JP2000345103A - Insulation varnish and multilayered printed circuit board using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject insulation varnish that has excellent insulation reliability and excellent handleability and is useful for multilayer printed circuit board, or the like, by using a polymer material with a specific number-average molecular weight. SOLUTION: This varnish consists of (A) a resin, (B) an electric insulation whisker and contains (C) a polymer material with a number-average molecular weight of >=10,000. It is preferable that the component C is a resin that is compatible to an epoxy resin or a phenoxy resin, a brominated phenoxy resin or a high molecular weight epoxy resin with a number-average molecular weight of >=30,000, particularly a super-high molecular weight epoxy resin with a number-average molecular weight of >=80,000, and the content of the component C is in the range of from 5 to 7 wt.% on the solid basis in the varnish resin and the component B is a ceramic whisker with an average diameter of 0.3-3.0 μm and with an average length of 3-50 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating varnish and a multilayer printed wiring board using the same.

[0002]

2. Description of the Related Art A printed wiring board is usually obtained by laminating a copper foil and a prepreg, and performing circuit processing on a copper-clad laminate obtained by hot pressing. Further, a multilayer printed wiring board was obtained by hot-pressing these printed wiring boards via a prepreg, or by hot-pressing these printed wiring boards and copper foil through a prepreg and integrating them. It is obtained by forming a circuit on the surface of a multilayer copper clad laminate containing an inner layer circuit.

Conventionally, a prepreg for a printed wiring board includes a glass cloth prepreg obtained by impregnating a glass cloth with a resin and drying the resin to make the resin semi-cured. Adhesive film in which a resin having a film forming ability, which is a prepreg that does not use a glass cloth, is made into a semi-cured state (JP-A-6-20
0216, JP-A-6-242465) and an adhesive film with a copper foil formed on one side of a copper foil (see JP-A-6-196682). The film-forming ability referred to here means that troubles such as cracking or chipping of the resin hardly occur during the steps of transporting, cutting, and laminating the prepreg, and the interlayer insulating layer is formed in the portion where the inner layer circuit exists at the time of subsequent hot pressing. This means that the film hardly causes troubles such as abnormal thinning, a decrease in interlayer insulation resistance and a short circuit.

[0004]

In recent years, electronic devices have been reduced in size, weight, performance, and cost, and printed wiring boards have been required to have higher density, thinner, higher reliability, and lower cost. Has been requested. For high density, fine wiring is required, and for that purpose, the surface must have good flatness and good dimensional stability.

[0005] Further, fine through holes and interstitial via holes (IVH) are required, and good drill hole workability and laser hole workability are required. In order to improve the flatness of the surface, it is necessary to increase the fluidity of the resin at the time of multilayer lamination molding, and it is desirable to use a thermosetting resin such as an epoxy resin.

[0006] However, epoxy resins exhibit high fluidity due to their low molecular weight before molding, but are brittle.
It does not have the property of forming a sheet-like insulating material. Therefore, conventionally, a prepreg in which a reinforcing base material such as a glass cloth is impregnated with an insulating resin has been prepared in advance and used for the insulating layer.

However, in the glass cloth used in the conventional prepreg, the gap between the yarns (glass fiber bundles) becomes larger as the thickness becomes thinner. The warp and weft, which should intersect at right angles, do not intersect at right angles but intersect with each other. A phenomenon called "bent" is likely to occur, and this bend tends to cause abnormal dimensional change and warpage after hot pressing.

Further, the thinner the glass cloth, the larger the gap between the yarns, the lower the volume fraction of the fiber of the prepreg, and the lower the rigidity of the interlayer insulating layer. Therefore, in the component mounting process after processing the outer layer circuit, The deflection tends to increase, which is an obstacle to component mounting. Currently, the thinnest glass cloth generally used is 30μ.
m, and the thickness of the prepreg using this is about 40 μm. If the resin content is reduced in order to further reduce the thickness of the prepreg, the ability to fill holes in the unevenness of the inner layer circuit with the resin is reduced and voids are generated. Also,
If the glass cloth is made thinner than this, the strength of the cloth itself decreases, so that the glass cloth is easily broken in the step of impregnating the resin with the glass cloth, and it becomes difficult to manufacture the prepreg. Furthermore, a multilayer printed wiring board manufactured by using a prepreg using a glass cloth with a reduced resin content or a thinner glass cloth "is easily misaligned due to unevenly distributed glass cloth at the time of small-diameter drilling, and the drill is easily folded. And "the presence of glass fibers makes laser drilling difficult, and irregularities in the inner layer circuit are likely to appear on the surface, resulting in poor surface flatness".

On the other hand, the adhesive film which is a prepreg without a glass cloth or the adhesive film with a copper foil can be made thinner, and is excellent in small-diameter drill workability, laser workability, and surface flatness. However, the multilayer printed wiring boards made with these prepregs have extremely low rigidity because the outer insulating layer does not have a glass cloth base material. This low rigidity is extremely remarkable at a high temperature, and is likely to bend in the component mounting process, and the wire bonding property is extremely poor. In addition, since there is no glass cloth substrate in the outer insulating layer and the coefficient of thermal expansion is large, the difference in thermal expansion with the mounted component is large, the connection reliability with the mounted component is low, and the solder joint due to the thermal expansion and contraction of heating and cooling It has many problems, such as cracks and breakage. Therefore, it is not possible to meet the increasing demand for higher density and thinner multilayer printed wiring boards by using an adhesive film which is a prepreg without a glass cloth or an adhesive film with a copper foil.

Therefore, a base material such as glass cloth is used as a new insulating material for solving the problems of high density, thinness, high reliability, and low cost for a multilayer printed wiring board that cannot be solved by a conventional prepreg. It has been found that a sheet-like insulating material obtained by casting a varnish obtained by dispersing an electrically insulating whisker for shape retention in an insulating resin on a carrier base material is effective. .

However, when a sheet-like insulating material in which a filler such as an electrically insulating whisker or the like is compounded in an insulating resin is used, broken pieces are generated in a cutting process of the product, and a multilayer structure is formed due to a lack of flexibility. During handling in the process, etc., problems such as cracking of the adhesive film are likely to occur, and broken fragments cause dents on the outer layer copper foil surface during pressing for multilayering, and insulation resin at the part where the adhesive film is broken However, problems such as abnormal thinning occur, and the yield is reduced.

In order to improve the flexibility, it is usual to add various rubbers such as acrylic rubber and acrylonitrile butadiene rubber to the epoxy resin, but there is a method, but various rubbers are compatible with the epoxy resin. Is bad,
Since the epoxy resin and the rubber are separated, when a printed wiring board is manufactured using a rubber-added epoxy resin, there is a problem that insulation reliability, heat resistance, and solvent resistance are poor.

An object of the present invention is to provide an insulating varnish excellent in insulation reliability and handleability and a multilayer printed wiring board using the insulating varnish.

[0014]

Means for Solving the Problems The insulating varnish of the present invention comprises:
An insulating varnish comprising a thermosetting resin and an electrically insulating whisker, wherein a polymer material having a number average molecular weight of 10,000 or more is added.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION (Polymer material) The polymer material used in the present invention has a number average molecular weight of 10,000 or more.
Phenoxy resin, flame retarded brominated phenoxy resin, high molecular weight epoxy resin having a number average molecular weight of 30,000 to 80,000, and further, a number average molecular weight of 80,0
An ultra-high molecular weight epoxy resin exceeding 00 can be used. In the present invention, the number average molecular weight is measured by gel permeation chromatography using a standard polystyrene calibration curve.

These polymer materials are preferably used in the range of 5 to 75% by weight, more preferably 10 to 60% by weight, and more preferably 10 to 50% by weight based on the resin solid content of the insulating varnish.
t% is particularly preferable because the balance between properties and moldability is good. If it is less than 5 wt%, there is no effect in improving the handleability of the produced adhesive film, and if it exceeds 75 wt%, the fluidity of the resin for filling the inner layer circuit and the through hole is insufficient at the time of press lamination for multilayering. I do.

(Whisker) The whisker used in the present invention is an electrically insulating ceramic whisker.
As the type of whisker, for example, one or more selected from aluminum borate, wollastonite, potassium titanate, basic magnesium sulfate, silicon nitride, and α-alumina can be used. Among them,
Aluminum borate whiskers have a high modulus of elasticity, a low coefficient of thermal expansion, and are relatively inexpensive. The printed wiring board manufactured using the prepreg of the present invention using this aluminum borate whisker has higher rigidity at ordinary temperature and high temperature than the conventional printed wiring board using glass cloth, and has excellent wire bonding properties. Excellent electrical signal transmission characteristics, low coefficient of thermal expansion, and excellent dimensional stability.

If the average diameter of the whiskers is less than 0.3 μm, mixing with the resin varnish becomes difficult and the coating operability decreases. If the average diameter exceeds 3 μm, the flatness of the surface is adversely affected, and the whisker fineness is reduced. Visual uniform dispersibility is impaired. Therefore, the average diameter of the whiskers is 0.3μ
m to 3 μm are preferred. Further, for the same reason and good coatability (easy to coat smoothly), the average diameter is 0.5 μm.
The range of m to 1 μm is more preferred. By selecting a whisker having such a diameter, a printed wiring board having better surface flatness can be obtained than using a prepreg using a conventional glass cloth as a base material.

On the other hand, if the average length of the whiskers is less than 10 times the average diameter, the reinforcing effect of the fibers becomes small, and at the same time, the two-dimensional orientation of the whiskers described later in the resin layer becomes difficult. However, sufficient rigidity cannot be obtained when the wiring board is used. If the whiskers are too long,
Uniform dispersion in the varnish becomes difficult, and the coatability decreases. Also, the probability that a whisker in contact with one conductor circuit comes into contact with another conductor circuit increases, which may cause a short circuit between circuits due to migration of copper ions that tend to move along the fiber. There's a problem. Therefore, the average length of the whiskers is preferably in the range of 10 times or more and 50 μm or less of the average diameter. A printed wiring board manufactured using the insulating material of the present invention using the whiskers having such a length has better migration resistance than a conventional printed wiring board using a prepreg based on a glass cloth.

(Treatment Solution) In the present invention, a coupling agent can be used to improve the adhesion at the interface between the insulating resin and the whisker surface. As such a coupling agent, a silane coupling agent can be used. And titanate-based coupling agents, and as the silane-based coupling agent,
Generally, there are an epoxy silane type, an amino silane type, a cationic silane type, a vinyl silane type, an acryl silane type, a mercapto silane type and a composite type thereof. Any number of additives may be used in combination, and the amount of the additives is not particularly limited.

(Resin) The resin used in the present invention is used for a resin used for a conventional prepreg based on a glass cloth and an adhesive film containing no glass cloth substrate or an adhesive film with a copper foil. Resin can be used. The resin as used herein means a resin, a curing agent, a curing accelerator, and if necessary, a coupling agent or a diluent.

The resin used in conventional prepregs based on glass cloth has no film-forming ability by itself, so it is formed as an adhesive layer on one side of a copper foil by coating, and the solvent is heated. When the resin is removed and semi-cured, troubles such as cracking or missing of the resin are likely to occur during the process of transport, cutting, lamination, etc. Conventionally, it was difficult to use for an adhesive film with a copper foil because it was abnormally thin, and it was easy to cause troubles such as a decrease in interlayer insulation resistance and a short circuit. However, in the present invention, whiskers are dispersed in the resin, and the resin is reinforced by the filler, so that the prepreg layer composed of the resin of the present invention and the whiskers exhibits a film forming ability, and is transported, cut and cut. In the process of lamination etc., compared to the case where whiskers are not included, troubles such as cracking and chipping of resin are less likely to occur, and the presence of whiskers causes the interlayer insulating layer during hot pressing to become abnormally thin. Occurrence can also be prevented. It is also effective to use a resin conventionally used for an adhesive film or an adhesive film with a copper foil. These resins have a film forming ability even when used alone by containing a high molecular weight component and the like.However, by dispersing whiskers in the resin according to the present invention, the film forming ability is further enhanced and the handleability is improved. In addition, the insulation reliability can be further improved. In addition, it is also possible to reduce the amount of the high molecular weight component to be added by the amount corresponding to the enhancement of the film forming ability by dispersing the whiskers, thereby improving the heat resistance and adhesiveness of the resin in some cases.

Examples of the type of resin include epoxy resin, bismaleimide triazine resin, polyimide resin,
Phenol resins, melamine resins, silicon resins, unsaturated polyester resins, cyanate ester resins, isocyanate resins, polyimide resins and various modified resins thereof are preferred. Among them, bismaleimide triazine resin and epoxy resin are particularly preferable in terms of printed wiring board characteristics. As the epoxy resin, bisphenol A
Epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, phenol novolak epoxy resin, cresol novolak epoxy resin, bisphenol A novolak epoxy resin, salicylaldehyde novolak epoxy resin, bisphenol F novolak epoxy resin, fat Cyclic epoxy resins, glycidyl ester type epoxy resins, glycidylamine type epoxy resins, hydantoin type epoxy resins, isocyanurate type epoxy resins, aliphatic cyclic epoxy resins and their halides, hydrogenated products, and mixtures of the above resins are preferred. It is. Among them, bisphenol A novolak type epoxy resin or salicylaldehyde novolak type epoxy resin is preferable because of its excellent heat resistance.

(Curing agent) As the curing agent for such a resin, those conventionally used can be used. When the resin is an epoxy resin, for example, dicyandiamide, bisphenol A, bisphenol F, polyvinyl phenol, phenol novolak resin, Bisphenol A novolak resins and halides and hydrides of these phenolic resins can be used. Among them, bisphenol A novolak resin is preferable because of its excellent heat resistance. In the case where the curing agent is used for the resin, the ratio conventionally used may be sufficient.
The amount is preferably in the range of 2 to 100 parts by weight with respect to 0 parts by weight, and further, in dicyandiamide, 2 to 5 parts by weight,
For other curing agents, the range is preferably 30 to 80 parts by weight. If the amount of the curing agent is less than 2 parts by weight, insufficient curing is likely to occur, and if it exceeds 100 parts by weight, the unreacted curing agent acts as a plasticizer, and all of the properties deteriorate.

(Curing Accelerator) When the resin is an epoxy resin, an imidazole compound, an organic phosphorus compound, a tertiary amine, a quaternary ammonium salt or the like is used as the curing accelerator. The ratio of the curing accelerator to the resin may be a conventionally used ratio, and is based on 100 parts by weight of the resin.
It is preferably in the range of 0.01 to 20 parts by weight, and 0.1 to 1.
A range of 0 parts by weight is more preferred. If the amount of effect promoter is
If the amount is less than 0.01 part by weight, insufficient curing is likely to occur, and 2
If the amount exceeds 0 parts by weight, the pot life of the produced varnish decreases and the cost increases, which is not desirable.

(Diluent) The thermosetting resin used in the present invention can be diluted with a solvent and used as a resin varnish. Solvents include acetone, methyl ethyl ketone, toluene, xylene, methyl isobutyl ketone, ethyl acetate, ethylene glycol monomethyl ether, methanol, ethanol, N, N-dimethylformamide, N, N
N-dimethylacetamide and the like can be used. The ratio of the diluent to the resin may be a conventionally used ratio, and is preferably in the range of 1 to 200 parts by weight, more preferably 30 to 100 parts by weight, per 100 parts by weight of the resin. If the amount of the diluent is less than 1 part by weight, the handleability is poor, and if it exceeds 200 parts by weight, the workability is poor, which is not desirable.

(Other Compounding Agents) In the present invention, in addition to the above-mentioned components, if necessary, conventionally known coupling agents, fillers, ion scavengers, high molecular weight resins and the like may be added to the resin. You may mix suitably.

(Proportion of Resin and Whisker) When the amount of the electrically insulating whisker in the resin is less than 5 parts by weight based on 100 parts by weight of the resin solid content, the resin is finely crushed and scattered at the time of cutting the prepreg. In addition, the handleability is deteriorated, for example, and sufficient rigidity cannot be obtained when the wiring board is used. On the other hand, when the compounding amount of the whisker is 350 parts by weight or more, the filling property of the inner layer circuit and the resin filling property between the circuits during the hot pressing are impaired, and the whisker composite resin layer after the hot pressing is voided. Fainting is likely to occur, and the characteristics of the wiring board may be impaired. Therefore, the amount of the whisker is preferably 5 to 350 parts by weight based on 100 parts by weight of the resin solids. In addition, it has excellent fillability of the inner layer circuit and resin filling between the circuits, and the manufactured wiring board has the same or higher rigidity as compared to the wiring board manufactured using the prepreg using the conventional glass cloth. Because it can have dimensional stability and wire bonding properties,
The mixing amount of the whiskers is more preferably 30 to 230 parts by weight based on 100 parts by weight of the resin solids.

(Kneading Method) In order to improve the dispersibility of the electrically insulating whiskers, after preparing an insulating varnish, kneading can be performed in combination with a grinder, a three-roll mill or a bead mill. After kneading, it is desirable to remove bubbles in the varnish by stirring and defoaming under reduced pressure.

(Carrier Film) In the present invention, the carrier film on which the whisker composite resin layer (B-stage state), which is an insulating layer, is formed on one surface thereof is a metal foil such as a copper foil or an aluminum foil, a polyester film, or the like. A polyimide film or a film obtained by treating the surfaces of the metal foil and the film with a release agent is used.

(Whisker Orientation in Prepreg Layer) A whisker in an insulating material composed of the electrically insulating whisker of the present invention and a resin in a B-stage state is in a state close to two-dimensional orientation (whisker is in an axial direction). (A state close to parallel to the surface on which the material layer is formed). By orienting such whiskers, the insulating material of the present invention can obtain good handleability, and at the same time, can obtain high rigidity, good dimensional stability and surface flatness when formed into a wiring board.

(Coating method) In order to orient the whiskers as described above, a whisker having a fiber length in the above-described preferred range is used, and at the same time, when a resin varnish in which whiskers are mixed with a copper foil is coated, a blade is used. Coating that can apply a shearing force in the direction parallel to the copper foil such as a coater, rod coater, knife coater, squeeze coater, reverse roll coater, transfer roll coater, etc., or can apply a compressive force in the direction perpendicular to the copper foil surface. The construction method may be adopted.

(Function) According to the present invention described above, the flexibility and handleability of the adhesive film can be improved by using a polymer material compatible with the epoxy resin for the insulating varnish using the electrically insulating whiskers. Thus, the yield at the time of manufacturing can be improved. In addition, the insulating layer manufactured using the insulating material of the present invention has a better workability with respect to the laser than the glass cloth and is a fine whisker. Therefore, the insulating layer using the conventional glass cloth prepreg is used. Then, laser drilling, which was difficult, can be easily performed. Therefore, a small-diameter interstitial via hole (IVH) having a diameter of 100 μm or less can be easily manufactured,
The circuit of the printed wiring board can be miniaturized, which can greatly contribute to higher density and higher performance of electronic devices.

[0034]

EXAMPLE 1 100 parts by weight of bisphenol A novolak type epoxy resin (epoxy equivalent 210) was composed of 40 parts by weight of bisphenol A novolak resin, 40 parts by weight of 4-brominated bisphenol A, and 0.4 part by weight of an imidazole curing accelerator. A brominated phenoxy resin (number average molecular weight of 12,0
00) 20 parts by weight (10 wt% of the resin solid content) and methyl ethyl ketone were added to prepare a 60 wt% varnish. An aluminum borate whisker having an average diameter of 0.8 μm and an average fiber length of 20 μm was added to the obtained varnish in an amount of 30 wt.
%, Kneaded using a bead mill, and then vacuum degassed. The obtained varnish was applied to a copper foil having a thickness of 18 μm and a polyethylene terephthalate (PET) film having a thickness of 50 μm using a knife coater.
By heating and drying at 50 ° C. for 10 minutes to remove the solvent and semi-curing the resin, the whisker weight fraction is 30 w
The insulating layer made of a whisker and a semi-cured epoxy resin having a thickness of 80 μm and 100 μm is removed by removing the insulating material with a copper foil having a thickness of 100 μm and PET, and an 80 μm-thick epoxy resin made of a semi-cured state is removed. An insulating material was manufactured.

Example 2 An insulating material was produced in the same manner as in Example 1, except that the amount of the brominated phenoxy resin was changed to 80 parts by weight (33 wt% of the solid content of the resin).

Example 3 An insulating material was produced in the same manner as in Example 1 except that the amount of the brominated phenoxy resin was changed to 300 parts by weight (63 wt% of the solid content of the resin).

Example 4 A brominated phenoxy resin was converted to 60 parts by weight of phenoxy resin (number average molecular weight 30,000) (25 wt% of resin solid content).
%), Except that the insulating material was manufactured in the same manner as in Example 1.

Example 5 Insulation was carried out in the same manner as in Example 1, except that the brominated phenoxy resin was changed to 60 parts by weight (25 wt% of the resin solid content) of an ultrahigh molecular weight epoxy resin (number average molecular weight 300,000). Materials were made.

Comparative Example 1 5 parts by weight of brominated phenoxy resin (3% of resin solids)
wt%), except that an insulating material was produced in the same manner as in Example 1.

Comparative Example 2 An insulating material was produced in the same manner as in Example 1, except that the amount of the brominated phenoxy resin was changed to 600 parts by weight (77% by weight of the solid content of the resin).

Comparative Example 3 Brominated phenoxy resin was replaced with acrylic rubber (number average molecular weight 5
(00,000) 80 parts by weight (33 wt% of resin solid content)
%), Except that the insulating material was manufactured in the same manner as in Example 1.

Comparative Example 4 An insulating material was produced in the same manner as in Example 1 except that the brominated phenoxy resin was not used.

With respect to the produced insulating material, the following items were evaluated. (B-stage film handleability) The handleability was evaluated as "O" when the material could be cut cleanly by a cutter knife and a shear without scattering of resin, and no blocking occurred between insulating materials.

(Cured Product Properties) The insulating material with a copper foil having a thickness of 80 μm and prepared as described above was laminated and laminated so that the insulating layers faced each other, and was subjected to hot pressing. After the molding, the copper foil was removed by etching to obtain a resin plate. The elastic modulus and the coefficient of thermal expansion of this resin plate were measured. The modulus of elasticity was measured in a tensile mode of TMA, and the coefficient of thermal expansion was measured in a tensile mode of TMA.

(Circuit filling test) A pattern (pattern width (mm) / inter-pattern distance (mm)) was formed on a 0.8 mm thick glass epoxy double-sided copper-clad laminate (copper foil thickness 18 μm).
5.0 / 5.0, 1.0 / 1.0, 0.5 / 0.5,
0.2 / 0.2) and through holes (hole diameter (mm) / hole pitch (mm) = 0.3 / 1.27, 0.3 / 1.9)
After forming a pattern to be an electrode on the inner layer surface by etching, electroless copper plating (15 μm) was performed to prepare an inner layer plate for evaluating circuit filling properties. The insulating material with the copper foil having the thickness of 80 μm of the insulating layer prepared above was laminated on the upper and lower sides such that the insulating material was in contact with the pattern to be the electrode of the inner layer plate for evaluating circuit filling properties, and the resultant was hot-pressed. Thereafter, the outer layer copper foil was removed by etching, and the circuit filling property was evaluated by observation with a stereoscopic microscope. After that, the cross section of the through hole was observed using a stereoscopic microscope. A sample in which no void was generated inside the through hole was evaluated as ○, and the others were evaluated as ×.

(Surface Roughness) A single-sided roughened copper foil having a thickness of 18 μm was laminated on and under the prepared insulating material having a thickness of 100 μm so that the roughened surface faced the insulating material, followed by hot pressing.
This copper-clad laminate is subjected to circuit processing, and the insulating material of the present invention having a thickness of 80 μm previously prepared is provided on both surfaces thereof, and a single-side roughened copper foil having a thickness of 18 μm is further provided on the outer side thereof with the roughened surface as the insulating material. They were laminated so as to face each other, and were hot-pressed to produce a multilayer copper-clad laminate containing an inner circuit. The surface roughness of the multilayer copper-clad laminate containing the inner layer circuit was measured with a stylus type surface roughness meter. The measurement location was the outer layer surface on a straight line having a length of 25 mm including a portion with and without an inner layer circuit immediately below. When the 10-point average of the level difference between the portion having the inner layer circuit and the portion not having the inner layer circuit was 3 μm or less, it was evaluated as ○, and the others were evaluated as ×.

(Electro-corrosion resistance test) A pattern to be used as an electrode on the inner layer surface of the electro-corrosion test was formed on a 0.8 mm thick glass epoxy double-sided copper-clad laminate by etching, and the thickness of the insulating layer formed above and below was formed above and below this. An insulating material with a copper foil having a thickness of 80 μm was overlapped and laminated so that the insulating material was in contact with a pattern to be an electrode on the inner layer surface of the electrolytic corrosion test, and was hot-pressed. An outer layer electrode pattern was formed by etching in accordance with the position of the inner layer electrode corrosion test pattern of the obtained laminate, and an electrolytic corrosion test piece was obtained. A voltage of 50 V was applied between the inner layer electrode and the outer layer electrode, and the insulation resistance value was measured after a lapse of 1000 hours in an atmosphere of 85 ° C. and 85% RH. 100
As a result of measuring the insulation resistance value after the elapse of 0 hour, those showing a good value of 10 ⁹ Ω or more were evaluated as ○, and the others were evaluated as ×.
Table 1 summarizes the above results.

[0048]

[Table 1]

The following can be understood from the above results. In Examples 1 to 5, the handleability and the high corrosion resistance are achieved without lowering the properties of the laminated plate as compared with the comparative examples. Therefore, the insulating varnish of the present invention improves the handleability of the insulating material in the form of a film by adding a polymer material to a resin varnish obtained by mixing an electrically insulating whisker with a low-molecular-weight epoxy resin. Yield can be improved. Further, it is possible to improve the yield when manufacturing a multilayer printed wiring board using this insulating varnish, and to achieve high insulation reliability of the multilayer printed wiring board. The insulating material obtained by using the insulating varnish manufactured according to the present invention can improve the handleability when a sheet-like insulating material is formed by adding a polymer substance to the insulating material using an electrically insulating whisker. A printed wiring board using this has good circuit filling properties, and can form a multilayer IVH, etc., and has a flat surface, good circuit workability, high rigidity, high mounting reliability, and high heat resistance. Since the coefficient of expansion is small, dimensional stability is improved.

[0050]

As described above, according to the present invention, it is possible to provide an insulating varnish excellent in insulation reliability and handleability and a multilayer printed wiring board using the insulating varnish.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Atsuyuki Takahashi 1500 Odai Ogawa, Shimodate City, Ibaraki Pref.Hitachi Chemical Industry Co., Ltd. Inside the Shimodate Research Laboratory (72) Inventor Takahiro Tanabe 1500 Oji Ogawa, Shimodate City, Ibaraki Prefecture F-term in the Shimodate Plant of Hitachi Chemical Co., Ltd. KA19 MA14 NA21 PB09 5E346 AA12 AA15 CC08 CC09 GG02 HH08 HH13 HH18

Claims (9)

[Claims] 1. An insulating varnish comprising a resin and an electrically insulating whisker, wherein the insulating varnish contains a polymer material having a number average molecular weight of 10,000 or more. 2. The insulating varnish according to claim 1, wherein the polymer material having a number average molecular weight of 10,000 or more is a resin compatible with an epoxy resin. 3. The insulating varnish according to claim 1, wherein the polymer material having a number average molecular weight of 10,000 or more is a phenoxy resin. 4. The insulating varnish according to claim 1, wherein the polymer material having a number average molecular weight of 10,000 or more is a brominated phenoxy resin. 5. The insulating varnish according to claim 1, wherein the polymer material having a number average molecular weight of 10,000 or more is a high molecular weight epoxy resin having a number average molecular weight of 30,000 or more. 6. A high molecular weight epoxy resin having a number average molecular weight of 10,000 or more is an ultrahigh molecular weight epoxy resin having a number average molecular weight of 80,000 or more. An insulating varnish according to any of the claims. 7. The method according to claim 1, wherein the polymer material having a number average molecular weight of 10,000 or more is in the range of 5 to 75 wt% of the resin solid content in the insulating varnish. An insulating varnish as described. 8. The electrically insulating whisker is a ceramic whisker, wherein the whisker has an average diameter of 0.3 to 0.3.
The insulating varnish according to any one of claims 1 to 7, wherein the insulating varnish is in a range of 3.0 µm and has an average length of 3 to 50 µm. 9. An insulating material obtained by applying the insulating varnish according to any one of claims 1 to 8 to a copper foil or a carrier film, and laminating the insulating material on an inner circuit board. A multilayer printed wiring board formed and electrically connected to an inner layer circuit.