JP3465829B2 - Insulating material composition and circuit board and module using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating material composition used for electronic parts such as electric appliances, communication devices and automobiles, a metal base circuit board using the same, and a module using the same.

[0002]

2. Description of the Related Art Insulating materials having high thermal conductivity and high withstand voltage are required for applications such as metal base circuit boards, semiconductor devices and other electronic and electrical parts encapsulants, adhesives and potting agents. For example, since the metal base circuit board is used in the high power field, the insulating layer of the board is required to have high electrical insulation and high thermal conductivity. Furthermore, the frequency of circuits is increasing for the purpose of miniaturization and higher functionality of circuits, and circuit boards having a low relative dielectric constant and insulating materials therefor are desired. In particular, in recent years, power devices such as IGBT devices have been mounted, and a metal base circuit board having a low dielectric constant, a high electric insulation property, and a high thermal conductivity is required. There is a need for insulating material compositions for forming.

In a metal base circuit board, a metal plate and a conductive foil are bonded to each other with an electrically insulating adhesive made of a resin filled with aluminum oxide or the like. An insulating layer is formed on. Various compositions have been disclosed because the properties of metal-based circuit boards are highly dependent on the properties of the insulating layer and thus the insulating material.

For example, in JP-A-2-286768, by using an inorganic filler having a specific particle size, the inorganic filler can be highly filled, and the insulating adhesive for a circuit board has a high thermal conductivity. It is disclosed that a composition is obtained, and a metal substrate and a conductive foil are laminated via the adhesive composition to obtain a circuit board.

Further, in Japanese Patent Laid-Open No. 6-44824,
A bisphenol A type epoxy resin with a purity of 90% or more is filled with an inorganic filler such as aluminum oxide, aluminum nitride or boron nitride, and the thermal conductivity is 5.0 × 10 ^{-3 to} 18.0 × 10 ^-3 cal / cm ・
An insulating material having a sec · ° C. temperature and a glass transition temperature of 164-240 ° C. and a circuit board using the insulating material are disclosed.

[0006]

However, in an insulating material made of a resin highly filled with a substance having a high dielectric constant such as aluminum oxide (dielectric constant 9.0), a large amount of inorganic filler is filled. The higher the relative dielectric constant of the insulating material, the higher. At the same time, since the viscosity is increased and the number of voids involved is increased, there is a problem that the electrical insulation property is deteriorated and the withstand voltage characteristic is deteriorated.

Generally, the voltage applied to the voids present in the layered insulating material is higher as the relative dielectric constant of the insulating material is higher, so that the voids are more likely to be discharged. For this reason, the higher the relative dielectric constant of the filler, the easier the electrical insulation of the insulating layer and thus the circuit board using the same tends to deteriorate.

It is also known that the circuit board gradually deteriorates in its electrical insulation property under the conditions of its use and eventually causes a dielectric breakdown phenomenon to reach the end of its life. The progress of the deterioration of the electrical insulation exhibits a partial discharge phenomenon inside the insulating layer such as voids at the initial stage, and this partial discharge accelerates the deterioration of the insulating layer and finally passes through the insulating layer. It causes a discharge phenomenon and leads to dielectric breakdown. Therefore, in order to achieve long-term reliability of electrical insulation, it is important to increase the discharge starting voltage.

In the conventional metal-based circuit board, aluminum oxide having a high relative dielectric constant is mainly used as an inorganic filler with an emphasis on high thermal conductivity. Alternatively, the electrical insulating property is emphasized and the inorganic filler is not added, or even if added, only a small amount is filled. The former has high thermal conductivity but low electrical insulation and is inferior in long-term reliability, and the latter is excellent in electrical insulation but inferior in thermal conductivity, and therefore cannot be used for applications requiring high heat dissipation. As described above, there is a problem that it is difficult to combine high electrical insulation and long-term reliability thereof while maintaining high thermal conductivity.

An object of the present invention is to provide an insulating material composition used for a metal-based circuit board or the like which has a high thermal conductivity and can maintain a high electric insulating property for a long period of time.

It is another object of the present invention to provide a circuit board and a module which are excellent in heat dissipation, electric insulation and reliability even when high-power devices are mounted at high density.

[0012]

SUMMARY OF THE INVENTION The present invention comprises an inorganic filler and
It is made by curing a mixture of epoxy resins and has a thermal conductivity of 3.0 x 10 ^-3 cal / cm · sec · ° C or higher.
The insulating material composition for a circuit board is characterized in that it is 31.1 × 10 ⁻³ cal / cm · sec · ° C. or less and has a relative dielectric constant of 3.9 or more and 4.5 or less.

In the present invention, the inorganic filler is boron nitride,
An insulating material composition comprising one or more of diamond and beryllium oxide.

The present invention is also an insulating material composition characterized in that the inorganic filler contains surface-treated hexagonal boron nitride having a degree of graphitization (GI value) of 2.0 or less.

Further, the present invention has a thermal conductivity of 3.0 × 10 ^-3 cal.
A circuit board in which conductive foils are laminated with an insulating material composition having a relative dielectric constant of 4.5 or less / cm · sec · ° C. or more, and a module using the circuit board. is there.

The present invention will be described in detail below with reference to the drawings. FIG. 1 shows a cross-sectional view of a module using a metal base circuit board having an insulating layer formed of the insulating material composition of the present invention. After obtaining the metal base circuit board in which the conductive foil 3 is laminated on the metal plate 1 through the insulating layer 2 made of the insulating material composition of the present invention, the metal base circuit board is subjected to a treatment such as etching to obtain the ceramic chip component 5 and the semiconductor. The element 6, the terminal 7 and the like are laminated via the solder 4.

Here, for the metal plate 1, aluminum and aluminum alloys having a plate thickness of about 0.5 to 3.0 mm, copper, iron, stainless steel-based alloys, Invar-based multi-layered metals and the like are used.

The insulating layer 2 is an insulating material composition in which an inorganic filler and a resin are mixed and cured, and has a thermal conductivity of 3.0 × 10 ⁻³ c.
Al / cm · sec · ° C or higher and relative permittivity of 4.5 or lower.
When the relative dielectric constant of the insulating layer 2 exceeds 4.5, the discharge starting voltage is extremely lowered and the discharge deterioration is apt to occur, so that the long-term reliability of the electric insulation of the circuit board is significantly impaired. Regarding the thermal conductivity, if it is less than 3.0 × 10 ^-3 cal / cm · sec · ° C, the heat generated from the power element cannot be efficiently released,
If the temperature of the element exceeds the junction temperature (about 150 ℃), the element may malfunction or the life may be shortened.

[0019] As the resin used in the insulating material composition for forming the insulating layer 2, the epoxy resins are used. As the epoxy resin, bisphenol A type epoxy resin,
The bisphenol F type epoxy resin has a low viscosity and is suitable for high filling of the inorganic filler, which is preferable. Although the thickness of the insulating layer 2 is not particularly specified, it is preferably 20 to 500 μm in consideration of the balance between the dielectric breakdown voltage and the thermal resistance.

It is essential that the inorganic filler used in the insulating material composition forming the insulating layer 2 is a substance having a low relative dielectric constant. In order to obtain an insulating material composition having a thermal conductivity of 3.0 × 10 ⁻³ cal / cm · sec · ° C. or more and a relative dielectric constant of 4.5 or less, beryllium oxide, diamond,
Boron nitride is selected. Boron nitride is the most industrially suitable inorganic filler in consideration of economy or safety.
Further, as long as the desired desired thermal conductivity and relative permittivity are obtained by including one or more of these, other inorganic fillers such as alumina may be used in combination.

Regarding the particle size of these inorganic fillers,
It is preferably 15 μm or less. If it exceeds 15 μm, it is easy to generate lumps when mixed with the resin, or voids are likely to remain in the cured insulating layer, resulting in a decrease in thermal conductivity and a decrease in electrical insulation. I can't get it. 15 μm
If it is the following, a crushed product of a sintered body and the like can be used in the same manner as ordinary powder. Regarding the particle shape, it is desirable that the inorganic filler is highly filled in order to improve the thermal conductivity, and a shape close to a sphere is preferable.

Examples of the boron nitride include h-BN, P-BN, c-BN, t
Various materials such as -BN are used, but it is also possible to use them in combination. In particular, h-BN is preferable because it belongs to the hexagonal system and has a high electric insulation property, and is a raw material that can be obtained at low cost. The crystallinity of hexagonal boron nitride is indicated by the degree of graphitization (GI value) as a measure. The GI value is (1
00) (101) (102) plane diffraction intensity (peak area)
Therefore, it is calculated by the equation (1).

[0023]

[Equation 1]   GI value = ((100) area + (101) area) / ((102) area) ... (1)

The smaller the GI value, the higher the crystallinity. Hexagonal boron nitride that has been completely crystallized has a GI value of 1.4. The crystallinity of the hexagonal boron nitride used in the present invention is preferably 2.0 or less, more preferably 1.6 or less. Hexagonal boron nitride having a degree of graphitization of more than 2.0 generally has low purity, and when mixed with a resin, gas is easily generated and voids are easily entrapped, so that the electric insulation resistance is low, or the thermal conductivity is low. Occur.

The above-mentioned boron nitride is a silicone coupling agent in order to enhance the adhesiveness at the interface between the resin and boron nitride.
It is preferable that the surface treatment is performed with a titanate coupling agent, a silylating agent, or the like. Of these, those subjected to surface treatment with an organic silane compound are more preferable. The surface treatment of boron nitride with a surface treatment agent can also be performed by adding the surface treatment agent when the resin and boron nitride are mixed.

The compounding ratio of boron nitride is 40 vol% or more and 85 vol%
The following is preferable, but it is preferably 50 vol% or more and 70 vol% or less. If the compounding ratio of boron nitride is 40 vol% or less, the thermal conductivity of the obtained insulating material composition will not reach 3.0 × 10 −3 cal / cm · sec · ° C. On the other hand, if it exceeds 85 vol%, an elastic resin mixture cannot be obtained even if the above-mentioned surface treatment is performed, and the cured product is in a tattered state, so that the object of the present invention cannot be achieved. With 50 vol% or more and 70 vol% or less, high thermal conductivity,
Moreover, it is possible to stably produce a well-balanced insulating material composition having a low relative dielectric constant.

As the conductive foil 3, a general-purpose foil such as a copper foil for a conductor circuit, a composite foil, an alloy containing two or more kinds of metals such as copper, aluminum and nickel, or a clad foil using the above metals is used. Its thickness is from 5 μm to 1 mm. Further, nickel plating or nickel-gold plating may be applied on the conductive foil in order to impart wire bonding characteristics.

[0028]

[Operation and Examples] Examples will be specifically described below. (Example 1) Boron nitride powder (manufactured by Denki Kagaku Kogyo KK, GPS-
2) Hexamethyldisilazane (Toshiba Silicone Co., Ltd.)
(Manufactured by Mfg. Co., Ltd.) and silylated boron nitride powder was prepared. Using this silylated boron nitride powder as an inorganic filler, a mixture was prepared in which a bisphenol F type epoxy resin was filled at 61 vol%. An amine-based curing agent was added to this mixture, and the cured product obtained by heating and curing was subjected to the following thermal conductivity measurement and relative dielectric constant measurement. Then, the mixture
A metal base circuit board was produced by coating a 1.5 mm thick aluminum plate to form a layer having a thickness of 100 μm, and further laminating a copper foil having a thickness of 35 μm thereon and heating. Using this circuit board, the following discharge start voltage measurement and rise temperature measurement when the transistor was energized were performed. or,
In order to examine the dielectric breakdown life of the circuit board, the Vt characteristic was measured repeatedly at 20 times. The results obtained are shown in Table 1.
Shown in.

<Measurement method of thermal conductivity> Thickness 2 mm x diameter 1
Laser flash method thermal conductivity measuring device (Rigaku Denki Kogyo Co., Ltd. “LF / TCM-FA-
8510B ”), ATT range: 20 μV, sampling rate: 1000 μsec, filter: 100 Hz.

<Measurement method of relative permittivity> Based on JIS C6481, the measurement frequency was 100 kHz and the measurement temperature was 25 ° C.

<Measurement Method of Discharge Inception Voltage> A circular electrode pattern having a diameter of 20 mm was formed on the prepared metal base substrate by an etching method. The discharge start voltage between the base metal part and the pattern part was measured at a measurement frequency of 100 kHz with a partial discharge measuring instrument (QM-20, Mitsubishi Cable Industries, Ltd.).

<Measurement Method of Transistor Temperature Rise> A conductive foil of a metal base substrate is etched to form a pad portion of 10 × 15 mm, and a transistor (TO-220, TO-220,
Sold by Toshiba Corporation. While the metal plate surface side was being cooled, 100 W of electricity was applied to the transistor and the temperature at the top surface of the transistor was measured.

<Method of measuring Vt characteristic> A circular electrode pattern having a diameter of 20 mm is formed on a metal base substrate by an etching method, and an AC pattern is formed between the base metal portion and the pattern portion.
A half-wave voltage of 2 kV was applied. The measurement was performed in an environment of 125 ° C. to accelerate the test. The time from the start of voltage application to dielectric breakdown was measured, and the average life was calculated by the Weibull plot method.

Examples 2 to 9 and Comparative Examples 1 to 4 Commercially available boron nitride, diamond, beryllium oxide, aluminum oxide and the like having various particle sizes were prepared as inorganic fillers.
With the compounding ratios shown in Table 1, cured products of various insulating material compositions were prepared in the same manner as in Example 1, and the thermal conductivity and the relative dielectric constant were measured. Some of them were not surface-treated. Further, a circuit board was prepared using the insulating material composition, and the discharge starting voltage, the transistor rising temperature and the Vt characteristic were measured in the same manner as in Example 1. The results are shown in Table 1 together with the results of Example 1.

[0035]

[Table 1]

[0036]

According to the present invention, an insulating material composition having a high thermal conductivity, a low relative permittivity and an excellent electric insulating property can be obtained, and the discharge starting voltage is high and the long-term reliability is excellent. A circuit board and a module could be obtained. Since the insulating material composition of the present invention has a high thermal conductivity and a low relative dielectric constant, it is suitable as a sealing material for semiconductor elements.

[0037]

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a module using a metal base circuit board of the present invention. 1. Metal plate 2. Insulating layer 3. Conductive foil 4. Solder 5. Ceramic chip component 6. Semiconductor element 7. Terminal

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-5-198711 (JP, A) JP-A-55-166806 (JP, A) JP-A-6-44824 (JP, A) US Pat. No. 5,232,970 (US) , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01B 3/00 H05K 1/05 B32B 15/08

Claims (5)

(57) [Claims] 1. A cured product of a mixture of an inorganic filler and an epoxy resin, the thermal conductivity of which is 3.0 × 10 ⁻³ c.
al / cm · sec · ° C or higher 31.1 × 10 ^-3 cal /
cm · sec · ° C. or less and a relative dielectric constant of 3.9
An insulating material composition for a circuit board, which is not less than 4.5 and not more than 4.5. 2. The insulating material composition according to claim 1, wherein the inorganic filler contains one or more of boron nitride, diamond and beryllium oxide. 3. The inorganic filler has a degree of graphitization of 2.0 or less.
The insulating material composition according to claim 1, further comprising surface-treated hexagonal boron nitride. 4. A circuit board obtained by laminating a conductive foil on a metal plate with the insulating material composition according to claim 1, 2 or 3 interposed therebetween. 5. A module using the circuit board according to claim 4.