United States Patent (19) 11 4,415,624 Prabhu et al. 45) Nov. 15, 1983 54 AIR-FIREABLE THICK FILM INKS 3,673,117 6/1972 Schroeder et al. ................. 252/512 3,776,772 12/1973 Asada et al. .......... ... 117/227 75 Inventors: Ashok N. Prabhu, Plainsboro; 3,827,891 8/1974 Larry ...................................... 106/1 Kenneth W. Hang, Princeton 3,838,071 9/1974 Amin ......... ... 252A514 Junction, both of N.J. 4,029,605 6/1977 Kosiorek ... 252/54 4,051,074 9/1977 Asada ........ ... 252/503 73) Assignee: RCA Corporation, New York, N.Y. 4,141,727 2/1979 Shida et al. ... ..., 75/232 4,172,922 10/1979 Merz et al. ... ... 428/432 21 Appl. No.: 455,310 4,204,863 5/1980 Schreiner .............................. 75/234 22 Filed: Jan. 3, 1983 4,215,020 7/1980 Wahlers et al. ... 252/519 4,230,493 10/1980 Felten ................................. 106/13 4,256,796 3/1981 Hang et al........................... 428/210 Related U.S. Application Data 4,286,251 8/1981 Howell ...... ... 338/309 63 Continuation-in-part of Ser. No. 280,936, Jul. 6, 1981, 4,318,830 3/1982 Horowitz ............................ 252/519 abandoned. Primary Examiner-Ellis P. Robinson 51) Int. Cl............................ B32B 3/10; HO1B 1/02 Attorney, Agent, or Firm-Birgit E. Morris; R. Hain 52 U.S. C. .................................... 428/209; 252/512; Swope 252/518; 252/519; 338/308; 427/96; 427/101; 427/102; 427/126.2; 427/126.3; 427/123; 57 ABSTRACT 428/210; 428/427; 428/428; 428/432; 428/433; 428/434; 428/471; 428/472; 428/701; 428/901 Improved air-fireable resistor and conductor inks useful. 58) Field of Search ............... 252/519, 514,512, 511; in constructing multilayer integrated circuits on por 428/432, 433, 209, 210,901, 428,427,472, 471, celain-coated metal substrates are provided. The subject 701, 901; 427/126.2, 126.3, 123, 96, 101, 102; inks comprise a barium calcium borosilicate glass frit, a 338/308 suitable organic vehicle, and a functional component, i.e., ruthenium dioxide, in the resistor inks and one or (56) References Cited more precious metals plus bismuth oxide in the conduc U.S. PATENT DOCUMENTS tor inks. 3,304,199 2/1967 Faber et al. ......................... 17/201 3,484,284 12/1969 Dates et al. ......................... 117/22 24 Claims, No Drawings 4,415,624 1. 2 AIR-FIREABLE THECK FILM INKS SUMMARY OF THE INVENTION Improved air-fireable inks provided in accordance RELATED APPLICATIONS with this invention comprise a barium calcium borosili This application is a continuation-in-part of U.S. pa cate glass, a suitable organic vehicle and a functional tent application Ser. No. 280,936 filed July 6, 1981 now component. The functional component in the resistor abandoned. inks is ruthenium dioxide and in the conductor inks a This invention pertains to air-fireable thick film resis precious metal in combination with bismuth oxide to tor and conductor inks and their use in multilayer elec improve solderability. trical circuit structures on porcelain-coated metal sub O DETAILED DESCRIPTION OF THE Strates. INVENTION BACKGROUND OF THE INVENTION In accordance with this invention, there are provided The use of specialized ink formulations to form thick air-fireable resistor and conductor inks of high reliabil 15 ity useful in forming thick-film circuits on porcelain films having various functions on suitable substrates in metal circuit boards. The inks of this invention are par the construction of multilayer integrated circuit struc ticularly compatible with the Hang et al. circuit boards, tures is well known in the art. Such technology is of with each other, and with air-fireable inks of other increasing interest in the fabrication of very dense mul functions specifically formulated for the Hang et al. tilayer circuit patterns on various substrates for a wide 20 boards. The economic advantage of producing elec variety of applications in the electronics industry. tronic circuits wherein all inks are fireable in air as Significantly improved substrates for the fabrication opposed to an inert atmosphere such as nitrogen is of such circuits are disclosed and claimed in Hang et al., readily apparent to those skilled in the art. U.S. Pat. No. 4,256,796, issued Mar. 17, 1981, the disclo The novel inks of this invention are comprised of a sure of which is incorporated herein by reference. The 25 barium calcium borosilicate glass frit, a suitable organic Hang el al. substrates are comprised of a metal core vehicle, and one or more functional components. In the coated with an improved porcelain comprised of a mix resistor inks, the functional component is ruthenium ture, based on its oxide content, of magnesium oxide dioxide and, if desired, a temperature coefficient of (MgO) or mixtures of magnesium oxide and certain resistance (TCR) modifier. In the conductor inks, the other oxides, barium oxide (BaO), boron trioxide (B2O3) 30 functional component is one or more precious metals and silicon dioxide (SiO2). The preferred metal is steel, and, as a soldering enhancer, bismuth oxide. particularly low carbon steel, which may be coated The glass frit of the novel inks of this invention is a with various other metals such as, for example, copper. barium calcium borosilicate glass consisting of, on a The porcelain compositions are applied to the metal weight basis: core and fired to provide a partially devitrified porce 35 (a) from about 40 to about 55 percent of barium oxide; lain coating thereon. The coating has a very low viscos (b) from about 10 to about 15 percent of calcium ity at its initial fusion point and then almost instanta oxide; neously obtains a high viscosity due to devitrification. (c) from about 14 to about 25 percent of boron triox The fired coatings, which are preferred for hybrid cir ide; and cuit applications, have a deformation temperature of at 40 (d) from about 13 to about 23 percent of silicon diox least 700° C. and a high coefficient of thermal expansion ide. of at least about 110X 10-7/C. The presence of a minimum often percent by weight While the porcelain-coated metal substrates of Hang of calcium oxide in the subject glass frits is necessary in et al. represent a significant improvement over previ order to prepare an air-fireable ink which does not ously known substrate materials, they are disadvanta 45 contain ingredients conventional in air-fireable inks, e.g. geous only in being incompatible or poorly compatible lead oxide or zinc oxide, which would be incompatible with commercially available thick-film inks. For exam with the Hang et al. substrates. The subject inks also ple, a resistor ink containing a significant amount of lead have an optimum balancing of viscosity and surface oxide, which is conventionally used in air-fireable inks, tension. The subject glass frits have a high surface ten is a flux for the Hang et al. substrates. During firing, the 50 sion which is desirable so that the glass recedes from the glass in such an ink will drain to the substrate, pass surface of the functional particles. The subject glass frits therein and become diffused throughout to varying also have a low viscosity which is necessary in order concentrations. This leaves the functional particles on that the glass will flow and densify uniformly during the surface in a glass deficient state and substantially firing. changes the makeup and properties of the substrate. The 55 The glass frit comprises from about 1 to about 80 migration of the glass into the substrate produces very percent by weight of the novel air-fireable inks of this low resistance values and substantially increases the invention. The subject resistor inks preferably contain possibility that the ink can chip or flake off the surface. from about 25 to about 80 percent by weight of the glass The resistance values abruptly decrease because the frit with from about 50 to about 75 percent, by weight glass acts as an insulating barrier for the conductive 60 being particularly preferred. The subject conductor functional ingredient, i.e. ruthenium dioxide. When the inks contain from about 1 to about 15 percent by weight glass migrates into the substrate, the functional ingredi of the glass frit with from about 1 to about 7 percent by ent particles are drawn closer together without an insu weight being particularly preferred. lator. This therefore significantly raises conductivity A preferred glass frit for the resistor inks of this in and, conversely, lowers resistance to unacceptably low 65 vention consists of, on a weight basis, about 52 percent levels. Air-fireable conductor and resistor inks compati of barium oxide; about 12 percent of calcium oxide; ble with the Hang et al. substrates are provided in ac about 16 percent of boron trioxide; and about 20 percent cordance with this invention. of silicon dioxide. A preferred glass frit for the subject 4,415,624 3 4. conductor inks consists of, on a weight basis, about 52 example, a castor oil derivative available from N & L percent of barium oxide, about 12 percent of calcium Industries under the trademark Thixatrol. The organic oxide, about 19 percent of boron trioxide, and about 17 vehicle comprises from about 8 to about 35 percent by percent of silicon dioxide. weight of the inks of this invention. The subject resistor The functional component, i.e. ruthenium dioxide or inks preferably contain from about 20 to about 30 per precious metal, of the subject air-fireable inks is present cent, by weight, of the vehicle. The subject conductor - in from about 2 to about 90 percent by weight.