DETAILED DISCRIPTION OF THE INVENTION

[0128] The present invention is now described in detail. Unless otherwise indicated, the thickness of any copper foil, conductor layer or conductor circuit as mentioned in this specification is the mean of thicknesses measured on a light or electron microphotograph of its cross-section.

[0129] The first invention among the inventions belonging to the first group is concerned with an electroplating process for electroplating a conductive substrate surface wherein said electroplating is performed intermittently using said substrate surface as cathode and a plating metal as anode at a constant voltage between said anode and said cathode.

[0130] The intermittent electroplating in the above electroplating process is carried out by repeating application of a voltage between the cathode and anode and interruption thereof in an alternating pattern, and preferably the voltage time/interruption time ratio is 0.01 to 100, the voltage time is not longer than 10 seconds and the interruption time is not shorter than 1×10 ⁻² seconds.

[0131] The second invention among the inventions belonging to the first group is concerned with a process for producing a circuit board which comprises forming a conductor circuit on a substrate board by electroplating,

[0132] wherein said electroplating is performed intermittently using the conductive surface on which a conductor circuit is to be formed as cathode and a plating metal as anode at a constant voltage between said anode and said cathode.

[0133] In the above process for producing a circuit board, said intermittent electroplating is carried out by repeating application of a voltage between the cathode and anode and interruption thereof in an alternating pattern, and preferably the voltage time/interruption time ratio is 0.01 to 100, the voltage time is not longer than 10 seconds and the interruption time is not shorter than 1×10 ⁻² seconds.

[0134] It should be understood that the above circuit comprises electrodes and mounting pads in addition to a conductor circuit pattern.

[0135] The third invention among the inventions belonging to the first group is concerned with a process for producing a printed circuit board which comprises disposing a resist on a conductive layer on a substrate board, performing electroplating, stripping the resist off, and etching said conductive layer to provide a conductor circuit,

[0136] wherein said electroplating is performed intermittently using said conductive layer as cathode and a plating metal as anode at a constant voltage between said anode and said cathode.

[0137] The fourth invention among the inventions belonging to the first group is concerned with a process for producing a printed circuit board which comprises constructing an interlayer resin insulating layer on a conductor circuit-forming substrate board, forming openings for via holes in said interlayer resin insulating layer, forming an electroless plated metal layer over said interlayer resin insulating layer, disposing a resist thereon, performing electroplating, stripping the resist off and etching the electroless plated metal layer to form a conductor circuit pattern and via holes, wherein said electroplating is performed intermittently using said electroless plated metal layer as cathode and a plating metal as anode at a constant voltage between said anode and said cathode.

[0138] In the above process for producing a printed circuit board, a metal layer may have been formed on the surface of the interlayer resin insulating layer.

[0139] The intermittent electroplating in the above third and fourth inventions comprises application of a voltage between the cathode and anode and interruption thereof in an alternating pattern, and preferably the voltage time/interruption time ratio is 0.01 to 100, the voltage time is not longer than 10 seconds and the interruption time is not shorter than 1×10 ⁻² seconds.

[0140] The fifth invention among the inventions belonging to the first group is concerned with a circuit board having a copper film circuit on a substrate board, wherein said copper film has properties ( a ) its crystallinity is such that the half-width of X-ray diffraction of the (331) plane of copper is less than 0.3 deg. and (b) the variation in thickness of said copper film (electroplated copper layer) measured over the whole surface of said substrate, i.e. ((maximum thickness-minimum thickness)/average thickness), is not greater than 0.4.

[0141] In the circuit board mentioned above, the percent elongation of said copper film as a characteristic parameter is preferably not less than 7%.

[0142] The sixth invention among the inventions belonging to the first group is concerned with a printed circuit board comprising a copper film circuit on a substrate board, wherein said copper film has properties that (a) its crystallinity is such that the half-width of X-ray diffraction of the (331) plane of copper is less than 0.3 deg. and (b) the variation in thickness of plated metal layer measured over the whole surface of said substrate, i.e. ((maximum thickness-minimum thickness)/average thickness), is not greater than 0.4.

[0143] The seventh invention among the inventions belonging to the first group is concerned with a printed circuit board comprising an interlayer resin insulating layer on a substrate board for the formation of a conductor circuit and, as disposed on top of said interlayer resin insulating layer, a copper-film conductor circuit, with via holes provided in said interlayer resin insulating layer interconnecting said conductor circuits,

[0144] wherein said copper film has properties that (a) its crystallinity is such that the half-width of X-ray diffraction of the (331) plane of copper is less than 0.3 deg. and (b) the variation in thickness of said copper film (electroplated copper layer) measured over the whole surface of said substrate, i.e. ((maximum thickness-minimum thickness)/average thickness), is not greater than 0.4.

[0145] The copper film in the above sixth and seventh inventions is preferably further has its percent elongation of not less than 7%.

[0146] The inventions of the first group relate broadly to a technology for fabricating conductor circuits for semiconductor devices and printed circuit boards and an electroplating technology such that intermittent electroplating is performed in a plating metal ion-containing plating solution using the substrate surface as cathode and the plating metal as anode with the voltage between said anode and cathode being kept constant.

[0147] The intermittent electroplating described above insures a uniform plating thickness. The reason seems to be that while the plating metal deposit is preferentially dissolved by the spike current flowing momentarily toward the anode in the marginal area of the substrate board surface and around the openings for via holes where the amount of deposition of the plating metal tends to be larger, the plating metal is precipitated by the spike current flowing momentarily toward the cathode in the central area of the substrate surface and the interior parts of the via holes where the amount of plating metal deposition tends to be smaller as in the remainder of the region, with the result that a highly uniform thickness of electrodeposition is insured.

[0148] Furthermore, intermittent electroplating results in an increased crystallinity of the plated metal film. The reason is suspected to be that as the application of a voltage is interrupted, the metal ions in the neighborhood of the interface of the substrate diffuse to maintain a constant concentration at all times so that no defect occurs in the crystal lattice of the precipitated metal layer, thus contributing to a higher degree of crystallinity.

[0149] By the constant-voltage pulse plating technique in the inventions of the first group, which insures a uniform plate thickness, the thickness of the conductor circuits for circuit boards such as semiconductor devices and printed circuit boards can be rendered uniform. Therefore, not only is impedance alignment facilitated but, because the thickness of the interlayer resin insulating layer is uniform, an improved interlayer insulation is materialized. Furthermore, because of high crystallinity and high elongation characteristics, the residual stress in the plated metal layer is low so that even fine line-definition patterns can be protected against peeling. Therefore, the connection reliability of circuits is improved.

[0150] The above intermittent electroplating process comprises application of a voltage between the cathode and anode and interruption thereof in an alternating pattern, and preferably the voltage time/interruption time ratio is 0.01 to 100, the voltage time is not longer than 10 seconds and the interruption time is not shorter than 1×10 ⁻¹² seconds. If the voltage time exceeds 10 seconds, the film thickness will become uneven as it is the case with the conventional direct-current electroplating, and when the interruption time is less than 1×10 ⁻¹² seconds, the diffusion of metal ions will be insufficient to detract from crystallinity. The optimum voltage time/interruption time ratio is 0.1 to 1.0.

[0151] The electroplating mentioned above is preferably copper plating, nickel plating, cobalt plating, tin plating or gold plating.

[0152] The copper plating solution is preferably an aqueous solution of sulfuric acid and copper sulfate. The nickel plating solution may for example be an aqueous solution of nickel sulfate, nickel chloride, and boric acid. The cobalt plating solution may be an aqueous solution of cobalt chloride, basic cobalt carbonate and phosphorus acid. The tin plating solution may be an aqueous solution of stannous chloride. For gold plating, an aqueous solution of gold chloride, potassium cyanide and gold metal can be used.

[0153] Since the electroplating bath need not be supplemented with a brightener and other additives, the crystallinity of the plated metal deposit is remarkably high.

[0154] As the plating metal which serves as the anode, the metal in the form of a ball or a rod, for instance, can be used.

[0155] The technology of manufacturing circuit boards in accordance with the inventions belonging to the first group in now described.

[0156] The substrate board which can be used includes metal, semiconductor, resin and ceramic substrates, among others.

[0157] First, the surface of the substrate board is made electrically conductive so that it may be successfully electroplated. The technique for imparting electrical conductivity to a resin substrate or a ceramic substrate comprises forming metal layer by using an electroless plated deposit layer or a sputter-metalized layer. As an alternative, the technique of incorporating a colloidal or powdery metal in the matrix resin can be used.

[0158] On the substrate rendered electrically conductive on the surface, a resist is disposed where necessary. The plating metal adheres to the conductive surface not covered with resist but exposed.

[0159] This substrate is immersed in the electroplating solution and subjected to intermittent electroplating using the substrate as cathode and the plating metal as anode.

[0160] Referring to the inventions of the first group, the production process relevant to cases in which the circuit board is a printed circuit board is now described.

[0161] The substrate which can be used includes insulating substrates such as a resin substrate and a ceramic substrate.

[0162] The resin substrate mentioned above includes an insulating board prepared by laminating prepregs each comprising a fibrous matrix impregnated with a thermosetting resin, a thermoplastic resin or a thermosetting resin-thermoplastic resin complex or a copper-clad laminate board prepared by laying up such prepregs and copper foils and hot-pressing them.

[0163] As the fibrous matrix mentioned above, glass cloth, aramid cloth, etc. can be used.

[0164] An electroless plating catalyst such as a Pd catalyst is applied to the surface of said insulating substrate board to form an electroless plated layer. When a copper-clad laminate board is used, the copper foil as such can be utilized as cathode.

[0165] A plating resist is then disposed thereon. The plating resist can be formed by a process which comprises pasting a photosensitive dry film followed by exposure and development or a process which comprises coating the substrate board with a liquid resist followed by exposure and development.

[0166] The conductor circuit is formed by intermittent electroplating using the conductive layer not covered with resist but exposed, e.g. electroless plated metal layer as cathode and the plating metal as anode.

[0167] Then, the plating resist is stripped off and the conductive layer, e.g. electroless plated metal layer, is etched off with an etching solution to complete the conductor circuit.

[0168] As the etching solution mentioned above, an aqueous system of sulfuric acid-hydrogen peroxide, ferric chloride, cupric chloride or ammonium persulfate, for instance, can be used.

[0169] The following procedure is followed for the production of a multilayer printed circuit board.

[0170] A conductor circuit-forming substrate board is first provided with an interlayer resin insulating layer, which is then formed with openings for via holes. The openings are provided by exposure, development or irradiation with laser light.

[0171] For the interlayer resin insulating layer mentioned above, a thermosetting resin, a thermoplastic resin, a partially photosensitized thermosetting resin, or a complex resin comprising thereof can be used.

[0172] The above interlayer resin insulating layer can be formed by coating with an uncured resin or an uncured resin film by pressure bonding under heating. As an alternative, an uncured resin film carrying a metal layer, e.g. copper foil, on one side can be bonded. When such a resin film is used, the areas of the metal layer which correspond to via holes are etched off, followed by irradiation with a laser beam to provide necessary openings.

[0173] The above resin film formed with a metal layer may for example be a copper foil having resin film.

[0174] As the interlayer resin insulating layer mentioned above, the layer formed of an adhesive for electroless plating use can be used. The optimum adhesive for electroplating use is a dispersion of a cured acid- or oxidizing agent-soluble heat-resistant resin powder in a substantially acid- or oxidizing agent-insoluble uncured heat-resistant resin. This is because upon treatment with an acid or an oxidizing agent, the heat-resistant resin particles are dissolved and removed so that a roughened surface comprising narrow-necked bottle-like anchors can be provided.

[0175] Referring to said adhesive for electroless plating use, the cured heat-resistant resin powder mentioned above, in particular, is preferably {circle over (1)} a heat-resistant resin powder having an average particle diameter of not more than 10 μm, {circle over (2)} a block powder available on aggregation of heat-resistant resin particles having an average particle diameter of not more than 2 μm, {circle over (3)} a mixture of a heat-resistant resin powder having an average particle diameter of 2 to 10 μm and a heat-resistant resin powder having an average particle diameter of not more than 2 μm, {circle over (4)} a pseudo-particle comprising a heat-resistant resin powder having an average particle diameter of 2 to 10 μm and at least one of a heat-resistant resin powder and an inorganic powder each having an average particle diameter of not more than 2 μm as adhered to the surface of the first-mentioned resin powder, {circle over (5)} a mixture of a heat-resistant resin powder having an average particle diameter of 0.1 to 0.8 μm and a heat-resistant resin powder having an average particle diameter of over 0.8 μm to less than 2 μm, or {circle over (6)} a heat-resistant resin powder having an average particle diameter of 0.1 to 1.0 μm is preferred. With any of those materials, the more sophisticated anchors can be provided.

[0176] The depth of the roughened surface structure is preferably Rmax=0.01 to 20 μm. This is preferred for insuring a sufficient degree of adhesion. Particularly in the semi-additive process, the depth of 0.1 to 5 μm is preferred, for the electroless plated metal layer can then be removed without detracting from adhesion.

[0177] The substantially acid- or oxidizing agent-insoluble heat-resistant resin mentioned above is preferably a “complex resin comprising a thermosetting resin and a thermoplastic resin” or a “complex resin comprising a photosensitive resin and a thermoplastic resin”. This is because while the former is highly heat-resistant, the latter is capable of forming openings for via holes by a photolithographic technique.

[0178] The thermosetting resin which can be used as above includes epoxy resin, phenolic resin and polyimide resin. For imparting photosensitivity, the thermosetting groups are acrylated with methacrylic acid or acrylic acid. The optimum resin is an acrylated epoxy resin.

[0179] As the above-mentioned epoxy resin, there can be used novolac epoxy resins such as phenol novolac resin and cresol novolac resin and dicyclopentadiene-modified alicyclic epoxy resin.

[0180] As the thermoplastic resin, there can be used polyethersulfone (PES), polysulfone (PSF), polyphenylenesulfone (PPS), polyphenylene sulfide (PPES), polyphenyl ether (PPE), polyetherimide (PI) and fluororesin.

[0181] The blending ratio of the thermosetting resin (photosensitive resin) to the thermoplastic resin, i.e. thermosetting (photosensitive) resin/thermoplastic resin, is. preferably 95/5 to 50/50. This range contributes to a high level of toughness without compromise in heat resistance.

[0182] The blending weight ratio of said heat-resistant resin powder is preferably 5 to 50 weight % based on the solid matter of the heat-resistant resin matrix. The more preferable ratio is 10 to 40 weight %.

[0183] The heat-resistant resin powder is preferably an amino resin (melamine resin, urea resin, guanamine resin) or an epoxy resin, for instance.

[0184] Further, an electroless plated metal layer is formed over said interlayer resin insulating layer (on the copper foil when a resin-containing copper foil is used) inclusive of surface of openings and after placement of a resist, electroplating is performed to provide a conductor circuit and via holes.

[0185] The electroplating is performed intermittently using said electroless plated metal layer as cathode and the plating metal as anode with the voltage between the anode and cathode being kept constant.

[0186] Then, the resist is stripped off and the electroless plated metal layer is etched off.

[0187] The circuit board and printed circuit board formed by the electroplating process according to the first group of the present inventions, in which the conductor wiring or conductor circuit is made of copper, should satisfy the following conditions (a) and (b).

[0188] Thus, (a) as to crystallinity, the half-width of X-diffraction of the (331) plane of copper is not greater than 0.3 deg, and (b) the variation in plating thickness of the copper layer (electrolated copper layer) as measured all over the surface of said substrate board ((maximum thickness-minimum thickness)/average thickness) is not greater than 0.4.

[0189] When the half-width of X-ray diffraction of the (331) plane of copper is 0.3 deg. or larger, the residual stress will be increased and, in the case of a delicate pattern, there will be a risk for peeling. If the variation ((maximum thickness-minimum thickness)/average thickness) is greater than 0.4, impedance alignment may hardly be obtained.

[0190] The reason for selection of the (331) plane of copper is that this is the plane revealing the most striking change in crystallinity in X-ray diffraction analysis.

[0191] The percent elongation mentioned above for the copper layer is preferably not less than 7%. If the elongation is less than 7%, cracks are liable to develop on cold thermal shock.

[0192] In the inventions of the first group, the purity of copper deposited is as high as 99.8% or more. Therefore, the inherent ductility of copper is fully expressed to provide a high elongation rate.

[0193] The circuit board mentioned above includes printed circuit boards, IC chips and semiconductor devices such as LSI.

[0194] The first invention among inventions belonging to a second group is concerned with an electroless plating solution comprising an aqueous solution containing 0.025 to 0.25 mol/L of a basic compound, 0.03 to 0.15 mol/L of a reducing agent, 0.02 to 0.06 mol/L of copper ion and 0.05 to 0.30 mol/L of tartaric acid or a salt thereof.

[0195] The second invention among inventions of the second group is concerned with an electroless plating solution comprising an alkaline compound, a reducing agent, copper ion, tartaric acid or a salt thereof and at least one metal ion species selected from the group consisting of nickel ion, cobalt ion and iron ion.

[0196] The preferred specific gravity of the electroless plating solutions according to the above first and second inventions is 1.02 to 1.10.

[0197] Furthermore, the preferred temperature of those electroless plating solutions is 25 to 40° C. In addition, the copper deposition rate of those electroless plating solutions is preferably 1 to 2 μm/hour.

[0198] The third invention among inventions of the second group is concerned with an electroless plating process which comprises immersing a substrate in the electroless plating solution of said first or second invention and performing electroless copper plating with the deposition rate set to 1 to 2 μm/hour.

[0199] In the above electroless plating process, said substrate is preferably provided with a roughened surface in advance.

[0200] The fourth invention among inventions of the second group is concerned with a process for manufacturing a printed circuit board comprising immersing a resin insulating substrate board in the electroless plating solution of said first or second invention and performing electroless copper plating with the deposition rate set to 1 to 2 μm/hour to provide a conductor circuit.

[0201] The fifth invention among inventions of the second group is concerned with a printed circuit board comprising a resin insulating substrate board having a roughened surface and, as electroless plated layer thereon, a conductor circuit, wherein said electroless plated layer has a stress value of 0 to +10 kg/mm ² .

[0202] The sixth invention among inventions of the second group is concerned with a printed circuit board comprising a resin insulating substrate board having a roughened surface and, as an electroless plated layer thereon, a conductor circuit, wherein said electroless plated layer is complementary to said roughened surface and relatively increased in thickness in convex areas of the roughened surface as compared with concave areas of said surface.

[0203] The concave and convex areas mentioned above mean the concave and convex parts of the primary anchor and do not refer to the secondary anchor formed on the convex part thereof or the like (ref. FIG. 16 ).

[0204] The seventh invention among inventions of the second group is concerned with a printed circuit board which comprises a substrate board formed with a lower conductor circuit, an interlayer resin insulating layer thereon and an upper conductor circuit as built up with said lower conductor circuit connected to said upper conductor circuit through via holes, wherein said upper-layer conductor circuit comprises at least an electroless plated metal film, said interlayer resin insulating layer has a roughened surface, said electroless plated metal film is complementary to said roughened surface throughout and the bottom parts of said via holes are also provided with a electroless plated layer in a thickness equal to 50 to 100% of the electroless plated layer formed on said interlayer resin insulating layer.

[0205] The eighth invention among inventions of the second group is concerned with a printed circuit board comprising a resin insulating substrate board and as built thereon a conductor circuit comprising at least an electroless plated metal layer, wherein said electroless plated metal layer comprises copper and at least one metal selected from the group consisting of nickel, iron and cobalt.

[0206] In the printed circuit board according to the above eighth invention of the second group, the preferred content of said at least one metal selected from nickel, iron and cobalt is 0.1 to 0.5 weight %.

[0207] The electroless plating solution according to the first invention among inventions of the second group comprises an aqueous solution containing 0.025 to 0.25 mol/L of a basic compound, 0.03 to 0.15 mol/L of a reducing agent, 0.02 to 0.06 mol/L of copper ion and 0.05 to 0.3 mol/L of tartaric acid or a salt thereof.

[0208] The electroless plating solution according to the second invention among inventions of the second group comprises an aqueous solution containing a basic compound, a reducing agent, copper ion, tartaric acid or a salt thereof and at least one ion species selected from the group consisting of nickel ion, cobalt ion and iron ion.

[0209] Since those electroless plating solutions contain tartaric acid or its salt, the amount of hydrogen uptake in the plating metal deposit is so small that a tensile stress is generated in the plated metal layer. Since its absolute value is small compared with the conventional case (when EDTA is used as a complexing agent) but appropriate, the plated metal layer adheres intimately to the substrate and hardly peels off from the substrate.

[0210] Furthermore, by controlling the proportion of said basic compound within the range of 0.025 to 0.25 mol/L and that of said reducing agent within the range of 0.03 to 0.15 mol/L, the deposition rate of the plating solution can be reduced to 1 to 2 μm/hr. Therefore, when a plating metal is deposited in the openings for via holes, the copper ions are allowed to diffuse far enough down the openings for via holes so that a sufficiently thick plated metal film can be formed even within fine via holes.

[0211] Since the electroless plating solution according to the above second invention of the second group contains at least one metal ion species selected from the group consisting of nickel ion, cobalt ion and iron ion in addition to tartaric acid or a salt thereof, the evolution of hydrogen is suppressed with the result that an appropriate tensile stress is generated in the plated metal layer to insure a good adhesion to the substrate and, hence, exfoliation of the plated metal from the substrate is hard to take place.

[0212] The specific gravity of those electroless plating solutions is preferably adjusted to 1.02 to 1.10. This is because a plating metal can then be precipitated in the fine openings for via holes.

[0213] The preferred temperature of those electroless plating solutions is 25 to 40° C. If the temperature is excessively high, the deposition will be accelerated so much that the plating metal can hardly be deposited within fine openings for via holes. If the temprature is less than 25° C., it takes so much time to deposit the plated metal layer, therefor the temperature is not practical.

[0214] Furthermore, the above electroless plating solutions preferably contain 0.01 to 0.05 weight % of nickel ion, iron ion and/or cobalt ion.

[0215] By setting the concentration of nickel and/or other ion within the above range, the concentration of said at least one metal ion species selected from the group consisting of nickel, iron and cobalt ions can be controlled within the range of 0.1 to 0.5 weight % to thereby provide a plated metal film which is hard enough and shows good adhesion to the resin insulating layer.

[0216] Referring to the electroless plating solution according to the first invention among said inventions of the second group, said basic compound may for example be sodium hydroxide, potassium hydroxide or ammonia.

[0217] The reducing agent mentioned above includes formaldehyde, sodium hypophosphite, NaBH ₄ and hydrazine.

[0218] The compound mentioned above as a copper ion includes copper sulfate and copper chloride.

[0219] The above-mentioned salt of tartaric acid includes the corresponding sodium salt and potassium salt and any of those salts may be the salt derived by substituting only one of the available two carboxyl groups with the above-mentioned particular metal or the salt derived by substituting both the carboxyl groups with the above-mentioned metal.

[0220] Referring to the electroless plating solution according to the above second invention of the second group, the compound for providing said nickel ion includes nickel chloride and nickel sulfate; the compound for providing said cobalt ion includes cobalt chloride; and the compound providing for said iron ion includes iron chloride.

[0221] The third invention of the second group is concerned with an electroless plating process which comprises immersing a substrate in said electroless plating solution and performing copper electroless plating at the deposition rate set to 1 to 2 μm/hr as mentioned above.

[0222] The fourth invention of the second group is concerned with a process for manufacturing a printed circuit board which comprises immersing a resin insulating substrate board in said electroless plating solution and performing copper electroless plating by the above-mentioned electroless copper plating process to provide a conductor circuit.

[0223] The resin insulating substrate board mentioned above means not only a resin insulating substrate board not formed with a conductor circuit but a resin insulating substrate board formed with a conductor circuit and, in superimposition, further with an interlayer resin insulating layer having openings for via holes.

[0224] In the above electroless plating process or in the above process for manufacturing a printed circuit board, the surface of resin insulating layer constituting said substrate and the resin insulating substrate is preferably a roughened surface.

[0225] The roughened surface mentioned above comprises concave areas and convex areas and the plating metal is deposited tracing those concave and convex areas but the thickness of the deposit is larger in the convex areas of the roughened surface than in the concave areas thereof and this thickness profile offers the following advantages.

[0226] Thus, in the process generally called the semi-additive process which comprises disposing a plating resist on an electroless plated metal layer, performing electroplating to form a thick plated metal film, stripping off said plating resist and etching the electroless plated metal layer beneath the plating resist, the etching operation is easier when the thichness of the electroless plated metal film is relatively thin in the concave areas as compared with the convex areas and the whole plated metal deposit can be easily removed by this etching without leaving unetched areas, with the result that the insulation reliability of the resulting circuit is very satisfactory.

[0227] The printed circuit board fabricated by the process for manufacturing a printed circuit board according to the fourth invention of the second group has the following characteristics.

[0228] Thus, the printed circuit board according to the fifth invention of the second group comprises a resin insulating substrate board having a roughened surface and as built thereon a conductor circuit comprising at least an electroless plated metal film,

[0229] wherein said electroless plated metal film has a stress value of 0 to +10 kg/mm ² .

[0230] The sign of the above stress value is positive, i.e. +, which means that a tensile stress has been generated in the above-mentioned plated metal film. This stress can be measured with a spiral stress meter (manufactured by Yamamoto Plating Co., Ltd.).

[0231] Moreover, within the above stress range, the plated metal film does not undergo blistering or peeling so that the connection reliability of the conductor circuits is high.

[0232] The printed circuit board according to the sixth invention of the second group is a printed circuit board comprising a resin insulating substrate board formed with a roughened surface and as built thereon a conductor circuit comprising at least an electroless plated metal film, wherein said electroless plated metal film is complementary to said roughened surface and the thickness of said electroless plated metal film is relatively thick in the convex areas of the roughened surface compared with the concave areas thereof (that is to say, the electroless plated metal film in the concave areas is relatively thin as compared with the convex areas thereof).

[0233] Therefore, when a conductor circuit is to be formed by the semi-additive process mentioned above, the electroless plated metal film in the concave areas of said roughened surface, which is thinner than that in the convex areas, can be more readily and completely stripped off, with the result that the problem of unetched residues is obviated in the etching step and a high inter-conductor insulation dependability is assured.

[0234] The printed circuit board according to the seventh invention of the second group is concerned with a circuit board which comprises a substrate board carrying a lower conductor circuit built thereon, an interlayer resin insulating layer and an upper conductor circuit as built up with said lower conductor circuit and upper conductor circuit being interconnected by via holes,

[0235] wherein said upper conductor circuit comprises at least electroless plated metal film, said interlayer resin insulating layer has a roughened surface, said electroless plated metal film is complementary to said roughened surface, and bottoms of said via holes also carry the electroless plated metal film in a thickness equal to 50 to 100% of the thickness of the electroless plated metal film on said interlayer resin insulating layer.

[0236] The above printed circuit board is fabricated using the above-described electroless plating solution and, therefore, via holes can be provided because, even when the openings for via holes are as fine as 80 μm or less in diameter, a sufficiently thick plated metal film can be formed on the hole bottoms.

[0237] The printed circuit board according to the eighth invention of the second group comprises a resin insulating substrate board and, as built thereon, a conductor circuit comprising at least an electroless plated metal film, wherein said electroless plated metal film comprises copper and at least one metal species selected from the group consisting of nickel, iron and cobalt.

[0238] Here, addition of a salt of such a metal ion inhibits the uptake of hydrogen into the plated metal to reduce the compressive stress of plating so that the resulting film may have an improved adhesion to the resin insulating layer. Furthermore, those metals form alloys with copper to increase the hardness of the plated metal film, thus contributing further to the adhesion to the resin insulating layer.

[0239] An electrodeposition layer which is high in hardness and adhesion to the resin insulating layer can be obtained when the content of said at least one metal species selected from among nickel, iron and cobalt is within the range of 0.1 to 0.5 weight %.

[0240] The technology for manufacture of printed circuit boards according to the inventions of the second group is now described, taking the semi-additive process as an example.

[0241] (1) First, a substrate board carrying an inner-layer copper pattern (lower conductor circuit) on the surface of a core board is constructed.

[0242] Formation of the conductor circuit on the core board can be achieved typically by a process which comprises etching a copper-clad laminate board according to a predetermined pattern, a process which comprises depositing an electroless plating adhesive layer on a glass-epoxy substrate board, polyimide substrate board, ceramic substrate board or metal substrate board, roughening the adhesive layer to impart a roughened surface and performing electroless plating, or a process which comprises performing electroless plating all over said roughened surface, disposing a plating resist, performing electroplating over the areas other than the plating resist areas, stripping off the plating resist and performing etching to provide a conductor circuit comprising the electroplated metal film and the electroless plated metal film (semi-additive process).

[0243] In addition, the surface of the conductor circuit of the above circuit board may be formed with a roughened surface or a roughened layer.

[0244] The roughened surface or roughened layer mentioned above is preferably formed by any of sanding, etching, blackening-reduction, and plating techniques.

[0245] Blackening-reduction, among the above techniques, is preferably carried out by a method using a blackening bath (oxidizing bath) comprising an aqueous solution of NaOH (20 g/l), NaClO ₂ (50 g/l) and Na ₃ PO ₄ (15.0 g/l) and a reducing bath comprising an aqueous solution of NaOH (2.7 g/l) and NaBH ₄ (1.0 g/l).

[0246] The preferred procedure for forming a roughened layer by a plating technique comprises performing electroless plating using an electroless plating solution (pH=9) containing copper sulfate (1 to 40 g/l), nickel sulfate (0.1 to 6.0 g/l), citric acid (10 to 20 g/l), sodium hypophosphite (10 to 100 g/l), boric acid (10 to 40 g/l) and a surfactant (Surfinol 465, Nisshin Chemical Industries, Ltd.) (0.01 to 10 g/l) to provide a roughened layer composed of Cu—Ni—P alloy.

[0247] The crystal of the plated metal deposit formed within the above range has an acicular structure which has an excellent anchor effect. This electroless plating bath may contain a complexing agent and various additives in addition to the above compounds.

[0248] The method for providing a roughened layer by etching includes a process which comprises permitting an etching solution containing a cupric complex compound and an organic acid to act upon the surface of the conductor circuit in the presence of oxygen to thereby roughen said surface.

[0249] In this case, etching proceeds according to the chemical reactions represented by the following expression (1) and expression (2).

[0250] 1

[0251] (wherein A represents a complexing agent (which functions as a chelating agent) and n represents a coordination number).

[0252] The cupric complex mentioned above is preferably a cupric azole complex. This cupric azole acts as an oxidizing agent which oxidizes metallic copper or the like. The azole may for example be a diazole, a triazole or a tetrazole. Particularly preferred species are imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, etc. The cupric azole complex content of said etching solution is preferably 1 to 15 weight %. Within this range, the complex is good in solubility and stability and capable of dissolving even a noble metal, such as Pd, which constitutes the catalyst nucleus.

[0253] To insure dissolution of copper oxide, an organic acid is used in association with the cupric azole complex. The organic acid includes formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, acrylic acid, crotonic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid, benzoic acid, glycolic acid, lactic acid, malic acid and sulfamic acid. Those acids may be used each independently or in a combination of two or more species.

[0254] The preferred organic acid content of the etching solution is 0.1 to 30 weight %. In this range, the solubility of oxidized copper and the solution stability can be sufficiently insured. As expressed by the above expression (2), the cuprous complex generated is dissolved under the influence of the acid and binds oxygen to form the cupric complex, thus contributing to the oxidation of copper again.

[0255] To assist in the dissolution of copper and the oxidizing action of the azole compound, the etching solution mentioned above may be supplemented with a halide ion, e.g. fluoride ion, chloride ionorbromide ion. The halide ion may also be supplied by adding hydrochloric acid, sodium chloride or the like. The halide ion content of the etching solution is preferably 0.01 to 20 weight %. In this range, a good adhesion can be insured between the roughened surface and the interlayer resin insulating layer.

[0256] In preparing the etching solution, said cupric azole complex and organic acid (where necessary, one having a halide ion is used) are dissolved in water. As said etching solution, a commercial etching solution, for example “Meck Etch Bond”, trade mark, manufactured by Meck Co., Ltd., can be used. The etching amount, when the above etching solution is used, is preferably 0.1 to 10 μm, the optimum range being 1 to 5 μm. If the etching amount exceeds 10 μm, a connection defect occurs between the roughened surface and the via hole conductor. On the other hand, if the etching amount is less than 0.1 μm, the adhesion to the interlayer resin insulating layer to be built thereon will not be sufficiently high.

[0257] The roughened layer or roughened surface may be covered with a layer made of a metal having an ionization tendency greater than copper but not greater than titanium or a noble metal layer (hereinafter referred to as the metal layer). The metal mentioned above includes titanium, aluminum, zinc, iron, indium, thallium, cobalt, nickel, tin, lead and bismuth. The noble metal includes gold, silver, platinum and palladium. Those metal species may be used either independently or in a combination of two or more species to form a plurality of layers.

[0258] Such a metal layer covers the roughened layer and roughens the interlayer resin insulating layer to prevent local electrode reactions and thereby protect the conductor circuit against dissolution. The preferred thickness of such a metal layer is 0.1 to 2 μm.

[0259] Among the metals used to constitute said metal layer, tin is preferred. This is because tin may form a thinner layer on lectroless substituted plated layer faithfully tracing the roughened layer.

[0260] To form a metal layer composed of tin, substitution plating is carried out using a tin borofluoride-thiourea containing solution or a tin chloride-thiourea containing solution. In this case, an Sn layer about 0.1 to 2 μm thick is formed by the Cu—Sn substitution reaction. To form a metal layer composed of a noble metal, sputtering or vapor deposition can be used, for instance.

[0261] The core substrate board may be equipped with plated-through holes so that the wiring layer on the face side and the reverse side may be electrically connected through said plated-through holes.

[0262] Moreover, between the plated-through holes and conduc