JPH0660719A - Composite dielectric - Google Patents

Abstract

PURPOSE:To provide a composite dielectric having a high dielectric constant, fine adhesion to an electrode, and a small dielectric tangent. CONSTITUTION:Dielectric ceramics powder of 5-90 percentage in volume is mixed into a phenoxy resin. And further the phenoxy resin is crosslinked by a crosslinking agent so as to form composite dielectric. Consequently, the composite dielectric has high degree of freedom in form, and heat resistance, and further, during the process of its forming, an electrode such as copper foil or the like can be bonded to the composite dielectric.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a built-in capacitor type wiring board in which a wiring board itself can freely form a capacitor, and a composite dielectric used for forming a capacitor.

[0002]

2. Description of the Related Art Conventionally, various methods of incorporating high dielectric constant ceramic powder into a polymer material have been studied for the purpose of improving workability and crack resistance of ceramics. Among them, in order to increase the dielectric constant, it has been proposed to use a dielectric ceramic powder having a dielectric constant as high as possible and to increase the filling degree of the ceramic powder.

However, with epoxy resins and phenolic resins that are commonly used in this type of technology, the ceramic powder has a limit of 60 to 70% by volume. It tends to be smaller due to the inclusion of Further, when copper foil or the like used as an electrode is adhered, the adhesiveness is deteriorated. Therefore, there is a limit to the improvement of the dielectric constant.

In order to improve this, JP-A-53-881
In Japanese Patent Laid-Open No. 98, a method of mixing two or more kinds of ceramic powders having different particle diameters to increase the filling rate has been proposed. However, in reality, the ceramic powders have a wide particle size because they are obtained by pulverization. It is practically difficult to accurately mix two or more kinds of particles having a distribution and different particle sizes.

In addition to this, a method of adding a small amount of a conductive component in order to increase the dielectric constant has been proposed, but the dielectric loss tangent (tan δ) becomes larger than the dielectric constant, so that a capacitor, a wiring board with a built-in capacitor, etc. Can not be used for.

Therefore, the main object of the present invention is to provide a composite dielectric having a high dielectric constant, good electrode adhesion, and a small dielectric loss tangent.

[0007]

In order to achieve the above object, the composite dielectric of the present invention comprises a phenoxy resin mixed with 5 to 90% by volume of dielectric ceramic powder, and the phenoxy resin is crosslinked with a crosslinking agent. It is characterized by being formed.

[0008]

In the case of the composite dielectric, the filling amount of the ceramic powder is usually 60 to 70% by volume as described above,
By using a phenoxy resin, which is a high molecular weight linear polymer, as a binder as in the present invention, it becomes possible to fill the ceramic powder up to about 90% by volume without deteriorating the adhesiveness of the electrode, and thereby the dielectric constant. It has been confirmed that it can be dramatically improved.

The reason why the ceramic powder can be highly filled in this way is considered that the phenoxy resin has good wettability with the ceramic powder and can improve the dispersibility of the ceramic powder.

However, when the amount of the ceramic powder added exceeds 90% by volume, the dielectric constant tends to be small, the mechanical strength is extremely lowered, and the adhesion of the electrodes is extremely deteriorated. If the amount of the ceramic powder added is less than 5% by volume, the effect of adding the ceramic powder does not appear in the dielectric properties. For this reason, the amount of ceramic powder added is limited to the above range.

[0011]

EXAMPLES Specific examples of materials and the like used for the composite dielectric of the present invention will be described below.

The phenoxy resin is a linear polymer obtained by the condensation reaction of bisphenol A and epichlorohydrin, and has the same central structure as the epoxy resin, but has a very large molecular weight of, for example, 30,000 to 200,000 and is thermoplastic.
The larger the molecular weight of the phenoxy resin used in this invention, the better the wettability with the ceramic powder.

As the crosslinking agent used for crosslinking the phenoxy resin, butylated melamine resin, butylated urea resin, blocked isocyanate, benzoguanamine resin and the like can be used.

The dielectric ceramic powder needs to be appropriately selected depending on the application, but for example, BaTiO ₃ , SrTiO ₃ , C
In addition to aTiO ₃ and TiO ₂ , Pb for obtaining a higher dielectric constant
A lead compound such as (Zr, Ti) O ₃ series ceramics may be used.

As described above, when the amount of the ceramic powder added exceeds 90% by volume, the dielectric constant tends to be small and the mechanical strength is extremely lowered. If it is less than 5% by volume, the effect of adding the ceramic powder does not appear in the dielectric properties.

Regarding the particle size of the ceramic powder, the moldability,
Considering the kneading property, it is preferably about 1 to 50 μm, and 1 μm
If it is smaller than m, the specific surface area of the whole ceramic powder becomes large, the wettability with the polymer material deteriorates, and the moldability deteriorates. On the other hand, when it is larger than 50 μm, it is difficult to disperse the particles uniformly, and there is a possibility that characteristic variations may occur locally.

Further, to the mixture of the phenoxy resin, the ceramic powder and the cross-linking agent, a lubricant such as stearic acid, a dispersant, and a coupling agent for improving adhesion are added to the extent that the dielectric properties are not impaired. Is also good.

The phenoxy resin, the ceramic powder, the cross-linking agent and the like may be kneaded by a commonly used method such as a ball mill, roll or kneader.

The thus kneaded material is thermocompression bonded. As a result, the phenoxy resin, which is a thermoplastic resin, is crosslinked to form an insoluble and infusible thermosetting material, and the composite dielectric of the present invention is obtained.

As a method of forming an electrode on the composite dielectric of the present invention, plating, vapor deposition, sputtering or the like may be used in addition to the method of attaching a copper foil at the time of molding as shown in the following examples. As a result, a strong and precise electrode or electric circuit can be formed.

Next, more specific examples according to the present invention and comparative examples corresponding to conventional examples will be described.

Example 1 A phenoxy resin varnish (solid content 35% by weight: manufactured by Tohto Kasei Co., Ltd.) was calculated as 1 in terms of solid content.
6% by volume, 4% by volume of modified melamine resin (manufactured by Mitsui Toatsu Chemicals, Inc.) as a crosslinking agent for phenoxy resin, and 80% by volume of barium titanate powder having a relative dielectric constant of 200 as dielectric ceramic powder, An appropriate amount of methyl ethyl ketone was added for kneading, and the mixture was thoroughly kneaded with a roll.

After sufficiently drying the solvent of this kneaded product, it was pulverized into a fine powder. The fine powder was evenly spread between two electrolytic copper foils having a thickness of 70 μm, and hot pressed at 160 ° C. for 30 minutes. The pressing pressure was about 500 kg / cm ² .

The dielectric properties of the thus obtained (substrate) were measured with an LCR meter at a frequency of 1 MHz. Also, the adhesion between the composite dielectric and the copper foil is JIS64
Based on 81, the peel strength in the 90 degree direction was evaluated. The results are shown in Table 1.

Example 2 The phenoxy resin varnish of Example 1 was used in an amount of 24% by volume in terms of solid content, and the modified melamine resin was added in an amount of 6%.
70% by volume of barium titanate of Example 1 was added thereto. The subsequent production and evaluation of the sample were the same as in Example 1.

(Comparative Examples 1 to 3) Epoxy resin (trade name Epicoat # 1001: manufactured by Yuka Shell Epoxy Co., Ltd.)
Dicyandiamide as a curing agent and imidazole as an accelerator were added to the same, and the same dielectric ceramic powder as in Examples 1 and 2 was added to 60% by volume (Comparative Example 1), 70% by volume (Comparative Example 2), 80% by volume (Comparative Example). 3) It was mixed. Then, a sample was prepared in the same manner as in Examples 1 and 2, and the characteristics were measured. The results are shown in Table 1.

[0027]

[Table 1]

In Table 1, "inability to make a sample" means that the resin did not sufficiently wet the ceramic powder and the ceramic powder collapsed after molding.

As can be seen from Table 1, when 80% by volume of the ceramic powder was added, the sample could not be prepared in Comparative Example 3, whereas in Example 1, there was no such problem and it was very A large dielectric constant was obtained. Further, even when 70% by volume of the ceramic powder was added, the dielectric constant of Example 2 was about twice that of Comparative Example 2.

The peel strength of the copper foil was also measured in Examples 1 and 2.
The value of the product of Comparative Example 2 was much larger than that of Comparative Example 2.

Further, the dielectric loss tangents of Examples 1 and 2 were as small as those of the comparative examples, and were sufficient as dielectrics for capacitors and the like.

Moreover, since the phenoxy resin is soluble in a solvent, it can be used as a paste or a powder. Therefore, the composite dielectric of the present invention can be thinned to a thickness of several μm by a doctor blade method or a screen printing method. A thick plate-shaped object or a complex dielectric having a complicated shape can be manufactured from the layered complex dielectric, and there is also an advantage that the degree of freedom of the form is high.

Further, the phenoxy resin is originally a thermoplastic resin, but by thermally cross-linking this with a cross-linking agent, it becomes a thermosetting resin, and heat resistance that can withstand heat and the like during soldering can be obtained.

Since the composite dielectric of the present invention is thermosetting as described above, it is possible to bond electrodes such as copper foil by pressure and heating during molding.

[0035]

As described above, according to the present invention, it is possible to realize a composite dielectric having a high dielectric constant, good electrode adhesion, and a small dielectric loss tangent. Moreover, this composite dielectric has a high degree of freedom in form and also has heat resistance, and it is also possible to bond electrodes such as copper foil during molding.

Claims (1)

[Claims] 1. A composite dielectric comprising a phenoxy resin mixed with dielectric ceramic powder in an amount of 5 to 90% by volume, and the phenoxy resin being crosslinked with a crosslinking agent.