JP4555946B2 - Insulating material with copper foil and multilayer printed wiring board using the same - Google Patents

Description

  The present invention relates to an insulating material with copper foil applied to an insulating material for a printed wiring board that can meet the demands for thinning and high density of a printed wiring board on which electronic components are mounted, and a multilayer printed wiring board using the same. Is.

  The printed wiring board is usually obtained by processing a circuit on a copper-clad laminate obtained by laminating a copper foil and a prepreg and hot pressing. Moreover, the multilayer printed wiring board was obtained by hot-pressing these printed wiring boards through prepregs, or by integrating these printed wiring boards and copper foil by hot-pressing through prepregs. It is obtained by forming a circuit on the surface of a multilayer copper clad laminate containing an inner layer circuit.

  Conventionally, glass cloth prepregs in which a glass cloth is impregnated with resin and dried to make the resin semi-cured are used as prepregs for printed wiring boards. For multilayer printed wiring boards, glass cloth prepregs are used in addition to glass cloth prepregs. An adhesive film (see Patent Document 1 and Patent Document 2) in which a resin having film-forming ability, which is a prepreg not using cloth, is in a semi-cured state, and an adhesive film with a copper foil formed on one surface of the copper foil (Patent) Reference 3) is used. In addition, the film forming ability here is less likely to cause trouble such as cracking or missing of the resin during the process of transporting, cutting, and laminating the prepreg, and the interlayer insulating layer is the inner layer circuit existing portion at the subsequent hot press molding. It means the performance that is less likely to cause trouble such as abnormally thinning due to, for example, a decrease in interlayer insulation resistance or a short circuit.

Japanese Patent Laid-Open No. 6-200216 JP-A-6-242465 JP-A-6-196862

  In recent years, electronic devices have been reduced in size, weight, performance, and cost, and printed wiring boards are required to have higher density, thinner thickness, higher reliability, and lower cost. In order to increase the density, fine wiring is necessary. For this purpose, the surface must have good flatness and good dimensional stability.

  Furthermore, fine through holes and interstitial via holes (IVH) are required, and drill hole workability and laser hole workability are required to be good. 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 apply a thermosetting resin such as an epoxy resin.

  However, the epoxy resin exhibits high fluidity because of its low molecular weight in the stage before molding, but is brittle, and therefore does not have the property of forming a sheet-like insulating material. Therefore, conventionally, a prepreg obtained by impregnating a reinforcing substrate such as a glass cloth with an insulating resin has been prepared in advance and used for the insulating layer.

  However, with conventional prepregs, it is inferior in surface flatness, it is difficult to produce thin prepregs, and minute through holes and interstitial via holes (IVH) are formed for electrical connection between different circuit layers. It has become difficult to respond to the above-mentioned demands for reasons such as being difficult. The current glass cloth base prepreg cannot meet the increasing demand for higher density and thinner multilayer printed wiring boards.

  On the other hand, the adhesive film which is a prepreg without a glass cloth and the adhesive film with copper foil can be made thinner, and is excellent in small diameter drilling workability, laser hole workability and surface flatness. However, since the multilayer printed wiring board produced with these prepregs has no glass cloth substrate in the outer insulating layer, the rigidity is extremely low. This low rigidity is extremely remarkable at high temperatures, and is likely to bend in the component mounting process, and the wire bonding property is extremely poor. In addition, since the outer insulating layer has no glass cloth base and has a large coefficient of thermal expansion, the difference in thermal expansion from the mounted component is large, the connection reliability with the mounted component is low, and the solder connection part due to thermal expansion and contraction of heating and cooling Have many problems such as easy cracking and breakage. Therefore, the use of an adhesive film that is a prepreg without a glass cloth or an adhesive film with copper foil cannot meet the increasing demand for higher density and thinner multilayer printed wiring boards.

  Therefore, as a new insulating material to solve the problems of high density, thinning, high reliability, and low cost for multilayer printed wiring boards that cannot be solved by conventional prepreg, it does not include a substrate such as glass cloth, It has been found that a sheet-like insulating material obtained by casting a varnish obtained by dispersing an electrically insulating filler for shape retention in an insulating resin onto a carrier substrate is effective.

  However, when such an insulating material is used for a multilayer printed wiring board, there is a problem that insulation failure often occurs.

  The present invention provides a low thermal expansion coefficient insulating material with copper foil having excellent insulation reliability and a multilayer printed wiring board using the same.

  The insulating material with a copper foil of the present invention is an insulating material with a copper foil obtained from an insulating varnish and a copper foil and does not contain glass cloth, the insulating varnish comprising an electrically insulating whisker and a resin component, The average diameter of the whisker is in the range of 0.3 to 3.0 μm, the average length is 10 times or more of the average diameter, and the average length is in the range of 3 to 50 μm. Metallic foreign matter is removed from the whisker, and the metallic foreign matter remaining on the whisker is 70 ppm or less.

  Normally, the filler does not place importance on electrical insulation, and is often used for applications that require rigidity, for example, molded products made of reinforced plastics, and its electrical characteristics are not particularly required. Therefore, sufficient attention has not been paid to foreign matters mixed in during the manufacturing process. In order to adapt such a filler to the use of a printed wiring board, the present inventors have conducted intensive studies, and as a result, insulation reliability generated when an insulating varnish composed of an electrically insulating filler and a resin component is used. It has been found that the cause of the deterioration is caused by foreign matters mixed in the manufacturing and packaging process of the electrically insulating filler, particularly conductive foreign matters, which are also metallic foreign matters. did it.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a low thermal expansion coefficient insulating material with a copper foil excellent in insulation reliability and a multilayer printed wiring board using the same.

(Electrically insulating filler)
The filler used in the present invention may be in any shape such as needle shape, rod shape, and fiber shape. Further, the size of the filler is preferably about 0.1 to 50 μm. If the thickness is less than 0.1 μm, the handleability of the produced film is poor. If the thickness exceeds 50 μm, the probability that a filler that has contacted one conductor circuit will be in contact with another conductor circuit increases. There is a problem that a short circuit accident between circuits may occur due to migration of copper ions that tend to move along the interface.

  In addition, the material is electrically insulating, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, calcium oxide, magnesium oxide, alumina powder, aluminum nitride powder, boron nitride powder, crystal Silica, amorphous silica, aluminum borate and the like can be used.

  Among the fillers, whiskers are excellent in film forming ability and handleability when producing a film-like insulating material. If the average diameter of the whisker is less than 0.3 μm, mixing with the resin varnish becomes difficult and the coating workability decreases. If the average diameter exceeds 3 μm, the flatness of the surface is adversely affected and the whisker is microscopically uniform. Dispersibility is impaired. Therefore, the average diameter of the whisker is preferably in the range of 0.3 μm to 3 μm. Furthermore, the average diameter is more preferably in the range of 0.5 μm to 1 μm because of the same reason and good coatability (easy to apply smoothly). By selecting whiskers having such a diameter, it is possible to obtain a printed wiring board having a surface flatness superior to that of using a prepreg based on a conventional glass cloth.

  Moreover, it is preferable that the average length of a whisker is 10 times or more of an average diameter. If it is less than 10 times, the reinforcing effect as a fiber becomes small, and at the same time, the two-dimensional orientation in the resin layer of the whisker becomes difficult, so that sufficient rigidity cannot be obtained when the wiring board is formed. However, if the whisker is too long, uniform dispersion in the varnish becomes difficult, and coatability is lowered. In addition, there is a high probability that a whisker in contact with one conductor circuit will come into contact with another conductor circuit, which may cause a short circuit between circuits due to migration of copper ions that tend to move along the fiber. There is. Therefore, the average length of whiskers is preferably 50 μm or less.

  The whisker used in the present invention is an electrically insulating ceramic whisker. Examples of whiskers include aluminum borate, wollastonite, potassium titanate, basic magnesium sulfate, silicon nitride, and α-alumina. One or more selected from can be used. Among these, aluminum borate whiskers have a high elastic modulus, a low coefficient of thermal expansion, and are relatively inexpensive. The printed wiring board produced using the prepreg of the present invention using this aluminum borate whisker has higher rigidity at room 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.

(Foreign matter removal method)
In the present invention, as a method for removing foreign substances other than the target material from the filler, any method can be used as long as it can separate a substance different from the target material, such as sieving using a mesh-like sheet or a centrifuge, or a magnet. For example, it is possible to perform adsorption removal of foreign substances, dissolution removal using a solution that dissolves materials other than the target material, and the like. In particular, for foreign matters including iron that have a great influence on electrical insulation, adsorption removal with a magnet, dissolution removal using an acid solution such as hydrochloric acid, and a combination thereof are effective means.

(Surface treatment of filler)
In the present invention, a coupling agent can be used as a treatment liquid for the filler in order to improve the adhesion at the interface between the insulating resin and the filler. Examples of such coupling agents include silane coupling agents and titanate coupling agents. Generally, silane coupling agents include epoxy silane, amino silane, cationic silane, vinyl silane, and acrylic silane. Systems, mercaptosilane systems, and composite systems thereof. Any number of additives may be used in combination, and the surface treatment may be performed before, during or after dispersion in the insulating varnish, and the amount of the additive is not particularly limited.

(resin)
The resin used in the present invention is a resin used for a prepreg based on a conventional glass cloth and an adhesive film not containing a glass cloth base, or a thermosetting resin used for an adhesive film with a copper foil. Can be used. The resin here means a resin, a curing agent, a curing accelerator, and a resin containing a coupling agent or a diluent as necessary.

  Since the resin used for the prepreg based on the conventional glass cloth is not capable of forming a film by itself, it is formed as an adhesive layer on one side of the copper foil by coating, and the solvent is removed by heating to remove the resin. When the resin is semi-cured, problems such as resin cracking and chipping are likely to occur during processes such as transport, cutting, and lamination, or the interlayer insulation layer becomes abnormally thin at the inner layer circuit existing part during subsequent hot pressing. Since it was easy to cause troubles such as a decrease in interlayer insulation resistance and a short circuit, it was conventionally difficult to use it for adhesive films with copper foil. However, in the present invention, since the filler is dispersed in the resin and the resin is reinforced by the filler, the prepreg layer composed of the resin and the filler of the present invention exhibits a film forming ability, During the processes such as cutting and laminating, troubles such as cracking or missing of the resin are unlikely to occur, and the presence of the filler can prevent the phenomenon that the interlayer insulating layer during hot pressing is abnormally thinned. It is also effective to use a resin conventionally used for an adhesive film or an adhesive film with a copper foil. These resins contain a high molecular weight component, etc., so that the resin alone has a film-forming ability, but by dispersing the filler in the resin, the film-forming ability is further improved and the handling property is improved. Insulation reliability can be further increased. Further, it is possible to reduce the amount of the high molecular weight component added by increasing the film-forming ability by dispersing the filler, which may improve the heat resistance and adhesiveness of the resin.

  Examples of the resin include epoxy resin, bismaleimide triazine resin, polyimide resin, phenol resin, melamine resin, silicon resin, unsaturated polyester resin, cyanate ester resin, isocyanate resin, polyimide resin or various modified resins thereof. Are preferred. Among these, bismaleimide triazine resin and epoxy resin are particularly preferable in terms of printed wiring board characteristics. As the epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolak type epoxy resin, salicylaldehyde novolak type epoxy resin, Bisphenol F novolac type epoxy resin, alicyclic epoxy resin, glycidyl ester type epoxy resin, glycidyl amine type epoxy resin, hydantoin type epoxy resin, isocyanurate type epoxy resin, aliphatic cyclic epoxy resin and their halides, hydrogenated products , And mixtures of the resins are preferred. Among them, bisphenol A novolac type epoxy resins or salicylaldehyde novolac type epoxy resins are preferable because of 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, polyvinylphenol, phenol novolac resin, bisphenol A novolac resin, and these Phenolic halides and hydrides can be used. Among them, bisphenol A novolac resin is preferable because of its excellent heat resistance. The ratio of the curing agent to the resin may be a ratio conventionally used, and is preferably in the range of 2 to 100 parts by weight with respect to 100 parts by weight of the resin, and further 2 to 5 parts by weight of dicyandiamide. For other curing agents, the range of 30 to 80 parts by weight is preferred. If the amount of the curing agent is less than 2 parts by weight, insufficient curing tends to occur, and if it exceeds 100 parts by weight, the unreacted curing agent acts as a plasticizer component, and all of them deteriorate characteristics.

(Curing accelerator)
As the 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. The ratio of the curing accelerator to the resin may be a ratio conventionally used, and is preferably in the range of 0.01 to 20 parts by weight with respect to 100 parts by weight of the resin, and 0.1 to 1.0 parts by weight. A range is more preferred. If the amount of the curing accelerator is less than 0.01 parts by weight, curing is likely to be insufficient, and if it exceeds 20 parts by weight, the pot life of the prepared varnish is reduced and the cost is increased.

(Diluent)
The thermosetting resin used in the present invention can be diluted with a solvent and used as a resin varnish. As the solvent, acetone, methyl ethyl ketone, toluene, xylene, methyl isobutyl ketone, ethyl acetate, ethylene glycol monomethyl ether, methanol, ethanol, N, N-dimethylformamide, N, N-dimethylacetamide and the like can be used. The ratio of the diluent to the resin may be a ratio conventionally used, preferably 1 to 200 parts by weight, more preferably 30 to 100 parts by weight with respect to 100 parts by weight of the resin. When the amount of the diluent is less than 1 part by weight, the handleability of the varnish is inferior, and when it exceeds 200 parts by weight, the workability is inferior.

(Other ingredients)
Furthermore, in the present invention, in addition to the above-described components, conventionally known coupling agents, ion scavengers, high molecular weight resins and the like may be appropriately blended in the resin as necessary.

(Ratio of resin and filler)
When the amount of the filler added to the resin is less than 5 parts by weight based on 100 parts by weight of the resin solid content, this prepreg has poor handling properties such as the resin being finely crushed and easily scattered during cutting, and wiring. When it is made into a plate, sufficient rigidity cannot be obtained. On the other hand, if the blending amount of the filler exceeds 500 parts by weight, the hole filling property of the inner layer circuit at the time of hot pressing and the resin filling property between the circuits are impaired, and in the filler composite resin layer after the hot pressing, Voids and blurring are likely to occur, and the wiring board characteristics may be impaired. Therefore, the blending amount of the filler is preferably 5 to 500 parts by weight with respect to 100 parts by weight of the resin solid content.

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

(Carrier film)
In the present invention, as a carrier film which is a target for forming a filler composite resin layer (B stage state) which is an insulating layer on one side thereof, a metal foil such as copper foil or aluminum foil, a polyester film, a polyimide film, or the metal What processed the surface of foil and the film with the mold release agent is used.

(Formation of insulation film)
In the coating method, each component is dissolved and dispersed in a solvent to form a varnish, which is coated on a carrier film, heated to remove the solvent, and then used as an adhesive film in a semi-cured state.

  In particular, when an electrically insulating whisker is used, the whisker in the insulating material composed of the B-stage resin and the electrically insulating whisker is in a state close to two-dimensional orientation (the whisker axial direction is the formation of the insulating material layer). It is preferable to make the surface close to parallel to the surface to be processed. In order to orient the whiskers as described above, whisker having a fiber length in the preferred range described above is used, and at the same time, when coating a resin varnish containing whiskers on a copper foil, a blade coater, a rod coater, a knife coater, a squeeze A coating method that can apply a shearing force in a plane direction parallel to the copper foil, such as a coater, a reverse roll coater, a transfer roll coater, or a compression force in a direction perpendicular to the surface of the copper foil may be employed.

  According to the present invention described above, by using the filler from which foreign substances have been removed, high insulation is obtained when an insulating material combined with the filler produced by this method is used as a material for a multilayer printed wiring board. Reliability and low thermal expansion can be achieved. In addition, since the insulating layer produced using the insulating material of the present invention is a fine filler with a base material having better processability to laser than glass cloth, insulation using conventional glass cloth prepreg In the layer, 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, and the electronic device can greatly contribute to higher density and higher performance. EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to this.

Example 1
A 10 wt% aqueous suspension of aluminum borate whiskers having an average diameter of 0.8 μm and an average fiber length of 20 μm was prepared, and this suspension was filtered through a nylon mesh (74 μm sieve opening) to obtain a suspension after filtration. . The suspended solution was passed through a 10,000 Gauss magnet arranged in a lattice pattern to adsorb foreign matter. This suspension solution was dried to obtain aluminum borate powder. When this whisker was extracted with a 15 wt% hydrochloric acid solution and the iron concentration was measured, the iron concentration was 65 ppm. 60 wt% of methylbisketone added to a composition comprising 40 parts by weight of bisphenol A novolac resin, 40 parts by weight of bisphenol A novolak resin and 0.4 parts by weight of imidazole curing accelerator, to 100 parts by weight of bisphenol A novolac type epoxy resin (epoxy equivalent 210) % Varnish was adjusted. The obtained varnish was mixed with 160 parts by weight of an aluminum borate whisker, kneaded using a bead mill, and then vacuum degassed.

Example 2
A 10 wt% aqueous suspension of aluminum borate whiskers having an average diameter of 0.8 μm and an average fiber length of 20 μm was prepared, and this suspension was filtered through a nylon mesh (74 μm sieve opening) to obtain a suspension after filtration. . Hydrochloric acid was added to the suspension so as to have a concentration of 3N, and the mixture was stirred at a liquid temperature of 80 ° C. for 3 hours. Thereafter, it was washed with pure water, and silver chloride was dropped into the washing solution to confirm that it did not become cloudy. This suspension solution was dried to obtain aluminum borate powder. When this whisker was extracted with a 15 wt% hydrochloric acid solution and the iron concentration was measured, the iron concentration was 35 ppm. Methyl ethyl ketone was added to a composition comprising 4 parts of dicyandiamide and 100 parts by weight of dicyandiamide and 100 parts by weight of brominated bisphenol A epoxy resin (epoxy equivalent 530) to prepare a 60 wt% varnish. The obtained varnish was mixed with 90 parts by weight of aluminum borate whisker, kneaded using a bead mill, and then vacuum degassed.

Example 3
A 10 wt% aqueous suspension of aluminum borate whiskers having an average diameter of 0.8 μm and an average fiber length of 20 μm was prepared, and this suspension was filtered through a nylon mesh (74 μm sieve opening) to obtain a suspension after filtration. . The suspended solution was passed through a 10,000 Gauss magnet arranged in a lattice pattern to adsorb foreign matter. Hydrochloric acid was added to the suspension so as to have a concentration of 3N, and the mixture was stirred at a liquid temperature of 80 ° C. for 3 hours. Thereafter, it was washed with pure water, and silver chloride was dropped into the washing solution to confirm that it did not become cloudy. This suspension solution was dried to obtain aluminum borate powder. When this whisker was extracted with a 15 wt% hydrochloric acid solution and the iron concentration was measured, the iron concentration was 1 ppm or less. 60 wt% of methyl bisketone added to a composition consisting of 35 parts by weight of bisphenol A novolac resin, 45 parts by weight of bisphenol A novolac resin and 0.4 parts by weight of imidazole curing accelerator, to 100 parts by weight of bisphenol A novolac type epoxy resin (epoxy equivalent 210) % Varnish was adjusted. The obtained varnish was mixed with 160 parts by weight of an aluminum borate whisker, kneaded using a bead mill, and then vacuum degassed.

Comparative Example 1
The purchased aluminum borate whiskers having an average diameter of 0.8 μm and an average fiber length of 20 μm were extracted with a 15 wt% hydrochloric acid solution, and the iron concentration was measured. As a result, the mixed iron concentration was 100 ppm. A varnish was prepared in the same manner as in Example 1 except that this whisker was used.

Comparative Example 2
A 10 wt% aqueous suspension of aluminum borate whiskers having an average diameter of 0.8 μm and an average fiber length of 20 μm is prepared. The suspension is filtered through a nylon mesh (2 mm sieve opening), and the suspension is dried after filtration. An aluminum borate powder was obtained. When this whisker was extracted with a 15 wt% hydrochloric acid solution and the iron concentration was measured, the iron concentration was 100 ppm. A varnish was produced in the same manner as in Example 1 except that the whisker obtained by the above operation was used.

Comparative Example 3
A 10 wt% aqueous suspension of aluminum borate whiskers with an average diameter of 0.8 μm and an average fiber length of 20 μm is prepared. The suspension is filtered through a nylon mesh (75 μm sieve opening), and the suspension is dried after filtration. An aluminum borate powder was obtained. When this whisker was extracted with a 15 wt% hydrochloric acid solution and the iron concentration was measured, the iron concentration was 95 ppm. A varnish was produced in the same manner as in Example 1 except that the whisker obtained by the above operation was used.

Comparative Example 4
A 10 wt% aqueous suspension of aluminum borate whiskers having an average diameter of 0.8 μm and an average fiber length of 20 μm was prepared, and the suspension was filtered with a nylon mesh (a sieve opening of 43 μm), but clogging occurred. A suspension solution could not be obtained after filtration.

(Preparation of insulating material)
The varnishes obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were applied to a copper foil having a thickness of 18 μm and a polyethylene terephthalate (PET) film having a thickness of 50 μm with a knife coater, and dried by heating at 150 ° C. for 10 minutes. Then, while removing the solvent and semi-curing the resin, the insulating material with copper foil having a whisker volume fraction of 30% and an insulating layer made of epoxy resin in a semi-cured state with the whisker is 50 μm and 100 μm And PET was removed by peeling, and the insulating material which consists of a semi-hardened epoxy resin and whose thickness was 50 micrometers was produced.

(Measurement of iron concentration)
The iron concentration was measured using an atomic absorption measuring device.

Regarding the manufactured insulating material, the following items were evaluated.
(B stage film handling)
When handling is performed with a cutter knife or shear, the resin is not scattered and the cutting edge can be cut without cracking, and the insulating material does not block. did.
(Cured product properties)
The insulating material with a copper foil having a thickness of 50 μm, which was produced as described above, was laminated so that the insulating layers face each other, and hot-pressed. After molding, the copper foil portion was removed by etching to obtain a resin plate. The elastic modulus and thermal expansion coefficient of this resin plate were measured. The elastic modulus was measured in the TMA tensile mode, and the thermal expansion coefficient was measured in the TMA tensile mode.
(Electrolytic corrosion resistance test)
On the glass epoxy double-sided copper-clad laminate with a thickness of 0.8 mm, a pattern to be an electrode on the inner layer surface of the electrolytic corrosion test was produced by etching, and above and below the insulation layer produced above was an insulation with a copper foil with a thickness of 50 μm. The materials were laminated and laminated so that the insulating material was in contact with the pattern that would be the electrode on the inner layer surface of the electrolytic corrosion test, and hot pressing was performed. In accordance with the position of the electrolytic corrosion test pattern serving as the inner layer electrode of the obtained laminate, a pattern serving as the outer layer electrode was produced by etching to obtain an electrolytic corrosion test piece. A voltage of 50 V was applied between the inner layer and outer layer electrodes, and the insulation resistance value after 1000 hours was measured in an atmosphere of 85 ° C. and 85% RH. As a result of measuring the insulation resistance value after the elapse of 1000 hours, a sample showing a good value of 10 ⁹ Ω or more was marked with ◯, and the others were marked with ×. The above results are summarized in Table 1.

  From the above results, the following can be understood. Examples 1 to 3 achieve higher electrical corrosion resistance without lowering the characteristics of the insulating material as compared to the case where foreign matter is not removed.

  The insulating material with a copper foil of the present invention can achieve high reliability of the insulating material by using the electrically insulating filler from which foreign matters mixed in the electrically insulating filler are removed. In particular, a multilayer printed wiring board using an insulating material in which electrically insulating whiskers are combined can achieve a low thermal expansion coefficient and high insulation reliability. The insulating material obtained using the insulating varnish produced in accordance with the present invention was able to form an epoxy resin in the form of a sheet by adding an electrically insulating filler, particularly an electrically insulating whisker. The printed wiring board has a flat surface, good circuit processability, high rigidity, high mounting reliability, and low coefficient of thermal expansion, thus improving dimensional stability. Therefore, the multilayer printed wiring board is greatly contributed to high density, thinning, high reliability, and low cost.

Claims (5)

An insulating material with a copper foil obtained from an insulating varnish and a copper foil and containing no glass cloth, the insulating varnish comprising an electrically insulating whisker and a resin component, and the whisker having an average diameter of 0.3 to 3 The average length is 10 times or more of the average diameter and the average length is in the range of 3 to 50 μm, and the whiskers are obtained by removing metallic foreign matters from the electrically insulating whiskers; metallic foreign matter remaining in the whisker Ri der less 70 ppm, electrically insulating whiskers, characterized by electrically insulating whiskers, by a process comprising adsorption and removal treatment with at least a magnet, an der Rukoto obtained by removing the metal foreign matter Insulating material with copper foil.   2. The insulating material with copper foil according to claim 1, wherein the metal foreign matter remaining on the electrically insulating whiskers is 40 ppm or less.   The insulating material with copper foil according to claim 1 or 2, wherein the metal foreign matter remaining on the electrically insulating whiskers is 1 ppm or less. Electrically insulating whiskers, the electrically insulating whiskers, adsorption removal treatment with at least a magnet, and by a method comprising the removal process using an acid solution, to any one of claims 1 to 3, in which the removal of the metal foreign matter The insulating material with copper foil as described. And the copper foil with an insulating material according to any one of claims 1-4, consists an inner layer circuit board, a multilayer printed wiring board and the inner circuit and the outer circuit is characterized in that it is electrically connected.