JP2003197032A - Conductive paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive paste capable of improving migration resistance further than a conductive paste using alloyed powder of silver and copper. <P>SOLUTION: The conductive paste is composed by dispersing an alloyed powder body comprising silver, copper and nickel in an organic binder. It is preferable that an addition rate of the nickel with respect to the silver and copper is 0.3-2 wt.% from an aspect of improving the migration resistance and suppressing a contact resistance value. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste having excellent migration resistance and corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, as a conductive paste used for screen printing, through hole formation, etc., there has been a conductive paste prepared by dispersing silver powder in an organic binder. However, the conductive paste using only silver powder as the conductive powder has a problem that migration easily occurs in a hot and humid atmosphere. Here, migration means that when a voltage is applied in the presence of water between a pair of conductors, silver is ionized on the positive potential conductor side by an electrochemical reaction and moves to the negative potential conductor side to deposit. Say the phenomenon.

Therefore, in order to prevent the above drawbacks, conductive powder made of a powder of an alloy of silver and copper is used as the conductive powder. That is, there is little oxidation on the surface of the metal powder, and good conductivity can be maintained, but silver, which is a noble metal with poor migration resistance, and oxidation of the surface of the metal powder progresses, but electrical resistance gradually increases. By alloying with copper, which is a superior base metal, the advantages of each are utilized, and the conductive powder that is excellent in migration resistance and can maintain good conductivity with little oxidation of the metal powder surface is used. There is.

However, since migration also occurs in the conductive paste using the conductive powder made of the above-mentioned silver-copper alloy, it cannot be said that the migration resistance is sufficient depending on the location and method of use of the conductive paste, and the migration resistance is further improved. Improved conductive pastes have been desired.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object thereof is to provide a conductive paste which can further improve migration resistance as compared with a conductive paste using an alloy powder of silver and copper. To provide.

[0006]

When the inventors of the present invention analyzed the alloy of silver and copper used in the conductive paste, they found that the dispersibility of silver and copper in the alloy was not very good. That is, when the alloy (Ag-Cu = 70: 30 (% by weight)) is magnified and viewed as shown in FIG. 1, a lump of copper (black) is relatively large in the silver (white) of the alloy. Exists, which is considered to hinder the improvement of migration resistance. Therefore, in order to improve the dispersibility of the alloy of silver and copper, the inventor of the present application added a small amount of nickel to the alloy, thereby improving the dispersibility of silver and copper and improving the migration resistance. .
That is, as shown in FIG. 2, when a ternary alloy in which nickel is added to silver and copper (Ag-Cu-Ni = 70: 29.5: 0.5 (wt%)) is enlarged and seen, a lump portion of copper It can be seen that is smaller and the dispersibility is improved. Therefore, the present invention is
An alloy powder composed of silver, copper and nickel was dispersed in an organic binder to form a conductive paste.

According to an experiment, the mixing ratio of silver, copper and nickel in the alloy powder is 0.3 to 2.0% by weight of nickel with respect to silver and copper in order to obtain the migration resistance. It is preferable for improving the contact resistance and suppressing the contact resistance.

[0008] Further, the mixing ratio of silver and copper is not suitable as a conductive paste used for a circuit pattern or the like from the viewpoint of conductivity when too much silver impairs migration resistance and too much copper. From these things, silver is 90-6
The range of 0% by weight and the range of 39.7 to 8.0% by weight of copper are preferable.

Further, the mixing ratio of the alloy powder and the organic binder in the conductive paste is such that the organic binder is added to 70 to 90 parts by weight of the alloy powder in order to exhibit normal functions such as conductivity as the conductive paste. It is preferably about 25 parts by weight.

Therefore, a conductive paste that satisfies the following alloy powder composition and conductive paste composition conditions is suitable. [Alloy powder composition] Ag: 90-60 wt% Cu: 39.7-8.0 wt% Ni: 2.0-0.3 wt% [Conductive paste composition] Alloy powder: 70-90 wt% Resin (Organic binder, for example, phenolic): 5-2
5 parts by weight solvent (for example, carbitol-based): 5 to 25 parts by weight It should be noted that the solvent is not limited to the above-mentioned mixing ratio depending on the viscosity of the conductive paste required, and may be any mixing ratio. .

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The reason why an alloy powder made of a ternary alloy by mixing nickel with silver / copper is used and the reason why the mixing ratio of nickel is limited to the above conditions will be described together with the embodiments. To do. [Reason for mixing ternary alloy with nickel in silver / copper] The inventor of the present application has found that a conductive paste using only silver powder as alloy powder, a conductive paste using silver / copper alloy powder, and silver / copper A water drop test for measuring the migration resistance of each conductive paste was performed for comparison with the conductive paste using nickel alloy powder.

The following three kinds of conductive pastes were used as samples. Sample: Alloy powder composition (wt%) Ag-Cu-Ni = 80: 19.5: 0.5 Conductive paste composition Alloy powder: 70 parts by weight Resin (phenolic): 17.5 parts by weight Solvent (carbitol-based) ): 12.5 parts by weight External shape of alloy powder Powder diameter: 1 to 40 μm (average particle diameter 10 μm) Shape: Flake sample: Alloy powder composition (wt%) Ag-Cu = 80: 20 Conductive paste composition Same external shape of alloy powder Same as sample Sample: Metal powder composition (wt%) Ag = 100 Conductive paste composition Same as sample External shape of alloy powder Same as sample

A water drop test was conducted on each of the above samples under the same conditions. The test method is the substrate (polyethylene terephthalate film (PE
Two patterns P1 and P2 are formed on the T film)) with a predetermined gap therebetween by screen printing (thickness 0.01 mm), and a predetermined voltage (DC5V) is applied between them to drop water in the gap. It measures the time from to short circuit. For each sample, the short circuit time was measured while changing the gap interval in the range of 0.15 to 0.5 mm. The result is shown in FIG.

As shown in the figure, the sample which is a conductive paste mixed with nickel has a short circuit time longer than that of the other samples regardless of the gap intervals. You can see that it will improve.

[Reasons for Limiting the Mixing Ratio of Nickel to 2.0 to 0.3% by Weight] The inventor of the present invention has prepared alloy powders of silver / copper alloy and silver / copper / nickel alloy, respectively. A water drop test was performed to measure the migration resistance of the one in which the mixing ratio of silver and copper was changed and the one in which the mixing ratio of nickel was changed, and the results were compared. The samples used were not conductive pastes,
It is the alloy itself that is the source.

Specimen: Alloy composition: Ag-Cu, 5 kinds of which the blending ratio (wt%) of silver and copper was changed in the range of 100 to 0 Specimen: Alloy composition: Ag-Cu-Ni, Ni 5 kinds of samples in which the mixing ratio (wt%) was changed to 0.2 and the mixing ratio (wt%) of silver and copper was changed in the range of 99.8 to 0 Sample: Metal composition: Ag-Cu-Ni Then, 5 kinds of Ni (0.5% by weight) were used, and the mixing ratio (wt%) of silver and copper was changed in the range of 99.5-0.

Then, a water drop test was conducted on each of the above samples under the same conditions. The test method is two plate-shaped alloy plates (length x width x thickness = 20) on the substrate.
X 10 x 3 mm) is installed on the base (PET film) with a gap of 1 mm, tap water is hung down to the gap by about 1 cc, and a time of applying a voltage of DC 5 V between both alloy plates and short-circuiting is taken. It is something to measure. The result is shown in FIG.

As shown in the figure, no matter what the mixing ratio of silver and copper is, an alloy containing 0.5% by weight of nickel is an alloy containing no nickel and 0.2% by weight of nickel. The short-circuit time was longer and the migration resistance was improved as compared with the alloys mixed only with each other. On the other hand, it was found that the mixture of nickel in an amount of 0.2% by weight did not show an improvement in migration resistance, and the mixture of nickel at least in an amount of 0.3% by weight or more improved the migration resistance.

When the blending ratio of nickel was increased to 0.5% by weight or more, the short circuit time was longer than that of the sample regardless of the blending ratio of silver and copper. From this, it was found that the improvement of migration resistance can be expected if the mixing ratio of nickel is 0.3% by weight or more.

However, if the mixing ratio of nickel is too large, the contact resistance value on the exposed surface increases, and from this point, it is necessary to limit the mixing ratio of nickel. That is, the inventor of the present application prepared four kinds of silver / copper / nickel alloys having different amounts of nickel, and measured the contact resistance values of each in a high humidity tank over time. The prepared samples are as follows.

Sample-1: Alloy composition (% by weight): Ag-
Cu-Ni = 60: 39.5: 0.5 Sample-2: Alloy composition (% by weight): Ag-Cu-Ni =
80: 19.5: 0.5 Sample-3: Alloy composition (wt%): Ag-Cu-Ni =
Sample with 80: 18.0: 2.0-4: Alloy composition (wt%): Ag-Cu-Ni =
80: 17.5: 2.5

The alloys of Samples 1 to 4 were allowed to stand in a high humidity tank having a temperature of 40 ° C. and a humidity of 90 to 95%, and their contact resistance values were measured over time. As shown in FIG. 6, the measuring method is as follows:
The contacting portion 21 was contacted with a contacting pressure of 20 g, and the resistance value between the contact point and the end side L of the metal plate 10 was measured. As the contact 20, a phosphor bronze plated with silver and a contact portion 21 having a spherical radius of 0.5 mm was used. The measurement result is shown in FIG.

As shown in Samples-1 and -2 of FIG.
Although the contact resistance value hardly changed even when the mixing ratio of silver and copper was changed, as shown in Samples 2, 3 and 4, the contact resistance value changed when the nickel content was changed. When the nickel content is 2.5% by weight, the change in contact resistance value over time becomes large, which causes a practical problem in the conductive paste using this alloy. This phenomenon is considered as follows. That is, nickel is likely to be oxidized, but when the content of nickel exceeds 2% by weight, nickel is likely to be raised on the alloy surface, and as a result, the contact resistance value of the alloy is increased. Therefore, from the viewpoint of the contact resistance value, the amount of nickel contained in the alloy is preferably 2.0% by weight or less.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the claims and the technical idea described in the specification and drawings. Can be modified.

[0025]

As described in detail above, according to the present invention, it is possible to provide a conductive paste having further improved migration resistance as compared with a conductive paste using an alloy powder of silver and copper.

[Brief description of drawings]

FIG. 1 is an enlarged view of a silver / copper alloy.

FIG. 2 is an enlarged view of a silver / copper / nickel alloy.

FIG. 3 is a diagram showing results of water drop tests of various conductive pastes.

FIG. 4 is a diagram showing results of water drop tests of various alloys.

FIG. 5 is a diagram for measuring changes with time in contact resistance values of various alloys.

6 is a diagram showing a method for measuring the contact resistance value shown in FIG.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroshi Suzuki             335 Kayajuku, Nakahara-ku, Kawasaki City, Kanagawa Prefecture             Communication Industry Co., Ltd. F-term (reference) 5G301 DA03 DA06 DA10 DA42 DA55                       DD01

Claims (2)

[Claims] 1. A conductive paste comprising an alloy powder composed of silver, copper and nickel dispersed in an organic binder. 2. The conductive paste according to claim 1, wherein a mixing ratio of nickel to silver and copper in the alloy powder is 0.3 to 2.0% by weight of nickel.