JP6006539B2 - Circuit board and electronic component mounting board - Google Patents

Description

  The present invention relates to a circuit board and an electronic component mounting board that can incorporate a capacitor having a large capacitance.

  As a circuit board for mounting a highly exothermic electronic component, a metal base circuit board is known in which an insulating layer made of an epoxy resin or the like filled with an inorganic filler is provided on a metal board, and a circuit is formed thereon with a conductor layer. . In addition, for the purpose of reducing noise and downsizing of a circuit board, a technique for increasing the dielectric constant of an insulating layer and using the insulating layer as a dielectric of a bypass capacitor is known (for example, Patent Document 1).

JP-A-10-242607

  In the circuit board of Patent Document 1, although the dielectric constant of the insulating layer is a relatively large value, the dielectric constant described in Patent Document 1 is insufficient for applications that require a large capacitance, There is a need to further increase the dielectric constant.

  The present invention has been made in view of such circumstances, and provides a circuit board capable of incorporating a capacitor having a large capacitance.

  According to the present invention, it has a metal substrate, an insulating layer formed on the substrate, and a conductor layer formed on the insulating layer, the insulating layer including a resin and an inorganic filler, The inorganic filler has a relative dielectric constant of 50 or more, the filling rate of the inorganic filler is 73 to 79% by volume, the inorganic filler has a coarse powder having an average particle diameter of 3 to 7 μm, and an average particle diameter. Is provided, and a circuit board is provided in which the ratio of the fine powder is 20 to 30% by volume when the total of the coarse powder and the fine powder is 100% by volume. .

  First, the inventors pay attention to the fact that in the experimental example described in Patent Document 1, the filling rate of the inorganic filler is 55.6% by volume at the maximum and the relative dielectric constant is 36 to 65. In order to increase the relative dielectric constant, the inventors have come up with an inorganic filler filling ratio of 73% by volume or more. And when the insulating layer which has such a filling rate was actually produced and the relative dielectric constant was measured, it succeeded in raising the relative dielectric constant of an insulating layer. However, when the filling rate is 80% by volume or more, although the relative dielectric constant increases, the conductor layer becomes difficult to adhere to the insulating layer, making it difficult to create a circuit board. Therefore, the upper limit of the filling rate is 79% by volume. It turned out to be important.

  Thus, it succeeded in raising the dielectric constant of an insulating layer by raising the filling rate of an inorganic filler. However, when the withstand voltage of the obtained insulating layer was measured, it was found that the withstand voltage might be unexpectedly lowered.

  In such a situation, when the present inventors further investigated, the withstand voltage becomes a high value when using an inorganic filler containing a specific average particle size of coarse powder and fine powder and a specific ratio. I found out.

  Based on the above knowledge, the present inventors have included a specific ratio of coarse powder and fine powder having a specific average particle diameter and a specific ratio and an inorganic filler having a specific dielectric constant. For the first time, it has been found that a circuit board capable of incorporating a capacitor having a large capacitance can be obtained by the synergistic effect, and the present invention has been completed.

Preferably, the inorganic filler is barium titanate.
Preferably, the resin is an epoxy resin.

  Moreover, according to this invention, the electronic component mounting board | substrate which has the said circuit board and the electronic component mounted on this circuit board is provided.

It is sectional drawing which shows the circuit board of one Embodiment of this invention.

Hereinafter, a circuit board according to an embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 1, the circuit board of this embodiment includes a metal substrate 1, an insulating layer 2 formed on the metal substrate 1, and a conductor layer 3 formed on the insulating layer 2.

1. Metal substrate 1
There is no restriction | limiting in particular in the material of the board | substrate 1, Iron, copper, aluminum, and its alloy can be used. Although the thickness of the board | substrate 1 is not specifically limited, For example, they are 0.5 mm or more and 4 mm or less. This is because if the substrate 1 is too thin, handling is difficult or heat dissipation is deteriorated, and if the substrate 1 is too thick, the entire circuit board becomes unnecessarily thick.

2. Insulating layer 2
The insulating layer 2 contains a resin and an inorganic filler.

2-1. Thickness of Insulating Layer In the present embodiment, the thickness of the insulating layer is preferably 30 to 200 μm, and more preferably 50 to 100 μm. This is because if the insulating layer is too thin, electrical insulation properties tend not to be ensured, and if it is too thick, heat dissipation tends to decrease, and further, it tends to be unable to contribute to miniaturization and thinning.

2-2. Resin The type of resin is not particularly limited, and an epoxy resin, a polyimide resin, a phenol resin, or the like can be used, and a flexibility-imparting component that is a polymer material with good electrical insulation can be added to this. Preferably, examples of the flexibility-imparting component include acrylic rubber, NBR, epoxy-modified acrylic rubber, epoxidized polybutadiene, and phenoxy resin. Moreover, it is preferable to use a coupling agent in order to improve the adhesiveness between the conductor layer and the insulating layer. As the coupling agent, a silane coupling agent is preferable, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, N-β. -Aminoethyl-γ-aminopropyltrimethoxysilane and the like.

2-3. Epoxy resin Examples of the epoxy resin include known epoxy resins such as naphthalene type, phenylmethane type, tetrakisphenol methane type, biphenyl type, and bisphenol A alkylene oxide adduct type epoxy resins, among which the stress relaxation property For this reason, an epoxy resin in which the main chain has a polyether skeleton and is linear is preferable.
The epoxy resin whose main chain has a polyether skeleton and is linear is bisphenol A type, bisphenol F type epoxy resin, bisphenol A type hydrogenated epoxy resin, polypropylene glycol type epoxy resin, polytetramethylene glycol type epoxy. There are aliphatic epoxy resins typified by resins, polysulfide-modified epoxy resins, and the like, and a plurality of these may be combined.
Of these epoxy resins, when high heat resistance is required for the circuit board, it is preferable to use a bisphenol A type epoxy resin that has a high electrical insulation property and thermal conductivity, and a cured resin body having high heat resistance can be obtained. . Moreover, as long as the effect of this bisphenol A type epoxy resin is exhibited, another epoxy resin may be used in combination with the bisphenol A type epoxy resin.

2-4. Bisphenol A type epoxy resin When a bisphenol A type epoxy resin is used, it is more preferable that the epoxy equivalent is 300 or less. This is because if the epoxy equivalent is 300 or less, it is possible to prevent a decrease in Tg (glass transition temperature) due to a decrease in crosslink density, which is observed when a polymer type is obtained, and hence a decrease in heat resistance. Further, when the molecular weight is increased, the liquid state becomes a solid state, and it becomes difficult to blend the inorganic filler into the curable resin, and the problem that a uniform resin composition cannot be obtained can be avoided.

2-5. Curing agent It is preferable to add a curing agent to the epoxy resin. The curing agent is not particularly limited as long as it can be cured by reacting with an epoxy resin, and specific examples thereof include, for example, phenol novolac resin, cresol novolac resin, various novolacs synthesized from bisphenol A, resorcin, and the like. Examples include various polyphenol compounds, acid anhydrides such as maleic anhydride and pyromellitic anhydride, and aromatic amines such as metaphenylenediamine, diaminodiphenylmethane, and diaminophenylsulfone. For semiconductor device sealing, novolak resins such as phenol novolak and cresol novolak are preferably used from the viewpoint of heat resistance, moisture resistance and storage stability, and two or more kinds of curing agents may be used in combination depending on the application.

2-6. Although the addition amount of a hardening | curing agent is not specifically limited, It is preferable that they are 5 mass parts or more and 50 mass parts or less with respect to 100 mass parts of epoxy resins, for example, 5, 10, 15, 20, 25 , 30, 35, 40, 45, 50 parts by mass, and may be within a range between any two of the numerical values exemplified here.

2-7. Inorganic filler The inorganic filler contained in the insulating layer 2 has a relative dielectric constant of 50 or more. For example, titanium dioxide, barium titanate, calcium titanate, strontium titanate, lead titanate, barium zirconate, Calcium zirconate, barium stannate and calcium stannate are used alone or in combination, and barium titanate is preferred from the viewpoint of high dielectric constant. In this specification, the dielectric constant means a value measured based on JIS C6481 under conditions of a temperature of 25 ° C., a frequency of 1 MHz, and a voltage of 1 V. The relative dielectric constant of the inorganic filler is, for example, 50, 100, 200, 300, 500, 1000, 1500, and may be any one or more of the numerical values exemplified here, and within the range between any two There may be.

  The filling rate of the inorganic filler is 73 to 79% by volume, preferably 77 to 79% by volume. If the filling rate is less than 73% by volume, the dielectric constant of the insulating layer 2 becomes too low, and if the filling rate exceeds 79% by volume, the adhesion between the conductor layer 3 and the insulating layer 2 becomes too bad. It is essential that the filling rate be within the above range.

  The inorganic filler includes coarse powder having an average particle diameter of 3 to 7 μm and fine powder having an average particle diameter of 0.05 to 0.7 μm, and the fine powder when the total of the coarse powder and fine powder is 100% by volume. Is 20 to 30% by volume. The average particle diameter of the coarse powder is, for example, 3, 4, 5, 6, 7 μm, and may be within a range between any two of the numerical values exemplified here. The average particle size of the fine powder is, for example, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 μm, and any of the numerical values exemplified here It may be within a range between the two. Specifically, the proportion of fine powder is, for example, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30% by volume, and is within the range between any two of the numerical values exemplified here. It may be. The withstand voltage can be increased by containing the coarse particles and fine particles having the above-mentioned particle sizes in the above proportion. The inorganic filler may be composed of these two types of powders, and may further include other types of powders having different average particle sizes. In this specification, the “average particle size” means a particle size at an integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method.

3. Conductor layer 3
Examples of the material for the conductor layer include copper, aluminum, iron, tin, gold, silver, molybdenum, nickel, titanium, and an alloy containing two or more of these metals, and copper having high versatility is preferable. Examples of the shape of the conductor layer include a plate, a sheet, a foil, and a laminate thereof. Although the thickness of a conductor layer is not specifically limited, For example, it is 10-300 micrometers. The surface of the conductor layer 3 may be subjected to a plating process such as nickel plating or nickel-gold plating.

4). Manufacturing Method The circuit board manufacturing method of the present embodiment may be a conventionally known circuit board manufacturing method. For example, after applying an insulating material as an insulating layer to a base material, the substrate is heated and semi-cured, and further applied to the surface of the insulating layer. There are a manufacturing method in which a metal foil as a conductor layer is laminated or hot pressed, and a manufacturing method in which a base material and a metal foil as a conductor layer are bonded to each other through a sheet of insulating material.

  The circuit board of the present invention was actually produced and evaluated by the following method.

(Production of insulating agent)
The insulating agent for forming the insulating layer 2 was produced as follows. Bisphenol A type epoxy resin (manufactured by DIC, “EXA850CRP”) and phenol novolac type curing agent (manufactured by Meiwa Kasei Co., Ltd., “Acmex MEH8005H”) or amine curing agent (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., “Acmex H” -84B ") (diaminodiphenylmethane) and an inorganic filler were stirred and mixed for 5 minutes with a rotation and revolution supermixer" Awatori Nertaro "AR-250 (manufactured by Shinky Co., Ltd., registered trademark) to produce an insulating agent. The epoxy resin and the curing agent were mixed at the ratio shown in Table 1. The inorganic filler used was a mixture of the following barium titanate at the filling rate and ratio shown in Table 1. In Table 1, the numerical value for the filler filling rate indicates volume%, and the numerical value for barium titanate indicates the volume% of each powder when the entire barium titanate is 100 volume%.

BT-01 d50 = 0.1 μm manufactured by Sakai Chemical
BT-03 made by Sakai Chemical Co., Ltd. d50 = 0.3μm
BT-05 made by Sakai Chemical Co., Ltd. d50 = 0.5μm
BT-UP1 d50 = 2μm manufactured by Nippon Chemical Industry Co., Ltd.
BT-UP1 d50 = 5μm manufactured by Nippon Chemical Industry Co., Ltd.
BT-UP1 d50 = 10μm manufactured by Nippon Chemical Industry Co., Ltd.

(Lamination of conductor layer 3)
The produced insulating material is applied onto a 2.0 mm thick aluminum plate (material: 4045, manufactured by Showa Denko KK) as the substrate 1 so that the thickness after drying is 75 μm by screen printing. An insulating layer 2 was formed. A 70 μm thick copper foil GTS-MP (trade name, manufactured by Furukawa Circuit Foil Co., Ltd.) as the conductor layer 3 is bonded onto the insulating layer 2 and heated at 180 ° C. for 7 hours to cure the insulating layer 2. It was.

(Circuit pattern is formed on conductor layer 3)
The conductor layer 3 was etched to form a circuit pattern to obtain a circuit board.

(Evaluation)
About the obtained circuit board, the dielectric constant, withstand voltage, and adhesiveness were evaluated in accordance with the following method. The obtained results are shown in Table 1.

<Measurement method of relative permittivity>
The periphery of the copper foil of the circuit board was etched, and a circular portion having a diameter of 20 mm was left as a sample. The measurement was performed based on JIS C6481 under conditions of a temperature of 25 ° C., a frequency of 1 MHz, and a voltage of 1 V. An LCR meter (manufactured by Yokogawa, Hewlett-Packard, “HP4284A”) was used as a measuring instrument.
The capacitance (X; unit, F) was measured under the above conditions. The relative dielectric constant (E) is the capacitance (X; unit, F), the thickness of the insulating layer (Y; unit, m), the area of the electrode plate (Z; unit, m ² ), and the dielectric constant (8 .85 × 10 ⁻¹² ; units, F / m)
E = X × Y / (8.85 × 10 ⁻¹² × Z)
This was calculated using the following formula.
The evaluation criteria for the relative dielectric constant are as follows.
◎: 180 or more ○: 170 or more and less than 180 Δ: 160 or more and less than 170 ×: less than 160

<Measurement method of withstand voltage>
A circular electrode having a diameter of 20 mm was formed on the circuit board by an etching method, and the withstand voltage between the circular electrode and the aluminum plate was measured by a step-up method defined in JIS C2110. The evaluation criteria are as follows.
A: 1.2 kV or more ○: 1.0 kV or more and less than 1.2 kV Δ: 0.8 kV or more and less than 1.0 kV ×: less than 0.8

<Adhesive evaluation method>
A circuit board was processed so as to leave a copper foil having a width of 10 mm to obtain a sample. Copper foil and a board | substrate were made into the angle of 90 degree | times, it peeled with the pulling speed of 50 mm / min, and the peeling strength was measured. Other conditions were based on JIS C6481. Tensilon (Toyo Baldwin, “U-1160”) was used as a measuring machine. The evaluation criteria are as follows.
◎: 2.2 kgf / cm or more ○: 2.0 kgf / cm or more and less than 2.2 kgf / cm Δ: 1.8 kgf / cm or more and less than 2.0 kgf / cm ×: less than 1.8 kgf / cm

(Discussion)
Referring to Table 1, in Examples 1 to 6, good results were obtained in all of relative permittivity, withstand voltage, and adhesiveness. On the other hand, in Comparative Examples 1-2, the filler filling rate was low, and a sufficiently high relative dielectric constant could not be obtained. In Comparative Example 3, the filler filling rate was increased too much, so that the adhesiveness deteriorated. In Comparative Example 4, the particle size of the coarse powder was too small, resulting in poor adhesion. In Comparative Example 5, the withstand voltage deteriorated because the particle size of the coarse powder was too large. In Comparative Example 6, the particle size of the fine powder was too large, and the filler filling rate could not be 78% by volume, and could not be evaluated. In Comparative Example 7, the proportion of fine powder was too large, and good results were not obtained in any of the dielectric constant, withstand voltage, and adhesiveness. In Comparative Example 8, the proportion of fine powder was too small, and good results were not obtained in relative permittivity and withstand voltage.

Claims (4)

A metal substrate, an insulating layer formed on the substrate, and a conductor layer formed on the insulating layer;
The insulating layer includes a resin and an inorganic filler,
The inorganic filler has a relative dielectric constant of 50 or more,
Filling ratio of the inorganic filler is 73-7 8% by volume,
The inorganic filler includes coarse powder having an average particle diameter of 3 to 7 μm and fine powder having an average particle diameter of 0.05 to 0.7 μm, and the total of the coarse powder and the fine powder is 100% by volume. The circuit board whose ratio of the said fine powder is 20-30 volume%. The circuit board according to claim 1, wherein the inorganic filler is barium titanate. The circuit board according to claim 1, wherein the resin is an epoxy resin. An electronic component mounting board comprising: the circuit board according to claim 1; and an electronic component mounted on the circuit board.