JP2738076B2 - Metal base circuit board - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a metal-based circuit board, and more particularly to a metal-based circuit board having excellent heat dissipation properties and high insulation reliability that can be used for bending. .

[Prior Art] With the miniaturization and high performance of electronic devices, a large number of components are also mounted on circuit boards at high density, and it is important to efficiently remove heat generated from these components. ing. This problem is particularly important when a component with a large power consumption such as a power IC is used or when a component called a hybrid IC is mounted at a very high density to form a single component as a composite.

Conventionally, in order to improve the heat dissipation of the circuit board, a metal-based circuit board is used in which a copper foil is laminated with an adhesive layer having an insulating function interposed on a metal plate such as aluminum and the circuit is formed by etching this. Was often done. However, this configuration has a problem in insulation reliability due to problems such as pinholes in the adhesive layer, and the heat dissipation is not sufficient because the adhesive needs to be applied more thickly than necessary. Further, aluminum plates and the like are easy to bend and the like, but are not widely used due to concerns about insulation properties due to cracking of the adhesive layer. For the purpose of overcoming this drawback, a configuration in which a polyimide film having good solder resistance is laminated in an adhesive layer has been proposed.

[Problems to be Solved by the Invention] However, a polyimide film is generally difficult to produce a thin film, and particularly a film thinner than about 25 μm is very expensive. Furthermore, the polyimide film has poor adhesiveness, and a sufficient adhesive strength cannot be obtained with a thin adhesive layer, a thick coating of the adhesive is required, and there has been a problem that heat dissipation cannot be sufficiently improved.

An object of the present invention is to provide a metal-based circuit board which solves the above-described problems, has excellent heat dissipation properties and insulation reliability, and can be formed by folding or the like.

[Means for Solving the Problems] The present invention relates to a metal base circuit board having an electric circuit formed on at least one surface of a base metal plate via an insulating layer, wherein the insulating layer has a moisture absorption rate of 4.0% by weight or less. , Thickness 2-20
A metal-based circuit board having a μm aromatic polyamide film.

The aromatic polyamide film in the present invention has a general formula: A film comprising an aromatic polyamide polymer containing the repeating structural unit represented by the formula (1) alone or in the form of a copolymer, and containing the above structural unit in an amount of 70 mol% or more, preferably 90 mol% or more. Here, Ar ₁ , Ar ₂ , and Ar ₃ contain at least one aromatic ring, and may be the same or different. Representative examples include the following.

Some of the hydrogen atoms on these aromatic rings are halogen group, a nitro group, an alkyl group of C ₁ -C _3, also those which are substituted with a substituent selected from alkoxy groups of C ₁ -C ₃ Including
X _{also, -O -, - CH 2 -} , - SO 2 -, - S-, Selected from

Among the above aromatic polyamides, those in which the benzene ring in which the amide bond is bonded at the para position is 50% or more, preferably 70% or more of the total aromatic ring, have improved heat resistance and mechanical properties and have a coefficient of thermal expansion. Is preferred in that the benzene ring in which part of the hydrogen atoms on the benzene ring is substituted with a halogen group, particularly a chloro group, is at least 30%, preferably at least 50%, of the whole aromatic ring. It is preferably used for reducing the coefficient of humidity expansion and the rate of moisture absorption and improving the adhesiveness.

The aromatic polyamide film of the present invention has a moisture absorption of 4.0% by weight or less, preferably 3.0% by weight or less. When the moisture absorption rate is large, when laminating the base metal plate, the film and the copper foil etc. constituting the electric circuit in three layers via an adhesive, since both sides of the film do not transmit gas at all, This is a major problem in the manufacture of circuit boards because the absorbed moisture causes bumping and swells on the copper foil side.

This phenomenon of swelling during lamination is related to the adhesiveness of the film. That is, since the swelling occurs when the water vapor pressure overcomes the adhesive force of the adhesive, if the adhesiveness of the film is good, the swelling is less likely to occur. When the contact angle of water on the film surface is used as an index of the adhesiveness of the film, the contact angle is preferably 80 degrees or less, more preferably 75 degrees or less. The smaller the contact angle of water, the higher the adhesive strength of the film. Although the contact angle of water is related to the type of the constituent unit of the polymer, it is possible to reduce the contact angle by performing a surface treatment such as a corona discharge treatment or a glow discharge treatment.

The aromatic polyamide film of the present invention has a thickness of 2 to 20 μm.
m, preferably 15 μm or less. If the thickness is less than 2 μm, there is a problem in handling such as wrinkling at the time of lamination. Even if such a thin film is made of an aromatic polyamide, the mechanical strength is easily increased and the handling is easy. However, the tensile modulus of the film is preferably 400 (kg / mm ² ) or more in at least one direction, and 500 (kg) or more. / mm ² ) or more is more preferable.

Regarding dimensional stability, in the case of the present invention, since a metal plate having a sufficient rigidity is laminated, the coefficient of thermal expansion and the coefficient of humidity expansion of the film are little affected, but in particular, the heat shrinkage during soldering is caused by shrinkage stress. Therefore, the thermal shrinkage of the film at 250 ° C. for 10 minutes without load is preferably 1.5% or less.

 Next, a method for producing the base film of the present invention will be described.

The polymer is synthesized by polymerizing a low-temperature solution in an amide organic polar solvent such as N-methylpyrrolidone or dimethylacetamide, or by interfacial polymerization using an aqueous solvent. When acid chloride and diamine are used as monomers in the polymer solution, hydrogen chloride is by-produced.To neutralize this, add an inorganic neutralizer such as calcium carbonate or an organic neutralizer such as ethylene oxide. I do. This polymer solution may be used as a stock solution for forming a film as it is, or a polymer may be isolated once and then redissolved in the above solvent to prepare a stock solution. Calcium chloride, lithium chloride, or the like may be added as a dissolution aid to the film-forming stock solution, but the amount and type of addition may vary depending on the type and amount of the repeating structural unit and copolymer unit.

A film is formed from the prepared stock solution by a general solution casting method. The film forming stock solution is cast and extruded from a die onto a drum or an endless belt to form a thin film, and the solvent or the solvent and the inorganic salt are removed by a dry, wet, dry or wet process, and then heat-treated to obtain a final film. During this film forming process, the film is stretched by about 1.0 to 2.5 times in area ratio, and heat treatment is performed at 250 to 350 ° C. for 1 to 5 minutes. These conditions may be appropriately set according to the type of polymer. This is important for obtaining the desired physical properties.

The produced aromatic polyamide film is laminated in the order of base metal plate / film / metal foil. Although there is no particular limitation on the lamination means, a general heat-resistant adhesive can be used,
Adhesives include epoxy, acrylic, urethane,
Examples thereof include polyimide-based and modified types thereof, and a thermosetting type is preferred from the viewpoint of heat resistance. The thickness of the adhesive layer is about 5 to 30 μm, but is preferably thinner in order to improve heat dissipation.

The base metal plate to be laminated has a thickness of about 0.05 to 5.0 mm and is not particularly limited to a material such as aluminum, steel plate, and stainless steel. Copper foil is the most common metal foil, and aluminum foil, tin foil, and the like can also be used, and the thickness is about 5 to 50 μm.

The laminate thus obtained is subjected to processing such as circuit formation by etching of a metal foil and coating of an insulating resist, thereby obtaining the metal-based circuit board of the present invention.

[Use] The metal-based circuit board of the present invention thus obtained is suitably used as a circuit board requiring general heat dissipation, and is further suitable as a board for a hybrid IC, a power IC, or the like. It is preferably used when the substrate is bent and formed with irregularities for the purpose of arranging the substrate.

[Method of Measuring Characteristic Value] The method of measuring the characteristic value of the present invention is as follows.

(1) Moisture absorption rate A film sample piece was placed in an atmosphere of 25 ° C and 75% RH for 24 hours.
After leaving it for a while to adjust the humidity, the weight is measured quickly. Next, the sample was heated and dried in a hot air oven at 200 ° C. for 5 minutes, the dry weight was measured, and the change in weight was divided by the dry weight to calculate the moisture absorption.

(2) Contact angle of water A small drop of distilled water was contacted and dropped on a horizontally placed film, a droplet having a diameter of 1 to 3 mm was placed, and the contact angle of the droplet on the film was measured by a goniometer. Measurement temperature is 25 ° C
It is.

(3) Tensile modulus The tensile modulus was determined from the tangent gradient at a position of 2% elongation of the strain / stress curve at 25 ° C. using a Tensilon type tensile tester. The sample has a width of 10 mm and a test length of 100 mm.
The test was performed at 00 mm / min.

(4) Heat Shrinkage A film sample having a width of 10 mm and a test length of 100 mm was heat-treated in a hot air oven at 250 ° C. for 10 minutes without load, and the heat shrinkage was calculated by the following equation.

[Examples] The present invention will be described based on examples.

Example 1 2-N-methylpyrrolidone, corresponding to a 0.9 molar ratio of 2-
Chlor-p-phenylenediamine and 4,4'-diaminodiphenyl ether corresponding to a 0.1 molar ratio are dissolved,
To this, terephthalic acid chloride equivalent to 0.2 mole ratio and 0.8 mole ratio
2-Chloro-terephthalic acid chloride corresponding to the molar ratio was added, and the mixture was stirred for 2 hours to complete the polymerization. Next, the mixture was neutralized with calcium hydroxide to obtain an aromatic polyamide solution having a polymer concentration of 11% by weight and a viscosity of 3100 poise.

The polymer solution was cast on an endless belt made of stainless steel and heated with hot air at 130 ° C. for 4 minutes to dry the solvent, thereby continuously peeling the film having self-holding property from the belt. Next, the film was introduced into a water tank to extract a residual solvent and calcium chloride generated by the neutralization, and then dried and heat-treated with a tenter to obtain an aromatic polyamide film having a thickness of 12.5 μm. During this film forming process, the film was stretched 1.1 times and 1.3 times in the longitudinal and width directions, respectively, and the heat treatment was performed at 320 ° C. for 3 minutes.

The physical properties of the obtained film were as follows: moisture absorption rate 1.8% by weight, water contact angle 58 °, tensile elastic modulus in the longitudinal direction and width direction of the film were 1040 (kg / mm ² ), 990 (kg / mm ² ), The heat shrinkage is
0.9% and 0.7%.

Next, an aluminum plate having a thickness of 1.0 mm on one side of the film and a copper foil having a thickness of 35 μm on the other side were laminated with a thermosetting epoxy-nylon adhesive. The thickness of the adhesive layer is 20 μm.

The copper foil of the laminate was etched to form a circuit pattern, and an aluminum-based circuit board was obtained.

The obtained circuit board had good heat resistance without change even when immersed in a solder bath without swelling or peeling generated during lamination.

In addition, the diameter from aluminum plate, film and copper foil laminate
A 25 mm disk-shaped sample was cut out, and the dielectric breakdown voltage was measured as it was and when the disk was bent at 90 ° with a straight line corresponding to the diameter of the circle. No change occurred.

Comparative Example 1 A polymetaphenylene isophthalamide resin was dissolved in N-methylpyrrolidone with a small amount of calcium chloride to obtain a polymer solution having a polymer concentration of 18% by weight and a viscosity of 2700 poise.

Using this polymer solution, a film was formed in the same manner as in Example 1 to obtain an aromatic polyamide film having a thickness of 12.5 μm. The film has a moisture absorption of 5.7% by weight and a water contact angle of 5
3 degrees.

Next, when the lamination of the aluminum plate / film / copper foil and the formation of the circuit pattern were performed in the same manner as in Example 1, swelling was observed between the copper foil / film and the adhesive during thermosetting. , Resulting in a defective circuit board.

Comparative Example 2 When an aluminum plate / film / copper foil was laminated and a circuit pattern was formed on an aromatic polyamide resin film (25 μm thick) in the same manner as in Example 1, swelling occurred between the copper foil and the film. , Resulting in a defective circuit board. The polyimide film used had a moisture absorption of 2.2% by weight and a contact angle of water of 73 degrees.

Comparative Example 3 The aluminum plate and copper foil used in Example 1 and the aluminum plate and copper foil were directly laminated with an adhesive, and the same dielectric strength test as in Example 1 was performed. However, the adhesive thickness is 55μm
Met. The dielectric breakdown voltage was 2.9 kV when the disc-shaped sample was not bent, but was 1.4
It was reduced to half of kV, and insulation was reduced.

[Effect of the Invention] By laminating a thin aromatic polyamide film having a specific moisture absorption rate in the insulating layer of the metal-based circuit board of the present invention, swelling, peeling, etc. of the metal foil in the laminating step of the substrate forming step are prevented. It has no insulation, has high insulation reliability and heat dissipation, and has the effect that it can be bent and used.

Claims (1)

(57) [Claims] 1. A metal base circuit board having an electric circuit formed on at least one surface of a base metal plate via an insulating layer, wherein the insulating layer has a moisture absorption of 4.0% by weight or less and a thickness of 2 to 20%.
A metal-based circuit board comprising a μm aromatic polyamide film.