JPWO2014051149A1 - Conductive adhesive - Google Patents

Abstract

Conductive bonding having heat resistance to heat treatment in a temperature range of 200 ° C. to 300 ° C., having a curing temperature lower than that of an organic resin substrate, and causing no crack after the curing reaction Provide the agent. SOLUTION: Conductive powder is 60% by mass to 92% by mass, epoxy resin is 1% by mass to 25% by mass, thermoplastic phenol resin having a number average molecular weight of 1000 to 5000 is 0.1% by mass to 20% by mass, and cured. The content of each composition is adjusted so that the accelerator is 0.01% by mass to 5% by mass and the organic liquid component is 2% by mass to 35% by mass. The conductive adhesive is obtained by controlling the temperature within the range of 40 ° C. and kneading for 0.2 to 10 hours. [Selection figure] None

Description

  The present invention relates to a conductive adhesive used when a semiconductor element or a chip component is bonded to a substrate such as a lead frame or when a wiring is formed on a substrate.

  Conventionally, semiconductor components or chip components such as chip resistors and chip LEDs are bonded to a substrate such as a lead frame, a printed wiring board (PWB), and a flexible printed circuit board (FPC) to achieve electrical or thermal conduction. When trying to obtain, Au-Si solder or Sn-Pb solder is generally used. However, Au-Si solder has problems that gold (Au) is expensive, lacks stress relaxation and heat resistance, and has a relatively high working temperature. On the other hand, Sn—Pb solder has a problem that lead (Pb) is harmful to the human body and its use is restricted in consideration of the influence on the environment. For this reason, it is becoming mainstream to use a conductive adhesive instead of these solders.

  In addition, it is common to form wiring on a substrate by etching a copper foil plate, but this method has limitations in forming fine wiring patterns, so jumpers, through holes, via holes, etc. For the formation (printing) of the wiring in some applications, a conductive adhesive has been used instead.

  With the miniaturization and high performance of semiconductor elements and chip parts, the amount of heat generated by the semiconductor elements and chip parts themselves is increasing. Further, in the semiconductor element and chip component mounting process and the wiring manufacturing process on the substrate, the heat treatment at 200 ° C. to 300 ° C. is repeated a plurality of times during the immersion in the solder bath and the wire bonding. For this reason, conductive adhesives used for mounting semiconductor elements and chip parts and manufacturing wiring are required to have thermal conductivity comparable to that of solder and heat resistance in a temperature range of 200 ° C to 300 ° C. .

  The conductive adhesive is a composition composed of conductive powder (conductive filler), organic resin (organic binder), solvent, catalyst, and the like. As the conductive powder, metal powders of gold, silver, copper, nickel, and powders of carbon and graphite are used. In addition, as an organic resin, the conductive powder is bound, and the conductive powder is connected by volume shrinkage, and at the same time, it acts as an epoxy resin for bonding and connecting to the adherend and an epoxy resin curing agent. A phenol resin having a molecular weight of 100 to 900 is used. However, this conductive adhesive does not have sufficient heat resistance, and there is a problem that the bond of the organic resin is broken by heat treatment at 200 ° C. to 300 ° C., and the adhesiveness is extremely lowered.

  In response to such a problem, the present applicant has proposed in Japanese Patent No. 3975728 to mix a bisallyl nadiimide resin having high heat resistance with an epoxy resin. The conductive adhesive using bisallyl nadiimide resin is superior in heat resistance in the temperature range of 200 ° C. to 300 ° C. as compared with the conventional conductive adhesive, and has adhesiveness, conductivity and thermal conductivity. Has excellent characteristics. However, since the curing temperature of the bisallylnadiimide resin is about 200 ° C. to 300 ° C., the curing temperature of this conductive adhesive is also the heat resistant temperature of an organic resin substrate generally used as a wiring substrate (continuous about 200 ° C. This conductive adhesive cannot be applied to mounting on a wiring board or manufacturing of a wiring board.

  In Japanese Patent Application Laid-Open No. 2007-51248, conductivity is also obtained using 100 parts by mass of a glycidylamine-type liquid epoxy resin and 25 parts by mass to 100 parts by mass of a bismaleimide group-containing polyimide resin having a number average molecular weight of 200 to 10000 as an organic resin. Adhesives have been proposed. In this conductive adhesive, a specific epoxy resin and a specific polyimide resin are compatible with each other at room temperature, and excellent adhesiveness can be realized in a temperature range of 150 ° C. to 260 ° C. However, this conductive adhesive also has a curing temperature higher than the heat resistance temperature of the organic resin substrate, and the cured product after the curing reaction has a very rigid structure, and has been subjected to a mechanical shock or a thermal shock. At this time, since it is inferior in stress relaxation after curing so that cracks are easily generated, application to a wiring board is difficult.

Japanese Patent No. 3975728 JP 2007-51248 A

  In view of the above problems, the present invention has heat resistance to heat treatment in a temperature range of 200 ° C. to 300 ° C., has a curing temperature lower than that of a general organic resin substrate, and is cured after a curing reaction. An object of the present invention is to provide a conductive adhesive that does not crack.

  The conductive adhesive of the present invention comprises 60% to 92% by weight of conductive powder, 1% to 25% by weight of epoxy resin, and 0.1% by weight of thermoplastic phenol resin having a number average molecular weight of 1000 to 5000. It contains 20% by mass, 0.01% to 5% by mass of a curing accelerator, and 2% by mass to 35% by mass of an organic liquid component.

  The thermoplastic phenol resin is preferably a novolac type phenol resin, a cresol type phenol resin, or a mixture thereof.

  The curing accelerator preferably contains a latent curing accelerator that does not accelerate the curing reaction between the epoxy resin and the thermoplastic phenol resin in a temperature range of 40 ° C. or lower.

  The conductive powder is preferably made of at least one selected from gold, silver, platinum, palladium, nickel, and copper. When the conductive powder is nickel powder or copper powder, the nickel powder or copper powder is preferably coated with at least one metal component selected from gold, silver, platinum, and palladium.

Tap density of the conductive powder is preferably ^{2.8g / cm 3 ~6.0g / cm 3} .

  Moreover, the manufacturing method of the electrically conductive adhesive of this invention is 0 to 92 mass% of conductive powders, 1 mass% to 25 mass% of epoxy resins, and 0 of thermoplastic phenol resins having a number average molecular weight of 1000 to 5000. 0.1 mass% to 20 mass%, the curing accelerator is 0.01 mass% to 5 mass%, and the organic liquid component is 2 mass% to 35 mass%, respectively, in the temperature range of 0 ° C. to 40 ° C., It is characterized by kneading for 0.2 hours to 10 hours.

  The conductive adhesive of the present invention has heat resistance in a temperature range of 200 ° C. to 300 ° C., a curing temperature lower than the heat resistance temperature of a general organic resin substrate, and high stress relaxation after a curing reaction. A conductive adhesive is provided.

  As a result of intensive studies on the conductive adhesive, the present inventors use a thermoplastic phenol resin having a number average molecular weight larger than that of a conventional curing agent, that is, a number average molecular weight in the range of 1000 to 5000. The knowledge that it is possible to obtain a conductive adhesive having all the characteristics of not only conductivity, adhesiveness and thermal conductivity, but also heat resistance, low curing temperature, and high stress relaxation after reaction curing. Thus, the present invention has been completed. Hereinafter, the present invention will be described in detail.

1. Conductive Adhesive The conductive adhesive of the present invention comprises a conductive powder of 60% to 92% by mass, an epoxy resin of 1% to 25% by mass, and a thermoplastic phenol resin having a number average molecular weight of 1000 to 5000 of 0.00%. 1% to 20% by mass, 0.01% to 5% by mass of a curing accelerator, and 2% to 35% by mass of an organic liquid component.

(1) Composition First, each component which comprises the conductive adhesive of this invention is demonstrated.

(1-a) Conductive powder The conductive powder (conductive filler) forms a network in the conductive adhesive and imparts conductivity to the conductive adhesive.

  In the composition constituting the conductive adhesive of the present invention, the content of the conductive powder is 60% by mass to 92% by mass, preferably 65% by mass to 90% by mass, and more preferably 70% by mass to 85% by mass. It is. When the content of the conductive powder is less than 60% by mass, sufficient conductivity and thermal conductivity cannot be obtained. On the other hand, when the content of the conductive powder exceeds 92% by mass, the content of other components such as an epoxy resin is reduced, resulting in a problem that the adhesive strength is reduced.

In order to sufficiently secure the conductivity of the conductive powder, the volume resistivity of the conductive powder needs to be 1 × 10 ⁻³ Ω · cm or less. As such a conductive powder, a metal made of gold (Au), silver (Ag), platinum (Pt), palladium (Pd), nickel (Ni), copper (Cu), an alloy thereof, or a mixture thereof Powders can be used. In addition, since these metal powders are excellent not only in electroconductivity but also in thermal conductivity, they can be suitably used as the electroconductive powder of the present invention from this point of view.

  Among these metal powders, copper powder and nickel powder have a problem that their surfaces are easily oxidized in air. For this reason, when using these copper powder and nickel powder, it is preferable to coat | cover the surface with the metal components which are not oxidized in air, such as gold | metal | money, silver, platinum, and palladium. When copper powder or nickel powder that is not coated as described above is used as the conductive powder, it is preferable to cure the obtained conductive adhesive in a reducing atmosphere.

  The shape of the conductive powder is not particularly limited, and flakes, spheres, needles, or a mixture of these can be used. In view of the above, it is preferable to use flaky conductive powder.

  Further, the size of the conductive powder is not particularly limited and can be appropriately selected according to the intended application. However, in consideration of printability, the average particle size of the conductive powder is 10 μm or less. It is preferable that it is 3 μm or less. In the present invention, the average particle diameter means a particle diameter (D50) in which the cumulative volume is 50% of the total volume of all particles when the number of particles in each particle diameter is accumulated from the smaller particle diameter. Means. The method for obtaining the average particle diameter (D50) is not particularly limited, but can be obtained, for example, from the volume integrated value measured with a laser light diffraction / scattering particle size analyzer.

The tap density of the conductive powder is preferably 2.8 g / cm ^{3 to} 6.0 g / cm ³ , more preferably 3.0 g / cm ³ in consideration of ease of kneading when kneading with a resin or a solvent. ~5.5g / cm ^3, more preferably to ^{3.2g / cm 3 ~5.0g / cm 3} . When the tap density is less than 2.8 g / cm ³ , the conductive powder may aggregate and secondary particles having a large particle size may be formed. On the other hand, when the tap density exceeds 6.0 g / cm ³ , the particle size distribution may become wide. For this reason, in any case, the dispersibility of the conductive powder is lowered, and accordingly, the conductivity and thermal conductivity of the conductive adhesive may be lowered. In addition, in this invention, a tap density means the bulk density after tapping the sample powder extract | collected to the container 100 times based on JISZ-2504.

(1-b) Epoxy Resin The epoxy resin constitutes an organic binder together with the thermoplastic phenol resin, is cured by reaction with the thermoplastic phenol resin, and imparts adhesiveness to the conductive adhesive.

  In the composition constituting the conductive adhesive of the present invention, the content of the epoxy resin is 1% by mass to 25% by mass, preferably 2% by mass to 15% by mass, more preferably 5% by mass to 12% by mass. To do. When the content of the epoxy resin is less than 1% by mass, sufficient adhesion cannot be obtained. On the other hand, when the content of the epoxy resin exceeds 25% by mass, the content of the conductive powder is less than 60% by mass in relation to other components, and the conductivity and thermal conductivity are reduced.

  The epoxy resin is not particularly limited as long as the curing temperature of the obtained conductive adhesive can be controlled in the temperature range of 100 ° C. to 200 ° C. in relation to the thermoplastic phenol resin, and is well known. Epoxy resins can be used. Examples of such an epoxy resin include bisphenol A type liquid epoxy resin (epoxy equivalent: 170 g / eq to 190 g / eq, viscosity (25 ° C.): 3500 mPa · s to 25000 mPa · s), cresol novolac type epoxy resin (epoxy Equivalent: 190 g / eq to 220 g / eq, softening point: 54 ° C. to 100 ° C., melt viscosity (150 ° C.): 0.5 dPa · s to 35.0 dPa · s, bisphenol F type epoxy resin (epoxy equivalent: 155 g / eq to 180 g / eq, viscosity (25 ° C.): 1100 mPa · s to 4500 mPa · s). More specifically, bisphenol A diglycidyl ether, novolac glycidyl ether, bisphenol F diglycidyl ether, epoxidized soybean oil, 3,4, which are used for the production and adhesion of electronic materials. Epoxy-6 methyl cyclohexyl methyl carboxylate, 3,4 epoxy cyclohexyl methyl carboxylate, tetraglycidyl diaminodiphenylmethane, etc. can be used, and a mixture selected from two or more of these can also be used. it can.

  However, considering that the conductive adhesive of the present invention is used for electronic materials, the content of halogen ions such as chlorine ions in the epoxy resin is preferably regulated to 800 ppm or less, and regulated to 500 ppm or less. It is more preferable. Also, considering that the conductive adhesive according to the present invention can be obtained by kneading conductive powder, epoxy resin, thermoplastic phenol resin, curing accelerator and organic liquid component, an epoxy resin that is liquid at room temperature is used. It is preferable to do.

  The epoxy equivalent of the epoxy resin is preferably in the range of 120 g / eq to 1000 g / eq, more preferably in the range of 150 g / eq to 300 g / eq, and still more preferably in the range of 170 g / eq to 190 g / eq. Here, the epoxy equivalent means the mass of an epoxy resin containing one equivalent of an epoxy group, and is a value represented by (molecular weight of epoxy resin) / (number of epoxy groups in one molecule). If the epoxy equivalent is in the above range, a conductive adhesive using the epoxy equivalent can have an appropriate viscosity and sufficient heat resistance. On the other hand, when the epoxy equivalent is less than 120 g / eq, the viscosity of the conductive adhesive is lowered, and workability may be lowered. On the other hand, when the epoxy equivalent exceeds 1000 g / eq, the molecular chain becomes long, and the heat resistance of the conductive adhesive using the same may decrease.

(1-c) Thermoplastic phenol resin The thermoplastic phenol resin constitutes an organic binder together with the epoxy resin, and functions as a curing agent for the epoxy resin. As an epoxy resin curing agent, amine compounds, amide compounds, acid anhydride compounds, phenol compounds, etc. are widely used, but in the present invention, in the cured product after the curing reaction with the epoxy resin, From the viewpoint of imparting a moderately rigid structure to the cured product by incorporating an aromatic six-membered ring, it is necessary to use a specific thermoplastic phenol resin.

  Even in conventional conductive adhesives, a thermoplastic phenol resin is sometimes used as a curing agent for an epoxy resin. In this case, a thermoplastic phenol resin having a number average molecular weight in the range of 100 to 900 is generally used. It was used.

  In contrast, the present invention is characterized in that it is used as a thermoplastic phenol resin having a number average molecular weight of 1000 to 5000, preferably 1500 to 4500, and more preferably 2000 to 4000. When the number average molecular weight of the thermoplastic resin is in such a range, the properties of the thermoplastic resin are maintained even after the curing reaction with the epoxy resin. That is, when the number average molecular weight is in such a range, the aromatic six-membered ring is present in a moderately dense density in one molecule of the thermoplastic phenol resin, and this structure is obtained by a curing reaction with the epoxy resin. It will be taken in the cured epoxy resin. As a result, even in the cured product after the curing reaction, the aromatic six-membered ring can be present in a moderately dense manner, so this cured product has a moderately rigid structure and is excellent in heat resistance. Not only can the occurrence of cracks be suppressed. Furthermore, since intrusion of other molecules such as water is prevented, moisture resistance and chemical resistance can be improved.

  If the number average molecular weight of the thermoplastic phenol resin is less than 1000, the aromatic six-membered rings cannot be present densely, so the cured product after the curing reaction cannot take a reasonably rigid structure, and is heat resistant. Is inferior. On the other hand, if the number average molecular weight of the thermoplastic phenol resin exceeds 5,000, aromatic six-membered rings exist in an extremely dense manner, so that the cured product after the curing reaction takes a very rigid structure. As a result, the cured product after the reaction curing is excellent in heat resistance, but becomes hard and brittle, and when subjected to a mechanical impact or a thermal impact, the occurrence of cracks cannot be suppressed. In other words, the conductive adhesive of the present invention balances the flexibility of the epoxy resin and the reasonably rigid structure of the thermoplastic phenol resin by using a thermoplastic phenol resin having a number average molecular weight in the above range. In addition to being excellent in heat resistance, it is possible to suppress the occurrence of cracks.

  The thermoplastic phenol resin of the present invention is not particularly limited as long as the number average molecular weight is in the above range, but from the viewpoint of ensuring high moisture resistance and conductivity, a novolak type phenol resin (hydroxyl equivalent: 100 g). / Eq to 110 g / eq, softening point: 75 ° C. to 125 ° C.), cresol type phenol resin (hydroxyl equivalent: 110 g / eq to 120 g / eq, softening point: 80 ° C. to 130 ° C.), or a mixture thereof. It is preferable.

  In the composition constituting the conductive adhesive of the present invention, the content of the thermoplastic phenol resin needs to be 0.1% by mass to 20% by mass. If the content of the thermoplastic phenol resin is less than 0.1% by mass, sufficient adhesive strength cannot be obtained. On the other hand, when the content of the thermoplastic phenol resin exceeds 20% by mass, the content of the conductive powder is less than 60% by mass in relation to other compositions, and the conductivity and thermal conductivity are reduced. The content of the thermoplastic phenol resin is preferably 1% by mass to 15% by mass, and more preferably 3% by mass to 10% by mass from the viewpoint of further improving the adhesive strength and heat resistance strength at room temperature. More preferred.

  When an epoxy resin having an epoxy equivalent in the range of 120 g / eq to 1000 g / eq is used, the hydroxyl equivalent (OH equivalent) of the thermoplastic phenol resin is preferably 100 g / eq to the solvent. Those in the range of 200 g / eq, more preferably in the range of 100 g / eq to 160 g / eq, still more preferably in the range of 100 g / eq to 120 g / eq are used. Here, OH equivalent means the mass of the thermoplastic phenol resin containing 1 equivalent of OH groups, and is a value represented by (molecular weight of thermoplastic phenol resin) / (number of OH groups in one molecule).

(1-d) Curing accelerator Since a curing accelerator can exhibit more stable storage stability as the reaction does not start at a high temperature, it is preferable to use a curing accelerator having a high temperature range for promoting the curing reaction.

  Such a curing accelerator is preferably a curing reaction between an epoxy resin and a thermoplastic phenol resin in a temperature range of 40 ° C. or lower, more preferably a temperature range of 60 ° C. or lower, and even more preferably a temperature range of 70 ° C. or lower. A curing accelerator (hereinafter referred to as “latent curing accelerator”) that does not accelerate the process can be suitably used. By using such a latent curing accelerator, in the present invention, even when a thermoplastic phenol resin having a number average molecular weight of 1000 to 5000 is used, a composition including conductive powder can be uniformly formed. It becomes easy to knead. As a result, the network structure by the conductive powder can be constructed over the entire cured product after the curing reaction, and the conductivity and thermal conductivity of the conductive adhesive can be further improved. On the other hand, when using what accelerates | stimulates hardening reaction of an epoxy resin and a thermoplastic phenol resin in the temperature range of 0 degreeC-40 degreeC as a hardening accelerator, the composition which comprises a conductive adhesive is uniformly formed. It becomes difficult to knead.

  Examples of the latent curing accelerator include triphenylphosphine and imidazoles such as 2-ethyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-. Examples include 5-hydroxymethylimidazole and 2-heptadecylimidazole.

  In the composition constituting the conductive adhesive of the present invention, the content of the curing accelerator needs to be 0.01% by mass to 5% by mass. If the content of the curing accelerator is less than 0.01% by mass, sufficient adhesive strength cannot be obtained. On the other hand, when the content of the curing accelerator exceeds 5% by mass, the curing time is shortened, so that the kneading time for obtaining the conductive adhesive according to the present invention is insufficient. In addition, it is preferable that content of a hardening accelerator shall be 0.2 mass%-3.0 mass% from a viewpoint of further improving the adhesive strength and heat-resistant strength in room temperature.

(1-e) Organic liquid component The organic liquid component is used as a viscosity modifier for a conductive adhesive. Moreover, when using a solid epoxy resin or a solid thermoplastic phenol resin, it is used as these solvents.

  In the composition constituting the conductive adhesive of the present invention, the content of the organic liquid component is 2% by mass to 35% by mass, preferably 3% by mass to 30% by mass, more preferably 4% by mass to 20% by mass. And When the content of the organic liquid component is less than 2% by mass, it is difficult to uniformly knead the compositions (1-a) to (1-d). On the other hand, when the content of the organic liquid component exceeds 35% by mass, the viscosity of the obtained conductive adhesive becomes too low, so that the conductive adhesive cannot be uniformly applied or printed.

  As the organic liquid component, a composition of a conductive adhesive that needs to be dissolved at the time of kneading, specifically, one that is soluble in an epoxy resin, a thermoplastic phenol resin, or the like is used. Examples of such organic liquid components include 2,2,4-trimethyl-3-hydroxydipentane isobutylate, 2,2,4-trimethylpentane 1,3-, which does not react with an epoxy resin and a curing agent. Isobutylate, isobutylbutyrate, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether and the like can be used. In addition, phenylglycidyl ether, ethylene glycol diglycidyl ether, t-butylphenyl glycidyl ether, ethylhexyl glycidyl ether, and 3-aminopropyltrimethyl ether react with epoxy resin and thermoplastic phenol resin during heating. Ethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, and the like can also be used.

(1-f) Others The conductive adhesive of the present invention has the above-described compositions (1-a) to (1-e) as essential components, but other compositions may be used depending on the application. It can also be added as appropriate. For example, in order to adjust the viscosity of the conductive adhesive, a viscosity modifier made of an organic substance other than a liquid or a fine ceramic powder can be added. Such viscosity modifiers, for example, organic substances such as fatty acid amides and oxidized polyolefins, ceramic powder such as silica powder and carbon powder in the range a specific surface area of 10m ² / g~500m ² / g Can be mentioned. Moreover, liquid additives, such as organic acids and formaldehyde, can also be added for the purpose of improving electroconductivity, ie, obtaining the conductive adhesive which has a low resistance value. Furthermore, when nickel powder or copper powder is used as the conductive powder, an antioxidant such as oleic acid can be added to prevent such oxidation.

  In addition, in the conductive adhesive of the present invention, the above-described thermoplastic resin as a curing agent for the epoxy resin, as long as the balance between the flexibility of the epoxy resin and the moderately rigid structure of the thermoplastic phenol resin is not lost. Curing agents other than phenolic resins can be used by mixing with thermoplastic phenolic resins. Examples of such curing agents include dicyandiamide, acid anhydride curing agents, and epoxyamine duct compounds. In this case, the ratio of the thermoplastic phenol resin and the curing agent other than the thermoplastic phenol resin is preferably about 10: 0.1 to 3.0.

  However, when these components are added, the content is less than 3% by mass, preferably less than 1% by mass. When the content of these additive components exceeds 3% by mass, the object of the present invention may not be achieved in relation to the compositions (1-a) to (1-e).

(2) Characteristics of conductive adhesive As described above, the conductive adhesive of the present invention has the composition of (1-a) to (1-e) or (1-a) to (1-f). Since the content is appropriately controlled and these compositions are uniformly dispersed, the composition has adhesiveness, conductivity and thermal conductivity equivalent to or higher than those of conventional conductive adhesives.

  Further, since it has a moderately rigid structure after the curing reaction, it has excellent heat resistance and crack resistance. Furthermore, since such a structure can effectively prevent other molecules such as water from entering, it can be said that it is excellent in moisture resistance and chemical resistance.

  In addition, in the present invention, the curing temperature of the conductive adhesive obtained by a specific epoxy resin and a thermoplastic phenol resin, or a combination of these with a curing accelerator is 100 ° C. to 200 ° C., preferably 100 ° C. to It can be set to 180 ° C, more preferably 100 ° C to 150 ° C. That is, since the curing temperature of the conductive adhesive of the present invention is lower than the heat resistance temperature (about 200 ° C.) of a general organic resin substrate, it can be suitably used for these organic resin substrates. it can. The curing temperature of the conductive adhesive refers to a temperature at which the conductive adhesive reacts by being heated and becomes a three-dimensional structure or a network structure. After the curing reaction, the various characteristics of the conductive adhesive are stable, so the curing reaction proceeds while changing the heating temperature and heating time using a thermal analyzer, etc. By measuring, the curing temperature can be determined.

  In the conductive adhesive of the present invention, the curing time can be preferably 1 minute to 180 minutes, more preferably 1 minute to 60 minutes. If the curing time is less than 1 minute, the storage stability of the conductive adhesive may be inferior. On the other hand, if it exceeds 180 minutes, the time from application or printing of the conductive adhesive to curing is too long, and thus the productivity deteriorates.

  Furthermore, in the conductive adhesive of the present invention, the viscosity at room temperature (25 ° C.) is preferably adjusted to 5 Pa · s to 50 Pa · s, and more preferably adjusted to 10 Pa · s to 40 Pa · s. . If the viscosity of the conductive adhesive is out of the above range, the conductive adhesive may not be applied (printed) with a uniform thickness on the substrate. The viscosity of the conductive adhesive can be measured with an HBT type rotational viscometer.

2. Next, a method for producing a conductive adhesive of the present invention will be described. In addition, since the manufacturing method of the conductive adhesive of this invention is fundamentally the same as the manufacturing method of the conductive adhesive of a prior art, the characteristic part of this invention is demonstrated below.

  As described above, the method for producing a conductive adhesive of the present invention is characterized in that a thermoplastic phenol resin having a number average molecular weight larger than that of a conventional one is used as a curing agent. Specifically, the conductive powder is 60 mass% to 92 mass%, the epoxy resin is 1 mass% to 25 mass%, the thermoplastic phenol resin having a number average molecular weight of 1000 to 5000 is 0.1 mass% to 20 mass%, The content of each composition is adjusted so that the curing accelerator is 0.01% by mass to 5% by mass and the organic liquid component is 2% by mass to 35% by mass. It is characterized by being controlled to a temperature range of -40C to kneading for about 0.2-10 hours. In addition, in addition to the said composition, when adding a viscosity modifier, antioxidant, etc., it is necessary to adjust so that the content may be 3 mass% or less. Thereby, the conductive adhesive which has the characteristic mentioned above can be obtained easily.

  At the time of kneading, the temperature of the composition needs to be controlled in a temperature range of 0 ° C to 40 ° C, preferably 10 ° C to 30 ° C, more preferably 15 ° C to 30 ° C. If the temperature of the composition is less than 0 ° C., the viscosity at the time of kneading becomes too high, so that the composition cannot be uniformly dispersed. On the other hand, when the temperature of the composition exceeds 40 ° C., the volatilization amount of the liquid component increases, and it becomes difficult to keep the viscosity constant during kneading.

  The kneading time is not particularly limited as long as each component in the composition is uniformly dispersed, but is kneaded for about 0.2 hours to 10 hours, preferably about 0.2 hours to 4 hours. It is enough.

  Moreover, in the manufacturing method of the conductive adhesive of this invention, the kneading | mixing means of the composition which comprises this is not specifically limited, A well-known means is employable. Specifically, a centrifugal stirring mixer, a planetary mixer, a three-roll kneader, or the like can be employed.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

(Examples 1-16, Comparative Examples 1-10)
As the composition of the conductive adhesive, conductive powder, epoxy resin, thermoplastic phenol resin, curing accelerator, organic liquid component, additive and ceramic powder described in Table 1 were prepared. As shown in Table 2, the content of each composition was adjusted and kneaded using a three-roll kneader (Inoue Seisakusho Co., Ltd.) to obtain a conductive adhesive. The temperature and kneading time of the composition at this time were as shown in Table 2. In Examples 7 and 8, oleic acid was used for the purpose of preventing oxidation of the nickel powder or silver-coated nickel powder used as the conductive powder. In Example 9, ceramic powder (silica was used for the purpose of adjusting the viscosity of the conductive adhesive. Powder) was further added.

  The viscosity of the conductive adhesive thus obtained was measured using an HBT viscometer (manufactured by Brookfield). Moreover, the curing temperature and the curing time were measured using an oven furnace and a stopwatch. These results are shown in Table 3.

[Conductivity test]
A conductive adhesive is printed in a rectangular shape of 2 mm x 5 mm between the electrodes 2 mm apart on the alumina substrate, and left in an oven at 150 ° C for 60 minutes to conduct conductive bonding. After curing the agent, the sample was obtained by cooling to room temperature. The area resistance value R (mΩ) between the electrodes of this sample was measured using a digital multimeter (Advantest). Next, the film thickness t (μm) of the conductive adhesive printed on the alumina substrate was measured. Then, by substituting these values into ρ = R × t × 10 ⁻⁸ , the volume resistivity ρ (Ω · cm) was obtained, and the conductivity was evaluated.

[Adhesive strength test]
A conductive adhesive was dropped on a silver-plated 2.5 cm × 2.5 cm copper substrate, and 20 1.5 mm square silicon chips were placed thereon. This was left in an oven at 150 ° C. for 60 minutes to cure the conductive adhesive, confirm that the silicon chip was fixed, and then cooled to room temperature to obtain a sample. A force is applied from the horizontal direction to the silicon chip on the surface of this sample, and the force when the silicon chip peels from the copper substrate (hereinafter referred to as “adhesive strength”) is used as an adhesive strength tester (manufactured by Imada Co., Ltd.). It measured using. The same test was performed on 20 samples, and the adhesive strength was measured for each of them. The average value of these was obtained as the adhesive strength F, and the adhesion at room temperature was evaluated.

[Heat resistance test]
The sample obtained in the same manner as in the adhesive strength test was left on a hot plate heated to 280 ° C. for 20 seconds, and then a force was applied from the horizontal direction to the silicon chip on the surface of the sample while being heated, The force when the silicon chip peeled from the copper substrate (hereinafter referred to as “heat resistance strength”) was measured using a handy force gauge. The same test was performed on 20 samples, the heat resistance was measured for each, and the average value of these was determined as the first heat resistance F ₂₈₀ and the heat resistance at 280 ° C. was evaluated. Further, the test was performed in the same manner except that the heating temperature of the hot plate was set to 350 ° C., and the average value of the heat resistant strength at this time was obtained as the second heat resistant strength F ₃₅₀ to evaluate the heat resistance at 350 ° C. It was.

[Moisture resistance test]
As a sample, ten square conductive adhesive films having a thickness of 100 μm and 1 cm × 1 cm were produced, and the dry mass (W ₁ ) was measured. Next, this sample was allowed to stand for 120 hours in a high-temperature tank maintained at a temperature of 85 ° C. and a humidity of 85% to absorb moisture in the tank. After elapse of a predetermined time, the sample was taken out from the high temperature bath, and the mass (W ₂ ) after moisture absorption was measured. From these values, the moisture absorption rate W of the following formula was obtained, and the moisture resistance was evaluated.
Moisture absorption rate (%): W = (W ₂ −W ₁ ) / W ₁ × 100

[Heat cycle test]
A conductive adhesive was printed in a square shape of 100 μm thickness and 1 cm × 1 cm on a 2.5 cm × 2.5 cm copper substrate plated with silver, and this was left in an oven at 150 ° C. for 60 minutes. Then, after the conductive adhesive was cured, a sample was obtained by cooling to room temperature. This sample was subjected to a heat cycle test in which a cycle in which the sample was allowed to stand for 30 minutes in an environment of −40 ° C. and then left for 30 minutes in an environment of 150 ° C. was repeated 500 times. After the heat cycle test was completed, the presence or absence of cracks or peeling was observed using an electron microscope (JSM-6510, manufactured by JEOL Ltd.), and crack resistance was evaluated.

[Comprehensive evaluation]
For the above six evaluation items (ρ, F, F ₂₈₀ , F ₃₅₀ , W, crack resistance), the volume resistivity ρ is 1 × 10 ⁻³ Ω · cm or less, the adhesive strength F is 35 N or more, one heat resistance F ₂₈₀ is more than 25 N, the second heat intensity F ₃₅₀ is more than 15N, with moisture absorption W satisfies the requirement of 0.2% or less, not cracking or peeling discoveries and industrial use to What was judged to be possible was evaluated as “good”. On the other hand, even if one of the above requirements is not satisfied, one where cracks or peeling is found, or one that satisfies the above requirements and no crack or peeling is found, the curing time is 1 minute to 180 minutes. Those that were not in the range of minutes and were judged to be unusable industrially were evaluated as “bad” (x).

(Evaluation)
From Table 3, the conductive adhesives of Examples 1 to 16 belonging to the technical scope of the present invention were excellent in all of conductivity (thermal conductivity), adhesiveness, heat resistance, moisture resistance, and crack resistance. It was confirmed to show characteristics. However, since the content of the epoxy resin is larger than that of Examples 1 to 13 and 16, and the content of the conductive powder (silver powder a) is small in Example 14, the overall evaluation is “good”. The volume resistivity ρ was a high value. Moreover, since Example 15 had much content of electroconductive powder (silver powder b) compared with Examples 1-13 and 16 and there was little content of an epoxy resin, adhesive strength F was a low value. .

  The curing temperatures of the conductive resins of Examples 1 to 16 were all in the temperature range of 120 ° C. to 180 ° C., and were confirmed to be lower than the heat resistance temperature of a general organic resin substrate. Moreover, it was confirmed that the curing time is in an appropriate range. Therefore, it can be said that the conductive adhesive of the present invention can be used for general organic resin substrates and can be industrially used.

  On the other hand, the conductive adhesives of Comparative Examples 1 to 10 could not achieve the desired characteristics in at least one of conductivity, adhesiveness, heat resistance, moisture resistance, and crack resistance. .

Comparative Examples 1 to 5 are examples in which the number average molecular weight of the thermoplastic phenol resin deviates from the range defined in the present invention. In Comparative Examples 1 to 3, since the thermoplastic phenol resin e having a number average molecular weight of less than 1000 was used, both the first heat resistance strength F ₂₈₀ and the second heat resistance strength F ₃₅₀ were low, and the moisture absorption rate W was also 0. It has exceeded 2%. In the conductive adhesive of Comparative Example 3, the first heat resistance F ₂₈₀ exceeds 25N. This is because the first heat resistance F ₂₈₀ is slightly improved by the combination of the epoxy resin a and the epoxy resin b. it is conceivable that. On the other hand, the second heat resistance strength F ₃₅₀ is less than 15N. Therefore, when the thermoplastic phenol resin e is used, the heat resistance in the high temperature range cannot be sufficiently improved. I understand. Similarly, in Comparative Example 4, since the thermoplastic phenol resin f having a number average molecular weight of less than 1000 was used, both the first heat resistance strength F ₂₈₀ and the second heat resistance strength F ₃₅₀ are low values. In Comparative Example 5, since the thermoplastic phenol resin g having a number average molecular weight exceeding 5000 was used, it could not be sufficiently kneaded, and the adhesive strength F was low. Moreover, since the cured epoxy resin after the curing reaction had a very rigid structure and was too hard and brittle, the occurrence of cracks was observed.

Comparative Examples 6 and 7 are examples in which the content of the conductive powder deviates from the range defined in the present invention. In Comparative Example 6, since the content of the conductive powder (silver powder a) was too small, the adhesive strength F was sufficient, but the volume resistivity ρ showed a high value. Further, the first heat resistance strength F ₂₈₀ and the second heat resistance strength F ₃₅₀ were also low values. On the other hand, in Comparative Example 7, since the content of the conductive powder (silver powder b) was too large, the contents of the epoxy resin a and the thermoplastic phenol resin a were relatively decreased, and the adhesive strength F, the first heat resistance strength F ₂₈₀ and second heat resistance strength F ₃₅₀ were low values. In Comparative Example 7, although the content of the conductive powder is large, the volume resistivity ρ shows a relatively high value. This is because the content of the epoxy resin a and the thermoplastic phenol resin a is too small with respect to the content of the conductive powder, so that the composition is not uniformly kneaded and the network by the conductive powder is not sufficiently constructed. This is probably because

Comparative Examples 8 and 9 are examples in which the content of the curing accelerator deviates from the range defined in the present invention. In Comparative Example 8, the volume resistivity ρ, the adhesive strength F, the first heat resistance strength F ₂₈₀ , the second heat resistance strength F _350, and the moisture absorption rate W all satisfied the above-mentioned standard values, and no cracks were found. However, since the content of the curing accelerator exceeded 5.0% by mass, the curing time was short, and the curing proceeded before the conductive adhesive was applied to a predetermined position. In addition, it was confirmed that storage is difficult and it cannot be used industrially. In Comparative Example 9, since no curing accelerator was contained, the curing reaction between the epoxy resin a and the thermoplastic phenol resin a was not accelerated, and the adhesive strength F was a low value. Moreover, since it softened by heating, the value of the first heat resistance strength F ₂₈₀ and the second heat resistance strength F ₃₅₀ became zero. Furthermore, the moisture absorption rate W was also a high value.

Comparative Example 10 is an example in which the manufacturing conditions deviate from the range defined in the present invention. In Comparative Example 10, the temperature of the composition at the time of kneading exceeded 40 ° C., so the volatilization amount of the liquid component was large during kneading, and the viscosity became high.

Claims (7)

  60% by mass to 92% by mass of conductive powder, 1% by mass to 25% by mass of epoxy resin, 0.1% by mass to 20% by mass of thermoplastic phenol resin having a number average molecular weight of 1000 to 5000, and 0 of curing accelerator. A conductive adhesive comprising 0.01% by mass to 5% by mass and 2% by mass to 35% by mass of an organic liquid component.   The conductive adhesive according to claim 1, wherein the thermoplastic phenol resin is a novolac type phenol resin, a cresol type phenol resin, or a mixture thereof.   The conductive adhesive according to claim 1, wherein the curing accelerator includes a latent curing accelerator that does not accelerate a curing reaction between an epoxy resin and a thermoplastic phenol resin in a temperature range of 40 ° C. or less.   The conductive adhesive according to claim 1, wherein the conductive powder is made of at least one selected from gold, silver, platinum, palladium, nickel, and copper.   2. The conductive adhesive according to claim 1, wherein the conductive powder is nickel powder or copper powder coated with at least one metal component selected from gold, silver, platinum, and palladium. Tap density of the conductive powder is ^{2.8g / cm 3 ~6.0g / cm 3} , a conductive adhesive according to claim 1.   The conductive powder is 60% by mass to 92% by mass, the epoxy resin is 1% by mass to 25% by mass, the thermoplastic phenol resin having a number average molecular weight of 1000 to 5000 is 0.1% by mass to 20% by mass, and the curing accelerator is 0%. The content of each composition is adjusted so that the organic liquid component may be 0.01 mass% to 5 mass% and the organic liquid component is 2 mass% to 35 mass%, and the temperature of these compositions is set to a temperature of 0C to 40C. A method for producing a conductive adhesive, which is controlled within a range and kneaded for 0.2 to 10 hours.