JPH02181495A - Manufacture of superconducting circuit board - Google Patents

Abstract

PURPOSE:To obtain a superconducting device based on an alumina substrate by a method wherein after the alumina substrate provided with a through hole for via use is dipped into a buffer layer formation material, the substrate is fired, powder of a superconductive composition is filled in the through hole and wiring patterns are respectively formed on both surfaces of the substrate. CONSTITUTION:A green sheet is punched to perforate (A) and thereafter, the sheet is fired to form an alumina substrate 2 and after being dipped into a fluid buffer layer formation material, the substrate is fired to film-form (B) a buffer layer 3 on the substrate including a through hole 1. Then, superconductive ceramic powder 4 is cast in the hole 1 with the layer provided in it to fill (C) the hole. Then, superconductive ceramics pastes 5 are screen- printed to form (D) electronic circuit patterns, a high-temperature firing is performed and a superconducting ceramics circuit is completed. In this case, there is the need of forming uniformly the layer 3 on the substrate. Therefore, a hydrophilic surface active agent has only to be applied on the substrate for wettability improvement use.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for manufacturing a superconducting circuit board, the purpose is to use an alumina substrate as the substrate, and the present invention involves forming a buffer layer using a fluidized alumina substrate with through holes for forming vias. A step of forming a buffer layer on an alumina substrate including through holes by immersing it in the material and firing it, a step of filling powder of a superconducting composition into the through holes of the alumina substrate, and a step of filling powder of a superconducting composition on both sides of the alumina substrate. The method for manufacturing a superconducting circuit board includes the steps of forming a wiring pattern made of paste and firing the alumina substrate.

[Industrial application field]

The present invention relates to a method for manufacturing a superconducting circuit board using an alumina substrate.

Aluminum (8l), titanium? It has been known that 22 elements such as Ti) and metal compounds such as niobium germanide (Nb, Ge) and molybdenum carbide (MoC) exhibit superconductivity, but for metal elements, the IOK is at most
23 of Nb and Ge for metal compounds.
．． 5K was the best.

However, in 1986, lanthanum, barium, copper, and oxygen (L
Since the discovery of high-temperature superconductivity in a-Ba-Cu-0) based oxide ceramics, research has progressed and led to the discovery of superconducting ceramics with a critical temperature (Tc) of approximately 90. Research on practical application is currently underway.

Now, information processing devices that process large amounts of information at high speed, especially in the computer sector that requires high speed, include high electron mobility transistors (abbreviated as HEMT) and resonant tunneling hot electron transistors (abbreviated as 1?1 IET). ,
Semiconductor elements made of gallium arsenide (GaAs) are being introduced, but these semiconductor elements cannot be manufactured using liquid nitrogen (N2).
), it is extremely effective to form an electronic circuit in which such a semiconductor element is mounted using a superconducting material and use it in a superconducting state.

The present invention relates to a ceramic substrate forming this superconducting circuit.

[Conventional technology] Alumina (α-Ap, 2O) is commonly used as a substrate material.

) has a relatively low dielectric constant of 9.34 and a melting point of 2050
It is a chemically stable oxide with an extremely high temperature of °C.

Alumina substrate is aluminum oxide (α-Aj2.O8)
An alumina substrate is manufactured by making a green sheet whose main component is alumina, and sintering it by firing at a high temperature.

Silver/palladium (Ag-I'
A conductive pattern made of conductive paste such as d) is made and fired to form an electronic circuit.
Integrated circuits such as SI are being installed.

Note that double-sided wiring is often performed from the standpoint of high-density packaging, but in that case, holes are punched at the wiring positions that connect the upper and lower circuits at the green sheet stage, and then they are fired, or the fired board is A laser beam is irradiated to make six openings,
Ceramic circuit boards are made by making upper and lower circuit connections when screen printing conductive paste, and then firing this.

Therefore, when forming a superconducting wiring circuit, a superconducting circuit can be formed by using a paste with a superconducting composition, screen-printing this to form an electronic circuit pattern, and firing this.

However, the critical temperature (
Tc) is much lower than expected.

The cause of this is the alumina substrate! This is because atoms and superconducting ceramics react, and the inventors have confirmed this.

(H, Yokoyama et al., M RS Intern
ational Meeting Advance
ed Materials, D2-8.1988) For example, yttrium oxide (YzOa), barium oxide (
The critical temperature (Tc) of a superconducting ceramic using a superconducting ceramic paste made of copper oxide (Cub) is 90, but decreases to 54 when formed on an alumina substrate.

In this way, the characteristics of superconducting ceramics formed on an alumina substrate deteriorate due to the influence of ^l atoms, so conventionally zirconia (ZrO□) or magnesia (MgO) substrates, which have less characteristic deterioration, have been used. was.

However, the cost of these substrates is more than an order of magnitude higher than that of alumina substrates, which has been a major obstacle to the practical application of superconducting circuits.

[Problem to be solved by the invention]

Alumina substrates are used as substrates for forming integrated circuits, and substrates with relatively low dielectric constants and smooth surfaces have also been put into practical use, and they are also much cheaper than zirconia and magnesia substrates. .

However, the AN atoms constituting the substrate diffuse into the superconducting ceramic, degrading its properties and lowering its critical temperature (Te), so it cannot be used as is.

Therefore, the challenge is to make it possible to use alumina substrates.

[Means to solve the problem]

The above-mentioned problem involves the process of immersing an alumina substrate with through holes for forming vias into a fluidized buffer layer forming material and then firing it to form a buffer layer on the alumina substrate including the through holes, and the alumina substrate. a step of filling the through-hole with a powder having a superconducting composition; a step of forming a wiring pattern made of a paste having a superconducting composition on both sides of the alumina substrate;
This problem can be solved by a method for manufacturing a superconducting circuit board that includes a step of firing this alumina substrate.

[Effect]

The inventors believe that since the distance that An atoms constituting an alumina substrate diffuse into superconducting ceramics is at most 5 μm or less, if a buffer layer with a thickness of about 5 μm is provided on the alumina substrate, superconductivity can be achieved. The idea was that it would prevent the deterioration of ceramics.

In this case, the necessary conditions for the buffer layer should be an inorganic material that has good adhesion to the alumina substrate and has excellent heat resistance, but the problem is that the diameter of the many holes made in the alumina substrate for forming vias should be sufficient. Forms a buffer layer inside the hole of about 0.2mmΦ, and then! The diffusion of atoms into the superconducting ceramic must be prevented.

The inventors have proposed two methods for forming a buffer layer on an alumina substrate including holes: ■ A method of forming a superconducting thin film on an alumina substrate by immersing it in a solution with a superconducting composition and then firing it to form a buffer layer. .

■ Calcinate after immersing in a solution of magnesium salt, and
A method in which spinel, which is formed by the reaction of O and Afz(h), is used as a buffer layer.

■ A method in which the material is immersed in a superconducting ceramic slurry of reduced viscosity and then fired to form a buffer layer.

We carried out three tests and obtained good results.

FIG. 1 is a sectional view showing the manufacturing method according to the present invention,
An alumina substrate is created by punching holes in a green sheet and then firing the alumina substrate, or by laser beam irradiation to make holes at the intended connection locations for electronic circuits that are patterned on the front and back surfaces of the alumina substrate. An alumina substrate 2 is prepared. (A in the same figure) Next, the buffer layer 3 is formed on the alumina substrate 2 including the through hole 1 by any of the methods ① to ② described above. (See Figure B) Next, the through hole 1 provided with the buffer layer 3 is filled with powder 4 made of superconducting ceramics to fill the hole. (C in the same figure) Next, a superconducting ceramic circuit is completed by screen printing the paste 5 made of superconducting ceramic to form an electronic circuit pattern and then firing it at a high temperature.

(The above is D in the same figure) Note that the necessary condition for implementing the present invention is that the buffer layer 3
is formed uniformly on the alumina substrate, and for this purpose it is necessary to improve the wettability, and it is effective to apply a hydrophilic surfactant to the alumina substrate. .

〔Example〕

Example 1: (Related to the second claim)
zO+), 2 moles of barium oxide (Bad), and 3 moles of copper oxide (Cub) were mixed in a ball mill for 48 hours, calcined at 950°C for 12 hours, and pulverized to a particle size of about 2 μm. We made raw material powder made of superconducting ceramic.

Next, polymethyl methacrylate (abbreviated PMMA resin) Log and terpineol 25 g were added to 100 g of this raw material powder.
100 g of methyl ethyl ketone was added to g and 1 g of the titanium coupling agent, and the mixture was mixed in a ball mill for 72 hours.

Thereafter, the mixture was kneaded for 3 hours using a disintegrator manufactured by Shitsutsu Corporation to scatter methyl ethyl ketone, which is a low boiling point solvent, and further kneaded using a three-roll mill to produce a superconducting ceramic paste with a viscosity of 1500 to 2000 voids.

Next, copper naphthenate, barium naphthenate, and yttrium stearate were mixed in a molar ratio of 1=2:3, and then dissolved in methyl alcohol to create a superconducting solution with a viscosity of 50 poise. .

Next, use a YAG (yttrium aluminum garnet) laser to drill holes with a diameter of 0.4 mm on a high-purity alumina substrate (Fujitsu fine blend alumina substrate) with a thickness of 0.65 mm at the locations where vias will be formed. After thorough washing, this substrate was immersed in a 10% terpineol solution of a titanium coupling agent (product name KR9S, Ajinomoto ■) for 1 minute, and then dried at 130''C for 10 minutes to make it hydrophilic.

This alumina substrate was immersed in a solution with a superconducting composition for 5 minutes,
After drying at 80° C. for 10 minutes, it was fired in the air at 1050° C. for 10 minutes to form a buffer layer with a thickness of about 5 μm including the pores.

Next, after filling the holes in the substrate with raw material powder of superconducting composition,
3m width on both sides of the board using superconducting ceramic paste
After screen printing a wiring pattern with a thickness of 100 μm and drying it, it was heated at a heating rate of 5 °C/min in the atmosphere for 10
After raising the temperature to 00°C and baking at this temperature for 1°,
A superconducting circuit board was completed by lowering the temperature at a rate of °C/min.

As a result of measuring the electrical resistance of such a circuit board from liquid helium (LLE) temperature to room temperature using the four-probe method, the critical temperature (Tc) was found to be 65, which is much higher than 54K for a conventional alumina board. I was able to get the temperature.

Example 2: (Related to Claim 3) Magnesium stearate was dissolved in methyl alcohol as a buffer layer forming material to prepare a magnesium solution having a viscosity of 5o poise.

A substrate with holes drilled in the same manner as in Example 1 was immersed in a surfactant solution to make it hydrophilic, then immersed in this magnesium salt solution for 5 minutes, and dried at 80"C for 10 minutes. It was baked in the air at 1500''C for 1 hour to form a buffer layer with a thickness of about 5 μm on the substrate including the holes.

Thereafter, a superconducting circuit board was formed on this in the same manner as in Example 1.

The critical temperature (Tc) of the superconducting ceramic circuit thus formed was 65.

Example 3: (Related to Claim 4) Methyl ethyl ketone was added to superconducting ceramic paste as a buffer layer forming material to prepare a slurry having a viscosity of 2° poise.

A substrate with holes drilled in the same manner as in Example 1 was immersed in a surfactant solution to make it hydrophilic, then immersed in this slurry for 1 minute, dried at 120°C for 30 minutes, and then exposed to air. It was baked at 900°C for 10 minutes to form a buffer layer with a thickness of about 5 μm on the substrate including the holes.

Thereafter, a superconducting circuit board was formed on this in the same manner as in Example 1.

The critical temperature (Tc) of the superconducting ceramic circuit thus formed was 65.

〔Effect of the invention〕

By carrying out the present invention, it becomes possible to use an alumina substrate as a superconducting ceramic circuit board, thereby making it possible to reduce costs and promoting the practical use of superconducting devices.

[Brief explanation of the drawing]

FIG. 1 is a sectional view illustrating the manufacturing method according to the present invention. In the figure, 1 is a through hole, 2 is an alumina substrate, 3 is a buffer layer, 4 is a powder, and 5 is a paste.

Claims (4)

[Claims] (1) A step of immersing an alumina substrate with through holes for forming vias in a fluidized buffer layer forming material and then firing it to form a buffer layer on the alumina substrate including the through holes; A step of filling a through-hole of a substrate with powder of a superconducting composition, a step of forming a wiring pattern made of a paste of a superconducting composition on both sides of the alumina substrate, and a step of firing the alumina substrate with the wiring pattern formed thereon. A method for manufacturing a superconducting circuit board, comprising: (2) A method for manufacturing a superconducting circuit board, characterized in that the fluid buffer layer forming material according to claim 1 is made of a metal salt having a superconducting composition. (3) A method for manufacturing a superconducting circuit board, characterized in that the fluid buffer layer forming material according to claim 1 is made of a magnesium salt. (4) A method for manufacturing a superconducting circuit board, characterized in that the fluid buffer layer forming material according to claim 1 comprises a slurry of superconducting ceramics.