JP2003306659A - Electrically conductive adhesive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroconductive adhesive solving the problem that conventional electroconductive adhesives have been regarded as requiring 65-85 wt.% noble metallic powder for ensuring electroconductivity, and for the sake thereof, silver has been put into practical use as the powder, but it is very expensive. <P>SOLUTION: The electroconductive adhesive is obtained by incorporating 5-40 wt.% metallic powder in a reactive polymeric material imparted with thixotropy, wherein the shape of each particle of the metallic powder is almost spherical. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a conductive adhesive used for bonding electronic parts and the like.

[0002]

2. Description of the Related Art Lead-free solder having a high melting point has been put into practical use for mounting electronic parts, but it is not preferable in consideration of thermal influence on electronic parts during use, and therefore, a conductive adhesive is required. There is. Therefore, in the conventional conductive adhesive, in order to obtain conductivity, noble metal powder is added to the resin at 65 to 85.
It is used by mixing in a weight percentage.

[0003]

According to such a conventional conductive adhesive, 65-65 is required to obtain a reliable current-carrying performance.
There is a problem that 85% by weight of noble metal powder is required, and Ag is practically used for the noble metal powder, which is a very expensive material. In addition, since the Ag is highly filled, the adhesive has no optical transparency, and there is a problem that it cannot be cured by ultraviolet rays or electron beams.

Further, for the anisotropic conductive adhesive or conductive film, a metal powder to be mixed is used in a smaller amount than the above, but it is necessary to apply pressure for a long time when bonding. There is a problem that the location is extremely limited.

[0005]

SUMMARY OF THE INVENTION Therefore, according to the present invention, in a conductive adhesive prepared by mixing a metal powder with a reactive polymer having a thixotropy, the metal powder has a substantially spherical shape, and a polymer material is used. It is characterized in that it is mixed in the range of 5 to 40% by weight. As described above, in the present invention, by making the shape of the powder into a substantially spherical shape, the connection resistance becomes very stable as compared with the powder having other shapes such as flakes and irregular shapes.

Here, the addition amount is set to 5 to 40% by weight, because if the lower limit value is 5% by weight, sufficient contact resistance may not be obtained. Therefore, for example, if the weight should be 4%, that value may be acceptable, but on the average, reliability is obtained with 5% by weight. The upper limit of 40% by weight is 40%.
This is because a conductive adhesive of low price cannot be obtained if the content is more than 5% by weight. For example, if it is 35% by weight, it may be necessary to use that value, but on average 40% by weight is reliable. Is obtained.

Further, according to the present invention, in the particle size distribution of the metal powder to be dispersed, the cumulative value from the smaller particle size is 10%, 50
%, 90%, 100%, the average particle diameter D ₅₀ of the metal powder is 0.5 μm ≦ D, where D ₁₀ , D ₅₀ , D ₉₀ , and D ₁₀₀ are respectively the particle diameters of the metal powder. The range of ₅₀ ≦ 50 μm is suitable. Here, the average particle size is 0.5μ
If it is smaller than m, the contact area between the metal powder and the electrode necessary for energization may not be obtained, in which case the connection resistance will be high, and if it is larger than 0.5 μm on average, reliability will be obtained. Is to be done.

If the average particle size is larger than 50 μm, the probability of contact between the metal powder and the electrode may decrease, and defects such as insulation may occur, in which case the defects increase. That is, reliability is obtained when the average diameter is smaller than 50 μm. Further, in the present invention, it is suitable that the particle size distribution of the metal powder satisfies the inequality (D ₉₀ −D ₁₀ ) / D ₅₀ ≦ 1.0.

This is because if it exceeds 1.0, the probability of contact between the metal powder and the electrode may decrease, in which case defects such as insulation may occur, and on average 1.0
The smaller is the reliability. Further, according to the present invention, the maximum particle size D ₁₀₀ of the metal powder is the inequality D ₁₀₀ /
It is suitable to satisfy D ₅₀ ≦ 2.5.

This is because it depends on the distribution of the metal powder having a large particle diameter of more than 2.5, so that the probability of contact with the electrode is reduced and the occurrence of defects such as insulation occurs as in the above. It means that reliability is obtained when the average value is smaller than 2.5. Next, the type of metal powder is A
A simple substance of u, Ag, Cu, or Ni, an alloy thereof, or a mixture thereof can be used.

However, when using Cu or Ni alone or an alloy, it is necessary to use together with a reducing agent. Note that Ag is preferable in terms of electrical conductivity, corrosion resistance, and price. As the reactive polymer, an epoxy resin, a phenol resin, a urethane resin, a polyester resin, an acrylic resin, a silicone resin, a polyimide resin, an oxetane resin, or a mixture of two or more thereof can be used. When using a solid or highly viscous resin, a solvent or the like may be added.

These reactive polymers are selected according to the application, but considering adhesive strength, electrical characteristics, workability, etc.,
Epoxy resins are preferred. The reactive polymer is basically a thermosetting type, but an ultraviolet ray or electron beam curing type reactive polymer can also be used as required. Further, the thixo index (viscosity at 2 rpm / 20 viscosity at 20 rpm) of these reactive polymer materials is suitably 5.0 or more.

This is because if the thixo index is 5.0 or less, heat is generated during heating, the metal powder and the electrode are prevented from approaching each other, and the connection resistance becomes unstable. As the material imparting thixotropy, aluminum stearate, zinc stearate, aluminum octylate, water-added castor oil, fatty acid amide, polyethylene oxide, dextrin fatty acid ester, vegetable oil-based polymerized oil, organic bentonite,
Silica and the like can be used alone or as a mixture.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment As a reactive polymer, a one-part thermosetting epoxy resin containing a latent curing agent and silica as a thixotropy-imparting agent is used. Using an E-type viscometer, the viscosity of the reactive polymer at a rubbing speed of 2 rpm and 20 rpm was measured,
The thixo index = 10.83 was calculated. The viscosity was measured at 25 ° C.

Next, as the metal powder for which the particle size distribution was measured, D ₅₀ = 2.67 μm, (D ₉₀ −D ₁₀ ) / D ₅₀ =
0.52, was used spherical silver powder of D ₁₀₀ / D ₅₀ = 2.07. The viscosity distribution was measured by the scattered light intensity analysis based on the laser diffraction / scattering method. After 95 parts of the epoxy resin and 5 parts of spherical silver powder were sufficiently kneaded by a crusher, they were further uniformly dispersed with a three-roll mill to produce a conductive adhesive A.

Second Embodiment As a conductive metal powder, D ₅₀ = 2.67 μm, (D _{90
-D 10) / D 50 = 0.52} , it was used spherical silver powder of D ₁₀₀ / D ₅₀ = 2.07. After 90 parts of the same epoxy resin as above and 10 parts of spherical silver powder were sufficiently kneaded by a crusher, the mixture was further uniformly distributed by three rolls to produce a conductive adhesive B.

Third Embodiment As a conductive metal powder, D ₅₀ = 2.67 μm, (D _{90
-D 10) / D 50 = 0.52} , it was used spherical silver powder of D ₁₀₀ / D ₅₀ = 2.07. Eighty-five parts of the same epoxy resin as described above and 15 parts of spherical silver powder were sufficiently kneaded by a crusher, and further uniformly distributed by three rolls to produce a conductive adhesive C.

Embodiment 4 according to the same manufacturing method as described above
~ 20 to produce conductive adhesives D ~ T. Conventional Example 1 As a comparative example, a silver content of 80% using an adhesive as a binder
A commercially available conductive adhesive for replacing solder was obtained.

Conventional Example 2 As a comparative example, a silver content of 75% using an adhesive as a binder
The commercially available general-purpose type conductive adhesive of was obtained. The following tests were conducted on the conductive adhesives according to the above-described embodiments and conventional examples.

First, in order to measure the connection resistance of a conductive adhesive, a commercially available conductive paint (area resistance = about 30 mΩ) on a slide glass 1 as shown in FIG.
After printing with a height of 1.5 mm and an electrode interval of 2 mm, baking was performed to form an electrode 2. Next, as shown in FIG. 2, the conductive adhesive 3 is applied to the end portion of the electrode 2 of the slide glass 1 with a dispenser, a chip resistor 4 (0Ω, 3216 type) is placed, and it is lightly pressed once. Set it to 1
It is put in a hot air dryer at 50 ° C. for a predetermined time (5 to 30 minutes) and cured by heating.

After cooling it at room temperature, the resistance value between the parallel electrodes 2 was measured, and this was taken as the connection resistance value. The measurement was carried out by a four-terminal measuring method using a low resistance measuring device, and the fulcrum of the voltage detecting terminal was the central part of the electrode 2. Table 1 shows the results.

[Table 1] FIG. 3 shows a sectional explanatory view of a practical example in which a chip resistor (0Ω, 3216 type) is mounted on an alumina substrate, and FIG. 4 shows a partially enlarged sectional explanatory view thereof.

In the figure, 5 is an alumina substrate, 6 is a silver electrode, 4 is a chip resistor, 7 is a solder electrode, 3 is a conductive adhesive, 8 is a reactive polymer, and 9 is spherical silver powder. As shown in the figure, a plurality of spherical silver powders 9 are directly electrically connected between the silver electrode 6 and the solder electrode 7 of the chip resistor 4, respectively.

[0023]

According to the present invention described in detail above, in a conductive adhesive prepared by mixing a metal powder with a reactive polymer having a thixotropy, the metal powder has a spherical shape and is made of a polymer material. By mixing it in the range of 5 to 40% by weight, there is an effect that the connection resistance is stable and moreover, a long time pressurization is not required at the time of adhesion.

Further, not only curing by heating but also the use of a polymerization initiator has the effect of becoming a light-transmissive conductive adhesive which can be cured by ultraviolet rays or electron beams. In addition, by making the shape of the metal powder spherical, it is possible to achieve the same characteristics as the commercially available conductive adhesive for solder replacement containing 80% silver at about 10%. The amount of the body used is extremely small, the price can be made extremely low, and it has the effect of becoming a widely available conductive adhesive.

[Brief description of drawings]

[Fig.1] Illustration of slide glass with electrodes

FIG. 2 is an explanatory view of a process of mounting a chip resistor on a slide glass.

FIG. 3 is an explanatory sectional view showing a state where a chip resistor is mounted on an alumina substrate.

FIG. 4 is a partially enlarged sectional explanatory view.

[Explanation of symbols]

1 slide glass 2 electrodes 3 Conductive adhesive 4 chip resistance 5 Alumina substrate 6 silver electrode 7 Solder electrode 8 Reactive polymer 9 Spherical silver powder

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4J040 DF001 EB031 EC001 ED001                       EE031 EF001 EH031 EK001                       HA066 HB30 HD41 JB02                       JB07 JB08 KA03 KA32 KA42                       LA09 NA19                 5G301 DA02 DA03 DA05 DA06 DA10                       DA42 DA51 DA53 DA55 DA57                       DA59 DD03

Claims (8)

[Claims] 1. A conductive adhesive in which a metal powder is mixed with a reactive polymer having a thixotropic property, wherein the metal powder has a substantially spherical shape, and the polymer powder contains
A conductive adhesive characterized by being mixed in a range of 40% by weight. 2. The particle size distribution of metal powder according to claim 1, wherein cumulative values from the smaller particle size are 10%, 50% and 9%.
The particle diameters at the positions of 0% and 100% are D ₁₀ , D
_{When 50} , D ₉₀ and D ₁₀₀ are used, the particle size thereof is (A) 0.5 μm ≦ D ₅₀ ≦ 50 μm (B) (D ₉₀ −D ₁₀ ) / D ₅₀ ≦ 1.0 (C) D ₁₀₀ / D ₅₀ ≦ 2.5 at the same time, a conductive adhesive. 3. The metal powder according to claim 1, wherein the metal powder is Au,
A conductive adhesive characterized by being Ag, Cu, or Ni. 4. The metal powder according to claim 1, wherein the metal powder is Au,
A conductive adhesive, which is a mixed powder of two or more kinds of Ag, Cu, and Ni. 5. The metal powder according to claim 1, wherein the metal powder is Au,
A conductive adhesive characterized by being an alloy powder of two or more kinds of Ag, Cu and Ni. 6. The metal powder according to claim 1, wherein the metal powder is Au,
A conductive adhesive, which is a mixed powder of two or more kinds of alloy powders of two or more kinds of Ag, Cu, and Ni. 7. The conductive material according to claim 1, wherein the reactive polymer is one or more of epoxy resin, phenol resin, urethane resin, polyester resin, acrylic resin, silicone resin, polyimide resin and oxetane resin. Adhesive. 8. The thixo index according to claim 7, which is 5.0.
The conductive adhesive having the above characteristics.