TW202246423A - Conductive paste and multilayer substrate using same - Google Patents

Abstract

The present invention provides: a conductive paste which has excellent thermal conductivity, electrical conductivity, fillability of a hole that is formed in a substrate, and long-term reliability; and a multilayer substrate which uses this conductive paste. This conductive paste contains, per 100 parts by mass of a liquid epoxy resin (A): 2,300 to 5,000 parts by mass of a metal filler (B) which contains two or more metal powders including at least one metal powder (B1) that comprises a high-melting-point metal which contains silver and/or copper, while having a melting point of 800 DEG C or more, and at least one metal powder (B2) that comprises a low-melting-point metal which is composed of an alloy of two or more metals selected from the group consisting of tin, lead, bismuth and indium, while having a melting point of 180 DEG C or less; 10 to 40 parts by mass of a curing agent (C) which contains a hydroxyl group-containing aromatic compound; and 60 to 230 parts by mass of a flux (D).

Description

Conductive paste and multilayer substrate using same

field of invention The present invention relates to a conductive paste excellent in thermal conductivity, electrical conductivity, filling property for holes formed on a substrate, and long-term reliability, and a multilayer substrate using the same.

Background technique As for the conductive paste used for filling the holes of the substrate, etc., Patent Document 1 describes a conductive paste which is mixed with a conductive filler, a flux, and a hardener in a thermosetting resin. When it is heated under certain conditions, the resin will harden, and the metal powder will melt and become metallized.

However, since the conductive paste described in Patent Document 1 has a small content of metal powder, there is a problem that the thermal conductivity of the conductive paste is insufficient. On the other hand, if the content of the metal powder is increased in order to improve thermal conductivity, the viscosity of the conductive paste will increase, and there is a problem that the filling of the holes of the substrate is poor.

Patent Document 2 discloses a thermally conductive conductive paste. However, when it is used for hole filling of multilayer substrates, there is still room for improvement in long-term reliability.

prior art literature patent documents Patent Document 1: Japanese Patent Laid-Open No. 2008-108629 Patent Document 2: Japanese Patent Laid-Open No. 2019-165155

Summary of the invention The problem to be solved by the invention The present invention is made in view of the above, and an object of the present invention is to provide a conductive paste excellent in thermal conductivity, electrical conductivity, filling property for holes formed on a substrate, and long-term reliability, and a multilayer substrate using the same.

means to solve problems The conductive paste of the present invention contains: relative to 100 parts by mass of (A) liquid epoxy resin; The powder includes at least one type of metal powder (B1) and at least one type of metal powder (B2), the above-mentioned metal powder (B1) has a high melting point metal with a melting point of 800°C or higher, the high melting point metal contains silver and/or copper, and the above-mentioned The metal powder (B2) has a low-melting-point metal having a melting point of 180°C or lower, and the low-melting-point metal is composed of two or more alloys selected from the group consisting of tin, lead, bismuth, and indium; 10 to 40 parts by mass (C) curing agent, which contains a hydroxyl-containing aromatic compound; and 60-230 parts by mass of (D) fluxing agent.

The content ratio ((B1)/(B2)) of the metal powder (B1) having a high melting point metal and the metal powder (B2) having a low melting point metal in the metal filler (B) may be 0.3 to 1.0.

The above-mentioned hydroxyl-containing aromatic compound may be at least one selected from the group consisting of phenol-based curing agents and naphthol-based curing agents.

The multi-layer substrate of the present invention is formed by alternately laminating a plurality of layers of conductive layers and insulating layers. The multi-layer substrate is formed with a hole penetrating at least one of the above-mentioned insulating layers, and the hardened product of the above-mentioned conductive paste is filled in the above-mentioned hole. In the cured product, the above-mentioned conductive layers located at both ends of the above-mentioned hole are connected to each other.

Invention effect According to the conductive paste of the present invention, excellent thermal conductivity, electrical conductivity, filling properties of holes formed on a substrate, and long-term reliability can be obtained.

form for carrying out the invention As mentioned above, the conductive paste of the present invention contains: relative to 100 parts by mass of (A) liquid epoxy resin; The above metal powders include at least one type of metal powder (B1) and at least one type of metal powder (B2), the metal powder (B1) has a high melting point metal with a melting point of 800°C or higher, and the high melting point metal contains silver and/or Copper, the above-mentioned metal powder (B2) has a low melting point metal with a melting point of 180°C or lower, and the low melting point metal is composed of two or more alloys selected from the group consisting of tin, lead, bismuth and indium; 10~ 40 parts by mass of (C) hardener containing a hydroxyl-containing aromatic compound; and 60-230 parts by mass of (D) flux.

The use of the conductive paste is not particularly limited, but it is suitable for use as a composition for filling holes, and the holes are formed on a multi-layer substrate in which multiple layers of conductive layers and insulating layers are alternately laminated. The hole formed on the multilayer substrate may be a hole penetrating through at least one insulating layer, or may be a hole penetrating multiple conductive layers and insulating layers. When the conductive paste of the present invention is used in a multi-layer substrate, the conductive paste of the present invention is filled in the holes, and the conductive layers at both ends of the holes are connected to each other through the cured product obtained by hardening the conductive paste.

Liquid epoxy resins are not particularly limited as long as they contain epoxy groups in the molecule and are liquid at room temperature (25°C). Specific examples include: bisphenol A epoxy resin, bisphenol F epoxy resin , Glycidylamine-based epoxy resin, glycidyl ether-based epoxy resin, etc.

The epoxy equivalent of the liquid epoxy resin is not particularly limited, preferably 100-500 g/eq, more preferably 200-400 g/eq. When the epoxy equivalent is within the above range, a conductive paste excellent in filling properties of holes formed on a substrate can be easily produced.

The metal filler (B) contains: metal powder (B1) having a high melting point metal with a melting point of 800°C or higher; and metal powder (B2) having a low melting point metal with a melting point of 180°C or lower; and by heating, the metal powder (B2) ) will melt and cause metallization.

The content of the metal filler (B) is not particularly limited as long as it is 2300-5000 parts by mass relative to 100 parts by mass of the liquid epoxy resin, preferably 2500-4500 parts by mass, more preferably 3100-4000 parts by mass. When the content of the metal filler (B) is within the above range, excellent thermal conductivity, electrical conductivity and long-term reliability can be easily obtained.

The content of the metal powder (B1) is not particularly limited, and it is preferably 300-3000 parts by mass, more preferably 500-2500 parts by mass, relative to 100 parts by mass of the liquid epoxy resin. When the content of the metal powder (B1) is within the above range, excellent thermal conductivity, electrical conductivity and long-term reliability can be easily obtained.

The content of the metal powder (B2) is not particularly limited, but it is preferably 1000-4000 parts by mass, more preferably 1000-2500 parts by mass, relative to 100 parts by mass of the liquid epoxy resin. When the content of the metal powder (B2) is within the above range, excellent thermal conductivity, electrical conductivity and long-term reliability can be easily obtained.

The ratio ((B1)/(B2)) of the metal powder (B1) to the metal powder (B2) in the metal filler (B) is not particularly limited, preferably 0.3-1.0, more preferably 0.4-0.8. When the content ratio of the metal powder (B1) to the metal powder (B2) is within the above range, excellent thermal conductivity, electrical conductivity and long-term reliability can be easily obtained.

Metal powder (B1) or metal powder (B2) is not limited to the form of the metal, for example: a form of mixing a certain metal powder with a metal powder composed of other types of metals, or coating a certain metal powder with another type of metal form, or a form in which the above two are mixed.

The refractory metal may be composed of a single metal or an alloy of two or more metals. Preferable examples of high melting point metals include one or more of silver (melting point: 961°C), copper (melting point: 1083°C), and silver-coated copper powder.

Alloys of two or more metals can be used as low melting point metals. Preferable examples of low-melting-point metals include alloying two or more of tin (melting point: 231°C), lead (melting point: 327°C), bismuth (melting point: 271°C) and indium (melting point: 156°C) And it becomes one with a melting point of 180°C or lower. The above-mentioned low melting point metal preferably contains tin, and an alloy of tin (Sn) and bismuth (Bi) is preferred, and the alloy ratio is particularly preferably Sn:Bi=80:20˜42:58.

The shape of the metal powder is not particularly limited, and examples include: small flakes (scales), dendrites, spheres, fibers, amorphous (polyhedron), etc., from which the resistance value is lower and the thermal conductivity is improved. From the point of view of the composition, spherical shape is preferable.

The average particle size of the metal filler (B) is not particularly limited, preferably 0.5-20 μm, more preferably 1-10 μm. When the average particle diameter of the metal filler (B) is within the above range, excellent thermal conductivity and long-term reliability can be easily obtained.

The average particle size of the metal powder (B1) is not particularly limited, preferably 0.5-10 μm, more preferably 1-5 μm. When the average particle diameter of the metal powder (B1) is within the above-mentioned range, the contact between the metal powders increases, and excellent thermal conductivity can be easily obtained.

The average particle size of the metal powder (B2) is not particularly limited, preferably 1-20 μm, more preferably 5-10 μm. When the average particle diameter of the metal powder (B2) is within the above range, excellent filling properties and long-term reliability can be easily obtained.

In addition, in this specification, the average particle diameter means the particle diameter (primary particle diameter) which is 50% of the integrated value in the particle size distribution obtained by the laser diffraction scattering method.

The tap density of the metal filler (B) is not particularly limited, and is preferably 3.0-7.0 g/cm ³ . When the tap density is within the above range, excellent thermal conductivity and electrical conductivity can be easily obtained.

The tap density of the metal powder (B1) is not particularly limited, and is preferably 5.0~7.0 g/cm ³ . When the tap density is within the above range, excellent thermal conductivity and electrical conductivity can be easily obtained.

The tap density of the metal powder (B2) is not particularly limited, and is preferably 3.0-5.0 g/cm ³ . When the tap density is within the above range, excellent thermal conductivity and electrical conductivity can be easily obtained.

The hardener (C) is not particularly limited as long as it contains a hydroxyl-containing aromatic compound, and the hydroxyl-containing aromatic compound is preferably a phenol-based compound or a naphthol-based compound. That is, examples of such hardeners include phenol-based hardeners and naphthol-based hardeners, and hardeners that are not classified into the above-mentioned two may be included within the range that does not violate the object of the present invention.

The so-called phenol-based hardener is used as a hardener for phenol novolac and its derivatives, and the so-called naphthol-based hardener is used for naphthol and its derivatives.

The content of the curing agent (C) is preferably 10 to 40 parts by mass, preferably 15 to 30 parts by mass, relative to 100 parts by mass of the liquid epoxy resin. When the content of the hardener (C) is 10 parts by mass or more, sufficient hardening of the conductive paste can be easily obtained. When the content of the hardener (C) is 40 parts by mass or less, the pot life is not easily shortened, and excellent Electrical conductivity and thermal conductivity, long-term reliability.

Flux (D) is used to promote the metallization of metal powder, the following examples can be cited: zinc chloride, lactic acid, citric acid, oleic acid, stearic acid, glutamic acid, benzoic acid, oxalic acid, glutamine Hydrochloride, aniline hydrochloride, cetylpyridine bromide, urea, hydroxyethyl laurylamine, macrogol laurylamine, oleyl propylenediamine, triethanolamine, glycerol, hydrazine, rosin, 8- Ethyl octadecanedioic acid, etc. Among them, 8-ethyloctadecanedioic acid is preferable from the viewpoint of obtaining excellent filling properties and long-term reliability.

The content of the flux (D) is not particularly limited as long as it is 60-230 parts by mass relative to 100 parts by mass of the liquid epoxy resin, preferably 80-200 parts by mass, more preferably 100-180 parts by mass. When the content of the flux (D) is 60 parts by mass or more, metallization of the metal powder can be easily obtained, and excellent long-term reliability and filling properties of holes formed on the substrate can be easily obtained. When the flux (D) ) in an amount of 230 parts by mass or less, excellent electrical conductivity and thermal conductivity can be easily obtained.

Known additives such as defoamers, thickeners, adhesives, fillers, flame retardants, and colorants can be added to the conductive paste of the present invention within the range that does not impair the purpose of the invention.

In order to fill the conductive paste into the holes formed on the multi-layer substrate by dispensing method, atmospheric pressure printing method, vacuum printing method, etc., the conductive paste of the present invention is preferably low viscosity.

Here, the dispensing method refers to a method in which conductive paste is extruded from the tip of a syringe-shaped nozzle and applied. Also, the so-called atmospheric pressure printing method refers to the following method: in the case of stencil printing, a chemical fiber screen is used to cover the printing plate, and a screen is optically formed on the screen to block the It needs to make a printing plate with meshes other than graphics and text, and apply printing ink through the holes of the plate film under atmospheric pressure, so as to print the printing surface of the printed object set under the printing plate; the so-called vacuum printing method means Refers to the following method: in terms of stencil printing, it is to use a chemical fiber mesh cloth on the printing plate, and optically make a plate film on the mesh cloth to block the meshes other than the required graphics to make a printing plate , and apply printing ink through the holes of the plate film under vacuum, thereby printing the printing surface of the object to be printed under the printing plate.

The viscosity of the conductive paste of the present invention should be properly adjusted according to the application or the machine used for coating. Although there is no special limitation, as a general standard, when the temperature of the conductive paste is 25°C, it should be 1200~ 2500dPa. s. The viscosity measurement method can comply with JIS K7117-1, using a single cylindrical rotational viscometer (so-called B-type or BH-type viscometer) to measure at 10 rpm using rotor No. 7.

From the viewpoint of preventing voids, it is preferable that the conductive paste of the present invention does not contain a solvent.

Example Hereinafter, the content of the present invention will be described in detail according to the examples, but the present invention is not limited as follows. In addition, "parts" or "%" in the following are based on mass unless otherwise stated in advance.

[Examples 1-7, Comparative Examples 1-8] Each component was mixed in the ratio (parts by mass) described in Table 1 and Table 2, and an electroconductive paste was prepared. The details of each ingredient used are as follows.

． Liquid epoxy resin: "jER871" manufactured by Mitsubishi Chemical Co., Ltd., epoxy equivalent=390g/eq ． High melting point metal powder 1: Dowa Electronics (DOWA ELECTRONICS) Co., Ltd., silver-coated copper powder (average particle size 3 μm) ． High melting point metal powder 2: Dowa Electronics (DOWA ELECTRONICS) Co., Ltd. product, silver powder (average particle diameter 3 μm) ． High melting point metal powder 3: Copper powder (average particle diameter 3 μm) manufactured by Fukuda Metal Foil Powder Co., Ltd. ． Low melting point metal powder: Sn-Bi alloy metal powder (Sn:Bi=42:58, melting point 138°C, average particle size 6μm) ． Phenol-based curing agent: "TAMANOL758" manufactured by Arakawa Chemical Industry Co., Ltd. ． Flux: manufactured by Okamura Oil Co., Ltd., 8-ethyloctadecanedioic acid

For the prepared conductive paste, evaluate the specific resistance, thermal conductivity, fillability and long-term reliability 1~4. Tables 1 and 2 show the evaluation results. The evaluation method is as follows.

<Resistance (×10 ^-5 Ω.cm)> Using a metal printing plate, the conductive paste was printed on a glass epoxy substrate by line printing (length 60mm, width 1mm, thickness about 100μm), and the It was heated at 180° C. for 60 minutes to fully harden it, and a substrate for evaluation on which a conductive pattern was formed was produced. Next, using a tester, the resistance value between both ends of the conductive pattern was measured, and the specific resistance was calculated from the cross-sectional area (S, cm ² ) and the length (L, cm) using the following formula (1). Also, 5 lines of line printing were applied to each of the 3 glass epoxy substrates to form a total of 15 conductive patterns, and the average value of the equiresistive resistance was obtained. When the specific resistance is 5.0×10 ^-5 Ω. When it is less than cm, it is evaluated that the conductivity is excellent. Specific resistance=(S/L)×R‥‥(1)

<Thermal conductivity> The thermal conductivity of the conductive paste was evaluated using Thermowave Analyzer TA-33 (manufactured by Bethel). Specifically, prepare a Teflon (TEFLON, registered trademark) sheet (100mm×100mm×3mm), cover it with polyimide tape to form an opening with a width of 50mm and a length of 50mm in the center of the Teflon sheet, and perform The conductive pastes of each embodiment and each comparative example were printed in the same way. Then, the conductive paste was cured by heating at 180° C. for 60 minutes, and the polyimide tape was peeled off to form a coating film (50 mm in width, 50 mm in length, and about 100 μm in thickness). The obtained coating film was peeled off from the Teflon (registered trademark) sheet, and it was set as the sample of hardened|cured material. Use Thermowave Analyzer to measure the thermal diffusivity α (m ² /S), and use the following formula (2) to calculate from the density ρ (kg/m ³ ) and specific heat Cp (J/Kg.K) of the hardened sample The thermal conductivity K (W/m.K). When the thermal conductivity is 30 W/mK or more, it is evaluated that the thermal conductivity is excellent. Thermal conductivity K=thermal diffusivity α×density ρ×specific heat Cp...(2)

<Samples for evaluation of long-term reliability> Using a CO ₂ laser, a 169-hole connection pattern with a diameter of 100 μm was formed on a prepreg with a thickness of about 100 μm (manufactured by Panasonic Co., Ltd., “R-1551”), and printed After filling the conductive paste in the hole, use a vacuum press to press under the following pressure and temperature conditions to make a sample. The conductive pastes of Examples 1 to 7 and Comparative Examples 2 and 4 to 8 can be filled into the holes formed in the prepreg without seeping out of the holes, so they are evaluated as having excellent filling properties, Table 1, 2 In Table 2, "○" is shown in the middle; in Comparative Examples 1 and 3, unfilled parts and/or cracks occurred during curing, so it was evaluated that sufficient filling properties could not be obtained, and Table 2 is shown as "×".

Pressure: It took 17 minutes to increase the pressure from 0 kg/cm ² to a surface pressure of 10.2 kg/cm ² , and maintain this state for 10 minutes. Next, the pressure was raised to a surface pressure of 30.6 kg/cm ² over 24 minutes, maintained in this state for 46 minutes, and then depressurized to 0 kg/cm ² over 23 minutes.

Temperature: It took 17 minutes to raise the temperature from 30° C. to 130° C., and keep it in this state for 10 minutes. Next, after heating up to 180 degreeC over 24 minutes and holding|maintaining in this state for 46 minutes, it cooled to 30 degreeC over 23 minutes.

<Long-term reliability 1 (resistance value change rate before and after thermal cycle (HC) test)> In the thermal cycle test, 1000 cycles of thermal cycler were performed at -65° C. for 30 minutes and at 125° C. for 30 minutes for each sample prepared above. The measurement of the resistance value is to measure the resistance value between the two ends of the connection pattern before and after the heat cycle test, divide the resistance value by the number of each hole, obtain the resistance value of each hole, and calculate the average value.

The resistance value change rate before and after the thermal cycle test is the resistance value measured before the test as a, and the resistance value measured after the test as b, and the resistance value change rate is calculated by the following formula. When the rate of change in resistance value was within ±10%, it was evaluated that the reliability was excellent. Resistance value change rate (%)=(b-a)×100/a

<Long-term reliability 2 (resistance value change rate before and after reflow test)> In the reflow test, each sample prepared above was subjected to a reflow step at 260° C. for 10 seconds five times. The rate of change in resistance value before and after the reflow test was measured in the same manner as the thermal cycle test.

<Long-term reliability 3 (resistance value change rate before and after heat resistance test)> In the heat resistance test, each sample prepared above was left to stand at an ambient temperature of 100° C. for 1000 hours. The rate of change in resistance value before and after the heat resistance test was measured in the same manner as the heat cycle test.

<Long-term reliability 4 (change rate of resistance value before and after humidity test)> For the humidity resistance test, each sample prepared above was left to stand for 1000 hours at an ambient temperature of 85°C and a humidity of 85%. The rate of change in resistance value before and after the humidity resistance test was measured in the same manner as in the thermal cycle test.

[Table 1]

[Table 2]

From the results shown in Table 1, it can be seen that Examples 1 to 7 are all excellent in electrical conductivity, thermal conductivity, fillability and long-term reliability.

From the results shown in Table 2, Comparative Example 1 is an example in which the content of the metal filler (B) is greater than the upper limit, and its long-term reliability 1-4 is poor.

Comparative Example 2 is an example in which the content of metal filler (B) is less than the lower limit, and its long-term reliability 1 and 2 are poor.

Comparative Example 3 is an example in which the content of the metal filler (B) is greater than the upper limit, and its electrical conductivity, thermal conductivity, fillability and long-term reliability 1 and 2 are poor.

Comparative Example 4 is an example in which the content of the metal filler (B) is less than the lower limit, and its electrical conductivity, thermal conductivity and long-term reliability 2 are poor.

Comparative Example 5 is an example in which the content of the curing agent (C) is less than the lower limit, and its thermal conductivity and long-term reliability 1-4 are poor. In addition, long-term reliability 1 was unable to measure the resistance value, and it was confirmed that the cause was cracks by observing the cross-section in the hole.

Comparative Example 6 is an example in which the content of the curing agent (C) is greater than the upper limit, and its electrical conductivity and thermal conductivity are poor.

Comparative Example 7 is an example in which the flux (D) content is less than the lower limit, and its long-term reliability 1-4 is poor. In addition, long-term reliability 1 was unable to measure the resistance value, and it was confirmed that the cause was cracks by observing the cross-section in the hole.

Comparative Example 8 is an example in which the flux (D) content is greater than the upper limit, and its electrical conductivity and thermal conductivity are poor.

(none)

Claims (4)

A conductive paste comprising: Relative to 100 parts by mass of (A) liquid epoxy resin; 2300~5000 parts by mass of (B) metal filler, which contains two or more kinds of metal powders, and the two or more kinds of metal powders include at least one kind of metal powder (B1) and at least one kind of metal powder (B2). The powder (B1) has a high melting point metal with a melting point of 800°C or higher, the high melting point metal includes silver and/or copper, the aforementioned metal powder (B2) has a low melting point metal with a melting point of 180°C or lower, and the low melting point metal is selected from Composed of two or more alloys from the group consisting of tin, lead, bismuth and indium; 10-40 parts by mass of (C) a hardener containing a hydroxyl-containing aromatic compound; and 60-230 parts by mass of (D) flux. The conductive paste according to claim 1, wherein the content ratio ((B1)/(B2)) of the metal powder (B1) to the metal powder (B2) in the metal filler (B) is 0.3~1.0. The conductive paste according to claim 1 or 2, wherein the hydroxyl-containing aromatic compound is at least one selected from the group consisting of phenol-based hardeners and naphthol-based hardeners. A multi-layer substrate, which is formed by alternately laminating a plurality of layers of conductive layers and insulating layers, the multi-layer substrate is formed with holes penetrating at least one of the aforementioned insulating layers, and the aforementioned holes are filled with conductive materials according to any one of claims 1 to 3. The cured product of the adhesive paste, through which the aforementioned conductive layers located at both ends of the aforementioned hole are connected to each other.