JPH11346059A - Printed circuit board with reliable via hole - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a via hole that does not require desmearing treatment and has a small diameter speedily, by eliminating one part of a copper outer surface directly below the outer-surface copper foil of the copper-clad plate of a plurality of layers by a carbon dioxide gas laser, at the same time, forming a via hole that does not pass through copper foil, and allowing an outermost layer and a copper layer directly below it to conduct electricity by metal plating or the like. SOLUTION: In a method for forming a via hole on the surfaces of a double-sided copper-clad plate with at least two copper layers and a multi-layer plate, a carbon dioxide gas laser beam with a high output of approximately 20-60 mJ/pulse is directly applied for making a hole in copper foil on the surface. After that, the laser beam is applied with an output of approximately 20-35 mJ/pulse, one part of the lower inner layer or the surface of an outer-layer copper foil at an opposite side where the double-sided plates oppose each other is machined while the copper foil does not pass, and the via hole is formed. Then, a via part is subjected to metal plating (h) or the like, and the outermost layer is connected to the copper foil being directly below the outermost layer, thus eliminating the need for desmearing treatment, providing a superior working property, and at the same time obtaining a printed-circuit board where the connection reliability of the via hole is excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a printed wiring board having via holes. More specifically, a portion of the surface of the copper foil located below the surface layer is removed so that the copper foil does not penetrate, and the via hole obtained by metal plating or a conductive paint is applied to the surface layer and the copper layer thereunder. The present invention relates to a printed wiring board having a structure for conducting with a foil and having excellent conduction reliability. The obtained printed wiring board is mainly used for small semiconductor plastic packages.

[0002]

2. Description of the Related Art Hitherto, in a high-density multilayer printed wiring board used for a semiconductor plastic package or the like, a via hole is drilled by a drill or a carbon dioxide gas laser. When drilling, if the thickness of the inner layer copper foil is thin or the thickness variation of the multilayer board is large, it is difficult to stop the via hole in the middle of the intended inner layer copper foil, and sometimes it penetrates through the inner layer copper foil. And reached the copper foil layer therebelow, causing a defect. When a hole is formed by a carbon dioxide laser, a resin layer of about 1 μm remains on the surface of the copper foil on the lower surface of the via hole, and it is necessary to perform a desmear treatment before copper plating. In this case, if the desmear treatment was insufficient, the conductivity between the surface layer after the copper plating and the copper foil immediately below the copper layer was not good, and poor conduction occurred.
In addition, the desmearing process requires two to three times as long as the time required for desmearing a general through hole or the like, and has disadvantages and problems such as poor workability.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and drawbacks, and provides a printed wiring board having a small-diameter via hole which does not require desmearing. Further, according to the present invention, there is provided a printed wiring board having via holes that can be formed at a high speed.

[0004]

According to the present invention, a micro via hole for electrically conducting between a first layer copper foil on a surface layer of a printed wiring board and a copper foil immediately below the copper foil is formed with a carbon dioxide gas laser. At this time, a part of the copper surface layer immediately below the surface copper foil of the copper clad board having at least two copper layers is removed by a carbon dioxide laser, and a via hole is formed in a form that does not penetrate the copper foil, Provided is a printed wiring board having at least one or more via holes having a structure in which the outermost layer is electrically connected to a copper layer immediately below the outermost layer by metal plating or conductive paint. Via holes of the present invention, a double-sided copper-clad having copper foil on both sides, and at least the surface of the copper foil on the surface of the multilayer board, which is irradiated with a carbon dioxide laser, is subjected to metal oxide treatment, or has a melting point of 900 ° C. or higher. so,
In addition, one or more of metal compounds, carbon powder, or metal powder having a binding energy of 300 kJ / mol or more and a coating film or sheet made of an organic material are disposed, and 20 to 60 mJ from above.
Using the energy selected from / pulse, make a hole in the surface copper foil with pulsed CO2 laser oscillation, and then
20-35mJ / pulse energy, inner layer just below,
Alternatively, a part of the facing outer copper foil layer of the double-sided board is processed so that the copper foil does not penetrate, thereby forming a via hole in which a new surface inside the copper foil immediately below is exposed. Alternatively, the copper foil is etched and removed from the surface copper foil in advance, and the resin layer is processed with a low-output carbon dioxide laser. By increasing the output of the CO2 laser to 20-35 mJ / pulse and processing only a part of the surface layer so as not to penetrate the copper foil, a via hole exposing a new surface of the copper foil is formed. Thereafter, the surface of the copper foil is treated by mechanical polishing or a chemical solution. In the case of treatment with a chemical solution, in forming a via hole using a double-sided copper-clad laminate, the copper foil in the via hole portion is prevented from being dissolved. When a via hole is formed by directly irradiating a carbon dioxide gas laser, burrs of the copper foil are generated in the hole formed on the surface of the copper foil. Since it is difficult to remove by mechanical polishing, it is preferable to etch with a chemical solution. By etching both surfaces of the copper foil two-dimensionally and removing part of the original copper foil by etching, the copper foil burr that overhangs the hole at the same time is also etched away, making the copper foil thinner Therefore, in the circuit formation of the fine wires of the front and back copper foil obtained by plating up by the subsequent metal plating, it was possible to produce a high-density printed wiring board without occurrence of defects such as short circuit and pattern breakage. .
Also, there is no need to perform desmear treatment, and it has excellent workability,
When the outermost layer and the copper foil therebelow are connected by metal plating or conductive paint, a connection area is large, and a connection with excellent via hole connection reliability can be obtained.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a double-sided copper-clad board having at least two or more copper layers, and a printed wiring board having via holes in the surface of a multilayer board. The method for forming via holes on the surface is not particularly limited. For example, a metal oxide treatment may be applied to the copper foil on the surface, or a metal compound powder having a melting point of 900 ° C. or more and a binding energy of 300 mJ / pulse, or a carbon powder. Or one or more metal powders
A resin composition containing 3 to 97% by volume is applied to the surface of the copper foil to form a coating film, or is arranged as a sheet, and an energy selected from a high-output 20 to 60 mJ / pulse carbon dioxide laser directly from above. Irradiate a hole in the copper foil on the surface, and then, with an energy selected from 20 to 35 mJ / pulse, the inner layer below it, or a part of the outer copper foil surface layer on the opposite side opposite the double-sided board, The copper foil is processed so that it does not penetrate, and a via hole is formed in which the new surface inside the copper foil immediately below is exposed. Also,
The copper foil is etched and removed from the surface copper foil in advance at the location where the via hole is to be made by etching, and the resin is processed from above using a low-output carbon dioxide gas laser. The output of the carbon dioxide laser is increased to 20-35 mJ / pulse, and only the surface layer is processed so as not to penetrate the copper foil to form a via hole exposing a new surface of the copper foil. Thereafter, mechanical polishing or surface treatment of the copper foil with a chemical solution is performed. In the case of mechanical polishing, a general polishing machine can be used, but when burrs occur in the holes, it is necessary to perform polishing several times, but the dimensional change rate of the plate becomes large. Sometimes, the surface layer is etched with a chemical solution,
It is preferable to perform the copper foil surface treatment by a method of dissolving and removing burrs. Since both surfaces of the copper foil are etched away in a plane, the copper foil becomes thinner.In the circuit formation of the fine wire of the front and back copper foil obtained by plating up with the subsequent metal plating, short circuit, pattern cut, etc. A high-density printed wiring board can be produced without occurrence of defects. Also, the via hole of the present invention is excellent in workability because it is not necessary to perform desmear treatment, the copper foil exposure at the bottom of the via hole becomes large, or the via portion is plated with metal or embedded with a conductive paint, When connecting the outermost layer and the copper foil immediately below the outermost layer, a printed wiring board having a large connection area and excellent connection reliability of the via hole was obtained. As a chemical solution to be etched, generally known ones can be used. For example, JP-A-02-22887,
02-22896, 02-25089, 02-25090, 02-59337, 02
-60189, 02-166789, 03-25995, 03-60183, 03-
Nos. 94491, 04-199592 and 04-263488. Etching is performed by a method of dissolving and removing the metal surface with these chemicals (referred to as a SUEP method). The etching speed is generally 0.02 to 1.0 μm / sec.

The double-sided board and multilayer board having at least two or more copper layers used in the present invention are preferably made of a glass cloth as a base material and a thermosetting resin composition containing a dye or pigment. Black, and 10-60% by weight of inorganic insulating filler
A double-sided copper-clad laminate having a mixed and homogeneous structure is preferably used. Further, the multilayer board is preferably formed by processing the above-mentioned double-sided copper-clad laminate of a glass cloth base material for the inner layer plate, subjecting the surface to metal copper oxide treatment if necessary, and vertically forming an inorganic or organic cloth base material. A prepreg, a resin sheet, a copper foil with a resin, or a coating film made of a paint is arranged, and laminated and formed under heat, pressure, and preferably under vacuum. In addition to the above-mentioned copper-clad board, a double-sided board or a multilayer board of a generally known high heat-resistant film such as a Kapton film, a polyester film, and a polyparabanic acid film may be used.

As the substrate, generally known inorganic and organic woven and nonwoven fabrics can be used. Specifically, examples of the inorganic substrate include woven and non-woven fabrics of fibers such as E, S, D, and M glass. Examples of the organic fibers include woven and non-woven fabrics of fibers such as liquid crystal polyester and wholly aromatic polyamide.

As the resin of the thermosetting resin composition used in the present invention, generally known thermosetting resins are used. Specifically, an epoxy resin, a polyfunctional cyanate ester resin, a polyfunctional maleimide-cyanate ester resin, a polyfunctional maleimide resin, an unsaturated group-containing polyphenylene ether resin, and the like, and one or more kinds Are used in combination. From the viewpoint of through-hole shape in processing by high-output carbon dioxide laser irradiation, a thermosetting resin composition having a glass transition temperature of 150 ° C or higher is preferable, and has moisture resistance, migration resistance, and electrical characteristics after moisture absorption. In view of the above, a polyfunctional cyanate resin composition is preferred.

The polyfunctional cyanate compound which is the 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-dicyanato Naphthalene, 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) sulfone, tris (4-cyanatophenyl) phosphite, tris
(4-cyanatophenyl) phosphate, and cyanates obtained by reacting novolak with cyanogen halide.

In addition to these, Japanese Patent Publication Nos. 41-1928 and 43-1846
8, polyfunctional cyanate compounds described in JP-A-44-4791, JP-A-45-11712, JP-A-46-41112, JP-A-47-26853 and JP-A-51-63149 can also be used. Further, a prepolymer having a molecular weight of 400 to 6,000 and having a triazine ring formed by trimerization of a cyanato group of these polyfunctional cyanate compounds is used. This prepolymer is obtained by polymerizing the above-mentioned polyfunctional cyanate ester monomer with a catalyst such as an acid such as a mineral acid or a Lewis acid; a base such as a tertiary amine such as sodium alcoholate; or a salt such as sodium carbonate. It can be obtained by: The prepolymer also contains some unreacted monomers and is in the form of a mixture of the monomer and the prepolymer, and such a raw material is also suitably used for the purpose of the present invention. Generally, it is used after being dissolved in a soluble organic solvent.

As the epoxy resin, a generally known epoxy resin can be used. Specifically, liquid or solid bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, alicyclic epoxy resin; butadiene, pentadiene, vinylcyclohexene, dicyclopentyl ether, etc. And polyglycidyl compounds obtained by reacting a polyol, a hydroxyl-containing silicone resin with an epohalohydrin, and the like. These may be used alone or in combination of two or more.

As the polyimide resin, generally known ones can be used. Specific examples include a reaction product of a polyfunctional maleimide and a polyamine, and a polyimide 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 an appropriate combination in consideration of the balance of properties.

Various additives can be added to the thermosetting resin composition of the present invention, if desired, as long as the inherent properties of the composition are not impaired. These additives include polymerizable double bond-containing monomers such as unsaturated polyesters 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,
Polyethylene-propylene copolymer, 4-fluoroethylene-
6-fluorinated ethylene copolymers; high molecular weight prepolymers or oligomers such as polycarbonate, polyphenylene ether, polysulfone, polyester, and polyphenylene sulfide; and polyurethane are exemplified and used as appropriate. Also, other known organic fillers, thickeners,
Various additives such as a lubricant, an antifoaming agent, a dispersant, a leveling agent, a photosensitizer, a flame retardant, a brightener, a polymerization inhibitor, and a thixotropy-imparting agent are used in an appropriate combination as required. If necessary, the compound having a reactive group is appropriately blended with a curing agent and a catalyst.

The thermosetting resin composition of the present invention can be cured by heating itself, but has a low curing rate and is inferior in workability and economic efficiency. Can be used. The amount used is 0.005 to 10 parts by weight, preferably 0.01 to 5 parts by weight, per 100 parts by weight of the thermosetting resin.

As the inorganic insulating filler, generally known ones can be used. Specifically, silicas such as natural silica, calcined silica, and amorphous silica; white carbon, titanium white, aerosil, clay, talc,
Examples include wollastonite, natural mica, synthetic mica, kaolin, magnesia, alumina, and pearlite. The amount added is 10 to 60% by weight, preferably 15 to 50% by weight.

Preferably, a black dye or pigment is added to the resin so that the light is not dispersed by the irradiation of the carbon dioxide laser. The particle size is preferably 1 μm or less for uniform dispersion. As the types of the dye and the pigment, generally known insulating ones can be used. The addition amount is preferably 0.1 to 10% by weight. Further, glass fibers or the like in which the surface of the fibers is dyed black may be used.

A generally known copper foil can be used as the outermost layer. Preferably, an electrolytic copper foil having a thickness of 3 to 18 μm or the like is used. As the copper foil of the inner layer, an electrolytic copper foil of 12 to 70 μm is preferably used.

The glass cloth substrate-reinforced copper-clad laminate preferably used is prepared by first impregnating the above-mentioned glass cloth substrate with a thermosetting resin composition and drying it to form a B stage, and having a glass content of 30 to 85%.
A prepreg is prepared so as to be the weight%. Next, a predetermined number of the prepregs are used, copper foils are arranged on the upper and lower sides, and laminated under heat and pressure to form a double-sided copper-clad laminate. In the cross section of the copper clad laminate, a resin other than glass and an inorganic filler are uniformly dispersed, and the holes are uniformly formed when holes are formed by a laser. In addition, because of the black color, the laser beam is hardly dispersed, and a uniform hole with little unevenness is formed on the hole wall.

Metal oxide treatment is applied to the copper foil surface of the double-sided copper-clad laminate or the surface of the multilayer board to be irradiated with carbon dioxide laser, or the melting point is 900 ° C. or more and the binding energy is 300 kJ.
/ mol or more of metal compound powder, carbon powder, or metal powder
Drilling is performed by arranging a coating film or sheet of a resin composition containing up to 97% by volume and directly irradiating a carbon dioxide gas laser.

One of the auxiliary materials used in the present invention,
As the metal compound having a melting point of 900 ° C. or more and a binding energy of 300 kJ / mol or more, generally known metal compounds can be used. For example, titanias as oxides; magnesias; iron oxides; zinc oxides; cobalt oxides; tin oxides and the like, and the sad oxides include silicon carbide, tungsten carbide, boron nitride, Examples include silicon nitride, titanium nitride, barium sulfate, and the like. In addition, carbon can also be used. These are used alone or in combination of two or more. Further, generally known metal powders are also used. These have an average particle diameter of 5 μm or less, preferably 1 μm or less.

The organic material of the auxiliary material is not particularly limited, but is selected from those which do not peel off from the copper foil surface when mixed and applied to the copper foil surface and dried or when formed into a sheet. Preferably, a resin is used. In particular, generally known resins such as water-soluble resins, for example, polyvinyl alcohol, saponified polyvinyl alcohol, polyester, starch and the like are preferably used from the viewpoint of the environment.

The method for preparing the metal compound powder, carbon powder or a composition comprising a metal powder and an organic substance is not particularly limited. Using a resin composition that dissolves, add the above powder to this, uniformly stir and mix, use this, apply it to the copper foil surface as a paint, dry it to make a film, apply it to the film and sheet it And a sheet obtained by impregnating and drying a glass substrate or the like.

The carbon dioxide laser is in the infrared wavelength range.
Wavelengths of 9.3 to 10.6 μm are commonly used. Output is 20-60
At the mJ / pulse, the first layer of copper foil on the surface is processed and drilled first, the output is reduced to 20-35mJ / pulse, and the surface layer of the copper foil under it is processed in the last shot. Is preferred. Generally, the thickness of the insulating layer of a glass cloth base copper-clad laminate, etc.
Process with 1 to 10 shots per 100 μm.

As the plating of the via hole, generally known copper plating or the like can be used. Also, put conductive paint in the via hole,
The upper and lower copper foil layers are made conductive. As the conductive paint, generally known ones can be used. Specifically, copper paste, silver paste, solder paste, and other solders can be used.

[0026]

The present invention will be specifically described below with reference to examples and comparative examples. Unless otherwise specified, “parts” indicates parts by weight. Example 1 900 parts of 2,2-bis (4-cyanatophenyl) propane,
100 parts of (maleimidophenyl) methane are melted at 150 ° C,
The mixture was reacted for 4 hours while stirring to obtain a prepolymer. This was dissolved in a mixed solvent of methyl ethyl ketone and dimethylformamide. Add bisphenol A type epoxy resin (trade name: Epicoat 1001, Yuka Shell Epoxy Co., Ltd.)
) And 600 parts of a cresol novolac type epoxy resin (trade name: ESCN-220F, manufactured by Sumitomo Chemical Co., Ltd.) were uniformly mixed and dissolved. Further, as a catalyst, zinc octylate 0.4
Was added and dissolved and mixed. To this, 500 parts of an inorganic insulating filler (trade name: BST # 200, having an average particle diameter of 0.4 μm, manufactured by Nippon Talc Co., Ltd.), and 8 parts of a black pigment were added. Varnish A was obtained by uniform stirring and mixing. This varnish is impregnated with a glass woven fabric having a thickness of 100 μm and dried at 150 ° C., and a gel time (at 170 ° C.)
For 120 seconds, a prepreg (prepreg B) having a glass cloth content of 57% by weight was prepared. An electrolytic copper foil having a thickness of 18 μm is placed above and below one prepreg B, and the temperature is 200 ° C., 20 kgf / cm ² , 30
Laminate for 2 hours under vacuum of less than mmHg, and insulation layer thickness 100
A μm double-sided copper-clad laminate B was obtained. On the other hand, average particle size 0.86μm
Was added to a varnish prepared by dissolving partially saponified polyvinyl alcohol powder in water, and uniformly stirred and mixed (varnish C). This was applied on a 50 μm-thick polyethylene terephthalate film to a thickness of 20 μm,
After drying at 30 ° C. for 30 minutes, a sheet with a film having a metal copper powder content of 20% by volume was formed. This is placed on the double-sided copper-clad laminate B, and from above, holes with a hole diameter of 100 μm and an interval of 400 μm are formed.
One pulse (shot) was applied with an output of 40 mJ / pulse using 900 direct carbon dioxide lasers, and then the output was reduced to 30 mJ / pulse. The surface layer of the copper foil on the lower outer layer was processed and removed with two pulses. A total of 70 blocks of via holes (63,000 total holes) were drilled. Thereafter, the back surface was covered with an etching resist, the entire surface was treated by the SUEP method, and the copper foil burrs around the holes were dissolved and removed, and the copper foil on the surface was also dissolved to 7 μm. After removing the etching resist, this time the entire surface is covered with an etching resist, and the copper foil on the back surface is dissolved and removed to 7 μm by the SUEP method. After removing the etching resist, the plate is plated with copper by 15 μm (total thickness: 22 μm). gave.
A land with a diameter of 250 μm is formed at the location of this via hole, and the copper foil at the bottom of the via hole is used as a ball pad.
A heat cycle test was conducted by connecting a total of 900 holes.
In addition, a circuit (line / space = 50 / 50μm 200 pieces) is formed, a solder ball land is formed on this, and at least a semiconductor chip, a bonding pad, and a solder ball pad are covered with a plating resist. Then, nickel and gold plating were performed to produce a printed wiring board. Table 1 shows the evaluation results of the printed wiring board.

Example 2 1,400 parts of epoxy resin (trade name: Epicoat 5045), 600 parts of epoxy resin (trade name: ESCN220F), dicyandiamide 70
Part of 2-ethyl-4-methylimidazole was dissolved in a mixed solvent of methyl ethyl ketone and dimethylformamide, and further 500 parts of the insulating inorganic filler of Example 1 was added. Obtained. This is 50μm thick
Was impregnated and dried to prepare a prepreg (prepreg E) having a gelling time of 150 seconds and a glass cloth content of 35% by weight. Use one piece of this prepreg E, 18μm on both sides
Was placed and laminated under a vacuum of 190 ° C., 20 kgf / cm ² , and 30 mmHg or less for 2 hours to prepare a double-sided copper-clad laminate F. The thickness of the insulating layer was 100 μm. After forming circuits on the upper and lower sides and performing copper oxide treatment, prepregs E are arranged on the upper and lower sides, and 12 μm electrolytic copper foils are placed on both outer sides of the prepregs E, and similarly laminated and molded to form a four-layer board with double-sided copper foils F. On the other hand, copper powder having an average particle diameter of 0.7 μm was dissolved in a polyvinyl alcohol solution to prepare a varnish G containing 70% by volume of copper powder. This was applied on the double-sided copper-clad four-layer board F so as to have a thickness of 40 μm, and dried at 110 ° C. for 30 minutes to obtain a coating film (FIG. 1).
(1)). From above, the output of carbon dioxide laser is 40mJ /
A hole with a diameter of 100 μm is made in the copper foil by two pulses (shots), then processed in the same manner by two pulses at 28 mJ / pulse, and a via hole having a diameter of 100 μm is formed in the same manner as in Example 1. A multilayer printed wiring board was prepared (FIGS. 1 and 2).
(2), (3), (4), (5)). Table 1 shows the evaluation results.

Comparative Example 1 Using the double-sided copper-clad laminate of Example 1 and the double-sided copper-clad multilayer board of Example 2, no surface treatment was performed, and holes were similarly formed with a carbon dioxide laser without using an auxiliary material on the surface. Drilled, but no holes.

Comparative Example 2 In Example 2 (FIG. 3A), a mechanical drill having a drill diameter of 100 μm was used to similarly drill 63,000 holes from the surface layer to the copper foil immediately below. The entire cross section of this hole was confirmed, and 13% of the holes were present as shown in FIG. 3 (2). The others stopped through the inner copper foil. After performing the desmear process once without performing the SUEP process, a printed wiring board was prepared in the same manner. Table 1 shows the evaluation results.

Comparative Example 3 Using the double-sided copper-clad multilayer board of Example 2 (FIG. 1 (1)), the copper foil on this surface was 63,000 at 400 μm intervals in the same manner as in Example 1.
Etching was performed with a hole having a diameter of 100 μm, and three pulses were formed with a carbon dioxide energy of 18 mJ / pulse. A well-known desmear treatment was repeated twice without performing the SUEP treatment, copper plating was similarly adhered at 15 μm, circuits were formed on the front and back surfaces, and processed in the same manner to produce a printed wiring board. Table 1 shows the evaluation results.

Comparative Example 4 In Example 2, a via hole was made in the double-sided copper-clad multilayer board in the same manner at an output of 40 mJ / pulse of the carbon dioxide gas laser and 4 pulses. This penetrated the center of the inner layer copper foil (FIGS. 4 and 5), and was subjected to a SUEP treatment, and was similarly plated to produce a printed board. Table 1 shows the evaluation results.

Table 1 Item Practical example Comparative example 1 2 2 3 4 Via hole hole bottom Almost almost Inner layer copper foil Smooth Inner layer copper foil Flat Flat Perforated Perforated Desmearing No No Yes Yes No Necessity Presence or absence of pattern and 0 / 200 0/200 54/100 55/200 0/200 Short (pcs) Glass transition temperature 235 160 160 160 160 (℃) Via hole / heat cycle test (%) 100 cycles 2.0 2.4 ー 3.0 2.9 300 cycles 2.5 2.7 ー8.7 5.5 500 cycles 2.4 2.7 ー 23.7 11.3 Drilling time 10 12 630 ー ー (min)

<Measurement Method> 1) The bottom section of the via hole was observed. 2) Via drilling time The time required for drilling 63,000 holes / sheet in the case of drilling with a carbon dioxide laser and a mechanical drill was shown. 3) Circuit pattern break and short circuit In Examples and Comparative Examples, a pattern of line / space = 50/50 μm was visually observed with a magnifying glass by 200 patterns, and the total of the pattern cut and the short circuit was calculated as a numerator. Indicated. 4) Glass transition temperature Measured by the DMA method. 5) Via hole heat cycle test Connect 900 via holes alternately on both sides, one cycle is 260 ° C
・ Soldering, soaking 30 seconds → room temperature ・ 5 minutes, 200 cycles were performed, and the maximum value of the change in resistance was shown.

[0034]

According to the present invention, when a micro via hole for electrically conducting between the first layer copper foil on the surface layer of the printed wiring board and the copper foil therebelow is opened by a carbon dioxide gas laser, A via hole having a structure in which a part of the surface layer of the copper surface below is removed and a via hole is formed so as not to penetrate the copper foil, and the outermost layer is electrically connected to the copper layer therebelow by metal plating or conductive paint. Is provided. The printed wiring board of the present invention did not require desmear treatment and was able to obtain a printed wiring board having excellent connection reliability between the outermost layer and the copper foil thereunder. Further, the processing speed is much faster than drilling, and the productivity can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a process chart of via hole drilling [(1), (2), (3)] by a carbon dioxide gas laser of Example 2.

FIG. 2 is a process chart of via hole drilling [deburring by SUEP [(4)] and copper plating [(5)] by a carbon dioxide gas laser of Example 2.

FIG. 3 is a process diagram of via hole drilling by a carbon dioxide gas laser of Comparative Example 2.

FIG. 4 is a process chart of via hole drilling by a carbon dioxide gas laser of Comparative Example 4.

FIG. 5 is a process chart of copper plating (4) of Comparative Example 4.

[Explanation of symbols]

a Resin sheet containing metal powder b Copper foil c Thermosetting resin layer of glass cloth base d Carbon dioxide laser of 30 mJ / pulse e Burr generated f Carbon dioxide laser of 28 mJ / pulse g Copper foil surface layer at bottom of via hole h Via hole Copper plated part i Mechanical drill j Hole that penetrated to the fourth layer (lower outer layer copper foil) k Location that penetrated the inner layer copper foil by high-output carbon dioxide laser

Claims (1)

[Claims] At least two or more layers of copper are provided when a micro-via hole for electrically conducting between a first layer of copper foil on a surface layer of a printed wiring board and a copper foil therebelow is formed by a carbon dioxide laser. A part of the copper surface layer at the bottom of the via hole directly under the surface copper foil of the copper clad board having a layer of copper is removed with a carbon dioxide gas laser, and a via hole is formed in a form that does not penetrate the copper foil, metal plating or conductive A printed wiring board having at least one or more via holes having a structure for conducting between the outermost layer and a copper layer immediately below the outermost layer with a conductive paint.