JPH0573358B2 - - Google Patents

Description

[Detailed description of the invention]

[Summary] The present invention relates to a circuit board in which superconducting ceramics are formed on a high-purity alumina substrate and used as a wiring material. [Industrial Application Field] This relates to circuit boards for high-speed computers such as supercomputers. In order for circuit boards for high-speed processing to transmit signals efficiently, the dielectric constant of the insulating material used for the circuit board is low, and
The electrical resistance of the conductor material is also required to be low. Research and development of ceramic superconductor materials whose electrical resistance becomes zero at liquid nitrogen temperature (77K) is progressing rapidly. Screen-printing superconducting ceramics as a paste onto alumina substrates used in hybrid ICs, etc., and firing the paste to use it as a superconductor wiring material is essential to the application technology of superconducting ceramics. be. [Prior Art and its Problems] Conventionally, typical methods for manufacturing multilayer ceramic substrates include thick film multilayer method, printed multilayer method, and lamination method. First, the thick film multilayer method involves printing and firing a conductive paste made of a low-resistance metal on a fired ceramic plate to form a conductive layer, and then repeatedly forming an insulating layer by printing and firing a thick layer of glass paste on top of this. Be multilayered. On the other hand, in the printing multilayer method and the lamination method, raw ceramic and conductive paste made of metal are alternately provided and then fired. In other words, the printing multilayer method prints ceramic paste and conductor paste alternately on a raw ceramic sheet to create a multilayer structure.
In the lamination method, a large number of raw ceramic sheets printed with conductive paste are formed and then laminated. The general ceramic substrates used in the above-mentioned thick film multilayer method are not limited to alumina substrates, except for completely crystalline materials, but also include crystal grains (grains), crystal grain boundaries called glass phases (grain boundaries), and voids ( It has an organization consisting of a combination of three members (pores).
The more glass phase there is, that is, the lower the purity, the lower the temperature can be used for firing. For this reason, in order to lower the firing temperature of general ceramic substrates, components that form a glass phase are added.
Fired at around 1500℃. On the other hand, printed circuit boards using superconducting materials, in which electrical circuit wiring is formed using ceramic-based superconducting materials on ceramic insulating substrates, are also being developed. (Nikkei Shimbun, April 22, 1988) However, although compacted compacts of superconducting ceramics exhibit superconductivity, superconducting ceramics made into a paste and formed on low-purity alumina substrates do not exhibit superconductivity. A problem arises. [Means for solving the problems of the conventional technology] Superconducting ceramics is used as a paste and screen printed on an alumina substrate used in hybrid ICs, etc., and then fired to become a superconductor wiring material. However, the reason why superconducting ceramic compacts exhibit superconductivity, but superconducting ceramics formed into a paste and formed on low-purity alumina substrates does not exhibit superconductivity is explained by the examples described below. Commercially available alumina substrates have low purity and contain impurities such as glass chamber components, amorphous SiO ₂ ,
_{Contains H2O3} . It was found that this glass component reacts with the superconducting ceramic to cause segregation, causing a shift in the composition of the superconducting ceramic as a wiring conductor, which causes the superconducting phenomenon to no longer be exhibited. In the present invention, when a superconducting ceramic paste is fired to produce a superconducting ceramic wiring material, an insulating substrate is used from which impurities such as glassy components and amorphous SiO ₂ that react with the superconducting ceramic are removed. That is, the present invention does not become a glass phase component.
It was discovered that it is necessary to use a high-purity substrate to which trace amounts of MgO and Cr ₂ O ₃ have been added and densely fired at high temperature (1600°C). In this case, the ceramic substrate is an alumina substrate having excellent thermal, mechanical strength, and electrical properties. (The manufacturing method for such alumina substrates was published in 1983.
11483, etc.) Furthermore, as a wiring conductor, a patent application filed on the same day, 1982-
114328 "Oxide superconducting materials and their manufacturing method" The following [1] formula shows superconductivity at liquid nitrogen temperature (77K) {(MO) _X (M ₂ O ₃ ) _1-X } _Y・( CuO) ₂ (O)σ ...[1] M: Ba, Sr, Ca, Mg M: Y, Sc, La, Ce, Pr, Nd, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu 0.5≦X≦0.9 1≦Y≦2 1≦Z≦2 (O)σ: Chemical formula indicated by the deviation of oxygen from the stoichiometric composition. It is possible to use an oxide superconducting material, more specifically, a Ba-Y-Cu-O-based high-temperature superconducting material. Example 1 0.6 mol of RaCO ₃ with a particle size of 1 μm and 0.6 mol of RaCO 3 with a particle size of 1 μm
A raw material powder was prepared by mixing 0.4 mol of Y ₂ O ₃ and 1 mol of CuO with a particle size of 2 μm for 48 hours by ball milling. 100 parts of this raw material powder, 1 part of ethyl cellulose,
10 parts of terpineol, 0.6 parts of a thixotropic agent (castor bean), and 20 parts of methyl ethyl ketone were added and mixed by ball milling for 72 hours. After this, the mixture was kneaded for 1.5 hours in a daikon machine (agate mortar), and further kneaded in a three-roll mill. This produced a superconducting ceramic paste. This paste was applied to a 99.7% alumina substrate (Al ₂ O ₃ −
A wiring pattern was created by screen printing on a MgO-Cr ₂ O ₃ system (FGA board). and 1020 in the atmosphere
It was baked at ℃ for 4 hours. The substrate on which this 25-μm-thick pattern was formed was immersed in liquid nitrogen, and the electrical characteristics of the wiring pattern were examined, and the results showed that it exhibited superconductivity. Next, the results of experiments conducted on various substrates with different wiring pattern thicknesses are shown in the table. As shown in the table, by using a high-purity alumina substrate that does not contain glass, the superconducting ceramic paste exhibits superconducting properties even if the pattern thickness is thin. In addition, a highly purified substrate containing a glass phase exhibits superconducting properties if the pattern thickness is increased.

[Fabrication of superconducting thick film]

(1) Superconducting paste Figure 1 shows an outline of the process for producing superconducting paste to obtain superconducting circuit wiring using the screen printing method. Preferably, the paste is made from a bulk superconductor of Y--Ba--Cu--O. For the bulk, powders such as yttoria (Y ₂ O ₃ ), barium oxide (BaO), strontium oxide (SrO), copper oxide (CuO), etc. are used. After thoroughly kneading these powders using a ball mill, they are compacted. Next, this green compact is fired at 800-1100°C in the air to create a bulk superconductor. Next, this bulk pulverized powder is uniformly dispersed in an organic binder and an organic solvent to produce a spreadable paste. The organic binder used in the paste must be one that decomposes and scatters when fired. thermal depolymerization decompose
By using PMMA, the amount of organic binder remaining after firing can be kept to a minimum. Also, the amount of vehicle to powder has a large effect on the viscosity and printability of the paste.
For this reason, the amount of vehicle was optimized, and the paste contained approximately 100% of superconducting ceramic component powder.
Binder, non-volatile solvent, etc. 5.5 to parts by weight
Approximately 40 parts by weight of vehicle should be included. This makes it possible to form fine patterns. (2) Formation of circuit pattern Using the above superconducting paste, print patterns on various ceramic substrates by screen method.
The substrate is fired in the air at 800-1000°C for several to several tens of hours. [Characteristics of superconducting thick film] High purity alumina substrate (FGA substrate: Fine
It was confirmed that the paste printed on the Grained Aumina substrate (Grained Aumina substrate) becomes a superconductor after firing.
Figure 2 shows the temperature change in electrical resistance of the thick film formed on the FGA base. Tcend is 89K, which is not much different from the bulk characteristics. Also, when measuring the magnetization of a sample using a vibrating sample magnet (VSM),
Although the proportion of demagnetization in the thick film sample was smaller than that in the bulk sample, the Meissner effect was confirmed. On the other hand, the results of examining the crystal structure by X-ray diffraction are shown in FIG. Y ₂ BaCu ₃ O _7-d similar to bulk
peak is observed. Example 4 Patent application filed on January 11, 1985 as a superconducting paste
62-114328, which is filed and described based on the priority claim, is a Y-Ba-Cu-O based ceramic.
By replacing the superconducting phase with Y-(Ba-Sr)-Cu-O-based paste and printing it on a PGA substrate, wiring with a high density of superconducting phase is produced. The microstructure of the bulk was observed by measuring Tco (onset temperature) with respect to the amount of Sr substitution and by SEM. Observation of the microstructure reveals that as the Sr concentration increases, the grain size decreases and the density increases. The specific resistance of the sample with x<0.5 at room temperature is strongly influenced by this and gradually decreases. From changes in the composition of the lattice constant determined from X-ray diffraction, it was found that substitution with Sr causes oxygen to escape as its concentration increases, that is, it acts like a reduction effect. Also, since it shows superconductivity despite the transition from orthorhombic to tetragonal system at x = 0.5,
It is highly likely that superconductivity is dominated by two-dimensional planes of CuO rather than one-dimensional chains of Cu-O. The compositional change in resistivity at room temperature has a minimum value, Tco (onset temperature)
The reason why the decrease becomes large when the composition change of x=0.5 or more is considered to be that the sites from which oxygen escapes differ around the boundary of x=0.5. (Sr _X Ba _1-X ) ₈ Y ₂ Cu ₁₀ O _7-d- based oxide superconducting oxides have physical properties that change at a composition of x=0.5, where the ratio of Ba to Sr is 1:1. At x=0.5, the crystal structure transitions from orthorhombic to tetragonal, and Tco increases to about 83K. [Sample preparation] Starting materials include Y ₂ O ₃ (99.9%, 2-3 μm),
_BaCO3 (99.9%, 2μm), SrO (99%, 280μm),
CuO (99.9%, 2 μm) was used. Each powder ( _Sr
Ba _1-X ) ₈ Y ₂ Cu ₁₀ O _7-d (x=0, 0.125, 0.25,
0.375, 0.5, 0.75).
These powders were mixed by ball milling for 24 hours. Alumina balls were used in the ball mill.
Next, the powder is molded by applying pressure at 200 MPa/ ^cm2 , and the radius
Pellets with a size of 15 mm and a thickness of about 3 mm were produced. Finally, it was fired on an alumina substrate at 950°C for 12 hours in the air. Electrical resistance measurement The dependence of Tco (onset temperature) on Sr concentration was
As shown in the figure. As Sr concentration increases, Tco decreases, but
When the ratio of Sr and Ba is 1:1, Tco suddenly recovers. Microstructure Observation of the microstructure of the sample using SEM at x=0.125 and x=0.5 revealed that as the Sr concentration increased, the grain size became smaller and the density increased. A qualitative diagram of the Sr concentration dependence of Tco and density is shown in the fifth figure.
As shown in the figure. _{From this , in ( Sr}
It can be seen that Tco is also high. Therefore, if a paste is produced within this composition range, stable wiring can be produced because the density of the superconducting phase is high. Oxide superconductor (Sr _X Ba _1-X ) ₈ Y ₂ Cu ₁₀ O _7-d , x = 0.4 ~
By creating pastes, wires, and thin films using substances with a composition of 0.6, circuit boards using superconducting ceramics with a high superconducting phase density as wiring materials can be formed. [Effects of the invention] It has become possible to create wiring using superconducting ceramic paste. ●Hybrid of superconducting ceramic paste
It could be used as a wiring material for ICs, etc.

[Brief explanation of the drawing]

Figure 1 is an example process diagram for producing superconducting paste, and Figure 2 shows superconducting bulk (〇-〇) and superconducting wiring (□) formed on a circuit board by the thick film method.
Figure 3 shows the X-ray diffraction pattern of superconducting wiring formed on a circuit board by the thick film method, and Figure 4 shows the temperature change in electrical resistance of ( _Sr
Electrical properties of Ba _1-X ) ₈ Y ₂ Cu ₁₀ O _7-d superconducting materials,
Figure 5 shows the Sr concentration dependence of electrical resistance and Tco _{( onset} temperature).
_{FIG. 8} is a diagram showing the Sr concentration dependence of Tco (onset temperature) and density of 8 Y ₂ Cu ₁₀ O _7-d based superconducting material.

Claims (1)

[Claims] 1. A circuit board characterized by using superconducting ceramics as a wiring material by printing a superconducting ceramic paste on a 99% or higher purity alumina substrate to form a wiring pattern and firing it.