JPH0228911B2 - KONETSUDENDOSEIDENKIZETSUENKIBAN - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly reliable electrically insulating substrate with good heat dissipation properties and withstand voltage, and high thermal conductivity.

Ceramic and glass substrates have traditionally been used as substrates for hybrid integrated circuits including power ICs that require heat dissipation, but these substrates are difficult to perform post-processing such as cutting and drilling holes, and they also have poor heat dissipation properties. Sexuality was also insufficient.

In addition, composite insulating plates made of a metal plate and thermosetting resin, and those with an electrically insulating alumite film formed on the surface of an aluminum plate, etc., have been developed, but the former has an organic insulating layer that makes it difficult to conduct heat. bad sex,
The latter also had the disadvantage that the alumite film cracked when the temperature of the substrate increased, resulting in a significant drop in electrical insulation.

The present invention eliminates these drawbacks and provides a highly reliable, highly thermally conductive electrically insulating substrate that has good thermal conductivity and withstand voltage, and has a uniform electrically insulating layer thickness. This substrate is suitable for various integrated circuit boards, other printed wiring boards, heat sinks, and the like.

In connection with the present invention, by first providing on a metal plate a film made of a mixture of polyhedral metal oxide particles having a shape factor of 1.0 to 1.4 and smooth surfaces dispersed in an organic polymer, We discovered that a highly thermally conductive electrically insulating substrate with good heat dissipation properties could be obtained and proposed this, but subsequent research revealed that in order to make this substrate, we applied the above mixture onto a metal plate and required a drying process. When the metal plate is pressurized and heated to harden into a single body, the organic polymer and metal oxide particles flow out from the edge of the metal plate, causing the thickness of the insulating layer to become uneven and the insulation to deteriorate. There are problems such as non-uniform voltage resistance due to air bubbles remaining in the layer, and if this is to be avoided, a separate means to prevent organic polymers from flowing out must be provided, resulting in a decrease in productivity, etc. I found out.

In order to improve these problems, as a result of further studies, we found that the above mixture was interposed in the glass cloth, and the glass cloth was fixed on a metal plate to form an integrated substrate. It was discovered that a highly reliable, highly thermally conductive electrical insulating substrate with good withstand voltage and a uniform thickness of the insulating layer can be obtained without impairing heat dissipation properties, and a patent application has been filed. These include those to which hexagonal BN, BeO, etc., which have good thermal conductivity, are added in addition to the above-mentioned metal oxide particles of a specific shape in order to further improve thermal conductivity.

However, in this case, since it was used in combination with the metal oxide, there was a limit to the amount added.

On the other hand, as the density of ICs continues to increase, substrates are required to have even better heat dissipation properties. In view of these circumstances, as a result of a prototype evaluation of adding a large amount of hexagonal BN or adding only hexagonal BN to the above substrate,
The following problems were found. In other words, the generally commercially available BN fine powder has a small particle size and
In addition, it was found that due to poor wetting with organic polymers, the withstand voltage of the substrate was lowered, and the adhesion strength to metal plates and glass cloth was lowered.

The present invention eliminates these drawbacks and improves thermal conductivity,
It was developed with the aim of obtaining a highly reliable, highly thermally conductive electrically insulating substrate that has good withstand voltage and adhesion strength, and has a uniform electrically insulating layer thickness. The point is that boron nitride fine powder is used in the form of sintered particles using a specific binder.

That is, the first aspect of the present invention is that a metal plate and a glass cloth are fixed together with a mixture of sintered particles of hexagonal boron nitride and an organic polymer using calcium borate or borosilicate glass as a binder. The second invention is a highly thermally conductive electrically insulating substrate in which a metal foil is integrally fixed on the glass cloth of this substrate. In these cases, the glass cloth and metal foil can be fixed to one or both sides of the metal plate.

The present invention will be explained in detail below.

Various types of sintering binders for hexagonal boron nitride fine powder are known, but when sintered particles are used in the substrate of the present invention, calcium borate or borosilicate glass is used as the binder. preferable.

Calcium borate is 3CaO・B ₂ O ₃ , CaO・
It has a composition of B ₂ O ₃ , CaO.2B ₂ O _{3 ,} etc., and of course a mixture of these may be used. That is, CaO and
It is preferable to use a composition in which CaO/B _{2 O 3 is} in the range of 0.5 to 3 in terms of the molar ratio of B ₂ O 3 . CaO／
When B ₂ O ₃ is less than 0.5, it exhibits hygroscopicity and the withstand voltage of the substrate decreases, and when it is more than 3, the bonding force as a binder is weak.

As for borosilicate glass, the content of boric acid is 3
~10% by weight is preferred. If boric acid exceeds 10% by weight, it becomes hygroscopic and the withstand voltage of the substrate decreases.
If it is less than % by weight, the binding force as a binder is weak.

The amount of these binders added is preferably 1 to 20% by weight based on hexagonal boron nitride, preferably 2 to 15% by weight.
Weight%. If the amount added is less than 1% by weight, the strength of the sintered hexagonal boron nitride powder particles will be weak, and the particles will collapse when mixed with the organic polymer material, reducing the withstand voltage of the substrate. If the value exceeds 100%, the thermal conductivity of the substrate will decrease.

To obtain sintered particles of hexagonal boron nitride, first, hexagonal boron nitride and the above-mentioned binder are mixed in a ball mill, etc., then the mixed powder is molded under pressure at room temperature, and then heated under non-oxidizing atmosphere at temperature. 1000～
Sinter at 2000℃ or pressure 50-450 under the above conditions
A sintered body of hexagonal boron nitride is formed by hot pressure molding at Kg/cm ² . Next, this sintered body of hexagonal boron nitride is crushed with a crusher or cut with a cutting machine, etc., and then crushed and further sieved to particles with a desired particle size or less to obtain hexagonal boron nitride. Let it be sintered particles of Ride. As for the size of the particles, it is preferable that the maximum particle size is about the same as the thickness of the glass cloth.
Also, it is necessary to be able to enter the glass cloth, but normally a maximum of about 50μ is appropriate, and the lower limit is preferably about 2μ, since if it is too small, the above-mentioned problem will occur.

In order to integrate a glass cloth and a metal plate using a mixture of these particle powders and an organic polymer, for example, the mixture is applied to a glass cloth, the mixture is placed on a metal plate, dried, and then Heat cured under pressure. Furthermore, in order to integrate the metal foil, the metal foil may be placed on a glass cloth and treated in the same manner as described above. The metal foil used is copper, aluminum, nickel, or the like.

The sintered hexagonal boron nitride particles are uniformly dispersed within the mesh of the glass cloth, forming a uniform insulating layer during pressing, resulting in a highly reliable, highly thermally conductive electrically insulating substrate with no residual bubbles.

The appropriate amount of hexagonal boron nitride powder added to the organic polymer is 10 to 150% by weight.

The organic polymers used in the present invention include epoxy resins, phenolic resins, polyimide resins, etc. The glass cloth may be either plain weave or satin weave, and the presence or absence of surface treatment and type of glass cloth are particularly limited. However, it is preferable to use a coupling agent or the like that is compatible with the organic polymer used.

The thickness of the glass cloth is selected from a range of 30 to 110 μm depending on the thickness of the required insulating layer, and the mixture of hexagonal boron nitride and organic polymer is selected so that the inside of the mesh of the glass cloth is filled. It is composed of

The metal plate used in the present invention is aluminum,
Iron, copper, etc. are used, and the presence or absence of surface treatment is not limited. The thickness of these metal plates is generally in the range of 0.5 to 3 mm for IC boards and the like.

Next, an example of a method for integrating glass cloth with the mixture onto a metal plate will be described.

First, a glass cloth is placed on a metal plate, and a mixture is applied onto the glass cloth using a spray gun, a flow coater, a gluing machine, or the like. The appropriate amount of application is enough to cover the glass cloth. After application
Dry at 120-150℃ for several minutes. Then the pressure is 70~
Pressure and heat are applied to bond the metal plate and the glass cloth at a pressure of 120 kg/cm ² and a temperature of 150 to 200° C. for about 40 to 70 minutes. At this time, by placing a metal foil on the glass cloth and press-bonding it, a metal foil-covered insulating substrate with high thermal conductivity can be obtained.

The present invention will be specifically explained below using Examples.

Example 1 Hexagonal boron nitride powder to which 5% by weight of CaO・B ₂ O ₃ binder was added was mixed in an alumina ball mill, then hot-press molded at a temperature of 1800°C and a pressure of 120 kg/cm ² and sintered. obtain the body, then crush it,
Sintered particles of hexagonal boron nitride were obtained by sieving to a particle size of 44μ or less.

2m/m thick aluminum plate (height 20cm, width 20cm
cm) with 50 μm thick glass cloth (Nittobo WE-
05), and on this glass cloth, a mixed solution of 30 parts by weight of the above particle powder, 75 parts by weight of epoxy resin, and 35 parts by weight of methyl ethyl ketone consisting of an amine hardening liquid was applied using a gluing machine. , at 120℃
After drying for 10 minutes, pressurize at a pressure of 100Kg/ ^cm2 and a temperature of 150℃.
A highly thermally conductive electrically insulating substrate was obtained by curing for 60 minutes under heating. The translayer breakdown voltage of this board is 45-55
(KV/mm), and the peel strength was 1.5 Kg/cm.

In order to measure thermal conductivity, sheets with a thickness of 0.5 mm were prepared from glass cloth, hexagonal boron nitride, and epoxy resin having the same composition as described above. After curing in the same manner as above, the thermal conductivity was measured and found to be 0.6 Kcal/m·hr·°C. For comparison, a sheet was made in the same manner as described above, except that corundum particles with a shape factor (major axis/rectangular shape) of 1.0 to 1.4 and the same particle size were used instead of hexagonal boron nitride, and the thermal conductivity was measured. Result is
It was 0.42 Kcal/m·hr·°C, which was smaller than that of the present invention.

Example 2 As hexagonal boron nitride sintered particles,
A material obtained in the same manner as in Example 1 with the addition of 8% by weight of a binder with SiO ₂ /B ₂ O ₃ =9/1 (weight ratio) was used. The substrate was also manufactured in the same manner as in Example 1. The through-layer breakdown voltage of this product is 40 to 50 (KV/mm),
The peel strength was 1.4 kg/cm.

Comparative Example 1 A commercially available hexagonal boron nitride powder (particle size of 2 μm or less) was used as it was. The translayer breakdown voltage of the substrate using this material is 0 to 30
(KV/mm), and the peel strength was 0.5 Kg/cm.

Claims (1)

[Claims] 1. A metal plate and a glass cloth are fixed together with a mixture of sintered particles of hexagonal boron nitride and an organic polymer using calcium borate or borosilicate glass as a binder. A highly thermally conductive electrically insulating substrate. 2. The metal plate, the glass cloth, and the metal foil on it are fixed together with a mixture of sintered particles of hexagonal boron nitride and organic polymer using calcium borate or borosilicate glass as a binder. A highly thermally conductive electrically insulating substrate.