JPH07133359A - High-permittivity prepreg - Google Patents

Abstract

PURPOSE:To provide the title prepreg freed from voids and improved in humidity resistance, heat-resistance and surface smoothness by applying a specified epoxy resin composition to the surface of a prepreg prepared by impregnating a fibrous base with arm epoxy resin containing a high-permittivity filler. CONSTITUTION:A fibrous base is impregnated with a varnish prepared by mixing 100 pts.wt. epoxy resin of an epoxy equivalent of 160-250 with 10-300 pts.wt. high-permittivity filler of a mean particle diameter of 0.05-9mum to obtain a prepreg. An unfilled solventless epoxy resin composition having a viscosity of 100mPa.s or below is applied to the surface of the prepreg.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high dielectric constant prepreg used for printed wiring boards, multilayer printed wiring boards and the like.

[0002]

2. Description of the Related Art Conventionally, printed wiring boards and multilayer printed wiring boards have been dried by impregnating a fibrous base material such as paper, glass fiber or aromatic polyamide fiber with thermosetting resin such as phenol resin, epoxy resin or polyimide resin. Then, a prepreg is manufactured, and a laminated plate formed by laminating a metal foil such as a copper foil on the surface of the prepreg and then heating and pressurizing the same with a press molding machine has been widely used. However, recently, in a communication device using a high frequency band such as a car phone and a mobile phone, a substrate having a high dielectric constant and a low dielectric loss tangent has been required due to the need for miniaturization. Moreover, as a noise countermeasure for the power supply board, a laminated board having a high dielectric constant is required in order to increase the capacitance, such as using the board insulator as the dielectric of the capacitor and using it as a bypass capacitor for removing high frequency components. . In addition, demands for prepregs for interlayer adhesion of multilayer boards have also increased to increase the density of electronic devices. For this reason, as a substrate mixed with a filler having a high dielectric constant, a laminated plate obtained by impregnating a fiber base material with a thermoplastic modified thermosetting polyphenylene ether resin or a laminated plate obtained by mixing an alumina powder with a fluororesin Is attracting attention.

However, the laminated plates made of these thermoplastically modified thermosetting resins and thermoplastic resins have the following problems. In other words, since the resin is special, the melt viscosity during heat molding is higher than that of thermosetting resins such as epoxy resin prepreg, so the fluidity is poor, and in the multilayer prepreg, the copper foil circuit space of the inner layer board used for the multilayer board is The resin cannot be filled with the filler-containing resin and voids occur. In addition, since the fluidity during heating was poor, it was not possible to add a large amount of filler having a high dielectric constant. This is because a prepreg is obtained by mixing these resins with a filler in the form of a varnish or a dispersion, impregnating a fiber base material and drying the prepreg.The prepreg is a solvent for the varnish or a dispersion of the dispersion. Therefore, it is porous. When this is heated and pressed by press molding etc., the porosity is crushed by the flow of the resin and disappears, but if the amount of filler increases, the flowability deteriorates further, so it is necessary to secure the flowability and eliminate the porosity. Is limited. Furthermore, the prepreg needs to have fluidity that fills the copper foil circuit space of the inner layer substrate, and fluidity that is greater than that required to eliminate the porosity. Therefore, the amount of the filler added is further reduced. Further, there is a problem that the price is higher than that of a general-purpose laminated board.

[0004]

Therefore, a laminated board in which a highly versatile and inexpensive epoxy resin is added with a high-dielectric-constant, high-dielectric-constant, high-dielectric-constant filler, is considered. Became. However, in this method, when a large amount of the high-dielectric-constant filler is added, the voids between the high-dielectric-constant filler particles cannot be filled with the resin, the peeling strength of the copper foil is reduced, and the heat resistance after moisture absorption is reduced. Cause a drop. In addition, when the high-permittivity filler is dropped from the prepreg during the laminated structure before press molding and adheres to the copper foil surface of the laminated plate during the laminated plate forming process and is molded, the resin adheres to the copper foil surface and causes etching. Therefore, there is a problem that a defect occurs when forming a circuit or causes a dent. Furthermore, when a prepreg containing a high-dielectric constant, low-dielectric-tangent high-dielectric-constant filler is used as a prepreg for multi-layered adhesion, the filler-containing resin of the prepreg does not easily flow, so that it is formed on the inner layer substrate surface. The copper foil circuit space cannot be completely filled with the resin containing the filler, and voids are generated in a part of the copper foil, which causes a decrease in heat resistance.

The present invention has been made to solve these problems, and eliminates the voids that are generated when the copper foil circuit space formed on the surface of the inner layer substrate cannot be filled.
It is an object of the present invention to provide a low-cost, high-dielectric-constant prepreg that has a high degree of copper foil peeling strength and can be easily multilayered and bonded, with a reduction in the electrical characteristics and heat resistance after moisture absorption treatment.

[0006]

The present invention provides a prepreg obtained by impregnating a fibrous base material with an epoxy resin having a high dielectric constant filler added in advance and heating and drying the solvent-free prepreg. The present invention provides a filler-added high-dielectric-constant epoxy resin prepreg having an epoxy resin composition applied on the surface thereof. As the high dielectric constant filler, titanium dioxide, a mixture of titanium dioxide and a titanium compound are preferable because of their high dielectric constant and low dielectric loss tangent. Titanium dioxide is preferably of the rutile type, which has a high dielectric constant. Examples of titanium compounds include barium titanate, strontium titanate, calcium titanate, lead titanate, and bismuth titanate. Among these, strontium titanate and calcium titanate are preferable because the change in dielectric constant with temperature is small.
For these, a commercially available high dielectric constant filler can be used as it is.

The average particle size of the high dielectric constant filler is 0.
05-9 μm is preferable. When the average particle diameter of the high dielectric constant filler is 9 μm or more, the dispersibility of the filler is reduced, which causes uneven thickness, which is not preferable. On the other hand, if it is less than 0.05 μm, the fine powder tends to agglomerate and the handleability is deteriorated, which is not preferable. Furthermore, the maximum particle size of the high dielectric constant filler is 70
When the thickness exceeds μm, when the prepreg is sandwiched between the inner layer substrate and the inner layer substrate to perform multi-layer adhesion, particles act as spacers and pressure is not applied to the prepreg, and voids are easily generated around the high dielectric constant filler particles, It is not preferable because problems such as deterioration of heat resistance, uneven thickness, and disconnection of the conductor circuit formed on the surface of the inner layer substrate occur. When the minimum particle size of the high dielectric constant filler is 0.005 μm or less,
The filler-mixed resin exhibits thixotropy, the apparent viscosity of the filler-mixed resin increases, and the workability of mixing and coating decreases. The amount of the high dielectric constant filler added to the epoxy resin is 10 to 300 with respect to 100 parts by weight of the epoxy resin.
Weight parts are preferred. Further, when the high dielectric constant filler is added in an amount of 300 parts by weight or more, the viscosity of the epoxy resin is increased, workability is deteriorated, and voids are caused, which is not preferable. If the amount is less than 10 parts by weight, the dielectric constant of the substrate is not high and it is not effective.

The filler-free epoxy resin composition applied to the surface of the prepreg impregnated with the epoxy resin containing the high dielectric constant filler is a solvent-free epoxy resin composition. This solventless epoxy resin composition is a mixture of an epoxy resin with a curing agent, a curing accelerator, a flame retardant, a coupling agent, a reducing agent, etc., and at least the epoxy resin is liquid at room temperature or heated to be liquid. It will be. The viscosity of this composition at room temperature or when heated is preferably 100 mPa · s or less. Solventless epoxy resin viscosity is 100mPa
When it is s or more, the high dielectric constant filler-added epoxy resin impregnated into the fiber base material at the time of coating is pulled by the epoxy resin composition applied to the surface and is missing, the dielectric constant of the prepreg,
This causes variations in dielectric loss tangent and uneven thickness. The coating thickness of the solventless epoxy resin layer may be 1 to 20 μm when a copper foil is laminated on one or more prepregs to form a laminated substrate. When it is used as a prepreg for interlayer adhesion of a multilayer board, it is necessary to apply it to approximately the same thickness as the copper foil thickness of the inner layer board. However, this depends on the residual copper rate of the copper foil circuit, and when the residual copper rate is high, a smaller thickness is sufficient.

Epoxy resin containing a high dielectric constant filler,
The solventless epoxy resin not added may be an epoxy compound having two or more epoxy groups in one molecule,
Diglycidyl ether of bisphenol A and its multimers such as epibis type epoxy resin, bisphenol F type epoxy resin, novolac type epoxy resin, resorcin type epoxy resin and the like can be used. These may contain halogen for flame retardancy. As the novolac type epoxy resin, a phenol novolac epoxy resin having an epoxy equivalent of 160 to 250 and an orthocresol novolac epoxy resin having an epoxy equivalent of 180 to 250 are generally used. As a solventless epoxy resin,
Bisphenol A type and bisphenol F type epoxy resins are suitable and can be used in combination with the novolac type epoxy resin.

As the fiber base material used for the prepreg, there is a sheet-like woven cloth, non-woven cloth, mat or the like made of glass fiber or aromatic polyamide fiber. Preferably,
A woven fabric of glass fibers having excellent mechanical properties and electrical properties is used.

[0011]

In the prepreg of the present invention, an epoxy resin layer containing a high dielectric constant filler in a fiber base and a solventless epoxy resin composition layer containing no high dielectric constant filler are formed on the outer surface thereof. Usually, the maximum amount of the filler that can be added to the epoxy resin is such that the gaps between the filler particles can be filled with the epoxy resin. If it is added more than this, the gap between the fillers cannot be filled with the epoxy resin and a large amount of voids will be contained. The voids are mostly air, and the inclusion of air having a dielectric constant of 1 significantly lowers the overall dielectric constant and diminishes the effect of adding a large amount of filler. A substrate with voids is porous and has a large surface area and a large amount of moisture absorption, resulting in delamination and blistering when soldered.

According to the present invention, even when the voids cannot be filled with the epoxy resin by increasing the amount of the high dielectric constant filler added, the outer surface of the prepreg does not contain the filler. Since it is coated with a solventless epoxy resin composition, the epoxy resin on the outside can be liquefied and filled with voids during molding, so that a large amount of high dielectric constant filler can be added. As a result, the heat absorption becomes good because the moisture absorption amount is small and there is no void. Further, since the outer surface is a solvent-free epoxy resin composition, the adhesiveness to the inner layer substrate used for the multilayer board is good, and the peeling strength of the copper foil does not decrease.

The decrease in the dielectric constant due to the solvent-free epoxy resin composition on the outer surface to which the high dielectric constant filler is not added is caused by adding a large amount of the high dielectric constant filler to the epoxy resin varnish applied to the fiber base. You can reduce it. Furthermore, the present invention, since the epoxy resin layer of the outer surface uses a solvent-free epoxy resin composition, unlike the case of a varnish using a solvent, epoxy resin containing a high dielectric constant filler once coated No melting or peeling occurs, and variations in dielectric constant and dielectric loss tangent due to melting or peeling of the high dielectric constant filler are reduced. If the epoxy resin to be coated is a varnish, the high-permittivity filler-containing epoxy resin prepreg that was first coated is porous and its adhesion to the fiber base is poor, so the solvent in the varnish penetrates. The coater partially peels off due to the shearing force of the coater that regulates the thickness at the time of coating, causing streaks on the coater and variations in the dielectric properties due to the peeled-off part.

Further, in the present invention, unlike the case of the varnish, it is not necessary to evaporate the solvent, so that the coating speed can be increased and the temperature of the furnace can be lowered, and the degree of curing of the epoxy resin initially coated can be further increased. The fluidity of the prepreg can be maintained and the copper foil circuit space can be satisfactorily filled. Further, since the outer surface is covered with the epoxy resin layer, the epoxy resin containing the high dielectric constant filler, which is easily dropped from the prepreg, does not fall off, and the adhesion and dents of the resin on the surface of the copper foil during the molding of the substrate are significantly reduced.

[0015]

EXAMPLES The present invention will be described below based on examples, but the present invention is not limited thereto. Table 1 shows the composition of the epoxy resin varnish used in Examples and Comparative Examples.

[0016]

[Table 1]

EXAMPLE Titanium dioxide, TM as a high dielectric constant filler in the resin of Table 1
-1 (manufactured by Fuji Titanium Industry Co., Ltd., average particle size 0.64μ)
m) is added to 220 parts by weight of 100 parts by weight of resin, and a high dielectric constant filler-added epoxy resin varnish is added to the glass cloth, W
EA116E (manufactured by Nitto Boseki Co., Ltd., thickness: 100 μm) was impregnated and dried at 160 ° C. for 2 minutes, and then the solventless epoxy resin composition shown in Table 2 was applied on the surface in an amount of 10 μm.
It was dried at 160 ° C. for 2 minutes to obtain a prepreg having a thickness of 160 μm.

[0018]

[Table 2]

Comparative Example 1 200 parts of TM-1 were added to 100 parts by weight of the resin shown in Table 1.
16 parts by weight and impregnated with glass cloth WE116E,
After drying at 0 ° C. for 2 minutes, 100 parts by weight of the high dielectric constant filler TM-1 was added to the epoxy resin shown in Table 1 to give 10
It was applied to a thickness of 160 μm and dried at 160 ° C. for 2 minutes to obtain a prepreg having a thickness of 160 μm.

Comparative Example 2 200 parts of TM-1 were added to 100 parts by weight of the resin shown in Table 1.
160 parts by weight of glass cloth is coated onto WE116E,
It was dried at 2 ° C. for 2 minutes to obtain a prepreg having a thickness of 160 μm.

Comparative Example 3 The resin shown in Table 1 was impregnated with a glass cloth WE116E without adding a high dielectric constant filler and dried at 160 ° C. for 2 minutes to obtain a prepreg having a thickness of 160 μm.

Using the filler-added epoxy resin prepregs and the epoxy resin prepregs obtained in the above Examples and Comparative Examples as an inner layer substrate, one side is a full-scale copper foil (back side) and the other side is a copper foil circuit in which the residual copper rate is changed. Pattern (surface copper foil 35μ
m) using two substrates as (front), the two inner-layer substrates are the front and the back, respectively, and the prepreg is sandwiched therebetween, the molding temperature is 170 ° C., the heating time is 90 minutes,
A four-layer board was produced by heat-press molding at a molding pressure of 4 MPa. The voids remaining in the copper foil circuit pattern in contact with the prepreg are evaluated by polishing from the surface of the 4-layer board, and the ratio of the number of voids to the number of evaluations is expressed as the void generation rate. Shown in 3.

[0023]

[Table 3]

As shown in Table 3, the examples in which the solvent-free epoxy resin composition containing no high dielectric constant filler was applied to the epoxy resin layer containing the high dielectric constant filler on the glass cloth are inner layer substrates. The copper foil circuit space can be filled with the prepreg composition, and the void generation rate is small and good. However, as shown in Comparative Examples 1 and 2, the high dielectric constant filler was
A prepreg (Comparative Example 2) obtained by coating glass cloth with an epoxy resin containing 100 parts by weight, and a high dielectric constant filler 10
In the prepreg obtained by applying an epoxy resin varnish containing 0 part by weight (Comparative Example 1), Comparative Example 2 in which the addition amount of the high dielectric constant filler is large has a higher void generation rate than Comparative Example 1 and the prepreg. Performance is poor. Comparative example 1 in which the addition amount of the high dielectric constant filler applied the second time was as small as 100 parts by weight
Is an example in which a high dielectric constant filler is not added and Comparative Example 3
The void generation rate is remarkably high and the prepreg performance is poor as compared with. The moisture resistance and heat resistance of the four-layer board were evaluated by dipping in solder after the pressure cooker test. In Comparative Examples 1 and 2, peeling occurred at the interface between the prepreg and the inner layer board. The example was good without peeling or blistering.

Further, the peeling strength of the copper foil of the inner layer substrate in contact with the prepreg of Example was as high as that of Comparative Example 3, but decreased in order of Comparative Examples 2 and 1. In terms of surface smoothness, the four-layer plate of the example was smooth, but in Comparative Examples 1 and 2, the influence caused by the prepreg appeared. In Comparative Example 1, thickness unevenness was generated in which the thickness varied depending on the location. In Comparative Example 2, the surface became uneven. Using one prepreg obtained in each of the examples and comparative examples, copper foil was laminated on both sides of the prepreg and press-molded to obtain a substrate, and the copper foil of the substrate was removed by etching, and the dielectric constant of the substrate was measured. The difference between the maximum value and the minimum value of the rate is 0.05 in the example, 0.1 in the comparative example 1, and the comparative example 2.
Was 0.5 and Comparative Example 3 was 0.04.

[0026]

As shown in Table 3, in the present invention, the solvent-free epoxy resin composition containing no high dielectric constant filler is impregnated with the high dielectric constant filler-added epoxy resin in the fiber base material. Since it is applied to the surface of the obtained prepreg, it is possible to fill the copper foil circuit space of the inner layer substrate with a significantly reduced number of voids when manufacturing the multilayer board. Moreover, the peeling strength from the copper foil can be kept high. Furthermore, since the prepreg and the substrate obtained from it have a structure that reduces the amount of porosity that reduces moisture absorption, moisture resistance and heat resistance can be improved, and surface smoothness is improved because the prepreg has good fluidity during molding. . And since there is almost no high dielectric constant filler-containing epoxy resin that falls off from the prepreg when the board or multilayer board is laminated, it does not get mixed up and adhere to the copper foil surface at the time of molding to form a circuit by etching. Can solve defects and dents.

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Claims (4)

[Claims] 1. A prepreg obtained by impregnating a fibrous base material with an epoxy resin having a high dielectric constant filler added thereto is coated with a solventless epoxy resin composition to which no filler is added. A characteristic high-permittivity prepreg. 2. The high dielectric constant prepreg according to claim 1, wherein the high dielectric constant filler is titanium dioxide, a mixture of titanium dioxide or a titanium compound. 3. The high dielectric constant filler has an average particle size of 0.05 to
The maximum particle size of the high dielectric constant filler is 9 μm, the maximum particle size is 70 μm or less, and the minimum particle size is 0.005 μm.
The high dielectric constant prepreg described. 4. The high dielectric constant prepreg according to claim 1, wherein the fiber base material impregnated with the high dielectric constant filler-added epoxy resin is a glass fiber woven fabric.