JP3581618B2 - Conductive fine particles, anisotropic conductive adhesive, and conductive connection structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to conductive fine particles, anisotropic conductive adhesive, and a conductive connection structure used for connection between fine electrodes.
[0002]
[Prior art]
Anisotropic conductive materials are used in electronic products such as liquid crystal displays, personal computers, and portable communication devices to electrically connect small components such as semiconductor elements to substrates or to electrically connect substrates to each other. ing.
As such an anisotropic conductive connecting material, a material in which conductive fine particles are mixed with a binder resin is used.
[0003]
As the conductive fine particles, those obtained by subjecting the surface of organic base particles or inorganic base particles to metal plating have been used. Examples of such conductive fine particles include those disclosed in JP-B-6-96771, JP-A-4-36902, JP-A-4-269720, JP-A-3-257710, and the like. It is done.
[0004]
Examples of anisotropic conductive adhesive materials in which such conductive fine particles are mixed with a binder resin to form a film or a paste include, for example, JP-A-63-231889 and JP-A-4-259766. Examples disclosed in Japanese Laid-Open Patent Publication No. 3-291807, Japanese Laid-Open Patent Publication No. 5-75250, and the like.
[0005]
In a conventional anisotropic conductive material, an electrically insulating material such as a polymer is used as a base material for conductive fine particles, and a nickel plating layer is usually applied as a conductive layer on the surface thereof. For this reason, there is a problem in that the current capacity at the time of connection is small, and further, the metal coating layer cannot follow the deformation of the polymer serving as the base material and cracks occur.
[0006]
Particularly in recent years, as electronic devices and electronic components are miniaturized, wiring on a substrate or the like tends to become finer and the electrical resistance of a connection portion tends to increase. Furthermore, recently developed IC and LSI packages for portable devices are becoming closer to the chip size by flip chip bonding or the like, and the wiring tends to become finer. Resistance is becoming necessary. There is a method of increasing the concentration of the conductive fine particles in the anisotropic conductive adhesive to reduce the resistance of the connection portion. However, there is a problem that leakage between the electrodes tends to occur when the concentration is increased.
There is a method of providing an insulating coating layer or the like on the conductive fine particles, but there is a problem that the process becomes complicated.
[0007]
A technique using metal powder as the conductive fine particles is disclosed in Japanese Patent Laid-Open No. 8-273440. However, although the metal powder can have a large current capacity, it is difficult to obtain a true sphere when it becomes fine, and many of the so-called true spheres have a relatively large aspect ratio. In addition, since the particle diameters are not uniform and the CV value is large, there is a drawback that a large amount of particles that are not involved in conduction are generated and a leak phenomenon between the electrodes tends to occur. Furthermore, since there is little elastic deformation area and plastic deformation is likely to occur, there is a case where it does not follow the thermal deformation of the joint.
[0008]
[Problems to be solved by the invention]
In view of the above, the present invention has a low connection resistance, a large current capacity at the time of connection, a stable connection, and no leakage phenomenon. An object is to provide an adhesive and a conductive connection structure.
[0009]
[Means for Solving the Problems]
The present invention is a conductive fine particle in which the non-metallic fine particles are coated with a metal layer containing 50% by weight or more of copper, and the non-metallic fine particles have an average particle diameter of 1 to 500 μm, an aspect ratio of less than 1.3, Conductive fine particles having a CV value of 25% or less and a K value of 200 to 50,000 MPa.
The present invention is described in detail below.
[0010]
The conductive fine particles of the present invention are those in which nonmetallic fine particles are coated with a metal layer containing 50% by weight or more of copper.
The non-metallic fine particles are not particularly limited, and examples thereof include polymer base materials, inorganic particles, and mixtures and compounds thereof. Among these, a polymer base material having a small CV value and an aspect ratio and capable of easily obtaining an appropriate K value, recovery rate, and fracture strain is preferable.
[0011]
As the polymer substrate, a polymer having a fracture strain of 40% or more is preferably used. When the fracture strain is less than 40%, the conductive fine particles produced using the polymer may cause poor connection due to deformation or the like. The fracture strain is more preferably 50 to 90%.
[0012]
Moreover, as the polymer substrate, a polymer having a recovery rate of 40% or more is preferably used. When the recovery rate is less than 40%, conductive fine particles produced using a polymer may cause a connection failure due to deformation or the like. The recovery rate is more preferably 50 to 90%. In the present invention, the recovery rate is a value after compression deformation at 20 ° C. and 10%.
[0013]
The metal layer contains 50% by weight or more of copper. A metal layer containing 50% by weight or more of copper is flexible and can be easily cracked even when the base material is deformed, thereby obtaining stable connection reliability. In addition, when the conductive fine particles of the present invention are held in a state sandwiched between a plurality of electrodes, current flows from one electrode to the other electrode through the conductive fine particles, but copper is 50% by weight or more. Since it is covered with the included metal layer, the current capacity during connection is large.
[0014]
The copper content of the metal layer is preferably 50 to 100% by weight. If the copper content is less than 50% by weight, a sufficient current capacity cannot be obtained, or the metal layer tends to break. More preferably, it is 90 to 100% by weight.
[0015]
If the metal layer containing copper is used as it is, when exposed to a high-temperature and high-humidity state, oxidation may occur, the connection resistance value may remarkably increase, and connection reliability may be lowered. Therefore, under such conditions, in order to maintain connection reliability, the metal layer is preferably covered with an antioxidant layer.
Examples of the antioxidant layer include those composed of low molecular weight organic substances, noble metals and the like. Among these, it is preferable to be made of a noble metal.
Gold can be suitably used as the noble metal.
The method for coating the metal layer with a noble metal is not particularly limited, and examples thereof include an electroless plating method, a displacement plating method, and an electroplating method.
[0016]
When gold is used as the noble metal, since copper diffuses into gold at a high temperature, it is preferable that a barrier layer is provided between the metal layer and the antioxidant layer. The barrier layer is preferably made of nickel.
[0017]
The thickness of each of the above layers is preferably a metal layer of 0.03 to 10 μm, a barrier layer of 0.01 to 2 μm, and an antioxidant layer of 0.01 to 2 μm. If the thickness of each layer is less than this range, the coating effect may not be sufficiently obtained. On the contrary, if this range is exceeded, the characteristics of the substrate may be lost.
More preferably, the metal layer is 0.08 to 1 μm, the barrier layer is 0.03 to 0.2 μm, and the antioxidant layer is 0.02 to 0.1 μm.
[0018]
Nonmetallic fine particles serving as the core of the conductive fine particles of the present invention have an average particle diameter of 1 to 500 μm, an aspect ratio of less than 1.3, a CV value of 25% or less, and a K value of 200 to 50,000 MPa.
[0019]
When the average particle diameter of the non-metallic fine particles is less than 1 μm, the conductive fine particles produced using the non-metallic fine particles do not contact the electrode surface to be contacted, and a gap is formed between the electrodes, resulting in poor contact. Wake up. When the average particle diameter of the nonmetallic fine particles exceeds 500 μm, the conductive fine particles produced using the nonmetallic fine particles are large, so that there is a problem that the adjacent electrode is short-circuited. The average particle diameter of the nonmetallic fine particles is preferably 3 to 100 μm, more preferably 5 to 30 μm. In the present invention, the average particle diameter is a value obtained by observing and measuring 300 arbitrary fine particles with an electron microscope.
[0020]
When the aspect ratio of the non-metallic fine particles is 1.3 or more, the particle diameters are not uniform, so when connecting the electrodes through the conductive fine particles produced using the non-metallic fine particles, they are not involved in the connection. A large amount of particles are generated, and a leak phenomenon between the electrodes tends to occur. The aspect ratio is preferably less than 1.1, more preferably less than 1.05.
[0021]
The aspect ratio is a value obtained by dividing the average major axis of fine particles by the average minor axis. In the present invention, the aspect ratio is a value obtained by observing and measuring 300 arbitrary fine particles with an electron microscope.
[0022]
When the CV value of the nonmetallic fine particles exceeds 25%, the particle diameters are not uniform. Therefore, when the electrodes are connected to each other through the conductive fine particles produced using the nonmetallic fine particles, the conductivity that is not involved in the connection is obtained. Fine particles may be generated and a leak phenomenon may occur between adjacent electrodes. The CV value is preferably 10% or less, more preferably 5% or less. Needless to say, the CV value is 0% or more.
[0023]
The CV value is the following formula (1);
CV value = (σ / Dn) × 100 (1)
(In the formula, σ represents a standard deviation of particle diameters, and Dn represents a number average particle diameter). In the present invention, the standard deviation and the number average particle diameter are values obtained by observing and measuring 300 arbitrary fine particles with an electron microscope.
[0024]
If the K value of the nonmetallic fine particles is less than 200 MPa, connection failure may occur due to impact or the like, and if the K value exceeds 50,000 MPa, the electrode may be damaged. The K value is preferably 300 to 8000 MPa, more preferably 400 to 3000 MPa.
[0025]
In the present invention, the K value refers to the K value at the time of 10% deformation, and the following formula (2):
^{(3 / √2) · F ·} S -3/2 · R -1/2 ···· (2)
(In the formula, F represents a load value (MPa × mm ² ) at 20 ° C. and 10% compression deformation, S represents a compression displacement (mm), and R represents a radius (mm)). is there.
[0026]
As described above, the conductive fine particles of the present invention are obtained by coating nonmetallic fine particles with a metal containing 50% by weight or more of copper, an average particle size of 1 to 500 μm, an aspect ratio of less than 1.3, and a CV value of 25%. Hereinafter, there is no particular limitation as long as non-metallic fine particles having a K value of 200 to 50,000 MPa are used as the core, but preferred embodiments of the present invention include the following (1) and (2). It is done.
(1) Conductive fine particles in which polymer fine particles having a fracture strain of 40% or more are coated with a metal layer containing copper by 50% by weight or more, wherein the polymer fine particles have an average particle diameter of 3 to 100 μm and an aspect ratio. Conductive fine particles having a CV value of less than 1.1, a CV value of 10% or less, and a K value of 300 to 8000 MPa.
(2) Conductive fine particles in which polymer fine particles having a recovery rate of 40% or more are coated with a metal layer containing 50% by weight or more of copper, and the polymer fine particles have an average particle diameter of 5 to 30 μm and an aspect ratio. Conductive fine particles having a CV value of less than 1.05, a CV value of 5% or less, and a K value of 400 to 3000 MPa.
The conductive fine particles of the present invention may be further coated with an organic compound, resin, inorganic substance or the like.
[0027]
As described above, the conductive fine particles of the present invention are non-metallic at the core and have a specific K value, so that the electrodes are hardly damaged or poorly connected. Furthermore, since the CV value and the aspect ratio are small, leakage between the electrodes hardly occurs. In addition, since it is coated with a metal containing 50% by weight or more of copper, the electric capacity at the time of connection is large, and since the metal layer is flexible, it is difficult to crack even if the core is deformed, and a stable connection can be maintained. it can.
[0028]
The conductive fine particles of the present invention are mainly used when two opposing electrodes are electrically connected. The method for electrically connecting the two electrodes facing each other using the conductive fine particles is not particularly limited. For example, an anisotropic conductive adhesive is prepared by dispersing conductive fine particles in a binder resin. Examples thereof include a method of bonding and connecting two electrodes using this anisotropic conductive adhesive, a method of connecting using a binder resin and conductive fine particles separately, and the like.
[0029]
In the present invention, the anisotropic conductive adhesive is not particularly limited as long as the conductive fine particles are dispersed in an insulating binder resin. An anisotropic conductive film, anisotropic conductive paste, anisotropic Containing conductive conductive ink and the like.
The anisotropic conductive adhesive produced by using the conductive fine particles of the present invention is also one aspect of the present invention.
[0030]
The binder resin constituting the anisotropic conductive adhesive of the present invention is not particularly limited. For example, a thermoplastic resin such as an acrylate resin, an ethylene-vinyl acetate resin, a styrene-butadiene block copolymer; a monomer having a glycidyl group And a composition that is cured by heat or light, such as a curable resin composition obtained by a reaction with a curing agent such as oligomer and isocyanate.
Although the coating film thickness of the said anisotropic conductive adhesive is not specifically limited, 10 to several hundred micrometers is preferable.
[0031]
Examples of the object to be connected by the conductive fine particles of the present invention and the anisotropic conductive adhesive include, for example, a substrate having an electrode part formed on the surface, a component having an electrode part formed on the surface of a semiconductor or the like. Can be mentioned. The substrate is roughly classified into a flexible substrate and a rigid substrate. Examples of the flexible substrate include a resin sheet having a thickness of 50 to 500 μm. Examples of the material for the resin sheet include polyimide, polyamide, polyester, and polysulfone.
[0032]
The rigid substrates are roughly classified into those made of resin and those made of ceramic. Examples of the resin-made resin include glass fiber reinforced epoxy resin, phenol resin, and cellulose fiber reinforced phenol resin. Examples of the ceramics include silicon dioxide and alumina.
[0033]
The substrate structure may be a single layer structure, and in order to increase the number of electrodes per unit area, for example, a plurality of layers are formed by means such as through-hole formation, and are electrically connected to each other. A multi-layered substrate may be used.
[0034]
The components are not particularly limited, and examples thereof include active components such as semiconductors such as transistors, diodes, ICs, and LSIs; passive components such as resistors, capacitors, and crystal resonators.
[0035]
The shape of the electrode formed on the surface of the substrate or component is not particularly limited, and examples thereof include stripes, dots, and arbitrary shapes.
The material for the electrode is not particularly limited, and examples thereof include gold, silver, copper, nickel, palladium, carbon, aluminum, and ITO. Moreover, in order to reduce contact resistance, what further coat | covered gold | metal | money on copper, nickel, etc. can also be used.
The thickness of the electrode is preferably 0.1 to 100 μm. The width of the electrode is preferably 1 to 500 μm.
[0036]
As described above, various types of substrates and electronic components that can be used with the anisotropic conductive adhesive using the conductive fine particles of the present invention include various types. Among these, particularly for chip bonding. It can be preferably used.
[0037]
As a method for joining the conductive fine particles of the present invention to a substrate, a component, etc., for example, an anisotropic conductive film containing conductive fine particles is placed on a substrate or component having an electrode formed on the surface, There is a method in which a substrate or a component having another electrode surface is placed on top and heated and pressurized. Instead of the anisotropic conductive film, a predetermined amount of conductive paste using conductive fine particles can be used by printing means such as screen printing or a dispenser.
For the heating and pressurization, a crimping machine with a heater or a bonding machine is used.
[0038]
As a method for joining the conductive fine particles of the present invention to a substrate, a component, etc., a method that does not use an anisotropic conductive film and an anisotropic conductive paste is also possible. For example, 2 bonded together through conductive fine particles A method of curing after injecting a liquid binder into the gap between the two electrode portions can be used.
[0039]
A conductive connection structure in which the electrode portions of the substrate or components are connected using the conductive fine particles or the anisotropic conductive adhesive of the present invention is also one aspect of the present invention.
Since the conductive connection structure obtained as described above uses the conductive fine particles of the present invention, it has good conductivity and high connection reliability.
[0040]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.
[0041]
Example 1
A long-chain alkyl diacrylate copolymer having an average particle size of 15 μm, an aspect ratio of 1.04, a CV value of 4%, a K value of 2000 MPa, a fracture strain of 50%, and a recovery rate of 50% is electrolessly plated to a thickness of 0.2 μm. Copper was coated. Furthermore, after coating nickel with a thickness of 0.1 μm by electroless plating, gold was coated with a thickness of 0.04 μm by displacement plating to obtain conductive fine particles.
[0042]
The obtained conductive fine particles were mixed and dispersed in a binder resin solution in which a mixture of an epoxy resin and an acrylic resin was dissolved in toluene. Next, this conductive fine particle dispersion was applied on the release film to a certain thickness, and toluene was evaporated to produce an anisotropic conductive film. The film thickness was 40 μm, and the concentration of conductive fine particles was 15%.
The obtained anisotropic conductive film was attached to a transparent glass substrate and heated and pressed, but no cracks in the metal coating layer were observed.
[0043]
The obtained anisotropic conductive film was pasted on a ceramic substrate in which 20 electrodes of 100 μm × 100 μm were arranged in two rows at a pitch of 150 μm. The same ceramic substrate was overlaid thereon, and heated and pressurized at 150 ° C. for 2 minutes to produce a conductive connection structure. A current of 2 A was passed through the obtained conductive connection structure, but it showed good conductivity and resistance was sufficiently low. Further, the connection resistance between adjacent electrodes was 1 × 10 ⁹ Ω or more, and the insulation between lines was sufficiently maintained.
After conducting a heat and humidity resistance test at 70 ° C. and 85% for 200 hours, when a current of 2 A was passed through the conductive connection structure, there was almost no change in the characteristics of the conductive connection structure.
[0044]
Example 2
In Example 1, the same operation was performed except that only 0.2 μm thick copper was coated by electroless plating to obtain conductive fine particles. Using this conductive fine particle, an anisotropic conductive film and a conductive connection structure were produced in the same manner as in Example 1.
The obtained anisotropic conductive film was attached to a transparent glass substrate and heated and pressed, but no cracks in the metal coating layer were observed.
[0045]
A current of 2 A was passed through the obtained conductive connection structure, but it showed good conductivity and resistance was sufficiently low. Further, the connection resistance between adjacent electrodes was 1 × 10 ⁹ Ω or more, and the insulation between lines was sufficiently maintained.
After conducting a heat and humidity resistance test at 70 ° C. and 85% for 200 hours, when a current of 2 A was passed through the conductive connection structure, an increase in resistance due to oxidation and partial conduction breakdown were observed. If there were no conditions, it seemed that there was no problem.
[0046]
Comparative Example 1
In Example 1, electroconductive fine particles were obtained in the same manner as in Example 1 except that nickel was coated instead of 0.2 μm thick copper by electroless plating. Using this conductive fine particle, an anisotropic conductive film and a conductive connection structure were produced in the same manner as in Example 1.
[0047]
When the obtained anisotropic conductive film was applied to a transparent glass substrate and heated and pressed, cracks in the metal coating layer were observed.
In the obtained conductive connection structure, the connection resistance between adjacent electrodes was 1 × 10 ⁹ Ω or more and the insulation between lines was sufficiently maintained, but when a current of 2 A was passed, conduction breakdown was observed. .
[0048]
Comparative Example 2
An acrylate copolymer having a fracture strain of 50% and a recovery rate of 20% was subjected to plating treatment in the same manner as in Example 1, and conductive fine particles having an average particle size of 15 μm, an aspect ratio of 1.3, a CV value of 30%, and a K value of 100 MPa. Got. Using this conductive fine particle, an anisotropic conductive film and a conductive connection structure were produced in the same manner as in Example 1.
[0049]
The obtained anisotropic conductive film was attached to a transparent glass substrate and heated and pressed, but no cracks in the metal coating layer were observed.
When a current of 2A was passed through the obtained conductive connection structure, conduction breakdown was observed, and a short circuit occurred between adjacent electrodes.
[0050]
Comparative Example 3
The glass was plated in the same manner as in Example 1 to obtain conductive fine particles having an average particle diameter of 15 μm, an aspect ratio of 1.1, a CV value of 10%, and a K value of 70,000 MPa. Using this conductive fine particle, an anisotropic conductive film and a conductive connection structure were produced in the same manner as in Example 1.
[0051]
When the obtained anisotropic conductive film was applied to a transparent glass substrate and heated and pressed, the electrode on the glass substrate was damaged and a partial conduction failure occurred.
Although the obtained conductive connection structure had a connection resistance between adjacent electrodes of 1 × 10 ⁹ Ω or more and the insulation between lines was sufficiently maintained, when a current of 2A was passed, a partial conduction breakdown was observed. It was.
[0052]
【The invention's effect】
Since the conductive fine particles of the present invention have the above-described configuration, the connection resistance is low, the current capacity at the time of connection is large, the connection is stable, and no leakage phenomenon occurs. Moreover, the conductive connection structure using the conductive fine particles of the present invention has good conductivity and high connection reliability.

Claims (19)

The non-metallic fine particles are conductive fine particles formed by coating with a metal layer containing 50% by weight or more of copper,
The non-metallic fine particles have an average particle diameter of 1 to 500 μm, an aspect ratio of less than 1.3, a CV value of 25% or less, and a K value of 200 to 50,000 MPa. The conductive fine particles according to claim 1, wherein the non-metallic fine particles are polymers having a fracture strain of 40% or more. 3. The conductive fine particle according to claim 1, wherein the non-metallic fine particle is a polymer having a recovery rate of 40% or more. The conductive fine particles according to claim 1, 2 or 3, wherein the non-metallic fine particles are coated with a metal layer containing 90% by weight or more of copper. 5. The conductive fine particle according to claim 1, wherein the metal layer containing copper is covered with an antioxidant layer. 6. The conductive fine particle according to claim 5, wherein the antioxidant layer is made of a noble metal. 7. The conductive fine particle according to claim 6, wherein the noble metal is gold. The conductive fine particles according to claim 5, 6 or 7, wherein a barrier layer is provided between the metal layer containing copper and the antioxidant layer. 9. The conductive fine particle according to claim 8, wherein the barrier layer is made of nickel. The conductive fine particles according to claim 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the average particle diameter is 3 to 100 µm. The conductive fine particles according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, wherein the average particle diameter is 5 to 30 µm. The conductive fine particles according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, wherein the aspect ratio is less than 1.1. The conductive fine particles according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein the aspect ratio is less than 1.05. The conductive fine particles according to claim 1, 2 or 3, wherein the CV value is 10% or less. CV value is 5% or less, The electroconductive fine particles of Claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 characterized by the above-mentioned. The electroconductive fine particles according to claim 1, wherein the K value is 300 to 8000 MPa. The conductive fine particles according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15. . K value is 400-3000 MPa, The electroconductivity of Claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 or 16 characterized by the above-mentioned. Fine particles. A conductive fine particle according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, or 17. Isotropic conductive adhesive. 19. Conductive fine particles according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or 17, or anisotropic according to claim 18. A conductive connection structure characterized by being connected by a conductive conductive adhesive.