JP2012216770A - Anisotropic conductive paste, and connection method of electronic component using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anisotropic conductive paste having a sufficient repairability and high connection reliability.SOLUTION: The anisotropic conductive paste is such an anisotropic conductive paste as an electronic component and a wiring board are connected. The anisotropic conductive paste contains the lead free solder powder with melting point 240°C or lower by 10 mass% or more to 50 mass% or less and a thermosetting resin composition containing thermosetting resin and organic acid by 50 mass% or more to 90 mass% or less. The acid value of the thermosetting resin composition is 15 mgKOH/g or more to 55 mgKOH/g or less.

Description

  The present invention relates to an anisotropic conductive paste for connecting an electronic component and a wiring board and a method for connecting an electronic component using the same.

  In recent years, a connection method using an anisotropic conductive material (an anisotropic conductive film or an anisotropic conductive paste) has been used to connect an electronic component and a wiring board. For example, when an electronic component and a wiring board are connected, an anisotropic conductive material is disposed between the electronic component on which the electrode is formed and the wiring board on which the electrode pattern is formed, and the electronic component and the wiring are connected. The electrical connection is ensured by thermocompression bonding with the substrate.

  As an anisotropic conductive material, for example, a material in which a conductive filler such as a metal fine particle or a resin ball having a conductive film formed on a surface is dispersed in a binder resin as a base material has been proposed (for example, Patent Documents). 1). When the electronic component and the wiring board are thermocompression bonded, the conductive filler is arranged in a plane because there is a certain probability between the electronic component to be connected and the electrodes of the wiring board. It becomes a state. In this way, when the electrodes of the electronic component to be connected and the wiring board are brought into contact with each other via the conductive filler, conductivity between these electrodes is ensured. On the other hand, in the gap between the electrodes of the electronic component and the gap between the electrodes of the wiring board, the conductive filler is embedded in the binder resin, and insulation in the surface direction is ensured.

JP 2003-165825 A

  By the way, in the mounting method as described above, when a failure such as poor conduction or misalignment due to pressure occurs in the mounting state of the electronic component after thermocompression bonding, the electronic component or the anisotropic conductive film is mechanically removed. The wiring board is reused after the residue remaining on the wiring board is cleaned by wiping with a solvent or the like. Therefore, the anisotropic conductive material after thermocompression bonding is not only required to have sufficient mechanical strength as the thermosetting resin is cured, but also has sufficient repairability (no residue of anisotropic conductive material from the wiring board or It is required to have a property of being able to be peeled off with a small amount of residue and being able to achieve connection between the wiring board and the electronic component using an anisotropic conductive material again.

  However, in the anisotropic conductive material described in the above-mentioned patent document, it takes time to sufficiently remove residues such as resin and conductive filler on the wiring board, while some residue on the wiring board. When an anisotropic conductive material is used again to attempt connection with an electronic component in a state where there is remaining, there is a problem that the conductivity cannot be ensured. Thus, although the anisotropic conductive material described in the above-mentioned patent document has a certain degree of repair property, it is not always at a sufficient level. In addition, when the anisotropic conductive material described in the above-mentioned patent document is used, in order to ensure the connection reliability of the connection portion, the electronic component to be connected and the electrode of the wiring board are subjected to a gold plating process. There was a problem in connection reliability, such as necessity.

  Therefore, an object of the present invention is to provide an anisotropic conductive paste having sufficient repair properties and high connection reliability, and an electronic component connecting method using the same.

  The anisotropic conductive paste of the present invention is an anisotropic conductive paste for connecting an electronic component and a wiring board, and the anisotropic conductive paste has a lead-free solder powder 10 having a melting point of 240 ° C. or lower. Containing 50% by mass to 50% by mass and 50% by mass to 90% by mass of a thermosetting resin composition containing a thermosetting resin and an organic acid, and the acid value of the thermosetting resin composition is: It is 15 mgKOH / g or more and 55 mgKOH / g.

In the anisotropic conductive paste of the present invention, it is preferable that the thermosetting resin is an epoxy resin and the organic acid is a dibasic acid having an alkylene group.
In the anisotropic conductive paste of the present invention, the thermosetting resin composition further contains a thixotropic agent, and the content of the inorganic thixotropic agent in the thixotropic agent is 0.5% by mass or more and 22% by mass. The following is preferable.
In the anisotropic conductive paste of the present invention, it is preferable that an average particle diameter of the lead-free solder powder is 1 μm or more and 34 μm or less.

In the anisotropic conductive paste of the present invention, it is preferable that the lead-free solder powder contains at least one metal selected from the group consisting of tin, copper, silver, bismuth, antimony, indium and zinc.
In the anisotropic conductive paste of the present invention, it is preferable that at least one of the electrode of the electronic component or the electrode of the wiring board is not subjected to gold plating.

  The electronic component connecting method of the present invention is an electronic component connecting method using the anisotropic conductive paste, wherein the anisotropic conductive paste is applied onto the wiring board, Disposing the electronic component on an isotropic conductive paste, and thermocompression bonding the electronic component to the wiring board at a temperature higher than the melting point of the lead-free solder powder by 5 ° C or more. Features.

  In the electronic component connection method of the present invention, a peeling step of peeling the electronic component from the wiring board at a temperature higher by 5 ° C. than a melting point of the lead-free solder powder, and the wiring board after the peeling step on the wiring board Re-application step of applying anisotropic conductive paste, and placing the electronic component on the anisotropic conductive paste after the re-application step, at a temperature 5 ° C. or more higher than the melting point of the lead-free solder powder, It is preferable to further include a re-thermocompression bonding step of thermocompression bonding the electronic component to the wiring board.

In the present invention, the anisotropic conductive paste is conductive in the thermocompression bonding direction (thickness direction) at a place where heat of a predetermined value or more and pressure of a predetermined value or more are applied. This means a paste that can form an anisotropic conductive material having insulation in the surface direction.
The reason why the anisotropic conductive paste of the present invention has sufficient repairability and mechanical strength and high connection reliability is not necessarily clear, but the present inventors speculate as follows. .

That is, unlike the conventional anisotropic conductive material, the anisotropic conductive paste of the present invention contains lead-free solder powder. When this anisotropic conductive paste is thermocompression bonded at a temperature equal to or higher than the melting point of the lead-free solder powder, the lead-free solder powders melt and come close to each other. It becomes larger by joining together. On the other hand, since the distance between the electrodes of the electronic component and the wiring board is shortened by thermocompression bonding, the electrodes can be soldered to each other by the lead-free solder that has been enlarged as described above. As described above, in the present invention, since the electrodes of the electronic component and the wiring board are soldered to each other, the electrodes and the conductive filler are connected by contact with each other like a conventional anisotropic conductive material. The present inventors infer that the connection reliability is extremely high as compared with the case where it is present.
On the other hand, solder bonding is performed as described above in the places where the thermocompression bonding is not performed with the heat above the predetermined value and the pressure above the predetermined value (such as the gap between the electrodes of the electronic component and the gap between the electrodes of the wiring board). The lead-free solder powder is embedded in the thermosetting resin composition. Therefore, insulation is ensured for a portion that is not thermocompression bonded with heat of a predetermined value or higher and pressure of a predetermined value or higher.

When the electronic component and the wiring board are connected with the anisotropic conductive paste of the present invention, as described above, the electrodes of the electronic component and the wiring board are soldered together, and the soldered portion is a thermosetting resin. It is inferred that the composition is covered. And after thermocompression bonding, the solder can be melted by applying heat at or above the melting point of the lead-free solder powder, and the thermosetting resin composition can also be softened. Parts can be easily peeled off. Further, in the present invention, even when a certain amount of residue (solder or the like) remains on the electrode or the like when the wiring board and the electronic component are to be connected again using the anisotropic conductive paste after peeling, Residues can be joined together and soldered to ensure conductivity. On the other hand, with the conventional anisotropic conductive material, when a certain amount of residue (conductive filler, etc.) remains on the wiring board, the anisotropic conductive material is used again to connect the electronic component. Can not secure conductivity. Therefore, it is necessary to sufficiently remove residues such as resin and conductive filler on the wiring board, and there is a problem that the work is troublesome. As described above, the anisotropic conductive paste of the present invention is excellent in repairability as compared with conventional anisotropic conductive materials.
In the present invention, the solder joint portion is covered with the thermosetting resin composition, and since this thermosetting resin composition is cured by heat, the solder joint portion can be reinforced. Therefore, when an electronic component and a wiring board are connected with the anisotropic conductive paste of the present invention, sufficient mechanical strength can be ensured.

  ADVANTAGE OF THE INVENTION According to this invention, while having sufficient repair property, the anisotropic conductive paste which has high connection reliability, and the connection method of an electronic component using the same can be provided.

First, the anisotropic conductive paste of the present invention will be described.
The anisotropic conductive paste of the present invention is an anisotropic conductive paste for connecting an electronic component and a wiring board. And this anisotropic conductive paste contains 10 mass% or more and 50 mass% or less of the lead-free solder powder described below, and contains 50 mass% or more and 90 mass% or less of the thermosetting resin composition described below. It is.
When the content of the lead-free solder powder is less than 10% by mass (when the content of the thermosetting resin composition exceeds 90% by mass), the obtained anisotropic conductive paste is subjected to thermocompression bonding. When a sufficient solder joint cannot be formed between the electronic component and the wiring board, the conductivity between the electronic component and the wiring board becomes insufficient, and on the other hand, the content of the lead-free solder powder exceeds 50% by mass ( In the case where the content of the thermosetting resin composition is less than 50% by mass), the insulating property of the obtained anisotropic conductive paste, particularly the insulating property in the moisture when left in a humidified state, is insufficient. As a result, the solder bridges do not exhibit anisotropy. Further, in the obtained anisotropic conductive paste, the content of the lead-free solder powder is 20% by mass or more and 45% by mass or less from the viewpoint of balancing the insulation and the conductivity when thermocompression bonded. It is preferable that it is 30% by mass or more and 40% by mass or less.

The lead-free solder powder used in the present invention has a melting point of 240 ° C. or lower. When the lead-free solder powder having a melting point exceeding 240 ° C. is used, the lead-free solder powder cannot be melted at a normal thermocompression bonding temperature in the anisotropic conductive paste. Further, from the viewpoint of lowering the thermocompression bonding temperature in the anisotropic conductive paste, the melting point of the lead-free solder powder is preferably 220 ° C. or less, and more preferably 150 ° C. or less.
Here, the lead-free solder powder refers to a solder metal or alloy powder to which lead is not added. However, it is allowed that lead is present as an inevitable impurity in the lead-free solder powder, but in this case, the amount of lead is preferably 100 mass ppm or less.

The lead-free solder powder is at least one selected from the group consisting of tin (Sn), copper (Cu), silver (Ag), bismuth (Bi), antimony (Sb), indium (In), and zinc (Zn). It is preferred to include a seed metal.
Moreover, as a specific solder composition (mass ratio) in the said lead-free solder powder, the following can be illustrated.
As binary alloys, for example, Ag-Bi type such as 95.3Ag / 4.7Bi, Ag-Li type such as 66Ag / 34Li, Ag-In type such as 3Ag / 97In, Ag-type such as 67Ag / 33Te, etc. Te, Ag-Tl such as 97.2Ag / 2.8Tl, Ag-Zn such as 45.6Ag / 54.4Zn, Au-Sn such as 80Au / 20Sn, 52.7Bi / 47.3In, etc. Bi-In series, 35In / 65Sn, 51In / 49Sn, In-Sn series such as 52In / 48Sn, Bi-Zn series such as 8.1Bi / 91.9Zn, Sn-Bi series such as 43Sn / 57Bi, 42Sn / 58Bi , 98Sn / 2Ag, 96.5Sn / 3.5Ag, 96Sn / 4Ag, Sn-Ag series such as 95Sn / 5Ag, 91Sn / 9Zn, 30Sn / 7 Sn-Zn-based, such as Zn, Sn-Cu system, such 99.3Sn / 0.7Cu, include Sn-Sb system, such as 95Sn / 5Sb.
Examples of ternary alloys include Sn—Ag—In such as 95.5Sn / 3.5Ag / 1In, Sn—Zn—In such as 86Sn / 9Zn / 5In, 81Sn / 9Zn / 10In, and 95.5Sn. Sn-Ag-Cu system such as /0.5Ag/4Cu, 96.5Sn / 3.0Ag / 0.5Cu, Sn- such as 90.5Sn / 7.5Bi / 2Ag, 41.0Sn / 58Bi / 1, 0Ag Examples thereof include Sn—Zn—Bi systems such as Bi—Ag system and 89.0Sn / 8.0Zn / 3.0Bi.
Examples of other alloys include Sn / Ag / Cu / Bi system.

  The average particle size of the lead-free solder powder is preferably 1 μm or more and 34 μm or less, and more preferably 3 μm or more and 20 μm or less. If the average particle size of the lead-free solder powder is less than the lower limit, the conductivity between the electronic component and the wiring board tends to decrease. On the other hand, if the upper limit is exceeded, the insulating property in the anisotropic conductive paste decreases. There is a tendency. The average particle size can be measured with a dynamic light scattering type particle size measuring device.

  The thermosetting resin composition used in the present invention contains a thermosetting resin and an organic acid. And the acid value of this thermosetting resin composition needs to be 15 mgKOH / g or more and 55 mgKOH / g. When the acid value is less than 15 mgKOH / g, when the anisotropic conductive paste obtained is thermocompression bonded, the solder cannot be sufficiently activated, and the electrical conductivity between the electronic component and the wiring board is low. On the other hand, if it exceeds 55 mgKOH / g, the insulating property of the obtained anisotropic conductive paste, particularly the wet insulation when left in a humidified state, becomes insufficient. Further, in the obtained anisotropic conductive paste, the acid value of the thermosetting resin composition is 20 mgKOH / g or more and 50 mgKOH / g from the viewpoint of balancing the insulation and the conductivity when thermocompression bonded. It is preferable that it is 30 mgKOH / g or more and 45 mgKOH / g.

As the thermosetting resin used in the present invention, a known thermosetting resin can be used as appropriate, but it is particularly preferable to use an epoxy resin from the viewpoint of having a flux action.
In the present invention, having a flux action means that the coating film covers the metal surface of the object to be soldered and shields the atmosphere, like metal rosin flux, and the metal surface of the metal surface is oxidized during soldering. The material is reduced, and the coating film is pushed away by the molten solder to allow contact between the molten solder and the metal surface, and the residue has a function of insulating between the circuits.

As such an epoxy resin, a known epoxy resin can be appropriately used. Examples of such epoxy resins include bisphenol A type, bisphenol F type, biphenyl type, naphthalene type, cresol novolac type, phenol novolac type, and dicyclopentadiene type epoxy resin. These epoxy resins may be used individually by 1 type, and may mix and use 2 or more types. Further, these epoxy resins preferably contain a liquid at normal temperature, and when a solid at normal temperature is used, it is preferably used in combination with a liquid at normal temperature. In addition, among these epoxy resin molds, the dispersibility of the metal particles and the paste viscosity can be adjusted, and further, the resistance to the drop impact of the cured product can be improved, and the wettability of the solder can be improved. Liquid bisphenol A type, liquid bisphenol F type, liquid hydrogenated bisphenol A type, naphthalene type, and dicyclopentadiene type are preferable. Moreover, from the viewpoint of the storage stability of the obtained anisotropic conductive paste, it is preferable to use a combination of liquid bisphenol A type and liquid bisphenol F type.
As content of the said epoxy resin, it is preferable that it is 70 to 92 mass% with respect to 100 mass% of thermosetting resin compositions, and it is more preferable that it is 75 to 85 mass%. . If the content of the epoxy resin is less than the lower limit, sufficient strength for fixing the electronic component cannot be obtained, and thus the resistance to drop impact tends to decrease. On the other hand, if the content exceeds the upper limit, the thermosetting resin The content of organic acid and curing agent in the composition decreases, and the rate at which the epoxy resin is cured tends to be delayed.

As the organic acid used in the present invention, a known organic acid can be appropriately used. Among these organic acids, it is preferable to use a dibasic acid having an alkylene group from the viewpoint of excellent solubility with an epoxy resin and from the viewpoint that crystals are hardly precipitated during storage. Examples of such a dibasic acid having an alkylene group include adipic acid, 2,5-diethyladipic acid, glutaric acid, 2,4-diethylglutaric acid, 2,2-diethylglutaric acid, and 3-methylglutaric acid. 2-ethyl-3-propylglutaric acid, sebacic acid, succinic acid, malonic acid, diglycolic acid. Among these, adipic acid, glutaric acid, and succinic acid are preferable, and adipic acid is particularly preferable.
The content of the organic acid is preferably 1% by mass or more and 8% by mass or less, and more preferably 2% by mass or more and 7% by mass or less with respect to 100% by mass of the thermosetting resin composition. . If the content of the organic acid is less than the lower limit, the rate at which the thermosetting resin such as an epoxy resin is cured tends to be delayed, and on the other hand, if the upper limit is exceeded, the anisotropic conductivity obtained is obtained. There is a tendency for the insulating property of the conductive paste to decrease.

The thermosetting resin composition used in the present invention preferably uses a thixotropic agent and a curing agent in addition to the thermosetting resin and the organic acid.
As the thixotropic agent used in the present invention, a known thixotropic agent can be appropriately used. Examples of such thixotropic agents include organic thixotropic agents (fatty acid amide, hydrogenated castor oil, olefinic wax, etc.) and inorganic thixotropic agents (colloidal silica, benton, etc.). Among these, fatty acid amide, colloidal silica, and benton are preferable. Moreover, it is preferable to use it in combination with an organic thixotropic agent and an inorganic thixotropic agent from a viewpoint of the difficulty of bleeding of the anisotropic conductive paste obtained. Specifically, a combination of fatty acid amide and colloidal silica, and a combination of fatty acid amide and benton are exemplified.
The thixotropic agent content is preferably 0.5% by mass to 25% by mass and more preferably 0.5% by mass to 10% by mass with respect to 100% by mass of the thermosetting resin composition. More preferably, the content is 1% by mass or more and 5% by mass or less. If the content of the thixotropic agent is less than the above lower limit, thixotropy cannot be obtained, the sagging is likely to occur on the electrode of the wiring board, and the adhesive force when electronic components are mounted on the electrode of the wiring board tends to decrease. On the other hand, if the upper limit is exceeded, the thixotropy is too high and the syringe needles tend to become defective due to clogging.
When the thixotropic agent used in the present invention is used in combination with the organic thixotropic agent and the inorganic thixotropic agent, the content of the inorganic thixotropic agent is 100% by mass of the thermosetting resin composition. On the other hand, it is preferably 0.5% by mass or more and 22% by mass or less, and more preferably 1% by mass or more and 20% by mass or less.

As the curing agent used in the present invention, a known curing agent can be appropriately used. For example, when an epoxy resin is used as the thermosetting resin, the following can be used.
Examples of the latent curing agent include NOVACURE HX-3722, HX-3721, HX-3748, HX-3088, HX-3613, HX-392HP, and HX-3941HP (trade name, manufactured by Asahi Kasei Epoxy Co., Ltd.).
Examples of the aliphatic polyamine curing agent include Fujicure FXR-1020, FXR-1030, FXR-1050, FXR-1080 (trade name, manufactured by Fuji Kasei Kogyo Co., Ltd.).
Examples of the epoxy resin amine adduct curing agent include Amicure PN-23, PN-F, MY-24, VDH, UDH, PN-31, PN-40 (trade name, manufactured by Ajinomoto Fine Techno Co.), EH-3615S. , EH-3293S, EH-3366S, EH-3842, EH-3670S, EH-3636AS, EH-4346S (trade name, manufactured by Asahi Denka Kogyo Co., Ltd.).
Examples of the imidazole curing accelerator include 2P4MHZ, 2MZA, 2PZ, C11Z, C17Z, 2E4MZ, 2P4MZ, C11Z-CNS, and 2PZ-CNZ (and above, trade names).
These curing agents are preferably used in combination of a latent curing agent, an epoxy resin amine adduct curing agent, and an imidazole curing accelerator from the viewpoint of insulating properties of the obtained anisotropic conductive paste.

  As content of the said hardening | curing agent, it is preferable that it is 5 to 20 mass% with respect to 100 mass% of thermosetting resin compositions, and it is more preferable that it is 10 to 18 mass%. . If the content of the curing agent is less than the lower limit, the rate at which the thermosetting resin is cured tends to be delayed. On the other hand, if the upper limit is exceeded, the reactivity tends to be faster and the paste usage time tends to be shorter. .

  In addition to the epoxy resin, the organic acid, the thixotropic agent, and the curing agent, the thermosetting resin composition used in the present invention is optionally provided with a surfactant, a coupling agent, an antifoaming agent, and a powder surface treatment. An additive such as an agent, a reaction inhibitor, and an anti-settling agent may be contained. The content of these additives is preferably 0.01% by mass or more and 10% by mass or less, and 0.05% by mass or more and 5% by mass or less with respect to 100% by mass of the thermosetting resin composition. More preferably. If the content of the additive is less than the lower limit, the effect of each additive tends to be difficult to achieve. On the other hand, if the content exceeds the upper limit, the bonding strength due to the thermosetting resin composition tends to decrease.

Next, the connection method of the electronic component of this invention is demonstrated.
The electronic component connecting method of the present invention is an electronic component connecting method using the above-described anisotropic conductive paste of the present invention, wherein the anisotropic conductive paste is applied onto the wiring board. And placing the electronic component on the anisotropic conductive paste, and heating the electronic component to the wiring board at a temperature 5 ° C. or higher (preferably 20 ° C. or higher) higher than the melting point of the lead-free solder powder. And a thermocompression bonding step for pressure bonding.
Here, as an electronic component, a wiring board may be used in addition to a chip, a package component, and the like. As the wiring substrate, either a flexible substrate having flexibility or a rigid substrate having no flexibility can be used. Further, when a flexible substrate is used as an electronic component, the rigid substrates can be electrically connected to each other via the flexible substrate by connecting to two wiring substrates (rigid substrates). Further, the flexible boards may be electrically connected through the flexible boards.

In the applying step, the anisotropic conductive paste is applied on the wiring board.
Examples of the coating device used here include a dispenser, a screen printer, and a jet dispense metal mask printer.
The thickness of the coating film is not particularly limited, but is preferably 50 μm or more and 500 μm or less, and more preferably 100 μm or more and 300 μm or less. If the thickness is less than the lower limit, the adhesive force when electronic components are mounted on the electrodes of the wiring board tends to decrease. On the other hand, if the thickness exceeds the upper limit, the paste tends to protrude beyond the connection portion. .

In the thermocompression bonding step, the electronic component is disposed on the anisotropic conductive paste, and the electronic component is thermocompression bonded to the wiring board at a temperature higher by 5 ° C. than the melting point of the lead-free solder powder.
If the temperature at the time of thermocompression bonding does not satisfy the condition that the temperature is higher by 5 ° C. or more than the melting point of the lead-free solder powder, the lead-free solder cannot be sufficiently melted, and between the electronic component and the wiring board A sufficient solder joint cannot be formed, and the electrical conductivity between the electronic component and the wiring board becomes insufficient.
Although the pressure at the time of thermocompression bonding is not particularly limited, it is preferably 0.2 MPa or more and 2 MPa or less, and more preferably 0.5 MPa or more and 1.5 MPa or less. If the pressure is less than the upper limit, sufficient solder joints cannot be formed between the electronic component and the wiring board, and the electrical conductivity between the electronic component and the wiring board tends to decrease. It tends to be stressed and the dead space has to be widened.
In the present invention, as described above, the pressure at the time of thermocompression bonding can be set to a lower pressure range than in the case of the conventional method. Therefore, cost reduction of the apparatus used for a thermocompression bonding process can also be achieved.
The time for thermocompression bonding is not particularly limited, but is usually 5 seconds to 60 seconds and preferably 7 seconds to 20 seconds.

  Moreover, in the connection method of the electronic component of this invention, it is preferable to further provide the peeling process, the recoating process, and the rethermocompression bonding process which are demonstrated below.

In the peeling step, the electronic component is peeled from the wiring board at a temperature higher by 5 ° C. than the melting point of the lead-free solder powder.
Here, the method for peeling the electronic component from the wiring board is not particularly limited. As such a method, for example, a method of peeling the electronic component from the wiring board while heating the connection portion using a soldering hand or the like can be employed. In such a case, a known peeling device used for repair may be used.
Moreover, after peeling an electronic component from a wiring board, you may wash | clean the said wiring board with a solvent etc. as needed.

In the re-application process, the anisotropic conductive paste is applied onto the wiring substrate after the peeling process. Here, the thickness and thickness of the coating device and the coating film can be the same as those in the coating step and conditions.
In the re-thermocompression bonding step, the electronic component is disposed on the anisotropic conductive paste after the re-coating step, and the electronic component is placed at a temperature higher by 5 ° C. than the melting point of the lead-free solder powder. Thermocompression bonded to. Here, the conditions similar to the said application | coating process are employable as the temperature, pressure, and time at the time of thermocompression bonding.

  According to the electronic component connecting method of the present invention described above, since the electrodes of the electronic component and the wiring board are soldered to each other, the electrodes and the conductive filler are in contact with each other like a conventional anisotropic conductive material. Compared with the case of being connected by matching, extremely high connection reliability can be achieved. Moreover, if heat at a temperature equal to or higher than the melting point of the lead-free solder powder is applied after thermocompression bonding, the solder can be melted and the thermosetting resin composition can be softened. Parts can be easily peeled off. Further, in the present invention, even when a certain amount of residue (solder or the like) remains on the electrode or the like when the wiring board and the electronic component are to be connected again using the anisotropic conductive paste after peeling, Residues can be joined together and soldered to ensure conductivity. Therefore, the electronic component connecting method of the present invention is superior in repairability as compared with a conventional method using an anisotropic conductive material.

EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these examples.
[Example 1]
Thermosetting resin A (bisphenol A type epoxy resin, manufactured by DIC, trade name “EPICLON 860”) 82.9% by mass, thixotropic agent A (fatty acid amide, Nippon Kasei Co., Ltd., trade name “Slipax H”) 2 mass %, Organic acid A (adipic acid, manufactured by Kanto Denka Kogyo Co., Ltd.) 2.6% by mass, curing agent A (manufactured by Shikoku Kasei Co., Ltd., trade name “Curazole 2P4MHZ”) 11.5% by mass, surfactant (BIC Chemie Japan) 0.5% by mass, trade name “BYK361N”) and 0.5% by mass of an antifoaming agent (trade name “Floren AC-326F”, manufactured by Kyoeisha Chemical Co., Ltd.) are put into a container and used with a large machine. By mixing, a thermosetting resin composition was obtained.
Thereafter, 62.5% by mass of the obtained thermosetting resin composition, and 37.5% by mass of lead-free solder powder A (average particle size: 5 μm, melting point of solder: 139 ° C., solder composition: 42Sn / 58Bi) Was put into a container and mixed in a kneader for 2 hours to prepare an anisotropic conductive paste.
Next, the obtained anisotropic conductive paste was applied on a wiring board (electrode: copper electrode with gold plating (Cu / Ni / Au)) (thickness: 0.2 mm). Then, on the anisotropic conductive paste after application, an electronic component (electrode: gold plating treatment (Cu / Ni / Au) on a copper electrode) is placed, and the temperature is measured using a thermocompression bonding apparatus (manufactured by Advancel). The electronic component was thermocompression bonded to the wiring board under the conditions of 200 ° C., pressure 1 MPa, and pressure bonding time 8 to 10 seconds.

[Example 2]
Wiring the electronic components in the same manner as in Example 1 except that the wiring board used was a copper electrode with a water-soluble preflux treatment (trade name “WPF-8” manufactured by Tamura Corporation). The substrate was thermocompression bonded.
[Example 3]
The electronic component was thermocompression bonded to the wiring board in the same manner as in Example 2 except that the electrode was made of tin (Sn).

[Example 4]
A thermosetting resin composition and an anisotropic conductive paste were obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.
In the same manner as in Example 2 except that the anisotropic conductive paste obtained as described above was used instead of the anisotropic conductive paste used in Example 2, the electronic component was thermocompression bonded to the wiring board. did.
[Example 5]
A thermosetting resin composition and an anisotropic conductive paste were obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.
In Example 5, lead-free solder powder B (average particle size: 5 μm, solder melting point: 217 ° C., solder composition: 96.5 Sn / 3 Ag / 0.5 Cu) is used.
Then, in place of the anisotropic conductive paste used in Example 2, the anisotropic conductive paste obtained as described above was used, and the temperature at the time of thermocompression bonding was set to 240 ° C. Similarly, the electronic component was thermocompression bonded to the wiring board.

[Comparative Examples 1-4]
A thermosetting resin composition and an anisotropic conductive paste were obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.
In the same manner as in Example 2 except that the anisotropic conductive paste obtained as described above was used instead of the anisotropic conductive paste used in Example 2, the electronic component was thermocompression bonded to the wiring board. did.

[Comparative Example 5]
A thermosetting resin composition and an anisotropic conductive paste were obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.
In Comparative Example 5, resin powder subjected to gold plating (Au / Ni plating resin powder, manufactured by Sekisui Chemical Co., Ltd., trade name “Micropearl Au-205”) is used.
In the same manner as in Example 1 except that the anisotropic conductive paste obtained as described above was used instead of the anisotropic conductive paste used in Example 1, the electronic component was thermocompression bonded to the wiring board. did.

[Comparative Example 6]
Wiring the electronic components in the same manner as in Comparative Example 5 except that the wiring board used was a copper electrode with a water-soluble preflux treatment (trade name “WPF-8” manufactured by Tamura Corporation). The substrate was thermocompression bonded.
[Comparative Example 7]
The electronic component was thermocompression bonded to the wiring board in the same manner as in Comparative Example 5 except that the electrode was made of tin (Sn).

<Evaluation of connection method of anisotropic conductive paste and electronic component>
Evaluation of anisotropic conductive paste performance (acid value of resin composition, insulation resistance value after crimping) and connection method of electronic components (initial resistance value after crimping, repairability (breakdown of substrate during repair) Presence / absence, resistance value after repair)) was evaluated or measured by the following method. The obtained results are shown in Tables 1 and 2. In addition, about Comparative Examples 6-7, since the initial resistance value after crimping | compression-bonding was impossible and it was not able to measure, it did not evaluate about repair property.
(1) Acid value of resin composition The resin composition is weighed and dissolved in a solvent. Then, titration was performed at 0.5 mol / L · KOH using a phenolphthalein solution as an indicator.
(2) Initial resistance value after pressure bonding A wiring board having a 0.2 mm pitch land (line / space = 100 μm / 100 μm) as a circuit pattern was prepared. Then, electronic components having a 0.2 mm pitch land (line / space = 100 μm / 100 μm) were thermocompression-bonded on the lands of the wiring board by the methods described in the above-described examples and comparative examples, respectively. And the resistance value between the terminals of the connected land was measured using the digital multimeter (The product made by Agilent, brand name "34401A"). In addition, when the resistance value was too high (100 MΩ or more) and conduction was not possible, it was determined that “conduction was not possible”.
(3) Presence / absence of substrate destruction during repair Evaluation is performed using the substrate whose initial resistance value is measured in (2). While heating the connection portion of the substrate with the electronic component at the same temperature as the thermocompression bonding temperature, the electronic component was peeled from the substrate, and then the surface contamination was washed with ethyl acetate. And the state of the board | substrate after peeling was observed visually and the presence or absence of board | substrate destruction was investigated.
(4) Resistance value after repair Measured using the substrate evaluated for the presence or absence of substrate destruction in (3) above. On the land of this board | substrate, the electronic component was again thermocompression-bonded by the method as described in the said Example and comparative example, respectively. And the resistance value between the terminals of the connected land was measured using the digital multimeter (The product made by Agilent, brand name "34401A"). In addition, when the resistance value was too high (100 MΩ or more) and conduction was not possible, it was determined that “conduction was not possible”.
(5) Insulation resistance value after crimping On the copper foil lands of the comb-shaped electrode substrate (glass epoxy resin substrate) with a pitch of 0.2 mm (line / space = 100 μm / 100 μm), the differences obtained in Examples and Comparative Examples, respectively. After printing the isotropic conductive paste to a thickness of 0.1 mm, a test piece was obtained by heating to 240 ° C. in a reflow furnace (trade name “TNP”, manufactured by Tamura Corporation). A voltage of 15 V was applied to the test piece in 85 ° C. and 85% RH (relative humidity), and an insulation resistance value after 168 hours was measured.

As is clear from the results shown in Table 1 and Table 2, when the wiring board and the electronic component are connected using the anisotropic conductive paste of the present invention (Examples 1 to 5), it is sufficient. It was confirmed that repairability and high connection reliability can be ensured.
On the other hand, when the blending amount of the lead-free solder powder in the anisotropic conductive paste is 5% by mass (Comparative Example 1), the acid value of the resin composition in the anisotropic conductive paste is 5 mgKOH / In the case of g (Comparative Example 3), it was confirmed that the initial resistance value after crimping was high, and the conductivity between the wiring board and the electronic component could not be secured.
Moreover, when the compounding quantity of the lead-free solder powder in the anisotropic conductive paste is 60% by mass (Comparative Example 2), and the acid value of the resin composition in the anisotropic conductive paste is 70 mgKOH / g In some cases (Comparative Example 4), it was confirmed that the insulation resistance value after crimping was low, and it was not possible to ensure the insulation of the portion where thermocompression bonding was not performed.
Further, when an anisotropic conductive paste containing no solder powder is used (Comparative Examples 5 to 7), wiring is not performed unless both the wiring board electrode and the electronic component electrode are subjected to gold plating. It was not possible to achieve electrical connection between the board and the electronic component. Moreover, also when the gold plating process was performed to both the electrode of a wiring board and the electrode of an electronic component (comparative example 5), after repair, it was not able to aim at conduction, and it was confirmed that repair property is inferior. .

[Examples 6 to 17]
A thermosetting resin composition and an anisotropic conductive paste were obtained in the same manner as in Example 1 except that the respective materials were blended according to the compositions shown in Table 3 and Table 4.
In the same manner as in Example 1 except that the anisotropic conductive paste obtained as described above was used instead of the anisotropic conductive paste used in Example 1, the electronic component was thermocompression bonded to the wiring board. did.
In addition, the material used in Examples 6-17 is shown below.
Thermosetting resin A: bisphenol A type epoxy resin, trade name “EPICLON 860”, thermosetting resin B manufactured by DIC Corporation: Bisphenol F type epoxy resin, trade name “EPICLON 830CRP”, thermosetting resin C made by DIC Corporation: Mixed epoxy resin of bisphenol A type and bisphenol F type, trade name “EPICLON EXA-830LVP”, thermosetting resin D: dicyclopentadiene type epoxy resin, trade name “EPICLON HP-7200H”, manufactured by DIC Thermosetting resin E: Naphthalene type epoxy resin, trade name “EPICLON HP-4032D”, DIC's thixotropic agent A: fatty acid amide, Nippon Kasei Co., Ltd., trade name “Sripacs H”
Thixotropic agent B: colloidal silica, trade name “AEROSIL R974”, Nippon Aerosil Co., Ltd. thixotropic agent C: Benton, Wilber Ellis organic acid A: adipic acid, Kanto Denka Kogyo organic acid B: glutaric acid, Tokyo Chemical Industry Co., Ltd. Organic acid C: Succinic acid, Mitsubishi Chemical Co., Ltd. Curing agent A: Imidazole type curing accelerator, trade name “Cureazole 2P4MHZ”, Shikoku Kasei Co., Ltd. curing agent B: Trade name “Cureazole 2MZA-” PW ", Shikoku Kasei Co., Ltd. Curing Agent C: Epoxy Resin Amine Adduct Curing Agent," Amicure PN-F ", Ajinomoto Fine Techno Co., Ltd. Curing Agent D: Latent Curing Agent, Trade Name" Novacure HX-3721 ", Asahi Kasei Epoxy surfactant: Trade name “BYK361N”, Big Chemie Japan antifoam: Trade name “Floren AC” -326F ”, Kyoeisha Chemical Co., Ltd. lead-free solder powder A: the average particle size is 5 μm, the melting point of the solder is 139 ° C., and the composition of the solder is 42Sn / 58Bi
Lead-free solder powder B: average particle size is 5 μm, solder melting point is 217 ° C., solder composition is 96.5Sn / 3Ag / 0.5Cu

<Evaluation of connection method of anisotropic conductive paste and electronic component>
For Example 1 and Examples 6 to 17, the performance of the anisotropic conductive paste (acid value of resin composition, insulation resistance value after compression bonding, storage stability) and evaluation of the connection method of electronic components (crimping) The subsequent initial resistance value, repairability (whether or not the substrate was destroyed during repair, resistance value after repair), and bridge observation by X-ray) were evaluated or measured by the above-described method and the following method. The obtained results are shown in Tables 3 and 4.
(6) Bridge observation by X-ray Using a microfocus X-ray fluoroscope (manufactured by SHIMADZU: SMX-160E), the substrate after pressure bonding is observed by X-ray to check for bridges and bleeding of anisotropic conductive paste. Judgment was made based on the following criteria. In addition, a bridge means an unexpected short circuit between adjacent terminals.
A: There is no bridge, and there is no bleeding of the anisotropic conductive paste.
B: There is no bridge, but there is slight bleeding of the anisotropic conductive paste.
C: There is a bridge.
(7) Storage stability The viscosity of the anisotropic conductive paste after storage at 10 ° C. was measured, and the time when the change rate relative to the initial value did not exceed ± 20% was measured. The viscosity was measured using a viscometer (Malcom Corp .: PCU-205) for a resin in a plastic container adjusted to 25 ° C. in a thermostatic bath.

From the results shown in Table 3 and Table 4, the following points were confirmed.
From the results of Example 1 and Example 6, it was confirmed that when the organic thixotropic agent and the inorganic thixotropic agent were used in combination as the thixotropic agent, the anisotropic conductive paste was less likely to bleed.
From the results of Example 6 and Example 7, when used as a curing agent in combination with a latent curing agent, an epoxy resin amine adduct curing agent and an imidazole curing accelerator, the insulation resistance value after pressure bonding is It was confirmed to improve.
From the results of Examples 7, 8 and 12 to 14, when the epoxy resin is used in combination with liquid bisphenol A type and liquid bisphenol F type, the storage stability of the anisotropic conductive paste is improved. Was confirmed.
From the results of Examples 8, 15 and 16, it was confirmed that it is preferable to use a dibasic acid having an alkylene group as the organic acid. In particular, when adipic acid was used as the organic acid (Example 8), it was confirmed that the initial resistance value after pressure bonding and the resistance value after repair tended to decrease.

  The anisotropic conductive paste of the present invention can be suitably used as a technique for connecting an electronic component and a wiring board.

Claims (8)

An anisotropic conductive paste for connecting an electronic component and a wiring board,
The anisotropic conductive paste comprises 10% by mass to 50% by mass of lead-free solder powder having a melting point of 240 ° C. or less, and 50% by mass or more of a thermosetting resin composition containing a thermosetting resin and an organic acid. 90% by mass or less,
An anisotropic conductive paste, wherein an acid value of the thermosetting resin composition is 15 mgKOH / g or more and 55 mgKOH / g. The anisotropic conductive paste according to claim 1,
The thermosetting resin is an epoxy resin,
The anisotropic conductive paste, wherein the organic acid is a dibasic acid having an alkylene group. In the anisotropic conductive paste according to claim 1 or 2,
The thermosetting resin composition further contains a thixotropic agent, and the content of the inorganic thixotropic agent in the thixotropic agent is 0.5% by mass or more and 22% by mass or less. Sex paste. In the anisotropic conductive paste according to any one of claims 1 to 3,
An anisotropic conductive paste, wherein the lead-free solder powder has an average particle size of 1 μm or more and 34 μm or less. In the anisotropic conductive paste according to any one of claims 1 to 4,
The anisotropic conductive paste, wherein the lead-free solder powder contains at least one metal selected from the group consisting of tin, copper, silver, bismuth, antimony, indium and zinc. In the anisotropic conductive paste according to any one of claims 1 to 5,
An anisotropic conductive paste, wherein at least one of the electrode of the electronic component or the electrode of the wiring board is not subjected to gold plating. A method for connecting an electronic component using the anisotropic conductive paste according to any one of claims 1 to 6,
An application step of applying the anisotropic conductive paste on the wiring board;
Placing the electronic component on the anisotropic conductive paste, and thermocompression bonding the electronic component to the wiring board at a temperature higher than the melting point of the lead-free solder powder by 5 ° C or more;
A method for connecting electronic components, comprising: In the connection method of the electronic component of Claim 7,
A peeling step of peeling the electronic component from the wiring board at a temperature higher by 5 ° C. or more than the melting point of the lead-free solder powder;
A recoating step of applying the anisotropic conductive paste on the wiring substrate after the peeling step;
Re-thermocompression bonding wherein the electronic component is placed on the anisotropic conductive paste after the re-coating step, and the electronic component is thermocompression-bonded to the wiring board at a temperature 5 ° C. higher than the melting point of the lead-free solder powder. And a step of connecting the electronic component.