JP3828122B2 - Electrical component connection method - Google Patents

Description

The present invention relates to a rigid substrate and a flexible substrate, a flexible substrate, a connector or a semiconductor package having a rigid substrate or a flexible substrate and a lead frame-like metal terminal, a semiconductor chip having a bump made of a rigid substrate or a flexible substrate and a surface made of gold, etc. The present invention relates to a method of connecting the electrode terminals to each other.

Conventionally, a method of connecting an anisotropic conductive film between electrode terminals is widely used for connection between electrode terminals, and this is generally called an ACF method. As described in Patent Document 1 and Patent Document 2, this method includes conductive particles such as nickel, copper, gold, silver, or resin in a thermosetting resin or an adhesive containing a thermoplastic resin. A ball-plated nickel surface or a gold-plated surface is dispersed as conductive particles.

Then, by interposing such an anisotropic conductive material between the electrode terminals to be connected and pressurizing with an overheated bonding tool, the electrode terminal of the electrical component, the base material, or the resin ball is elastically deformed. The adhesive is cured while being maintained, thereby obtaining a contact pressure by the restoring force of the elastic deformation to realize a semi-permanent connection.

Here, the result of the connection method described above is shown as a schematic cross-sectional view. 2A shows a state in which the electrode terminal and the base material are elastically deformed as a result of pressurization, and FIG. 2B shows a state in which the resin ball is elastically deformed.
11 is one electrical component, 12 is an electrode terminal formed on the one electrical component 11, 13 is the other electrical component, 14 is an electrode terminal formed on the other electrical component 13, 15 is an adhesive, 1
6 is a conductive particle made of nickel or the like having a relatively high hardness, and 17 is a conductive particle obtained by applying metal plating to a resin ball.

In FIG. 2A, since the conductive particles 16 are hard, the electrode terminals 12 and 14 as a result of receiving a load.
Elastic deformation (indicated by arrow X) and elastic deformation (indicated by arrow Y) of the base material of the electrical component occur.
On the other hand, in FIG. 2B, since the conductive particles 17 are soft, elastic deformation (indicated by an arrow Z) of the conductive particles 17 occurs.

In the drawings attached to the present specification, in order to make the structure easy to understand, one electrode terminal formed on the electrical component is represented as one, and one conductive particle located on the electrode terminal is represented as one. Needless to say, in recent years it has become more and more dense.

In addition, as disclosed in Patent Document 2, a method has also been proposed in which the electrode terminal plating is tin plating in the joining structure as described above, and a gold-tin eutectic is formed between the conductive particles and the gold plating. ing.

As disclosed in Patent Document 3 as another embodiment, when an aluminum foil is used as the electrode terminal of the substrate, ultrasonic vibration is applied to the joint surface, and the oxide film on the surface of the aluminum foil is caused by friction with the conductive particles. In order to destroy a hard and thick oxide film of aluminum by friction in this case, nickel conductive particles having high hardness are usually used.

Japanese Patent Laying-Open No. 2003-152023 (page 4, FIG. 3) JP-A-10-189657 (page 3, page 5, FIG. 2 and FIG. 3) Japanese Patent Laid-Open No. 10-215055 (second page, FIG. 3)

However, when using hard nickel, copper, silver, or the like as the conductive particles, the electrode terminal or base material of the electrical component has a large elastic restoring force when using the resin balls plated as the conductive particles. Then, after removing the weight at the time of joining, there was a problem that the joining was separated by the restoring force and electrical connection was incomplete. In other words, this restoring force becomes residual stress and forms the principle of bonding, but it is necessary to cure the adhesive as a binder before removing the load at the time of bonding.

Therefore, in order to cure the adhesive simultaneously with pressing in this way, it is necessary to heat the joining tool at a temperature necessary for curing within a target time, and usually the adhesive temperature is 200 ° C. to 250 ° C. It was set to ° C.

Therefore, it takes 10 to 20 seconds to heat at the same time as pressurization,
Besides the problem of working time, the problem of misalignment due to the difference in thermal expansion of each part and the problem of residual stress after joining due to the difference in thermal expansion cannot be ignored. Especially in the problem of misalignment,
It has been necessary to consider this thermal expansion at the stage of electrode terminal design (dimension setting).

In addition, in these connection methods that depend on elastic deformation, the contact area due to elastic deformation is small,
In electrical connection, there was a problem in circuit functions such as a narrow current path. Furthermore, in the case of eutectic bonding using tin plating, the eutectic temperature of tin and gold is as high as 280 ° C., and thus the above-described thermal problem cannot be avoided.

In addition, there is a proposal that expects local frictional heat due to ultrasonic waves, but in order for the resin to reach the curing temperature due to heat generation due to friction, friction does not occur unless the resin viscosity is high, so a large load and ultrasonic vibration It required amplitude and was not practical.

The present invention has been created to solve the above-described problems, and aims to provide a strong and electrically good connection at a low temperature and in a short time.

As a first aspect of the present invention, at least the connection surface of the electrode terminal is made of gold, and an anisotropic conductive material in which a plurality of gold particles are dispersed in an adhesive is interposed between the electrode terminals to be connected, A load is applied in the direction in which the electrode terminals are brought close to each other and ultrasonic vibrations in a substantially parallel direction are applied to the connection surface, so that the gold particles come into contact with both of the electrode terminals to be connected and further receive a pressure from these electrode terminals. There is provided a method for connecting electrical parts, wherein the metal parts are plastically deformed and the diameter of the contact surface between the gold particle and the electrode terminal is equal to or larger than the particle diameter of the gold particle and metal-to-metal bonding is performed.

Moreover, this invention uses a thermosetting resin as an adhesive agent of the said anisotropic conductive material as a 2nd aspect,
The electricity according to the first aspect, wherein the adhesive is cured in a step different from the step of intermetallic joining without heating and curing the adhesive continuously after the intermetallic joining is completed. A method for connecting parts is provided.

According to the present invention, in order to easily realize plastic deformation of the conductive particles, the load and ultrasonic vibration are used in combination, and the conductive particles are gold particles. Realize metal-to-metal bonding without any residual stress by suppressing it as much as possible. As a result, it is possible not only to secure a large cross-sectional area of the conductive path by increasing the contact area per conductive particle and to obtain mechanical strength, but also to microscopically destroy the oxide film at the bonding interface by ultrasonic vibration. Even on the surface, the current path becomes thicker, and a good electrical connection can be obtained.

In addition, since electrical components can be connected to each other at a lower temperature and in a shorter time, this connection method can also be applied to electrical components that use materials with a relatively low heat-resistant temperature. Since the process and the adhesive curing process can be separated, the adhesive curing process can process a large number of products at once. That is, it is not necessary to spend time for individual joining on the joining apparatus, and energy saving can be achieved along with improvement in productivity.

According to the inventors, when using gold that is soft and easily plastically deformed as conductive particles of the anisotropic conductive material, it was confirmed that plastic deformation of the gold particles is accelerated by applying ultrasonic vibration in combination with the pressing force. It was.

This phenomenon is peculiar to ultrasonic bonding. Usually, in the case of gold of about 99.5%, the yield pressure (plastic deformation starting pressure) at room temperature is about 500 MPa, whereas ultrasonic vibration of a constant amplitude condition is observed. When applied, the yield pressure decreases from 200 MPa to 300 MPa.
By performing relatively low heating from 00 ° C. to 150 ° C., the yield pressure is from 100 MPa to 1
It was found that the pressure further decreased to 50 MPa.

In other words, by using relatively low temperature heating and ultrasonic vibration in combination with the load, the gold particles are greatly deformed,
Since this deformation is a deformation of only gold particles that are conductive particles, the elastic restoring force of the electrode terminals and base material of the electrical parts as described above becomes extremely small, and stable bonding is possible even after the load at the time of bonding is removed. Is maintained.

Next, the embodiment will be described in detail with reference to FIG. FIG. 1 is a schematic cross-sectional view of a connection method according to the present invention. In FIG. 1, 1 is a rigid substrate, 2 is an electrode terminal formed on the rigid substrate 1, and the surface is plated with gold. 3 is a flexible substrate, and 4 is an electrode terminal formed on the flexible substrate 3, which is also plated with gold. Reference numeral 5 denotes an adhesive made of a thermosetting resin, and reference numeral 6 denotes gold particles dispersed in the adhesive 5 substantially uniformly. An anisotropic conductive material 7 is composed of the adhesive 5 and the gold particles 6.

Here, if the size of the gold particle 6 is too large, it causes a short circuit between adjacent electrode terminals, and if it is too small, the gold particle 6 cannot cope with the influence of the coplanarity of a plurality of electrode terminal heights, or the surface roughness of the electrode terminals. Therefore, it is practically preferable to have a narrow particle size distribution such that the particle size is 2 μm to 5 μm with respect to a general electrode terminal having a surface roughness of about Rz 1.0 μm. .

First, the anisotropic conductive material 7 is placed in a region including the electrode terminal 2 of the rigid substrate 1. In this embodiment, the anisotropic conductive material 7 uses a sheet of adhesive 5 in which gold particles 6 are diffused substantially uniformly (so-called ACF), but a paste (so-called ACP) is used. You may supply so that it may apply | coat.

Next, the flexible substrate 3 is placed with the electrode terminals to be connected positioned from above, and a load F is applied from above. The gold particles 6 positioned between the electrode terminals 2 and 4 to be connected by this load come into contact with the electrode terminals. At this time, heating is also performed.
Bonding itself between the gold particles 6 and the electrode terminals 2 and 4 can be performed at room temperature, but the adhesive 5 made of resin.
It is desirable to raise the temperature in order to reduce the viscosity of the resin to a predetermined viscosity. Since this heating is not for curing the adhesive 5 but for reducing the influence on the ultrasonic vibration, the temperature is set to a relatively low temperature (resin temperature 100 ° C. to 150 ° C.).

Next, in addition to the load, an ultrasonic vibration V in a direction substantially perpendicular to the direction of the load is applied. The method for controlling the ultrasonic vibration V is preferably a constant amplitude method. In the case of simple output constant control, the amplitude also varies due to the variation in mechanical load resistance that occurs during the joining process, making it difficult to stabilize the joining quality.

When the ultrasonic vibration V is applied together with the load F in this way, the gold particles 6 are plastically deformed and crushed, and the contact area with the electrode terminals 2 and 4 is increased. At the same time, the contact surface is microscopically caused by ultrasonic vibration. The oxide film is divided and the new surface is exposed, and this interface is bonded between metals not by diffusion but by adhesion.

Further, regarding the load F at this time, the number of particles located on the electrode terminal is calculated from the dispersion density of the gold particles 6 and is calculated from the yield pressure when applying ultrasonic vibration and the target contact area of the gold particles 6. Is a load F.

As can be seen from the above description, in the metal-to-metal joining according to the present invention, the dynamic plastic deformation of the gold particles 6 occupies an important factor. It is desirable to determine on the basis of dimensions. Therefore, as an index for obtaining reliable plastic deformation of the gold particles, the diameter of the contact surface between the gold particles 6 and the electrode terminals 2 and 4 (FIG. 1).
Stable joint quality can be obtained by making the B dimension indicated by (2) equal to or larger than the particle size of the gold particles 6 before deformation (A dimension shown in FIG. 1).

In this way, the connection work is performed, but the joining itself involving plastic deformation by the load F and the ultrasonic vibration V is generally completed in a short time of about 0.5 seconds. Therefore, the adhesive 5 may be cured by further heating at a higher temperature after this, but according to this connection method, since the residual stress as described above is extremely small, a plurality of curing agents may be used in a separate curing furnace. All of the products can be processed together.

Although the embodiment has been described by taking the connection between the rigid substrate 1 and the flexible substrate 3 as an example, the connection according to the present invention can be performed even if the object to be connected is changed between the flexible substrates or between the substrates and the electronic components. Needless to say, this can be realized without any particular ingenuity.

1 is a schematic cross-sectional view showing a connection method according to an embodiment of the present invention. Cross-sectional schematic diagram showing conventional connection method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rigid board | substrate 2, 4, 12, 14 Electrode terminal 3 Flexible board 5, 15 Adhesive 6, 16, 17 Conductive particle 7 Anisotropic conductive material 11 One electrical component 13 The other electrical component

Claims (2)

An anisotropic conductive material for connecting electrical components each having an electrode terminal to be connected to each other, wherein at least a connection surface of the electrode terminal is made of gold, and a plurality of gold particles are dispersed in an adhesive Between the electrode terminals to be connected, a load is applied in a direction in which the electrode terminals are brought close to each other, and ultrasonic vibration in a substantially parallel direction is applied to the connection surface, so that the gold particles are both connected to the electrode terminals. In contact with the electrode terminals and plastically deformed by receiving pressure from these electrode terminals, and the diameter of the contact surface between the gold particles and the electrode terminals is equal to or greater than the particle diameter of the gold particles, and metal-to-metal bonding is performed. To connect electrical components. A thermosetting resin is used as an adhesive for the anisotropic conductive material, and the bonding is performed in a step separate from the step of intermetallic bonding without heating and curing the adhesive after the intermetallic bonding is completed. The method for connecting electrical components according to claim 1, wherein the agent is cured.

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