JP2743558B2 - Copper conductor paste - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a copper conductor paste used for forming electrodes and wiring patterns on an insulating substrate such as ceramics, and more particularly to conductivity and solder wetting. The present invention relates to a copper conductor paste having excellent adhesion and good adhesion to a substrate.

(Prior art) Conventionally, a conductor paste that forms a conductor thick film by applying it to an insulating substrate such as glass or ceramics by a screen printing method, a direct drawing method, or the like so as to have a predetermined pattern, and then firing it is known. , Gold, silver, silver / Pd, copper, nickel and the like are used, but it is well known that a copper conductor paste has recently been used.

That is, the gold conductor paste can be fired in the air but is expensive, the silver conductor paste is apt to cause electromigration, the silver / Pd conductor paste is also expensive, and the nickel conductor paste has disadvantages such as high wiring resistance, Copper conductor paste is not only low cost but also
It can be said that the wiring resistance is low, migration is less likely to occur, and the conductor material is ideal.

Conventional copper conductor paste, for example, average particle size 0.5 ~ 10μ
m is dispersed in an organic vehicle together with an inorganic binder powder to form a paste.

Copper powder can be sintered as conductive particles during firing to form a conductive film. The organic vehicle also provides a thixotropic rheology required for screen printing and the like as a liquid binder for the paste.

Further, the inorganic binding powder has a function of fixing the fired film to the substrate, and glass frit, metal oxide, or the like is used.

In particular, the fixing effect of the glass frit is called a glass bond, and the glass frit is melted at the time of firing and flows from the space between the copper powders to the substrate due to a wetting phenomenon, thereby fixing the fired copper film and the substrate. That is, after baking, the upper layer of the film has a large amount of copper component, and the lower layer has more glass, and the film and the substrate are mechanically bonded via the glass.

On the other hand, the fixing effect of the metal oxide is called a chemical bond, and the metal oxide reacts with the substrate to form a composite oxide, thereby fixing the fired film and the substrate. At this time, the joined portion has a feature of being resistant to erosion of solder.

(Problems to be Solved by the Invention) By the way, the properties required for the conductor film thus obtained include conductivity, solder wettability, and adhesion to a substrate.

However, conventional glass bonds and chemical bonds as described above cannot be satisfied at the same time.

That is, in the case of a glass bond, if left at high temperature (also referred to as aging) after soldering, the adhesive strength to the substrate is significantly reduced. One reason for this is that solder invades the interface between glass and copper, and a large amount of intermediate alloy phase (Cu ₆ Sn ₅ ) is generated.

On the other hand, in the case of a chemical bond, since a high temperature is required for dissolution and decomposition of the metal oxide, unreacted metal oxide tends to remain, and a desired adhesive strength may not be obtained.

In JP-A-60-35405 and JP-A-1-167907, chemibonding is effectively caused by using surface copper oxide powder, but a surface oxide layer that is not near the interface between the film and the substrate is It does not contribute to chemical bonding and, on the contrary, hinders sintering of copper powder and reduces solder wettability.

The present invention has been made in order to solve the above-mentioned drawbacks, and has as its object to provide a copper conductor paste having high adhesive strength to a substrate and sufficiently satisfying conductivity and solder wettability.

(Means for Solving the Problems) In order to achieve the above object, the present inventor has conducted various studies, and as a result, using glass frit as a composite of copper oxide powder or copper powder in advance as an inorganic binder. It was found that the conductor characteristics of the copper conductor paste were remarkably improved, and the present invention was completed.

That is, the present invention provides a copper conductor paste comprising a copper powder, an inorganic binding powder and a vehicle, wherein the inorganic binding powder coats the surface of the glass frit with copper or copper oxide, and preferably has an average particle size of the glass frit surface. 0.1μm
The gist of the invention is that it is coated with the following copper oxide powder or copper powder.

According to a preferred embodiment of the present invention, the glass frit 100
The surface of the glass frit may be coated with 5 to 15 parts by weight of copper oxide or copper based on parts by weight, and / or the inorganic binding powder may be 5 parts by weight or less based on 100 parts by weight of the main copper powder. May be blended.

The copper powder blended with the inorganic binding powder is referred to as “main copper powder”, and the copper powder covering the glass frit is referred to as “binding copper powder”
Are described separately for convenience.

(Operation) The configuration and operation of the present invention will be described.

As the main copper powder, the average particle size is 0.1 to 10 μm as in the past,
Preferably, 0.5 to 5 μm is sufficient, and there is no particular limitation. The production method and particle shape are not particularly limited, but spherical particles are desirable for screen printing.

Known glass frit can be used as the glass frit constituting the inorganic binding powder used in the present invention.
For example Cd a PbO-B ₂ O ₃ -SiO ₂ glass as the base, those obtained by adding various metals such as Zn can be used. The average particle size of the glass frit is not particularly limited, but is preferably 10 μm or less suitable for screen printing and 0.5 μm or more necessary for bonding the substrate and the coating.

According to the present invention, such a glass frit is coated on its surface with copper oxide and / or copper. A preferred embodiment of the coating is made of glass frit and copper oxide powder and / or copper oxide.
Or compounding with copper powder. In such an embodiment, the copper oxide powder constituting the inorganic binding powder according to the present invention together with the glass frit, and the method for producing the binding copper powder, the shape of the particles is not particularly limited, but the surface of the glass frit The average particle size is preferably less than 0.1 μm because it is necessary to ensure uniform adhesion and coating properties.

In addition, the surface oxidation of the bound copper powder having an average particle diameter of less than 0.1 μm considerably progresses in the atmosphere, and the oxygen content reaches about 10%, and the surface characteristics are the same as those of the copper oxide powder. Further, the copper oxide powder may be any of a first copper oxide powder, a second copper oxide powder and a mixture thereof.

As a method of coating the surface of the glass frit with copper oxide powder or copper powder to produce the inorganic binding powder used in the present invention, a method of coating with a mortar, a raikai machine or the like can be mentioned. The copper oxide powder and the bound copper powder may each independently cover the glass frit, but in some cases they may be mixed to cover the glass frit in advance. In that case, the mixing ratio between the copper oxide powder and the copper powder is not particularly limited, but preferably, the mixing ratio between the copper oxide powder and the bound copper powder is 1: 2.

In addition, plating method, vapor deposition method,
It is also effective to form a copper thin film by a sputtering method or the like.

According to a preferred embodiment of the present invention, the weight ratio of the glass frit to the copper oxide powder or copper powder coated on the surface thereof is preferably 5 to 15 parts by weight based on 100 parts by weight of the glass frit. If the amount of copper oxide powder and copper powder is less than 5 parts by weight, the surface of the glass frit cannot be completely covered, and if it exceeds 15 parts by weight, excess copper oxide not consumed for the surface coating of the glass frit It is not preferable because powder and copper powder are generated.

The inorganic binding powder thus obtained is mixed with the above-mentioned main copper powder, and the mixing ratio is preferably 5 parts by weight or less based on 100 parts by weight of the main copper powder.

By the way, using a mortar or the like as described above, a powder obtained by coating a surface of a glass frit with a copper oxide powder or a binding copper powder having an average particle size of 0.1 μm or less, even if it is put in water and subjected to ultrasonic vibration, It was confirmed that the composite powder did not separate from the two-phase separation, that is, the glass frit, the copper oxide powder, and the copper powder. In other words, "covering" the surface of the glass frit as described above means that it is sufficient that the surface is not separated even when subjected to ultrasonic vibration in water. In the following, such a coating state may be called composite.

The composite bonding powder obtained in this way flows onto the substrate during firing, similarly to a conventional glass frit, but also forms a copper fired film via copper oxide powder or bonding copper powder on the surface. react. That is, chemical bonding occurs between the glass component flowing onto the substrate and the copper fired film via fine copper oxide powder or bonded copper powder having an average particle diameter of 0.1 μm or less. And since such a joint part is strong against erosion of solder, a decrease in adhesive strength to a substrate due to high-temperature aging after soldering is small.

The copper conductor paste of the present invention is obtained by mixing and kneading the above-prepared components and then forming a paste.

Known vehicles can be used as the vehicle used in the present invention. For example, cellulose derivatives (especially ethyl cellulose) or synthetic resins (polyacrylate, polymethacrylate, polyester, polyolefin, especially
Resins such as polyisobutyl methacrylate) are dissolved in a suitable solvent, for example, terpineol, dibutyl carbitol, dibutyl phthalate, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate.

As the above-mentioned pasting method, various known pasting methods can be used. For example, mixing can be performed with a universal stirrer (planetarium mill), and kneading can be performed with a three-roll mill, kneader, or the like.

Next, the copper conductor paste of the present invention is applied on a substrate by printing or drawing, a solvent is fitted therein, evaporated, and fired to obtain a conductive film. In this case, a known printing method can be used for printing. Examples of such a printing method include a screen printing method, a printing method using a metal mask, and a direct drawing method.

As a firing method of the conductor paste of the present invention, a known firing method is possible, but a belt furnace is preferable in terms of productivity and stability.

In addition, since all the copper oxide powder on the surface of the glass frit is consumed for bonding, unreacted oxide is generated as in the case of adding a conventional copper oxide powder alone or adding a surface copper oxide powder. Since it does not remain or hinder the sintering of the copper powder, the conductivity and solder wettability are not impaired at all.

Although an example in which copper oxide powder or bonded copper powder is coated on the surface of a glass frit has been described, a metal oxide conventionally used for a chemical bond such as CdO, ZnO, Bi ₂ O ₃ is used as the glass frit. Needless to say, a glass frit coated with fine powder such as PbO ₂ has the same effect.

Hereinafter, the present invention will be described in more detail with reference to specific examples.

(Example) Each copper conductor paste prepared in the composition ratio shown in Table 1 was printed on an alumina substrate having a purity of 96% by weight in an appropriate pattern using a screen printer, and dried at 120 ° C for 10 minutes. After removing the solvent, baking is performed in a nitrogen atmosphere in a belt furnace at a peak temperature of 750 ° C and a profile of 40 minutes per cycle including a peak temperature holding time of 10 minutes.
A 20 μm thick copper film was obtained.

In the examples of the present invention, glass frit and copper oxide powder or copper powder used were previously compounded by a raikai machine, but in the comparative example, those obtained by simply mixing them were used.

Conductive properties such as conductivity, solder wettability, and adhesive strength were evaluated for the copper fired films thus obtained.
The results are summarized in Table 2. The evaluation procedure was as follows.

(Conductivity): Evaluated by measuring conductor resistance. Specifically, the specific resistance was determined from the four-terminal method resistance measurement and the line width and thickness of the copper thick film.

(Solder wettability): 63% Sn-37% P with fired parts maintained at 230 ± 3 ℃
bImmersion in a solder bath for 3 ± 0.5 seconds, and the adhesion rate of the solder applied on the 4 mm × 4 copper film was visually measured.

(Adhesive strength): Maintained at a temperature of 230 ± 3 ° C. on a 2 mm square copper conductor film 63
After being immersed in a% Sn-37% Pb solder bath for 3 ± 0.5 seconds, a 0.6 mmφ tin-plated copper wire was soldered thereon with a handheld iron. The tin-plated copper wire is bent 90 degrees at a position 1 mm from the edge of the coating to make it perpendicular to the substrate.With the substrate fixed, the tin-plated copper wire is pulled at a speed of 10 cm / min by a tensile tester, and the tin-plated copper wire comes off the substrate. The adhesive strength was measured. The bonding luminosity was measured immediately after soldering (initial bonding strength) and after aging at 150 ° C. for 100 hours.

As can be seen from the results shown in Table 2, the adhesive strength in the comparative example, particularly the adhesive strength after aging, was remarkably inferior, the copper conductor paste containing no glass frit was peeled off, and the glass frit was removed. It can be seen that sufficient adhesion strength cannot be obtained in the case of simply containing, or in the case of simply mixing even if containing copper oxide powder.

(Effects of the Invention) According to the present invention, the glass frit and the copper oxide powder or the copper powder are simply compounded in advance as described above,
The obtained copper conductor paste has excellent adhesion to the substrate and can form a good conductor film satisfying both conductivity and solder wettability, and is very useful in industry, and its significance is great.

Claims (3)

(57) [Claims] 1. A copper conductor paste comprising a copper powder, an inorganic binding powder, and a vehicle, wherein the inorganic binding powder is one in which the surface of a glass frit is previously coated with copper oxide or copper. . 2. The method according to claim 1, wherein said glass frit is 100 parts by weight.
The copper conductor paste according to claim 1, wherein the surface of the glass frit is previously coated with 5 parts by weight of copper oxide or copper. 3. The copper conductor paste according to claim 1, wherein the amount of the inorganic binding powder is 5 parts by weight or less.