JPH0579270B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a paste for forming an insulating layer, which has a low dielectric constant (hereinafter abbreviated as ε) and is used for adhesive layers, thickness adjustment layers, overlay layers, etc. in circuit boards and multilayer circuit boards. Regarding the composition. [Prior Art] In recent years, in the field of electronics, plastic insulating layers have been used in combination with conductive layers for an extremely wide range of applications such as circuit boards, and the required properties have also become more diverse. Among these, there is a need to develop an insulating layer with a low ε for the purpose of increasing the signal propagation speed, and in particular, recently it has been required that ε be 3 or less. Conventionally, there has been a method of forming an insulating layer from a thermosetting resin paste composition, but the ε of the insulating layer is greatly influenced by the ε of the resin itself, and it is difficult to use conventional thermosetting resins. If used, ε cannot be lowered. As a means of forming a plastic insulating layer with a low ε, a method of using a thermoplastic resin with a low ε such as a fluororesin, a polyethylene resin, a polybutadiene resin, a polysulfone resin, etc. in the form of a film is being considered. However, such insulating layer multilayer formability, dimensional change, drilling workability, heat resistance, etc. are inferior,
I have not been able to obtain anything highly reliable. [Problems to be Solved by the Invention] The present invention is capable of forming an insulating layer that has a low ε of 3 or less and has excellent reliability in adhesion with other layers, heat resistance, moisture resistance, water resistance, etc. An object of the present invention is to provide a paste composition that can be processed into a circuit board. [Means for Solving the Problems] The present invention provides a thermosetting resin varnish containing epoxy-modified polybutadiene, an epoxy resin, a carboxylic acid, an anhydride, and a radical polymerization initiator as main components, and 100 parts by weight of this resin component. The maximum particle size for
By adding and mixing 10 to 200 parts by weight of fluororesin powder having a particle size of 50 μm or less and subjected to plasma surface treatment. The epoxy-modified polybutadiene may be polybutadiene with epoxy groups added to the main chain and terminals, and the epoxy resin may include general-purpose epoxy resins such as bisphenol A type and alicyclic type, tetrabromobisphenol A type, Examples include flame-retardant epoxy resins such as dibromobisphenol A type. Carboxylic acid anhydrides include chlorendic anhydride, methylbutenyltetrahydrophthalic anhydride, alkenylsuccinic anhydride, 5-(2.5-dioxotetrahydrofuryl)-3methyl-3cyclohexene-1,
Examples include dicarboxylic acid anhydride, and examples of radical polymerization initiators include dicyl peroxide,
Examples include organic peroxides such as t-butyl perbenzoate, t-butyl peroxylaurate, and benzoyl peroxide. To make these into varnishes, one or more organic solvents such as dimethylformamide, methyl isobutyl ketone, and methyl cellosolve are used. Examples of the fluororesin powder used in the present invention include powders of tetrafluoroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, and tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer resin. Use one that has been plasma treated. Plasma treatment methods include external electrode and internal electrode methods, depending on the positional relationship between the electrode and the reactor.
There are methods to supply power using capacitive coupling, inductive coupling, and waveguides, and the power supply frequency ranges from DC to G
There is a range up to the Hz band, and either method is possible. In order to uniformly plasma-treat the entire powder charged in the reactor, it is necessary that the powder be stirred in the reactor during treatment. When a circuit board containing an insulating layer prepared using the paste of the present invention is drilled, the maximum particle size of the fluororesin powder is determined by the roughness of the inner wall of the through hole.
The thickness is preferably 50 μm or less, more preferably 20 μm or less. If the particle size of the fluororesin powder is large, the inner wall roughness of the insulating layer during through-hole formation becomes large. If the inner wall roughness of the through hole is large, it will adversely affect chemical resistance, plating resistance, and electrical properties. When adding plasma-treated fluororesin powder to resin varnish, the composition is an uncured resin mixture.
The amount of plasma-treated fluororesin powder is 10 to 200 parts by weight per 100 parts by weight. If it is less than 10 parts by weight, the effect of lowering ε will be weak, and if it is more than 200 parts by weight, the function of the thermosetting resin as a binder will deteriorate, and the strength, appearance, etc. will deteriorate. Particularly preferred is 50 to 180 parts by weight. It is important to uniformly disperse the fluororesin powder in the varnish made of the resin mixture. The paste obtained can be applied using a roll coater or
There are methods such as bar coater screen printing, and then the resin is cured by heating alone or by heating and pressurizing at atmospheric pressure or vacuum to form an insulating layer. [Function] Although polybutadiene has a low ε, it has poor colorability and heat resistance. By using epoxy-modified polybutadiene with epoxy groups added to the main chain and ends, and by mixing epoxy resin,
Adhesion and heat resistance are improved while maintaining low ε properties. Epoxy resins can be made flame retardant using bromides, and by adding fluororesin powder, the reduction in ε can be further promoted and ε can be made 3 or less. Since fluororesin is non-polar, adding it reduces the adhesiveness of the paste. In order to suppress this decrease, the fluororesin powder is treated with plasma to activate its surface. <Example> Example 1 Epoxy-modified polybutadiene with 90% 1,2 bonds and epoxy equivalent of 550, brominated bisphenol A
type epoxy resin, 5-(2,5-dioxotetrafuryl)-3-methyl 3-cyclohexene-1,
A varnish having a resin content of 58.3% by weight was prepared by mixing and dissolving 2-dicarboxylic acid anhydride and dicumyl peroxide in the composition shown in Table 1 in methyl isobutyl ketone and dimethylformamide.

[Table] 58.3 parts by weight of plasma-treated tetrafluoroethylene resin powder having a maximum particle size of 20 μm and 21 parts by weight of methyl cellosolve were added to the varnish and mixed for 5 minutes at 10,000 rpm using a commercially available homogenizer to obtain a paste composition. Plasma treatment of tetrafluoroethylene resin powder is
Using a 13.56 MHz power source, using an external electrode method with Ar gas as a gas, a vacuum of 0.01 Torr, power of 100 W, and 60 minutes. During the plasma treatment, the interior of the reactor was stirred using a stirring device. This composition was screen printed on a 35 μm thick copper foil, dried for 10 minutes at 100°C, and then two sheets of copper foil/coated layer were put together with the coated layer on the inside at a temperature of 170°C and a pressure of 30 Kg/mm ³ for a period of time. Pressed in 2 hours and 30 minutes to achieve total thickness
A double-sided copper clad plate of 170 μm was obtained. (Comparative Example 1) A double-sided copper-clad board was obtained in the same manner as in Example 1, except that the tetrafluoroethylene resin powder was not subjected to plasma treatment. (Comparative Example 2) A sample was prepared using only resin varnish without adding tetrafluoroethylene resin powder treatment. (Comparative Example 3) Adding 8 parts by weight of tetrafluoroethylene resin powder,
A sample was prepared in the same manner as in Example 1 except that the solvent methyl cellosolve was not added. (Comparative Example 4) 220 parts by weight of tetrafluoroethylene resin powder was added,
A sample was prepared in the same manner as in Example 1 except that 40 parts by weight of methyl cellosolve as a solvent was added. Evaluation of dielectric constant, dielectric loss tangent, peel strength, and solder heat resistance was based on JIS C6486. (D-48/50: 50℃
(48-hour treatment with hot water) The evaluation results of Examples and Comparative Examples are shown in Table 2.

[Table] * Sample cracks <Effects of the invention> The insulating layer obtained from the paste composition for forming an insulating layer of the present invention has a lower ε than an insulating layer made of a conventional paste composition, and in addition, By changing the amount and type of base resin, ε can be adjusted as desired. Furthermore, the paste composition for forming an insulating layer of the present invention has very excellent adhesiveness and water resistance. A circuit board containing an insulating layer made of the paste composition for forming an insulating layer of the present invention can be subjected to drilling, plating, etching, soldering, etc. in the same way as a board made of a normal laminate. Furthermore, if a brominated epoxy resin is used, flame retardancy can be imparted to the insulating layer formed from the paste composition. Therefore, the paste-like composition for forming an insulating layer of the present invention can be coated and dried on the surface of an inner layer containing a signal circuit, for example, to form an insulating layer as a semi-cured material, and then a plurality of insulating layers or other outer layers can be formed. It is most suitable for applications where the insulating layer becomes a thickness adjustment layer when a multilayer circuit board is obtained by laminating a combination of layers and applying heat and pressure.

Claims (1)

[Claims] 1 A thermosetting resin varnish whose main components are epoxy-modified polybutadiene, epoxy resin, carboxylic acid anhydride, and radical polymerization initiator has a maximum particle size of 50 μm based on 100 parts by weight of the resin component.
A paste composition for forming an insulating layer, which is prepared by adding and mixing 10 to 200 parts by weight of fluororesin powder which is as follows and has been subjected to plasma surface treatment.