JP4282580B2 - Porous wiring board - Google Patents

Description

  The present invention relates to a porous wiring board used in fields such as electricity, electronics, and communication.

  In recent years, various electrical and electronic parts such as semiconductor devices have been highly integrated and miniaturized. Along with this, research and development on circuit wiring miniaturization and multilayer wiring for enabling high-density mounting is being actively conducted on circuit wiring boards on which electronic components are mounted. A multilayer wiring technique and a fine wiring technique for a circuit wiring board are indispensable techniques for producing a high-density circuit wiring board, and various methods have been proposed so far. (For example, refer nonpatent literature 1).

  In this case, although circuit wiring is produced on a substrate having a porous structure, shrinkage between wirings resulting from wiring formation has occurred because the substrate is thin. In addition, since electroless plating is used for wiring formation, shrinkage between the wirings occurs due to tensile stress or compressive stress of the electroless plating film that occurs during plating deposition. As the wiring pitch becomes finer, a short circuit between the wirings occurs due to the shrinkage between the wirings. In addition, the wiring is displaced from the design, thereby reducing the connection reliability at the time of multilayering, and further making the design simulation at the time of electromagnetic wave countermeasure difficult.

  In the conventional multilayer wiring technology, when the lamination is performed only on one surface of the core substrate, the substrate largely warps in the direction of the laminated surface. For this reason, it is necessary to provide a similar laminated substrate on the opposite side where wiring is not required. This operation has a problem that the number of processes increases and the substrate thickness increases.

JP 2001-345537 A

  The present invention has been made in view of the above problems, and prevents shrinkage between wirings to prevent design dimension displacement, and improves connection reliability at the time of multilayering, so that sufficient conductivity can be obtained. An object is to provide a wiring board.

A porous wiring board according to an embodiment of the present invention includes a sheet-like insulator having a porous structure,
An inner conductive portion formed by filling a metal in the hole of the sheet-like insulator;
On the surface of the inner conductive part, the inner conductive part is formed with a discontinuous arc, and comprises an outer conductive part connectable to the outside,
Between the maximum width (w ₂ ) parallel to the sheet-like insulator boundary surface in the outer conductive portion and the maximum width (w ₁ ) parallel to the sheet-like insulator boundary surface in the inner conductive portion, There is a relationship represented by the following mathematical formula (1).

0.2 ≦ (w ₂ / w ₁ ) ≦ 0.98 (1)

  According to one aspect of the present invention, there is provided a multilayer wiring board that prevents contraction between wirings and prevents design dimension displacement, improves connection reliability when multilayered, and provides sufficient conductivity. The

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a cross-sectional view of a porous wiring board according to an embodiment of the present invention. As shown in the figure, a porous wiring board 10 according to an embodiment of the present invention includes a sheet-like insulator (porous sheet) 11 having a porous structure, and pores in a selected region of the porous sheet 11. It includes an inner conductive portion 12a formed by filling a metal therein and an outer conductive portion 12b formed outside the inner conductive portion 12a. The inner conductive portion 12a and the outer conductive portion 12b constitute a conductive portion 12, and the conductive portion 12 can be used as a wiring. Since the inner conductive portion 12a is formed by filling the pores of the porous sheet with metal, the inner conductive portion 12a is in a sparse state compared to the outer conductive portion 12b.

  The cross-sectional shape of the wiring is elliptical or rectangular. The ellipse includes a mathematically defined strict ellipse and similar shapes, and is not limited to the locus of points where the sum of distances from two fixed points in the plane is constant. Further, the rectangular shape is not limited to a mathematically defined exact square, that is, a shape in which four points intersect at 90 degrees, and includes a shape in which each corner is rounded. Furthermore, the sides facing each other are not always parallel, that is, an irregular quadrangular shape such as a trapezoid is included.

In the porous wiring board according to the embodiment of the present invention, a specific relationship is essential between the maximum width of the outer conductive portion 12b and the maximum width of the inner conductive portion 12a. Specifically, the maximum length parallel to the substrate boundary surface of the outer conductive portion 12b and the width w ₂ of the outer conductive portion 12b, the width w of the maximum length parallel to the substrate boundary surface of the inner conductive portion 12a inner conductive portion 12a The ratio to ₁ (maximum width ratio: w ₂ / w ₁ ) must be within the range represented by the following formula (1).

0.2 ≦ (w ₂ / w ₁ ) ≦ 0.98 (1)
If the maximum width ratio (w ₂ / w ₁ ) exceeds 0.98, the contraction between the wirings cannot be prevented and the design dimension position deviation cannot be prevented. On the other hand, if it is less than 0.2, it is impossible to use the conductive portion as a wiring. Preferably, the maximum width ratio (w ₂ / w ₁ ) of the conductive portion is 0.95 or less.

Below, with reference to FIG. 2 thru | or FIG. 7, the manufacturing method of the porous wiring board concerning embodiment of this invention is demonstrated in detail.
First, as shown in FIG. 2, a sheet-like insulator (porous sheet) 21 having a porous structure is prepared.
Arbitrary insulator materials can be used as the porous body, and specific examples include resins and ceramics.

  Examples of the resin include glass epoxy resin, bismaleimide-triazine resin and PPE resin, polyimide resin frequently used for the base film, other polyfluorinated ethylene-based, fluorinated ethylene-propylene copolymer, polyvinyl fluoride, etc. Fluorine-containing polymers, polyolefins, acrylic polymers, polyethers such as polyallyl ethers, polyesters such as polyarylates, polyamides, and polyether sulfones are generally used as resins called engineering plastics. Moreover, as ceramics, nonwoven fabrics, such as glass, an alumina, and aluminum nitride, etc. can be used, for example.

  The insulator as described above may contain ultrafine fibers, and examples thereof include fluorine fibers, nylon fibers, acrylic fibers, polyester fibers, aramid fibers, phenol fibers, glass fibers, and carbon fibers. . It is also possible to mix naturally derived components such as cellulose fibers.

  After pattern exposure is performed on such a porous sheet and a conductive portion forming region is provided in a predetermined region, a conductive portion is formed by filling a metal. The depth of the conductive portion forming region is determined by exposure light (for example, ultraviolet light). Depends on the exposure depth of visible light. For this reason, when forming an electroconductive part to the inside of a porous sheet, it is preferable that the hole diameter of a porous sheet is small enough with respect to an exposure wavelength. However, if the pore diameter is too small, it is difficult to impregnate the photosensitive material, and exposure transmission is also difficult. The average pore diameter of the porous sheet is preferably 30 to 3000 nm, more preferably 50 to 1500 nm, and most preferably set in the range of 500 to 700 nm.

  Even when the pore diameter deviates from the above-mentioned range and is significantly larger than the exposure wavelength, if the pore is filled with a liquid having a refractive index close to or the same as that of the porous sheet or an amorphous solid having a low melting point to prevent scattering. It is possible to improve light transmission by preventing scattering during exposure. However, if the pore diameter becomes too large, it becomes difficult to sufficiently fill the pores with metal by plating or the like. In addition, it is difficult to make the width of the metal wiring sufficiently small to be several tens of μm or less.

  The porous sheet is a porous insulating material having three-dimensionally continuous pores in order to produce a conductive part having a pattern in the film thickness direction, particularly a line-shaped part that is continuously conductive in the two-dimensional direction. The body is desirable.

  It is preferable that the continuous voids present in the porous sheet are regularly and uniformly formed in order to prevent excessive scattering of exposure. This is also effective for miniaturizing the wiring as the conductive portion. It is necessary that the continuous pores are opened to the outside of the porous sheet, and it is desirable that the number of closed cells having no open end is as small as possible. Further, in order to improve the dielectric constant of the wiring, it is desirable that the porosity is high in a range where the mechanical strength of the porous sheet is maintained. Specifically, the porosity is preferably 30% or more and 80% or less, and more preferably 50% or more and 70% or less.

  The porous sheet is impregnated with a photosensitive material having a photosensitive group that generates an ion-exchange group by exposure to form a photosensitive layer 22 as shown in FIG.

The photosensitive material contains a photosensitive group that generates an ion-exchange group. Examples of the ion exchange group include hydrophilic functional groups, specifically, —COOX group, —SO ₃ X group, —PO ₃ X ₂ group (where X is a hydrogen atom, alkali metal or alkaline earth metal, and typical metals belonging to periodic table 1 group, and are selected from ammonium groups) and -NH ₂ OH, and the like.

In particular, a cation exchange group is desirable because it easily exchanges ions with metal ions. Examples of such a cation exchange group include acidic groups such as —COOX group, —SO ₃ X group, and —PO ₃ X ₂ group (where X is a hydrogen atom, alkali metal or alkaline earth metal, periodic table I, A typical metal belonging to Group II, an ammonium group) is particularly preferred. If these are contained, after the metal ion exchange, which is a subsequent step, stable adsorption with the reduced metal or metal fine particles can be obtained.

  Specific examples of the compound having a photosensitive group include naphthoquinone diazide derivatives, o-nitrobenzyl ester derivatives, p-nitrobenzyl ester sulfonate derivatives, naphthyl or phthalimido trifluorosulfonate derivatives, and the like.

  In particular, when a naphthoquinone diazide derivative is used, sufficiently fine patterning can be performed in a short time with light having a wavelength of 280 nm or more with low energy. Further, the naphthoquinonediazide derivative causes light bleaching during exposure and becomes transparent in a wavelength region of about 300 nm or more. Therefore, it is possible to expose deeply in the film thickness direction.

  The photosensitive layer is exposed to a metal ion-containing aqueous solution, alkali or acidic aqueous solution in a subsequent step. Since the photosensitive material ionized by the ion exchange reaction is easily dissolved in the aqueous solution, it is easily peeled off from the porous sheet as the substrate. Therefore, in order to prevent peeling from the substrate, it is preferable that a group causing an ion-exchange group generating reaction is supported or bonded to a polymer or a polymer compound. From such a viewpoint, 1,2-naphthoquinonediazidosulfonyl-substituted phenol resin derivatives, 1,2-naphthoquinonediazidesulfonyl-substituted polystyrene derivatives, and the like are preferable as compounds that generate ion-exchangeable groups upon irradiation with light having a wavelength of 280 nm or longer. It is.

  Next, a predetermined region of the photosensitive layer 22 formed on the porous sheet 21 is exposed. For example, pattern exposure can be performed by irradiating light through a mask on which a predetermined conductive pattern is formed. Alternatively, exposure may be performed by drawing according to a conductive pattern using a laser beam or the like. Further, the periodic pattern may be exposed using a periodic light intensity pattern such as an interference fringe generated by light interference.

  By performing pattern exposure, ion exchange groups are selectively generated in the exposure unit 23 as shown in FIG.

  As exposure light irradiated in order to produce | generate an ion exchange group, a wavelength is 280 nm or more. In order to suppress deterioration of the porous sheet due to exposure to a low level, the exposure wavelength is preferably 300 nm or more, and more preferably 350 nm or more.

  In particular, when a porous sheet composed of an aromatic compound is exposed internally in the thickness direction, exposure light having a long wavelength is used. When the porous sheet is made of aromatic polyimide or the like, there are many cases where the absorption edge of polyimide absorption is 450 nm or more. In such a case, it is preferable to perform pattern exposure at a longer wavelength of 500 nm or more.

  As an exposure light source, in addition to an ultraviolet light source and a visible light source, a light source that generates exposure light of a predetermined wavelength can be selected from among light sources such as β rays (electron beams) and X rays. Specifically, the ultraviolet light source or visible light source is selected from hydrogen discharge tubes, rare gas discharge tubes, continuous spectrum light sources such as tungsten lamps and halogen lamps, various lasers, and discontinuous spectrum light sources such as mercury lamps. Use.

  Next, metal ions are selectively bonded to the ion exchange groups formed in the exposure unit 23. As a result, the exposure part 23 becomes a metal ion part 24 as shown in FIG.

  In order to cause an exchange reaction between the ion-exchange group and the metal ion, for example, the porous sheet 21 after pattern exposure may be immersed in an aqueous solution containing a metal salt. Examples of the metal element used as the metal ion include copper, silver, palladium, nickel, cobalt, tin, titanium, lead, platinum, gold, chromium, molybdenum, iron, iridium, tungsten, and rhodium.

  These metal elements can be contained in the solution as metal salts such as sulfates, acetates, nitrates, chlorides, carbonates, etc., and copper sulfate is particularly preferable. It is appropriate to mix such metal salts so that the concentration of metal ions in the solution is 0.001 to 10M, preferably 0.01 to 1M. The solvent for dissolving the metal salt may be water or an organic solvent system such as methanol or isopropanol.

  In some cases, a solution in which metal fine particles are dispersed can also be used. The ion-exchange group and the colloidal metal fine particles are selectively bonded by electrostatic interaction or the like. Therefore, the bond between the ion exchange group and the metal fine particles can be easily generated only by immersing the porous sheet in a solution in which the metal fine particles are dispersed.

  For example, palladium-tin colloid used as a catalyst for electroless plating prepared by mixing palladium chloride and tin chloride in hydrochloric acid aqueous solution, and porous in a dispersion of palladium halide, oxide, acetylated complex Immerse the sheet. As a result, the fine metal particles are easily bonded to the ion-exchange group in a position-selective manner.

  Any metal nucleus may be used as long as it is a metal on which the electroless plating is deposited because the metal ion to be used becomes a nucleus for metal deposition in the subsequent electroless plating process. However, it is desirable to select the same metal nucleus as the electroless plating solution from the viewpoint of conductivity.

  Thereafter, the metal ions are reduced to change the metal ion portion 24 into a conductive metal portion 25 as shown in FIG.

  The reducing agent used is not particularly limited, but dimethylamine borane, trimethylamine borane, hydrazine, formalin, sodium borohydride, hypophosphites such as sodium hypophosphite, peroxides such as potassium permanganate, Examples include sodium thiosulfate and hydroquinone. By immersing the porous sheet in which the metal ion part is formed in a solution obtained by dissolving such a reducing agent in water, alcohol or the like, the metal ion in the exposed part can be metallized.

Furthermore, electroless plating is performed on the metal formed on the exposed portion of the porous sheet 21 to improve the conductivity of the metal portion, whereby the conductive portion 26 is obtained as shown in FIG. It can be said that the conductive part is formed by selectively growing the conductive substance by generating a metal substance from the solution ionic substance by a reduction reaction. The details of the conductive portion 26 in FIG. 7 are configured as shown in FIG. That is, the conductive part 12 includes an inner conductive part 12a formed in the porous sheet and an outer conductive part 12b located on the surface of the inner conductive part. The ratio of the maximum widths of these conductive portions (w ₂ / w ₁ ) is 0.2 or more and 0.98 or less as already described.

  The metal for forming the conductive portion is most preferably copper with low electrical resistance and relatively low corrosion. Specifically, the metal wiring obtained in the previous step is brought into contact with the electroless plating solution using the catalyst core. Examples of the electroless plating solution include those containing metal ions such as copper, silver, palladium, nickel, cobalt, platinum, gold, and rhodium.

  In addition to the metal salt aqueous solution described above, this electroless plating solution includes reducing agents such as formaldehyde, hydrazine, sodium hypophosphite, sodium borohydride, ascorbic acid, glyoxylic acid, sodium acetate, EDTA, tartaric acid, malic acid. In addition, complexing agents such as citric acid and glycine, precipitation control agents, and the like are included, and many of these are commercially available and can be easily obtained. Therefore, the porous sheet may be immersed in these electroless plating solutions until the desired conductive film thickness or filling of the porous interior is completed.

  In the electroless plating, it is preferable to fix the porous sheet using a jig that does not directly contact the patterned portion. Thereby, it is possible to promote removal of bubbles generated during electroless plating to the liquid surface.

  As the material of the jig, general-purpose resins such as PTFE, polyimide, polyethylene, polypropylene, vinyl chloride and polyethylene terephthalate are desirable. Even if such a resin is immersed in an electroless plating solution in contact with the porous sheet, it does not cause abnormal deposition of the plating and can be easily molded. Moreover, the material which gave special processing to the surface, such as stainless steel, may be used. Furthermore, a metal, glass, cloth, organic resin or the like that has been subjected to water repellent treatment with polyether ether ketone (PEEK) or the like can also be used.

  The porous sheet is attached to a fixing jig using an adhesive. Examples of the adhesive include polyolefin resins such as polyimide, polyamide, polypropylene, polybutene, α-olefin copolymer, vinyl acetate copolymer, acrylic ester copolymer, and methacrylic ester copolymer, and polyester-based heat. Plastic elastomers and polyurethane thermoplastic elastomers can be used. In particular, an acrylic polymer or a polyimide derivative is preferable because it hardly causes plating deposition. In order to improve operability, the pressure-sensitive adhesive is preferably in the form of a tape.

  At the time of electroless plating, a fixing jig is installed in the electroless plating solution so as to be perpendicular or parallel to the liquid surface. If necessary, the liquid surface can be inclined. During electroless plating, bubbles may be generated due to the reduction reaction of metal ions. In such a case, it is desired to shake off the bubbles by vibrating the porous sheet placed on the fixing jig in the electroless plating solution vertically and horizontally. The bubbles can be shaken off by rotating the porous sheet. The installation shape is not particularly limited as long as the porous sheet is sufficiently immersed in the electroless plating solution.

  As the electroless plating progresses, the plating solution concentration distribution may be uneven. In this case, it is desirable to circulate the plating solution so that the concentration distribution of the plating solution is uniform. For example, the plating solution can be circulated by rotating the fixing jig in a state perpendicular to the liquid level. Further, the plating solution may be circulated by air bubbling or spraying. In bubbling, it is preferable to send air in order to maintain the dissolved oxygen amount of electroless plating. In the case of a non-oxidizing / reducing gas such as nitrogen gas or argon gas, the amount of dissolved oxygen in the electroless plating solution may decrease, and plating may not be deposited.

As already described, in the porous wiring board according to the embodiment of the present invention, the ratio (w ₂ / w 1 ₎ of the maximum widths of the conductive parts inside and outside the porous sheet is within a predetermined range. is required. This can be achieved by controlling the deposition rate of the electroless plating inside and outside the porous sheet. For example, a method of adding a stabilizer can be mentioned. The type of the stabilizer is not particularly limited as long as it has an action of reducing the plating deposition rate on the porous sheet surface. For example, 2,2′-bipyridyl, 4,4′-dimethyl-2,2′- Bipyridyl, 6,6′-dimethyl-2,2′-bipyridyl (neocuproin) or the like can be used. The effect can be acquired if the addition amount of a stabilizer is about 0.02-0.19 mg with respect to 200 mL of electroless-plating solutions. By adding such a stabilizer, plating nuclei on the surface of the porous sheet are reduced, and the deposition rate can be reduced by reducing the deposition rate.

Alternatively, air bubbling may be performed during electroless plating. When the air bubble collides with the wiring forming portion, formation of the conductive portion by plating deposition is hindered, and the conductive portion forming speed outside the porous sheet is reduced. The porous sheet is installed so that the air bubbles collide. The air bubbling pressure is preferably set in the range of 0.005 MPa to 0.1 MPa with respect to 200 ml of electroless plating solution and a 5 cm ² porous sheet. It is desirable to appropriately set the air so that it uniformly collides with the porous sheet according to the capacity of the electroless plating solution and the area of the porous sheet.

  By performing electroless plating by such a method, the conductive portion 26 is formed as shown in FIG. Thus, the porous wiring board according to the embodiment of the present invention can be manufactured.

As shown in the cross-sectional view of FIG. 1, the cross section of the manufactured wiring often has an elliptical shape, but the arc is not always continuous. Examples of such structures are shown in FIGS. In the structure shown in FIG. 8, the outer periphery of the inner conductive portion 12a and the outer conductive portion 12b is not connected. In this case, the inner conductive portion 12 a has an elliptical shape, and the maximum width w ₁ exists inside the porous sheet 11. Also in the structure shown in FIG. 9, the inner conductive portion 12 a and the outer conductive portion 12 b are not connected, and the maximum width w ₁ of the inner conductive portion 12 a exists on the boundary line of the porous sheet 11.

Since the abundance of plating nuclei and the plating deposition amount are different between the inside and the outside of the porous sheet 11, the shape may not be similar to an ellipse. Even in such a case, the maximum width in which the filling portion inside the porous sheet and the filling portion outside the porous sheet are parallel to the boundary surface of the porous sheet is measured, and (w ₂ / w ₁ ) Can lead the relationship.

Since the maximum width ratio (w ₂ / w ₁ ) is defined within a predetermined range, design dimension positional deviation is substantially prevented in the porous wiring board according to the embodiment of the present invention. The graph of FIG. 10 shows the ratio (La / Lb) between the actual wiring distance (La) and the designed wiring distance (Lb) in the porous wiring board, and the conductive part width ratio (w ₂ / w ₁ ). Show the relationship. The distance between wirings refers to the distance between the maximum point of one wiring and the maximum point of adjacent wirings, as schematically shown in FIG. The inter-design wiring distance (Lb) is a pattern exposure inter-wiring distance, and the actual inter-wiring distance (La) is an inter-wiring distance produced on the porous sheet. When contraction occurs between the wirings, the actual inter-wiring distance (La) does not coincide with the designed inter-wiring distance (Lb), and the ratio (La / Lb) is less than 1.

As shown in the graph of FIG. 10, when the maximum width ratio (w ₂ / w ₁ ) of the conductive portion inside and outside the porous sheet is 0.98 or less, the distance between the wirings is substantially secured as designed. can do. Of course, the ratio of the distance between wirings (La / Lb) is most preferably 1. However, if it is 0.995 or more, it is within the allowable range, and the wiring is formed with dimensions substantially as designed. be able to.

By defining the maximum width ratio (w ₂ / w ₁ ) of the conductive part to 0.98 or less, the stress applied to the porous sheet when the electroless plating is deposited is caused by the conductive part 12a inside the porous sheet. Is effectively absorbed. This is because, in the conductive portion 12a inside the porous sheet 11, the metal is filled in the pores using electroless plating, so that the metal is in a sparse state compared to the external conductive portion 12b. .

  In the dense plating film, a large number of metal grain boundaries of different sizes from several hundred nm to several tens of μm are continuously connected, and the interface between the metal grain boundaries is strong between the interfaces having different grain boundary sizes. Stress is generated. On the other hand, the sparse conductive part is formed by depositing plating inside the porous sheet, and in this porous sheet, uniform pores of several nm to several hundred nm are continuously arranged in three dimensions. Has been. As a result, since the plating is sparse in the porous sheet and the plating is divided in nano size, the plating grain boundary is efficiently divided and the generation of stress can be almost eliminated.

The dense conductive portion 12b outside the porous sheet 11 still generates strong stress, but by making the width w ₁ of the sparse inner conductive portion 12a larger than the width w ₂ of the dense outer conductive portion 12b. The stress of the dense conductive portion 12b outside the porous sheet is absorbed. As a result, the stress of the external dense conductive portion 12b is not directly transmitted to the porous sheet, and the shrinkage between the wirings can be greatly reduced.

By defining the thicknesses of the conductive portions 12a and 12b inside and outside the porous sheet 11 within a predetermined range, this effect is more remarkably exhibited. For example, in the case of a porous sheet having an average pore diameter of 100 nm, the relationship between the thickness t ₂ of the conductive portion 12 b outside the porous sheet and the thickness t ₁ of the conductive portion 12 a inside the porous sheet is t ₁ ≧ 0.5 t _2. It was confirmed that the effect becomes remarkable.

In this way, it is possible to effectively prevent the shrinkage between wirings of the wiring produced on the porous sheet, and remarkably increase the connection reliability of the circuit wiring. The shrinkage between the wirings as described above is not limited to the case where the stress direction of the electroless plating is applied to the outside from the central part of the wiring, and the stress direction of the electroless plating is inside the central part of the wiring. Even in the case of compressive stress loaded toward the wire, it was possible to prevent shrinkage between the wirings. This is because the conductive portion 12a produced inside the porous sheet has a large width w ₁ , thereby generating an anchor effect and absorbing the stress of the conductive portion 12b outside the porous sheet.

As described above, in the embodiment of the present invention, the relationship between the width w ₂ of the conductive portion 12b outside the porous sheet and the width w ₁ of the conductive portion 12a inside the substrate is defined within a specific range. It was possible to effectively prevent the shrinkage between. As a result, it is possible to improve the connection reliability between the circuit wiring and the mounted component and the connection reliability when the circuit wiring is stacked.

  Hereinafter, the present invention will be described in detail with specific examples.

Example 1
A porous tetrafluoroethylene (PTFE) resin sheet (area 5 cm ² , thickness 30 μm) was prepared. This porous sheet 21 had an average pore diameter of 700 nm and a porosity of 57%.

  As the photosensitive material, a phenol resin containing 46 equivalent mol% naphthoquinone diazide was used. As the solvent, tetrahydrofuran was used, and the above-described photosensitive material was dissolved so as to have a concentration of 80 mmol / L.

  The porous sheet was dipped in this solution for 30 seconds, pulled up, and allowed to stand at room temperature for 1 hour to dry, thereby forming a photosensitive layer 22 as shown in FIG.

Next, pattern exposure was performed on the photosensitive layer 22 by an exposure apparatus (Cannon-PLA 501) through an exposure mask having a line width of 50 μm and a space width of 400 μm. The exposure was contact exposure, and exposure was performed at an exposure amount of 1000 mJ / cm ² using a mercury lamp from one side of the photosensitive layer. As a result of such exposure, a pattern latent image composed of ion-exchangeable groups was formed on the exposed portion 23 of the photosensitive layer 22 as shown in FIG.

The porous sheet having the exposed photosensitive layer was immersed in 100 mM sodium bicarbonate (NaHCO ₃ ) solution for 10 minutes. This was washed with pure water for 30 seconds, and further immersed in a 50 mmol / L aqueous solution of copper acetate for 30 minutes. Copper ions adhered to the ion-exchangeable group generated in the exposed portion of the photosensitive layer, and a metal ion portion 24 as shown in FIG. 5 was formed.

In order to reduce the metal ions, the porous sheet formed with the metal ion part is immersed in a 50 mmol / L sodium borohydride (NaBH ₄ ) solution for 10 minutes, thereby reducing the copper ions and precipitating the metal copper. It was. Thereby, the metal part 25 as shown in FIG. 6 was formed.

  The electroless copper plating solution was prepared by mixing 1: 1 a solution obtained by diluting PB-503A and PB-503B (both manufactured by Ebara Eugelite) 5 times. To 200 ml of this electroless plating solution, 0.08 mg of 2,2'-bipyridyl as a stabilizer was added. The above-mentioned porous sheet was immersed in the obtained electroless copper plating solution, and electroless plating was performed at 25 ° C. for 3 hours. As a result, the conductive portion 26 was formed as shown in FIG.

When the cross section of the conductive part was observed with an ultra-deep laser microscope VK-8500 (KEYENCE), it was w ₂ / w ₁ = 0.89. Moreover, it was confirmed that La / Lb = 0.998.

(Example 2)
Electroless plating was performed in the same manner as in Example 1 except that the amount of 2,2′-bipyridyl as a stabilizer added to the electroless copper plating solution was changed to 0.13 mg. As a result, the conductive portion 26 shown in FIG. 7 was formed.

When the cross section of the conductive part was observed with an ultra-deep laser microscope VK-8500 (KEYENCE), it was w ₂ / w ₁ = 0.84. Moreover, it was confirmed that La / Lb = 0.998.

(Example 3)
Electroless plating was performed in the same manner as in Example 1 except that the amount of 2,2′-bipyridyl as a stabilizer added to the electroless copper plating solution was changed to 0.19 mg. As a result, the conductive portion 26 shown in FIG. 7 was formed.

When the cross section of the conductive part was observed with an ultra-deep laser microscope VK-8500 (KEYENCE), it was w ₂ / w ₁ = 0.80. Moreover, it was confirmed that La / Lb = 0.998.

(Example 4)
Using the same porous sheet as in Example 1, metallic copper was deposited by the same method. As the electroless plating solution, a mixed solution similar to Example 1 was prepared except that no stabilizer was added. A glass ball filter 502G (Kinoshita Rika Kogyo Co., Ltd.) was put into 200 ml of this electroless plating solution, and air was sent in. It was 0.03 MPa when the injection pressure of air was measured using digital pressure sensor AG-C40 (KEYENCE). Thus, the above-mentioned porous sheet was immersed in the electroless plating solution by air bubbling, and electroless plating was performed at 25 ° C. for 3 hours. As a result, the conductive portion 26 was produced as shown in FIG.

When the cross section of the conductive portion was observed with an ultra-deep laser microscope VK-8500 (KEYENCE), it was w ₂ / w ₁ = 0.61. It was also confirmed that La / Lb = 0.998.

(Example 5)
Except that the exposure mask was changed to a line width of 20 μm and a space width of 20 μm, and the amount of 2,2′-bipyridyl added to the electroless copper plating solution was changed to 0.07 mg, the same as in Example 1 above. Electroless plating was performed by the method described above. As a result, the conductive portion 26 shown in FIG. 7 was formed.

Observation of the conductive portion cross by ultradeep laser microscope VK-8500 (KEYENCE), was w ₂ / w ₁ = 0.91. Moreover, it was confirmed that La / Lb = 0.998.

(Example 6)
Except that the exposure mask was changed to a line width of 20 μm and a space width of 20 μm, and the amount of 2,2′-bipyridyl added to the electroless copper plating solution was changed to 0.05 mg, the same as in Example 1 above Electroless plating was performed by the method described above. As a result, the conductive portion 26 shown in FIG. 7 was formed.

Observation of the conductive portion cross by ultradeep laser microscope VK-8500 (KEYENCE), was w ₂ / w ₁ = 0.95. Moreover, it was confirmed that La / Lb = 0.998.

(Example 7)
Except that the exposure mask was changed to one having a line width of 20 μm and a space width of 20 μm, and the amount of 2,2′-bipyridyl added to the electroless copper plating solution was changed to 0.02 mg, the same as in Example 1 above. Electroless plating was performed by the method described above. As a result, the conductive portion 26 shown in FIG. 7 was formed.

When the cross section of the conductive portion was observed with an ultra-deep laser microscope VK-8500 (KEYENCE), it was w ₂ / w ₁ = 0.98. Moreover, it was confirmed that La / Lb = 0.997.

Thus, it was confirmed that the wiring can be formed with dimensions substantially as designed by defining the maximum width ratio (w ₂ / w ₁ ) of the conductive portion to 0.98 or less.

(Comparative Example 1)
Electroless plating was performed in the same manner as in Example 1 except that the amount of 2,2′-bipyridyl as a stabilizer was not added to the electroless copper plating solution. As a result, a conductive part was formed in the exposed part.

When the cross section of the conductive part was observed with an ultra-deep laser microscope VK-8500 (KEYENCE), it was w ₂ / w ₁ = 1.0. Moreover, it was confirmed that La / Lb = 0.965.

(Comparative Example 2)
As the electroless copper plating solution, a mixed solution in which PB-503A and PB-503B (both manufactured by Ebara Eugelite) were mixed by a factor of four was mixed 1: 1, and the temperature of the plating solution was set to 35 ° C. Except for the change, electroless plating was performed in the same manner as in Comparative Example 1. As a result, a conductive part was formed in the exposed part.

When the cross section of the conductive portion was observed with an ultra-deep laser microscope VK-8500 (KEYENCE), it was w ₂ / w ₁ = 1.2. Moreover, it was confirmed that La / Lb = 0.894.

As shown in the result of Comparative Example 1, when the maximum width ratio (w ₂ / w ₁ ) of the conductive portion is 1, La / Lb is only 0.965, and the shrinkage between the wirings is in an allowable range. Is over. It is clear from the result of Comparative Example 2 that the shrinkage between the wirings further increases when the maximum width ratio is 1.2.

1 is a cross-sectional view of a porous wiring board according to an embodiment of the present invention. Process sectional drawing showing the process of the manufacturing method of the porous wiring board concerning one Embodiment of this invention. Sectional drawing showing the process of following FIG. Sectional drawing showing the process of following FIG. Sectional drawing showing the process of following FIG. Sectional drawing showing the process of following FIG. Sectional drawing showing the process of following FIG. Sectional drawing of the porous wiring board concerning other embodiment of this invention. Sectional drawing of the porous wiring board concerning other embodiment of this invention. The ratio of the actual distance between wirings designed interconnect distance between the (La) (Lb) (La / Lb), graph representing the relationship between the ratio of the conductive portion maximum width (w ₂ / w _1). The schematic diagram explaining the distance between wiring.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Porous wiring board; 11 ... Porous insulating sheet; 12 ... Conductive part 12a ... Inner conductive part; 12b ... Outer conductive part; 21 ... Porous insulating sheet 22 ... Photosensitive layer; 23 ... Exposed part; 24; conductive metal part 26 ... conductive part; w ₁ ... maximum width of inner conductive part; w ₂ ... maximum width of outer conductive part t ₁ ... thickness of inner conductive part; t ₂ ... thickness of outer conductive part .

Claims (2)

A porous sheet-like insulator;
An inner conductive portion formed by filling a metal in the hole of the sheet-like insulator;
On the surface of the inner conductive part, the inner conductive part is formed with a discontinuous arc, and comprises an outer conductive part connectable to the outside,
Between the maximum width (w ₂ ) parallel to the sheet-like insulator boundary surface in the outer conductive portion and the maximum width (w ₁ ) parallel to the sheet-like insulator boundary surface in the inner conductive portion, A porous wiring board having a relationship represented by the following mathematical formula (1):
0.2 ≦ (w ₂ / w ₁ ) ≦ 0.98 (1) Between the maximum width (w ₂ ) parallel to the sheet-like insulator boundary surface in the outer conductive portion and the maximum width (w ₁ ) parallel to the sheet-like insulator boundary surface in the inner conductive portion, The porous wiring board according to claim 1, wherein there is a relationship represented by the following mathematical formula (2).
0.2 ≦ (w ₂ / w ₁ ) ≦ 0.95 (2)

Images