JPH0443859B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a conductive paste for forming a conductive film on a ceramic substrate. [Prior art] In order to form conductive films such as conductive circuits and electrodes on ceramic substrates, Ag, Ag, etc. are used as conductive powders.
Precious metal powder such as Pd, Pt, Au, etc. as a single substance, alloy or mixture is 80 to 96% by weight, 2 to 10% by weight of lead borosilicate glass powder with a softening point of 400 to 700℃, and inorganic materials such as bismuth oxide and copper oxide powder. Paste compositions have been used in which a solids content of 2 to 10% by weight of filler is mixed with a vehicle. Such a composition is applied onto a ceramic substrate in a desired shape by a screen printing method, a transfer method, etc.
By firing at 600 to 900°C, a conductive film in a desired shape can be formed on the substrate. In the above composition, the glass powder is a binder for fixing the conductive powder onto the ceramic substrate, and the bismuth oxide powder, which is an inorganic filler, is used to improve the wettability between the conductive powder and the glass, and between the glass and the ceramic substrate. Copper oxide powder is added to improve adhesive strength by reacting with alumina in the substrate. Conventional conductive coatings like this do not have any problems with adhesive strength when parts are soldered onto the coating, but if the soldered state is exposed to temperatures of about 150°C, the conductive coating will deteriorate. The drawback was that the adhesive strength with the ceramic substrate was significantly reduced. The strength after being left at high temperatures is called aging strength, and the quality of this property directly affects the reliability of the product. In order to prevent this decrease in aging strength, it is sufficient to include a large amount of glass powder, but this will conversely decrease solder wettability. Decrease in solder wettability not only reduces production efficiency but also causes deterioration in product yield. [Problems to be Solved by the Invention] An object of the present invention is to provide a conductive paste capable of obtaining a conductive film having necessary aging strength while maintaining solder wettability. [Means for Solving the Problems] Means for solving the above problems according to the present invention are as follows: (1) Containing copper oxide and manganese oxide in an amount of 5% by weight or more each, and bismuth oxide in an amount greater than the total amount of these. , and contains 2 to 10% by weight of glass powder having a composition containing 80% by weight or more of these components in total and 85 to 98% by weight of noble metal powder in 100% by weight of the total solid content. (2) The conductive paste according to (1) above, comprising a mixture of 100 parts by weight of total solids and 12 to 25 parts by weight of vehicle. The glass of the present invention is prepared by blending copper oxide, manganese oxide, bismuth oxide, and glass forming agents such as oxide powders such as silicon dioxide, lead oxide, boron oxide, zinc oxide, and molybdenum oxide, melting the mixture at 900 to 1500°C, and then rapidly cooling the mixture. and make it into glass. Although glass may be formed using only copper oxide, manganese oxide, and bismuth oxide, it is easier to form a glass by adding a glass forming agent. This glass powder is prepared to have a softening point in the range of 400 to 700°C in relation to the processing temperature at which it is processed into a conductive film. As the noble metal powder, powders such as Ag, Pd, Pt, and Au can be used alone, as an alloy, or as a mixture. If only Ag powder is used, high conductivity can be obtained, but it tends to dissolve into solder or flow, so to prevent this, it is better to use it in combination with Pd or Pt. The proportion of noble metal powder used as a conductive powder in the total solid content of the conductive paste is determined by considering conductivity, solder wettability, corrosion resistance to solder, etc., but it is 85 to 98% by weight, which is the same as conventional powder. Can be used within the range. Up to 5% by weight of inorganic filler powder such as molybdenum oxide, silicon dioxide, zinc oxide, lead oxide, and chromium oxide can be added to the total solid content of the conductive paste to adjust the coefficient of thermal expansion. . As in the conventional case, a vehicle prepared by dissolving ethyl cellulose, methacrylate resin, etc. in a solvent such as terpineol, butyl carbitol, or toluene is used. The blending amount of the vehicle is 12 to 25 parts by weight based on 100 parts by weight of the total solid content, as in the conventional case. The solid powder is kneaded with a vehicle to form a paste and applied to the substrate through a 150-400 mesh screen. In order for the paste to pass through the screen smoothly, it is best to use a powder containing almost no particles of 10 μm or larger in solid content.
It is preferable to use particles with an average particle size of 2 μm or less. Examples of the substrate to which this conductive paste is applied include refractory oxides such as alumina and silica-alumina. [Function] The glass of the present invention contains copper oxide, manganese oxide,
Bismuth oxide is an essential component, and if any of these is lacking, both aging strength and solder wettability cannot be satisfied. If the content of copper oxide and manganese oxide is less than 5% by weight, or if either of them is missing, the aging strength will be reduced. Furthermore, if the amount of bismuth oxide is less than the total amount of copper oxide and manganese oxide, the solder wettability will deteriorate and the softening point of the glass will increase. If these three components are less than 80% by weight in the glass, the solder wettability or aging strength will deteriorate. If the amount of glass powder is less than 2% by weight of the total solid content in the conductive paste, the aging strength of the conductive coating and the substrate will be significantly reduced, and if it exceeds 10% by weight, the solder wettability will deteriorate. The glass component of the present invention consists of 80% by weight or more of vitrified copper oxide, manganese oxide, and bismuth oxide. Copper oxide, manganese oxide, and bismuth oxide react with and adhere to the substrate, so it adheres more strongly to the substrate than conventional lead borosilicate glass, and can be aged while maintaining solder wettability. It is thought that the decrease in strength will be smaller. [Example] Table 1 shows the composition of the glass frit. The following paste was prepared using this glass frit. As a conductive powder, Ag powder with a particle size of 1.2 μm, Pd powder with a particle size of 0.1 μm, and glass frit shown in Table 1 were mixed in the proportions shown in Table 2, and 100 parts by weight of this solid content and 20 parts by weight of a liquid vehicle were mixed. Kneaded. A terpineol solution containing 8 parts by weight of ethyl cellulose was used as the organic vehicle. The above paste-like composition was screen printed in a test pattern on an alumina substrate, and the peak temperature
Firing was carried out in an air atmosphere in a belt-type firing furnace at 850°C, peak time 8 minutes, and total firing cycle 60 minutes, and the following tests were conducted on the fired film of the test pattern. (a) Solder wettability: Apply flux (XA-100, manufactured by Tamura Kaken) on a 10 mm square pattern and place the pattern in a 37Pb/63Sn solder bath (230℃) for 5 minutes.
Dip for a second, and after cooling, determine the wetted area ratio of the solder on the pattern. (b) Adhesive strength... 0.65mm diameter on a 2mm square pattern
Solder mm mm Sn-plated copper wire using 37Pb/63Sn solder, peel it by pulling it in the vertical direction, and measure the tensile force at the time of peeling. (c) Aging strength: A board to which Sn-plated copper wire was soldered in the same manner as above was left in a thermostat at 150°C for 300 hours, and then subjected to the same peel test as above. The results measured using methods (a) to (c) are solder wetness 80
% or more, adhesive strength 4.0Kg or more, aging strength 2.0
A value of Kg or more is required. According to Table 3, the solder wettability was 80% or more in Test Nos. 1 to 4 and 13 to 16, and the aging strength was also 1.5 times or more than the required 2.0 kg. This shows that aging strength can be increased without inhibition. On the other hand, in Nos. 5 to 12, the glass composition is limited because the solder wetting is insufficient and the aging strength is not particularly high. Further, according to Nos. 17 and 18, it is shown that too much glass has an adverse effect on solder wetting, and too little glass shows that the aging strength is weakened.

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〔Effect of the invention〕

As described above, according to the present invention, a conductive film having excellent solder wettability and aging strength can be formed, and the defect rate can be reduced by improving the solder wettability. Furthermore, since the adhesive strength and aging strength are increased, the reliability of the product is improved.

Claims (1)

[Claims] 1 5% by weight of each of copper oxide and manganese oxide
2 to 10% by weight of glass powder having a composition containing more bismuth oxide than the total amount of the above and 80% by weight or more of these components in total.
and 85-98% by weight of precious metal powder, total solid content
Conductive paste containing 100% by weight. 2. The conductive paste of claim 1, comprising a mixture of 100 parts by weight of total solids and 12 to 25 parts by weight of vehicle.