Method for manufacturing printed wiring board

Abstract

[Problem] To provide a method which is for manufacturing a printed wiring board and which can deal with a thin metal foil and improve manufacturing efficiency. [Solution] A laminated plate 13 is formed by laminating a metal foil 12 on at least one surface of an insulating layer 11 (laminated plate formation step). Next, a component composed of a different element than the metal foil 12 is deposited on the surface of the metal foil 12 to form a deposition layer 15 (deposition layer formation step). Subsequently, the surface of the deposition layer 15 is irradiated with a laser to form a hole in the laminated plate 13 (hole formation step).

Description

Printed wiring board manufacturing method

[0001] The present invention relates to a method for manufacturing a printed wiring board, which includes a hole forming step.

[0002] In recent years, in addition to miniaturization and high performance of semiconductor elements, it has become essential to increase the density and multilayering of printed wiring boards on which semiconductor elements are mounted, as well as to reduce the diameter and precision of via holes. In printed wiring boards, miniaturization is being promoted, for example, by using laser light such as a carbon dioxide laser to form via holes. Known hole processing methods using laser light include, for example, laminating a metal foil on an insulating layer and irradiating the metal foil with laser light to drill holes in the metal foil and the insulating layer (see Patent Document 1). However, with this method, for example, when the metal foil is a copper foil with a thickness of 1.5 μm, the minimum diameter of holes that can be processed using a carbon dioxide laser is limited to approximately 50 μm to 60 μm.

[0003] Japanese Patent Application Laid-Open No. 2004-31710

[0004] Therefore, for example, it is conceivable to subject the metal foil to a blackening treatment (BO treatment) before drilling. By subjecting the metal foil to a blackening treatment before drilling, the diameter of the holes that can be drilled with a carbon dioxide laser can be reduced to a minimum of approximately 38 μm. However, since the blackening treatment removes approximately 1.5 μm from the surface of the metal foil, in order to achieve a metal foil thickness of 1.5 μm when drilling holes, the thickness of the metal foil when laminated to the insulating layer must be 3.0 μm or more, which is a problem in that it cannot be applied when laminating a metal foil with a thickness of 1.5 μm to the insulating layer. Furthermore, the blackening treatment involves many steps, such as a degreasing step, a cleaning step, a microetching step, a cleaning step, a pre-dip treatment step, an oxide treatment step, a cleaning step, and a drying step. The total time required for all blackening treatment steps is 80 minutes or more, resulting in poor manufacturing efficiency.

[0005] The present invention has been made in response to such problems, and aims to provide a method for manufacturing a printed wiring board that can accommodate thin metal foil and can improve manufacturing efficiency.

[0006] The present invention is as follows: [1] A method for manufacturing a printed wiring board, comprising: a laminate-forming step of laminating a metal foil on at least one surface of an insulating layer and applying heat and pressure to form a laminate; a deposit-layer-forming step of, after the laminate-forming step, depositing a component composed of an element different from the metal foil on a surface of the metal foil opposite to the surface in contact with the insulating layer to form a deposit layer in the laminate; and a hole-forming step of, after the deposit-layer-forming step, irradiating the surface of the deposit layer with a laser to form holes in the laminate. [2] The method for manufacturing a printed wiring board according to [1], wherein the deposit layer contains one or more elements selected from the group consisting of carbon (C), aluminum (Al), zinc (Zn), cobalt (Co), chromium (Cr), copper (Cu), gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), nickel (Ni), and molybdenum (Mo). [3] The method for manufacturing a printed wiring board according to [1], wherein in the deposit layer forming step, the deposit layer is formed using a precipitating aqueous solution containing: (i) at least one water-soluble metal compound selected from the group consisting of a water-soluble palladium compound, a water-soluble ruthenium compound, and a water-soluble silver compound, (ii) at least one halide selected from the group consisting of hydrohalic acid, a metal halide, and an ammonium halide, and (iii) at least one nitrogen-containing compound selected from the group consisting of alkylenediamines, polyalkylenepolyamines, polyamidepolyamines, and crosslinked polyamidepolyamines. [4] The method for manufacturing a printed wiring board according to [3], wherein in the precipitating aqueous solution, a metal component of the water-soluble metal compound has a concentration of 0.0001 mol / L to 0.5 mol / L, a halide concentration of 0.1 g / L to 500 g / L, and a nitrogen-containing compound concentration of 0.001 g / L to 100 g / L.

[0007] According to the present invention, a deposition layer is formed on the surface of a metal foil by depositing a component composed of an element different from the metal foil. This allows the surface of the metal foil to be easily blackened without significantly changing the thickness of the metal foil. Therefore, even if the metal foil is thin, holes with small diameters can be easily formed. Furthermore, since the deposition layer can be easily formed in a short time, the manufacturing process can be simplified and manufacturing efficiency can be improved.

[0008] 1 is a diagram showing each step of a method for manufacturing a printed wiring board according to a first embodiment of the present invention; FIG. 2 is a diagram showing each step following FIG. 1; FIG. 3 is a diagram showing each step of a method for manufacturing a printed wiring board according to a second embodiment of the present invention; and FIG. 4 is a diagram showing each step following FIG.

[0009] Below, we will explain in detail the form for implementing the present invention (hereinafter referred to as the ``present embodiment''), but the present invention is not limited to this and various modifications are possible within the scope of the gist of the present invention.

[0010] 1 and 2 illustrate steps in a method for manufacturing a printed wiring board according to a first embodiment of the present invention. First, as shown in FIG. 1A, a metal foil 12 is laminated on at least one surface of an insulating layer 11, followed by heating and pressure to form a laminate 13 (laminate formation process). Specifically, for example, an insulating layer 11 containing a thermosetting resin and a metal foil 12 are placed in this order on an inner layer substrate 14, which includes an insulating substrate 14A and an inner layer circuit 14B formed thereon, and the insulating layer 11 is cured by heating and pressure to form the laminate 13. The insulating layer 11 and the metal foil 12 may be laminated on both the front and back surfaces of the inner layer substrate 14, or on only one surface.

[0011] The inner layer substrate 14 can be manufactured by a conventionally known method. To explain an example of the manufacturing process for the inner layer substrate 14, first, through holes (not shown) are formed in an insulating substrate 14A made of a resin substrate such as a glass epoxy or polyimide resin, and then electrolytic copper plating is performed on both the top and bottom surfaces of the insulating substrate 14A and the inner surfaces of the through holes using electroless copper plating as a base. Next, a resist pattern is formed on the surface, and a conductor pattern and through-hole conductors are formed as the inner layer circuit 14B by etching, and the cavities in the through-hole conductors are filled with a filling resin such as epoxy to flatten the surface.

[0012] Before laminating the insulating layer 11 and the metal foil 12 on the inner layer substrate 14, it is preferable to roughen the surface of the inner layer substrate 14, specifically the surface of the inner layer circuit 14B, for example, by etching or the like.

[0013] The insulating layer 11 can be formed, for example, from an insulating prepreg or resin sheet containing a thermosetting resin. Examples of prepregs include those obtained by impregnating or coating a substrate, such as a fibrous reinforcing material such as glass cloth or carbon fiber, with a thermosetting resin composition containing a thermosetting resin mixed with additives such as a curing agent and a coloring agent, and then semi-curing the material. Examples of resin sheets include those obtained by semi-curing a thermosetting resin composition containing a thermosetting resin mixed with additives such as a curing agent and a coloring agent. Examples of thermosetting resins used in prepregs or resin sheets include polyimide resins, epoxy compounds, cyanate ester compounds, maleimide compounds, phenolic compounds, polyphenylene ether compounds, benzoxazine compounds, organic group-modified silicone compounds, and compounds having polymerizable unsaturated groups. The prepregs or resin sheets that constitute the insulating layer 11 are cured by heating.

[0014] The thickness of the insulating layer 11 is, for example, 5 μm or more, preferably 10 μm or more, more preferably 15 μm or more, even more preferably 20 μm or more, and even more preferably 25 μm or more. It is also preferably 100 μm or less, more preferably 80 μm or less, even more preferably 60 μm or less, even more preferably 50 μm or less, even more preferably 40 μm or less, and particularly preferably 35 μm or less. By setting the thickness at or above the lower limit, insulation reliability tends to improve. Furthermore, by setting the thickness at or below the upper limit, product thickness tends to be reduced.

[0015] It is preferable to use a metal foil 12 whose surface has been roughened. This is because the roughened shape of the metal foil 12 can be transferred to the surface of the insulating layer 11 to form a roughened surface. For example, the metal foil 12 preferably has a surface roughness Rz of 2.0 μm or less, more preferably 1.8 μm or less, even more preferably 1.5 μm or less, and may even be 1.0 μm or less, on at least one side, as measured in accordance with JIS B0601 1994. Furthermore, while a surface roughness Rz of more than 0 μm is practical, it is preferably 0.2 μm or more, and more preferably 0.5 μm or more. By setting the surface roughness Rz of the metal foil 12 to the lower limit or greater, adhesion between the insulating layer 11 and the plating layer tends to be further improved. Furthermore, by setting the surface roughness Rz to the upper limit or less, the time required for the process of removing the metal foil 12 by etching tends to be further shortened. In addition, the time required for the flash etching process (e.g., etching that etches a portion of the electroless plating layer 16 to expose the insulating layer 11 in the wiring pattern formation process described below) can be further shortened, and it tends to be easier to form wiring patterns with smaller lines and spaces.

[0016] The thickness of the metal foil 12 is preferably 0.5 μm or more, more preferably 0.8 μm or more, even more preferably 1.0 μm or more, even more preferably 1.2 μm or more, and may be 1.5 μm or more. The thickness of the metal foil 12 is more preferably 5.0 μm or less, even more preferably 3.0 μm or less, and may be 2.5 μm or less, or 2.0 μm or less. By making the thickness of the metal foil 12 equal to or greater than the lower limit, handleability tends to be improved. By making the thickness equal to or less than the upper limit, the time required for the process of etching away the metal foil 12 can be further shortened, thereby reducing the manufacturing cost of the printed wiring board.

[0017] The metal constituting the metal foil 12 is at least one metal selected from copper, aluminum, nickel, titanium (Ti), iron (Fe), gold, silver, platinum, tin (Sn), zinc, tantalum (Ta), molybdenum, niobium (Nb), and other alloys, and is preferably composed of copper. Examples of copper foil that can be used include rolled copper foil and electrolytic copper foil. The surface of the metal foil 12 may be roughened at least on the surface on the insulating layer 11 side. Examples of roughening treatment for the metal foil 12 include electrolytic roughening treatment.

[0018] The laminate 13 can be formed, for example, by placing the insulating layer 11 on the inner layer substrate 14, placing the metal foil 12 thereon, and then heating and pressurizing the laminate. In this case, the metal foil 12 may be placed alone, or a metal foil with a carrier support may be used, with the metal foil 12 placed on the insulating layer 11, and the carrier support may be peeled off to form the laminate. Alternatively, the laminate 13 may be formed, for example, using a resin-layered metal foil in which an insulating resin layer containing a thermosetting resin is formed on the metal foil 12, or a composite sheet in which an insulating resin layer containing a thermosetting resin is formed on the metal foil 12 of a metal foil with a carrier support, with the resin layer serving as the insulating layer 11 being placed against the inner layer substrate 14, and then heating and pressurizing the laminate. Examples of materials constituting the resin layer include those similar to the prepreg or resin sheet described above. The method for providing the metal foil 12 on the surface of the resin sheet is not particularly limited, and can be achieved, for example, by applying a solution (varnish) of a thermosetting resin dissolved in a solvent to the metal foil 12 and drying it. Examples of application methods include a gravure coater, a bar coater, a die coater, a doctor blade, and a baker applicator.

[0019] In this embodiment, it is preferable to use a metal foil with a carrier support, in which the metal foil 12 and a carrier support are laminated together, to provide the metal foil 12 on the surface of the insulating layer 11. Specifically, for example, a thin copper foil with a carrier copper foil, which has a 1.5 μm thick thin copper foil as the metal foil 12 and a 18 μm thick carrier copper foil as the carrier support, is placed on the surface of the insulating layer 11 made of a prepreg or a resin sheet, and laminated and molded, and then the carrier copper foil is removed, thereby providing the metal foil 12 on the surface of the insulating layer 11.

[0020] Examples of the carrier support include metal foil and resin film, with metal foil being preferred and copper foil being more preferred. When the carrier support is copper foil, it is often referred to as carrier copper foil. For resin films, the description in paragraph 0031 of WO 2017 / 086418 can be referred to, the contents of which are incorporated herein by reference. The thickness of the carrier support is, for example, 5 μm or more, preferably 8 μm or more, and 100 μm or less, preferably 50 μm or less, and more preferably 30 μm or less. The carrier support-attached metal foil 12 may have other layers (such as an adhesive layer, a release layer, a roughening treatment layer, a heat-resistant treatment layer, a rust-proofing treatment layer, or a silane coupling agent treatment layer) provided between the carrier support and the metal foil 12.

[0021] The heating temperature when forming the laminate 13 is, for example, preferably 150°C or higher, more preferably 180°C or higher, and even more preferably 200°C or higher. The heating temperature is, for example, preferably 350°C or lower, more preferably 300°C or lower, and even more preferably 250°C or lower. The pressure applied when forming the laminate 13 is, for example, preferably 1.0 MPa or higher, more preferably 1.5 MPa or higher, and even more preferably 2.0 MPa or higher. The pressure applied is, for example, preferably 5.0 MPa or lower, more preferably 4.5 MPa or lower, and even more preferably 4.0 MPa or lower. As a result, the roughened shape of the metal foil 12 is transferred and hardened to the surface of the insulating layer 11 against which the metal foil 12 is abutted.

[0022] 1(B), a component composed of an element different from that of the metal foil 12 is precipitated on the surface of the metal foil 12 opposite to the surface in contact with the insulating layer 11, thereby forming a precipitate layer 15 on the laminate 13 (precipitate layer formation step). As a result, according to this embodiment, the surface of the metal foil 12 of the laminate 13 can be blackened without significantly changing the thickness of the metal foil 12.

[0023] The deposition layer 15 is preferably formed to contain one or more elements selected from the group consisting of carbon, aluminum, zinc, cobalt, chromium, copper, gold, silver, platinum, palladium, rhodium, iridium, ruthenium, osmium, nickel, and molybdenum. This is because this can improve the absorption of lasers such as carbon dioxide lasers in the hole formation process described below. In particular, when the metal foil 12 is made of copper foil, the deposition layer 15 is preferably formed to contain one or more elements selected from the group consisting of silver, palladium, and ruthenium.

[0024] The deposition layer 15 can be formed using, for example, a deposition aqueous solution containing the following active ingredients (i) to (iii): (i) at least one water-soluble metal compound selected from the group consisting of water-soluble palladium compounds, water-soluble ruthenium compounds, and water-soluble silver compounds; (ii) at least one halide selected from the group consisting of hydrohalic acid, metal halides, and ammonium halides; and (iii) at least one nitrogen-containing compound selected from the group consisting of alkylenediamines, polyalkylenepolyamines, polyamidepolyamines, and crosslinked polyamidepolyamines. An example of such a deposition aqueous solution is "OPC Black Copper" manufactured by Okuno Chemical Industries Co., Ltd.

[0025] (i) Water-Soluble Metal Compound The water-soluble metal compound is used to blacken the surface of the metal foil 12 by depositing a component composed of an element different from the metal foil 12. Any water-soluble metal compound can be used as long as it is soluble in the deposition aqueous solution. Examples of aqueous palladium compounds include palladium chloride, palladium sulfate, palladium oxide, palladium iodide, palladium bromide, palladium nitrate, palladium acetate, tetraamminepalladium chloride, dinitrodiamminepalladium, and dichlorodiethylenediaminepalladium. Examples of water-soluble ruthenium compounds include ruthenium chloride, ruthenium nitrate, ruthenium salts (sodium ruthenate, potassium ruthenate, etc.), and ruthenium oxide. Examples of water-soluble silver compounds include silver nitrate, silver hypocyanate, silver acetate, silver oxide, silver methanesulfonate, silver sulfide, and silver chloride. One water-soluble metal compound may be used alone, or two or more may be used in combination.

[0026] The concentration of the water-soluble metal compound in the aqueous solution for deposition, in terms of the concentration of the metal component contained in the water-soluble metal compound, is preferably 0.0001 mol / L or more and 0.5 mol / L or less, and more preferably 0.001 mol / L or more and 0.1 mol / L or less. If the concentration of the water-soluble metal compound is too low, the surface of the laminate 13 cannot be sufficiently blackened, while if the concentration is too high, the cost will increase, which is undesirable.

[0027] (ii) Halides By adding halides to the aqueous solution for deposition, the water-soluble metal compound can be stably present in the aqueous solution for deposition. Examples of halides that can be used include chlorides, bromides, iodides, and the like. Specific examples of halides include hydrohalic acids such as hydrochloric acid, hydrobromic acid, and hydroiodic acid; alkali metal halides such as sodium chloride and potassium bromide; metal halides such as alkaline earth metal halides such as magnesium chloride and calcium iodide; and ammonium halides such as ammonium chloride and ammonium bromide. The halides may be used alone or in combination of two or more.

[0028] The halide concentration in the aqueous solution for precipitation is preferably 0.1 g / L to 500 g / L, more preferably 1 g / L to 300 g / L. If the halide concentration is too low, the stability of the aqueous solution decreases, and if the halide concentration is too high, the cost increases, which is not preferable.

[0029] (iii) Nitrogen-Atom-Containing Compound By adding a nitrogen-atom-containing compound to the deposition aqueous solution in addition to the water-soluble metal compound and halide, it becomes possible to sufficiently blacken the surface of the metal foil 12. The concentration of the nitrogen-atom-containing compound in the deposition aqueous solution is preferably 0.001 g / L or more and 100 g / L or less, and more preferably 0.01 g / L or more and 50 g / L or less. Within this range, the metal foil 12 can be sufficiently blackened. Specific examples of nitrogen-atom-containing compounds can be found in paragraphs 0025 to 0065 of Japanese Patent No. 5,862,916, the contents of which are incorporated herein by reference.

[0030] The deposition layer 15 can be formed, for example, by contacting the metal foil 12 with a deposition aqueous solution. For example, the surface of the metal foil 12 may be immersed in the deposition aqueous solution, or the deposition aqueous solution may be sprayed onto the surface of the metal foil 12. When the deposition layer 15 is formed by immersion, the temperature of the deposition aqueous solution is preferably 10°C or higher and 90°C or lower, and more preferably 20°C or higher and 60°C or lower. The pH of the deposition aqueous solution is preferably 0 or higher and 13 or lower, and more preferably 0 or higher and 8 or lower. The treatment time for contacting the metal foil 12 with the deposition aqueous solution is not particularly limited as long as the desired blackening can be achieved. When the deposition layer 15 is formed by immersion, the treatment time may be, for example, about 0.1 to 10 minutes.

[0031] In the deposition layer forming step, for example, it is preferable to degrease the surface of the metal foil 12 to remove dirt as needed before contacting the deposition aqueous solution with the metal foil 12. After blackening the surface of the metal foil 12, it is preferable to wash the laminate 13 with water and dry it as needed.

[0032] After the deposition layer forming step, for example, as shown in FIG. 1C , a laser is irradiated onto the surface of the deposition layer 15 to form holes in the laminate 13 (hole forming step). Specifically, for example, holes are drilled in the metal foil 12 and the insulating layer 11 by laser processing using a carbon dioxide laser or the like, forming non-through holes 13A that reach the inner layer circuits 14B. In this embodiment, the deposition layer 15 is formed and the surface of the laminate 13 is blackened, allowing the diameter of the non-through holes 13A to be reduced. The diameter (top diameter) of the non-through holes 13A is preferably, for example, 60 μm or less, more preferably 50 μm or less, and even more preferably 40 μm or less. Thereafter, if necessary, wet desmearing such as etching, or dry desmearing using plasma treatment or UV treatment, is performed to remove smear remaining in the non-through holes 13A.

[0033] After the hole forming step, for example, as shown in Fig. 1(D), the deposit layer 15 and the metal foil 12 are removed from the laminate 13 using an etching solution to expose the insulating layer 11 (insulating layer exposing step). Etching can be performed by known methods such as spraying or swing immersion. Examples of the etching solution include hydrogen peroxide, sulfuric acid, persulfates, organic acids, hydrochloric acid, and cupric chloride.

[0034] After the insulating layer exposing step, for example, as shown in Fig. 2(E), electroless plating is performed on the surface of the insulating layer 11 and the inner walls of the blind holes 13A to form an electroless plated layer 16 (electroless plating step). The electroless plating is preferably copper plating.

[0035] After the electroless plating process, for example, as shown in FIG. 2(F), a dry film is thermocompressed onto the surface of the electroless plating layer 16 to laminate a photoresist film, and the photoresist film is exposed and developed to form a resist pattern 17 (resist pattern formation process). The resist pattern 17 is formed, for example, corresponding to the area from which the electroless plating layer 16 will be removed in the etching process described below. During exposure, active energy rays are irradiated onto predetermined portions of the photoresist film, causing the irradiated areas to harden. The active energy rays may be irradiated through a mask pattern, or a direct writing method may be used in which the active energy rays are directly irradiated. The active energy rays are not particularly limited, but examples include ultraviolet light, visible light, electron beams, and X-rays. It is desirable to select an appropriate active energy ray depending on the type of resist. Development is not particularly limited, as long as it selectively dissolves the unexposed portions. Development methods include known methods such as spraying, swing immersion, brushing, and scraping.

[0036] After the resist pattern formation step, electrolytic plating is applied to the electroless plated layer 16 via the resist pattern 17 to form an electrolytic plated layer 18 (electrolytic plating step), as shown in FIG. 2(G). The electrolytic plating is preferably copper electrolytic plating. Next, the resist pattern 17 is stripped (resist pattern stripping step). Then, as shown in FIG. 2(H), the portion of the electroless plated layer 16 exposed by the stripping of the resist pattern 17 is removed by etching to expose the insulating layer 11, thereby forming a wiring pattern 19 (wiring pattern formation step).

[0037] As described above, according to this embodiment, the deposition layer 15 is formed on the surface of the metal foil 12 by depositing a component composed of an element different from that of the metal foil 12. This allows the surface of the metal foil 12 to be easily blackened without significantly changing the thickness of the metal foil 12. Therefore, even if the thickness of the metal foil 12 is thin, holes with small diameters can be easily formed. Furthermore, since the deposition layer 15 can be easily formed in a short time, the manufacturing process can be simplified and manufacturing efficiency can be improved.

[0038] 3 and 4 show the steps of a method for manufacturing a printed wiring board according to a second embodiment of the present invention. In this embodiment, the same components as those in the first embodiment are described using the same reference numerals. The steps from the laminate formation step to the hole formation step in the second embodiment are the same as those in the first embodiment. That is, for example, the laminate formation step (see FIG. 3(A)), the deposition layer formation step (see FIG. 3(B)), and the hole formation step (see FIG. 3(C)) are performed in the same manner as in the first embodiment.

[0039] After the hole forming step, for example, as shown in FIG. 3(D), the deposit layer 15 is removed from the laminate 13 using an etching solution to expose the metal foil 12 (metal foil exposing step). The deposit layer 15 can be removed by known methods, such as spraying or swing immersion. Examples of etching solutions include hydrogen peroxide, sulfuric acid, persulfates, organic acids, hydrochloric acid, and cupric chloride. Thereafter, if necessary, wet desmearing, such as resin etching, or dry desmearing using plasma treatment or UV treatment is performed to remove smears remaining in the non-through holes 13A. Next, for example, as shown in FIG. 4(E), electroless plating is performed on the surface of the insulating layer 11 and the inner walls of the non-through holes 13A to form an electroless plated layer 16 (electroless plating step).

[0040] After the electroless plating process, as shown in FIG. 4(F), a dry film is thermocompressed onto the electroless plated layer 16 to form a resist layer, followed by exposure and development to form a resist pattern 17 as a plating resist (resist pattern formation process). The resist pattern 17 is formed corresponding to the areas from which the metal foil 12 and electroless plated layer 16 will be removed in the wiring pattern formation process described below. Subsequently, as shown in FIG. 4(G), electrolytic plating is performed on the electroless plated layer 16 using the resist pattern 17 as a plating resist to form an electrolytic plated layer 18 (electrolytic plating process). Next, as shown in FIG. 4(H), the resist pattern 17 is removed, and the electroless plated layer 16 and a portion of the metal foil 12 are removed by flash etching or the like to form a conductor pattern 19 (wiring pattern formation process). The specific conditions for each process except for the deposition layer removal process are the same as those in the first embodiment.

[0041] In this embodiment, as in the first embodiment, a precipitation layer 15 is formed on the surface of the metal foil 12 by precipitating a component consisting of an element different from the metal foil 12, so that the same effect as in the first embodiment can be obtained.

[0042] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. If the measuring instruments used in the examples are difficult to obtain due to discontinuation, etc., measurements can be made using other instruments with equivalent performance. In the following examples, the heating temperature and pressure applied are the set temperature and set pressure of the instruments.

[0043] Example 1 A test piece was prepared as follows.

[0044] <Laminate Forming Step (See FIG. 1(A)>> A glass cloth-based BT resin copper-clad laminate (HL832NS, manufactured by Mitsubishi Gas Chemical Company, Inc.) having a conductor thickness of 12 μm and a resin layer thickness of 0.1 mm was prepared as the inner layer substrate 14, and its surface was roughened. Specifically, first, as a pretreatment, the inner layer substrate 14 was cleaned with a residue remover (CA5330, manufactured by MEC Co., Ltd.), and after rinsing with water, the copper surface was roughened with a micro-etching agent (CZ8101, manufactured by MEC Co., Ltd.), and after rinsing with water, it was rust-prevented with a rust inhibitor (CL8300, manufactured by MEC Co., Ltd.), rinsed with water, and then dried. The etching depth with the micro-etching agent was 1 μm. A horizontal line spray device was used for roughening.

[0045] After roughening the surface of the inner layer substrate 14, a composite sheet (copper foil-attached resin sheet, CRS791L, manufactured by Mitsubishi Gas Chemical Company, Inc.) made by applying a varnish made of a thermosetting resin composition to an 1.5 μm ultrathin electrolytic copper foil with an 18 μm carrier copper foil (MT18FL, manufactured by Mitsui Mining & Smelting Co., Ltd.) and bringing it to a B-stage (semi-cured state) was placed on top (both front and back) of the inner layer substrate 14, and laminate molding was performed at a pressure of 3.0 MPa and a temperature of 220° C. for 60 minutes, after which the carrier copper foil was peeled off. This formed a laminate 13 in which an insulating layer 11 made of a resin sheet and a metal layer 12 made of electrolytic copper foil were laminated in this order on the inner layer substrate 14.

[0046] <Deposit Layer Forming Step (See FIG. 1(B)>> After producing the laminate 13, the surface of the metal foil 12 was subjected to a degreasing treatment, water washing, immersion in a deposition aqueous solution, water washing, and drying in that order, to form a deposit layer 15. The degreasing treatment involved immersion at 45°C for 180 seconds using a degreasing agent (DP-320, manufactured by Okuno Chemical Industries Co., Ltd.). The water washing after degreasing involved immersion at room temperature for 10 seconds. The deposition aqueous solution used was an electroless palladium plating solution (OPC Black Copper Solution, manufactured by Okuno Chemical Industries Co., Ltd.) containing 0.5 g / L of palladium, and the temperature of the deposition aqueous solution was 30°C, with the immersion time being 360 seconds. The water washing after immersion in the deposition aqueous solution involved immersion at room temperature for 10 seconds. The drying was carried out by air drying for 1 minute.

[0047] <Hole Forming Step (See FIG. 1(C))> After forming the deposit layer 15, the surface of the deposit layer 15 was irradiated with a carbon dioxide laser to form blind holes 13A. An apparatus ML605GTW4(-P)5350U (manufactured by Mitsubishi Electric Corporation) was used for the laser processing. A test piece was obtained in this manner.

[0048] Comparative Example 1 Test pieces were obtained in the same manner as in Example 1, except that in the laminate formation step, the thickness of the ultra-thin electrolytic copper foil of the composite sheet placed on the inner layer substrate 14 was set to 3.0 μm, and a black oxide treatment (BO treatment) step was carried out instead of the deposit layer formation step to form a black oxide treatment film. The black oxide treatment (BO treatment) step was carried out as follows.

[0049] <Black Oxide Treatment Step> After producing the laminate 13, the surface of the metal foil 12 was subjected to an immersion treatment in the following order: degreasing, hot water washing, water washing, soft etching, water washing, pre-dip treatment, oxide treatment, and water washing, followed by pre-drying and main drying. For degreasing, a degreasing agent (Meltex S-1707, manufactured by MacDermid Performance Solutions Japan Co., Ltd.) was used, and the metal foil 12 was immersed for 90 seconds at 60°C. For hot water washing, the metal foil 12 was immersed for 30 seconds at 50°C. For water washing after hot water washing, the metal foil 12 was immersed for 38 seconds at room temperature. For soft etching, a soft etching agent (NPE-300, manufactured by Mitsubishi Gas Chemical Company, Inc.) was used, and the metal foil 12 was immersed for 60 seconds at 30°C. For water washing after soft etching, the metal foil 12 was immersed for 690 seconds (11 minutes and 30 seconds) at room temperature. The pre-dip treatment involved immersion at 50°C for 90 seconds using a blackening treatment agent (a mixture of BO-200B and BO-200C, manufactured by MacDermid Performance Solutions Japan Co., Ltd.). The oxidization treatment involved immersion at 75°C for 215 seconds (3 minutes 35 seconds) using a blackening treatment agent (a mixture of BO-201A, BO-200B, and BO-200C, manufactured by MacDermid Performance Solutions Japan Co., Ltd.). After the oxidization treatment, the specimen was immersed in water for 650 seconds (10 minutes 50 seconds) at room temperature. Pre-drying was performed at 115°C for 390 seconds (6 minutes 30 seconds), and main drying was performed at 120°C for 50 minutes.

[0050] Comparative Example 2 A test piece was obtained in the same manner as in Example 1, except that the hole forming step was carried out without carrying out the deposit layer forming step.

[0051] [Comparative Example 3] After forming the laminate 13 in the same manner as in Example 1, the black oxide process was carried out in the same manner as in Comparative Example 1. As a result of the black oxide process, the metal foil 12 almost disappeared, and therefore hole formation processing was not possible.

[0052] (Characteristics Evaluation) The characteristics of Example 1 and Comparative Examples 1 to 3 were measured by the following methods.

[0053] [Measurement of thickness of metal foil 12 after multilayer board formation process] In Example 1 and Comparative Examples 1 to 3, the thickness of the metal foil 12 in the laminate 13 formed after the multilayer board formation process was measured. For the measurement, an electrical resistance type film thickness meter (CMI-760, manufactured by Hitachi High-Tech Analytical Science Corporation) was used, and measurements were taken at nine locations on the metal foil 12 to calculate the average value. The results obtained are shown in Table 1. The average thickness of the metal foil 12 after the multilayer board formation process was 1.73 μm in Example 1, 3.12 μm in Comparative Example 1, 1.72 μm in Comparative Example 2, and 1.72 μm in Comparative Example 3.

[0054] [Measurement of Thickness of Metal Foil 12 Before Hole Forming Step] In Example 1 and Comparative Examples 1 and 2, the thickness of the metal foil 12 before the hole forming step was measured. Specifically, in Example 1, the thickness of the metal foil 12 after the deposition layer forming step and before the hole forming step was measured. In Comparative Example 1, the thickness of the metal foil 12 after the black oxide treatment step and before the hole forming step was measured. In Comparative Example 2, the thickness of the metal foil 12 after the laminate forming step and before the hole forming step was measured. In Comparative Example 3, the metal foil 12 was almost completely removed by the black oxide treatment step, making measurement impossible. In Comparative Example 1, the thickness of the metal foil 12 could not be measured from above the black oxide treatment film, so the thickness of the metal foil 12 was measured after removing the black oxide treatment film. #2000 abrasive paper was used to remove the black oxide treatment film. For the measurements, an electrical resistance film thickness meter (CMI-760, manufactured by Hitachi High-Tech Analytical Science Corporation) was used, and measurements were taken at nine locations on the metal foil 12 to calculate an average value. The results obtained are shown in Table 1. The average thickness of the metal foil 12 before the hole forming step was 1.68 μm in Example 1, 1.82 μm in Comparative Example 1, and 1.72 μm in Comparative Example 2.

[0055] [Measurement of Top Diameter of Non-Through Holes 13A] In Example 1 and Comparative Examples 1 and 2, after the hole formation process, the top diameter (diameter at the surface of the insulating layer 11) of the non-through holes 13A was observed using an optical microscope when processed under laser conditions that formed the smallest diameter. For Comparative Example 3, the metal foil 12 was almost completely lost in the black oxide treatment process, so no non-through holes 13A were formed. For observation, a digital microscope (MS-200, manufactured by Asahi Optical Machinery Works, Ltd.) was used, and observations were made at 20 locations on each sample at a magnification of 450x, and the average value was calculated. The results obtained are shown in Table 1. The average top diameter of the non-through holes 13A was 35.7 μm for Example 1, 38.0 μm for Comparative Example 1, and 56.2 μm for Comparative Example 2.

[0056] [Surface Treatment Time] The treatment time of the deposit layer forming step or the black oxide treatment step was investigated in Example 1, Comparative Example 1, and Comparative Example 3. The treatment time of the deposit layer forming step carried out in Example 1 was approximately 10 minutes in total. The treatment time of the black oxide treatment step carried out in Comparative Examples 1 and 3 was approximately 88 minutes in total.

[0057]

[0058] As shown in Table 1, in Example 1, in which the deposition layer forming step was performed, the thickness of the metal foil 12 when forming the laminate 13 was the same as in Comparative Example 2, and the top diameter of the non-through holes 13A was smaller than in Comparative Example 2. In contrast, in Comparative Example 1, in which the black copper treatment step was performed, the top diameter of the non-through holes 13A was smaller than in Comparative Example 2, but the thickness of the metal foil 12 was thinner in the black copper treatment step, and the thickness of the metal foil 12 when forming the laminate 13 had to be thicker than in Comparative Example 2 to form the non-through holes 13A. In addition, the processing time for the deposition layer forming step in Example 1 was significantly shorter than the processing time for the black copper treatment step in Comparative Example 1.

[0059] That is, it was found that by performing the deposition layer forming step, it is possible to easily form small-diameter holes even when the thickness of the metal foil 12 is thin, and the processing time can be significantly reduced.

[0060] It can be used in the manufacture of printed wiring boards.

[0061] 11...insulating layer, 12...metal foil, 13...laminated plate, 13A...non-through hole, 14...inner layer substrate, 14A...insulating substrate, 14B...inner layer circuit, 15...deposit layer, 16...electroless plated layer, 17...resist pattern, 18...electrolytic plated layer, 19...wiring pattern

Claims

1. A method for manufacturing a printed wiring board, comprising: a laminate forming step of laminating a metal foil on at least one surface of an insulating layer and heating and pressing the metal foil to form a laminate; a deposit layer forming step of, after the laminate forming step, depositing a component consisting of an element different from that of the metal foil on the surface of the metal foil opposite to the surface in contact with the insulating layer, thereby forming a deposit layer in the laminate; and a hole forming step of, after the deposit layer forming step, irradiating a laser onto the surface of the deposit layer to form holes in the laminate.

2. The method for producing a printed wiring board according to claim 1, wherein the deposition layer contains one or more elements selected from the group consisting of carbon (C), aluminum (Al), zinc (Zn), cobalt (Co), chromium (Cr), copper (Cu), gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), nickel (Ni), and molybdenum (Mo).

3. The method for producing a printed wiring board according to claim 1, wherein in the deposit layer forming step, the deposit layer is formed using an aqueous depositing solution containing: (i) at least one water-soluble metal compound selected from the group consisting of water-soluble palladium compounds, water-soluble ruthenium compounds, and water-soluble silver compounds; (ii) at least one halide selected from the group consisting of hydrohalic acid, metal halides, and ammonium halides; and (iii) at least one nitrogen-containing compound selected from the group consisting of alkylenediamines, polyalkylenepolyamines, polyamidepolyamines, and crosslinked polyamidepolyamines.

4. The method for manufacturing a printed wiring board according to claim 3, wherein in the aqueous solution for deposition, the concentration of the metal component of the water-soluble metal compound is 0.0001 mol / L or more and 0.5 mol / L or less, the concentration of the halide is 0.1 g / L or more and 500 g / L or less, and the concentration of the nitrogen atom-containing compound is 0.001 g / L or more and 100 g / L or less.

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