KR20070078387A - Ag wiring board - Google Patents

Abstract

An Ag wiring board is provided to suppress largely migration of Ag by reducing oxidized Ag with metal particles having high ionization tendency. An Ag wiring board includes a substrate(11), a plurality of circuit elements(12,12a,12b), and a resin layer(13). The circuit elements include a thin film having Ag as a conductor. The resin layer is installed between two circuit elements having different potential. The resin layer includes particles(13a) of a metal having ionization tendency larger than ionization tendency of Ag. The particles of the metal are dispersed in the resin layer. The particles of the metal include Al or alloy having Al.

Description

Ag wiring board {Ag WIRING BOARD}

1 is a cross-sectional view showing the configuration of an Ag wiring board according to the present invention.

2 is a cross-sectional view showing another configuration of an Ag wiring board according to the present invention.

It is a schematic diagram of the board | substrate with which the Ag electrode pattern was formed on the glass substrate used in the Example.

4 is a diagram illustrating a result of measuring a failure time Tr of Example 1;

5 is a view showing a sample appearance of Example 2. FIG.

6 is a view showing a sample appearance after the aging test of Example 2. FIG.

7 shows a sample appearance after an aging test of Comparative Example 3. FIG.

<Explanation of symbols for the main parts of the drawings>

10, 20: Ag wiring board

11, 21, 31: substrate

12 (12a, 12b): circuit elements

13: resin layer

13a, 23a: metal particles

13b, 23b: base resin

22 (22a, 22b): electrode

32 (32a, 32b): electrode

23: anisotropic conductive adhesive layer

23c: conductive particles

30: flexible substrate

[Document 1] Japanese Patent Publication No. 59-12699

[Document 2] Japanese Unexamined Patent Publication No. 2001-274535

The present invention relates to an Ag wiring board capable of suppressing Ag migration.

Silver (Ag) is still used today as an electrode material for some wiring boards due to its high electronic conductivity and oxidation resistance. There are many examples especially used as a glass substrate electrode of a plasma display. Although silver wiring to a board | substrate is mainly performed by screen printing, it can also be performed by a sputtering method or an application method.

On the other hand, although silver is a metal element with a small tendency to ionize, it has been reported that ion migration is more likely to occur than other metals. The reason for this is not clearly explained, but suggests that the migration phenomenon cannot simply be compared with the magnitude of the ionization tendency.

The migration phenomenon is a phenomenon that occurs when a high voltage is applied between electrodes on a substrate forming a narrow inter-electrode distance, and a dendritic precipitate of metal is generated between the electrodes to induce a short circuit. Mainly, it is likely to occur in a high-humidity environment and in the presence of impurities. For example, the presence of chlorine causes Sn (tin) and Cu (copper) to have a faster migration rate and to be easily broken. The migration phenomenon occurs even if a polymer or the like exists between the electrodes, and also occurs when, for example, coating with an epoxy resin is performed.

In addition, there is various information on the mechanism of its development, but it is considered to be mainly due to reaction with moisture. If there is a silver-silver oxide on the positive electrode, first, _{Ag 2 O + H 2 O →} Ag (OH) → Ag + + OH - reaction occurs, and the next to Ag ⁺ towards the cathode move to the influence of the electric field and, Ag in the cathode ^{+ +} e ^- → Ag is known to be (for example, Japanese Patent Publication (sho) No. 59-12699).

Common to ion migration of metals such as silver is that the higher the field strength (V / m), the temperature (K), and the humidity between the electrodes, the more easily occur. That is, when the wiring pattern printed by paste is connected with terminals, such as an electronic component, the wiring metal may spread | diffuse and a short circuit may arise by moisture absorption or adhesion of water droplets, and the like. In addition, although it is decided by the user regarding the two parameters of the electric field strength and temperature, the main suppressive measures that can be devised are the moisture proof measures. In practice, most of the countermeasures against ion migration are moisture-proof technologies, for example, a method of coating an inorganic ITO film on a metal electrode has been proposed (for example, see Japanese Patent Laid-Open No. 2001-274535). Similarly, many migration prevention methods have been proposed for silver, and there are methods for alloying silver with Sn, Cu, and the above-described method for coating with ITO.

The reason why the migration phenomenon is not determined solely by the ionization tendency is because the diffusion rate of ions is a big factor as well as the ionization tendency. For example, since diffusion rates of Ag ions and the like are strongly influenced by anions, there is also a possibility that the down time due to migration can be reduced by selecting an appropriate anion. That is, as a method of suppressing migration, one of them is to select a metal (for example, gold) having a high ionization tendency as the wiring metal species, and it can be estimated that reducing the diffusion rate of ions is effective.

Thus, the conventional migration suppression method mainly selected the material with a small tendency of ionization, and prevented moisture permeation to an electrode. However, in many cases, the wiring metal species cannot be changed for reasons of conductivity and cost, and in order to prevent moisture permeation to the electrode, it is necessary to devise a coating agent or the like, and to change the polymer composition, which is difficult in terms of cost.

In addition, since the migration proceeds among the insulators in the electronic circuit, the insulation deterioration of the circuit occurs, resulting in the modulation of the electronic device.

Conventionally, migration prevention has been proposed by alloying with metals having a high ionization tendency and surface coating by IT0 or the like, but a method different from these methods has also been required.

This invention is made | formed in view of the problem in the above prior art, and an object of this invention is to provide the Ag wiring board which can suppress Ag migration.

As a result of various studies on the basis of the above situation, the present inventors have found a method of preventing short circuits due to migration by interposing a substance which prevents diffusion of silver ions between electrodes, rather than the conventional moisture permeation prevention method. The invention has been completed.

That is, this invention provided in order to solve the said subject is provided on the board | substrate at least between the several circuit elements containing the thin film which uses Ag as a conductor, and two circuit elements which become mutually different electric potentials among the said circuit elements. It is related with the Ag wiring board characterized by including the resin layer in which the metal particle which is larger in ionization tendency than Ag is disperse | distributed in it.

Here, the metal particles also preferably include Al or an alloy containing Al.

Moreover, it is also preferable that the said resin layer is crimped | bonded by the resin film containing the said metal particle on the said circuit element.

It is also preferable that the circuit element is a wiring and / or an electrode.

It is also preferable that the circuit element is an electrode, and the resin layer is an anisotropic conductive adhesive layer capable of electrically conducting in the thickness direction.

The structure of the Ag wiring board which concerns on this invention is demonstrated below.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows the structure in embodiment of the Ag wiring board which concerns on this invention.

As shown in FIG. 1, the Ag wiring board 10 includes, on the substrate 11, a plurality of circuit elements 12 including a thin film made of Ag as a conductor, and a potential different from each other among these circuit elements 12 adjacent thereto. For example, a metal layer 13a provided at least between two circuit elements 12a and 12b and having a greater ionization tendency than Ag is provided with the resin layer 13 dispersed in the base resin 13b.

Here, the board | substrate 11 is a board | substrate which consists of an insulator, for example, is a base board in a printed wiring board.

In addition, the circuit element 12 is a wiring and / or an electrode including a thin film made of Ag as a conductor.

That is, the circuit element 12 may be any one of a combination of wirings, a combination of wiring and electrodes, and a combination of electrodes.

In formation of the circuit element 12, the Ag paste which disperse | distributed and mixed Ag particle | grains of particle size 0.1-20 micrometers in a binder, for example can be printed in wiring or electrode shape. On the other hand, when thermosetting resins, such as a polyester resin, an epoxy resin, an acrylic resin, a polyimide resin, and a polyurethane resin, are used as a binder, the adhesive strength at the time of printing becomes strong, and it is preferable.

In addition, the metal particle 13a which comprises the resin layer 13 is microparticles | fine-particles of metal with a large tendency of ionization. At this time, it is preferable that the ion valence of this metal is as large as possible, for example, an alloy containing Al or Al is preferable. Alternatively, Sn, In, Zn may be included. In addition, fine particles of a reducing organic compound can be used instead of the metal particles. On the other hand, it is preferable that the particle diameter of the metal particle 13a is 5-10 micrometers.

Here, as the metal constituting the metal particles 13a, even if the ionization tendency is large, an alkali metal and an alkaline earth metal or an element having an ionic valence of +1 is not preferable. This is because alkali metals and alkaline earth metals are very unstable in the metal state and exhibit strong alkalinity by reaction with moisture. On the other hand, an element having an ion valence of 1+ has a high ion migration speed, and thus, migration itself comparable to Ag cannot be achieved and delay of short circuit time between electrodes cannot be achieved.

Base resin (13b) is not particularly limited, epoxy resin, acrylic resin, polyamide, polyimide, PBO (polybenzoxazole), PBI (polybenzoimidazole), polythiophene, polyethylene, PET (polyethylene terephthalate) ), And a fluororesin can be used.

There are various methods for forming the resin layer 13 in a state in which the metal particles 13a are dispersed in the base resin 13b, but it can be appropriately selected. For example, the metal particles are formed in the raw material of the base resin 13b. After mixing (13a), it is set as a slurry, and after apply | coating this slurry on the board | substrate 11 in which the circuit element 12 was formed, the raw material of the base resin 13b can be hardened and formed. Alternatively, the polymer film including the metal particles 13a may be prepared in advance, and bonded to the substrate 11 on which the circuit element 12 is formed by compression.

On the other hand, since the resin layer 13 is also an insulating protective film which protects the circuit element 12, the addition amount of the metal particle 13a to the base resin 13b is the grade which the insulation between the circuit elements 12 is maintained. It is preferable that it is a quantity. When the ratio Rmix of the weight of the metal particles 13a to the base resin amount net is set to (metal particle weight) / (base resin amount net), the amount of addition thereof is preferably 0.01 ≦ Rmix ≦ 0.1. However, since the preferable addition amount of the metal particle 13a changes with the magnitude | size of the voltage applied between the circuit elements 12 used as the object which suppresses migration, it is necessary to adjust within the range. In addition, when forming the resin layer 12 by application | coating, it is necessary to adjust addition amount also according to the viscosity of the raw material of the base resin 12b.

With the above structure, even if Ag in the circuit element 12 is ionized and changed into Ag product such as silver oxide or silver hydroxide, the Ag product is caused by the metal particles 13a (lower in redox potential) having a higher ionization tendency than Ag. Reduced, the Ag ions return to their original metal state. On the other hand, the ionized metal particles 13a become colloidal hydroxides and oxides. At this time, when the metal particles 13a contain Al, since Al is a higher number of ions (3+) than Ag, the ion diffusion rate is very slow, and as a result, the migration time can be delayed.

Next, the modification of the Ag wiring board which concerns on this invention is demonstrated.

2 is a cross-sectional view showing another configuration of an Ag wiring board according to the present invention.

As shown in FIG. 2, in this example, the Ag wiring board 20 is disposed on the substrate 21 adjacent to a plurality of electrodes 22 including a thin film made of Ag as a conductor, and one of these electrodes 22. For example, at least between two electrodes 22a and 22b at different potentials, the metal particles 23a having a larger ionization tendency than Ag are provided with the anisotropic conductive adhesive layer 23 dispersed in the base resin 23b. do.

Here, the board | substrate 21 and the metal particle 23a are the same as the board | substrate 11 and the metal particle 13a in the Ag wiring board 10 shown in FIG. In addition, the electrode 22 limits the circuit element 12 in the Ag wiring board 10 shown in FIG. 1 to an electrode.

The anisotropically conductive adhesive layer 23 is formed by dispersing the metal particles 23a and the conductive particles 23c in the base resin 23b, and by compressing them in the thickness direction, the conductive particles 23c therein are continuous and electrically in the thickness direction. Conduit is possible.

The flexible substrate 30 is bonded onto the Ag wiring board 20 by this anisotropic conductive adhesive layer 23.

The flexible substrate 30 has a plurality of electrodes 32 (for example, two electrodes 32a and 32b) on the substrate 31, for example Cu wired to a polyimide substrate and Au on the electrode portion. It is a conventionally known flexible substrate (FPC) as the plating was performed.

In this example, the two electrodes 32a and 32b provided on the flexible board 30 are bonded in a state opposite to the two electrodes 22a and 22b of the Ag wiring board 20, and the Ag wiring board 20 The electrode 22 and the electrode 32 of the flexible substrate 30 are electrically connected by the electroconductive particle 23c in the anisotropically conductive adhesive layer 23.

In this Ag wiring board 20, similarly to the Ag wiring board 10 shown in FIG. 1, even though Ag in the electrode 22 is ionized and changed into an Ag product, the ionization tendency is larger than Ag (oxidation reduction potential). Ag product is reduced, and Ag ions are returned to the original metal state. On the other hand, the ionized metal particles 23a become colloidal hydroxides and oxides. When the metal particles 23a contain Al, since Al is a higher number of ions (3+) than Ag, the ion diffusion rate is It is very slow, and as a result, it is possible to delay the migration time.

In addition, although the Ag wiring board of single layer structure was demonstrated as embodiment of this invention, this invention is not limited to this, A multilayer wiring structure may be sufficient.

<Example>

The example which implemented the Ag wiring board of this invention is demonstrated below.

(Example 1)

As shown in FIG. 3, the comb-shaped electrode pattern 100 of the comb-shaped two electrode patterns (circuit elements 12a and 12b) was formed on the glass substrate (substrate 11) using 100-micrometer-wide Ag paste. Substrates printed to be engaged at intervals of 탆 were prepared by washing and drying.

Next, the resin layer solution which melt | dissolved and added this aluminum fine particle to commercially available acrylic resin solution (brand name: acryldyne) so that it might become Rmix = 0.1 using the aluminum fine particle of an average particle diameter of 1 micrometer as metal particle 13a is FIG. It applied on the board | substrate of this, volatilized the solvent under normal temperature and normal humidity, the resin layer 13 was formed, and the Ag wiring board sample shown in FIG. 1 was completed. At this time, by forming a resin layer 13 on the Ag electrode, it was confirmed by the tester that no short circuit or sudden drop in insulation resistance occurred between the Ag electrodes.

(Comparative Example 1)

In Example 1, Ag wiring boards were manufactured under the same conditions as in Example 1 except that the aluminum fine particles were not added to the resin layer solution.

(Comparative Example 2)

In Example 1, Ag wiring board was manufactured on the same conditions as Example 1 except having changed the microparticles | fine-particles added to a resin layer solution from aluminum microparticles | fine-particles to nickel microparticles | fine-particles (average particle diameter: 1 micrometer).

After the obtained sample was immersed in pure water at room temperature, and the Ag wiring board was fully annealed, the voltage of DC 1V was applied between two Ag electrodes, and the change of current was measured with time. Here, the time which shows the increase of 2 or more digits with respect to an initial current is defined as the failure time Tr (second), and the suppression effect of migration was evaluated by the long and short of Tr. On the other hand, the reason why the applied voltage is 1 V is that the theoretical decomposition voltage of water is about 1.23 V and does not coincide with water decomposition.

The measurement result of the failure time Tr is shown in FIG.

The failure time Tr is 170 seconds in Example 1, 100 seconds in Comparative Example 1, and 105 seconds in Comparative Example 2, and in the Ag wiring board to which aluminum fine particles are added, the short-circuit time or failure time by migration is comparative example 1 , 1.7 and 1.6 times longer than 2 respectively.

(Example 2)

The polymer film semi-hardened using the anisotropically conductive adhesive layer solution of the following composition was manufactured as an anisotropically conductive adhesive layer.

30% by weight of solid epoxy resin

40% by weight of liquid epoxy resin

15% by weight of imidazole series curing agent

10% by weight of conductive particles (gold plated coating Ni particles (average particle diameter: 5 mu m))

5% by weight of aluminum fine particles (average particle diameter: 5 mu m)

Subsequently, the polymer film is adhered onto the substrate shown in FIG. 3, and the flexible substrate (Cu-wired to the polyimide substrate and placed on the polymer film so that the electrode is positioned at a position opposite the comb-shaped electrodes of the substrate of FIG. 3). After the Au plating was applied to the portion), the plate was pressed at a constant pressure to connect the electrodes of both substrates to prepare a sample of the Ag wiring board shown in FIG. 2.

5 shows the results of observing the surface of this sample with an optical microscope. A state in which aluminum fine particles are dispersed between Ag electrodes is observed.

(Comparative Example 3)

In Example 2, Ag wiring boards were manufactured under the same conditions as in Example 2 except that the aluminum fine particles were not added to the anisotropic conductive adhesive layer solution.

After leaving the obtained sample in a constant temperature and humidity of 60 degreeC and 95% RH, the aging test which hold | maintains the state which applied the voltage of DC70V between two Ag electrodes for 96 hours was done.

Fig. 6 (Example 2) and Fig. 7 (Comparative Example 3) show the results of observing the presence or absence of Ag migration with respect to the sample after the test under a microscope.

In Comparative Example 3 shown in FIG. 7, the occurrence of Ag migration was observed, whereas in Example 2 shown in FIG. 6, the Ag migration was not seen, and it can be seen that the migration resistance is improved according to the present invention.

According to the Ag wiring board of this invention, between two circuit elements which become a different electric potential adjacently among several circuit elements containing the thin film (for example, conductor resin film containing silver particle) which uses Ag as a conductor. The resin layer which disperse | distributed the metal particle (for example, Al microparticles | fine-particles) which has a larger ionization tendency than Ag exists, and since a circuit element and the metal microparticles | fine-particles which have a large tendency of ionization coexist, therefore, an external humidity, temperature, and an electric field Even if Ag in the circuit element is ionized (oxidized), etc., it is immediately reduced by the metal particles, and the migration of Ag can be significantly suppressed.

Claims (5)

On the substrate, A plurality of circuit elements including a thin film made of Ag as a conductor, and The resin layer which is provided at least between two circuit elements which become adjacent electric potentials among the said circuit elements, and the metal particle which is larger in ionization tendency than Ag is disperse | distributed in it. Ag wiring board comprising a. The Ag wiring board according to claim 1, wherein the metal particles comprise Al or an alloy containing Al. The Ag wiring board of Claim 1 in which the said resin layer is crimped | bonded on the said circuit element by the resin film containing the said metal particle. The Ag wiring board according to claim 1, wherein the circuit element is a wiring and / or an electrode. The Ag wiring board according to claim 1, wherein the circuit element is an electrode, and the resin layer is an anisotropic conductive adhesive layer that is electrically conductive in the thickness direction.

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