JPH0820758A - Adhesive - Google Patents

Abstract

PURPOSE:To obtain a conductive adhesive suitable for bonding electronic components to a circuit board by adding a conductive filler which is composed of a core and a shell and in which the hardness of the core is higher than that of the shell, and the resistivity of the shell is lower than that of the core to an adhesive. CONSTITUTION:An adhesive prepared by adding a filler to an adhesive. The filler is the one which is composed of a core and a shell surrounding the core and in which the hardness of the core is higher than that of the shell, while the resistivity of the core is lower than that of the core. Because the resistivity of the conductive filler is low, this adhesive can give a bond having a resistance lower than the conventional one between, for example, a bump and a pad. Further, because the conductive filler has sufficient hardness, the bond does not collapse even when a stress is exerted thereon, and the electrical resistance between, for example, a bump and a pad can be long kept at the initial value. Therefore, it is possible to bond electronic components with a reliability better than the conventional.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adhesive material, and more particularly to a conductive adhesive material used for joining electronic parts.

In recent years, conductive adhesives have been increasingly used as a bonding material for electronic parts instead of solder. For this reason, it is necessary to develop a conductive adhesive that satisfies various characteristics required as a conductive adhesive for electronic parts.
It is important in manufacturing a reliable electronic circuit assembly.

[0003]

2. Description of the Related Art An example of a conductive adhesive material that has been conventionally used is a conductive adhesive material that uses Ni particles as a conductive filler.

FIG. 5 is a view showing a usage state of the conductive adhesive material 1.

In FIG. 1, the conductive adhesive 1 has a structure in which a conductive filler 3 which is Ni particles is added to an adhesive 2 which is an insulator.

The body of the electronic component 7 is fixed to the substrate 6 by the conductive adhesive material 1, and the bumps 4 of the electronic component 7 are fixed to the pads 5 of the substrate 6.

FIG. 6 is an enlarged view of the bumps 4, the pads 5 and their peripheral portions in FIG.

The Ni particles 3 have conductivity. However, the conductive adhesive material 1 itself, in which the addition amount of the Ni particles 3 is usually several percent, is insulative. As shown in FIG. 6, the bump 4 part of the electronic component and the pad 5 part on the substrate 6 are close to each other, and the Ni particles 3
Enters the gap between the bump 4 and the pad 5 and is sandwiched between them. The sandwiched Ni particles 3 electrically connect the bumps 4 and the pads 5.

The conductive adhesive 1 containing the Ni particles 3 having the above-mentioned structure secures an electrical connection between the bump 4 of the electronic component which is in contact with the pad 5 of the substrate, and the adjacent bump 4 The electronic component 7 is adhered to the substrate 6 while maintaining the insulation between the pads or between the pads 5.

Another conventional conductive adhesive material is a conductive adhesive material using Au particles as a conductive filler.

FIG. 7 is a view showing this conductive adhesive material 11.

The conductive adhesive material 11 for electronic parts has a structure in which Au particles 13 are added to the adhesive material 12 which is an insulator.

FIG. 8 is an enlarged view of the bump 4 and the pad 5 in FIG.

Some of the Au particles 13 are bumps 4 and pads 5.
Sandwiched between. The bumps 4 and the pads 5 are electrically connected by the Au particles 13 sandwiched therebetween.

[0015]

The conductive adhesive 1 shown in FIG.
Has a problem that it is difficult to reduce the electric resistance.

That is, as shown in FIG. 5, the conductive adhesive 1
When the electronic component 7 was connected to the substrate 6 by using, the electrical resistance between the bump 4 and the pad 5 was relatively high at 4 to 10 mΩ. This is because the volume resistivity of Ni is 6.9 μΩ.
cm (see FIG. 9), which is considered to be relatively high.

The conductive adhesive 11 of FIG. 6 has a problem that the reliability of electrical connection is low.

That is, as shown in FIG. 8, the conductive adhesive 11
When the electronic component 7 is connected to the substrate 6 by using, the Au particles 13 sandwiched between the bumps 4 and the pads 5 are crushed when receiving a compressive force due to expansion and contraction of the conductive adhesive 11. It will be transformed. The Au particles 13 do not recover to the original state once they are crushed. Therefore, the Au particles 13
The bump 4 and the pad 5 may be separated from each other.

-40 ° C. for the electronic circuit assembly of FIG.
From 500 to 105 ° C for thermal shock test
Repeatedly, the electric resistance between the bump 4 and the pad 5 increased to about three times.

Therefore, in view of the above points, an object of the present invention is to provide a conductive adhesive material suitable for bonding electronic components to a substrate.

[0021]

According to the present invention, in a conductive adhesive containing a conductive filler, the conductive filler is composed of a core and a shell covering the core, and the core is a shell. It was made of a material having a higher hardness, and the shell was made of a material having a lower volume resistivity than the core.

[0022]

In the invention according to claim 1, the conductive filler is composed of a core and a shell covering the core, so that the conductive filler has both characteristics of the core and the shell. To work.

The structure in which the core is made of a material having a hardness higher than that of the shell acts to prevent the core from being crushed when a compressive force is applied.

[0024]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a conductive adhesive material 21 according to an embodiment of the present invention.

The conductive adhesive material 21 has a structure in which 5 vol% of Au coated Ni particles 23 are added to the adhesive material 22 as a conductive filler.

The adhesive 22 is made of an epoxy resin mixed with a capsule-type curing material obtained by coating imidazole with the resin. The conductive adhesive 21 is a one-component type.

FIG. 2 shows the structure of the Au-coated Ni particles 23 forming the essential part of the present invention.

The particles 23 are Ni particles 25 which form the nucleus.
(Particle size d = 7 ± 3 μm) and the film thickness covering this surface is 0.
The Au film 24 has a thickness of 5 to 1 μm.

The Au film 24 is formed by electroless plating.

As shown in FIG. 9, Ni has a hardness of 70H.
V, volume resistivity is 6.9 μΩ · cm. Au has a hardness of 25 HV and a volume resistivity of 2.2 μΩ · cm.

In terms of hardness, Ni> Au.

Looking at the volume resistivity, Au <Ni.

FIG. 3 shows a state in which the electronic component 7 is bonded to the substrate 6 using the above-mentioned conductive adhesive material 21.

First, the conductive adhesive material 21 is applied onto the substrate 6. The electronic component 7 having the bump 4 is pressed from above, the pad 5 and the bump 4 are connected, and the connection and fixing of the electronic component 7 and the substrate 6 are completed. Since the adhesive 22 is a thermosetting resin, the above-mentioned bonding process is performed while heating.

When the resistance between the bump 4 and the pad 5, which is the joint portion where the connection is completed, is measured, the resistance value is 1 to 2.
It was mΩ. This value is low enough to connect the electronic component 7 and the substrate 6. Moreover, the resistance value was stable over a long period of time.

Further, the resistance of the Au-coated Ni particles 23 to the stress due to the expansion and contraction of the adhesive 22 was evaluated. An electronic circuit assembly in which the electronic component 7 was joined to the substrate 6 was produced, and a test was repeated 500 times in which a thermal shock of periodically changing the temperature from −40 ° C. to 105 ° C. was repeated.
The resistance value between the bumps 4 and the pads 5 was the same as the initial value. From the above results, the conductive adhesive 21 described above makes the bumps 4 and the pads 5 of the electronic component 7 different from the conventional ones. It was found that a low resistance value and a reliable connection can be achieved in a state where electrical connection is guaranteed for a long time.

In order to demonstrate the effect of the present invention, an electronic circuit assembly similar to the above electronic circuit assembly was prepared using a conventional adhesive material containing Ni particles 3. The resistance between the bump 4 and the pad 5 after connection was as high as 4 to 10 mΩ.

An electronic circuit assembly similar to the above electronic circuit assembly was prepared by using the conventional adhesive material 11 containing the Au particles 13. The thermal shock test similar to the above also increased the resistance to three times the initial value. The hardness of each of the above materials,
9 and the volume resistivity, which is an index of resistivity, are collectively shown in FIG.

The present invention is not limited to the above embodiment. For example, the conductive filler may be a material whose core has a higher hardness than the shell and whose shell has a lower volume resistivity than the core. Further, the present invention is not limited to a one-component type adhesive, and may be a two-component type adhesive material.

[0041]

According to the present invention, since the electric resistance of the conductive filler is low, it is possible to connect, for example, the bump and the pad with a lower resistance than the conventional one.

Further, since the conductive filler has a sufficient hardness, it does not collapse even if stress is applied, and for example, the electric resistance between the bump and the pad can be kept at the initial value for a long time. I can. Therefore, it is possible to connect the electronic parts with higher reliability than the conventional one.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a conductive adhesive material according to an embodiment of the present invention.

FIG. 2 is a structural diagram of Au-coated Ni particles shown in FIG.

FIG. 3 is a diagram showing a state in which the conductive adhesive material of FIG. 1 is used to bond an electronic component and a substrate.

FIG. 4 is an enlarged view showing a state in which Au-coated Ni particles are sandwiched between bumps and pads in FIG.

FIG. 5 is a diagram showing a state where a conductive adhesive material of a conventional example is used for bonding an electronic component and a substrate.

6 is an enlarged view showing a state where Ni particles are sandwiched between bumps and pads in FIG. 5. FIG.

FIG. 7 is a diagram showing a state in which another conventional conductive adhesive is used for bonding an electronic component and a substrate.

FIG. 8 is an enlarged view showing a state where Au particles are sandwiched between bumps and pads in FIG. 7;

FIG. 9 is a diagram showing hardness and volume resistivity of each material constituting the conductive filler.

[Explanation of symbols]

 4 Bumps of Electronic Parts 5 Pads of Substrate 6 Circuit Board 7 Electronic Parts 21 Electronic Conductive Adhesive with Au Coated Ni Particles 22 Adhesive 23 Au Coated Ni Particles 24 Au Film (Shell) 25 Ni Particles (Nucleus)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H05K 3/32 B 8718-4E (72) Inventor Katsuhide Natori 1015 Kamitadanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Within Fujitsu Limited

Claims (1)

[Claims] 1. An adhesive comprising a filler added to the adhesive, wherein the filler comprises a core and a shell covering the core, and the core has a hardness higher than that of the shell. And the shell has a lower resistivity than the core.