JPS6050755B2 - How to form copper coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a copper coating, and particularly to a method for forming a copper coating by baking a copper paste.

Copper powder is dispersed in an organic varnish together with glass frit to form a paste, which is applied onto a ceramic substrate by means such as coating or printing, then dried, and then fired in a non-oxidizing atmosphere. Therefore, it is used as a thick copper coating for electrodes and conductive parts of circuit patterns.

In addition to the above, the content of glass frit is reduced and Cu is added to the copper powder. There are also so-called chemically bonded copper coatings that contain some metal oxides such as O, which can also be used for electrodes,
Alternatively, it is used as a conductive part of a circuit pattern. However, in the former method, a measure is taken to increase the glass frit in order to increase the adhesive strength with the substrate, but on the other hand, this results in a decrease in solderability and an increase in specific resistance.

In addition, in the latter case, in order to obtain sufficient adhesive strength with the substrate, the firing temperature of 850 ~
It is necessary to perform heat treatment at a temperature of 950 to 1000°C, which is higher than 900°C, and furthermore, Cu is removed after firing. Remaining O was observed, and deterioration of solderability was observed due to the presence of CU2O on the surface portion. Therefore, the present invention provides a method for forming a copper coating that can increase the adhesive strength of a thick copper coating formed on a substrate by baking treatment without impairing solderability or conductivity. There are things to do.

In other words, the key point of this invention is to apply a copper paste obtained by kneading copper powder, glass frit, and organic varnish onto a substrate, then dry it, and then place it in a non-oxidizing atmosphere. In the method for forming a copper film, which comprises performing a baking treatment, in the drying step,
The method is characterized in that a part of the copper powder is oxidized to produce copper oxide by heat treatment at a temperature of 00'C, and then the copper oxide is disappeared in the baking step. As the glass frit contained in the paste, one having reduction resistance is used because it is subjected to a baking process in a non-oxidizing atmosphere containing nitrogen.
Examples of glass frits that can meet such requirements include SiO25-20 mol%, ZnO25-20 mol%,
40 mol%, B2O3l 5-40 mol%, (CaO+M
gO) 5-30 mol%, A'2030-5 mol%, Li
There is one consisting of 200 to 10 mol%.

In addition, SlO238Wt%, TiO24Wt%, BaO
l8wt%, Ae2O27wt%, ZnO8wt%, M
There is one consisting of gO5Wt%, B2O3l5Wt%, and CaO5Wt%. Furthermore, examples of the organic binder include those obtained by dissolving ethyl cellulose resin in terpineol or cellosolve. copper powder, glass frit,
The mixing ratio of organic varnish and organic varnish is usually as follows.

Copper powder 50-82 Wt% Glass frit 3-8 Wt% Organic binder 15-35 Wt% The copper paste is applied onto a ceramic substrate such as alumina by means of coating, printing, etc., and then dried in a natural atmosphere. Ru.

Drying at this time is carried out at a temperature of 150 to 200'C. It is then baked in a non-oxidizing atmosphere such as nitrogen at a maximum temperature range of 850 to 900'C, thereby obtaining a thick copper coating. The copper film obtained by the above-mentioned process is formed by first oxidizing copper powder to produce copper oxide (Cu2O), and then baking it in a non-oxidizing atmosphere to form copper oxide (Cu2O).
), it was confirmed that by passing through a state in which the particles disappeared, a product with high adhesion strength to the substrate could be obtained.

In particular, in this invention, the drying step is carried out at a temperature of 150 to 200°C.
The reason for limiting the temperature range is that below 150'C, part of the copper powder can be converted into copper oxide (CVl2O) in this process, and above 200'C, the non-oxidizing atmosphere used later This is because even if the inside is baked, some copper oxide (Cu2O) remains in the copper coating.

Hereinafter, this invention will be explained in detail according to examples.

Example 1 75 Wt% spherical copper powder with a diameter of 1 μm and SiO2l (
7)%, B2O335wt%, Ae2O35wt%, C
A copper paste consisting of 23 wt% of an organic binder and 23 wt% of an organic binder was deposited on an alumina substrate by a printing method.

Next, the drying process was carried out at 120°C and 1150°C in a natural atmosphere.
2 at each temperature of 1180℃, 200℃, and 250℃
It was carried out in the interim. Thereafter, 6 powders were baked at a maximum baking temperature of 900° C. in a nitrogen atmosphere with a residual amount of oxygen of 20 ppm or less.

The results of X-ray diffraction analysis of the presence of copper oxide (CLl2O) after drying and the copper oxide (Cu2O) after baking for the copper coating obtained under each drying condition in the above-mentioned process are shown in Figures 1 and 2. It is shown in Figure 2.

The adhesive strength and solderability were also measured in the same manner, and the results are shown in Table 1.

Note that the adhesive strength is the value when the lead wire is soldered perpendicularly to the copper coating and the lead wire is pulled in the axial direction of the wire, and the soldering area is 2×3Tn1t.

Furthermore, solderability is determined by immersing an alumina board in a solder bath and visually measuring the adhesion area of the solder on the copper coating.Those with a solder adhesion area of 98 to 100% are considered to be of good quality. The other cases were judged as 1. Although it was determined that the solderability was slightly inferior when the drying condition was 200'C, this does not pose any particular problem in practical use. Example 2 The copper paste described in Example 1 was applied onto a substrate containing alumina by a printing method.

The substrate containing alumina described above had the following composition.

Ae2O3-44% by weight SrO-1 heel weight % SjO2-2 heel weight % MgO-1 weight % Thereafter, the same process as in Example 1 was carried out to bake onto a substrate containing alumina.

Then, the adhesive strength and solderability were measured in the same manner as in Example 1, and the results are shown in Table 2.

Example 3 Using the copper paste described in Example 1, this copper paste was applied to the surface of a ceramic substrate having the composition disclosed in Japanese Patent Application Laid-Open No. 53-246(1).

The composition of the ceramic substrate is ((BaO.9OCaO
．． lO))(TlO.84ZrO.l6)02 was used.

Thereafter, it was processed in the same manner as in Example 1 and baked onto this ceramic substrate.

Then, the adhesive strength and solderability were measured in the same manner as in Example 1, and the results are shown in Table 3.

As is clear from the above embodiments, according to the present invention, by setting the drying step at 150 to 200°C, when the copper paste is dried, some copper oxide (C
By baking a copper paste containing this copper oxide (Cu2O), a product with high adhesive strength and good soldering is obtained.

[Brief explanation of drawings]

Figures 1 and 2 are X-ray diffraction analysis diagrams; Figure 1 is after drying, and Figure 2 is after baking.

Claims (1)

[Claims] 1 Formation of a copper film by depositing a copper paste obtained by kneading copper powder, glass frit, and organic varnish on a ceramic substrate, drying it, and then baking it in a non-oxidizing atmosphere. The method is characterized in that in the drying step, a part of the copper powder is oxidized to produce copper oxide by heat treatment at a temperature of 150 to 200°C, and then the copper oxide is disappeared in the baking step. Method of forming copper coating.