Specialized metallurgical processes – compositions for use therei – Processes – Producing solid particulate free metal directly from liquid...
Reexamination Certificate
2000-09-22
2004-03-02
Wyszomierski, George (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing solid particulate free metal directly from liquid...
C075S338000, C075S351000, C075S355000
Reexamination Certificate
active
06699304
ABSTRACT:
FIELD OF THE INVENTION
The present invention involves an aerosol method for producing a palladium-containing particulate product, palladium-containing particulate products producible by the method, uses of the powders in the manufacture of electronic products, and electronic products so manufactured.
BACKGROUND OF THE INVENTION
Palladium is widely used in the manufacture of electrically conductive thick films for microelectronic devices. A trend continues, however, to produce ever smaller particles for thick film applications. Generally, desirable features in such small particles include a small particle size; a narrow particle size distribution; a dense, spherical particle morphology; and a crystalline grain structure. Existing technology for manufacturing palladium-containing particles could, however, be improved with respect to attaining all, or substantially all, of these desired features for particles used in thick film applications. Improvements in the particles could result in significant performance advantages and/or cost savings when used to make electronic or other products.
One method that has been used to make small particles is to precipitate the particles from a liquid medium. Such liquid precipitation techniques are often difficult to control to produce particles with the desired characteristics. It is especially difficult by the liquid precipitation route to obtain particles having dense, spherical particle morphology and with good crystallinity.
Aerosol methods have also been used to make small palladium particles. One aerosol method for making small particles is spray pyrolysis, in which an aerosol spray is generated and then converted in a reactor to the desired particles. Spray pyrolysis systems involving palladium have, however, been mostly experimental, and unsuitable for commercial particle production. Furthermore, control of particle size distribution is a concern with spray pyrolysis. Also, spray pyrolysis systems are often inefficient in the use of carrier gasses that suspend and carry liquid droplets of the aerosol. This inefficiency is a major consideration for commercial applications of spray pyrolysis systems.
Additionally, palladium is easily oxidizable and has a tendency to oxidize during the manufacture of electronic devices. The oxidation of palladium during manufacture of electronic devices is problematic because volume expansion that accompanies oxidation can cause film cracking and delamination. It has been proposed that the susceptibility of palladium particles to oxidation is reduced by the addition of a small amount of an alkaline earth metal and by making the palladium particles as single-crystal particles to eliminate diffusion of oxygen along grain boundaries. Even with an alkaline earth additive, however, oxidation of palladium during the manufacture of microelectronic devices is still a significant problem and the cost of making single-crystal particles is high because of the high processing temperatures and long residence times required.
There is a need for improved palladium-containing powders, for improved methods of manufacturing palladium-containing powders and for improved products incorporating or made using improved palladium-containing powders.
SUMMARY OF THE INVENTION
The present invention provides powders of high quality, micro-size palladium-containing particles of a variety of compositions and particle morphologies, and with carefully controlled particle size and size distribution, and an aerosol method for producing the particles. The particles are useful for making a variety of products.
Through careful control of the aerosol generation, and in combination with other features of the present invention concerning manufacture of palladium-containing powders, the process of the present invention permits preparation of very high quality powders of, palladium-containing particles that preferably have a weight average size of typically about 0.1 micron to about 4 microns in size, and for many applications from about 0.2 micron to about 0.8 micron in size. The powders also have a narrow size distribution such that typically at least about 90 weight percent of the particles being smaller than about twice the weight average size of the particles. Furthermore, typically less than about 10 weight percent, and preferably less than about 5 weight percent, of the particles are smaller than about one-half the weight average size of the particles.
The invention includes both single-phase and multi-phase, or composite, particles useful for a variety of product applications, including for use as catalysts and in the preparation of thick film paste formulations, such as are used for depositing palladium-containing films during manufacture of various electronic and other products. Multi-phase materials may be in a variety of morphological forms, such as an intimate mixture of two or more phases or with one phase forming a surface coating over a core including another phase.
One preferred class of multi-phase particles includes a metallic palladium-containing phase and a nonmetallic phase, which frequently includes a ceramic material. The nonmetallic phase could be in the form of a coating around a core of the metallic phase, in the form of small domains dispersed in a matrix of the metallic phase, or in some other form. A variety of ceramic and other materials can be used to effect a variety of beneficial modifications to particle properties, such as a modification of densification/sintering properties for improved. compatibility and bonding with ceramic dielectric layers in electronic devices, and especially when the palladium-containing powder is used to make internal electrodes in multi-layer capacitors. An important use of multi-phase particles is to reduce film shrinkage during firing in the manufacture of electronic devices. One preferred group of ceramic materials for use in the multi-phase particles are titanates, as are frequently used in dielectric layers of multi-layer capacitors. Another preferred group of ceramic materials for use in multi-phase particles includes silica, alumina, titania and zirconia, and especially silica and alumina.
The palladium-containing powders may also be made with surprisingly high resistance to palladium oxidation, providing a significant advantage during the manufacture of thick film electronic products by reducing volume expansion during firing. This is particularly important in the manufacture of multi-layer capacitors, multi-chip modules and other cofired products where volume expansions due to palladium oxidation can result in significant film cracking and delaminations. The high oxidation resistance of the particles is particularly surprising because the resistance to palladium oxidation may be obtained without the use of alkaline earth metal additives. This is even more surprising because the particles may be made to exhibit good oxidation resistance even when the particles are polycrystalline. This is particularly advantageous because particles of high oxidation resistance may be made without the significant operating expense required to make single crystal particles. In that regard, the maximum average stream temperature in the pyrolysis furnace should typically be in a range of from about 900° C. to about 1300° C., although other ranges may be more preferred in some circumstances. Furthermore, although the powders exhibit high resistance of palladium to oxidation without any additives, it has also been found with the present invention that oxidation resistance may be further improved by the addition of small quantitites of tin to the particles.
The palladium in the powder is typically in a metallic phase, whether in a single phase or multi-phase particles. In one embodiment of the invention, the particles of the powder includes high quality palladium alloys, and especially alloys with silver. It has been found that the quality of the alloy is highly dependent upon processing conditions. When preparing particles including a palladium/silver alloy, the maximum average stream temperatures i
Caruso James
Chandler Clive D.
Hampden-Smith Mark J.
Kodas Toivo T.
Powell Quint H.
Marsh & Fischmann & Breyfogle LLP
Superior Micropowders LLC
Wyszomierski George
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