RU2845451C1 - Heat-dissipating adhesive dielectric composition, base material of printed circuit boards based thereon and method of manufacturing base material of printed circuit boards on aluminium base (versions) - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: group of inventions relates to the field of high-filled dielectric adhesive polymer composite materials with increased heat conductivity for electrical purposes. Heat-dissipating adhesive dielectric composition for making printed-circuit board base material contains the following, wt. %: epoxy oligomer – 23.2-37, selected from epoxy polyfunctional oligomers and epoxy diane oligomers based on bisphenol-A or mixture thereof; modifier – 10-15.8; latent curing system – 10.8-17.2; boron nitride – 30-45. Modifier is rubber particles distributed in the epoxy oligomer; the latent curing system is dicyandiamide dissolved in dimethyl formamide. Invention also discloses base material for printed-circuit boards, which is a layered material containing an aluminium substrate coated with a layer of the disclosed composition, which is joined to a layer of copper foil, and two methods of making base material for printed-circuit boards.

EFFECT: invention provides an increase in the thermal conductivity of the composition with a simultaneously low value of the tangent of dielectric losses at 1 MHz, an increase in adhesion to metal products, electric strength, as well as increasing viability of dielectric composition at high temperatures; wherein the disclosed composition enables to obtain a layer between the cooled surface and the heat-removing device not only by film moulding, but by spraying as well.

11 cl, 2 tbl, 26 ex

Description

The inventions relate to the field of highly filled dielectric adhesive polymer composite materials with increased thermal conductivity for electrical engineering purposes, including for creating a strong adhesive connection of metal products of printed circuit boards on an aluminum base. The corresponding composite materials can be used to ensure an optimal thermal regime of electronic equipment and devices and to remove heat from heat-generating elements to a heat-removing base.

A thermal interface material is known from the prior art (see US application US20040241410, published 02.12.2004). The known material is obtained in several stages. In the first stage, a polymer adhesive compound is prepared by mixing 95 parts by weight of 2-ethylhexyl acrylate, 5 parts by weight of acrylic acid, 0.15 parts by weight of photoinitiator and 0.02 parts by weight of isooctyl thioglycolate, followed by UV exposure with heating in a water bath. In the second stage, heat-conducting particles of boron nitride with a concentration of 25-40% are introduced into the resulting mixture, and then a film material is formed in an extruder. The thermal conductivity of the known material is 0.5 W/m⋅K.

The disadvantages of the known material are low thermal conductivity, as well as the high labor intensity of the method of its production.

Also known is a heat-conducting dielectric composition (see Russian Patent No. 2645789, published on 28.02.2018) containing ED-20 epoxy resin, AC6100/80 synthetic diamond powder and L-18 epoxy resin hardener, which is an adduct of polyamines with vegetable oil acids. The composition is prepared by simply mixing the components and curing at a temperature of 25±10°C for 4-5 hours, then at a temperature of 75±10°C for 6-7 hours. The described heat-conducting dielectric composition has a high thermal conductivity of 7-8 W/m⋅K. The electrical strength values are in the range of 10-14 kV/mm.

The disadvantages of the known heat-conducting dielectric composition are low electrical strength, high cost of the filler, and also the short time during which the compound must be used.

An epoxy composition is known for producing a heat-conducting material blank, a b-stage sheet, a prepreg, a heat-dissipating material, a laminated plate, a metal substrate, and a printed circuit board (see international application WO2016190260A1, published on 01.12.2016). The epoxy composition consists of an epoxy resin, 50 wt.% of hexagonal boron nitride particles subjected to liquid-phase oxidation, and a hardener. The resulting composition is used to produce a sheet prepreg by forming a sheet from the compound with subsequent partial curing. It is also used to produce a laminated plate, a metal substrate, and a printed circuit board.

The known material has increased thermal conductivity values of 2.2-4.4 W/m⋅K, and electrical strength values are 22-29 kV/mm.

The main disadvantage of the material is the low values of electrical strength, which causes the breakdown current to pass exclusively through the polymer.

The closest analogue is a sheet insulating highly filled polymer material (see US patent US9497857B2, published on 15.11.2015) containing 70-85 wt.% boron nitride as a thermally conductive filler, epoxy resin and a hardener and obtained using a roller press at temperatures of 5-300 °C. Hexagonal boron nitride contains large particles with an average particle diameter of 10 to 400 μm and small particles with an average particle diameter of 0.5 to 4.0 μm, where the degree of mixing of large particles is 85% or more. The material has an increased thermal conductivity of 2.8-4.1 W/m⋅K and an electrical strength of 30-40 kV/mm.

The disadvantages of this material are the size limitations and the impossibility of manufacturing a non-standard shaped product, associated with the choice of rolling technology. The high filler content in the composition does not ensure uniform distribution of the binder on the filler surface, which reduces the electrical properties of the resulting material. In addition, such a highly filled composition can only be processed by limited methods, which narrows the areas of its application.

The technical problem that this group of inventions is aimed at solving is insufficient heat resistance, tracking resistance, weak adhesion between layers in the base materials of printed circuit boards and low dielectric properties that do not meet the requirements for the operation of printed circuit boards to ensure high heat dissipation of the power elements mounted on them (tracking resistance, electrical strength).

The technical result achieved by using the claimed inventions consists in increasing thermal conductivity with a simultaneously low value of dielectric constant, dielectric loss tangent at 1 MHz, increasing adhesion to metal products, electrical strength, and also increasing the viability of the dielectric composition at elevated temperatures. At the same time, the claimed composition allows obtaining a layer between the cooled surface and the heat-dissipating device not only by film molding, but also by spraying.

The technical problem is solved and the technical result is achieved due to the fact that the heat-dissipating adhesive dielectric composition contains an epoxy oligomer selected from epoxy polyfunctional oligomers and epoxy diane oligomers based on bisphenol-A or a mixture thereof, a modifier, a latent curing system, boron nitride in the following mass ratio of components, mass %:

epoxy oligomer 23.2 – 37 modifier 10 – 15.8 latent curing system 10.8 – 17.2 boron nitride 30 – 45

The modifier is rubber particles distributed in an epoxy oligomer, and the latent curing system is dicyandiamide dissolved in dimethylformamide.

Preferably, the latent curing system comprises a catalyst which is an imidazole derivative in a dicyandiamide:catalyst ratio of 100:0 to 100:20.

The presence of a catalyst in the latent curing system allows one to regulate the curing rate of the claimed composition, thereby accelerating the production of a solid layer if necessary.

Preferably, the composition contains a low-boiling solvent selected from methyl ethyl ketone, acetone, ethyl alcohol in an amount of from 0 to 20 parts by weight per 100 parts by weight of the composition.

The presence of a low-boiling solvent allows the viscosity of the declared composition to be adjusted, thereby expanding the possibilities of its application to a metal substrate in various ways.

Preferably, the boron nitride is a surface-modified filler with an average particle size of 1 to 10 μm.

The use of such boron nitride makes it possible to obtain a composition with high thermal conductivity and, at the same time, a low value of the dielectric loss tangent at 1 MHz.

Preferably, the composition contains silicon oxide nanoparticles in an amount of 0 to 3% by weight.

The use of such silicon oxide makes it possible to obtain a composition with a thixotropic structure and adjustable structure recovery time, which ensures the implementation of the spraying method.

In order to achieve the technical result, a base material for printed circuit boards is also proposed, which is a layered material containing an aluminum substrate with a layer of the claimed composition applied to it, which is connected to a layer of copper foil.

To achieve the technical result, a method for manufacturing the base material of printed circuit boards is also proposed, which includes the following stages:

a) degreasing the surface of the aluminum substrate;

b) applying a layer of heat-dissipating adhesive dielectric composition according to paragraph 1 to the degreased surface of the aluminum substrate;

c) drying the layer of applied heat-dissipating adhesive dielectric composition according to item 1 at a temperature of 25 - 125°C for 5-40 minutes;

d) applying a layer of copper foil to the layer of heat-dissipating adhesive dielectric composition according to paragraph 1;

d) hot pressing in a vacuum of the layered material obtained in stage d) at a specific pressure of 25-35 kgf/ ^cm2 for 60-90 minutes at a temperature of at least 180°C.

It is preferable that hot pressing at stage d) is carried out in a technical vacuum, with its level being 5-10 kPa. The method of hot pressing in a vacuum provides an increase in tracking resistance and electrical strength, due to the removal of volatile residues during the polymerization of the polymer matrix.

Preferably, the layer of heat-dissipating dielectric composition is applied to the aluminum substrate by spraying.

This method of application allows eliminating the stage of manufacturing a heat-conducting dielectric layer on an intermediate substrate, increasing the adhesion of the layer to metal bases due to the lower viscosity of the system and more efficient wetting of the substrate surface.

To achieve the technical result, a method for obtaining the base material of printed circuit boards is also proposed, which includes the following stages:

a) production of a film by applying a thin layer of heat-dissipating dielectric composition according to item 1 to an anti-adhesive surface, followed by drying at a temperature of 25 - 125°C for 5-40 minutes;

b) degreasing the surface of the aluminum substrate;

c) applying the film obtained in stage a) to the surface of the aluminum substrate;

d) applying a layer of copper foil to the film obtained in stage a) to obtain a layered material;

d) hot pressing in a vacuum of the layered material obtained in stage d) at a specific pressure of 25-35 kgf/ ^cm2 for 60-90 minutes at a temperature of at least 180°C, while the technical vacuum level is less than 5-10 kPa.

It is preferable that hot pressing at stage d) is carried out in a technical vacuum, with its level being 5-10 kPa. The method of hot pressing in a vacuum provides an increase in tracking resistance and electrical strength, due to the removal of volatile residues during the polymerization of the polymer matrix.

The composition of the proposed heat-dissipating adhesive dielectric composition is an optimal balanced amount of the components used. At the same time, both the composition of the composition and the methods for obtaining the base material of printed circuit boards provide increased technological viability of the composition at elevated temperatures, and also contribute to the formation of the base material of printed circuit boards and products based on it with increased thermal conductivity with a simultaneously low value of the tangent of the angle of dielectric losses at 1 MHz and a high indicator of electrical strength and tracking resistance.

Polyfunctional epoxy oligomers provide heat resistance and strength to the resulting material, as they allow the formation of a densely meshed structure of the polymer matrix.

Epoxy diane oligomers provide the resulting material with excellent dimensional stability, chemical resistance and thermal stability.

Hexagonal boron nitride (h-BN) was selected as a filler for the heat-dissipating adhesive dielectric composition, since it provides the resulting material with high thermal conductivity values, high dielectric characteristics, as well as high thermal and chemical resistance.

The filler content in the composition is 30-45% by weight, which allows for the simultaneous provision of high technological efficiency of the material manufacturing process, the necessary operational characteristics (tracking resistance) and improved thermal-physical properties.

Obtaining compositions and materials based on it with an h-BN content of more than 45% by weight is impractical, since on the one hand this leads to a deterioration in operational properties (adhesion to metal, moisture absorption) due to the extremely low adhesion and relatively high moisture absorption of h-BN, and on the other hand to a deterioration in mechanical properties due to a violation of the continuity of the polymer between the filler particles.

To create a heat-dissipating adhesive dielectric composition, epoxy oligomers based on N,N’-tetraglycidyl-4,4’-diaminodiphenylmethane are used as epoxy polyfunctional oligomers, for example, epoxy resin of the Araldite MY720, Araldite MY 721, Araldite MY9512 (manufacturer Huntsman Advanced Materials), ELM434 (manufacturer Sumitomo Chemical Co., Ltd.) brand.

based on aminophenol Araldite MY 0500 (manufactured by Huntsman Advanced Materials), jER630 (manufactured by Mitsubishi Chemical Corporation), Sumiepoxy ELM120 and Sumiepoxy ELM100 (manufactured by Sumitomo Chemical Company, Limited).

The modifier is rubber particles distributed in an epoxy oligomer in the form of core-shell particles, a material called Modifier M-1 (manufactured by SPM Research Center LLC)

Hexagonal boron nitride grade H-BN-A (manufacturer Tanyun Aerospace Materials (Yingkou) Technology Co., Ltd.), Therm-BN-A (manufacturer Suzhou Nutpool Materials Technology Co., Ltd), h-BN TU 2112-003-49534204-2002 (manufacturer  JSC UNIHIM)

Surface-modified hexagonal boron nitride grade SM-BN (manufacturer Suzhou Nutpool Materials Technology Co., Ltd).

Examples of implementation.

Preparation of the claimed heat-dissipating adhesive dielectric composition.

Example 1 (Table 1). To obtain the composition, an epoxy polyfunctional oligomer of the brand (Araldite MY720) was used, as a modifier "Modifier M-1", h-BN TU 2112-003-49534204-2002 with an average particle size of 3-10 μm was used as hexagonal boron nitride, dicyandiamide dissolved in dimethylformamide was used as a latent curing system.

A polyfunctional epoxy oligomer in an amount of 29 wt.%, a modifier in an amount of 12.5 wt.%, a latent curing system in an amount of 13.5 wt.%, and boron nitride in an amount of 45 wt.% were loaded into a clean and dry reactor with a drain nozzle, equipped with a stirrer for mixing the starting materials. Mixing was carried out using an overhead stirrer (IKA MINISTAR 40 control) at a peripheral speed of 250 rpm for 40 minutes at a temperature of 24-25°C.

Examples 2-13 (Table 1).

The production of the heat-dissipating adhesive dielectric composition was carried out similarly to Example 1, but with other components and in the ratios given in Table 1.

Examples 14, 16, 18-22, 25 (Table 2). Manufacturing of base material for printed circuit boards, with application of composition by spraying and application of composition in the form of a film and subsequent hot pressing.

The surface of the aluminum substrate was treated with alcohol and compressed air for degreasing and removing contaminants in order to improve adhesion. The compositions obtained in examples 1-13 were applied to the surface of the prepared substrate using a spray gun at an operating pressure of 2 bar. During the pass, the spray gun moved smoothly and evenly at a constant distance of 15-20 cm from the surface and perpendicular to it. Then the applied layer of the heat-dissipating adhesive dielectric composition obtained in examples 1-13 was dried at a temperature of 25 °C for 40 minutes, and then a layer of copper foil was applied to the dried layer of the heat-dissipating adhesive dielectric composition. The resulting base material was pressed at a specific pressure of 25-35 kgf/ ^cm2 for 60-90 minutes at a temperature of 180 °C.

To produce the base material of the printed circuit boards, a film was preliminarily produced by applying a thin layer of the heat-dissipating dielectric composition obtained as disclosed in Examples 1-13 to the anti-adhesive surface using a doctor blade.

Then dried at 110°C for 5 minutes in a continuous drying chamber.

The surface of the aluminum substrate was treated with alcohol and compressed air to degrease and remove contaminants in order to improve adhesion. Then, a pre-obtained film of heat-dissipating adhesive dielectric composition was laid on the aluminum substrate and the anti-adhesive substrate was removed. Then, a layer of copper foil was applied to the layer of heat-dissipating adhesive dielectric composition. The resulting base material was pressed at a specific pressure of 25-35 kgf/ ^cm2 for 60-90 minutes at a temperature of 180°C.

The compositions of the claimed heat-dissipating adhesive dielectric composition are given in Table 1. The properties of the heat-dissipating adhesive dielectric composite material are given in Table 2. The invention is not limited to the examples given.

Examples 15, 17, 23, 24, 26 (Table 2). Manufacturing of base material for printed circuit boards, with application of composition by spraying and application of composition in the form of a film and subsequent hot pressing in a technical vacuum.

The production of the base material of printed circuit boards as disclosed in Example 14, the obtained base material was pressed at a specific pressure of 25-35 kgf/ ^cm2 for 60-90 minutes at a temperature of 180°C in a technical vacuum environment (5-10 kPa).

Table 1. Composition of heat-dissipating adhesive dielectric composition.

Components Composition by examples, mass % 1 2 3 4 5 6 7 8 9 10 11 12 13 Polyfunctional epoxy oligomer based on 4,4'-diaminodiphenylmethane - 29 - 37 14.5 18.5 16.5 - 27.54 14.85 - 28.7 16.42 based on p-aminophenol 29 - 37 - 14.5 18.5 16.5 23.2 - 14.85 28.12 - 16.42 Modifier M-1 12.5 12.5 15.8 15.8 12.5 15.8 14.2 10 11.88 12.78 12,13 12.38 14.13 Curing system 13.5 13.5 17.2 17.2 13.5 17.2 15.3 10.8 12.83 13.77 13.1 13.37 15.22 Boron nitride 45 45 30 30 45 30 37.5 36 42.75 33.75 43.65 44.55 37.31 Low boiling solvent 0 0 0 0 0 0 0 20 5 10 Silicon dioxide - - - - - - - - - - 3 1 0.5

Table 2. Properties of the base material of printed circuit boards made on the basis of heat-dissipating adhesive dielectric composition.

Name No. of examples 14 15 16 17 18 19 20 21 22 23 24 25 26 Thermal conductivity λ, W/(m⋅K) 4.4 4.5 3.5 3.5 4.4 3.6 3.7 3.7 4.4 3.6 4.5 4.6 3.7 Tangent of the dielectric loss angle 0.033 0.031 0.03 0.03 0.035 0.028 0.029 0.029 0.035 0.029 0.035 0.034 0.029 Peel strength of foil from dielectric base, N/mm 1.4 1.5 1,2 1.6 1.4 1.3 1.3 1.5 1.4 1.4 1.6 1.4 1.5 Electrical strength, kW/mm 35-40 40-45 40-45 40-45 35-40 35-40 35-40 35-40 35-40 40-45 40-45 35-40 40-45 SIT according to GOST 27473-87 500 600 500 600 500 500 500 500 600 600 600 500 600 Coating production technology Sputtering and film on substrate, hot pressing without vacuum Sputtering and film on substrate, hot pressing in vacuum Spraying and
film on substrate, hot pressing without vacuum Sputtering and film on substrate, hot pressing in vacuum Sputtering and film on substrate, hot pressing without vacuum Sputtering and film on substrate, hot pressing without vacuum Sputtering and film on substrate, hot pressing without vacuum Sputtering and film on substrate, hot pressing without vacuum Sputtering and film on substrate, hot pressing without vacuum Sputtering and film on the substrate hot pressing in vacuum Sputtering and film on the substrate hot pressing in vacuum Sputtering and film on substrate, hot pressing without vacuum Sputtering and film on substrate, hot pressing in vacuum

The presented data show that the obtained material has high thermal conductivity with a simultaneously low value of the dielectric loss tangent at 1 MHz. In addition, the obtained base material has excellent adhesion to metal surfaces, in particular, to aluminum and copper. At the same time, the proposed composition allows obtaining a heat-conducting layer between the cooled surface and the heat-dissipating device not only by film molding, but also by spraying, which expands the possibility of using the composition on non-standard shaped parts. In turn, the method of hot pressing in a vacuum ensures an increase in the required performance indicators of printed circuit boards on an aluminum base, such as tracking resistance and electrical strength, due to the removal of volatile residues during the polymerization of the polymer matrix.

Claims (23)

1. A heat-dissipating adhesive dielectric composition for the production of a base material for printed circuit boards, containing an epoxy oligomer selected from epoxy polyfunctional oligomers and epoxy diane oligomers based on bisphenol-A or a mixture thereof, a modifier, a latent curing system, boron nitride in the following mass ratio of components, wt.%: epoxy oligomer 23.2–37 modifier 10–15.8 latent curing system 10.8–17.2 boron nitride 30–45, The modifier is rubber particles distributed in an epoxy oligomer, and the latent curing system is dicyandiamide dissolved in dimethylformamide. 2. The composition according to claim 1, characterized in that the latent curing system contains a catalyst, which is an imidazole derivative in a dicyandiamide:catalyst ratio of 100:0 to 100:20. 3. The composition according to claim 1, characterized in that it contains a low-boiling solvent selected from methyl ethyl ketone, acetone, ethyl alcohol in an amount of 0 to 20 parts by weight per 100 parts by weight of the composition. 4. The composition according to claim 1, characterized in that the boron nitride is a surface-modified filler with an average particle size of 1 to 5 μm. 5. The composition according to claim 1, characterized in that it contains silicon oxide nanoparticles in an amount of 0 to 3 wt.%. 6. A base material for printed circuit boards, which is a layered material containing an aluminum substrate with a layer of the composition according to item 1 applied thereto, which is connected to a layer of copper foil. 7. A method for manufacturing a base material for printed circuit boards according to item 6, comprising the following stages: a) degreasing the surface of the aluminum substrate; b) applying a layer of heat-dissipating adhesive dielectric composition according to paragraph 1 to the degreased surface of the aluminum substrate; c) drying the layer of applied heat-dissipating adhesive dielectric composition according to item 1 at a temperature of 25-125°C for 5-40 minutes; d) applying a layer of copper foil to the layer of heat-dissipating adhesive dielectric composition according to paragraph 1; d) pressing the layered material obtained in stage c) at a specific pressure of 25-35 kgf/ ^cm2 for 60-90 min at a temperature of at least 180°C. 8. The method according to claim 7, characterized in that the layer of heat-dissipating dielectric composition is applied to the aluminum substrate by spraying. 9. The method according to item 7, characterized in that hot pressing at stage d) is carried out in a technical vacuum, with its level being 5-10 kPa. 10. A method for manufacturing a base material for printed circuit boards according to item 6, comprising the following stages: a) producing a film by applying a thin layer of heat-dissipating dielectric composition according to item 1 to an anti-adhesive surface, followed by drying at a temperature of 25-125°C for 5-40 minutes; b) degreasing the surface of the aluminum substrate; c) applying the film obtained in stage a) to the surface of the aluminum substrate; d) applying a layer of copper foil to the film obtained in step a), thereby obtaining a layered material; d) pressing the layered material obtained in stage c) at a specific pressure of 25-35 kgf/ ^cm2 for 60-90 min at a temperature of at least 180°C. 11. The method according to item 10, characterized in that hot pressing at stage d) is carried out in a technical vacuum, with its level being 5-10 kPa.