JPS6339081B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to indium oxide thick film resistive inks that have excellent temperature coefficients of resistance and are used in multilayer electrical structures on porcelain coated metal substrates. It is known to those skilled in the art to use specialized inks to form thick films with various functions on suitable substrates in the manufacture of multilayer integrated circuit structures, and this technique is widely used in the electronics industry to form thick films with various functions on suitable substrates. This has become increasingly important when forming extremely dense multilayer circuit patterns on top. A particularly excellent substrate for the manufacture of such circuits is disclosed in U.S. Pat. No. 4,256,796, which is a metal coated with a superior porcelain composition, the porcelain composition being an oxide of the metal. Based on the composition, it consists of magnesium oxide (MgO) or a mixture of magnesium oxide and other oxides, barium oxide (BaO), boron trioxide (B ₂ O ₃ ) and silicon dioxide (SiO ₂ ). The preferred metal is steel, especially low carbon steel, which may be coated with other metals such as copper, and the mandrel is coated with a porcelain composition and fired to form a partially (semi) devitrified porcelain coating. It is formed on top of that. This coating has a very low viscosity at its initial melting point, but becomes highly viscous almost instantaneously due to devitrification. The recommended fired coating for hybrid circuits is at least 700
It has a heat distortion temperature of 0.degree. C. and a high coefficient of thermal expansion of at least about 110.times.10.sup. ^-7 /.degree. The porcelain-coated metal substrates of the above-mentioned US patent are significantly superior to previously known substrate materials, the only drawback being that they have little or no compatibility with commercially available thick film inks. In addition to the need to develop improved inks that are compatible with the substrate of this patent, there has been a general recognition of the need for a means to control the temperature coefficient of resistance which moves away from O or an optimum value rapidly as resistance increases. The present invention provides a means for controlling the temperature coefficient of resistance of an indium oxide resistor to within acceptable limits, ie, within about ±350 ppm/° C., even at high resistance values. The resistive ink of this invention consists of indium oxide, a resistance temperature coefficient controlling component of magnesium oxide, a barium-calcium borosilicate glass frit, and a suitable organic medium. The present invention provides an advanced intermediate resistance and high resistance ink, i.e., the ink has approximately
It has a sheet resistance of 500 Ω/□ to 1 MΩ/□ or more, making it useful for fabricating complex single-layer or multilayer thick film circuits on porcelain-coated metal circuit boards. The resistive inks of this invention are particularly useful for circuit formation on the porcelain coated metal plates of the above patent and various thick film inks specially formulated for this purpose, but are also effective on conventional substrates such as alumina plates. It can be used for. The novel resistance ink of this invention consists of indium oxide, magnesium oxide, barium-calcium borosilicate glass frit, and a suitable organic medium, with the addition of magnesium oxide as a resistance temperature coefficient controlling component. According to
High resistance values and surprisingly acceptable temperature coefficients of resistance are obtained. Indium oxide is highly pure and has a particle size of approximately 1.0-1.2μ
Preferably, it accounts for about 25-80%, preferably about 30-45% by weight of the total ink. Magnesium oxide, which is a component for controlling the temperature coefficient of resistance of the ink of this invention, accounts for about 1 to 20% of the total ink.
% by weight, preferably from about 3 to 8% by weight, and varying this content brings the normally highly negative temperature coefficient of resistance of the coatings made therefrom well within acceptable limits, often approaching O. be. The barium-calcium borosilicate glass frit of the ink of this invention has a weight ratio of barium oxide of about 40 to
55%, preferably about 52% and about 10% calcium oxide
~15%, preferably about 12% and boron trioxide ~14%
25%, preferably about 16% and about 13% silicon dioxide
-25%, preferably about 20%, and the glass frit powder accounts for about 5-60%, preferably about 30-45% by weight of the total ink. Organic media are, for example, binders such as cellulose derivatives such as ethylcellulose, synthetic resins such as polyacrylates or methacrylates, polyesters, polyolefins, etc., among others. Conventional solvents commonly used in inks of the type described herein can be used in the inks of this invention. Recommended commercially available solvents include, for example, pure liquid polybutenes Amoco H-25, H-50, and L-100 from Amoco Chemicals Corp. and polybutenes from Dupont Nemours & Co. n-butyl methacrylate and the like. The above resins may be used alone or in any combination of two or more. A suitable viscosity modifier can be added to this resin material if necessary. This modifier is commonly used in similar ink compositions, such as pine oil, terpineol, butyl carbitol acetate, Texas
Eastman Co.) trademark Texanol ester alcohol, etc. or e.g.
It can be a solid material, such as the castor oil derivative of Thixatrol, trademarked by Industries. The organic medium accounts for about 10-35% by weight of the total ink, preferably about 20-30%. The resistive inks of this invention may be applied to a substrate, such as a conventional alumina plate or the porcelain-coated metal plate of the aforementioned US patent, by conventional means such as screen printing, brushing, spraying, etc., although screen printing is recommended. Ru. The ink film is then dried in air at 100-125°C for about 15 minutes, and then baked in nitrogen at a maximum temperature of 850-950°C for 4-10 minutes. As is customary in the prior art, the resistive ink of the present invention is generally deposited and fired on the substrate surface after all conductive inks have been deposited and fired. The resistance of this fired coating can be adjusted by conventional means such as laser trimming or air abrasion trimming. The coatings formed from the resistive inks of this invention exhibit excellent temperature coefficients of resistance, laser cutability and stability to the effects of thermal shock, solder immersion, thermal storage, power loading and humidity, as well as the porcelain coatings of the above-identified U.S. patents. It has shown excellent compatibility with metal plates and coatings formed with inks specifically developed for the purpose. The invention will now be explained by way of example, but the invention is not limited to the details of the description. Percentages and percentages of ingredient amounts unless otherwise specified in this example
All are given as weight ratios and temperatures are given in °C. Example A resistive ink was prepared with the following composition.

[Table] The composition of the glass powder in the above composition is in weight%,
BaO (51.59), CaO (12.58), and B ₂ O ₃ (15.62)
and SiO ₂ (20.21). The medium was a 6% solution of ethyl cellulose in Texanol ester alcohol. Ink F and H are 1.51% and 3.03%, respectively, to adjust the fluidity.
Added Texanol. The powder components were combined with the organic medium, initially mixed by hand, and then sheared on a three-roll mill to obtain a smooth paste suitable for screen printing. Further media was added to compensate for losses during mixing and to ensure proper fluidity. The conductive copper ink was deposited on a porcelain-coated steel plate of the type of the above patent and fired. At this time, the ink is printed onto the substrate as an ink layer with a thickness of 7.6 to 15.2 μ through a 325 mesh stainless steel screen, dried in air at 125 ± 10 °C for about 15 minutes, and then heated to a maximum temperature of 900 °C in nitrogen. It was baked at ±10°C for 4 to 7 minutes. The sheet resistance and hot and cold temperature coefficient of resistance (TCR) of each ink were measured and the results are shown in the table below.

[Table] *Includes magnesium oxide.
The positive effect of magnesium oxide present in the compositions of this invention on the temperature coefficient of resistance is easily seen from this table. For example, when moving from ink E to F, it is thought that the temperature coefficient of resistance becomes approximately -1000 due to an increase of more than three times the sheet resistance. The coefficient unexpectedly decreased to less than 1/4.

Claims (1)

[Claims] 1. A resistor on a circuit board comprising 25-80% by weight of indium oxide, 1-20% by weight of magnesium oxide, 5-60% by weight of barium-calcium borosilicate glass frit, and 10-35% by weight of a suitable organic medium. Resistive ink suitable for forming a film.