MXPA99007655A - Low temperature method and compositions for producing electrical conductors - Google Patents

Abstract

A composition for matter having a metal powder or powders for specified characteristics in a Reactive Organic Medium (ROM). These compositions can be applied by any convenient printing process to produce patterns of electrical conductors on temperature-sensitive electronic substrates. The patterns can be thermally cured in seconds to form pure metal conductors at a temperature low enough to avoid damaging the substrate.

Description

METHOD AND LOW TEMPERATURE COMPOSITIONS TO PRODUCE ELECTRICAL CONDUCTORS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to compositions that can be used to apply conductors to electrical components such as printed circuit boards and semiconductors, particularly, to compositions that can be applied and converted into solid conductors to temperatures below 450 ° C. 2. Related Technique A common method for a printed circuit manufacturing process is subtractive or semi-additive processes in which conductors are formed by recording unwanted copper. A completely additive process would have many advantages over subtractive or semi-additive methods. The main problem in providing a completely additive process to produce printed circuits is the requirement of high electrical conductivity with a solidification temperature low enough to be compatible with polymer-based circuit boards. Another important problem is making connections with the additive traces, preferably by conventional welding. The present technology includes conductive epoxies with low solidification temperature and transient liquid phase that produce traces with poor electrical conductivity and poor solder capacity or high temperature thick film inks that produce traces with good electrical conductivity and good solderability but that are limited to ceramic substrates. These small, expensive and specialized substrates are required to withstand the high temperatures of thick film ink over 650 ° C and usually above 850 ° C. A method that could double the performance of thick film inks but not polymer-based substrates at 250 ° C to 350 ° C would allow the application of this technology widely in the $ 27 billion hard circuit board industry and the industry. flexible circuits of $ 2.5 billion worldwide.

The "thick film" technology is routinely practiced to produce hybrid circuits on ceramic substrates. R.W. Vest, "Electronic Ceramics", R. Breckenridge, ed., 1991. Conductive patterns are created by screen printing and stencil printing of coarse film pastes or inks on ceramic substrates and the application of temperatures of 850 to 1100 ° C to reduce the inks that contain metal in metal. An example of such inks are the silver and palladium compositions that have been recently reviewed by Wang, Dougherty, Huebner and Pepin, J. Am. Crem. Soc 77 (12), 3051-72 (1994). Typically thick film inks contain metallic powders, an inorganic glass bond and a vehicle consisting of a polymer bond and a solvent. The vehicle provides the correct consistency for screen printing and typically consists of a polymer such as ethyl cellulose, hydrogenated rosin or polyacrylates dissolved in a low volatility solvent. The common solvents are terpineol, dibutyl carbitol and several ethers and glycol esters. The inks are applied to the ceramic substrates by screen printing, dried until the solvent is removed and treated with heat, usually in a band furnace, to break down the polymer bond and melt the metal and inorganic glass bond. The glass phase provides the bond to the substrate which is usually alumina, and the metal provides the electrical conductivity. Typically conductors have a ribbed cross section with glass layers alternating with metal layers. Glass tends to Concentrate on the ceramic interface and the metal on the air interface. The conductivity is typically one-half to one-fourth of the raw metal.

A number of thick film compositions contain active surfactants to improve the application of screen printing and the stability of the dispersions of the metal powder. Often these active tense agents are metallo-organic compounds such as carboxylic acid soaps. These are convenient in that they will decompose at a relatively low temperature to deposit the metal or its oxide which can play a useful function in the burned driver.

U.S. Patent Nos. 5,071,826 issued December 10, 1991 and 5,338,507 issued August 16, 1994 to J.T. Anderson, V.K. Nagesdh and R.C. Ruby, present the addition of silver neodecanoate to mixtures of superconducting oxides in which the neodecanoate decomposes in the metal at 300 ° C to cover the superconducting grains with silver. The coated grains are sintered and then oxidized at 600-800 ° C to produce an improved superconducting oxide of force and critical current.

The addition of titanate to thick film conductors by the decomposition of an organometallic titanate is described by K.M. Nair in U.S. Patent No. 4,381,945 issued May 3, 1983.

U.S. Patent No. 4,599,277 issued July 8, 1986 to J.M. Burrows that presents the addition of metallic acid compounds to thick film inks to increase the densification temperature of the metal to correspond to that of the ceramic substrate at 850 - 900 ° C, the inverse of the process required to apply conductors to polymer circuits at low temperatures.

Conventional thick film paste compositions contain silver frost, glass filings and silver resinates, which are carboxylic acid soaps, as well as active surfactants such as Triton XI 00, are described in U.S. Patent Nos. 5,075,262 Issued on December 24, 1991 and 5,183,784 issued on February 2, 1993 to MN Nguyen and co-workers. The aim was to eliminate the drying step after printing, and it was said that the resinate promoted adhesion and minimized the slots and voids in the union of semiconductor molds with a ceramic substrate at 350-450 ° C.

They were issued to V.K. Nagesh and R.M. Fulrath Patent in United States number 4,130,671 on December 19, 1978, which was assigned to the Department of Energy. She presents a similar composition of glass filing and silver resatura that decomposed at low temperatures to provide glass particles coated with silver similar to the previous Anderson superconductor. The particles are applied to a substrate either before or after the decomposition of the resinate and ignited in an oxidizing atmosphere at 500 to 700 ° C to provide a conductor of glass particles covered with metal.

Still other conventional thick film compositions of glass and metal powders in an organic carrier but without the resinate are described in U.S. Patent Nos. 5,250,229 and 5,378,408.

To create a low temperature analog of the coarse film process, it will be necessary to find a new mechanism to obtain adhesion and cohesion of the deposited metal that can operate at temperatures below 450 ° C, which is the upper extreme temperature limit that the Most polymers can tolerate. The use of inorganic glass powder bonds that are universally used in coarse film inks is not possible in the application because none of them melts at a sufficiently low temperature, and the glass will not bond to metal or the polymer substrates.

Other approaches to this objective have been described. The most common is the creation of conductive inks or pastes of electricity by incorporating metal powder, usually silver dust, into an organic matrix, the materials called "Thick Polymer Film". This is an important industry with products available from Ablestik, AIT, Hokurika, M-Tech, Thermoset, Epoxy Technology and Ferro, among others. These materials can be printed on circuit boards, and have good adhesion. An example of the application of this technology is described in an article by K. Drefack in Electronics 62 (17), 2E - 4E, 1979, filtering in silk of Societe des Produits Industrielles ITT that covers conductors with graphite and silver base of this type on rigid and flexible circuits. A problem with this approach is that the inks conduct by random contacts between grains of dust in the organic matrix, and the conductivity is poor. The typical values of the resistivity, that the reciprocal of the conductivity, are of 40 to 60 microohm cm, in comparison to the crude silver of 1.59 microohm cm and the conductors of thick film of high temperatures of 3 - 6 microohm cm. Even more annoying is the fact that the electrical conductivity is not constant with time. Conductivity depends on upstart contacts between individual metal grains that are likely to become and breaking up randomly as the trail warms and cools and particularly as it is exposed to moisture and other environmental influences.

Another important problem with thick polymer film materials is that due to their organic content, they can not be welded.

A copper powder conductor bonded with typical resin is described in Japanese Patent Application No. 52-68507, June 1977. The Patent in US Pat.

United Issue 4,775,439 issued October 4, 1988 to R.E. Seeger and N.H.

Morgan, describes a much more elaborate thick polymer film approach. In this concept, metallic powder and a bond to a substrate are poured and dried.

The trace is then covered with a polymer film that is adhesively laminated to the substrate to hold the conductor in place. The above does not correct the problem of obtaining electrical conductivity comparable to raw metal.

The raw conductivity has been achieved at low temperature by the decomposition of organometallic compounds on various substrates. They can be applied by inkjet printing as described by R.W. Vest, E.P. Tweedll and R.C. Buchanan, Int. J. of Hybrid Microelectronics 6, 261-267, 1983. Vest, et al., Have investigated the technology called MOD (Organometallic Decomposition) for many years. The most relevant aspect of this research was reviewed in "Liquid Ink Injection Printing with MOD inks for Hybrid Microcircuits" Teng, K.F. and Vest, R.W., IEEE Transactions on Components, Hybrids and Manufacturing Technology, 12 (4), 545-549, 1987. The authors describe their work in printing silver and gold conductors as well as dielectrics and resistors. MOD compounds are pure synthetic metallo-organic compounds that decompose cleanly at low temperatures to precipitate the metal as the metallic element or oxide, depending on metal and atmosphere. The noble metals, e group of silver, gold and platinum are decomposed to metallic films in the air.

The organic mitas binds to the metal through a heteroatom which provides a weak bond that provides easy decomposition at low temperature. An oxygen bond, as in the carboxylic acid metal soaps, has been found satisfactory, as have the amine bonds for gold and platinum.

Vest et al., Investigated the metallization of ceramic and silicone substrates by ink-jet printing of xylene solutions of soaps such as silver neodecanoate and gold 2-ethylhexanoate amine. Satisfactory resolution images (0.003 inches or 75 microns) were obtained, but the conductivity was low due to the extremely small thickness of the layers after decomposition which was less than one miera. The preliminary experiments of Partnerships Limits on epoxy glass circuit boards with silver neodecanoate solutions demonstrated that tightly bonded conductors could be produced on polymer substrates. Again, the difficulty was that they were very thin and had inappropriate conductivity. It was found that the addition of more MOD compound resulted in wider but not thicker trails. The MOD compound melts before decomposition and expands on the surface uncontrollably. Since the fusion provides a well-consolidated metallic deposit after decomposition, which is desirable, and since some MOD compounds are actually liquid at room temperature, this is an unavoidable problem. A possible solution to this problem is to increase the thickness by printing many layers, which Vest et al., Found appropriate for the metallization of silicon solar cells, but the above deviates from the production in a single step of circuits, which is our goal Similar materials and techniques have been used to apply thin film metallization and initial coatings that are then increased with welding or electroplating. U.S. Patent No. 4,650,108 issued March 17, 1987 to B.D. Gallagher and assigned to the National Aeronautics and Space Administration, Washington, D.C.; U.S. Patent No. 4,808,274 issued February 28, 1989 to P.H. Nguyen; U.S. Patent No. 5,059,242 issued October 22, 1991 to M.G. Firmstone and A. Lindley and U.S. Patent No. 5,173,330 issued December 22, 1992 to T. Asano, S. Mizuguichi and T. Isikawa are examples. Thin films can not by themselves provide adequate conductivity.

A creative attempt to solve the problem of conductivity was described in U.S. Patent No. 4,487,811 issued December 11, 1984 to C.W. Eichelberger The patent describes increasing the conductivity by a metal replacement reaction in the deposit of a nobler metal in solution, for example the replacement of iron with copper. In the process of doing the above, the contact between the particles is improved by the greater volume of the replacement metal and its higher intrinsic conductivity. A resistivity of 7.5 microohm cm was achieved, substantially better than the silver-laden epoxies, but they do not reach the performance of thick film inks.

The replacement reaction solved yet another problem of polymer inks in that the material is more solderable, what conductive epoxy formulations are not generally. Another approach for the ability to weld is described in U.S. Patent No. 4,548,879 issued October 22. from 1985 to F. St. John t W. Martin. Nickel powder is covered with saturated monocarboxylic acid with ten or more carbon atoms. The coated powder was mixed with epoxy novolac resins in a vehicle of butyl carbitol acetate and filtered on silk on an epoxy glass board. After tanning at 165 ° C, the conductive trace could be covered with solder by flows and dips in molten solder, while a trace made with nickel if covered could not be welded. No improvement in electrical conductivity was described with this process.

A silver powder is described in "Novel Silver Powder Composition", United States Patent No. 4,186,244 issued January 29, 1980 and "Process for the Formation of Novel Silver Powder Composition", Patent in United States number 4,463,030 issued on July 31, 1984, both issued to R.J. Deffeyes and W.H. rmstrong and assigned to Graham Magnetics, Inc., North Richard HIlls, Texas. The silver powder was lined by the decomposition of dry silver oxalate in the presence of a long chain carboxylic acid, either saturated (stearic acid, palmitic acid) or without saturations (oleic acid, linoleic acid). The acid reacted with the metal powder as it was formed to provide a protective coating on the surface and to limit the particles to sizes smaller than one.

The particles were washed to remove the excess acid and mixed with an equal weight of a conventional thick film vehicle consisting of bonding of cellulose ethyl polymer and pine oil solvent.

The resulting tub was applied on a ceramic or polyimide substrate and heated at 250 ° C in air for 3 to 90 seconds to convert the coated powder into a silver conductor with a declared conductivity of one ohm per square, which is not suitable for practical circuits with traces many hundreds or thousands of long pictures. It is said that the cover can be welded without flow, which is credible if residual acids act as a flow. It is declared resistant to leaching in a molten solder bath, which is unexpected, based on the well known solubility of silver in solder.

A somewhat similar silver frost material was patented by Grundy of Johnson and Matthey, U.S. Patent No. 4,859,241 on August 22, 1989. The frost was prepared by melting silver powder with active silver stearate active agent in an organic solvent to produce silver frostings coated with silver stearate that provide a glass filled ink composition of superior stability. The above is a common method for preparing stable powders and frost.

Another class of materials used to produce additive electronic circuits on the Liquid Phase Transients materials developed by Toronaga Technologies under the commercial name of "Ormet". These materials and their applications are described by P. Gandhie Circuit World 23 (1), October 1996, pages 43-46 and Roberts, E .; Procedures of NEPCON WEST '96, 3, 1748-1752, 1996. The materials consist of a mixture of powdered silver or copper conductors with powder welding and a polymer bond. They can be printed as epoxy conductors but when they are heated the solder melts with the conductor which creates a network of molten metal.

Greater heating at temperatures in the area of 220 ° C for 10 minutes solidifies the polymer bond which provides the adhesion of the conduits to the polymer substrate. An alternative is to provide an adhesive layer on the substrate as presented by M.A. Capote and M.G. Todd from Toranaga Technologies in Patents of the United States No. 5,538,789 of July 3, 1996 and 5,565,267 of October 15, 1996.

Ormet compositions typically produce electrical resistivities in the range of 20-30 microohm cm. There is also a problem with the ability to weld due to the presence of the polymer bond.

None of the materials or mixtures described above achieve the goal of providing a composition that can be solidified to a well-bonded, well consolidated metallic conductor with electrical conductivity comparable to conventional thick film inks but with a solidification temperature below 350 ° C, preferably below 300 ° C, more preferably below 275 ° C, which is required for compatibility with circuit board substrates based on conventional polymers. None of these materials has made it possible to impact the circuit board industry with new technology for rapid production through a simple process without the production of hazardous waste. A new approach to provide this low temperature capability is needed.

SUMMARY OF THE INVENTION The present invention provides compositions and printable processes for applying them to temperature sensitive substrates and hardening them in traces of high electrical conductivity at temperatures that the substrates can withstand. The essential constituents of these compositions are 1) a mixture of metal powder of specified characteristics and 2) a Reactive Organic Medium (ROM) in which consolidation of the mixture of metal powder to a solid conductor takes place.

The metal powder mixture is composed of a mixture of at least two types of metal powders: 1) metal flakes with a preferred larger diameter of approximately 5 micrometers and a thickness to diameter ratio of 10 or more and 2) colloidal or semi-colloidal metal powders with actual diameters of less than about 100 nanometers that are not added to any large degree.

The ROM may consist of any organometallic compound that can be readily decomposed to the corresponding metal, or an organic compound that can react with the metal to produce such a compound. Examples are metal soaps and corresponding fatty acids. Other examples are metal amines and mercapto metal compounds and their corresponding amino and sulfur precursors.

The constituents of these compositions are weighed in appropriate proportions, mixed with additional surfactants or viscosity modifiers if necessary to provide the proper consistency and melted together as is in a three roll casting to provide a homogeneous composition and printable.

The composition is printed on the substrate using any convenient printing technology. Grid printing and stencil are suitable for rigid substrates in relatively small numbers with high resolution. Gravure, printing and offset printing are suitable for high production speeds on flexible substrates. Inkjet printing and electrostatic printing offer the additional advantage of direct compute control of the printed image. The above allows the circuits to be printed directly from Computer Aided Design (CAD) files and eliminates the need for special tools. Each circuit can be different, if desired, to code and prototype. The same end can be achieved at lower production speeds with computer controlled supply equipment. This equipment produces points or lines by moving a needle over the surface and supplying printing composition by a pressurized pump or syringe.

Substrates to which these compositions can be applied include rigid glass reinforced epoxy laminates, polyimide films for flexible circuits, other polymer-based electronic components, metal cushions and semiconductor components. The compositions adhere naturally to most epoxy surfaces. Good adhesion to polyimide films requires the presence of a cover. FEP Teflon covers and low glass transition point have been found satisfactory.

Adhesion to metals requires a clean surface, similar to the requirements for welding. The acid constituents in the ROM act to promote adhesion. The plating or galvanizing of the metal cushions is also effective. The use of organic welding protectors on copper cushions is effective. Adhesion to semiconductors requires the metallization with which the compositions are compatible.

The compositions are solidified by exposure to heat for a short period of time. This time varies with the temperature at which the substrate can safely be exposed, but is less than one minute to reach the highest temperature. electrical conductivity of which the composition is capable, and in some cases it is less than 10 seconds at temperature.

Silver and gold can be solidified in the air. Copper and other non-noble metals require a protective atmosphere. Nitrogen with less than 3 parts per million oxygen has been found suitable for processing copper compositions. The addition of water vapors during the solidification process, but not before or after, has been found beneficial for the solidification of copper compositions.

The compositions of the present invention can be applied selectively only where the conductors are required on a temperature sensitive substrate by any convenient printing technology. These include reticle printing, stencil, gravure printing, printing, offset printing, inkjet printing and electrostatic printing and copying. Unexpectedly, it has been found that when heated, these compositions solidify in seconds into well-bonded, well-bonded conductive traces of pure metals at temperatures hundreds of degrees less than those required for conventional metallurgical sintering processes. The above provides a completely new capability to create printed circuits at high speed and lower cost than with conventional technology. The production of hazardous waste characteristic of the processes of photolithography, plating and taxing is completely eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS The preferred specimens according to the present invention will be described in detail with reference to the following figures, wherein: Figure la is an Exploration Electron Micrograph (SEM) of copper flakes as used in the present invention.

Figure Ib is a SEM of silver flakes as used in the present invention.

Figure 2a is a Transmission Electron Micrograph (TEM) of agglomerated copper powder not suitable for the present invention.

Figure 2b is a TEM of colloidal silver powder as used in the present invention.

Figure 3a is a SEM cross section of an unconsolidated copper trace, characteristic of the prior art.

Figure 3b is a cross section of an unconsolidated silver trace characteristic of the prior art.

Figure 4a is a SEM cross section of a well-consolidated copper trace characteristic of the present invention.

Figure 4b is a SEM cross section of a well-consolidated silver trace characteristic of the present invention.

Figure 5 is a representation of the electrical resistivity against temperature for a copper composition of the present invention, in which: A) Resistivity, microohm - cm; B) 60 seconds; C) Ink C-136, 76% metallic weight; Y D) Temperature, ° C.

Figure 5b is a representation of the electrical resistivity against the temperature for a silver composition of the present invention, in which: A) Resistivity against temperature; B) microohm - cm; and C) Temperature, ° C.

Figure 6a is a plot of electrical resistivity versus time for a copper composition of the present invention, wherein A) Resistivity, microohm-cm; B) Flake + powder + mineral oil; C) flake + acid; D) flake + powder + acid; E) Raw Cu; and F) Time, seconds.

Figure 6b is a plot of electrical resistivity versus time for a silver composition of the present invention, wherein A) Resistivity, microohm; and B) Time, seconds.

Figure 7 is a representation of electrical resistivity of a copper trace of the present invention against the oxygen content of the solidification atmosphere, wherein: A) Resistivity, microohm-cm; and B) Oxygen ppm.

Figure 8 is a representation of electrical resistivity of a copper trace of the present invention against the moisture content of the solidification atmosphere, wherein: A) Resistivity, microohm-cm; and B)% water.

Figure 9a is a schematic illustration of the application of the compositions and processes of the present invention to create patches on circuits flexible, where: A) Make circuit; B) Print drivers crossing; and C) Treat in the oven; D) Add welding mask.

Figure 9b is a schematic illustration of the application of the compositions and the process of the present invention to create traces of circuits simultaneously and to attach components to them instead of welding, wherein: A) Print drivers and cushions crossing; B) Place components; and C) Oven treatment Figure 9c is a schematic illustration of the application of the compositions and processes of the present invention to a hybrid technology in which conductive traces developed in photodefinite dielectric materials are simply and rapidly metallized, wherein: A) Develop resistance; B) Print PARMOD; C) Place components; and D) Oven treatment.

Figure 10a is a schematic illustration of a method for producing inner layers by the compositions and processes of the present invention, wherein: A) Continuous network of substrate; B) Printing press; C) Oven; D) Court; and E) Interior layers.

Figure 10b is a schematic illustration of a method for producing multi-layer circuits terminated by the compositions and processes of the present invention, wherein: A) Printing; B) Heating; C) Laminate; and D) Court.

Figure 11 is an SEM of a multilayer circuit fabricated by the methods of the present invention, wherein: A) Aluminum; B) Polyimide; Chorus; Y D) PARMOD.

Figure 12 is a comparison of the characteristics of the compositions of the present invention compared to those of the prior art, wherein: A) Thick Film on Polymer Alternatives; B) solidification time, seconds; C) PARMOD; D) Temperature, ° C; E) Thick film range; F) 600, Resistance microohm - cm; G) Carbon - epoxy; H) Silver - epoxy; I) Transient liquid phase; J) PARMOD; K) Conventional thick film; L) Electrical resistivity, microohm - cm; M) Temperature, ° C; and N) solidification time, minutes.

DETAILED DESCRIPTION OF THE INVENTION The compositions of the present invention are composed of a mixture of metallic powder and an Organic Reactive Medium (ROM). These compositions can be applied to temperature sensitive substrates and solidified in well-established traces of circuits, well bonded by heat treatment at a temperature that does not damage the substrate. The compositions of the present invention exhibit a critical temperature above which they undergo a transformation to well-established electrical conductors with a resistivity only two or three times the gross resistivity of the metal in question. The electrical conductivity is equal to that obtained by sintering conventional high temperature metal powders in conventional thick film compositions on ceramic substrates. It is notorious how this consolidation process takes place at temperatures of 400 or 500 ° C less than those conventionally used in thick film technology, and in occasions are of order in magnitude much shorter than those required for sintering.

Suitable metals include copper, silver, gold, zinc, cadmium, palladium, iridium, ruthenium, osmium, rhodium, platinum, iron, cobalt, nickel, indium, tin, antimony, lead, bismuth and mixtures thereof. In a preferred specimen, the metal powder mixture contains metal flakes and colloidal or semi-colloidal metal powder in which the composition contains about 70 to 80% by weight of the metal powder mixture.

The metal flakes have a larger dimension of between 2 to 10 micrometers, preferably around 5 micrometers, and a thickness of less than 1 micrometer. They can be produced by techniques well known in the art by melting the corresponding metal powder with a lubricant, which is often a fatty acid or a fatty acid soap. The initial powders are usually produced by chemical precipitation to obtain the desired particle size and purity grade. The leaflets are sold for electronic applications as constituents of thick film inks and silver-bearing epoxy conductors, as mentioned above. Figures la and Ib show scanning electron micrographs of copper and silver flakes, respectively, that are used.

In the compositions of the present invention, the flakes perform several functions. They form a skeleton structure in the printed image that holds the other ingredients together and prevents loss of resolution when the mixture is heated to solidify. The flakes naturally assume a laminar structure like a stone wall that provides electrical conductivity in the direction parallel to the surface of the substrate and provides a framework for reducing the amount of metal transport necessary to achieve the well-established pure metallic conductors that are the object of this invention. They also provide flat surfaces of low surface energy, to which the other constituents of the composition can be joined and over which the metal can be deposited.

The other constituent of the metal powder mixture of the present invention are colloidal or semi-colloidal powders with diameters below 100 nanometers. The colloidal or semi-colloidal powder is preferably present in about 40% by weight of the total weight of the metal powder mixture. A primary function of these powders is to lower the temperature at which the compositions will consolidate into almost solid pure metallic conductors. The presence of fine metallic powder has been found useful in advancing this low temperature process with silver and essential for the consolidation of copper mixtures.

It is important that they are present as individual particles. The metallic particles so small have a strong tendency to agglomerate in agglomerates with an open skeleton structure as illustrated in Figure 2a. This is a copper powder produced by evaporating copper metal in inert gas where it condenses into particles of the desired size. In this case, however, the individual particles agglomerated completely in large agglomerates with a rigid skeleton structure which prevents consolidation of the mixtures made with the powder.

Figure 2b shows a TEM of colloidal silver particles with a nominal diameter of 20 nanometers in an excellent dispersion state. This material has been used in silver compositions and the consolidation temperature has decreased critical from 300 to 260 degrees C. These results and similar results with various copper powders are shown in Table 1.

TABLE 1 Electric Resistivity and Adhesion as a Function of Copper Dust Size Treated at 355 ° C for 3 minutes To reach and preserve the desired degree of dispersion of the colloidal metal it is essential to stabilize the particles so that they can not be added. In the case of the silver particles they were stabilized by the presence of an active taut agent that covered the surface of the particles and prevented metal-to-metal contact. The above favors chemical precipitation as a means to produce the powders, since they can be exposed to an environment that promotes stabilization from formation to final consolidation.

The Reactive Organic Medium (ROM) provides the environment in which the metallic powder mixture is united to form well-consolidated conductors. Many kinds of organic compounds can work like ROM. The common characteristic that they share and that makes them effective is that they have, or can form, a link with the metal via a heteroatom. The heteroatoms may be oxygen, nitrogen, sulfur, phosphorus, arsenic, selenium and other non-metallic elements, preferably oxygen, nitrogen or sulfur. This link is weaker than the links that hold half organic board, and can be thermally broken to deposit the metal. In most cases, the reaction is reversible, so that the acid or other organic residue can react with metal to reform the metallo-organic compound, as shown schematically w: R-M ^ > R + M where R is a reactive organic compound and M is the metal.

Examples of said compounds are the soaps of carboxylic acids, in which the heteroatom is oxygen; amino compounds, in which the heteroatom is nitrogen; and mercapto compounds, where the heteroatom is sulfur.

Specific examples of the ROM constituents are the carboxylic acids and the corresponding metal soaps of neodecanoic acid and 2-ethyl hexanoic acid with silver and copper, such as leg neodecanoate illustrated by the formula: wherein Rj, R2 and R3 are C9H19 and 2-ethyl silver hexanoate as illustrated by the formula: O C2H5 I 'í Ag- O - C - CH - C3H7 Gold hexanoate 2-ethyl amine is an example of a nitrogen compound: H Hexanoate and gold amine 2 - ethyl (gold octoate amine) T-dodecyl gold mercaptide is an example of a sulfur compound: wherein Ri, R2 and R are CnH2.

These ROM compositions can be made by methods well known in the art. All of the above compounds are capable of decomposition to the respective metals at relatively low temperatures. For the silver neodecanoate and the silver hexanoate 2-ethyl (silver octoate), the decomposition temperature is between 200 and 250 ° C. For the corresponding copper compounds, it is between 300 and 315 ° C. Gold sulfides decompose at very low temperatures around 150 ° C. The gold amine ocloate decomposes to 300 and 500. The copper and silver compounds can be reformed from the corresponding acids at the same temperature, so the reaction is reversible, as mentioned above.

In some cases it is convenient to add compounds that improve rheology well known in the art to improve the printing characteristics of the compositions of the invention. Alpha - terpincol has been used to produce the viscosity of copper and silver compositions to facilitate grid printing. The alpha -terpineol also participates in the consolidation reaction by virtue of the acid character of the OH group attached to an unsaturated chain. Through the selection of constituents and additives, it has been proven possible to produce a range of printable compositions ranging from fluid inks with a viscosity of 15 multipoles to solid powders.

The compositions of this invention have been applied by reticle, stencil, gravure printing, supply, inkjet printing and by applying the cover to an adhesive pattern with a dry powder composition or toner. The reticle, as used in the application of conventional thick film pastes, has been used more extensively to prepare samples for evaluation. A composition with a viscosity of approximately 500 poise is forced through a thin screen with a photodefined open image of the desired conductive pattern itself with a rubber applicator. The resolution that has been reached by this method is approximately 125 micron lines and spaces (5 mil), although the production grid printers can reach patterns as fine as 50 microns. Conductive traces with thicknesses of up to 50 microns have been printed, although most of these patterns have been around 12 microns thick, which is equivalent to 0.37 ounces of copper per square foot.

Substrates Preferred substrates include polymer-based substrates such as FR-4 glass-reinforced epoxy laminate and coated polyimide films for silver compositions. Copper compositions, due to their higher solidification temperature, are limited to covered polyimides. The tested compounds did not adhere to uncovered polyimide films, despite the fact that the films treated in an oxygen plasma show some improvement. The reason is that the adhesion depends on the chemical nature of the surface and some form of organic adhesive is necessary for good adhesion. The above may be inherent in the chemistry of the surface since it appears in many epoxies. The silver compositions of this invention will adhere very strongly to FR-4 surfaces, even when the epoxy has solidified in the original lamination process. It is possible to apply the materials of this invention to one side of the laminate, solidify it in the furnace, apply another pattern to the other side and solidify again without any appreciable decrease in the adhesion achievable on the second side.

The organic adhesive can be either thermoplastic or thermoset. FN Kapton® from DuPont, which has been used extensively in the development of the present compositions, has a Teflon® FEP coating on the surface that is melted and attached to the metal traces deposited by the present process. KJ Kapton® films have a low glass transition point polyimide surface coverage that can be softened to bond to the present compositions in the temperature range of 220 to 235 ° C. The polyamic acid coatings can be metallized with these compositions and solidified to dielectric polyimide which isolates and bonds the conductors thus formed. The photoimaginable depoxy acrylate surfaces provide excellent adhesion after solidification.

Silver compositions containing only the metallo-organic decomposition compound will adhere to copper surfaces with silver or tin or those protected with an organic welding protector such as benzotriazines. Silver compositions containing neodecanoic acid or other acids will also stick to the discovered copper. The copper compounds that contain acids will bond well to bare copper. The adhesion measured in tensile tests on various combinations of metals and substrates is summarized in the attached table.

Solidification Process and Critical Temperature for Consolidation When the metalloorganic decomposition compound or the acid from which it is formed is mixed with the metal flake and colloidal metal powder constituents described above, printed as a relatively thin layer on an appropriate substrate, and heated to a critical temperature above the decomposition temperature of the metalloorganic compound, a reaction takes place which results in the spontaneous consolidation of the loose aggregate metal constituents in an almost solid metallic trace with greatly reduced electrical resistivity. Cross sections of Scanning Electron Micrographs that have been heated to decompose the metalloorganic compound but below the critical temperature are illustrated in Figures 3a for copper blends and 3b for silver blends, respectively. In Figure 3b the silver layer is illustrated as 10 and the Kapton FEP substrate is a 12. The individual metal flakes and dust particles can still be observed in both SEMs, much like an image of the unheated mixture.

When the traces are heated above the critical temperature, there is a rapid decrease in the electrical resistivity, a drastic increase in the mechanical cohesive force of the deposit and the appearance of changes of deposits, as illustrated in Figures 4a, b and c. Here copper, silver and gold mixtures have been heated above the critical temperature, and the metal leaflets and metallic powder have been consolidated into a solid metal bonded working network. In Figure 4a the copper trace is 10 and the Kapton substrate FN is 12. In Figure 4b the silver deposit is illustrated as 20. The sample is tilted so that its surface shows as 16 the substrate at 14 and the edge of the reservoir at 18. Figure 14 is at a lower magnification so that the reservoir appears as 30, the polyimide substrate as 32 and Teflon FEP layers like 34 and 36.

The critical temperature for copper and silver mixtures is illustrated in the Figures 5a and 5b. In both cases traces were applied by means of a reticle on Kapton substrates and kept at the critical temperature for 60 seconds. For copper (and gold) the critical temperature is in excess of 300 ° C. It can be observed that between 305 and 325 ° C the resistivity of the traces falls by a factor of 100 to a value below 10 microohm-cm. The crude resistivity of copper is 1.7 microohm-cm. At the same temperature at which the resistivity drops, the mechanical properties of the traces improve in the same dramatic way. If fragile and with poor adhesion as measured by pleating the samples and removing the traces with Scotch Tape, the samples became sufficiently ductile to survive an acute 180 degree fold in the 75 micron (3 mil) substrate followed by the test of the tape. The pleat test is equivalent to an elongation of the metallic trace of 17%. The tape test is equivalent to an adhesion of approximately 10 Newtons / cm 16 pounds per linear inch). Heating to even higher temperatures decreases the resistivity only slightly.

For silver, the decrease in resistivity with the temperature of the process is not as dramatic as with copper but the conversion of a poorly consolidated material that easily fragments to a ductile metal is equally acute. The critical temperature is approximately 230 ° C.

The electrical resistivity of traces heated to a temperature above the critical temperature on several occasions is illustrated for the copper in Figure 6a and for the silver in Figure 6b. It can be seen that a dramatic decrease in resistivity occurs in a few seconds at temperature, followed in the case of copper by further consolidation over a period of a few minutes. It is this very rapid conversion of poorly consolidated metal particles to an almost solid metal at temperatures less than half the melting point of the raw metal which constitutes the present invention. The influence of the critical ingredients can be seen in Figure 6a. A mixture of copper flakes plus neodecanoic acid plus colloidal copper powder for the preferred specimen of the present invention achieves a resistivity of less than 10 microohm-cm in about 10 seconds. at the temperature. A mixture of flakes and acid only achieves some reduction in resistivity but only at 25-100 microohm-cm similar to thick polymer film compositions in which metal flakes are not well bonded. Similarly, when the mixture contains metal flakes plus colloidal metal powder plus tetradecane, an inert saturated hydrocarbon, instead of the reactive organic medium, the resistivity is poor and no consolidation occurs.

Metalloorganic Decomposition Chemistry in the Presence of Metallic Powders It is believed that an extraordinary reaction takes place between the ROM and the metallic powder constituents of the compositions of this invention which promotes consolidation.

The evidence for the above is in two points: 1) Consolidation of the metallic powder to a solid metal conductor is extremely rapid. 2) The consolidation of metallic dust to a solid metal conductor occurs at a much lower temperature than conventional sintering to produce solid metal objects from metallic powders, as practiced in the powder metal industry and in the electronics industry of thick films.

The results illustrated in Figures 5a and 5b together with Figure 6a and Figure 6b could not possibly be produced by conventional sintering or by conventional thick film technology. Sintering is a process of time and temperature in which necks are formed between the contacting particles that grow by diffusion of crude solids until the original particle compact is transformed into a solid metallic body. The activation energy for the crude diffusion is in the order of 45 - 60 Kcal / mole (180 - 250 J (mole) for copper, silver and gold. Typical copper is sintered at 650 ° C to 900 ° C, and sintering times vary from minutes to hours at pressures of tons per square inch. (Handbook of Metallurgy in Dust, Henry H. Hausner, Ed., Chemical Publishing Co., Inc., New York, New York, page 164 - 167 (1973), the sintering rate at 325 ° C can be expected to be less than that of the usual thick film sintering temperature of 850 ° C by a factor of seventy million (7 x 107) A ten minute process at 850 ° C will take 1300 years at 325 ° C.

It is not understood why the compositions of the present invention consolidate as rapidly as they do at a temperature compatible with polymer-based substrates. It may be that finely divided metal powders have a higher surface energy than the raw metal, and in the ROM environment in which they are processed, it is free of surface layers that would inhibit metal-to-metal contact and consolidation.

The surface energy of noble metals is as follows: (Chemistry in Bidimensional Surfaces, G.A. Somorjai, Cornell University Press (1981).

For copper the surface energy in excess of a particle of 10 nanometers above the crude solid is only 6800 J (Mole compared to the activation energy for the raw diffusion of 250,000 J / mole.) It does not appear that even colloidal metal had enough surface energy to consolidate by raw diffusion.

It is known that surface diffusion occurs at much lower temperatures than crude diffusion. A transition temperature exists above which diffusion is rapid, and this temperature is empirically found approximately 1/3 of the melting point in degrees K. (Thin film deposition; Principles and Practices, DL Smith, McGraw Hill, 1995, page 170). For silver this transition temperature is 138 ° C, so surface diffusion could play a part in the temperatures at which consolidation is observed taking place. It is difficult, however, to imagine how a surface process could weld the relatively massive flakes constituting the crude metal in the compositions of this invention.

Another explanation for these discoveries is that in mixtures of ROM-metallic dust, the metallo-organic compound decomposes directly on the pre-existing metallic particles, soldering them together by: AgCOOCaHiP; + put Ag = more metal Ag i + organic instead of by precipitation of new metal particles that are then added. It is likely to be an optimum metallic content large enough to provide adequate area for nuclear metalloorganic decomposition but small enough to allow bonding of metal particles together in a deposit with only the metalloorganic compound available. Existing metal undoubtedly provides a rigid frame, which prevents the sinking of deposited metal and the expansion of the molten ROM during decomposition which otherwise results in poor definition, poor adhesion and breaks in the traces.

Printing Processes Using the Compositions of this Invention Thick Polymer Film and Polymer Metallization Thick polymer film technology uses mixtures of carbon powders or flakes or metals in polymer adhesives, primarily epoxies, to make printable blends. These can be applied to polymer substrates and solidified at temperatures up to 176 ° C to create conductive patterns in the same way that coarse film inks and pastes are applied to ceramic and glass substrates at higher temperatures.

Metallization of metals is used to provide a conductive layer over polymer parts such as racks for desktop computers, usually for electrical insulation. Again, carbon or metal particles are suspended in a paint or other organic coating material.

Typically, carbon coatings are substantially less electrical conductive than metal-based coatings. The best are the epoxies loaded with silver flakes that can have resistivities as low as 50 - 60 microohm - cm.

There are applications in which the electrical conductivity achievable with epoxies loaded with metals is not adequate. An example is the application of a protective cover to wire insulated with polymer. In this case the conductivity of the protector should be comparable to the wire. Another example are applications in which thicknesses of one or two thousand of a thick polymer film conductor is objectionable, and the goal is to reach the driver as thin as possible. This requires an electrical resistivity comparable to 1.6 microohm - cm, which is the gross resistivity of silver. In addition, the conductivity of conventional polymer thick film materials is not stable over time due to changes in the resistance of the updraft contacts between the individual silver flakes that give them their conductivity. Mechanical stresses, thermal expansion and corrosion can all play a role in this degradation.

The present invention provides an alternative to conventional polymer thick film compositions that can be solidified at a temperature at which a polymer-based substrate can withstand, while providing an electrical conductivity comparable to pure metal and at least one factor of ten greater than the best thick polymer films.

The compositions of this invention can be applied to polymer substrates coated with adhesives by any convenient printing process.

One advantage of the printable metallization compounds is that three dimensional objects can be metallized which is not possible with metal foil and is very difficult with metal poured or evaporated.

The wire coverage can be carried out continuously with equipment analogous to the wire enamel towers. An example of this application is cited below in Example 10.

Flexible Circuit Patches In many cases you want to add a few traces of circuits to an existing printed circuit, either to repair errors, to implement changes or to complete the design without the expense of producing a complete multilayer circuit. The above is difficult to do by conventional means, particularly when traces must cross other traces, as they often do. This invention provides a simple and inexpensive method for printing additional traces on the substrate cover or welding mask that is used as a final layer on flexible and rigid printed circuits. Traces of additional circuits that connect exposed metal contact pads are printed on the polymer surface and solidify to metal upon heating to a temperature that the polymer components can withstand.

The method can also be used to create new metal cushions and to attach components to existing cushions to complete the assembly of the circuit. A hybrid technology can be used in which a photoresist is used to define the traces of the driver with high resolution and the conductors themselves are installed by printing and heating the mixtures of this invention. The process is illustrated schematically in Figure 9a.

The process of heat treatment is done under conditions very similar to welding and similar equipment. Additional cost savings can be made by combining the solidification of traversed traces and the coupling of components. The above is achieved by printing additional material on the coupling cushions for the components to be assembled in the circuit, placing the components on the material without solidifying with the optional addition of additional material to the components themselves by printing or immersion, and apply heat treatment to the assembly to consolidate and simultaneously join the additional traces and join the components to the circuit, as illustrated in Figure 9b.

To achieve the ultimate in high-resolution circuit traces, the technology currently presented can be combined with photosensitive materials to create a hybrid technology, as illustrated in Figure 9c. A photosensitive resistor or welding mask is applied to the surface of the circuit and exposed to the desired pattern of conductor traces, which can be very fine. The negative image develops in the usual way when washing the material without polymerizing and without exposing. The mixture of the present discovery is applied by printing or lamination within the circuit traces. The components can be placed at this stage if desired to make circuit traces and assemble the circuit simultaneously, as described above. The circuit is then treated with heat in an oven that consolidates the mixture and completely polymerizes the resistance or welding mask in an insoluble and insoluble dielectric. An additional layer of mask Welding or encapsulation compound can be applied to protect the finished circuit in the usual way.

Interior Printed Circuit Layers Most contemporary printed circuits have multiple layers with cushions attached to components on the two surfaces and the gross circuit connections on thin inner layers. The latter are laminated between the two surface layers to make the entire multiple layer. The inner layers are produced by the same technology of the outer layers and the wiring boards printed on one side or two sides. The substrate of the inner layer is similar to the epoxy material FR-4 reinforced with conventional glass but much thinner. The minimum is about 0.004 inches thick, limited by the fact that it is conventional to use two layers of glass cloth to prevent single glass lines from going side to side and acting as potential short circuit paths. Epoxy glass is laminated on copper paper on one or both sides to provide the electrical conductors to be developed by etching and / or plating.

To produce a finished inner layer, the copper-lined substrate is laminated to a dry film strength or covered with a liquid resistance. Then it is exposed to ultraviolet light to partially polymerize the resistance, which is usually a mixture of acrylic and epoxy. The unexposed resistance is removed by a caustic wash or weak solvent to develop a negative image. The image is then converted into circuits by recording exposed copper to leave the traces of the circuit protected by the resistance that is released by a strong caustic. An alternative method is to electroplate copper followed by resistance with tin-lead engraving on the exposed copper, discover the polymer resistance and burn the unprotected original copper paper.

The finished inner layers are stacked with the other layers on the outside of the pile and with intermediate sheets of "prepreg" which is, again, two layers of glass cloth impregnated with stage B epoxy resin. The pile then solidifies into a rolling process typically at 400 psi, 350 ° F for one hour. A vacuum press is often used to remove the introduced air and improve the quality.

It can be seen that producing the inner layers is a time-consuming and expensive process. The resistance costs approximately $ 1.00 per square foot, and the lamination process is demanding, as is the exposure. The cost of laminated copper paper to the substrate is in the order of $ 3.00 per square foot, and most of it removes with the engraving. The development step is slow and produces hazardous waste. The engraving step suffers from the same problems, as does the process to discover the resistance. There are numerous intermediate rinses that have not been described separately that add to the cost. The average layer count in the entire industry in the United States is approximately seven. Many multi-layer circuits have 20 or more layers. It can be seen that the production of interior layers is an important cost. Total production in the United States is approximately one trillion square feet of interior layers per year.

The compositions and processes of this invention replace this complexity with a simple printing and heating technique that can produce inner layers very quickly and economically. The material of the inner layer is simply cleaned, It prints and is treated with heat in a homo to convert the image into circuit conductors. The printed layers are then laminated in the usual manner.

To save even more and obtain higher production rates, the conductor pattern can be applied to a continuous network of substrates by means of a rotary press, much like newspaper but with finer resolution, as illustrated in Figure 10a. Gravure printing can be used in this application. Offset printing can also produce very high resolution. Inkjet printing and electrostatic printing at high speeds are candidates. After the printing step, the circuits will solidify in a homo, still as a continuous network. The ability of these mixtures to solidify into solid metal in seconds is critical to the realization of this concept. Longer processing times could make the oven disproportionately large relative to the press and waste much of the speed advantage of high speed printing.

The individual layers can be cut and laminated separately in the usual manner. A long term, for very high production runs, the analogy with the newspaper can be exploited more with multiple rotary presses that rotate inner layers simultaneously and solidify in a single homo and perhaps laminate to the step before cutting in mold to size. The lamination would be done by interposing the hot and solidified inner layers with hot prepreg and pressing them between rollers to expel the air between the layers and join the pile. After cooling, the batteries would be cut apart to create the individual circuits. An even less expensive approach is to use the adhesive on the back surface of inner layers of a single side to laminate the stack are the use of prepreg. The process is illustrated schematically in Figure 10b.

Coupling to the Direct Board and TAB Link The latest in electronic packaging technology is now the direct coupling of Integrated Circuits (ICs) to Printed Wiring Cards (PWBs). The conventional method of packing ICs is to cement them into a ceramic or plastic plate carrier and to wire the individual entry / exit cushions over the IC for individual needles on a metal-tipped frame. The IC is then encapsulated in plastic or ceramic and covered with a lid for protection. The tips are separated from the frame and folded to form inserts inside a socket or to solder them directly to cushions in the PWB (surface mount technology).

These packaging and the operation of the connection with cables are expensive, and the packaged semiconductors need several times the space of the IC itself. With the intense pressure for smaller devices and lower costs, there is a great incentive to remove the packaging and join the IC directly to the PWB. An intermediary step is to replace the packing and the joining operation with cables by joining the IC to a lead frame that can then be attached to the PWB. Since the lead frames in question are produced by engraving metallic laminate on a continuous polyimide tape, this technology is referred to as Automated Tape Joining ( ).

Some direct coupling Plate on Card (COB) is done when the IC is connected to cables on the PWB, but it, while conventional and reliable, is expensive and time consuming. The TAB joints and the most advanced COB applications join in groups by "bumping" the cushions over the IC with added metal and welding the blows with corresponding cushions on the tape or the PWB. The process of the collisions itself is slow and expensive because it is done by depositing a number of metallic layers under vacuum using photolithographic techniques. Preparing the ribbons or the cushions of circuits is expensive because it is at the limit of the resolution of conventional subtractive engraving technology with lines and spaces of 50 microns (0.002 inches). The tapes are further processed to remove the polymer in the central portion which leaves very fine and fragile metal fingers pointing towards the IC and which can be individually attached to the cushions. A technology in which the ICs could be joined in groups to traces on a PWB or a polyimide tape in a single operation could achieve greater simplification and cost reduction. The compositions of the present invention can be applied to ICs and / or to polymer-based substrates to act as a binding agent to secure the IC to the substrate with all electrical connections made simultaneously and reliably.

The cushions on the ICs are almost universally made of aluminum, which is compatible with the silicone semiconductor, is a good electrical conductor and is easily and economically applied by evaporation or shedding. Aluminum is not easy to bond due to the very tough native oxide that protects aluminum surfaces from oxidation and corrosion. The union of wires and the hit to the plate have overcome this obstacle to obtain reliable unions. In the case of wire links, the connections are made to balls formed on the end of 0.001 inch diameter gold wire when soldered to the aluminum, usually by means of ultrasonic agitation to mechanically interrupt the oxidized film and to cold weld the gold to the aluminum. In the case of plate hits, a layer of an intermediate bonding metal such as titanium and tungsten alloy is deposited by pouring to make contact with the aluminum and isolating it from the material of the blow that is harmful to the silicone. Other layers are also added as well as the material of copper beating or welding. All these operations require photolithographic masks and are very expensive. An insulating layer of polyimide is often applied to the surface of the plate to protect it from subsequent processing when covering everything except the cushions.

Two methods for applying the compositions of this invention to the plates without the need for expensive photolithographic steps are the following: Method 1 1) Spray clean the surface of the plate to remove the aluminum oxide and immediately clean it equally on a layer of gold, silver, copper, nickel, titanium, molybdenum, tungsten or other intermediate metal or alloy to which at the same time the aluminum and the composition of this invention will be joined. 2) Print the composition on the cushions to a thickness that will produce a little more than the desired protrusion height after solidification. 3) Solidify the composition to produce solid metallic protrusions. 4) Spray clean the plate again or etch chemically to remove the intermediate metal layer between the protrusions and a little but not all of the protrusion material.

This method is illustrated in Figure 1 a.

Method 2 1) Add a polyimide with a photo standard or another dielectric insulator layer to the surface of the plate as it is done now. 2) Clean by spraying and immediately cover with intermediate metals as before. 3) Print as before. 4) Clean by spraying or burn as before.

The compositions of this invention can be applied to the IC by any convenient printing process. Tests have been done by printing with a grid of driver images. The mixtures have also been applied by stencil and inkjet printing. The gravure, either direct and offset can be used to produce fine line images. Offset lithography can be used, as can direct impressions using rubber or metal platforms. If a mixture can be found which will bond directly to the aluminum without the gold layer or other bond, a particularly elegant lithographic method can be used. The compositions of this invention do not stick to untreated polyimide surfaces. The IC can be covered with polyimide and a pattern can be applied to expose the cushions as before. The composition can then be applied by lamination through the surface or by a rough printing process with poorer resolution than the cushions. During solidification, the composition will detach from the polyimide surface and become drops on the aluminum cushions producing the exact desired structure with higher resolution than the resolution process used to apply it. Such a mixture can include fluoride-based flows to dissolve the aluminum oxide layer during the heat treatment process. The same process could be used to apply a mask and print very thin conductors on the surface of the semiconductor IC itself to connect pads or I / O points of routes.

The struck plates of this invention must be attached either to a polyimide tape or to a PWB with traces of corresponding metallic circuits. Such traces can be produced by the methods of this invention by a simple printing process and heat with high resolution. Additional printing processes are applicable for polymer films that are not applicable to ICs. In particular, electrostatic methods (xerography) are possible and together with inkjet printing, it provides the ability to generate direct conductor patterns from CAD files. This provides great flexibility in design and manufacturing of small quantities and inventory control.

The highest possible resolution is provided by photolithographic techniques and a hybrid technology in which the dielectric is patterned photographically and a composition of this invention printed or rolled in the grooves is a highly reliable and promising way to produce very fine conductor patterns for TAB and direct coupling. The method is the same as method B described above for the application of patterns to the plate and the method illustrated in Figure 9c above.

The next highest resolution can be provided by electrostatic printing with liquid toner suspensions with particle diameters of a few microns. S.P. Schmidt, et al., "Manual of Imaging Materials", Chapter 5, pages 227.252, A.S. Diamond, Ed., (Marcel Dekker, New York).

A printing the IC and the substrate, the bonding process can be carried out in several ways: 1) Both sets of contacts can be solidified and additional composition and reheat similar to weld can be printed. (The welding could also be use as is now done, but the compositions of this invention provide a better solution by virtue of not needing a flow removal step and do not introduce foreign metals into the contact of the sensitive semiconductor.) 2) A set of contacts can be treated with heat and the other can be printed and adhered to the first one before reheating to reach the link. 3) A set of contacts is only printed and the other component adheres to it before dealing with heat to reach the application and the link simultaneously.

A printing, the image is converted to metal by the application of heat in a homo.

EXAMPLES The examples described below indicate how the individual constituents of the compositions and the preferred conditions for applying them work to provide the desired result. The examples will serve to further typify the nature of this invention, but should not be considered as a limitation within the scope thereof, said scope is defined solely in the appended claims.

Example 1. Copper composition with copper flakes, copper powder and acid. A composition has been prepared to produce conductive copper traces on dielectric substrates. 1) A mixture of 47 parts by weight of copper flakes, 29 parts by weight of copper powder ("Nanomita", Nanopower Enterprises, Piscataway, New Jersey) and 24 parts by weight of neodecanoic acid were combined and mixed by hand in a glove box under nitrogen. 2) The mixture is pressed in rolls in air to produce a homogeneous mixture. 3) The ink was printed by grating on a dielectric substrate FN 929 Kapton® 300 at room temperature in air. 4) Traces were heated in a tube oven at 350 ° C for 180 seconds in a nitrogen-steam atmosphere.

A heating, the circuit trace dried to the touch, the organic constituents had been completely removed. The electrical resistivity of the circuit trace (23.7 cm long, 0.4 mm wide) was calculated to be 5 microohm-cm when measuring the trace resistance and weighing the amount of metal deposited. The mass divided by the density gives the total volume of metal. The adhesive tape was applied to the trace of the circuit and immediately removed at a 90 degree angle to determine the bonding strength of the copper to the substrate. No metal was removed with the tape.

Example 2. Copper and acid flake. A composition has been prepared to produce conductive copper traces on dielectric substrates to show the deleterious effect of the removal of the colloidal copper powder ingredient. 1) A mixture of 76 parts by weight of copper flake and 24 parts by weight of neodecanoic acid were combined and mixed by hand in a glove box. 2) The mixture was pressed in roller in air to produce a homogeneous ink. 3) The ink was printed by grating on a FN 929 Kapton® 300 substrate at room temperature in air. 4) Traces are heated in a tube oven at 350 ° C for 180 seconds in an atmosphere of nitrogen vapor and water. a heating, the trace of the circuit dried to the touch, the organic constituents had been completely removed. The electrical resistivity of the circuit trace was calculated to be 24 microohm-cm. Scotch tape was applied to the circuit track and immediately removed at a 90 degree angle to determine the strength of the copper bond to the substrate. Some of the copper was removed with the tape.

Example 3. Copper and acid powder. A composition has been prepared to produce conductive copper traces on dielectric substrates illustrating the deleterious effect of removing the element from the copper flakes. 1) A mixture of 77 parts by weight of copper powder and 24 parts by weight of neodecanoic acid were combined and joined by hand in a glove box. 2) The mixture was pressed into rolls in air to produce a homogeneous ink. 3) The ink was printed in a grid on a Kapton® dielectric substrate 300 FN 900 at room temperature in air. 4) The traces were heated in a tube oven at 350 ° C for 180 seconds in an atmosphere of nitrogen vapor and water.

After heating, the trace of the circuit dried to the touch, the organic constituents having been completely removed. The trail of the circuit was not continuous, and thus did not conduct the electricity. Scotch tape was applied to the circuit track and immediately removed at a 90 degree angle to determine the strength of the copper bond to the substrate. No metal was removed with the tape.

Example 4. Copper flakes, copper powder and tetradecane. A composition has been prepared to produce conductive copper traces on dielectric substrates that show the damaging effect of replacing a non-reactive saturated hydrocarbon with the Reactive Organic Medium. 1) A mixture of 47 parts by weight of copper flake, 29 parts by weight of copper powder and 24 parts by weight of tetradecane were combined and mixed by hand in a glove box. 2) The mixture was pressed in roll in air to produce a homogeneous ink. 3) The ink was printed in a grid on a Kapton® 300 FN 900 substrate at room temperature in air. 4) The traces were heated in a tube oven at 350 ° C for 180 seconds in an atmosphere of nitrogen vapor and water.

After heating, the trace of the circuit dried to the touch, the organic constituents had been completely removed. The electrical resistivity of the trace of circuit (23.7 cm long, 0.4 mm wide) was calculated to be 25 microohm-cm. Scotch tape was applied to the trace of the circuit and immediately removed at a 90 degree angle to determine the strength of the copper bond on the substrate. Some of the copper was removed with the tape.

Example 5. Silver neodecanoate, silver flakes and a-terpineol. A composition has been prepared to produce conductive silver traces on dielectric substrates containing silver flakes, a metallo-organic silver decomposition compound and a reactive rheology modifier. 1) A mixture of 12 parts by weight of silver flakes, 3 parts by weight of silver neodecanoate and 1.8 parts by weight of a-terpineol was combined by hand in a glove box under nitrogen. 2) The mixture was pressed in roll in air to produce a homogeneous ink. 3) The ink was printed on a Kapton® 300 FN 900 substrate at room temperature in air. 4) Traces were heated in a box oven at 300 ° C for 60 seconds in air.

After heating, the trace of the circuit dried to the touch, the organic constituents had been completely removed. The electrical resistivity of the circuit trace (23.7 cm long, 0.4 mm wide was calculated to be 3.7 microohm - cm) Scotch tape was applied to the circuit trace and immediately removed at a 90 degree angle to determine the strength of the circuit. union of silver to the substrate No metal was removed.

Example 6. Silver flake, silver neodecanoate and acid.

A composition has been prepared to produce conductive silver traces on dielectric substrates with neodecanoic acid as a modifier of reactive rheology and flux. 1) A mixture of 12 parts by weight of silver flake, 3 parts by weight of silver neodecanoate and 1.6 parts by weight of neodecanoic acid were combined and mixed by hand in a glove box. 2) The mixture was pressed in roll in air to produce a homogeneous ink. 3) The ink was printed on a Kapton® 300 FN 900 substrate at room temperature in air. 4) Traces were heated in a box oven at 290 ° C for 60 seconds in air.

After heating, the trace of the circuit dried to the touch, the organic constituents had been completely removed. The electrical resistivity of the circuit trace (23.7 cm long, 0.4 mm wide was calculated to be 3.2 microohm - cm) Scotch tape was applied to the circuit trace and immediately removed at a 90 degree angle to determine the strength of the circuit. union of silver to the substrate No metal was removed.

Example 7. Gold flakes, gold neodecanoate and gold octane amine.

A composition has been prepared to produce conductive gold traces on dielectric substrates with a ROM containing two metalloorganic decomposition compounds for temperature optimization. 1) A mixture of 8 parts by weight of gold leaflet, 1 part by weight of neodecanoate and 1 part by weight of gold amine 2-ethyl hexanoate. The mixture was combined and mixed by hand in a glove box. 2) The mixture was pressed in roll in air to produce a homogeneous ink. 3) The ink was printed on a Kapton® 300 FN 900 substrate at room temperature in air. 4) Traces were heated in a box oven at 365 ° C for 600 seconds in air.

After heating, the trace of the circuit dried to the touch, the organic constituents had been completely removed. The electrical resistivity of the circuit trace (23.7 cm long, 0.4 mm wide was calculated to be 7.4 microohm - cm) scotch tape was applied to the circuit trace and immediately removed at a 90 degree angle to determine the strength of the union of silver to the substrate No metal was removed.

Example 8. Silver ink on substrate FR-4. A composition has been prepared to produce conductive silver traces on glass-reinforced epoxy dielectric substrates. 1) A mixture of 12 parts by weight of silver flake, 3 parts by weight of silver neodecanoate and 1.8 parts by weight of a-terpineol containing 15% colloidal silver was combined and mixed by hand in a glove box. 2) The mixture was pressed in roll in air to produce a homogeneous ink. 3) The ink was printed on a Kapton® 300 FN 929 substrate at room temperature in air. 4) The traces were heated in a box oven at 270 ° C for 60 seconds under nitrogen.

After heating, the trace of the circuit dried to the touch, the organic constituents had been completely removed. The electrical resistivity of the circuit trace (23.7 cm long, 0.4 mm wide was calculated to be 3.2 microohm - cm) Scotch tape was applied to the circuit trace and immediately removed at a 90 degree angle to determine the strength of the circuit. union of silver to the substrate No metal was removed.

Example 9. Copper on Kapton® EKJ A composition has been prepared to produce conductive copper traces on dielectric substrates coated with polyimide. 1) A mixture of 47 parts by weight of copper flake, 29 parts by weight of copper powder and 24 parts by weight of neodecanoic acid were combined and mixed by hand in a glove box. 2) The mixture was pressed in roll in air to produce a homogeneous ink. 3) The ink was printed on a dielectric substrate at room temperature in air. 4) The dielectric used was a Kapton® EKJ film consisting of type E polyimide film covered on both sides with a polyimide with a low glass transition temperature of 220 ° C which can act as a thermoplastic adhesive. 5) The traces were heated in a tube oven at 350 ° C for 180 seconds in an atmosphere of nitrogen and water.

After heating, the trace of the circuit dried to the touch, the organic constituents had been completely removed. The electrical resistivity of the circuit trace (23.7 cm long, 0.4 mm wide was calculated to be 4.5 microohm-cm. applied scotch tape to the trace of the circuit and was immediately removed at a 90-degree angle to determine the strength of the silver bond to the substrate. No metal was removed with the tape.

Example 10. Silver on Kapton® EKJ A silver composition has been prepared to produce conductive silver traces on dielectric substrates. 1) A mixture of 12 parts by weight of silver flake, 3 parts by weight of silver neodecanoate and 1.8 parts by weight of a-terpineol were combined and mixed by hand in a glove box. 2) The mixture was pressed in roll in air to produce a homogeneous ink. 3) The ink was printed on a dielectric Kapton® EKJ substrate at room temperature in air. 4) Traces were heated in a box oven at 300 ° C for 60 seconds in air.

After heating, the trace of the circuit dried to the touch, the organic constituents had been completely removed. The electrical resistivity of the circuit trace (23.7 cm long, 0.4 mm wide was calculated to be 3.1 microohm - cm) Scotch tape was applied to the circuit trace and immediately removed at a 90 degree angle to determine the strength of the circuit. union of silver to the substrate No metal was removed.

Example 11. Bond Copper with copper paper. A composition has been prepared to produce conductive copper traces attached to copper paper. 1) A mixture of 47 parts by weight of copper flake, 29 parts by weight of copper powder and 24 parts by weight of neodecanoic acid were combined and mixed by hand in a glove box. 2) The mixture was pressed in roll in air to produce a homogeneous ink. 3) The ink was printed on a copper paper substrate at room temperature in air. 4) The traces were heated in a tube oven at 350 ° C for 180 seconds in a nitrogen and water atmosphere.

After heating, the trace of the circuit dried to the touch, the organic constituents had been completely removed. Scotch tape was applied to the trace of the circuit and immediately removed at a 90-degree angle to determine the strength of the silver bond to the substrate. No metal was removed with the tape.

Example 12. Silver bonding to copper-lined FR-4 The composition of Example 6 has been applied to glass-reinforced epoxy substrates coated with copper. 1) A mixture of 12 parts by weight of silver flake, 3 parts by weight of silver neodecanoate and 1.6 parts by weight of neodecanoic acid was combined and mixed by hand in a glove box. 2) The mixture was pressed in roll in air to produce a homogeneous ink. 3) The ink was printed on a FR-4 substrate covered with copper at room temperature in air. 4) Traces were heated in a box oven at 260 ° C for 15 seconds in air.

After heating, the trace of the circuit dried to the touch, the organic constituents had been completely removed. Scotch tape was applied to the trace of the circuit and immediately removed at a 90-degree angle to determine the strength of the silver bond to the substrate. No metal was removed.

Example 13. Polymer metallization. An example of a mixture that has been used for experiments on the metallization of polymers is one made of 12 parts of silver flake, 3 parts of silver neodecanoate and 1.8 parts of a-terpineol per weight prepared as described in the previous examples. . A demonstration of metallization of polymers using this composition has been carried out by applying a protective cover to wrap in wire wire. Wire insulated with # 30 Kynar is covered by rubbing it with the silver mixture described above and solidifying it in a homo at 277 ° C. The resulting silver cover adhered firmly to the wire. The wire could be tied in a knot and tightened without detaching the cover. A linear resistance of 0.2 ohms per m was achieved with a coverage of 0.0006 grams of silver per cm, equivalent to a resistivity of 12 microohms - cm.

Example 14. Polymerization of metal. In another demonstration a sample of cable isolated with Kynar was covered with the silver mixture and heated to 360 ° C. The metal adhered well and could resist being tied in a knot. The resistance was approximately 0.04 ohm / cm.

To date the lowest critical temperatures obtained have been around 220 ° C with mixtures of silver, as described in the examples. Similar results They have reached copper and gold at the same time, even though temperatures are a little higher in the range of 300 - 350 ° C.

These conditions are still orders of magnitude less severe than those required for conventional sintering and processing of thick films. The examples cited repeatedly demonstrate with different metals and different substrates that the compositions and methods of the present invention can produce traces of thick film circuits well consolidated and well bonded onto substrates based on conventional polymers which could not have been anticipated by anyone with experience in circuit board manufacturing technology or thick film technology.

The compositions and methods of the present invention offer a completely new approach to creating fully adhered electronic circuits. Figure 12 shows a comparison of the electrical resistivity of traces made by the method of this invention compared to those of the prior art together with the respective processing conditions of temperature and solidification time. It can be appreciated that the present invention provides conductivity (and weldability) equivalent to conventional film processing but at a temperature hundreds of degrees lower. It is compatible with polymer substrates but offers orders of magnitude of better electrical conductivity and processing speed than the existing alternatives of polymer thick film and transient liquid phase.

Claims (15)

1. CLAIMS: 1. A composition of matter comprising an organic reactive medium and a metal powder mixture, wherein said composition can be applied on a substrate and can be heated to consolidate the composition to a pure and solid metallic conductor at a temperature of below about 450 ° C.
2. 2. The composition of Claim 1 wherein said reactive organic medium is selected from the group consisting of a metalloorganic decomposition compound, a reactive compound that can be reacted with said metal powder mixture to produce such a compound and a mixture thereof.
3. 3. The composition of Claim 1 wherein said reactive organic medium is composed of one or more reactive organic compounds and each of them has a different decomposition temperature, wherein the reactive organic medium has a decomposition temperature that is different from each other. of said reactive organic compounds.
4. 4. The composition of Claim 1 in which the metal powder mixture is composed of: a) 0-100% metal flakes having a diameter of about 5 microns and a thickness of less than 1 micrometer; and b) 0-100% of colloidal metal particles having a diameter of less than 0.1 microns where said metal particles do not aggregate significantly into larger particles.
5. 5. The composition of Claim 1 wherein the metal is selected from the group consisting of copper, silver, gold, zinc, cadmium, palladium, iridium, ruthenium, osmium, rhodium, platinum, iron, cobalt, nickel, indium, tin, antimony, lead and bismuth.
6. 6. A method for producing solid and pure metallic conductors on a substrate comprising the steps of: A) applying a conductive precursor in the desired pattern onto the substrate; B) heating the substrate in a homo at a critical temperature of less than about 450 ° C for a time of less than about 5 minutes; wherein said applied conductive precursor pattern is converted into a well consolidated and well-bonded pure metallic conductor; wherein said conductive precursor is composed of an organic reactive medium and a metal powder mixture.
7. 7. The method of Claim 6 in which said conductive precursor is applied to said substrate by a technology chosen from the group consisting of: grid printing, stencil printing, gravure printing, printing, offset printing, lithographic printing, dispersion, lamination, inkjet printing, xerographic copying and electrostatic printing.
8. 8. The method of Claim 6 wherein said conductive precursor is a copper-based composition and in which the atmosphere of the homo is nitrogen with less than 20 parts per million by volume of oxygen and preferably less than 3 parts per million.
9. 9. The method of Claim 8 wherein water vapor is added to the nitrogen to the extent of about 5 mole percent during the period in which said conductor precursor is heated but not before or after the heating phase.
10. 10. The method of Claim 6 wherein the substrate contains a polymer that is sensitive to temperatures above 450 ° C.
11. 11. The method of Claim 6 wherein the substrate contains a semiconductor that is sensitive to temperatures above 450 ° C.
12. 12. The method of Claim 6 wherein said conductor precursor is applied to metal conductors and dielectric insulators to make electrical connections between the conductors.
13. 13. The method of Claim 6 wherein said conductive precursor is applied in step A) to a dielectric photoprintable material to which a pattern has been applied by photolithography to define channels that will become conductors, whereby said channels are filled with said conductor precursor by lamination or printing; wherein after the heating step B), dielectric and consolidated material is applied simultaneously to said conductor precursor pattern.
14. 14. The method of Claim 6 wherein said conductive precursor is applied in step A) to a continuous network of thin substrate material and solidified in step B) as a continuous network in a homo, further comprising the step of: C) cutting said continuous network of thin substrate material into a final product.
15. 15. The method of Claim 6 wherein said conductive precursor is applied to semiconductor devices to make electrical and protruding conductive traces on said semiconductor surface. EXTRACT OF THE INVENTION A composition of matter that has a powder or metal powders for specified characteristics in a Reactive Organic Medium (ROM). These compositions can be applied by any convenient printing process to produce patterns of electrical conductors on electronic substrates sensitive to temperature. The patterns can be solidified in seconds to form metallic conductors at a temperature low enough to avoid damaging the substrate.