JP2008258309A - Punching method for printed circuit board, and printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a punching method for a printed circuit board by which high-density interconnection can be achieved by forming non-through via holes using thin copper and there is little probability that copper interconnections which should be left are formed with missing holes or damage. <P>SOLUTION: The punching method for a printed circuit board includes a process wherein laser light is cast on an insulation resin layer attached with a copper interconnection layer to remove only the insulation resin while leaving copper. In this punching method, the copper interconnection layer is applied with protection metal in advance, and after laser processing, the protection metal is removed. The printed circuit board formed with via holes using the punching method is also provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a printed wiring board drilling method and a printed wiring board.

  In recent years, electronic devices have been further reduced in size, weight, and functionality, and as a result, wiring has been miniaturized. In the multilayer wiring board, when making electrical connection between each layer, using laser light, after breaking the molecular bond of the insulating resin by the energy of the light or by evaporating the insulating resin by heat, This is often realized by performing metal plating such as copper on the wall surface of the hole or filling with a conductive paste.

The laser can stop the hole with an arbitrary insulating layer by adjusting the amount of energy to be irradiated.
Furthermore, since it is possible to make a hole having a diameter of 0.01 mm with a laser, it is possible to form a higher density wiring. Laser light includes carbon dioxide laser (wavelength 10,000 nm), excimer laser (wavelength 248 nm), YAG laser (wavelength 1,320 nm, 1,064 nm, etc.), etc., depending on the medium and excitation source.

  In many cases, a conductive metal such as copper is formed on both sides of the insulating layer, and it is necessary to remove the conductive metal on the surface in order to drill the insulating layer. Therefore, as disclosed in Patent Document 1, there is a method in which a conductor metal on a resin to be removed is etched in advance, and then a laser beam is irradiated to the same position to make a hole. In this method, by making the diameter of the laser beam larger than the hole diameter, a hole having the same shape as the hole shape by etching can be formed, and the positional accuracy and the accuracy of the hole shape can be improved.

  When the via hole is formed by the laser beam, as shown in FIG. 4, the laser beam 7 is applied from one of the insulating resins sandwiched between the base metal foil (conductor) 3 and the inner conductor metal (conductor) 5, and the conductor on one side A method for removing only the insulating resin is an example. In the case of forming a high-density wiring, it is desirable that the thickness of the base metal foil 3 is thin. In recent years, a conductor having a thickness of 5 μm or less is often used.

However, if the conductor becomes thin, the heat generated by the laser cannot be escaped, and the base metal foil 3 is damaged, resulting in a hole, a dent, or a protrusion.
In addition, if the copper foil is thin, when it is damaged from the outside, the copper foil is easily scratched or torn, and the copper wiring is lost or a dent is generated.

JP-A-4-3676

  The present invention uses thin copper and can form a high-density wiring by forming a non-through hole, and the printed wiring board is less likely to have a hole missing or damaged in the copper wiring to be left. It is an object of the present invention to provide a drilling method and a printed wiring board.

  The present invention relates to a method for drilling a printed wiring board having a step of leaving a copper by irradiating a laser beam to an insulating resin layer having a copper wiring layer to remove only the insulating resin and leaving a copper. The present invention relates to a method for drilling a printed wiring board, wherein the protective metal is removed after laser processing.

The present invention also relates to the above-described method for drilling a printed wiring board, wherein a protective metal and a copper wiring layer foil are laminated with an adhesive, and the protective metal is peeled off after laser processing.
Furthermore, the present invention relates to a printed wiring board in which via holes are formed using the above-described drilling method.

  According to the drilling method of the present invention, it is possible to form a laser hole having a small diameter and a high aspect ratio using a thin copper foil, and to provide a printed wiring board that is free from chipping and peeling of the copper foil. it can.

  As shown in FIG. 1, the printed wiring board used in the present invention includes a protective metal 6, a base metal foil 3, an insulating resin layer 4, and an internal conductor metal 5 as shown in FIG. 1. The inner-layer conductor metal 5 may use the inner-layer double-sided substrate 2 having a structure of two or more layers as an inner layer, or may be a single metal.

The base metal foil 3 may be a metal having conductivity, and representative examples include copper, aluminum, nickel, chromium, silver, and the like. The metal may be a single type of metal or an alloy.
Moreover, copper, aluminum, nickel, chromium, silver, etc. can be used for the protective metal 6, and methods, such as electroplating, electroless-plating, and a lamination press, are given as the method of providing a protective metal.

  The thickness of the protective metal may be sufficient to diffuse the heat generated by the laser beam. For example, when carbon dioxide laser processing is performed and copper is used as the protective metal, the thickness of the protective metal may be 12 μm or more. desirable.

  The thickness of the protective metal is preferably in the range of 12 to 35 μm. If the thickness is less than 12 μm, the heat generated by laser processing cannot be sufficiently diffused. If the thickness exceeds 35 μm, it takes time to remove it. This is not preferable because it increases the cost of removal, causes an increase in removal cost, and easily overetches the copper wiring layer during etching removal. The plating can be performed by an electrolytic plating method or an electroless plating method.

  Examples of the method for removing the protective metal include methods such as etching and peeling. For example, when using a peelable copper foil with carrier copper in which a base metal foil and a protective metal are bonded with an adhesive layer having a low peel strength such as an organic resin or a chromium alloy, the protective metal and the base copper metal foil are easily peeled off by hand. This is desirable because the material cost and working time are reduced and the productivity is improved.

  The peel strength of the carrier is preferably 0.01 kg / cm to 0.1 kg / cm, and if it is less than 0.01 kg / cm, it is not preferable because the possibility of the carrier peeling off in the middle process is increased. If it exceeds 0.1 kg / cm, the possibility that the substrate is warped or deformed by the peeled force tends to increase, such being undesirable.

  The antirust treatment performed on the resin bonding surface of the base metal foil can be performed using any of nickel, tin, zinc, chromium, molybdenum, cobalt, or an alloy thereof. In these methods, a thin film is formed on a metal foil by sputtering, electroplating or electroless plating, but electroplating is preferable from the viewpoint of cost.

  Specifically, the plating is performed using a plating layer containing one or more metal salts among nickel, tin, zinc, chromium, morbden, and cobalt. In order to facilitate the precipitation of metal ions, a complexing agent such as citrate, tartrate or sulfamic acid can be added in the required amount.

The plating solution is usually performed in an acidic region and at a temperature of room temperature to 80 ° C. The plating is appropriately selected from a range of usually a current density of 0.1 to 10 A / dm ² , a normal time of 1 to 60 seconds, and preferably 1 to 30 seconds. The amount of the rust-proofing metal varies depending on the type of metal, but is preferably 10 to 2000 μg / dm ^{2 in} total. If the rust prevention treatment is too thick, it tends to cause etching inhibition and a decrease in electrical characteristics, and if it is too thin, it tends to cause a reduction in peel strength with the resin.

Furthermore, if a chromate treatment layer is formed on the rust prevention treatment, it is useful because a reduction in peel strength with the resin can be suppressed. Specifically, it is performed using an aqueous solution containing hexavalent chromium ions. The chromate treatment can be performed by a simple immersion treatment, but is preferably carried out by a cathode treatment. Sodium bichromate 0.1~50g / L, pH1~13, bath temperature 0 to 60 ° C., may be carried out at a current density of 0.1~5A / dm ² and a current time from 0.1 to 100 seconds. It can also carry out using chromic acid or potassium dichromate instead of sodium dichromate.

  For the insulating resin layer 4, a known and customary resin composition used as an insulating material for a printed wiring board can be used. Usually, thermosetting resin with good heat resistance and chemical resistance is used as the base, and as thermosetting resin, phenol resin, epoxy resin, cyanate resin, maleimide resin, isocyanate resin, benzocyclobutene resin, vinyl Although resin etc. are illustrated, it does not necessarily restrict | limit to these. One type of thermosetting resin may be used alone, or two or more types may be mixed and used.

  Examples of the thermoplastic resin include fluororesin, polyphenylene ether, modified polyphenylene ether, polyphenylene sulfide, polycarbonate, polyether imide, polyether ether ketone, polyarylate, polyamide, polyamide imide, polybutadiene, and polyimide. It is not limited to. One type of thermoplastic resin may be used alone, or two or more types may be mixed and used. Moreover, the inorganic filler may be included.

  Among thermosetting resins, epoxy resins are particularly important because they are widely used as insulating resins because they are excellent in heat resistance, chemical resistance and electrical properties and are relatively inexpensive. Epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, alicyclic epoxy resin, aliphatic chain epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A. Novolac type epoxy resin, diglycidyl etherified product of biphenol, diglycidyl etherified product of naphthalenediol, diglycidyl etherified product of phenol, diglycidyl etherified product of alcohol and their alkyl-substituted products, halide, hydrogen An additive etc. are mentioned.

As the epoxy resin, one kind may be used alone, or two or more kinds may be mixed and used.
The curing agent used together with the epoxy resin can be used without limitation as long as it cures the epoxy resin, for example, polyfunctional phenols, polyfunctional alcohols, amines, imidazole compounds, acid anhydrides, There are organophosphorus compounds and their halides. These epoxy resin curing agents may be used alone or in combination of two or more.

  Among thermoplastic resins, polyamideimide resin is useful because it has excellent heat resistance and moisture resistance and has a good adhesive to metal. Among the raw materials of polyamideimide, trimellitic anhydride, trimellitic anhydride monochloride, as the acidic component, and metaphenylenediamine, paraphenylenediamine, 4,4′-diaminodiphenyl ether, 4,4′- as the amine component. Examples include, but are not limited to, diaminodiphenylmethane, bis [4- (aminophenoxy) phenyl] sulfone, 2,2′-bis [4- (4-aminophenoxy) phenyl] propane, and the like. . In order to improve the drying property, it may be modified with siloxane. In this case, siloxane diamine can be used as the amino component. In consideration of film processability, it is preferable to use a molecular weight of 50,000 or more.

  The resin composition used as the insulating material may be mixed with an inorganic filler. Examples of the inorganic filler include alumina, aluminum hydroxide, magnesium hydroxide, clay, talc, antimony trioxide, antimony pentoxide, zinc oxide, fused silica, glass powder, quartz powder, and shirasu balloon. These inorganic fillers may be used alone or in combination of two or more.

  Various additives such as curing agents, curing accelerators, thermoplastic particles, colorants, UV-opaque agents, antioxidants, reducing agents, etc., and fillers are added to the resin composition used as an insulating material as necessary. Add agent and mix.

  The circuit pattern forming method in the present invention may be a subtractive method in which a necessary conductor is protected by a photoresist method and unnecessary conductors are removed with an etching solution. The photoresist is used as a plating resist, and plating is deposited at a necessary portion. An additive method may be used.

  The resist layer may be, for example, a dry film or a liquid photoresist photoresist layer. As a method for removing the conductor by etching, for example, when removing copper, a liquid having a corrosive action such as ferric chloride or a copper chloride solution can be used. As a method for depositing plating, electrolytic copper plating using a copper sulfate solution or the like can be used.

Hereinafter, the first and second embodiments of the present invention will be described with reference to FIGS.
Example 1
Peelable copper foil MT35-S3 (Mitsui Metals Co., Ltd.) with a thin copper foil thickness of 3 μm and a carrier copper foil thickness of 35 μm bonded to both sides of a nominal prepreg GEA-679F (trade name, manufactured by Hitachi Chemical Co., Ltd.) Mining Co., Ltd., trade name) is configured so that the 3 μm copper foil surface adheres to the prepreg, and is vacuum-pressed under the conditions of a temperature of 175 ± 2 ° C., a pressure of 2.5 ± 0.2 MPa and a holding time of 60 minutes The copper clad laminated board was produced (FIG. 2 (a)).

  After forming guide holes in this copper-clad laminate with a router machine manufactured by Hitachi Via Mechanics Co., Ltd., dry film resist NIT225 (Nichigo Morton Co., Ltd.) under conditions of temperature 110 ± 10 ° C. and pressure 0.50 ± 0.02 MPa Product name). Then, after pasting the via hole 8 part and a negative mask for shielding the position recognition pattern at the time of laser processing, it was exposed with a mercury short arc lamp manufactured by Oak Manufacturing Co., Ltd. and a dry film resist with a 1 wt% sodium carbonate aqueous solution. Was developed to form an etching resist.

  Then, after removing copper of the part without an etching resist with ferric chloride aqueous solution, the dry film resist was removed with sodium hydroxide aqueous solution. By these processes, a conformal mask having a diameter of 0.05 mm (φ) and a position recognition pattern at the time of laser processing were formed in a portion serving as a via hole installation place for connection to the receiving side copper wiring layer (FIG. 2). (B)).

  On this substrate, carbon dioxide laser processing machine LC-1C / 21 (trade name, manufactured by Hitachi Via Mechanics Co., Ltd.) under the conditions of a beam irradiation diameter of 0.15 mm (φ), a frequency of 1000 Hz, a pulse width of 15 μs and an irradiation frequency of 7 shots. Each via hole was processed to form via holes 8 (FIG. 2 (c)).

  The resin piece generated by laser processing was removed from the substrate using an aqueous sodium permanganate solution having a temperature of 80 ± 5 ° C. and a concentration of 55 ± 10 g / L, and then the protective metal 6 was peeled off by hand. (Fig. 2 (d))

  After depositing copper with a thickness of 0.4 to 0.8 μm on the substrate by electroless copper plating, plating with a thickness of 15 to 20 μm was performed by electrolytic copper plating. Thereby, the base metal foil 3 and the internal conductor metal 5 are electrically connected by the via hole 8 (FIG. 2 (e)).

  Next, the surface of the substrate was trimmed, and a dry film resist NIT225 (trade name, manufactured by Nichigo Morton Co., Ltd.) was laminated under conditions of a temperature of 110 ± 10 ° C. and a pressure of 0.50 ± 0.02 MPa.

  Then, after pasting a negative mask, the circuit pattern is exposed with a mercury short arc lamp manufactured by Oak Manufacturing Co., Ltd., and a dry film resist is developed with a 1% by weight sodium carbonate aqueous solution to form an etching resist. After removing the copper with ferric chloride aqueous solution, the dry film resist was removed with sodium hydroxide aqueous solution, a circuit pattern was formed, and a wiring board was formed (FIG. 2 (f)).

  Although about 120,000 via holes were formed in the work panel 300 mm × 300 mm, the copper foil in the vicinity of the holes was not peeled off and no defects were generated.

Example 2
The inner surface double-sided substrate 2 was treated with CZ-8100 (trade name, manufactured by MEC Co., Ltd.) under conditions of a temperature of 30 ± 2 ° C. and a pressure of 0.20 ± 0.02 MPa to roughen the copper surface. A prepreg GEA-679F (trade name, manufactured by Hitachi Chemical Co., Ltd.) having a nominal thickness of 0.1 mm and a peelable copper foil F2 in which a carrier copper foil thickness of 35 μm is bonded to an ultrathin copper foil thickness of 3 μm on both surfaces of the substrate. WS3 (trade name, manufactured by Furukawa Electric Co., Ltd.) was constructed such that a 3 μm copper foil surface was bonded to the prepreg, and the temperature was 175 ± 2 ° C., the pressure was 2.5 ± 0.2 MPa, and the holding time was 60 minutes. A vacuum press was performed (FIG. 3A).

  After forming guide holes on this substrate with a router processing machine manufactured by Hitachi Via Mechanics Co., Ltd., dry film resist NIT225 (manufactured by Nichigo Morton Co., Ltd., product under conditions of temperature 110 ± 10 ° C. and pressure 0.50 ± 0.02 MPa) Name) was laminated. Next, the via hole 8 portion on the copper wiring layer side and a negative mask for shielding the position recognition pattern at the time of laser processing are pasted together, and then exposed with a mercury short arc lamp manufactured by Oak Manufacturing Co., Ltd., and a 1 wt% sodium carbonate aqueous solution. Then, the dry film resist was developed to form an etching resist.

  Then, after removing copper of the part without an etching resist with ferric chloride aqueous solution, the dry film resist was removed with sodium hydroxide aqueous solution. By these processes, a conformal mask having a diameter of 0.05 mm (φ) and a position recognition pattern at the time of laser processing were formed in a portion serving as a via hole installation place for connection with the receiving side copper wiring layer (FIG. 3). (B)).

  The substrate conductor foil side of this substrate was irradiated with a carbon dioxide laser processing machine LC-1C / 21 (trade name, manufactured by Hitachi Via Mechanics Co., Ltd.) with a beam irradiation diameter of 0.15 mm (φ), a frequency of 1000 Hz, a pulse width of 10 μs, and an irradiation frequency of 7 The via holes 8 were formed by processing one hole at a time under the shot conditions (FIG. 3C).

  The resin piece generated by laser processing was removed from the substrate using a sodium permanganate aqueous solution having a temperature of 80 ± 5 ° C. and a concentration of 55 ± 10 g / L, and then the protective metal 6 was peeled off by hand (FIG. 3 ( d)).

  Next, after depositing 0.4 to 0.8 μm of copper plating on the via hole wall surface, via hole bottom, and substrate surface by electroless copper plating, the temperature is 110 ± 10 ° C. and the pressure is 0.50 ± 0.02 MPa. Under the conditions, a dry film resist NIT225 (manufactured by Nichigo Morton Co., Ltd., trade name) was laminated.

  Then, after pasting a negative mask, the circuit pattern was exposed with a mercury short arc lamp manufactured by Oak Manufacturing Co., Ltd., and a dry film resist was developed with a 1% by weight sodium carbonate aqueous solution to form an etching resist. Copper was deposited using copper sulfate electroplating (FIG. 3 (e)).

  Thereafter, the dry film resist was removed with an aqueous sodium hydroxide solution, and a circuit pattern was formed by half-etching the copper foil and the plated copper using a sulfuric acid hydrogen peroxide solution to form a wiring board (FIG. 3F). ).

  Although about 120,000 via holes were formed in the work panel 300 mm × 300 mm, the copper foil in the vicinity of the holes was not peeled off and no defects were generated.

It is the schematic which shows the wiring board structure of this invention. FIG. 3 is a schematic view showing a process for producing a printed wiring board of Example 1. 6 is a schematic view showing a process for producing a printed wiring board of Example 2. FIG. It is the schematic which shows the conventional wiring board structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printed wiring board 2 Inner layer double-sided board 3 Underlying metal foil 4 Insulating resin layer 5 Inner conductor metal 6 Protective metal 7 Laser beam 8 Via 9 Plating conductor 10 Photoresist

Claims (3)

  In a method for drilling a printed wiring board having a step of irradiating a laser beam to an insulating resin layer with a copper wiring layer to remove only the insulating resin and leave copper, a protective metal is previously applied to the copper wiring layer. A method for drilling a printed wiring board, wherein the protective metal is removed after laser processing.   2. The printed wiring board drilling method according to claim 1, wherein the protective metal and the copper wiring layer foil are laminated with an adhesive, and the protective metal is peeled off and removed after laser processing.   A printed wiring board obtained by forming a via hole using the drilling method according to claim 1.

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