 152 may be filled with a conductor 154, such as a conductive paste of an organic carrier and particles of any desired conductive material, such as, for example, gold, silver, platinum, palladium, copper and alloys thereof. If desired, the glass used in the substrate 150 may be mixed with the conductor particles in orde -to increase the bond strength between the conductor 154 and the ceramic-glass-metal substrate 150. The through-holes may also contain a solid wire or be filled with a conductor such as solder. The layers of metal 156, 158 may be formed of any desirable conductive material, such as, for example, copper, aluminum, iron, copper-silver, copper-gold and alloys thereof.

Referring again to Figure 16B, layers 156 and 158 of metal foil may be disposed on one or both surfaces of the ceramic-glass-metal structure 150. Preferably, the layers 156, 158 of metal foil adhere to the glass in the ceramic-glass-metal substrates. However, it is within the terms of the present invention to bond the layers of foil to the substrate with a glass as disclosed in U.S. Patent Application Serial No. 811,846. For example, the metal foil may be selected from the group consisting of deoxidized copper alloy and oxygen free copper alloy; the glass may be selected from the group consisting of silicate, borosilicate, borate, and phosphate glasses. The structure 150 is first fired to a temperature burn out the organic binders. This burn out temperature is typically less than about 400°C, although it may be higher, if appropriate. The stacked assembly of foil and ceramic-glass-metal substrate are then heated to the glass softening temperature and subjected to a lamination pressure so that the layers of metal foil adhere to the glass matrix within the substrate 150 and the conductor 154 in the through-holes 152 contacts the layers of foil 156 and 158. It is also within the terms of the present invention to dispose a layer of glass between the substrate 150 and the layers of foil 156, 158. The structure is heated to a temperature where the layers of glass soften and bind the layers of foil 156, 158 to the substrate 150.

Referring to Figure 16C, multilayered circuit patterns 160, 162 may be formed in the foil layers 156, 158 by any desired process such as etching with conventional dry film, photoresist techniques. Using conventional photo-etching techniques includes coating the outer surfaces of foil layers 156 and 158 with a conventional positive photoresist which may consist of a light sensitive resin of the photodegradable type. Then, a prescribed patterned mask of material, opaque to exposing light, is placed in contact with the photoresist. On light exposure, only the unmasked portion of the photoresist layer gets exposed. The mask is then removed and the resist is developed. The exposed portions of the resist are removed and the circuitry formed in a subsequent etching process. The etching may be accomplished with any conventional solution such as potassium iodide or a FeCl^/HCl copper etchant. The assembly may be coated with photoresist and etched in this manner several times to produce the desired patterns and structures. This assembly may be adapted to be a hybrid circuit device. Then, as shown in Figure 16D, a second ceramic-glass-metal structure 164 which may be formed by the same process as structure 150, as described hereinbefore, is disposed or stacked on the top surface 166 of the foil bonded to structure 150. The assembly is heated to a temperature where the glass in each of the substrates 150 and 164 softens. Then, a lamination pressure may be applied to press the structure 150 against the structure 164 to cause adhesion between the glass of the two structures. A pressure of less than about 300 psi is thought to be adequate to carry out this step. However, any appropriate lamination pressure may be applied.

Although the invention thus far been described with the electrical patterns being cut into the foil subsequent to the adherence to the substrate 150, it is also within the terms of the present invention to form the electrical conductor patterns in the foil by any desired technique prior to applying the foil to the substrate. Then, the substrate and foil may be heated to the glass softening temperature and placed under lamination pressure so that the foil adheres to the ceramic-glass-metal substrate as shown in Figure 16C. Thereafter, the steps described above to produce a multilayer hybrid circuit assembly 167 as seen in Figure 16D, may be repeated to form any number of layers. The resulting structure 167 is particularly advantageous in that it is not substantially affected by thermal contraction typically experienced by the ceramic-glass-metal structures as they cool from the consolidation temperature to room temperature. The resulting hybrid circuit assembly is, therefore, reproducible and the circuitry between the conductor layers and the electrical interconnects maintain through-hole contact. For example, the conductors in through-holes 170 and 172 of structure 164 make contact with the circuitry 160 formed on the ceramic-glass-metal structure 150.

Referring again to Figure 16E, there is shown an additional substrate 178 which includes a plurality of conductor filled through-holes 180 in contact with the conductive circuitry on the surface 182 of substrate 150. The alignment of the through-holes 180 with the conductive circuitry 162 can be controlled to substantially eliminate problems with through-hole electrical contact. Finally, conductor pins 184 may be attached by any means, such as brazing, to the conductor filled through-holes 180 to form a pin grid array structure 168.

In another embodiment of the present invention, the circuitry 160 and 162 as illustrated in Figure 16C, may be applied to the substrate 150, as shown in Figure 16A, by screen printing a metal conductor paste onto the substrate 150. With this process, the substrate 150 may be formed with a high temperature glass and fired prior to the application of the conductor paste. Then, the conductor paste is preferably pressure sintered up to about 300 x 10 psi at a temperature.of from about 450° to about 1000°C.to consolidate the metallic particles in the printed conductors so that they become highly conductive as well as being bonded to the glass in the ceramic-glass-metal substrate 150. This step may be accomplished within a mold in order that the substrate does not lose its desired shape.

Thereafter, additional substrates may be disposed on either side of substrate 150, as shown in Figures 16D and 16E, so as to form a multilayer structure similar to 167 and 168 described hereinbefore.

This invention is also directed to ceramic articles that are easily formed with selected compositions depending upon the specific application. The disclosed composite is particularly advantageous for use in the general area of engineering ceramics. This includes a wide range of new applications for ceramics in areas such as ceramic engines and engine parts, cutting tools, body replacement parts and a wide variety of other possibilities. The invention is particularly useful to form products which both require the advantages inherent in a ceramic material as well as the need for close tolerances and ease of manufacture. The ceramic materials are particularly noted for their ability to withstand high temperatures, their low dielectric constant, their high strength, and their chemical stability.

Figures 17 through 21 show a variety of articles which may be formed of the composite of the present invention. Figure 17 is an example of ceramic rotor blade; Figure 19 is an example of an engine formed of primarily ceramic parts; Figure 18 is an example of a body part prosthesis; Figure 20 is an example of a grinding wheel; and Figure 21 is an example of a ceramic engine block with metal inserts; all formed of the composite in accordance with this invention. The examples shown in Figures 17 through 21 are not meant to be exhaustive of the possible uses of the disclosed composite but rather exemplifies the broad range of its use. Typically, the composite of this invention is most useful in applications where the physical characteristics of a ceramic are particularly advantageous.

The specific structure shown in Figures 17 through 21 are merely exemplary and are not meant to be limitive of the invention. Rather, each figure represents an example of the type of article in accordance with this invention. The structural shape shown are indeed well-known structural shapes and a wide variety of other well-known structural shapes could be employed in their place to provide the same type of articles. in accordance with this invention, it is preferred to form the articles from a mixture of the ceramic-glass-metal composite by conventional processes including hot forging and hot pressing in a mold. Alternatively, if desired, the composite may be preformed and held together with an organic, such as, for example, polymethylmetacrylate (PMMA) polyvinylalcholol (PVA) . In processing, the preform is first heated and held at a temperature and time whereby the volatilize organics are removed. Then, the preform may be hot pressed or hot formed so that the maximum density can be achieved in the final product.

Figure 17 illustrates a ceramic rotor 200 fabricated from the ceramic-glass-metal composite. For a number of years, there has been an attempt to improve the efficiency of turbo-charge turbines for engines by using ceramic components in areas exposed to high temperature exhaust. This is important for future generations of gas engines to be smaller and more efficient. Uncooled metal super alloys, which are presently used in turbo-charge turbines and particular for the rotors, will not perform adequately at these temperatures due to creep related failures. In addition, the rotors are in constant contact- with a highly corrosive, high temperature engine exhaust gases. Moreover, the fabricating of a rotor is very demanding because of its complex shape. Attempts have been made to replace the expensive super alloy turbine blades with ceramic blades. However, the processing is very expensive and not amenable to mass production. Due to the strength of the ceramic material, the final shaping requires expensive and time-consuming cutting with a material such as a diamond. A ceramic rotor, using the principles of the present invention, can be manufactured at a reasonable cost since it can be formed, in a one step process, into a precision, complex shape. Both the metal particles and the glass of the composite are preferably selected to withstand the operating temperatures experienced by the ceramic rotor. For example, the glass might be selected from a borosilicate which has a liquid temperature of about 1220°C. The metallic particles are preferably corrosion resistant ^'and can be selected from materials such as stainless steel, tungsten, molybdenum and nickel. The ceramic is selected to be able to withstand the temperatures and chemical properties of the gases. These include alumina, silicon-carbide and titanium-carbide. It is believed that the present invention provides an unusual opportunity to mold the ceramic rotor into its required complex curved shape due to the substantial elimination of skrinkage problems as was prevalent in the prior art. It is also believed that the present invention enables the fabrication of a ceramic rotor at a lower price, a lower temperature and with a significantly better shape tolerance.

Figure 19 illustrates an engine 220 having many components fabricated of the ceramic-glass-metal composite. The composite material is particularly advantageous for forming engine blocks since it can withstand a high operating temperature, is easily formed into precise, complex shapes and comprises relatively inexpensive materials. Moreover, if desired, metal inserts may be molded directly into the composite when it is formed, as required. It is thought that engines, primarily formed of ceramics, are particularly useful since they can operate at much higher temperatures than metal engines and possibly eliminate the need for cooling. The engine block 220 illustrated in Figure 19 may be formed of the ceramic-glass-metal composite. Metal inserts, such as the cylinders 26, may be incorporated in the engine block as appropriate. The ceramic-glass-metal composite suitable for an engine block may comprise about 20 to about 35 volume percent of a borosilicate glass, from about 5 to about 10 volume percent of iron or iron alloy particles and the remainder alumina particles. Moreover, the constituents of the composite can be selected in a proportion so that the material has a high thermal conductivity to further enhance the cooling of the engine block. This might include increasing the volume percent of iron or iron alloy particles to about 30 to about 40 volume percent so that they are in a continuous dispersion throughout the composite. In this case,^" the glass would most likely be present in a range of from about 15 to about 25 volume percent. Figure 18 shows a replacement body part 230. In particular, this is a human hip prosthesis. In the past, human body parts and in particular bones and joints have been formed from ceramics as well as stainless steel and titanium and cobalt alloys. The metallic materials are particularly susceptible to corrosive fatigue since they reside in a biological atmosphere. The needed physical properties of a bone replacement is toughness, non-corrosiveness and ease of formability. The composite material of the present invention is particularly advantageous for this application. Appropriate materials and proportions can be selected so that the composite is easy to form into a complex shape, non-corrosive and somewhat similar and, therefore, compatible to human bones, thus rapid adaptation to the human body. It is thought that a suitable composite might be formed of about 40 to about 65 volume percent of a ceramic such as alumina. Alumina is particularly advantageous because of the high quality in which it may be obtained. The metallic particles are preferably selected to be highly resistant to corrosion and may include silver, gold or stainless steel. Metallic particles will make up about 5 to about 15 volume percent of the final composite. The remainder of the composite is of a glass which is thought to have good chemical durability in a human body at the body temperature.- In this application, the composite is particularly advantageous because of the ease of forming the complex shapes required, the chemical durability and the ability to change the shape as required. This is particularly important for replacement parts since they must be custom made to a doctor's specifications. Although, a hip prosthesis is illustrated, it is within the terms of the present invention to form any desired body part as required.

Figure 20 illustrates a grinding wheel 240. One important characteristic of a grinding wheel is its hardness so that it may cut many other materials. Also, wear resistance is a factor regarding its life expectancy. The wheel is preferably brittle so the particles will come off and provide a new cutting surface. Heat dissipation is also important and, finally, the wheel should be thermal shock resistant. The ceramic-glass-metal composite of the present invention may be readily formed into a grinding wheel having each of these characteristics. The metallic particles make up about 5 to about 20 volume percent of the composite and are selected from materials including copper, tungsten. molybdenurα, nickel and alloys thereof. The glass makes up about 15 to about 25 volume percent of the composite and is preferably a borosilicate. The remainder of the composite is a ceramic and may be selected from materials including alumina, silicon-carbide and titanium-carbide. The metal particles, being dispersed throughout the wheel, provide a high thermal conductivity and enable good heat transfer from the wheel.

Figures 17 through 21, therefore, illustrate a wide variety of engineering ceramic products which can be formed of the composites in accordance with this invention. While specific materials were mentioned with respect to the various articles, they were meant to be exemplary and not limitive of the invention. Any desired ceramic-glass-metal composite in accordance with this invention could be employed in any of the articles shown. Other uses of the disclosed ceramic-glass-metal composite include cutting tools, seals, bearings, scissors, and knives.

In summary, these articles are provided in accordance with this invention having high strength, easy formability into complex shapes with tight tolerance and corrosion resistance.

Engineering ceramics include all fine ceramics mixed with other materials as required, i.e. the ceramic-glass-metal composite of the present invention, which are used in areas including electro-ceramics, mechanical and heat-resistance ceramics, functional ceramics, structural ceramics, bio-ceramics, electrical ceramics and optical ceramics.

For the purpose of this invention, a final, fired composite is defined as the composite after densification at the processing temperature. Discontinuously dispersed means that the particles are not generally interconnected so as to provide electrical conductivity. Continuously dispersed means that the particles are generally interconnected to provide electrical conductivity. The terminology "thermally compatible", as used within the specification, defines materials having coefficients of thermal expansion which are relatively close to one another. Each of the packages or substrates described in connection with this invention may be constructed by initially cold compacting a mixture of the ceramic-glass-metal particles with organic binders into a preform. Then, the preform can be heated to volatilize and drive off the binders.

Next, the preform may be hot formed into the final desired shape.

Although this case has been described in terms of hot forming under pressure, it is also within the terms of the present invention to form the ceramic-glass-metal slurry by any glass forming method such as casting, blowing, blow molding, etc. It is apparent that there has been provided in accordance with this invention electronic packaging of components incorporating a ceramic-glass-metal composite which satisfies the objects, means and advantages set forth hereinabove. While the invention has been described in combination with the embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and all variations as fall within the spirit and broad scope of the appended claims.

Claims

IN THE CLAIMS :

1. A ceramic-glass-metal composite, characterized by: from about 5 to about 45 volume % of metallic particles for enhancing the flow characteristics of said composite; from about 15 to about 50 volume % of a glass for adhering said composite together; and the balance essentially ceramic particles; said composite having a structure comprising substantially a matrix of said glass with said ceramic and metallic particles dispersed therein.

2. The composite of claim 1 characterized by said ceramic particles comprising from about 20 to about 80 vol. percent of said composite.

3. The composite of claim 2 characterized by said ceramic particles being selected from the group consisting of Al O , SiC, BeO, Ti0₂, Zr0₂, MgO, A1N, Si^ ^, BN and mixtures thereof.

4. The composite of claim 3 characterized in that said metallic particles are selected from the group consisting of aluminum, copper, iron, silver, gold, stainless steel and alloys thereof.

5. The composite of claim 4 characterized by said glass being selected from the group consisting of silicate, borosilicate, phosphate, zinc-borosilicate, soda-lime-silica, lead-silicate and lead-zinc-bora e glasses.

6. The process of forming a ceramic-glass-metal composite, characterized by the steps of: providing a mixture comprising: from about 5 to about 45 volume % of metallic particles for enhancing the flow characteristics of said composite; from about 15 to about 50 volume % of glass particles for adhering said composite together; and the balance of essentially ceramic particles; heating said mixture to a processing temperature, said processing temperature being selected so as to be above the glass softening point of said glass particles and below the melting point of said metallic particles; pressing said mixture at said processing temperature into a desired shape; and solidifying said glass to form a composite structure comprising substantially a matrix of said glass with said ceramic and metallic particles dispersed therein.

7. The process of claim 6 characterized by the step of selecting said ceramic particles to comprise from about 20 to about 80 vol. percent of said composite.

8. The process of claim 7 characterized by the step of selecting said ceramic particles from the group of A1₂0₃, SiC, BeO, Ti0₂, Zr0₂, MgO, A1N, Si,N., BN and mixtures thereof.

9. The process of claim 8 further characterized by the step of selecting the metallic particles from the group consisting of aluminum, copper, iron, silver, gold, stainless steel and alloys thereof.

10. The process of claim 9 further characterized by the step of selecting the glass from the group consisting of silicate, borosilicate, phosphate, zinc-borosilicate, soda-lime-silica, lead-silicate and lead-zinc—borate glasses.

11. A composite combined with a metallic component, characterized by: a base component 24 formed of a ceramic-glass-metal composite material; said composite material comprising an effective amount up to about 25 volume % of metallic particles for enhancing the flow characteristics of said composite; from about 15 to about 50 volume % of a glass for adhering said composite together; and the balance essentially ceramic particles; said composite having a structure comprising substantially a matrix of said glass with said ceramic and metallic particles dispersed therein; and a metallic component 36, said component 36 being embedded into said composite material.

12. The composite of claim 11 further characterized by the glass matrix being from the group consisting of vitreous and devitrified glass.

13. A semiconductor casing 22, characterized by: a first component 24 formed of a ceramic-glass-metal composite material; a second component 28 formed of a ceramic-glass-metal composite material, said composite material comprising an effective^" amount up to about 25 volume % of metallic particles for enhancing the flow characteristics of said composite; from about 15 to about 50 volume % of a glass for adhering said composite together; and the balance essentially ceramic particles; said composite having a structure comprising substantially a matrix of said glass with said ceramic and metallic particles dispersed therein; a metallic leadframe 30, said lead-frame 30 being embedded into said first component 24; and a sealing glass 32 bonding said second component 28 to said first component 24.

14. The semiconductor casing 22 of claim 13 characterized in that said first component 24 comprises a base and said second component 28 comprises a lid.

15. The process of forming a semiconductor casing 22, characterized by the steps of: providing a first component 24 and a second component 28 each formed of a ceramic-glass-metal composite material; said composite material having a structure comprising substantially a matrix of said glass with said ceramic and metallic particles dispersed therein; providing a metallic leadframe 30; embedding said leadframe 30 into said first component 24; disposing a sealing glass 32 between said first component 24 and said second component 28; and heating said second component 28, said first component 24 and said sealing glass 32 to_,a temperature where said sealing glass 32 is in the liquid state; pressing said first and second components 24, 28 together; and solidifying said sealing glass 32 to bond said first component 24 to said second component 28.

16. A multilayer circuit device, characterized by: a plurality of ceramic-glass-metal substrates; a layer of an electrically conductive circuit pattern bonded between adjacent ceramic-glass-metal substrates; and conductive means extending through each of said plurality of ceramic-glass-metal substrates to contact said electrically conductive circuit pattern.

17. An engineering ceramic product formed of a ceramic-glass-metal composite, characterized by: from about 5 to about 45 volume percent of metallic particles for enhancing the flow characteristics of said composite; from about 15 to about 50 volume percent of a glass for adhering said composite together; and the balance essentially ceramic particles; said composite having a structure comprising substantially a matrix of said glass with said ceramic and metallic particles dispersed therein.

18. The product of claim 17 characterized by it being selected from the group consisting of ceramic rotors 200, engine blocks 220, grinding wheels 240 and body prostheses 230.