JP2001144411A - Drilling method for printed wiring board and surface treatment agent used therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drilling method for a printed wiring board wherein, with less processes, drilling with the printed wiring board is performed only with infrared ray laser beam irradiation. SOLUTION: A laser beam absorption coat 7 which provides copper with thermal energy that absorbs infrared ray laser beam to evaporate copper is formed on the surface of the copper 5 of a printed wiring board 3, and then a hole 9 is opened by the irradiation of infrared ray laser beam 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for making holes in a printed wiring board by using a laser beam and a surface treating agent used for the method.

[0002]

2. Description of the Related Art A printed wiring board is a laminate of a conductive layer and an insulating layer, and copper is widely used as the conductive layer. For example, a general multilayer printed wiring board is manufactured by laminating an inner layer substrate having a circuit made of copper on both sides with an insulating layer interposed therebetween and another inner layer substrate or copper foil with a prepreg interposed therebetween. In the production of these printed wiring boards, holes are formed in order to form through holes that electrically connect conductive layers separated by insulating layers to conductive layers. This drilling has conventionally been performed with a mechanical drill. However, the hole diameter has been reduced due to the recent increase in wiring density, and it has become difficult to drill holes with a drill.

[0003] In addition, the drilling of the build-up layer of a build-up wiring board manufactured by laminating a copper foil with a resin on an inner layer substrate is performed by removing the copper foil at the portion to be drilled by chemical etching and then forming the insulating layer on the insulating layer. It is performed by irradiating an infrared laser. However, this method has a problem that the positional deviation between the hole in the copper foil due to the chemical etching and the hole in the insulating layer due to the infrared laser is apt to occur. In addition,
The reason why holes are previously formed in the copper foil by chemical etching is that the infrared laser is almost reflected on the copper surface and cannot be efficiently drilled. When high energy is applied to collectively drill the copper foil and the insulating layer with an infrared laser, the insulating layer is largely removed and removed, making it impossible to perform good plating in the next plating step, Or the diameter of the is not constant.

[0004] Further, since ultraviolet rays are less reflected on the copper surface than infrared rays, it is also considered to collectively punch holes in the copper foil and the insulating layer using a high energy ultraviolet laser (wavelength: 180 nm to 400 nm). However, equipment that can irradiate high-energy ultraviolet laser is expensive,
Not practical due to low processing efficiency.

Japanese Patent No. 2881515 discloses a method for making holes in a copper foil and an insulating layer only by an infrared laser (carbon dioxide laser) by forming a plating film having a thickness of several μm and having many irregularities on the surface of the copper foil. Further, there is disclosed a method of irradiating a laser beam after forming an epoxy-based or rubber-based synthetic resin film for absorbing energy of an infrared laser beam.

Further, Japanese Patent Application Laid-Open No. 3-57583 discloses that
A method of irradiating laser light after oxidizing a copper foil surface is disclosed.

Japanese Patent Application Laid-Open No. 11-266067 discloses a method of irradiating a laser beam after forming a film made of polyvinyl alcohol or starch containing a metal compound powder or carbon powder on the surface of a copper foil. It has been disclosed.

[0008]

However, in the method described in Japanese Patent No. 2881515, it is necessary to form two types of films, a plating film and a synthetic resin film, which increases the number of processing steps and increases the number of processing steps. The formation increases the thickness of the conductive layer, which is disadvantageous for thinning a circuit.

In the method described in Japanese Patent Application Laid-Open No. 3-57583, when a laser beam is applied to form a hole, scattered copper adheres around the hole. Since the attached copper cannot be removed by washing with a normal acidic aqueous solution, it is necessary to remove the copper by polishing with a brush or the like.

Further, in the method described in JP-A-11-266067, a thick (60 μm or 25 μm according to the embodiment) containing a metal compound powder or a carbon powder is contained.
Since a large amount of energy is consumed to form a film and decompose and evaporate the film with a laser beam, it is necessary to irradiate a strong laser beam (40 mJ or 30 mJ according to the embodiment). Further, after drilling, it is necessary to reduce the thickness of the copper foil to 1/2 to 1/3 by etching.

Accordingly, the present invention provides a method of punching a printed wiring board which overcomes the drawbacks of the prior art, shortens the processing steps, and allows the printed wiring board to be punched only by irradiating an infrared laser beam. I do.

[0012]

Means for Solving the Problems As a result of intensive studies, the present inventors have overcome the above-mentioned disadvantages of the prior art by the following constitution. That is, the present invention, on the surface of the copper of the printed wiring board, after forming a laser light absorbing layer that gives the copper thermal energy to absorb infrared laser light and evaporate copper,
A method for piercing a printed wiring board by piercing by irradiating an infrared laser beam, wherein the laser beam absorbing layer is selected from the group consisting of copper sulfide, copper halide, copper selenide and copper phosphate. Method for drilling a printed wiring board that is a layer containing one or more types of copper compounds, and for drilling holes on the copper surface of the printed wiring board with infrared laser light, so that a copper halide is formed on the copper surface. A surface treating agent for forming a layer consisting of 3 to 50% (by weight, the same applies hereinafter) of cupric halide and 0.1 to 10 of an organic film forming component
% Of a surface treatment agent comprising an aqueous solution.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The copper of a printed wiring board to which the drilling method of the present invention is applied may be a copper foil such as a rolled copper foil or an electrolytic copper foil bonded to an insulating layer. May be copper plated by electroplating or electroless plating.
The thickness of the copper is preferably 18 μm or less, more preferably 3 to 6 μm. As the thickness of copper increases, the amount of copper removed by laser light increases, requiring large energy and damaging the insulating layer. The thinner the copper is, the less energy is required when drilling and it is advantageous for forming fine wiring, but copper must be free from defects such as pinholes.

In forming the laser light absorbing layer on the copper surface, the copper surface may be treated with various chemicals in advance.
For example, a copper foil surface is subjected to a rust-preventive treatment in order to suppress the generation of rust during storage. Therefore, a uniform laser light absorbing layer may not be formed. In such a case, it is preferable to remove a rust preventive or the like by microetching the surface of the copper foil in advance.

In the drilling method of the present invention, a laser light absorbing layer is formed on the surface of copper. The laser light absorbing layer,
This layer has excellent infrared laser (wavelength: 0.8 to 15 μm) energy absorption and can give copper heat energy to evaporate copper. It is made of copper sulfide, copper halide, copper selenide and copper phosphate. It is a layer containing one or more selected from the group.

Examples of the copper sulfide include copper sulfide, copper ammonium sulfide, and copper potassium sulfide. The copper sulfide may have a plurality of valences, and any of them may be used in the present invention. As a method of forming the layer containing copper sulfide on the surface of copper, for example, sodium sulfide, ammonium sulfide, potassium sulfide, hydrogen sulfide, ammonium hydrogen sulfide, potassium hydrogen sulfide, calcium hydrogen sulfide, sodium hydrogen sulfide and sulfur Examples include a method of exposing to one or more kinds of vapors selected from the group and a method of applying a solution containing 0.1 to 10% thereof. Examples of the coating method include a dipping method, a spray method, a roll coating method, and a printing method.

Examples of the copper halide include copper fluoride, copper chloride, copper oxalate, and copper iodide. Some of the copper halides can have a plurality of valences, and any of them can be used in the present invention. As a method of forming a layer containing the copper halide on the copper surface, for example, one or two or more selected from the group consisting of cupric chloride, cupric fluoride, cupric bromide, bromine and iodine And a method of applying a solution containing 0.1% or more, preferably 3 to 50% of these.
Examples of the coating method include a dipping method, a spray method, a roll coating method, and a printing method.

In the method for forming a layer containing a copper halide, an aqueous solution containing 3 to 50% of cupric halide and 0.1 to 10% of an organic film-forming component is applied to the copper surface to form a copper surface. And a cupric halide are reacted with each other, and then dried to form an organic film, from the viewpoints of good workability and improved laser energy absorption. Further, it is preferable to apply the aqueous solution, leave it for 5 to 120 seconds, and then dry it, because the laser energy absorption is further improved. Further, the thickness of the formed organic film is preferably 20 μm or less, more preferably 0.1 to 10 μm. When the thickness of the organic film exceeds 20 μm, laser energy consumed for decomposition and evaporation of the organic film becomes too large, and it becomes necessary to irradiate high energy.

The cupric halide is preferably cupric chloride, cupric bromide or the like. As the organic film-forming component, one or more of water-soluble organic compounds such as cellulose ethers such as methylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose, and polyethylene oxide, polyvinyl alcohol, and polyvinylpyrrolidone are preferable.

Examples of the copper selenide include copper selenide, copper selenate, and copper selenite. The copper selenide may have a plurality of valences, but any of them can be used in the present invention. As a method of forming a layer containing the copper selenide on the copper surface, for example, selenic acid, selenous acid, selenium, selenium dioxide, copper selenate, one selected from the group consisting of copper selenide and copper selenite Alternatively, a method of applying a solution containing 0.1 to 50% of two or more kinds may be mentioned. Examples of the coating method include a dipping method, a spray method, a roll coating method, and a printing method.

The copper phosphate is, for example, copper phosphate. Some of the copper phosphates can have a plurality of valences, and any of them can be used in the present invention. As a method for forming the layer containing the copper phosphate on the copper surface, for example, one or two or more selected from the group consisting of phosphoric acid, dipotassium hydrogen phosphate and diammonium hydrogen phosphate may be used in an amount of 10 to 70%. Is applied. Examples of the coating method include a dipping method, a spray method, a roll coating method, and a printing method.

Among the laser light absorbing layers, a layer containing a copper halide is preferable from the viewpoint of safety in forming the layer. Further, when the laser light absorbing layer is formed by the coating method, in addition to the organic film forming component for preparing a coating solution, a surfactant for improving wettability and coating workability, a viscosity adjusting agent , An organic solvent, an antifoaming agent, and the like.

As described above, by forming the laser light absorbing layer on the copper surface, it becomes possible to make holes in copper with a carbon dioxide laser generally used for processing metal materials.

Next, the copper on which the layer is formed is irradiated with a laser beam to make holes. As the laser light,
In addition to infrared lasers such as a carbon dioxide laser and a YAG laser, there are visible lasers and ultraviolet lasers. In the present invention, a carbon dioxide laser that is widely used for processing metal materials and can extract high energy is used. Is preferred. Laser light energy is 5-20
mJ is preferable, and 7 to 15 mJ is more preferable. The size of the energy and the number of shots of irradiation, the thickness of copper,
It is appropriately adjusted depending on the thickness and type of the insulating layer.

After the hole is formed, the hole is washed with a solution that can dissolve the laser light absorbing layer, such as an acid such as water or hydrochloric acid, an alkaline solution such as aqueous ammonia, or an organic solvent such as alcohol. The laser light absorbing layer remaining on the copper surface around the substrate is removed. In addition, if carbides of resin, fine copper powder, and the like are attached to the layer, they are removed.

[0026]

EXAMPLES Example 1 A resin-coated copper foil (4 μm thick) was coated on both sides of a glass cloth-based epoxy resin-impregnated copper-clad laminate (FR-4 grade) 3 in which copper foil having a thickness of 18 μm was laminated on both sides. A copper foil 5 coated with epoxy resin 4 to a thickness of 70 μm (MR-600 × 4 manufactured by Mitsui Mining & Smelting Co., Ltd.)) 6 was laminated (FIG. 1). In the drawing, 1 is an insulating layer, and 2 is a copper foil.
The obtained laminate is immersed in a 10% aqueous solution of cupric chloride dihydrate at 20 ° C. for 1 minute, washed with water and dried to form a brown copper chloride layer on the surface of the copper foil 5. 7 was formed (FIG. 2). Next, the layer 7 was irradiated with one shot of a carbon dioxide gas laser at an output of 10 mJ, whereby a hole having a diameter of 80 μm could be formed in the copper foil 5 and the resin 4 of the copper foil with resin (FIG. 3). Further, the copper around the hole was not scattered.

Example 2 A resin-coated copper foil (12 μm thick copper) was coated on both sides of an epoxy resin-impregnated copper-clad laminate (FR-4 grade) 3 having a 18 μm thick copper foil laminated on both sides. Foil 5 coated with epoxy resin 4 to a thickness of 70 μm (MR-600-80V1 manufactured by Mitsui Kinzoku Mining Co., Ltd.)
2)) 6 were laminated (FIG. 1). Next, the surface of the copper foil 5 is
The copper foil 5 was etched with an etching solution HE-7000 manufactured by Mec Co., Ltd. to a thickness of 6 μm. The obtained laminate is immersed in an aqueous solution containing 1% of sodium sulfide / 9-hydrate and 10% of ammonium chloride at 20 ° C. for 1 minute, washed with water and dried to form a sulfide on the surface of the copper foil 5. A copper layer 7 was formed. Next, by irradiating the layer 7 with one shot of a carbon dioxide gas laser at an output of 15 mJ, a hole having a diameter of 80 μm could be formed in the copper foil 5 and the resin 4 of the copper foil with resin (FIG. 3). Further, the copper around the hole was not scattered.

Example 3 An aqueous solution containing 10% cupric bromide and 1% hydroxypropylcellulose was prepared. The obtained aqueous solution is
On the surface of a 6 μm thick copper foil 5 of the same laminate as in Example 2,
A layer 7 containing copper bromide was formed on the surface of the copper foil 5 by applying by a printing method so that the thickness became 10 μm, leaving it to stand for one minute, and then drying. Next, by irradiating the layer 7 with one shot of carbon dioxide laser at an output of 15 mJ, a hole having a diameter of 80 μm could be formed in the copper foil 5 and the resin 4 of the copper foil with resin (FIG. 3). Further, the copper around the hole was not scattered.

Comparative Example 1 The surface of the copper foil 5 on the same substrate as in Example 1 was irradiated with a carbon dioxide gas laser under the same conditions as in Example 1 without forming a laser light absorbing layer. However, holes could not be made in the copper foil.

Comparative Example 2 The same substrate as in Example 1 was immersed in a solution containing chlorite to form a brown copper oxide layer on the surface of the copper foil 5. Next, a carbon dioxide gas laser was irradiated under the same conditions as in Example 1. As a result, a hole could be formed in the copper foil, but copper was scattered on the surface of the copper foil around the hole, and it was necessary to polish the copper foil to remove it.

[0031]

According to the present invention, by forming a specific infrared laser light absorbing layer on the copper surface, the number of processing steps can be reduced, and holes can be simultaneously formed in the copper and the insulating layer only by irradiating the infrared laser light. Can be opened.

[0032]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a printed wiring board applied to a drilling method according to an embodiment.

FIG. 2 is a cross-sectional view of a printed wiring board for a drilling method according to an embodiment.

FIG. 3 is a conceptual diagram showing that holes are made by irradiating the printed wiring board shown in FIG. 2 with a carbon dioxide gas laser.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Insulation layer 2 Copper foil 3 Glass cloth base material epoxy resin impregnated copper-clad laminate with copper foil laminated on both sides 4 Epoxy resin 5 Copper foil 6 Resin-coated copper foil 7 Laser light absorber layer 8 Carbon dioxide laser 9 Hole

Claims (4)

[Claims] 1. A method for forming a laser light absorbing layer on a copper surface of a printed wiring board, the method comprising: applying a thermal energy to copper for absorbing infrared laser light and evaporating copper; In the method of making a hole in a printed wiring board, the laser light absorbing layer comprises one or more copper compounds selected from the group consisting of copper sulfide, copper halide, copper selenide and copper phosphate. A method for forming a hole in a printed wiring board, comprising: 2. The method according to claim 1, wherein the laser light absorbing layer is formed on the surface of copper by a group consisting of sodium sulfide, ammonium sulfide, potassium sulfide, hydrogen sulfide, ammonium hydrogen sulfide, potassium hydrogen sulfide, calcium hydrogen sulfide, sodium hydrogen sulfide and sulfur. One or more selected vapors or a solution containing 0.1 to 10% by weight thereof in contact with cupric chloride, cupric fluoride, cupric bromide, bromine and iodine Contacting with one or more selected vapors or a solution containing at least 0.1% by weight thereof, from selenic acid, selenite, selenium, selenium dioxide, copper selenate, copper selenide and copper selenite Contacting with a solution containing 0.1 to 50% by weight of one or more selected from the group consisting of phosphoric acid, dipotassium hydrogen phosphate and phosphoric acid water 2. The method according to claim 1, wherein the method is carried out by contacting with a solution containing 10 to 70% by weight of one or more selected from the group consisting of diammonium hydrogen. 3. The laser light absorbing layer is a copper halide, and is formed by applying an aqueous solution containing 3 to 50% by weight of cupric halide and 0.1 to 10% by weight of an organic film forming component on a copper surface. 2. The method according to claim 1, wherein the drying is performed by drying. 4. A surface treating agent for forming a copper halide layer on the surface of said copper to form a hole on the surface of said printed wiring board with infrared laser light. 50% by weight and organic film-forming component 0.1-1
A surface treating agent comprising an aqueous solution containing 0% by weight.