JP2003008172A - Formation method of through-hole by carbon dioxide laser - Google Patents

Abstract

To obtain a method of forming a small-diameter through-hole having a good shape by directly irradiating a carbon dioxide laser on a copper-clad plate. SOLUTION: A thermosetting resin copper clad plate having at least two copper layers is used as a backup sheet by bonding a low thermal conductivity layer to a lower copper foil, and a carbon dioxide laser is pulsed. A through hole is formed by directly irradiating the copper foil with one energy selected from energies of 5 to 60 mJ. Thereafter, in the case of a thick copper foil, a part in the thickness direction of the copper foil is removed by etching, and at the same time, the copper foil burr generated in the hole is dissolved and removed, and this is used as a printed wiring board. [Effect] A through hole having a good hole shape and excellent reliability could be formed, and a high-density printed wiring board having a small diameter and a fine circuit could be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a backup sheet suitable for directly irradiating a carbon dioxide gas laser on a copper foil surface of a copper clad plate having at least two copper layers to form through holes. The present invention relates to a method for forming a hole by forming a through hole for a double-sided copper-clad plate or a multi-layer plate. As a high density small printed wiring board with small diameter holes, it is used for new semiconductor plastic packages, mother boards, etc.

[0002]

2. Description of the Related Art Conventionally, in a high density printed wiring board used for a semiconductor plastic package or the like, a through hole for a through hole is drilled. In recent years, the diameter of drills has become smaller and smaller, and the hole diameter has become 0.15 mmφ or less.When drilling holes with such small diameters, the drill diameter is thin, so the drill bends, breaks, and the processing speed is high. However, there were drawbacks such as slowness, and there were problems with productivity, reliability, etc. In addition, when forming through-holes for through-holes, if holes of the same size are opened in advance in the upper and lower copper foils and the through-holes that penetrate the upper and lower sides are formed with a carbon dioxide laser, the positions of the upper and lower holes will be changed. Due to the misalignment, there are drawbacks such as difficulty in forming lands. Furthermore, when a through-hole was formed with a high-power carbon dioxide laser, an air layer was used on the lower side, but the processing dust adhered to the vicinity of the copper foil below the hole, which hindered subsequent processing. . in addition,
Defects such as the shape of the holes of the copper foil on the back surface being not circular were observed.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and uses a backup sheet for carbon dioxide laser drilling for forming a through hole for through holes having a good hole shape and having a small diameter. A forming method is provided.

[0004]

A layer having low thermal conductivity is arranged on the lower surface of a copper clad plate and is adhered, preferably adhered, to a copper foil to form a carbon dioxide laser on the surface copper foil of the copper clad plate. Output 5 ~ 6
By irradiating with one energy selected from 0 mJ, it becomes possible to form a through hole having a particularly good hole shape on the back surface.
When the through holes are formed by irradiating the copper foil on the front and back surfaces and the inner layer with a carbon dioxide gas laser, if the copper foil is thick, burrs will occur on the copper foil. Need to be removed. This front and back surface copper foil burr can also be removed by mechanical polishing, but in order to completely remove the burr, both surfaces of the copper foil should be planarized in the thickness direction and part of the original copper foil thickness should be removed. It is also preferable to remove the copper foil burr that overhangs at the same time by etching and removing the copper foil burr.By forming a through hole in which the copper foil around the hole remains, the connection reliability is excellent and the through hole It can be formed without bending, and since the surface copper foil becomes thin, defects such as shorts and pattern breaks may occur in the circuit formation of the fine wire of the front and back copper foil obtained by plating up with the subsequent metal plating. Without, it was possible to create a high-density printed wiring board. In addition, the processing speed was remarkably faster than that obtained with a drill, the productivity was good, and the economy was excellent.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a method for making a through hole having a small diameter and a good shape in a copper clad plate having two or more copper layers by using a carbon dioxide laser. By closely adhering to the copper foil on the back surface of the clad plate, preferably by arranging a layer with low thermal conductivity so as to adhere and forming a through hole,
The copper foil on the back surface is excellent in workability and a through hole having a good shape is formed. When the copper foil is thick, burrs of the copper foil are generated in the formed holes, but the burrs are removed by etching with a chemical solution, and at the same time, a part of the front and back copper foils in the thickness direction are removed by etching. Due to this thinning of copper and deburring, in the subsequent copper plating, there is no overhang due to the plating of the holes, the total thickness of the front and back copper foil after plating can be kept thin, and a suitable one for fine pattern formation can be obtained. A high-density printed wiring board can be manufactured.

In drilling a copper clad plate with a carbon dioxide laser, a metal oxide powder having a melting point of 900 ° C. and an atomic binding energy of 300 kJ / mol or more is formed on the surface to be irradiated with laser.
A coating that mixes carbon or metal powder with a resin such as a water-soluble resin is applied to the surface of the copper foil and dried to form a coating film, or it is attached to one side of a thermoplastic film to assist drilling. The sheet is arranged and preferably adhered to the copper foil surface, and a carbon dioxide gas laser is directly irradiated onto the metal surface to process and remove the copper foil. In addition, on the shiny surface of the copper foil, a copper clad plate is prepared using a copper foil having a nickel metal layer, a cobalt metal layer, and an alloy layer thereof, and a carbon dioxide laser is directly irradiated onto the copper clad plate to reduce the diameter of the copper foil. Through holes can be formed. Furthermore, the copper foil surface of a copper clad plate overlaid with a general copper foil is treated with black copper oxide treatment, or the copper foil surface is treated with a chemical solution to form fine irregularities, and then carbon dioxide is directly applied. Through holes can be formed by irradiating a gas laser. When the copper foil having a thickness of 5 μm or less is used, the copper foil is directly exposed to the carbon dioxide laser without any treatment, so that the copper foil has holes. However, when forming a through-hole, if the through-hole is not formed by adhering the backup sheet to the copper foil on the back surface, contamination by the processing dust on the back-side copper foil and damage to the XY table will occur. Use is mandatory.

Among the auxiliary materials used in the present invention, the melting point of 90
As the metal compound having a binding energy of 300 kJ / mol or more at 0 ° C. or higher, generally known compounds can be used. Specifically, as the oxide, titania such as titanium oxide, magnesia such as magnesium oxide, iron oxide such as iron oxide, nickel oxide such as nickel oxide, zinc oxide such as manganese dioxide and zinc oxide. , Silicon dioxide, aluminum oxide, rare earth oxides, cobalt oxides such as cobalt oxide, tin oxides such as tin oxide, and tungsten oxides such as tungsten oxide. Examples of the non-oxide include generally known ones such as silicon carbide, tungsten carbide, boron nitride, silicon nitride, titanium nitride, aluminum nitride, barium sulfate, and rare earth oxysulfide. In addition, carbon can also be used. Further, various kinds of glass which are a mixture of the metal oxide powder can be mentioned. Further, carbon powder may be mentioned, and further, simple substances such as silver, aluminum, bismuth, cobalt, copper, iron, magnesium, manganese, molybdenum, nickel, palladium, antimony, silicon, tin, titanium, vanadium, tungsten, zinc, or the like. The metal powder of the alloy is used. These are used alone or in combination of two or more. The average particle size is
Although not particularly limited, it is preferably 1 μm or less.

Since molecules are dissociated into atoms upon irradiation with a carbon dioxide laser, it is preferable that the metal adheres to the pore walls and the like and does not adversely affect the semiconductor chip, the adhesion to the pore walls and the like. Since Na, K, Cl ions, etc., particularly adversely affect the reliability of the semiconductor, those containing these components are not suitable. The compounding amount is 3 to 97% by volume, preferably 5 to 95% by volume.
Is mixed with the water-soluble resin and uniformly dispersed.

The resin in the auxiliary material is not particularly limited,
A water-soluble resin is preferable when it is removed when attached after processing. The water-soluble resin is not particularly limited, but is selected so that it does not peel off when it is kneaded, applied to the surface of the copper foil, dried, or formed into a sheet. For example, generally known substances such as polyvinyl alcohol, polyester, polyether polyol, polyethylene oxide, starch and the like are used.

The method for preparing the metal compound powder, the carbon powder, or the composition consisting of the metal powder and the resin is not particularly limited, but it is kneaded at a high temperature in a solventless manner at a high temperature and extruded in a sheet form on a thermoplastic film. Method of adhering by dissolving, water-soluble resin is dissolved in water or water-soluble organic solvent, the above powder is added to this, uniformly stirred and mixed, and using this, it is applied on a thermoplastic film as a paint and dried. A generally known method such as a method for forming a film can be used. The thickness is not particularly limited, but when applied, it is 20 to 200 μm, and when applied to a thermoplastic film, the total thickness is 30 to 200 μm.

In the carbon dioxide laser through hole drilling of the present invention, a backup is made so that the processed dust does not adhere to the lower (back) surface when the laser beam penetrates, and the through hole shape is good. A layer having low thermal conductivity is arranged as a sheet. This is because, when the backside copper foil is irradiated with a carbon dioxide laser beam, the backside is air, so that heat is diffused and the heat distribution of the copper foil becomes uneven, so that the hole shape tends to be indefinite. However, if a layer with low thermal conductivity is adhered to the copper foil on the back surface, when the copper foil on the back surface is irradiated with a carbon dioxide laser beam, heat is accumulated on the backup sheet on the bottom surface and the temperature of that portion is high. However, the subsequent irradiation tends to open holes in the copper foil, resulting in the formation of good holes. In this case, it is preferable that the back-up sheet on the back surface has as low thermal conductivity as possible. The backup sheet is
It can be used only in layers with low thermal conductivity. When irradiating a carbon dioxide laser, the method of irradiating a carbon dioxide laser with the backup sheet adhered to the copper clad plate in the air while the backup sheet is adhered is used. There is a method of irradiating with a carbon dioxide laser from above, and the latter method is generally used. In this case, it is preferable to increase the thickness of the backup sheet so that the laser beam stops in the middle of the backup sheet so that the laser beam does not penetrate through the backup sheet.

As the layer having low thermal conductivity, a generally known insulating layer can be mentioned. Specific examples include various resin compositions. The resin composition is not particularly limited, and examples thereof include a thermosetting resin simple substance, a thermoplastic resin simple substance, a mixture thereof, and a resin composition obtained by adding a generally known additive such as an inorganic filler to these resins. . A resin composition which is not water-soluble and can be dissolved in an organic solvent can also be used. However, with carbon dioxide laser irradiation, the resin may adhere to the periphery of the hole, and when the removal of this resin requires an organic solvent instead of water, the processing is complicated,
In addition, since problems such as contamination in the subsequent process occur, it is not preferable, and a water-soluble resin is preferably used. These water-soluble resins are not particularly limited, and generally known resins can be used, but polyvinyl alcohol, polyester, starch, polyether polyol, polyethylene oxide and the like are preferably used alone or in combination of two or more. . The thickness is not particularly limited and is preferably 50 to 200 μm. These are individually applied on the copper foil on the back surface of the copper clad board or laminated and adhered. Also, a backup sheet is formed by coating the film, organic plate, ceramic or the like on one side. The organic plate is not particularly limited, and a generally known one such as a thermoplastic resin plate, a thermosetting resin plate or a laminated plate can be used. or,
It may be a backup board which is applied integrally on a board such as wood or gypsum board and integrated. The integrated total thickness is not particularly limited, but is preferably 100 to 500 μm.

These resins are dissolved in water or an organic solvent and applied to the back surface of the copper clad board and dried to form a backup sheet, or applied to one surface of a film or the like to form an integral type sheet, and then the resin. Laminate under heat and pressure with the surface facing the copper foil side. Further, it is melted at a high temperature without a solvent and extruded into a sheet to form a backup sheet.

When laminating and bonding a hot-melt type backup sheet to the copper foil surface under heating and pressure, the sheet is placed on the back surface of the copper clad plate, and a film, an insulating plate, etc. are placed on the outer side of the sheet, and the sheet is rolled. The temperature is generally 40 to 150 ° C, preferably 60 to 120 ° C, and the linear pressure is generally laminated at 1 to 30 kg / cm, preferably 5 to 20 kg / cm, and the resin layer is melted to adhere to the copper foil surface. Let The selection of the temperature varies depending on the melting point of the resin used, the linear pressure and the laminating speed, but in general, the lamination is performed at a temperature 5 to 20 ° C. higher than the melting point of the water-soluble resin.

The copper-clad board used in the present invention is a copper-clad board having two or more copper layers. The thermosetting resin copper-clad laminate is a known thermosetting resin for inorganic and organic base materials. Copper clad laminate,
Examples thereof include a multilayer copper clad board, a multilayer board using a resin-coated copper foil sheet as a surface layer, and the like, and a copper clad board as a base material such as a polyimide film and a polyparabanic acid film.

In the base material-reinforced copper-clad laminate, a reinforcing base material is first impregnated with a thermosetting resin composition varnish and dried to form a B-stage to prepare a prepreg. Next, a predetermined number of the prepregs are stacked, a copper foil is arranged on the outer side of the prepregs, and the prepreg is laminated under heat and pressure to form a copper-clad laminate. The thickness of the copper foil is preferably 5 to 12 μm.

As the substrate, generally known organic and inorganic woven fabrics and nonwoven fabrics can be used. Specifically, examples of the inorganic fiber include fibers such as E, S, D, and NE glass. Examples of the organic fiber include generally known fibers such as wholly aromatic polyamide and liquid crystal polyester. These may be mixed papers. Moreover, a film base material can also be used.

As the resin of the thermosetting resin composition used in the present invention, generally known thermosetting resins are used. Specifically, epoxy resin, polyfunctional cyanate ester resin, polyfunctional maleimide-cyanate ester resin, polyfunctional maleimide resin, unsaturated group-containing polyphenylene ether resin and the like, one kind or two or more kinds. Are used in combination. From the viewpoint of through-hole shape in processing by high power carbon dioxide laser irradiation, glass transition temperature is preferably a thermosetting resin composition of 150 ℃ or more, further inorganic filler, preferably 10 to 80 wt% It is good to add. It is preferable to use the polyfunctional cyanate ester resin composition as an essential component from the viewpoints of moisture resistance, migration resistance, electrical characteristics after moisture absorption, and the like.

The polyfunctional cyanate ester compound which is a suitable thermosetting resin component of the present invention is a compound having two or more cyanato groups in the molecule. Specifically, 1,3- or 1,4-dicyanatobenzene, 1,3,5-tricyanatobenzene, 1,3-, 1,4-, 1,6-, 1,8-, 2 , 6- or 2,7-
Dicyanatonaphthalene, 1,3,6-tricyanatonaphthalene, 4,4-dicyanatobiphenyl, bis (4-dicyanatophenyl) methane, 2,2-bis (4-cyanatophenyl) propane, 2,2- Bis (3,5-dibromo-4-cyanatophenyl) propane, bis (4-cyanatophenyl) ether, bis (4-cyanatophenyl) thioether, bis (4-cyanatophenyl) sulphone, tris (4-cis) Anatophenyl) phosphite, tris (4-cyanatophenyl) phosphate, and cyanates obtained by the reaction of novolac with cyanogen halide. These known Br addition compounds are also included.

In addition to these, Japanese Patent Publications 41-1928 and 43-1846
8, polyfunctional cyanate ester compounds described in JP-A-51-63149 and JP-A-44-4791, JP-A-45-11712, JP-A-46-41112 and JP-A-47-26853 can also be used. Further, a prepolymer having a molecular weight of 400 to 6,000 and having a triazine ring formed by trimerizing the cyanato group of these polyfunctional cyanate ester compounds is used. This prepolymer is obtained by polymerizing the above-mentioned polyfunctional cyanate ester monomer using, for example, acids such as mineral acid and Lewis acid; bases such as sodium alcoholate and tertiary amines; salts such as sodium carbonate as a catalyst. It is obtained by The prepolymer also contains some unreacted monomer and is in the form of a mixture of the monomer and the prepolymer. Such a raw material is suitably used for the purpose of the present invention. Generally, it is used by dissolving it in a soluble organic solvent.

As the epoxy resin, generally known epoxy resins can be used. Specifically, liquid or solid bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, alicyclic epoxy resin; butadiene, pentadiene, vinylcyclohexene, dicyclopentyl ether, etc. And polyglycidyl compounds obtained by reacting a hydroxyl group-containing silicone resin with epohalohydrin. Moreover, these well-known Br addition resin is mentioned. These may be used alone or in combination of two or more.

As the polyimide resin, a generally known one can be used. Specific examples thereof include reaction products of polyfunctional maleimides and polyamines, and polyimides having a terminal triple bond described in JP-B-57-005406. These thermosetting resins may be used alone, but it is preferable to use them in combination as appropriate in consideration of the balance of properties.

Various additives can be added to the thermosetting resin composition of the present invention as desired, as long as the original properties of the composition are not impaired. These additives include polymerizable double bond-containing monomers such as unsaturated polyester and prepolymers thereof; polybutadiene, epoxidized butadiene, maleated butadiene, butadiene-
Low molecular weight liquid to high molecular weight elastic rubbers such as acrylonitrile copolymer, polychloroprene, butadiene-styrene copolymer, polyisoprene, butyl rubber, fluororubber, natural rubber; polyethylene, polypropylene, polybutene, poly-4-methyl Penten, polystyrene, AS
Resin, ABS resin, MBS resin, styrene-isoprene rubber,
Acrylic rubber, these core shell rubber, polyethylene
-Propylene copolymers, 4-fluorinated ethylene-6-fluorinated ethylene copolymers; high molecular weight prepolymers or oligomers such as polycarbonate, polyphenylene ether, polysulfone, polyester, polyphenylene sulfide; polyurethane and the like are used as appropriate. To be done. In addition, other known organic fillers, dyes, pigments, thickeners, lubricants, defoamers, dispersants, leveling agents, photosensitizers,
Various additives such as a flame retardant, a brightening agent, a polymerization inhibitor, and a thixotropic agent are appropriately combined and used as desired.
If necessary, the compound having a reactive group is appropriately mixed with a curing agent and a catalyst.

The thermosetting resin composition of the present invention itself is cured by heating, but the curing speed is slow and the workability and economy are poor. Therefore, the known thermosetting catalyst for the thermosetting resin used. Can be used. The amount used is 0.005 to 10 parts by weight, preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the thermosetting resin.

When a carbon dioxide laser is directly irradiated onto the copper foil of the copper clad plate by pulse oscillation with an output of 5 to 60 mJ to form through holes, burrs are generated around the holes. Therefore, after the carbon dioxide laser irradiation, both surfaces of the copper foil are planarly etched in the thickness direction, preferably with a chemical solution, and a part of the original copper foil is removed to simultaneously remove burrs. The removed and thinned copper foil is suitable for forming fine patterns,
A through hole in which a copper foil around the hole suitable for a high-density printed wiring board remains is formed. In this case, etching is more preferable than mechanical polishing from the viewpoints of removing burrs from the holes and changing the dimensions due to polishing.

The method of etching away the copper burr generated in the holes of the present invention is not particularly limited, but for example, JP-A-02-22887, 02-22896, 02-25089 and 02-2.
5090, 02-59337, 02-60189, 02-166789, 03-25
995, same 03-60183, same 03-94491, same 04-199592, same 04-263
Method for dissolving and removing metal surfaces with chemicals disclosed in 488
(Called the SUEP method). Etching rate is 0.02
Perform at ~ 1.0 μm / sec.

The carbon dioxide laser is in the infrared wavelength range.
Wavelengths of 9.3 to 10.6 μm are commonly used. Energy is
The copper foil is processed by pulse oscillation at 5 to 60 mJ, preferably 7 to 45 mJ, and holes are drilled. Energy is processed on the surface copper foil,
It is appropriately selected depending on the thickness of the copper foil. Further, the backup sheet of the present invention can be used with a UV laser such as a YAG laser.

[0028]

The present invention will be specifically described below with reference to Examples and Comparative Examples. Unless otherwise specified, “part” means part by weight. Example 1 900 parts of 2,2-bis (4-cyanatophenyl) propane, bis (4-
Maleimide phenyl) 100 parts of methane is melted to 150 ℃,
The reaction was carried out for 4 hours with stirring to obtain a prepolymer. This was dissolved in a mixed solvent of methyl ethyl ketone and dimethylformamide. In addition to this, bisphenol A type epoxy resin (trade name: Epicoat 1001, Japan Epoxy Resin <
Co., Ltd.) 400 parts, cresol novolac type epoxy resin
(Product name: ESCN-220F, manufactured by Sumitomo Chemical Co., Ltd.) 600 parts were added and uniformly dissolved and mixed. Furthermore, 0.4 part of zinc octylate as a catalyst was added, dissolved and mixed, and 2000 parts of an inorganic filler (trade name: calcined talc, manufactured by Nippon Talc Co., Ltd.) was added thereto, and uniformly stirred and mixed to obtain a varnish A. This varnish is 100μ thick
It is impregnated into a glass woven fabric of m
(t170 ° C.) 120 seconds, a prepreg (prepreg B) having a glass cloth content of 56% by weight was prepared. 12 μm thick electrolytic copper foil,
Arranged above and below the above four prepreg B sheets, 200 ℃, 20kgf / c
Laminate molding was performed under a vacuum of m ² and 30 mmHg or less for 2 hours to obtain a double-sided copper-clad laminate C having an insulating layer thickness of 400 μm.

On the other hand, 800 parts of black copper oxide powder (average particle diameter: 0.8 μm) as a metal powder was added to a varnish prepared by dissolving polyvinyl alcohol powder in water, and uniformly mixed by stirring (varnish D). This is coated on one side of a 25 μm thick polyethylene terephthalate film so that the thickness is 60 μm,
After drying at 110 ° C. for 30 minutes, auxiliary material E having a metal compound content of 65% by volume was formed. Further, a solution of the polyvinyl alcohol powder dissolved in water was applied to one surface of a polyethylene terephthalate plate having a thickness of 200 μm so that the resin layer had a thickness of 100 μm, and dried to prepare a backup sheet F having a total thickness of 300 μm. The auxiliary material E is placed on the copper-clad laminate B and the backup sheet F is placed below the copper-clad laminate B so that the resin surface faces the copper foil side, and a linear pressure of 5 kgf /
Laminated in cm and bonded. 100 mm pore size with 1 mm spacing
A carbon dioxide gas laser with 900 holes of m was irradiated for 6 shots with a pulse energy of 25 mJ, and 70 blocks of through holes for through holes were opened. After the desmear treatment, the copper foil burr around the hole was dissolved and removed by the SUEP method, and at the same time, the copper foil on the surface was also dissolved to 4 μm. The plate was plated with copper by 15 μm (total thickness: 19 μm) by a usual method. All the copper foil for land around this hole remained. Circuits (200 lines / space = 50 / 50μm), solder ball lands, etc. are formed on the front and back by the existing method, and at least the semiconductor chip mounting part, the bonding pad part, and the solder ball pad part are removed. A printed wiring board was prepared by coating with a plating resist and plating with nickel and gold. Table 1 shows the evaluation results of this printed wiring board.

Example 2 700 parts of epoxy resin (trade name: Epicoat 5045, manufactured by Japan Epoxy Resin Co., Ltd.), and epoxy resin (trade name: ESCN)
220F) 300 parts, dicyandiamide 35 parts, 2-ethyl-4-methylimidazole 1 part are dissolved in a mixed solvent of methyl ethyl ketone and dimethylformamide, and 800 parts of the calcined talc of Example 1 is added, and the mixture is forcibly stirred to uniformly disperse. And got a varnish. This was impregnated in a glass woven cloth having a thickness of 100 μm and dried to prepare a prepreg (prepreg G) having a gel time of 150 seconds and a glass cloth content of 55% by weight. This prepreg G
2 sheets are used, 12μm thick electrolytic copper foil with cobalt metal treatment on the copper foil shiny surface is placed on both sides, 190 ℃, 20kgf /
A double-sided copper-clad laminate H was prepared by laminating and molding under a vacuum of cm ² and 30 mmHg or less for 2 hours. The insulating layer had a thickness of 200 μm.

On the back surface of this double-sided copper-clad laminate H, Example 1
50 μm after coating with polyvinyl alcohol solution and drying
A m resin layer was formed and used as a backup sheet. An acrylic resin plate with a thickness of 1 mm is placed on the outside, the ends of the double-sided copper clad plate are fixed to the XY table with tape, and 4 shots are irradiated from above with a pulse energy of carbon dioxide laser of 20 mJ, and a hole diameter of 100 μm is penetrated. The holes were opened as in the example. The backup sheet was dissolved and removed, and the front and back surfaces were treated with SUEP in the same manner as in Example 1, and then a printed wiring board was similarly obtained. The evaluation results are shown in Table 1.

Comparative Example 1 Using the double-sided copper-clad laminate C of Example 1, without using a backing sheet on the lower surface, the copper-clad board was slightly floated to form an air layer on the lower surface, and a hole was similarly punched with a carbon dioxide laser. I did,
The processing dust adhered around the pilot hole. A SUEP treatment was performed and a printed wiring board was similarly obtained. The evaluation results are shown in Table 1.

Comparative Example 2 Using the double-sided copper-clad laminate C of Example 1, aluminum alone without a resin layer was placed as a backup sheet, and a carbon dioxide laser was similarly irradiated, but there were 37% through holes. It was Some of the drilled holes were not circular due to the reflection from the laser metal. A SUEP treatment was performed and a printed wiring board was similarly obtained. The evaluation results are shown in Table 1.

Comparative Example 3 A space of 300 μm was formed on the copper foil surface of the double-sided copper-clad laminate C of Example 1.
At 900, 900 holes having a diameter of 100 μm were formed by etching the copper foil. Similarly, on the back side, place holes with 100 μm diameter at the same position.
Open 00, 70 blocks for 900 patterns, total 63,000
From the surface, a carbon dioxide gas laser was applied for 6 shots at a pulse energy of 25 mJ to form a through hole. Desmear treatment was applied, SUEP treatment was applied, copper plating was applied to 15 μm, circuits were formed on the front and back surfaces, and a printed wiring board was prepared in the same manner. The evaluation results are shown in Table 1.

(Table 1) Example Comparative Example Item 1 2 1 2 3 Displacement of front and back hole positions (μm) <5 <5 <5 <5 24 Hole shape Almost circular Almost circular Irregular Irregular shape Almost circular Through hole drilling rate (%) 100 100 100 63 94 Pattern break and 0/200 0/200 31/200 11/100 0/200 Short (pieces) Land peripheral copper foil missing None None None None Yes Glass transition temperature (℃) 235 160 235 235 235 Through hole heat cycle test (%) 2.0 4.3 5.3 6.6 7.2

<Measurement method> 1) Misalignment of front and back hole positions: Hole size within a 250 mm square work size.
70 blocks (pore meter) with 100 μm holes as 900 holes / block
63,000 holes) A carbon dioxide laser was used to make holes, and 63,000 holes were made in one copper-clad laminate, and the maximum deviation of the front and back hole positions was shown. 2) Hole shape: The copper foil was removed by etching and the shape of the hole was observed. 3) Through-hole opening rate: The number of holes that penetrated vertically in 63,000 holes is shown in%. 4) Pattern break and short circuit: In Examples and Comparative Examples,
After making a copper clad plate with 15 μm copper plating on the prepared holes, create a pattern of line / space = 50/50 μm, and then visually observe the 200 patterns after etching with a magnifying glass. The total number of patterns, broken patterns, and short patterns is shown in the numerator. 5) Glass transition temperature: Measured by the DMA method of JIS C6481. 6) Through-hole heat cycle test: Create a land diameter of 200 μm in each through-hole, connect 900 holes alternately on the front and back, and 1 cycle is 260 ° C, solder, dipping 30 seconds → room temperature
It was carried out for 200 cycles in 5 minutes, and the maximum rate of change in resistance was shown. 7) Copper foil break around land: When a land with a diameter of 500 μm was formed around the hole, chipping of the copper foil at the land was observed.

[0037]

The carbon dioxide laser penetrates the copper surface of a copper clad plate having at least two copper layers by directly irradiating the copper foil with one energy to pierce the copper foil. On the lower copper foil surface, a layer with low thermal conductivity is adhered to the copper foil as a hole back-up sheet,
By directly irradiating a carbon dioxide laser from above to open the through holes, it is not necessary to remove the copper foil in advance by etching, and there is no deviation in the hole positions on the front and back sides of the copper clad plate, and a through hole with a good shape is formed. It is workable, and both surfaces of the copper foil are planarly etched in the post-treatment to partially remove the thickness of the original copper foil by etching, and at the same time burr of the copper foil generated in the holes is simultaneously formed. Can be removed by etching, and even in the circuit formation of the front and back copper foil obtained by plating up with copper plating, it is possible to create a high-density printed wiring board without defects such as shorts and pattern breaks, and it has excellent reliability I was able to get what I had.

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Claims (4)

[Claims] 1. The carbon dioxide laser is directly irradiated onto the copper foil by pulse oscillation of the carbon dioxide laser using one energy selected from 5 to 60 mJ which is sufficient to remove the copper foil with the carbon dioxide laser. , A penetration with a carbon dioxide gas laser, characterized in that a layer having a low heat conductivity is used as a backup sheet on the back surface of the copper foil in order to form a through hole in at least two or more layers of the copper clad plate by adhering to the copper clad plate. Method of forming holes. 2. The low thermal conductivity layer of the backup sheet is arranged on the back side of the copper foil of a copper clad plate, and laminated on the copper foil under heating and pressure for close contact. The method for forming a through hole according to 1. 3. The method of forming a through hole according to claim 1, wherein a layer of at least the back surface of the copper clad plate of the backup sheet is a water-soluble resin. 4. After the holes have been formed, the backup layer is peeled off, and a part of the front and back copper foils in the thickness direction is dissolved and removed with a chemical solution, and at the same time, copper burr generated around the holes is dissolved and removed. The method for forming a through hole according to claim 1, 2, or 3.