JP2001005178A - Image forming method, multilayer circuit board, and multilayer film used for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the defective connection of a via hole of a small diameter by making the average optical density fraction from one face of a resin insulating layer to the half of the thickness specified times the average optical density fraction from the other face of the layer to the half of the thickness. SOLUTION: A resin insulating layer in which the average optical density fraction from one face to the half of the thickness is 1.2 to 500 times the average optical density fraction from the other face to the half of the thickness is prepared in such a way that a plating layer can be held on the face having the lower average optical density fraction. The resin insulating layer is irradiated with light from the face having the lower average optical density fraction to form the objective image. In the multilayer circuit board, the average optical density fraction from the substrate side face of each resin insulating layer to the half of the thickness of the layer is 1.2 to 500 times the average optical density fraction from the opposite face of the layer to the half of the thickness of the layer. A circuit is first disposed on one face of the base substrate of the multilayer circuit board and then resin insulating layers and circuits are alternately formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an image on a resin insulating layer, a multilayer wiring board and a multilayer film used for the same, and more particularly to a method for manufacturing a multilayer wiring board (build-up board) by a build-up method. The present invention relates to a multilayer wiring board manufactured by using the manufacturing method, and a multilayer film used in the manufacturing method.

[0002]

2. Description of the Related Art In recent years, electronic equipment has been rapidly becoming lighter, smaller, more functional, and thinner. For this reason,
It is essential to mount electronic components at high density, and in order to cope with this, increasing the density of printed wiring boards has become a major issue. The build-up method has attracted attention as a method for increasing the density of printed wiring boards. The feature is that the connection between the wiring layers on both sides of the board was made by forming a through hole penetrating the board using a conventional drill, but a hole called a via hole was formed in the resin insulation layer on the surface of the board using light. Opening is to form an interlayer connection. Drilling using light enables drilling of a significantly smaller size (200 μm or less in diameter) than drilling (a hole having a diameter of about 1 mm), thereby enabling high-density substrates. Drilling methods using this light include a drilling method using a laser and a drilling method using photolithography.

[0003] A laser drilling method has good processing accuracy because the laser has good straightness and little spread.
Usually, processing at a level of 100 μm in diameter is possible. However, this method is inferior in productivity because the laser must be moved one by one while moving the laser for each of the small openings etched.

[0004] On the other hand, a hole making method using photolithography can form a large number of via holes by one-time exposure and development, so that productivity is good. However, the spread of light (usually, ultraviolet light) used for exposure is affected by a diffraction phenomenon or the like. large. For this reason, a diameter of 150 μm is usually used in the photolithography method.
It is difficult to form a via hole of m or less.

[0005]

The demand for high-density substrates is increasing year by year, and the diameter of the substrate is 100 μm or less (60 μm or less,
Via holes of 40 μm or less have been required. In a multilayer wiring board having such a small-diameter via hole, there is a high probability that a connection failure of the via hole occurs.

An object of the present invention is to improve poor connection of a via hole having a small diameter.

[0007]

Means for Solving the Problems The present inventor has solved the above problem,
The average optical density fraction from one surface to half the thickness of the resin insulating layer is 1.2 to 500 times the average optical density fraction from the other surface to half the thickness of the resin insulating layer. Thus, the present invention has been completed.

That is, according to the present invention, the average optical density fraction from one surface to half the thickness is 1.2 to 500 times the average optical density fraction from the other surface to half the thickness. An image is formed by irradiating light from the surface with the lower average optical density fraction of the resin insulating layer on which the surface with the lower optical density fraction can hold the plating layer thereon. And an image forming method.

Further, according to the present invention, the wiring and the resin insulating layer are alternately arranged on at least one surface of the base substrate so that at least two wirings and at least one resin insulating layer are formed. A multilayer wiring board in which via holes to be electrically connected are formed in a resin insulating layer, and the average optical density fraction from the substrate side surface of each resin insulating layer to half the thickness of the layer is the same as that of the insulating layer substrate. Provided is a multilayer wiring board having an average optical density fraction of 1.2 to 500 times the thickness from the opposite side to half the thickness of the layer.

Further, the present invention comprises a first resin insulating layer and a second resin insulating layer capable of forming a via hole by light irradiation, and the first resin insulating layer can hold a plating layer thereon. Wherein the average optical density fraction of the second resin insulation layer is 1.2 to 500 times the average optical density fraction of the first resin insulation layer.

According to the present invention, the average optical density fraction of half of the resin insulating layer on the light irradiation side is 1.2 to 50 of that of the other half.
Since it is 0 times, the light irradiated to form a fine via hole reaches below the resin insulating layer and is completely absorbed below the resin insulating layer, so that it is not reflected by the wiring. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

Various materials such as an insulating material and a metal material can be used for the base substrate of the present invention. As the insulating material, an organic material, an inorganic material, or a composite of both can be used. However, a material obtained by impregnating a glass cloth with an epoxy resin, for example, NEMA standard FR-4 or ceramics is preferably used. NEMA standard FR for base substrate
Resins such as -5 and BT (bismaleimide triazine-based resin) can also be used.

In the present invention, a wiring is first provided on at least one surface of the base substrate, and thereafter, a resin insulating layer and a wiring are alternately formed. In the present invention, at least two wiring layers and at least one resin insulating layer are provided.

As materials used for wiring, silver, copper,
Metals such as aluminum are exemplified.

[0016] In addition to the above resin binder, the resin insulating layer
A component that absorbs light having a wavelength used for light irradiation, for example,
It can contain a dye, a photopolymerization initiator, a monomer, and the like. Preferably, an addition-polymerizable monomer having a photopolymerization initiator or a photopolymerization initiator system and an ethylenically unsaturated double bond, as disclosed in JP-A-7-110577 and JP-A-7-209866. And a photopolymerizable composition containing a resin modified with an amine (benzylamine, cyclohexylamine, etc.) of a styrene / maleic anhydride copolymer.

The dyes used in the present invention include dyes (light-absorbing substances soluble in solvents) and pigments (light-absorbing substances insoluble in solvents).

When the light to be irradiated is ultraviolet light, a salicylate-based, benzophenone-based, benzotriazole-based or coumarin-based ultraviolet absorber is used as a dye. When the light to be irradiated is ultraviolet light, carbon black such as acetylene black, C.I. I. = PB
For example, there is a pigment such as 15: 6 that absorbs ultraviolet rays.

The thickness of the resin insulating layer is preferably 1 to 50 μm, more preferably 2 to 40 μm, and particularly preferably 5 to 30 μm.

In the present invention, the average optical density fraction from the surface on the side opposite to the light irradiation side (substrate side) of the resin insulating layer to half the thickness is from the surface on the light irradiation side (opposite side to the substrate) of the resin layer. It is formed at a ratio of 1.2 to 500 times the average optical density fraction up to half the thickness.

In the present invention, the optical density (OD) is
It refers to the degree to which light having the wavelength used for light irradiation is absorbed when passing through the resin insulating layer.

Assuming that the intensity when the light of the wavelength enters is I ₀ and the intensity after passing is I, OD = log ₁₀ (I ₀ / I)
Is calculated.

If the resin insulating layer has the property of scattering, reflecting, and refracting light of the wavelength, the measured value is corrected by estimating the amount in advance, and the value of only absorption is calculated.

In the present invention, the “optical density fraction” is defined as a value obtained by converting an OD per minute thickness into an OD per 1 μm thickness. For example, the thickness is determined by measuring the thickness d (μm) and the OD of the minute thickness portion of the resin layer, and “optical density fraction = O
D / d ”.

In the present invention, the “average optical density fraction” is defined as “the average of the optical density fractions in the target region in the thickness direction”. As an example, the optical density fraction of the target thickness direction region and the thickness d ₂ (μm) of the target region are measured and calculated by the formula “average optical density fraction = OD / d ₂ ”.

When the average optical density fraction is less than 1.2,
Light that has reached below the resin insulating layer is reflected at the interface between the resin insulating layer and the wiring, and the reliability of the via hole is reduced. Also,
If the average optical density fraction exceeds 500 times, the irradiated light does not reach below the resin insulating layer, so that the reliability of the via hole decreases. The average optical density fraction is preferably from 2 to 200, most preferably from 4 to 100.

The resin insulating layer is formed by applying a resin solution having a different composition onto the wiring, attaching a film on the wiring,
It can be formed by using both application and film attachment.

In the case of application, the first resin insulating layer is applied, dried, then the second layer is applied, and dried sequentially. The first layer is applied before the second layer is dried. Simultaneous multi-layer coating, a method in which the coating operation is completed with one coating, and the light absorbing component is allowed to settle during drying after the coating. Any of the methods for moving the absorption component can be used.

The concentration of a light absorbing component such as a dye, a photopolymerization initiator, a binder, and a monomer in the resin solution or film used in the layer on the substrate side is determined by the resin solution or film used in the layer on the side opposite to the substrate. Thicker than that of

As a solvent used for coating, methyl ethyl ketone, cyclohexanone and the like are preferably used.

After the application of the resin solution, a polypropylene film, a polyethylene film or the like may be laminated on the resin insulating layer to protect the surface.

In application and lamination, it is more preferable to laminate a film having a multilayer structure in advance on the wiring.

When a multi-layer film is used for the resin insulating layer, the multi-layer film is laminated on a wiring-formed base material. Can not do it. If there is no obstacle in this respect, the performance required for the multilayer wiring board by the build-up method, such as processability such as insulation property, pattern forming property, adhesion, strength, electroless plating resistance, and electroplating resistance, is satisfied. As long as the material used is not limited, the binder can be used.

Assuming that the average optical density fraction of the second layer is C and the average optical density fraction of the first layer is D, the ratio of C to D (C
/ D) is preferably from 1.2 to 500, more preferably from 2 to 200, most preferably from 4 to 100.
The multilayer film is attached to the substrate such that the higher average optical density is on the substrate side.

The thickness of the second layer is in the range of about 1/1000 to about 1/2, 1/200 to about 1/5, and most preferably 1/100 to about 1/10 of the total thickness of the resin insulating layer. Range.

In order to form a multilayer film, a first resin insulating layer is applied on a temporary support, a second resin insulating layer is applied on another temporary support, and these are attached after drying. Match. As the temporary support, a plastic film such as a polyethylene terephthalate film, or a metal film such as an aluminum foil, a copper foil, a nickel foil, or a stainless steel foil can be used. When a plastic film is used as the temporary support, the temporary support can be used as a cover sheet after the film is formed. In addition, if the temporary support is made of aluminum foil, the temporary support becomes a heat-resistant sheet, and can be attached by a press (heated to a high temperature for a relatively long time), and Because it is cheap,
preferable.

The thickness of the temporary support is suitably from 5 to 100 μm.

Such a multilayer film is heated and pressed under pressure on a base substrate on which a wiring pattern is formed. Pressing such as a laminator and a vacuum pressing machine is used for heating and pressure bonding. If there is a polypropylene protective film or the like, it is peeled off and the resin insulating layer is exposed.

The wiring is provided on the resin insulating layer by plating or the like. In general, when plating is performed on the resin, the plating is often peeled off during the plating process, or the plating is often peeled off during handling after plating. . Therefore, it is necessary that the portion of the resin insulating layer opposite to the substrate can hold plating thereon. The peeling of the plating is prevented by providing irregularities on the surface or making the surface adsorbable by plating. The function imparted to the resin layer in order to perform these plating peeling measures is called a plating anchor function.

In order to use a resin insulating layer having an uneven surface, there are a case where a resin insulating layer having an uneven surface is used in advance, and a case where an uneven surface is formed on the resin insulating layer later.

As an example of the resin insulating layer which has been made uneven in advance,
Use of a resin film which has been previously roughened as described in JP-A-9-244239 may be used. Further, a film formed by coating the resin layer on the uneven surface of the electrolytic copper foil may be used. Here, in the present invention, “roughening” refers to JIS
The number of protrusions is evaluated according to the method specified in K5400, and there is at least 8 protrusions in a grid test at intervals of 5 mm.

The previously roughened resin film is prepared by applying a resin layer to a temporary support. The resin used for the resin layer is, for example, selected from water-soluble resins and swellable resins, preferably polyvinyl alcohol and its derivatives, polyvinylpyrrolidone and its derivatives, cellulose and its derivatives, gelatin and its derivatives , Polyacrylic acid and derivatives thereof, and amine-modified styrene / maleic acid copolymers. These may be used alone or in combination.

The resin layer contains fine particles. The fine particles are not particularly limited, such as inorganic, organic low molecular weight, or organic high molecular weight fine particles.
Examples thereof include calcium silicate, calcium carbonate, zinc oxide, titanium oxide, zirconia, mullite, calcium hydroxide, talc, aluminum hydroxide, diatomaceous earth, and barium sulfate. These may be used alone or in combination of two or more. The average particle diameter or aggregate diameter of the fine particles is preferably 0.05 to 10 μm.

The weight ratio of the fine particles to the resin is suitably in the range of about 0.5 to 5.

The resin solution containing such fine particles is as follows:
Usually, it is obtained by mixing and stirring a solution in which a resin is dissolved or a mixed solution of a solvent such as methanol and water and water and fine particles. When the aggregate size of the fine particles is large, it is also possible to stir vigorously with a homogenizer or the like, or to disperse them with a paint shaker or the like. In addition, it is also possible to obtain a fine particle dispersion liquid and an aqueous resin in advance, and the method for preparing the resin solution is not particularly limited.

Further, a surfactant or a matting agent (fine particles) may be added to the resin solution, or a dispersant or the like may be added for the purpose of preventing sedimentation of the fine particles.

The resin solution containing such fine particles is applied on a film. The film thickness after drying is about 0.2
It is desirable that the thickness be in the range of 15 μm.

As a method for providing irregularities later, Japanese Patent Publication No.
Addition of easily removable fine particles such as -55555 (Ibiden) to a resin solution to form a resin insulating layer, and removal of the fine particles after formation of via holes to make the surface uneven.

In the present invention, a via hole is formed by light irradiation. The method includes a laser irradiation method and a photolithography method.

The laser irradiation method refers to a solid laser (YA)
Laser light generated by G laser, sapphire laser, gas laser (carbon dioxide laser, argon ion laser, helium-neon laser, etc.), semiconductor laser, dye laser, excimer laser, free electron laser, etc. is applied to the resin insulation layer. Drilling is performed by irradiation, and the resin insulating layer is decomposed and removed by laser energy. When a laser is used to form a via hole, part or all of the temporary support is peeled off.

The photolithography method is to irradiate a photosensitive resin-insulating layer imagewise with light (this is called exposure) and remove the non-irradiated portion (or light-irradiated portion) by development. This is a method of forming a via hole. A photomask is usually used for the exposure, but finely narrowed light such as laser light may be scanned without using the photomask.

In the present invention, a photolithography method is more preferable because of high productivity.

When the via hole is formed by photolithography, the temporary support may be left as it is or may be peeled off at the time of exposure. When high resolution is required, it is desirable that the temporary support be peeled off and exposed. Alternatively, a laminated product of two supports may be used as a temporary support, and the thicker support may be peeled off before exposure.

An ultra-high pressure mercury lamp or the like can be used for exposure, and either diffused light or parallel light can be used.

In the case of the photolithography method, development is performed with a solvent or an aqueous alkali solution to form a via hole. When the developing solution is a solvent, a chloro-based solvent such as chlorocene is used. When the developing solution is an alkaline aqueous solution, about 0.3 to 2% of sodium carbonate, sodium hydroxide, potassium hydroxide, triethanolimine as a developing agent is used. An aqueous solution in which diethanolamine or tetramethylammonium hydroxide is dissolved can be used.

If necessary, a surfactant or a solvent such as benzyl alcohol can be added to the alkaline aqueous solution-based developer. As a developing method, shower developing, brush developing, or a method combining both can be used.

After the development is completed, it is desirable to perform post-baking at a temperature of 20 ° C. to 200 ° C.

After development in a developing bath containing the developer,
Although the substrate is washed with a washing bath, it is preferable to provide a processing step in an auxiliary treatment bath between the developing bath and the washing bath in order to surely form fine via holes.

For the auxiliary treatment bath, an aqueous solution of an acid such as hydrochloric acid, sulfuric acid, ammonium persulfate, or sodium persulfate, or an aqueous solution of sodium hydroxide or the like is used.

As described above, 1 to 100 μm, preferably 2 μm
Via holes of up to 60 μm, more preferably 4 to 40 μm can be formed. The density of via holes formed according to the present invention is 0.5 to 200 holes / mm ² , preferably 1 to 150 holes / mm ² , and more preferably 5 to 120 holes / mm ² .

Electroless copper plating, electrolytic copper plating, or the like is performed on the resin insulating layer having the above via holes,
It becomes wiring.

By repeating the above steps, a multilayer wiring is formed.

[0063]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.
Example 1 (1) Production of Multilayer Film A resin solution for simple surface roughening having the following composition was dispersed on a polyethylene terephthalate (PET) film having a thickness of 20 μm as a temporary support with a homogenizer, and then the thickness was reduced to 6 μm. And dried at 100 ° C. for 10 minutes.

The coated product was cloudy, and surface irregularities were observed by SEM. <Composition of the resin solution for simple roughening> ・ 37.5 parts by weight of polyvinyl alcohol PVA205 (manufactured by Kuraray) ・ 18.75 parts by weight of polyvinylpyrrolidone K30 (manufactured by Shin-Etsu Chemical Co., Ltd.) ・ Hydroxypropylmethylcellulose TC5E (gokyo industry) 37.50 parts by weight-Calcium carbonate (Shiraishi Kogyo Co., Ltd.) vapor-phase crushed to an average particle size of 2 µm 26.9 parts by weight-Fluorosurfactant Surflon S131 (manufactured by Asahi Glass Co., Ltd.) 2 parts by weight ・ Pure water 97.8 parts by weight Next, resin solutions A and B having the following composition were simultaneously applied on the cloudy layer of the above-mentioned coated product using an extrusion-type two-stage Gieser to form a cover sheet. The obtained film was wound up while attaching a polyethylene (PE) film.

The thickness of the resin insulating layer A after drying is 16 μm,
The thickness of the resin insulating layer B was 2 μm. These values are
The resin insulating layers A and B applied to portions where the surface-roughening resin solution was not applied were cut, and the thickness of each layer in the cross section was measured with an optical microscope.

The optical density fractions of the dried resin insulating layers A and B were 0.0125 and 0.4, respectively. Each optical density fraction is provided by providing the resin insulating layer A alone on the support,
The optical density of the resin insulating layer A was determined by measuring the coating film that was peeled off after drying, and then the resin insulating layers A and B were simultaneously coated on the support and dried, and then the resin insulating layers A and B were integrally peeled off. By measuring the optical density of the coating film, the sum of the optical densities of the resin insulating layers A and B was obtained, and the total was calculated based on this. <Resin solution composition of A> Binder [styrene / benzylamine maleate modified product / methacryloyloxyethyldiphenyl phosphate copolymer (40/32/28 (molar ratio)), solid content 36% by weight, remaining component methyl ethyl ketone , Molecular weight 30,000] 50 parts by weight ・ 2,2-dimethoxy-1,2-diphenylethan-1-one 2.15 parts by weight ・ Phenidone 0.0056 parts by weight ・ Cyclohexanone 17.4 parts by weight ・ DPHA (Nippon Kayaku 9.03 parts by weight R-712 (manufactured by Nippon Kayaku Co., Ltd.) 6.77 parts by weight M-315 (manufactured by Nippon Kayaku Co., Ltd.) 6.77 parts by weight < B. Resin Solution Composition> Binder [styrene / benzylamine maleate modified product / methacryloyloxyethyldiphenyl phosphate copolymer (28 / 44/28 (molar ratio)), solid content 31% by weight, remaining component methyl ethyl ketone, molecular weight 30,000] 50 parts by weight • 2,2-dimethoxy-1,2-diphenylethan-1-one 1.49 parts by weight • Phenidone 0.0039 parts by weight-Fluorosurfactant Surflon S131 1.720 parts by weight-Methyl ethyl ketone 83 parts by weight-Cyclohexanone 55 parts by weight-DPHA 6.22 parts by weight-R-712 4.67 parts by weight-M-315 4 .67 parts by weight ・ Pigment (CI = PB15: 6) 3.48 parts by weight (lamination on base substrate) Glass having 8 μm thick BO (black oxide) haloless-treated copper wiring on the surface as a base substrate On both sides of the epoxy substrate, the above multilayer film from which the cover sheet (PE film) was peeled off,
Vacuum laminator (After reducing the pressure to 3 hPa in 30 seconds, 10
A hot plate at 0 ° C. was pressed for 30 seconds at 5000 hPa) so that the resin insulating layer B was on the substrate side.

The total thickness of the resin insulating layer on the wiring is 16 μm,
The thickness of the roughened layer is 2 μm, the thickness of the resin insulating layer A is 12 μm,
The thickness of the resin insulating layer B was 2 μm.

In the thickness direction, the average optical density fraction of the half on the base substrate side was 0.1, the average optical density fraction of the half on the base substrate half and the half was 0.0125, and the ratio between the two was 8. (Exposure) Using a mask having a via hole density of 10 holes / mm ² , pattern exposure was performed with parallel light at an exposure amount of 30 mJ / cm ² . (Development) After removing the temporary support (PET film),
A 2.8% by weight aqueous solution of triethanolamine adjusted to a temperature of ° C. was sprayed onto both surfaces of the substrate at a pressure of 1500 hPa for 70 seconds to perform shower development. 12% by weight of room temperature
An aqueous solution of ammonium persulfate is applied at a pressure of 1500 hPa for 60 hours.
Shower spray was performed for 60 seconds, and then water at room temperature was shower-sprayed at a pressure of 1500 hPa for 60 seconds, and the substrate was dried with hot air at 60 ° C. As a result, a via hole having a diameter of 30 μm was formed, and irregularities were formed on the surface of the resin layer. (Post bake) The substrate was heated at 160 ° C. for 60 minutes to completely cure the resin layer to form an insulating layer. (Plating) Next, using a treatment agent manufactured by Meltex Co., the process up to electroless copper plating was performed in the following procedure.

The substrate was immersed in a pretreatment agent (PC236) at 25 ° C. for 3 minutes, and then washed with pure water for 2 minutes. Then
The substrate was immersed in a catalyst imparting agent (activator 444) at 25 ° C. for 6 minutes, and then washed with pure water for 2 minutes. Next, the substrate was immersed in an activating agent (PA491) at 25 ° C. for 6 minutes, and then washed with pure water for 2 minutes. Next, the substrate was immersed in an electroless copper plating solution (CU390) at 25 ° C. and a pH of 12.9 for 10 minutes, and then washed with pure water for 5 minutes.
After washing with water, the substrate was dried at 100 ° C. for 15 minutes. As a result, an electroless copper plating film having a thickness of about 0.3 μm was formed.

Subsequently, the substrate was immersed in a degreasing agent (PC455) manufactured by Meltex Corporation at 25 ° C. for 30 seconds, washed with water for 2 minutes, and then subjected to electrolytic copper plating. The electrolytic copper plating solution is a composition of copper sulfate 75 g / l, sulfuric acid 190 g / l, chlorine ion about 50 ppm, and Copperglyme PCM 5 ml / l manufactured by Meltex Co., Ltd.
Plating was performed on both sides of the substrate under the conditions of A / 100 cm ² for 24 minutes. As a result, about 12 μm of copper was deposited. Next, the substrate was placed in an oven, left at 160 ° C. for 60 minutes, and then copper was etched using a dry film resist to form wirings and interlayer connections. This was subjected to BO haloless treatment to obtain an 8 μm thick wiring.

Further, a multilayer film was laminated thereon, and a third-layer wiring was formed in the same manner as described above. (Solder Heat Resistance Test) When a solder heat resistance test was performed at 260 ° C. for 20 seconds, no connection failure of the via hole occurred. Comparative Example 1 A multilayer film was prepared in the same manner as in Example 1 except that the resin solution B was not used (a single layer of the resin solution A was provided), and a multilayer wiring board was prepared using the multilayer film.

The total thickness of the resin insulating layer on the wiring is 16 μm,
The thickness of the roughened layer was 2 μm. The thickness of the resin insulating layer A was 14 μm.

In the thickness direction, the average optical density fraction of the half on the base substrate side was 0.0125, the average optical density fraction of the half on the side opposite to the base substrate was 0.0125, and the ratio between the two was 1.

The defective connection rate of the via hole after the soldering heat test was 32%.

[0075]

According to the present invention, the ratio of the average optical density fraction above and below the resin insulating layer is within a predetermined range, so that the diameter of the resin insulating layer is 100 μm.
It is possible to improve poor connection of via holes in a multilayer wiring board having via holes of not more than m.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H025 AA00 AA02 AB15 AB17 AB20 AC01 AC08 AD01 BC13 BC31 DA11 DA20 DA21 DA40 FA17 FA43 2H096 AA27 BA05 CA01 EA02 EA04 HA27 5E346 AA12 AA16 AA38 AA43 BB01 CC08 DD02 DD03 GG31 EE31

Claims (3)

[Claims] The average optical density fraction from one surface to half the thickness is 1.2 to 500 times the average optical density fraction from the other surface to half the thickness. An image characterized in that an image is formed by irradiating light from a surface having a lower average optical density fraction of a resin insulating layer on which a surface having a lower ratio can hold a plating layer thereon. Forming method. 2. Wiring and resin insulating layers are alternately arranged on at least one surface of a base substrate so that at least two wirings and at least one resin insulating layer are formed, and upper and lower wirings are electrically connected. A multilayer wiring board in which via holes to be connected are formed in a resin insulating layer, wherein the average optical density fraction from the substrate side surface of each resin insulating layer to half the thickness of the layer is the opposite of the insulating layer from the substrate. 1.2 times to 50 times the average optical density fraction from the surface to half the thickness of the layer
Multilayer wiring board that is 0x. 3. A first resin insulating layer and a second resin insulating layer capable of forming a via hole by light irradiation, wherein the first resin insulating layer can hold a plating layer thereon. A multilayer film in which the average optical density fraction of the second resin insulating layer is 1.2 to 500 times the average optical density fraction of the first resin insulating layer.