JP2008179834A - Electrically-conductive elastic resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly electrically-conductive resin having high elasticity and capable of reducing its content of a filler for obtaining high electrical conductivity by use of a filler having a high aspect ratio. <P>SOLUTION: The electrically conductive elastic resin comprises a resin having rubbery elasticity and a conductive filler made of a needle-shaped filler with a surface layer thereof coated with Au, Ag, Ni or Cu. A diameter of the needle-shaped filler is in a range between 0.5 to 2.0 μm. A length of the filler is in a range between 10 to 100 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an elastic conductive resin and an elastic conductive joint structure using an elastic conductive resin, and can be used for mounting electronic components and mechanical contact connectors.

Japanese Patent Laid-Open No. 10-242616 discloses a related art relating to a conductive elastic resin. In this case, the connection portion can be mounted with high reliability without filling the gap between the circuit board and the IC chip with a sealing resin. As shown in FIG. The conductive adhesive 3 connects the bump seat 2 and the conductive elastic resin bump (projection electrode formed on the electrode portion of the wireless bonding element in the integrated circuit) 4 provided at the lower part of the package 1. ing. The conductive elastic resin bumps 4 are made of silicon resin mixed with conductive powder (filler) such as 180-200 μm copper powder plated with gold (mixing ratio 2: 1). Absorbs stress due to strain. There is a component mounting seat 6 for the circuit board 5, which is electrically connected to the conductive elastic resin bump 4.
In addition, there is one described in Japanese Patent Application Laid-Open No. 10-256304. As shown in FIG. 12, after the conductive adhesive having rubbery elasticity is cured, the semiconductor integrated circuit is cooled and cooled. Even if shear stress is applied to the conductive adhesive 15 due to the difference in coefficient of thermal expansion between the chip 11 and the insulating substrate 12, the conductive adhesive 15 relaxes this shear stress, causing peeling or destruction of the adhesive layer. The resin component of the conductive adhesive 15 does not hinder the longitudinal stress generated by the use of the sealing resin 16 having a large curing shrinkage, and the protruding electrode 13 and the substrate electrode 14 are formed of the conductive adhesive 15. A good electrical connection is obtained by pressure contact through conductive particles.
Japanese Patent Laid-Open No. 10-242616 JP-A-10-256304

  Conventionally, solder bonding is generally performed in mounting an IC package. However, since the difference in thermal expansion coefficient between the package product and the wiring board is greatly different, a stress is repeatedly generated in the connection portion when a temperature cycle is applied. For this reason, resin reinforcement is performed for the purpose of preventing the occurrence of abnormalities such as breakage of the connecting portion. Furthermore, for the recent package mounting which has been increased in the number of pins and increased in size, a conductive adhesive having rubber-like elasticity is used as described in the above-mentioned JP-A-10-256304. There is something to connect. Although this can surely improve the connection reliability, the stress relaxation function is insufficient, so that reinforcement with a resin is necessary.

  In addition, the mounting structure described in the above-mentioned Japanese Patent Application Laid-Open No. 10-242616 is to form an electrically conductive elastic resin in the form of a bump and press this to ensure electrical connection. Since the conductive elastic resin is a mixture of Cu-plated Au resin and silicone resin, a high pressure contact force is required to make an electrical connection to the electrode that has a high elastic modulus and is formed in an area array. In addition, if the bump heights are not precisely aligned, a uniform pressure contact force is not applied to each bump, and therefore there is a problem that the stability and reliability of the connection of all the electrodes is inferior.

The conventional elastic conductive resin is a silicone resin having rubber-like elasticity containing spherical conductive particles or flaky conductive filler, and in order to ensure high conductivity using the spherical particles and flaky filler, Since it is necessary to increase the blending amount of the filler, the rubber elastic property of the silicone resin cannot be fully utilized as a cured product. For this reason, when electrical bonding is performed by mechanical contact using elastic conductive bumps, it is necessary to use a structure in which pressure is applied with a large load, and it is necessary to control the variation in bump height with high accuracy.
Therefore, the present invention aims to provide an elastic conductor having a high deformability with respect to a compressive force and a high conductivity, and specific problems for that purpose are as follows.

[Problem 1]
Problem 1 is to devise a highly conductive resin that can reduce the filler content for obtaining high conductivity by using a filler having a high aspect ratio (longitudinal ratio) and is rich in elasticity.
[Problem 2]
Problem 2 is to reduce the specific gravity of the conductive filler and prevent non-uniform filler distribution due to filler precipitation in the rubber-like elastic resin.
[Problem 3]
In addition, the problem 3 is that a mechanical contact type joining structure that allows easy replacement of electronic components, and that the pressing force during mechanical contact with the opposing electrode can be reduced and the allowable range of variation in bump height can be increased. It is to be.
[Problem 4]
Further, Problem 4 is to ensure a stable contact resistance even when an oxide film and dirt are present on the surface of the electrode electrically connected to the elastic conductive bump by mechanical contact.
[Problem 5]
Furthermore, the problem 5 is to further increase the allowable range of bump height variation by making the bump shape more easily deformable by compression.
[Problem 6]
Furthermore, the problem 6 is to make it possible to form bumps having low resistance and high elasticity by a screen printing method with high mass productivity.
[Problem 7]
Furthermore, the problem 7 is to devise an elastic conductive bump that can be easily handled and a manufacturing method capable of reducing the cost.
[Problem 8]
Furthermore, the problem 8 is to enable formation of elastic conductive bumps at a low temperature in a short time.

[Solution 1]
Means 1 (corresponding to claim 1) taken in order to solve the problem 1 includes a resin having rubber-like elasticity and a conductive filler in which a surface layer of a needle-shaped filler is coated with Au, Ag, Ni or Cu. In the elastic conductive resin containing,
The needle-shaped filler has a diameter of 0.5 to 2.0 μm and a filler length of 10 to 100 μm.
The “needle-shaped filler” is generally fibrous and means a three-dimensional network structure formed in the resin so that the fillers are in contact with each other.
[Work]
Since the filler is a needle-shaped filler as described above and is a conductive filler whose surface layer is coated with Au, Ag, Ni, or Cu, its aspect ratio is high. Since the aspect ratio is high, the restraining force against the elastic deformation of the resin is small, and thus the high elasticity of the resin is maintained. Moreover, since the aspect ratio is high, high conductivity can be imparted to the resin with a small conductive filler content, so the filler content can be reduced.
Therefore, the elastic conductive resin mixed with a small amount of needle-shaped filler is a highly elastic elastic conductive resin which is rich in elasticity and stable.

[Embodiment 1]
Embodiment 1 is that the core material of the needle-shaped filler in Solution 1 is a whisker.
[Work]
Since the core material of the needle-shaped filler uses whiskers, a conductive filler having a small diameter and a high aspect ratio can be easily manufactured. Therefore, the elastic conductive resin can be miniaturized.

[Embodiment 2]
Embodiment 2 is that the core material of the needle-shaped filler of Embodiment 1 is a polymer whisker. (Corresponding to claim 2)
For example, the polymer whisker has a diameter of 0.5 to 2.0 μm, a filler length of 10 to 100 μm, and an aspect ratio of 10 to 100. As a suitable polymer material, poly (p-oxybenzoyl) And poly (2-oxy-6-naphthoyl).
[Work]
Since the core material using the whisker is a polymer whisker, the specific gravity of the conductive filler is low, and therefore, the conductive filler is less likely to be dispersed and precipitated in the rubber-like elastic resin. Distribution is even. Therefore, there is no instability of the volume resistivity due to the bias of the conductive filler distribution, and the volume resistivity can be stabilized.

[Solution 2]
Solution means 2 is means for solving the above-mentioned problem 3, and about the joining structure by the elastic conductor,
The elastic conductive resin is formed in a bump shape on the electrode of one of the parts to be joined and is electrically joined by mechanically contacting the other side.
[Work]
By forming the elastic conductor, which is a highly conductive conductor, in a bump shape with a high deformability against compressive force, the elastic conductor can be mechanically contacted and the applied pressure when deformed by a predetermined amount can be reduced, Therefore, it is possible to increase the allowable range of the bump height variation.

[Embodiment 1]
In the first embodiment, the bonding structure using elastic conductors of Solution 2 includes a resin having rubber-like elasticity and an elastic conductive resin including a needle-shaped filler whose surface layer is coated with Au, Ag, Ni, or Cu. Electrical bonding is performed by forming bumps on the electrodes of the bonded components and bringing them into mechanical contact with the other side.

[Embodiment 2]
Embodiment 2 is the bump shape in the conductive bonding of Solution 2 or Embodiment 1 above.
The elastic conductive bumps become thinner toward the tip, and the aspect ratio is 0.1 to 1.0.
[Work]
Since the elastic conductive bumps become thinner toward the tip and the aspect ratio is 0.1 to 1.0, the deformability of the bumps against the compressive stress applied to the elastic conductive bumps during bonding is large. Therefore, the applied pressure at the time of mechanical contact can be further reduced, and the allowable range of the bump height variation can be further increased.

[Embodiment 3]
Embodiment 3 is a method for forming a bump shape in Embodiment 2 above.
A bump is formed by screen-printing a conductive paste containing a heat-curable silicone resin, a diluent, and a needle-shaped conductive filler on the electrode, and then heat-curing with two or more temperature rise profiles.

[Embodiment 4]
Embodiment 4 is that the resin having rubber-like elasticity in Embodiment 2 is a silicone resin having both ultraviolet curable properties and moisture curable properties.
[Work]
Since a silicone resin having ultraviolet curable properties and moisture curable properties is used as a rubber-like elastic resin, the curing time can be shortened, and heating for bonding is not required, so heating can be performed. Even electronic parts that are not allowed can be electrically bonded using elastic conductive bumps.

[Solution 3]
Solution means 3 is means for solving the above problem 7;
That is, an elastic conductor is configured by attaching a metal foil to an elastic conductive resin including a rubber-like elastic resin and a needle-shaped conductive filler.
[Work]
By attaching the metal foil to the elastic conductive resin containing the rubber-like elastic resin and the needle-shaped conductive filler, the elastic conductive resin can be given shape retention alone. Therefore, it is possible to form a low-resistance, low-elasticity, high-elasticity bump type bump as a single component by screen printing and a heat reflow process with high productivity, and this is retrofitted to a predetermined structure or the like. It is possible.

[Embodiment 1]
Embodiment 1 is a method for producing an elastic conductor with a metal foil according to Solution 3, wherein an elastic conductive resin is coated on a metal foil with a predetermined thickness on one side, cured, and cut to obtain a predetermined Forming an elastic conductor.

The effects of the present invention are organized as follows for each claim.
1. Effect of Invention According to Claim 1 By using a conductive filler having a high aspect ratio, the filler content for obtaining high conductivity can be reduced, and a conductive resin rich in elasticity can be obtained by combining with a rubber-like elastic resin. It is done.
2. Effect of the Invention According to Claim 2 Since whiskers are used as the core material of the needle-shaped filler, a conductive filler having a small diameter and a high aspect ratio can be easily manufactured, and the elastic conductive resin can be made finer.
Moreover, since the polymer whisker is used, the specific gravity of the conductive filler can be reduced and precipitation of the conductive filler in the rubber-like elastic resin can be prevented, so that the volume resistivity of the elastic conductor can be stabilized.

Next, examples will be described with reference to the drawings.
[Example 1]
The volume resistivity and rubber hardness (JIS A) of a conductive rubber-like elastic resin in which a needle-shaped conductive filler is contained in a silicone resin, which is a typical rubber-like elastic resin, are shown in FIGS. 1 and 2, respectively. The silicone resin used in this example is a thermosetting type and has a rubber hardness (JIS A) of 28. Further, as the needle-shaped conductive filler, an inorganic compound whisker with Ag plating was used, and a filler having a filler diameter of about 0.5 μm and a filler length of about 20 μm was used.
By mixing the needle-shaped conductive filler into the rubber-like elastic resin and kneading and sufficiently dispersing, higher conductivity than that obtained when the flaky filler is contained is obtained as shown in FIG. As shown, the rubber hardness can be lowered.

[Example 2]
FIG. 3 shows a joint structure for electrically connecting the electronic component and the substrate by forming the conductive rubber-like elastic resin in a bump shape and bringing it into mechanical contact. As shown in FIG. 2 and FIG. 1, the bump made of the conductive rubber-like elastic resin has a high deformability against compressive force and can ensure high conductivity. Therefore, even in electrode bonding formed in a large number of area arrays. A stable contact can be ensured at a low load, and therefore the holding structure for pressing and holding the electronic component on which the bump is formed on the substrate can be simplified.
For one elastic conductive bump formed into a bump shape with a bump diameter of 0.5 mmφ and a bump height of 0.15 mm with this elastic conductive resin, its compression deformation characteristics and contact resistance were measured with an indenter tool with a diameter of 0.5 mmφ. Evaluation was performed with repeated weighting at a weighting of 9.8 to 490 mN. The relationship between the amount of repeated deformation and the needle filler mixing ratio (wt%) in this case is as shown in FIG. 5, and the compression deformation characteristics when 40 wt% of the needle filler is added are shown as representative data. 4 shows. From this, it is clear that the amount of displacement against repeated compression is stable and substantially elastically deformed during that time.
Further, the relationship between the contact resistance and the needle filler mixture ratio (wt%) when this elastic conductive bump is pressed against the Au electrode at a load of 490 mN is as shown in FIG.

From the above evaluation results, it is clear that the elastic deformation characteristics that are stable with respect to repeated compression are maintained, and that the contact resistance is also at a low level.
In addition, about the compounding ratio of a needle-shaped electrically conductive filler, it can select suitably according to the amount of elastic deformation requested | required and a contact resistance value with reference to the said evaluation result.
Further, since the elastic conductive bump is a mechanical contact type conductive member, the electronic component on which the elastic conductive bump is formed can be easily attached and detached. Therefore, the electronic component can be reused and the electronic component can be reused.

Example 3
FIG. 7 shows an example in which an elastic conductive resin in which a tetrapot type conductive filler is contained in a resin having rubber-like elasticity is formed in a bump shape. This tetrapot type conductive filler 21 is made by coating a zinc oxide crystal grown from the center of gravity of a regular tetrahedron toward the four vertices with various metals (for example, Au, Ag, Ni, Cu) to provide conductivity. is there. In this example, the tetrapod-type conductive filler 21 has an average needle-like length of 20 μm and an average needle-like base diameter of about 1 μm. The elastic conductive bump 20 formed of a conductive elastic body in which the tetrapot type conductive filler 21 is mixed with a rubber-like elastic resin has numerous conductive filler needles protruding from the bump surface. When the counter electrode is pressed against the elastic conductive bump 20, the elastic conductive bump is deformed, and the needle portion protruding from the bump surface slides on the surface of the counter electrode. For this reason, even if the surface of the counter electrode is oxidized or contaminated, it is eliminated, and the tip of the needle part reliably contacts the conductive surface of the counter electrode, so that the contact resistance of the joint is stabilized.

Example 4
If the cross-sectional shape of the elastic conductive bump is a shape with its tip gradually narrowed, the amount of deformation of the bump against the compressive force of the entire bump should be increased because the amount of deformation of the bump is large by the amount of the tip. Can do. This further increases the tolerance for bump height variation. In the embodiment shown in FIG. 8, the bump has a bowl shape in cross section, but the same effect can be obtained by forming a conical shape. Here, if the bump aspect ratio is 0.1 or less, the amount of compressive deformation of the elastic conductive bumps cannot be secured, so that it is impossible to stably secure electrical connection with a plurality of electrodes, and when the aspect ratio is 1.0 or more. There is a possibility that the elastic conductive bump collapses and the variation of the contact resistance is increased, and contact with the adjacent electrode is caused.

Next, a material and a manufacturing method for forming a bowl-shaped elastic conductive bump at a low cost will be described.
If this elastic conductive resin has sufficient rubber elasticity, the resin compounding ratio can be increased while ensuring the necessary elasticity. On the other hand, sufficient rubber elasticity is ensured by using a thermosetting silicone resin as the resin having rubber elasticity and further adding a diluent. In this case, even if the shape of the elastic conductive resin supply on the electrode is indefinite, the viscosity becomes low at the beginning of the high temperature environment during heat curing, so the surface tension of the resin and diluent acts to form a bowl-shaped bump. So there is no problem. Accordingly, by supplying the elastic conductive resin onto the electrodes by the screen printing method, it is possible to efficiently form the bowl-shaped elastic conductive bump. However, since it contains a diluent, if it is suddenly heated to the full curing temperature and cured, voids may be involved and this may lead to higher resistance. It is necessary to heat at a low temperature, slowly blow off the diluent, then raise the temperature to the main curing temperature and cure.

Example 5
An embodiment of an elastic conductor to which a metal foil is added is shown in FIG. The elastic conductive resin in this embodiment is not different from the above embodiment, and a metal foil 22 is added to one side thereof. The metal foil 22 may be a Cu foil alone, but it is desirable that the surface layer of the metal foil 22 be plated with Au or Ag in order to reduce the contact resistance with the elastic conductive resin 30a. This elastic conductor 30 with metal foil is effective when elastic conductive bumps are formed on a three-dimensional structure or the like where it is difficult to form elastic bumps by directly supplying elastic conductive resin to the electrodes. Then, it can be retrofitted to a three-dimensional structure or the like. As a post-installation method, soldering, joining with a conductive adhesive, or the like can be used. Here, when joining an elastic conductor without a metal foil to an electrode, it cannot be soldered, and the adhesive wettability of the elastic resin is poor, so sufficient strength for adhesive bonding with a conductive adhesive is secured. It is not possible to do this, but this problem can be solved easily by applying metal foil.

Example 6
Next, a method for producing an elastic conductor with a metal foil will be described with reference to FIG.
The elastic conductive resin 30a is applied to a predetermined thickness on the metal foil 22 and cured. As a curing method, an appropriate method such as a heat curing method or a moisture curing method is employed depending on the type of the rubber-like elastic resin. After curing, the elastic conductive resin and the metal foil can be cut together and cut to a required size to create an elastic conductor with metal foil. In addition, the adhesive tape that loses the adhesive strength by UV irradiation on the back side of the metal foil is attached in advance, and the elastic conductor after cutting is broken by leaving the adhesive tape portion at the time of cutting. You can avoid that. At the time of use, only the used part is irradiated with UV from the back surface, and the elastic conductor with metal foil can be removed, so that workability is greatly improved.

Example 7
The elastic conductive resin of this Example 7 can obtain high conductivity even if the content of the conductive filler is reduced, and the filler shape is needle-shaped, so that it is more than when flaky filler is contained. The light penetrates to the inner layer, and the rubber-like elastic resin is composed of a silicone resin having ultraviolet curing properties and moisture curing properties. As a specific material, an ultraviolet curable silicone resin 3164 manufactured by ThreeBond can be used. After an elastic conductive resin is supplied onto the electrode, it is completely cured to the inside by irradiation with ultraviolet rays. Alternatively, after curing only the surface layer, it can be stored in a normal temperature and humidity environment and fully cured by utilizing the moisture curing function. Even in both curing steps, complete curing at least near the surface layer is completed in a short time and heating is not required, so that an elastic conductor can be formed on an electronic component that cannot be heated.

  In addition, as described in the above embodiment, as the needle filler, it is possible to use a conductive filler that is metal-coated on the surface layer of an inorganic whisker such as a metal whisker, a calcium carbonate whisker, and a potassium titanate whisker as a core material. The rubber-like resin is not limited to the silicone resin, and any resin having rubber-like elasticity can be used.

These are figures which show the relationship between a conductive filler compounding ratio and the volume resistivity of elastic conductive resin with a graph. These are figures which show the graph of the relationship between a conductive filler compounding ratio and the rubber hardness of an elastic conductive resin. These are sectional drawings which expand and show typically the joining structure of an elastic conductive bump. These are figures which show the graph of the repeated compression deformation characteristic of an elastic conductive bump. These are figures which show the graph of the relationship between a needle filler compounding ratio and the amount of repeated deformations of an elastic conductive bump. These are figures which show the graph of the relationship between the acicular filler compounding ratio and the contact resistance of an elastic conductive bump. These are the front views which expand and show the elastic conductive bump of an Example typically. These are figures which show typically an example of the bowl-shaped bump formation method. (A) is a figure which shows typically the structure of an elastic conductor with metal foil, etc., (b) is a figure which shows the usage of an elastic conductor with metal foil typically. These are figures which show typically how to make the elastic conductor with metal foil. These are sectional drawings of a prior art example. These are sectional drawings of other conventional examples.

Explanation of symbols

20: Elastic conductive bump 21: Tetrapot type conductive filler 22: Metal foil 30: Elastic conductor 30a: Elastic conductive resin

Claims (2)

In an elastic conductive resin comprising a resin having rubber-like elasticity and a conductive filler in which a surface layer of a needle-shaped filler is coated with Au, Ag, Ni, or Cu,
An elastic conductive resin, wherein the needle-shaped filler has a diameter of 0.5 to 2.0 μm and a filler length of 10 to 100 μm.   The elastic conductive resin according to claim 1, wherein the core material of the needle-shaped filler is a polymer whisker.

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