JPH04330796A - Metal base printed wiring board and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a circuit board having excellent heat radiation by forming a hard carbon film having high thermal conductivity as an insulating layer on a surface of a board made of a metal material, and forming a conductive layer, or an adhesive layer and a conductive layer thereon. CONSTITUTION:A board of a metal material is coated between a conductive layer and an adhesive layer with an insulating layer made of a hard carbon film having high thermal conductivity. The film is formed by an ion beam method. As the material of the board, various alloy such as iron-based, aluminum-based, titanium-based alloy, and as the conductive layer, various metal such as copper, silver, gold, aluminum, etc., and their alloys are used. As the adhesive layer, thermoplastic adhesive, thermosetting resin, rubber-based adhesive and mineral adhesive are used. In order to coat with the film, it is irradiated with an ion beam containing carbon atom of Kaufmann type or bucket type ion source, etc. Thus, a metal base printed circuit board having excellent heat radiation can be obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-based printed wiring board used as a hybrid IC board, a power supply circuit board, etc., and a method for manufacturing the same.

0002

[Prior Art] Metal-based printed wiring boards are mainly made by laminating epoxy resin or glass cloth impregnated with epoxy resin and electrolytic copper foil on the surface of an aluminum plate, silicon steel plate, galvanized steel plate, etc. as a substrate. It is used as a hybrid IC board and a power supply circuit board.

[0003] Compared to general resin printed wiring boards and ceramic printed wiring boards, metal-based printed wiring boards have
Since the board is made of a metal material with good thermal conductivity, it is possible to prevent the temperature of the mounted components and the board itself from rising, and it has excellent heat dissipation. However, the above metal-based printed wiring boards use epoxy resin or glass cloth impregnated with epoxy resin, which has lower thermal conductivity than metal substrates, as the insulating layer, so it is difficult to take advantage of the metal substrate's good thermal conductivity. do not have. That is, conventional insulating materials sometimes cause problems in terms of heat dissipation. Therefore, it is necessary to develop an insulating layer with high thermal conductivity.

Hard carbon films are known as insulating materials with high thermal conductivity. This hard carbon film has been created by various vapor phase growth methods, but conventional methods cannot be used for limited materials such as tungsten carbide.
Although it has been possible to coat with adhesive strength strong enough to withstand practical use, it has been difficult to coat iron-based metal materials.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an insulating layer and a conductive layer with high thermal conductivity on the surface of a substrate made of a metal material.
Another object of the present invention is to provide a metal-based printed wiring board with excellent heat dissipation properties and a method for manufacturing the same by sequentially forming an insulating layer, an adhesive layer, and a conductive layer with high thermal conductivity.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the metal-based printed wiring board of the present invention includes an insulating layer made of a hard carbon film with high thermal conductivity on the surface of a substrate made of a metal material as a conductive layer or adhesive. coating between the agent layers. The method for manufacturing a metal-based printed wiring board of the present invention is characterized in that the hard carbon film is formed by an ion beam method.

That is, with other vapor phase growth methods such as the CVD method, it was difficult to form a hard carbon film on the surface of a metal substrate with a strong enough adhesion force to withstand practical use, but the ion beam method was adopted. By doing so, it became possible to form an insulating layer suitable for metal-based printed wiring boards, and the present invention was completed.

[0008]

[Operation] The metal-based printed wiring board of the present invention has a structure in which a hard carbon film and a conductive layer, or a hard carbon film, an adhesive layer, and a conductive layer are sequentially provided on the surface of a substrate made of a metal material. The hard carbon film or diamond-like carbon film referred to in the present invention is as follows. Its main elemental composition is carbon, and it has a hardness similar to that of natural diamond.It is amorphous and shows a halo pattern in its electric diffraction image. In the Raman spectrum, it is around 1580 cm-1 and 1
It shows a broad peak characteristic of amorphous materials near 360-1. Even when a hard carbon film is observed with a scanning electron microscope at a magnification of about 10,000 times, it is a uniform and smooth film with no crystal grains observed. Hard carbon films are generally produced by a gas phase synthesis method using hydrocarbon compounds as raw materials, and according to Rutherford scattering analysis using argon ions, they contain less than 40 atom% of hydrogen, and hydrogen is a dangling bond of carbon atoms. The amorphous state is stabilized by entering the
It is thought that the structure will also have a high degree of hardness.

[0009] It is assumed that the presence of an appropriate amount of hydrogen makes the hard carbon film exhibit a high hardness similar to that of natural diamond; however, if there is too much hydrogen in the hard carbon film, the film becomes a soft organic film. Therefore, the proportion of hydrogen in the film is 35 atom% or less, preferably 20 to 30 atom%, when measured by Rutherford scattering analysis using argon ions.
% is preferable.

Table 1 shows, for example, a comparison of the thermal conductivity and specific resistance of the above-mentioned hard carbon film with that of an epoxy resin and a glass cloth impregnated with an epoxy resin.

[0011]

[Table 1]

[0012] From the above, the thermal conductivity of a hard carbon film is on the same level as or higher than that of metal, so when a hard carbon film is used as an insulating layer, heat dissipation is improved, and the temperature of the mounted components and the board itself is lowered. It can prevent the rise. Heat dissipation performance is generally measured by soldering a TO-220 transistor to a printed wiring board and comparing the thermal resistance, which is the slope of temperature rise (° C.) against collector loss (W).

[0013] A generally used 1.5 mm thick aluminum plate is coated with 45 μm of epoxy resin as an insulating layer.
Or glass cloth 125μm impregnated with epoxy resin
The thermal resistance of an aluminum-based printed wiring board laminated with 18 μm thick electrolytic copper foil is, for example, 4
．． 5°C/W and 6.5°C/W. Next, in the present invention, a method of coating a hard carbon film on the surface of a metal substrate is a method of irradiating an ion beam containing carbon atoms generated by various ion sources such as a Kauffman type ion source and a bucket type ion source. can be applied. Here, a coating method using the Kauffman type ion source shown in FIG. 1 will be explained as an example. Hydrocarbon gas, which is a raw material for a hard carbon film, is introduced under reduced pressure, ionized by glow discharge and red-hot filament 3, and extracted by the expanding magnetic field of electromagnet 4. This part covered with electromagnets is called the ion source. The extracted ions are accelerated toward the base material 1 to which a negative bias voltage is applied, collide with the material, and vapor deposit.

As the raw material gas, hydrocarbons such as methane, ethane, acetylene, and benzene, which can be easily introduced as a gas, may be used, and among them, methane is preferred. Hydrogen gas may be used as a diluent gas for the above-mentioned raw material gas. The pressure inside the container is 1 x 10-6 because it is necessary to generate plasma and accelerate ions.
Torr to 1 Torr is sufficient, but in terms of film quality and film formation rate, 1 x 10-4 Torr to 1 x 10-1 Torr is recommended.
r is desirable. The temperature of the material is room temperature (about 25℃)
to 350° C., a good thin film is formed. Within this range, a particularly preferred range is from room temperature (about 25°C) to 300°C.

The bias voltage between the material and the ion source is -
From 50V to -1500V, especially from -500V to -
1200V is a preferred range. When hydrocarbon ions are accelerated by a bias voltage and collide with a material, the C-H bonds of the colliding ions are broken due to the collision energy.
Hydrogen atoms are ejected. The amount of hydrogen atoms ejected depends on the kinetic energy of the colliding ions, that is, the bias voltage; if the bias voltage is too low, a soft, organic film with a large amount of hydrogen tends to form, whereas if the bias voltage is too high, a graphite-like film tends to form. Furthermore, self-sputtering of the film occurs, reducing the film formation rate. The appropriate magnetic flux density at the ion source is in the range of 100G to 1000G.
A more preferable range is 300G to 500G. Since the detailed manufacturing conditions vary depending on the arrangement of the gas inlet in the apparatus, the size of the ion source, the position of the material, etc., it is desirable to set optimal conditions as appropriate.

Metal materials that can be applied to the substrate in the present invention include various alloys such as iron-based, aluminum-based, and titanium-based alloys, but among these, conventional film-forming methods have not been able to form hard carbon films with good adhesion. This is particularly effective when dealing with difficult-to-harden iron-based materials. Specifically, steel materials including commercially available alloy steels such as pure iron, carbon steel containing a particularly large amount of carbon, stainless steel containing mainly chromium, silicon steel containing mainly silicon, iron-based amorphous alloys, and these materials. Examples include those in which other elements are implanted into the surface by ion implantation or carburizing treatment. The finish roughness of the surface to be coated with the hard carbon film does not matter, but in order to coat the surface with a film with strong adhesion, it is desirable to remove deposits such as oil, fat, rust, etc. beforehand.

Next, a conductive layer or an adhesive layer and a conductive layer are coated on the metal substrate coated with the hard carbon film. To coat the conductive layer directly on the hard carbon film, there are several methods: crimping the conductive foil by pressing, etc., wet plating by electroplating, electroless plating, etc., hot-dip plating, metal spraying, vapor phase plating, and vacuum plating. There are dry plating methods such as vacuum plating such as vapor deposition, sputtering, and ion plating.

Materials that can be applied to the conductive layer in the present invention include copper,
Examples include various metals such as silver, gold, and aluminum, and alloys thereof. In the method of bonding conductive foil by press working, it is effective to provide an adhesive layer on the hard carbon film. To provide the adhesive layer, there are a method of supplying it as a coated paper (adhesive sheet), a method of applying an adhesive, etc., as in the general manufacturing of printed wiring boards.

Materials that can be applied to the adhesive layer in the present invention include vinyl resins, acrylic resins, cellulose resins, thermoplastic adhesives such as asphalt, epoxy resins, phenolic resins,
Examples include thermosetting resins such as melamine resin, polyamide resin, polyester resin, alkyd resin, urethane resin, and silicone resin, rubber adhesives such as butadiene/acrylonitrile rubber and chloride rubber, and mineral adhesives such as sodium silicate.

Now, as an insulating layer, epoxy resin or
When using glass cloth impregnated with epoxy resin, the film thicknesses are, for example, 45 μm and 125 μm, respectively. Since insulation can be ensured by the hard carbon film, the thickness of the adhesive layer is thinner than these and is sufficient.

[0021]

【Example】

Example 1 A 0.5 mm thick silicon steel plate (Si content: 3%) was used as a substrate, and first coated with a hard carbon film under the conditions shown in Table 2 using the Kauffman type ion source shown in FIG. Ion source-substrate distance: 50 mm The physical properties and structure of the obtained film are as follows.

Film thickness: 1.2 μm 10 gf loading Vickers hardness: 4500 kgf/m
m2 Film adhesion strength by scratch test method: 5 x 107
N/m2 Thermal conductivity: 800 x 10-3 cal/cm・
sec・℃ resistivity: 0.9×1014Ω・cm Raman spectrum: around 1580cm-1 and 1360c
A wide peak is shown near m-1.

Hydrogen content: 28 atom% Electron diffraction image: Halo pattern with no clear diffraction lines Next, chemical copper plating (electroless plating) on the hard carbon film
A sample of a metal-based printed wiring board was obtained by applying 0.2 μm of electroplating using a copper cyanide plating bath as a base plating. A TO-220 transistor was soldered to this sample, and the thermal resistance was measured.

Thermal resistance: 0.6°C/W Example 2 A 0.5 mm thick silicon steel plate (3% Si content) was used as the substrate, and the Kauffman type ion source shown in FIG. A hard carbon film was coated under the conditions shown below.

[0025]

[Table 2]

Ion source-substrate distance: 50 mm The physical properties and structure of the obtained hard carbon film were the same as those shown in Example 1. Next, an epoxy resin adhesive was applied to the hard carbon film to a thickness of approximately 10 μm, and an 18 μm thick electrolytic copper foil was bonded by pressing to obtain a metal-based printed wiring board sample. A TO-220 transistor was soldered to this sample, and the thermal resistance was measured.

Thermal resistance: 1.2°C/W Example 3 A 0.5 mm thick silicon steel plate (Si content: 3%) was used as the substrate, and the Kauffman type ion source shown in FIG. Pre-sputtering and hard carbon film formation were performed under the conditions shown below.

[0028]

[Table 3]

Ion source-substrate distance: 50 mm The physical properties and structure of the obtained film are as follows. Film thickness: 1.2μm 10gf loading Vickers hardness: 4500kgf/m
m2 Film adhesion strength by scratch test method: 18×107
N/m2 Thermal conductivity: 800 x 10-3 cal/cm・sec・℃
Specific resistance: 0.9×1014Ω・cm Raman spectrum: around 1580cm-1 and 1360c
Hydrogen content showing a wide peak near m-1: 28 atom% Electron diffraction image: halo pattern with no clear diffraction lines Compared to the hard carbon film of Example 1, the carbon film was irradiated with an oxygen ion beam in advance. In this case, the adhesion of the film was improved by more than three times.

Next, 0.2 μm of chemical copper plating (electroless plating) was applied on the hard carbon film, and using this as a base plating, electroplating was performed for 20 minutes using a copper cyanide plating bath.
A metal-based printed wiring board sample was obtained by applying μm. A TO-220 transistor was soldered to this sample, and the thermal resistance was measured. Thermal resistance: 0.6°C/W Example 4 A 0.5 mm thick silicon steel plate (Si content: 3%) was used as the substrate, and the Kauffman type ion source shown in Figure 1 was used under the conditions shown in Table 3. Pre-sputtering and hard carbon film formation were performed.

Ion source-substrate distance: 50 mm The physical properties and structure of the obtained hard carbon film were the same as those shown in Example 3. Next, an epoxy resin adhesive was applied to the hard carbon film to a thickness of approximately 10 μm, and an 18 μm thick electrolytic copper foil was bonded by pressing to obtain a metal-based printed wiring board sample. A TO-220 transistor was soldered to this sample, and the thermal resistance was measured.

Thermal resistance: 1.2°C/W Example 5 Amorphous alloy Fe80.5 with a thickness of 25 μm each on the substrate
Si6. 5B12C1,Fe78Si12B10,C
Using three types of o70Fe5Si15B10 (atom%), preliminary sputtering and film formation of a hard carbon film were performed under the conditions shown in Table 3 using the Kauffman type ion source shown in FIG.

Ion source-substrate distance: 50 mm The physical properties and structure of the obtained film are as follows. Film thickness: 1.3 μm Thermal conductivity: 900 x 10-3 cal/cm・sec・℃
Specific resistance: 0.8×1014Ω・cm Raman spectrum: around 1580cm-1 and 1360c
Hydrogen content showing a wide peak near m-1: 28 atom% Electron diffraction image: Halo pattern with no clear diffraction lines Next, chemical copper plating (electroless plating) on the hard carbon film
A sample of a metal-based printed wiring board was obtained by applying 0.2 μm of electroplating using a copper cyanide plating bath as a base plating. A TO-220 transistor was soldered to this sample, and the thermal resistance was measured.

Thermal resistance: 0.6° C./W Since amorphous alloys have high strength, by using them for substrates, it is possible to reduce the thickness and weight. The tensile strength and Young's modulus are, for example, 30 for Fe-based alloys, respectively.
0~400kgf/mm2, 0.02~0.03k
gf/mm2, which is considerably higher than the highest value of metal materials currently in practical use.

Furthermore, since the amorphous alloy has high magnetic permeability, it is possible to provide a metal-based printed wiring board with excellent magnetic shielding properties. Example 6 Substrate composition: Fe73.5Si13.5B9 Cu1
Nb3 (atom%) amorphous alloy at 550℃
, grain size 10 crystallized by annealing in N2 gas for 1 hour.
Using a soft magnetic ribbon with a thickness of 25 μm and an ultra-fine grain structure of 100 nm, pre-sputtering and film formation of a hard carbon film were first performed using the Kauffman type ion source shown in Figure 1 under the conditions shown in Table 3. Ta.

Ion source-substrate distance: 50 mm The physical properties and structure of the obtained hard carbon film were the same as those shown in Example 5. Next, an epoxy resin adhesive was applied to the hard carbon film to a thickness of approximately 10 μm, and an 18 μm thick electrolytic copper foil was bonded by pressing to obtain a metal-based printed wiring board sample. A TO-220 transistor was soldered to this sample, and the thermal resistance was measured.

Thermal resistance: 1.2°C/W The soft magnetic ribbon with ultrafine structure used this time has high magnetic permeability, so by using it in the substrate, a metal-based lint wiring board with excellent magnetic shielding properties can be provided. can.

[0038]

Effects of the Invention The present invention provides heat dissipation by forming a hard carbon film with high thermal conductivity as an insulating layer on the surface of a substrate made of metal material, and forming a conductive layer or an adhesive layer and a conductive layer thereon. A metal-based printed wiring board with excellent properties is obtained.
Also, the plate thickness can be reduced. In addition, by adopting the ion beam method, it is possible to coat the surface of various metal materials, especially iron-based materials.
A hard carbon film can be formed with a strong enough adhesion to be used as an insulating layer.

Furthermore, by using an amorphous alloy or a soft magnetic ribbon having an ultrafine grain structure obtained by crystallizing the same alloy for the substrate, it is possible to reduce the weight or improve the magnetic shielding property.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of an ionization vapor deposition apparatus.

[Explanation of symbols]

1 Base material 2 Grid 3 Filament 4 Electromagnet 5 Gas introduction pipe

Claims (5)

[Claims] 1. A metal-based printed wiring board comprising a hard carbon film and a conductive layer sequentially provided on the surface of a substrate made of a metal material. 2. A metal-based printed wiring board comprising a hard carbon film, an adhesive layer, and a conductive layer sequentially provided on the surface of a metal substrate. 3. The metal-based printed wiring board according to claim 1, wherein the metal material is iron-based. 4. A method for manufacturing a metal-based printed wiring board, comprising forming a hard carbon film on the surface of a metal substrate by an ion beam method. 5. The method for manufacturing a metal-based printed wiring board according to claim 4, wherein the metal material is iron-based.