JPH07320534A - Thick film conductor, its forming method and method of using this conductor - Google Patents

Abstract

PURPOSE:To provide an Ag thick film, improving a characteristic in the Ag rich thick film, migration and resistance against solder biting, and to provide a method of manufacturing this Ag thick film. CONSTITUTION:An Ag rich thick film 12 is printed to be formed in a ceramics substrate 11, to print a Pd film to coat a part required for migration resistance on this film 12. When burned at 500 deg.C, by alloying a boundary layer between Ag and Pd, a thick film conductor is formed on the substrate. That is, after the Ag thick film is formed, by coating a surface with Pd alloied, a structure, having fine Ag to large contain Pd limited to the surface, is obtained. By this structure, low resistance and fine structure by Ag and preventing Ag migration by Pd can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a thick film conductor formed on a ceramic substrate in a hybrid IC or the like, for example, a structure of a conductor thick film having a silver-palladium (Ag-Pd) alloy layer.

[0002]

2. Description of the Related Art Ag thick films have poor Ag migration and solder resistance. Therefore, Pd powder is mixed with the main component Ag powder to form a paste, which is printed on a substrate and baked to form a thick film. However, this Ag-Pd alloy thick film has poorer solder puncture resistance. This is because if a large amount of Pd is added, the sinterability deteriorates, and as a result, a porous structure is formed, and the commonly used solder (Pb-Sn alloy) can easily penetrate.

For a thick film containing an Ag-Pd alloy, a glass component is mixed with Ag powder and Pd powder, and a vehicle is further mixed to prepare a paste. The Ag-based conductor paste contains Pd in order to obtain migration resistance. When Pd is added by about 20 to 30% by weight,
A migration resistance effect can be obtained. Therefore, as a result of printing this Ag-Pd conductor paste on a ceramic substrate and drying and firing, a conductor wiring of an Ag-Pd alloy is formed. This Ag-Pd alloy is Ag
The migration of is suppressed.

However, P is contained in the Ag-Pd conductor paste.
When the amount of d added is increased, the amount of Ag-Pd alloy in the conductor increases, but the resistance value of the entire conductor decreases by the amount of Pd added, and the characteristics of the conductor deteriorate. In recent years, in thick-film circuits, there has been a demand for lower resistance of conductors in response to the trend toward higher frequencies and fine lines. Therefore, it is necessary to minimize the Pd content even in the Ag-Pd conductor.

[0005]

As described above, in the conventional Ag-Pd thick film conductor, the paste is simply printed on the substrate,
Since it was only a fired structure, there was a limit to increase solder resistance and solder resistance while reducing migration resistance. For example, when the migration resistance is increased, a porous structure in which solder shaving easily progresses and a resistance value increases.
On the contrary, if a dense structure is used to suppress solder shavings and a low resistance value is to be obtained, migration will proceed.

[0006]

Therefore, the inventor of the present application
It was noted that in the Ag-Pd conductor, g migration is ionized by Ag in the surface portion to become Ag ⁺ and elutes from the conductor to the outside to proceed. Then, it was found that the Pd amount should be increased only on the surface portion to prevent Ag ionization.

[0007]

SUMMARY OF THE INVENTION Therefore, the present invention improves the migration resistance and the solder puncture resistance, and
Its purpose is to obtain a thick film conductor having a low resistance value and a method of forming and using the same.

[0008]

According to a first aspect of the present invention, there is provided a conductive layer containing silver as a main component, which is deposited on an insulating substrate.
A thick film conductor having a coating layer made of an alloy of silver and a migration resistant metal for coating the conductor layer. As the migration resistant metal, for example, palladium, platinum, nickel or the like can be used. The insulating substrate is a ceramic substrate such as an AlN substrate or Al2.
An O3 substrate or the like is used.

According to a second aspect of the invention, the alloy is silver-
The thick film conductor according to claim 1, which is a palladium alloy. Palladium in this alloy is, for example, 20 to 30% by weight.
It is suitable to add it at a ratio of.

According to a third aspect of the present invention, a conductor layer containing silver as a main component is deposited on an insulating substrate, and the conductor layer is covered with a migration resistant metal layer and baked to obtain silver and migration resistance. It is a method of forming a thick film conductor in which an alloy layer with a metal is formed.

According to a fourth aspect of the present invention, there is provided a method of forming a thick film conductor according to the third aspect, in which a silver paste is printed on an insulating substrate and the silver paste is printed with a migration resistant metal paste to cover the silver paste. is there.

According to a fifth aspect of the present invention, there is provided a circuit wiring arranged on an insulating substrate, wherein the thick film conductor according to the first or second aspect is used in a portion where the wirings are close to each other. It is a method of using a thick film conductor.

[0013]

According to the first aspect of the invention, the conductor layer containing silver as a main component has a low resistance value and does not impair the function as a conductor. Further, since the conductor layer is coated with an alloy, silver migration can be suppressed. At the same time, solderability is not impaired as a thick film conductor.

In the invention described in claim 2, as a result of coating the conductor layer containing silver as a main component with the silver-palladium alloy,
It has excellent Ag migration resistance and low resistance.
It is possible to obtain a thick film conductor having excellent solder resistance. The palladium prevents migration due to Ag.

In the invention described in claim 3, by firing,
The conductor layer containing silver as a main component is covered with an alloy layer of silver and a migration resistant metal. As a result, the conductor layer has a low resistance value and excellent solder nicking resistance, and the alloy coating layer exhibits a migration resistance effect.

In a fourth aspect of the invention, a thick film conductor is formed by sequentially printing a silver paste and a migration resistant metal paste on an insulating substrate. Therefore, as compared with the case where the metal paste is coated in another sputtering process or vapor deposition process, the process can be further simplified.
Further, the silver paste has a dense structure and does not impair the solder resistance.

According to the sixth aspect of the invention, when the conductor thick film is used in the portion of the circuit wiring arranged on the insulating substrate where migration easily occurs, the migration resistance effect can be sufficiently exhibited. It is only necessary to screen-print the organometallic paste of palladium only on the portions where the wirings are close to each other, and it is possible to obtain a circuit wiring structure that is inexpensive and has excellent migration resistance as a whole.

[0018]

EXAMPLES Examples of the Ag-based thick film conductor according to the present invention will be described below. FIG. 1 shows a thick film conductor structure according to the first embodiment. As shown in this figure, 11 is a ceramics substrate, for example, an Al2O3 substrate, on which an Ag thick film 12 having a thickness of 10 .mu.m is deposited, and further, this Ag thick film 12 is formed by Ag-Pd. The alloyed thick film 13 covers it. The thickness of the Ag-Pd alloyed thick film is 1-2 μm.
Is.

The method of manufacturing the thick film conductor will be described in detail. First, an Ag paste is prepared. The Ag paste was prepared by mixing Ag powder having a particle size of 0.5 to 5 μm with terpineol as a vehicle to which 10% ethyl cellulose was added. The prepared Ag paste is shown in Table 1.
Shown in. Instead of this Ag powder, an Ag-Pt alloy powder may be used. Similarly, the palladium paste is prepared by mixing Pd powder with an organic solvent and an organic vehicle.

[0020]

[Table 1]

Next, a method of forming a thick conductor film on a circuit board will be described. Screen-print a predetermined pattern on the ceramic substrate 11 using Ag paste and
X Dry for 10 minutes. The Pd paste is also screen-printed on the Ag thick film and dried. That is, A
The g thick film is coated with the Pd thick film. And 50
Bake at 0 ° C to 700 ° C. As a result, A on the Ag thick film
A g-Pd alloy film was formed. Alloying proceeds at the interface between Ag and Pd. A suitable alloyed layer can be obtained by controlling the firing conditions. Therefore, it is possible to suppress the migration with the minimum amount of Pd. At this time, the internal Ag layer does not have a high resistance value. Further, by using an organic metal paste or an independent dispersion ultrafine particle paste as the Pd paste, alloying is possible even by heating and firing at about 400 ° C.
Note that Pd can be formed into a film by a method such as a plating method, a sputtering method, or a vapor deposition method other than the screen printing using a paste. Also, P coating Ag
Pt, Ni, or the like may be used instead of the d film.

Table 2 shows the Ag-P formed according to the present invention.
The result of the migration test of the Ag thick film coated with the d alloy film is shown. For comparison, a conventional Ag-Pd thick film,
The migration test results for the Ag thick film are shown in Table 2 at the same time. The migration resistance test is shown in FIG.
As shown in, a pair of conductor wirings 12 are formed on the ceramic substrate 11 so as to face each other with a predetermined distance therebetween, and the conductor wirings 12 are connected to both positive and negative electrodes and a predetermined voltage is applied. In this case, water droplets are dropped on the facing portion of the conductor 12. Ag is eluted from the conductor on the positive electrode side and moves to the negative electrode side. This is detected and measured with an ammeter or the like. The time until this elution is the migration time.

[0023]

[Table 2]

Further, in the solder curl test shown in Table 2, the thick film was immersed in a Sn-Pb eutectic solder bath at 250 ° C., and the number of immersions until the circuit resistance was doubled was measured. It is a thing. The surface sheet resistance values are also shown in Table 2.

As shown in Table 2, the conductor layer formed of the two-layer film according to the present invention has a considerably large effect on the migration time. That is, according to the present invention, it is apparent that the migration time can be extended. In addition, solderability is also excellent. Furthermore, the resistance value is the same as that of the Ag thick film.

[0026]

According to the present invention, it is possible to obtain a thick film conductor which has a low resistance value and does not impair the characteristics as a conductor.
Further, migration of Ag and short circuit of the circuit as a result can be prevented. This can be easily coped with even when the conductor thick film is covered with the cover glass, and it can be applied to a complicated circuit.
Furthermore, the solder puncture resistance can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a thick film conductor according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a migration test according to an example of the present invention.

[Explanation of symbols]

 11 Ceramics Substrate 12 Conductor Layer (Ag Thick Film) 13 Coating Layer (Ag-Pd Alloy Thick Film)

Claims (5)

[Claims] 1. A thick film conductor having a conductor layer containing silver as a main component, which is deposited on an insulating substrate, and a coating layer made of an alloy of silver and a migration resistant metal, which coats the conductor layer. 2. The thick film conductor according to claim 1, wherein the alloy is a silver-palladium alloy. 3. A conductive layer containing silver as a main component is deposited on an insulating substrate, and the conductive layer is covered with a migration resistant metal layer and baked to form an alloy layer of silver and the migration resistant metal. Of forming thick film conductor. 4. The method for forming a thick film conductor according to claim 3, wherein a silver paste is printed on an insulating substrate, and the silver paste is printed and coated with a migration resistant metal paste. 5. A method of using a thick film conductor, wherein the thick film conductor according to claim 1 or 2 is used in a portion where the wirings are close to each other in a circuit wiring arranged on an insulating substrate. .