US3681261A - Resistors,compositions,pastes,and method of making and using same - Google Patents

Abstract

PALLADIUM OXIDE OR OTHER METAL OXIDE REISTORS FOR MICROELECTRONIC CIRCUITRY ARE PROVIDED WITH A HIGH DEGREE OF REPRODUCIBILITY AND STABILITY BY FIRST CONCENTRATING TO POWDER FORM A LIQUID MIXTURE OF A RESISTOR METAL-ORGANO METALLIC COMPOUND, AT LEAST ONE OTHER STABLILIZER METAL IN ORGANOMETALLIC FORM, AND AN ANTI-AGGLOMERATING AGENT WHICH WILL NOT BURN OFF DURING PROCESSING TO FINAL RESISTOR FORM. THE POWDER IS THEN ALLOYED AND THE RESISTOR METAL OXIDIZED. THE RESULTING ALLOY IS THEN FORMED INTO A RESISTOR PASTE BY ADMIXING IT WITH A GLASS BINDER (EITHER BEFORE OR AFTER OXIDATION) AND A LIQUID CARRIER VEHICLE. THE PASTE IS PRINTED IN THE DESIRED PATTERN, DRIED AND FIRED TO PRODUCE THE RESISTOR IN FINAL FORM.

Description

United States Patent 3,681,261 RESISTORS, COMPOSITIONS, PASTES, AND METHOD OF MAKING AND USING SAME Daniel W. Mason, West Peabody, Mass., and Bernard Greenstein and John M. Woulbroun, Toledo, Ohio, assignors to Owens-Illinois, Inc. No Drawing. Filed July 27, 1970, Ser. No. 58,740 Int. Cl. B44d 1/02; H01b 1/06 US. Cl. 252-514 7 Claims ABSTRACT OF THE DISCLOSURE Palladium oxide or other metal oxide resistors for microelectronic circuitry are provided with a high degree of reproducibility and stability by first concentrating to powder form a liquid mixture of a resistor metal-organo metallic compound, at least one other stabilizer metal in organometallic form, and an anti-agglomerating agent which will not burn ofl? during processing to final resistor form. The powder is then alloyed and the resistor metal oxidized. The resulting alloy is then formed into a resistor paste by admixing it with a glass binder (either before or after oxidation) and a liquid carrier vehicle. The paste is printed in the desired pattern, dried and fired to produce the resistor in final form. t

This invention relates to electronic resistors. More particularly, this invention relates to electronic resistors, compositions, pastes, and methods of making and using same particularly within the environment of microelectronic circuitry. t

The art has long known of the value of palladium oxide (PdO) for use as a resistor material, particularly in microelectronic circuitry. Generally speaking, palladium oxide is formed into a resistor by admixing palladium with a glass binder and organic vehicle to form a printing paste. In the case of microelectronic circuitry, the paste is then printed onto a dielectric substrate such as aluminum oxide or the like by the use of a screen or mask of the desired mesh and formed to provide the desired pattern. The patterned design is then fired in air to oxidize the Pd to PdO and form the ultimate resistor lamina.

In order to increase the negative temperature coeflicient of resistivity (hereinafter referred to as TCR), to regulate ultimate resistivity, and to render the stability of the PdO system acceptable, certain metals are employed in admixture with the palladium in the paste. Such metals, which are referred to hereinafter as stabilizers, are those which do not oxidize at the temperatures used to fire the printed paste.

Many problems attend these prior art PdO resistor systems. One major problem is the great sensitivity of these systems to the firing process as a whole. Slight fluctuations or variations in the firing temperature, for example, greatly changed the resistivity of the resulting product. Air flow and firing times are further variables to which the ultimate characteristics of the final product are extremely sensitive. Such sensitivity, of course, renders these PdO systems extremely difficult to reproduce. Not only is reproducibility low, but for some reason, not entirely understood, stability is also very low.

The term stability is well understood in the art and is used herein in accordance with this well know meaning. That is to say, stability defines that characteristic of a resistor which enables it to maintain its resistivity within tolerable limits over extended periods of time and use.

While the stabilizer metals used in admixture with the palladium oxide generally provide commercially tolerable stability to the system, they are generally found to detri- Patented Aug. 1, 1972 mentally increase the TCR of the systems, usually far above the i0 p.p.m./ C. level ideally desired. In some instances, especially when Ag is used, stability must be sacrificed for acceptable TCR while, on the other hand, TCR must be sacrificed for acceptable stability. In almost all instances, reproducibility, regardless of the metal stabilizers used, is detrimentally low.

In order to overcome these problems, the art has sought out many solutions. Some have sought to use various additional additives to improve the system. Others have sought to alter the starting materials employed such as by employing finely divided palladium oxide in the paste or initially employing crystalline palladium or its oxide within critical particle sizes and surface areas. Others used combinations of the above solutions or turned completely from the PdO system to seek other resistive metal oxide systems which might have higher stability and/or reproducibility. In many instances, only a modicum of success was actually achieved. In many other instances, the manufacture was rendered so expensive as to make it economically undesirable.

It, therefore, is apparent from the above that there exists a definite need in the art for a PdO or other resistive metal oxide system which is highly reproducible, has high stability, exhibits excellent TCRs, produces high quality resistors, and is economical to manufacture.

It is a purpose of this invention to fulfill this need in the art. Generally speaking, this invention fulfills this need by providing a resistor composition and/or paste which is uniquely formed in a manner which insures optimum alloying of the metals and controlled homogeneous oxidation of the Pd or other resistive metal prior to firing, to the extent that the resistivity characteristics are not detrimentally sensitive to air flow, time, and temperature variations during firing; thus to provide a highly stable, reproducible resistor for good quality. In addition, because of the optimum alloying and other factors, low TCRs are obtainable.

Basically, the resistor compositions are formulated in accordance with this invention by:

(a) Forming an admixture of a resistive metal-organometallic compound, at least one metal stabilizer in or- .ganometallic form and an anti-agglomerating agent which will remain in the system throughout processing;

(b) Heating the admixture at a sufiicient temperature and for a sufiicient period of time to drive 01f the organoconstituents and concentrate the admixture to a powder; and

(0) Heating the powder at a sufiicient temperature and for a sufficient period of time to alloy said metals and in some instances to oxidize the resistive metal.

The above-described resistor compositions may be employed in a wide variety of ways and environments for their resistive properties. Any of these ways and environments, conventional in the art, are contemplated by this invention. As alluded to hereinabove, a preferred way in which these resistor compositions may be used is to formulate them into printing pastes and print them on appropriate substrates for use in microelectronic circuitry.

Such pastes are formed in accordance with this invention by admixing the resistor composition in powder form with a conventional glass binder and in some instances oxidizing the resistive metals at this point. Thereafter the oxidized mixture is added to a liquid organic vehicle. The resulting paste may then be screen printed in accordance with conventional techniques in a desired pattern, dried and fired to produce the final resistor lamina. The resistors so formed generally exhibit a stability factor of less than about :l% drift during normal load life (e.g., 1000-10,- 000 hours) and a reproducibility usually on the order of about :20% of the specified resistivity.

Generally speaking any one or a combination of the conventional resistive metals may be used in the practice of this invention. Examples of such metals include palladium, rhodium, iridium, ruthenium, indium, and mixtures thereof. Because of the economic advantages, ease of processing, good stability, and good reproducibility, the palladium oxide system, and thus palladium, is preferred for the purposes of this invention.

Any of the well known stabilizing metals may be used in the practice of this invention. Generally, these metals are chosen for their inertness to oxygen at the operating conditions of this invention. Although only one of these metals may be employed, it is preferred to use at least two metals together in amounts which have been found to synergistically minimize their affect upon TCR. EX- amples of these stabilizing metals include silver, gold, and platinum. Examples of preferred admixtures in parts-byweight ratio for minimization of effect on TCR include AgtAu, about 4:1-1z4; PtzAg, about 8: 1-1:8; and PtzAu, about 8:1-1z8. Particularly preferred for the purposes of this invention is the AgzAu admixture since it is found that this admixture when alloyed with Pd will form a single phase alloy, thus further minimizing the affect of firing on the system.

Any of the well known organo-metallic compounds of the above metals may be used, provided that they are capable of being concentrated from admixture to a powder form. Such, of course, generally assumes that the organo-metallic compounds are liquids or are solids dispersed or dissolved in conventional liquid media. In addition, the organo-metallic compounds contemplated are those from which the organic constituents are capable of being driven off during concentration and/or to a lesser extent, during firing.

Preferred organo-metallics for the purposes of this invention are the well known metal resinates. Particularly preferred among the metal resinates are the conventional metal mercaptans because of the ease by which they may be concentrated to a substantially homogeneous powder, their availability and the like. Such mercaptans are well known and may be obtained, for example, from Englehard Industries, under such trade designations as Gold #8300, a mercaptan having 28.0% by weight Au; Rhodium #8826, a mercaptan having 10.0% by weight Rh; Platinum #9450, a mercaptan having 26.0% by weight Pt; Palladium #7611, a mercaptan having 20.0% by weight Pd; Iridium 8057, a mercaptan having 24.0% by weight Ir; and Silver 9144, a mercaptan having 30.0% by weight Ag.

Other resinates useful include the balsam based resinates examples of which, obtainable from the indicated company, include Gold A-1118 and A-1119, a balsam having 24% by weight Au and 12.0% by weight Au, respectively; Rhodium A-1120, a balsam having by weight Rh; Platinum A-l 121, a balsam having 12.0% by weight Pt; Palladium A-l122, a balsam having 9.0% by weight Pd; Iridium A-ll23, a balsam having 6.0% by weight Ir; and Ruthenium A-l124, a balsam having 4.0% by weight Ru.

Specific examples of the mercaptides of the above resistive and stabilizer metals include metallic ethyl mercaptide, n-octyl mercaptide, benzyl mercaptide, tertiary amyl mercaptide, tertiary hexadecyl mercaptide and the like. Other examples include the chlorometallic mercaptide such as chlorometallic tertiary hexylmercaptide-methyl sulfide, chloro-metallic (e.g. Pt) methyl mercaptide-propyl sulfide, chloro-metallic isoamylmercaptide methyl sultide and the like.

The anti-agglomerating agents useful for the purposes of this invention are those conventional materials which are inert to the system and which will not burn out at alloying and/ or firing temperatures. Such anti-agglomerating agents are usually of a fine particle size, e.g., less than about 5 microns. Examples of these agents include: ultrafine alumina, ultrafine TiO and other ultrafine refractories. Preferred for the purposes of this invention is ultrafine silica which is purchasable under the trademark Cab-O-Sil L-5.

This invention also envisions the use of other additives, known in the art, to the above ingredients in order to enhance, in a known fashion, one or more of the desired characteristics of the system.

As stated, the above resistor compositions of this invention are formed by first admixing the requisite amounts of resinates together in liquid form. Homogeneity is desired and thus thorough mixing of the resinates should be effected. For the preferred palladium systems contemplated, the resinates are admixed in proportions so as to present about 5-95 by weight of the metal content as palladium. Preferably, the Pd content is 15-75% of the total metal content and more preferably from 20-65%. The remainder of the metal content usually consists of one or more stabilizer metals.

To this homogeneous admixture of resinates there is added, with continuous stirring, an anti-agglomerating agent. Generally speaking this agent is added in an amount sufficient to prevent any substantial amount of agglomeration from taking place during the later alloying step. Although not limited to any particular theory, it is felt that the use of this agent greatly aids in improving the stability and reproducibility of the system.

The exact amount of anti-agglomerating agent used will, of course, vary, depending upon the system used and the type of agent employed. Generally speaking, however, the agent is used in an amount of about 0.5 to about 15% by weight of the metal powder formed upon concentration. When a PdO system is employed and the agent is finely divided silica, about 5% agent by weight of the metal powder is preferred.

After addition of the anti-agglomerating agent, the mixture is heated with stirring for a sufficient period of time and temperature to concentrate the mixture to a powdery solid. Generally speaking, and when the resinates are mercaptide based, heating to powder is conducted at about -200 (3., preferably at about C., for about 3-4 hours. The resulting powder is an extremely homogeneous mixture of the metals having the anti-agglomerating agent dispersed therein and from which substantially all of the organic constituents have been removed.

The powder so formed is heated at a temperature and for a period of time sufficient to alloy the metal. Because of the homogeneity and non-agglomerated nature of the starting powder, alloying is homogeneous and thus optimized. The resulting powdered alloy is, therefore, an antiagglomerated homogeneous powder ready for further processing.

The temperature at which alloying is effected will depend upon whether or not oxidation of the resistive metal is desired at this point. In those instances where the resistive metal is to be oxidized, the process will take place in air and the temperature of alloying will be sufliciently high to permit the oxide to form but not so high as to prevent oxidation from taking place. In a palladium system, such a temperature is about 650-750 C. Of course, alloying time will be extended to insure the requisite amount of oxidation. In those instances Where oxidation is not to be effected at ths point, but rather effected in a separate step, alloying is accomplished either in an inert atmosphere and/ or at temperatures at which oxidation of the resistive metal will not occur.

In preferred embodiments of this invention, the oxidation is effected in a separate step. Preferably, the second oxidation step is effected either immediately following the alloying step, or after the addition to the alloy of the glass binder when a paste is to be formed.

In those instances where oxidation is elfected immediately after alloying, alloying is preferably carried out at a temperature higher than that at which any substantial amount of oxidation of the resistive metal will occur. For the preferred Pd system such a temperature is usually above about 725 C. and usually from SOD-900 C. Since alloying is time-temperature dependent, suflicient time should be allotted to allow for complete alloying. About 1-48 hours, depending upon the size of the batched powder, is usually sufficient for this purpose. After alloying is effected, the temperature is then lowered to a convenient oxidizing temperature, and if an inert atmosphere was employed, air is pumped into the environment to effect the oxidation step. Oxidation is also time-temperature dependent and thus sufiicient time is allotted preferably for as complete oxidation of the resistive metal as possible. Generally speaking, the preferred range of oxidation temperatures for the PdO system is from about 300 C.-725 C., and more preferably, about 650-725 C. Times will vary but generally speaking, times of about 1-48 hours are found to be sufficient.

In those instances, as stated above, where the alloys are to be made into pastes, oxidation may be effected after the alloyed powder is admixed with the glass binder of the paste composition. Generally speaking, this is accomplished by ball-milling a particulate glass binder having an average particle size less than about 5 microns with the powdered, anti-agglomerated alloy. After these ingredients are thoroughly ball-milled and thus admixed, the mixture is subjected to oxidizing conditions (i.e., the oxidation times and temperatures set forth hereinabove) to effect oxdation of the resistive metal in the alloy. Although not limited to any particular theory, it is believed that oxidation at this point preferably to as complete an extent as is possible, optimizes reproducibility and stability and minimizes T CRs since the substance oxidized will be that presented to the firing step without any further physical comminution or the like. Where complete oxidation is effected, reproducibility is optimized since substantially no oxidation can occur during firing. In this respect the term complete oxidation is being used to define that point at which substantially all of the resistive metal presented for oxidation is oxidized. Thus this term is being used to define that degree of oxidation at which substantially no further oxidation will take place during firing. This is not to say that all of the resistive metal in the system is oxidized, since in many instances, alloying masks some of the alloy from oxidation.

In a preferred embodiment wherein the Pd system is employed, oxidation after glass binder addition is conducted between about 300 to 450 C. for a period of about 8 to 48 hours. Using such conditions, oxidation is found to be substantially complete.

With respect to the degree of oxidation effected, resistivity can be controlled by the amount of oxdation, and thus it is contemplated that oxidation, regardless of how it is effected, does not necessarily have to be complete, but rather only to a degree sufiicient to afford the desired resistivity. This invention, however, contemplates in its preferred form and regardless of how oxidation is accomplished, the use of oxidizing conditions such that as complete oxidation (as defined above) as possible is obtained. This insures maximum reproducibility while ultimate resistivity is controlled by the amount of resistive metal initially employed and/ or the alloying cycle chosen.

As stated hereinabove and regardless of which oxidation procedure is employed, the resistor compositions of this invention may be formulated into printing pastes, especially for use in microelectronic circuitry printing. Such printing pastes may be formed by any conventional technique. Generally speaking a preferred technique is to admix the alloyed powder with a glass binder (before or after oxidation as described) and a suitable volatile organic liquid binder.

Glass binders for use in the pastes of this invention are conventional and generally speaking, any of these conventional binders may be employed. Examples of such binders include the boro-silicates and particularly the lead-alumina-borosilicates. A particularly preferred glass binder, in particulate form, having an average particle size of less than about 5 microns, is represented by (in weight percent):

The organic liquids used are conventional and generally speaking, any one of these well-known liquids may be employed. Examples of these liquids include butyl Carbitol acetate (diethylene glycol monobutyl ether acetate), iso-amyl salicylate and mixtures thereof. A particularly preferred liquid vehicle is a mixture of 2 parts by weight butyl Carbitol acetate to 1 part by weight iso-amyl salicylate.

In a preferred manner of formulating the pastes contemplated by this invention, the alloy and glass binder are first thoroughly admixed as by ball-milling and thereafter the resulting admixture is stirred and roller milled into the requisite amount of liquid vehicle to provide a printing paste of the desired consistency. The paste so formed may then be printed in a desired pattern using a conventional screen or mask. Thereafter, the printed design is dried and fired to produce the final resistor, usually upon a dielectric substrate. Drying after printing may be effected by either air drying and/or oven drying, usually at a temperature of about -125 C. for about 5-10 minutes. Firing is usually accomplished thereafter at a temperature of about 700 C. i50 C. (for the PdO- system) using a heat-up peak and cool-down cycle of about 20-60 minutes with firing at peak temperatures for about 2-15 minutes.

As stated hereinabove, the resulting printed resistors of this invention are found to be highly reproducible, have excellent stability, and generally have TCRs less than :500 p.p.m./ C., usually less than i200 p.p.m./ C., and in some instances, substantially close to 0 p.p.m./ C.

The following examples are presented as illustrative of this invention:

EXAMPLES 1-20 Liquid admixtures were formulated from metallic mercaptans having the indicated metal content and Cab-O- Sil L-5 as an anti-agglomerant in an amount of 5% by weight of the total metal content. The liquid mixtures were then heated in open porcelain crucibles for about 3-4 hours, i.e., until a powder formed, at a temperature of C. Sufficient liquid was formulated and heated for each example so that about 50 gms. of powder resulted.

The temperatures resulting were then raised in an air environment to the indicated alloying temperature and held at this temperature for the indicated period of time to insure substantially homogeneous alloying and removal of substantially all remaining organics. In some instances (where no oxidation time and temperatures are reported) oxidation was conducted simultaneously with alloying. In other instances, oxidation took place after alloying in a separate step at the indicated temperature and for the indicated period of time. In Examples 1-11 and 20 oxidation was effected before glass binder addition while in Examples 12-19, oxidation was effected after addition of the glass binder and ball milling hereinafter described.

Powder-glass binder mixtures were made by ball-milling for 96 hours at 50-50 weight percent size less than about der with a glass frit having a particle size less than about 5 microns and consisting of by weight: 10% SiO 25% B 0 5% A1 0 25 ZnO; and 35% PhD. The ball-mill employed was a size 00 mill and milling was done with an aluminum oxide based mill and acetone. The resulting powders were then dried of acetone (and in Examples 12- 19 where then oxidized) and pastes were made.

The pastes were formulated by using 3 parts by weight powder and 1 part by weight organic liquid vehicle. The organic liquid vehicle consisted of 15% by weight T-10 ethyl cellulose dissolved in 85% by weight of 2 parts by said anti-agglomerating agent being selected from ultrafine silica and an ultrafine refractory. 2. A resistor composition according to claim 1 wherein said resistive metal is palladium.

weight butyl Carbitol acetate and 1 part by weight iso- 3. A resistor composition according to claim 1 whereamyl salicylate. in said organometallc compounds are mercaptans.

The pastes were then printed upon 1 inch square alu- 4. A resistor composition according to claim 1 which minum oxide substrates using a 200 mesh stencil screen. includes two metal stabilizers having a metal content The printed design was then air dried at about 100 C. weight ratio selected from AgzAu, about 4:1-124; PtrAg, for about 5 minutes and then fired in an open air conabout 8:1-1z8; and PtzAu, about 8:1-1z8. tinuous belt conveyor kiln, except in Examples -17 5. A resistor composition according to claim 4 wherein where a box kiln was used, using the indicated firing cycle. said resistive metal is palladium.

The results, reported in the following table were obtained: 6. A resistor composition according to claim 1 wherein TABLE A Firing Total Alloying Alloying oxidizing oxidizing Firing time firing Metal wt. percent, temp. time temp. time temp., (min. at time Resistance TOR,

Example organo metallic 0.) (hrs) 0.) (hrs.) 0. (peak) at peak) (min.) K ohms/sq. p.p.m./C.

1 Pd, 65; Ag, 28; Au, 7 800 16 725 72 700 6.0 24.0 11.0 +40 2 Pd, 65; Ag, 28; Au, 7 725 16 700 6.0 24.0 5.0 +145 3 Pd, 40; Ag,48; Au, 12-.-; 725 16 700 6.0 24.0 6.2 +396 4 Pd, 40; Ag, 48; Au, 12... 800 16 725 16 700 6.0 24.0 1.8 +415 5 Pd, 60; Ag, 32; Au, 8 850 8 725 8 700 6.0 24.0 4. 0 +325 6 Pd, 50; Ag, 40; Au, 10 725 16 700 6.0 24.0 17 +100 12 Pd, 35; Ag, 52; Au, 13.-." 800 16 400 16 710 8 40 1.17 10 13 Pd, Ag, 52; Au, 13.--" 400 16 710 s 0125 A25 14 Pd, 35; Ag, 52; An, 13 a 725 8 400 710 8 40 4. 9 +315 15 Pa, 35; Ag, 52;Au,13 800 16 400 16 700 10 30 1.3 0

16 Pd, 35; Ag, 52; An, 13"... 400 16 700 10 30 180 0 17 Pd, 35; Ag, 52; Au, 13--. 3 725 8 400 16 700 10 30 50 600 18 Pdf 50; A 40; Au, 10 331; 1g 400 16 710 6 30 .800 +439 19 Pd, 50; Ag, 40; Au, 10 1 12 13 400 40 710 6 30 1.5 +450 20 Pd, 35; Pt, 8; Ag,57 800 16 700 6 24 .0073 +169 1 48% glass binder used. 2 48.6% glass binder used.

Once given the above disclosure, many other features, modifications and improvements will become apparent to the skilled artisan. Such other features, modifications and improvements are, therefore, considered to be a part of this invention, the scope of which is to be determined by the following claims.

We claim:

1. A resistor composition comprising a resistive metalorganometallic compound, at least one metal stabilizer in organometallic form and an anti-agglomerating agent which is inert to the system and which prevents agglomeration of the resistive metal and metal stabilizer during alloying thereof, which alloying is conducted prior to the firing of the composition into a resistor structure,

said resistive metal being selected from the group consisting of palladium, rhodium, iridium, ruthenium, indium, and mixtures thereof;

said metal stabilizer being selected from the group consisting of silver, gold, and platinum and mixtures thereof; and

a In run 3 insufficient alloying (too low temp. and time) was effected to achieve good reproducibility.

the metal content of the composition is 5-95% by weight resistive metal.

7. A resistor composition according to claim 1 wherein said resistive metal is palladium and the metal content of said composition is l5-75% by weight palladium, the remainder of the metal content consisting essentially of said stabilizer metal.

References Cited