JP2003008203A - Method of boring blind via hole in double-sided board using carbon dioxide laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of boring a blind via hole of high reliability in a thin copper foil laminate, by irradiating the laminate direct with a carbon dioxide gas laser beam. SOLUTION: A thin copper foil (a) having a protective metal plate (c) is used as the back copper foil of a copper-plated laminate with at least two or more-layered copper layers (a), and a blind via hole (d) is bored in the copper-plated laminate by irradiating it directly with a carbon dioxide laser pulse beam, having an energy of 5 to 60 mJ. Thereafter, the rear protective metal plate (c) is separated off, and the copper-plated laminate is made to serve as a printed wiring board through a conventional method after it is subjected to a smear removing treatment. Therefore, there is no via hole bored in the back copper foil, and the reliable and well-shaped blind via hole can be bored at a high speed, so that a high-density printed wiring board which is improved in cost benefit can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a thin copper foil having a thickness of 3 to 5 μm and a metal plate reinforced thin copper foil having a thick metal plate attached to the shanny side of the thin copper foil, which is stretched on at least the rear surface of the blind via hole. The present invention relates to a method of forming blind via holes by directly irradiating a surface of a copper clad plate having two or more copper layers with a carbon dioxide gas laser having a pulse energy sufficient to process a copper foil. The double-sided printed wiring board and the multi-layered printed wiring board are used as a new semiconductor plastic package, a mother board, etc. as a high-density small printed wiring board having holes of small diameter.

[0002]

2. Description of the Related Art Conventionally, in the case of forming a blind via hole in a high density printed wiring board used for a semiconductor plastic package or the like, a copper foil having a predetermined size is previously formed in a surface copper foil by a predetermined method. Etching, YAG
Remove by laser, mechanical drill, etc.
This portion was irradiated with a carbon dioxide laser to process the insulating layer to form a blind via hole. In this case, there is a defect that workability is poor because a step of making holes in the copper foil in advance is required. In addition, a method is known in which black copper oxide treatment is applied to the copper foil surface, and a carbon dioxide gas laser is directly radiated from above to open a blind via hole.
The copper foil on the back surface, which is the bottom of the blind via hole, had a through hole, and the yield was poor.

[0003]

SUMMARY OF THE INVENTION The present invention provides a method for forming a blind via hole having a small diameter in a thin double-sided copper clad plate with a thin copper foil, which solves the above problems.

[0004]

Means for Solving the Invention At least on the back surface of a copper clad plate, a protective metal plate is adhered to a thin copper foil shiny surface. A blind via hole is formed by directly irradiating one energy of a carbon dioxide laser with a pulse energy selected from 5 to 60 mJ. The backside copper foil is adhered to the metal plate, and when the carbon dioxide laser is applied to the backside copper foil, the heat diffuses through the backside metal plate, so there is no hole in the backside copper foil, and a good blind Via holes are formed. When the copper foil on the surface is thin, there is almost no burr on the copper foil around the hole during drilling, and after removing the reinforcing metal on the back surface, the resin layer remaining at the bottom of the hole is removed by desmear treatment, plasma treatment, etc. Plate and make a printed wiring board by the usual method.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is a method for forming a blind via hole having a small diameter in a thin copper clad plate having two or more copper layers using a carbon dioxide laser. The copper foil on the back side, which is at least the bottom of the blind via hole of the double-sided copper clad board,
A protective metal plate bonded to a copper foil having a thickness of 3 to 5 μm is used, and even if a carbon dioxide laser is irradiated, the bottom hole is not opened and a good blind via hole can be formed.

At least the back surface of the thin copper clad plate is
Use a metal plate to which a copper foil with a thickness of 3 to 5 μm is bonded. The surface may be the same copper foil. If the thickness is 3-5 μm,
The holes can be formed by directly irradiating the copper foil with a high-energy carbon dioxide gas laser without treating the surface of the copper foil. However, it is preferable to use a copper foil in which nickel metal, cobalt metal, or an alloy thereof is applied to the shiny surface of the copper foil. Further, a general copper foil that has been subjected to black copper oxide treatment, chemical treatment, etc. can also be used.

As the copper foil adhered to the protective metal plate used in the present invention, generally known ones can be mentioned. The thickness of copper foil
The thickness is 3 to 5 μm, and the shiny surface of the copper foil is preferably nickel metal, cobalt metal, or an alloy thereof. When metal treatment is applied, copper foil is laminated on the surface, the protective metal plate on the surface is removed, and then a hole is formed by directly irradiating a relatively low energy carbon dioxide laser of 5 to 20 mJ from above. Therefore, it is possible to form a good blind via hole without penetrating the hole at the bottom.

The copper-clad board used in the present invention is a copper-clad board having two or more layers of copper. 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 and dried to form a B-stage to prepare a prepreg. Next, a predetermined number of these prepregs are stacked, a copper foil with a protective metal plate is placed on the outside thereof, and laminated under heat and pressure to form a copper clad laminate. Multilayer board, after producing a copper clad board of copper foil thickness 12 ~ 70 (mu) m, the copper foil of this double-sided copper clad laminate is processed to form a circuit, the copper foil surface is processed to produce an inner layer board, and Place a prepreg or B-stage resin sheet on the outside and place a thin copper foil with a protective metal plate on the outside and laminate it, or place a B-stage resin sheet with a thin copper foil with a protective metal plate on the outside of the inner layer plate. And then laminated and molded to form a multilayer copper clad plate. Since the hole diameter of carbon dioxide laser is generally 80 to 180 μm, if the thickness of the copper clad plate is thick, problems such as copper not adhering inside will occur during subsequent copper plating.
It is preferably about μm to 150 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 M 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,
Examples thereof include polyfunctional maleimide resins and unsaturated group-containing polyphenylene ether resins, and they may be used alone or in combination of two or more. From the viewpoint of through-hole shape in processing by high-power carbon dioxide laser irradiation, a thermosetting resin composition having a glass transition temperature of 150 ° C. or higher is preferable,
Further, an inorganic filler is preferably added in an amount of 10 to 80% by weight. A polyfunctional cyanate ester resin composition is preferable from the viewpoints of moisture resistance, migration resistance, electrical characteristics after moisture absorption, and the like.

The polyfunctional cyanate ester compound which is a preferable 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) Examples thereof include anatophenyl) phosphite, tris (4-cyanatophenyl) phosphate, and cyanates obtained by reacting novolac with a cyanogen halide. Examples thereof include Br addition compounds in the known molecule.

In addition to these, Japanese Examined Patent Publications No. 41-1928 and No. 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, the Br addition resin to these well-known molecules 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 is itself cured by heating, but has a slow curing rate and is inferior in workability, economical efficiency and the like. Therefore, a known thermosetting catalyst is used 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.

Carbon dioxide lasers are 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. Of course, a UV laser such as a YAG laser can also be used.

[0018]

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-
Melt 1000 parts of maleimidophenyl) methane to 150 ° C,
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 has a thickness of 60 μm
Impregnated into a glass woven fabric and dried at 150 ℃, gelation time (at
A prepreg (prepreg B) having a resin composition content of 60% by weight at 170 ° C. for 110 seconds was prepared. Copper foil treated with cobalt alloy on the shiny surface of 5 μm thick electrolytic copper foil (trade name:
F3B-WS, made by Furukawa Circuit Foil Co., Ltd.), a protective metal plate with a 35 μm thick copper plate adhered to the shiny surface and placed on both sides of the above prepreg B.
Laminate molding was performed for 2 hours at a temperature of 20 kgf / cm ² and a vacuum of 30 mmHg or less to obtain a double-sided copper-clad laminate C having an insulating layer thickness of 80 μm.

The protective copper plate of 35 μm on the surface of this copper-clad laminate C was peeled off, the protective copper plate on the back side was left as it was, and one shot of carbon dioxide laser pulse energy of 10 mJ was irradiated from the front surface to form a blind having a pore diameter of 100 μm. A via hole was opened. Peel off the protective copper plate on the back side and dissolve the cobalt alloy layer on the surface of the shiny surface with a chemical solution to reduce the copper foil thickness.
It was 3.5 μm. After that, desmear treatment was performed to deposit copper plating of 15 μm. This front and back, the circuit by the existing method
(200 lines / space = 50/50 μm), solder ball lands, etc. are formed, and at least the semiconductor chip mounting area, bonding pad area, solder ball land area are covered with plating resist, and nickel and gold plating are applied. Giving,
A printed wiring board was created. 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 further added, and the mixture is forcibly stirred to uniformly disperse. And got Varnish D. This was impregnated in a glass woven fabric having a thickness of 20 μm and dried, and a gelling time of 150 seconds, a resin composition content of 76 wt% prepreg (prepreg E) and a gelling time of 178 seconds, a resin composition content of 80 weight% % Prepreg (prepreg F) was created. Using one piece of this prepreg E, put a general electrolytic copper foil with a thickness of 12 μm on both sides, and laminate-mold it for 2 hours under a vacuum of 190 ° C, 20 kgf / cm ² , 30 mmHg or less, and have an insulating layer thickness of 35 μm on both sides. A copper clad laminate G was produced. Circuits are formed on both sides of this, black copper oxide treatment is applied, one piece of each of the above prepregs F is placed on both outer sides, and 35 µm electrolytic copper is placed on the shiny side of a general electrolytic copper foil with a thickness of 3 µm on the outside. A copper foil (Micro Thin copper foil, manufactured by Mitsui Kinzoku Co., Ltd.) in which foils were adhered and stretched was placed and laminated in the same manner to produce a four-layer board. Peel off the protective metal plate on the front side and leave the copper plate as the protective metal plate on the back side as it is, irradiate 1 shot with carbon dioxide laser pulse energy of 15 mJ on the copper foil on the front side, insulating layer thickness 120 μm and hole diameter 15
A blind via hole of 0 μm was drilled to reach the backside copper foil. This was put in a plasma device, the residual resin at the bottom was removed, and after copper plating of 15 μm was applied, circuits were formed on both sides of this in the same manner as in Example 1 by a conventional method to obtain a printed wiring board. The evaluation results are shown in Table 1.

Comparative Example 1 A general electrolytic copper foil having a thickness of 7 μm was placed on both sides of the prepreg B of Example 1 and laminated in the same manner to prepare a double-sided copper clad laminate. This copper foil surface layer was subjected to black copper oxide treatment, placed on an XY table, and irradiated with 2 shots from the surface at a carbon dioxide gas laser pulse energy of 25 mJ to form blind via holes with a hole diameter of 100 μm. Of these holes, 84% had holes in the backside copper foil. Desmearing this, copper plating 15μm
It was attached and similarly used as a printed wiring board. The evaluation results are shown in Table 1.

Comparative Example 2 Instead of a copper foil with a metal plate, a general electrolytic copper foil having a thickness of 12 μm was applied to the surface layer of the four-layer copper clad laminate of Example 2 and the average thickness was 3
Etching was performed up to μm to form a 3 μm unevenness on the surface.
This was placed on an XY table and a blind via hole was formed by irradiating one shot of carbon dioxide laser pulse energy of 15 mJ from the surface of the front copper foil, but the backside copper foil had 93% holes. Copper plating was applied to 15 μm, circuits were formed on the front and back, and a printed wiring board was similarly prepared. The evaluation results are shown in Table 1.

(Table 1) Example Comparative Example Item 1 2 1 2 Backside copper foil penetration rate (%) 0 0 84 93 Glass transition temperature (° C) 235 160 235 160 Blind via hole / heat cycle test (%) 2.3 4.8 7.9 9.5 migration resistance ordinary state ^{5x10 14 6x10 14 5x10 14 4x10 14} 200hrs. 3x10 11 4x10 8 7x10 10 <1x10 8 700hrs. 6x10 10 <1x10 8 6x10 9 over

<Measurement method> 1) Backside copper foil penetration rate: Within the work size of 250 mm square, 70 blind blind via holes were made at 1 mm intervals as 900 holes / block (63,000 holes in total), and the copper foil on the backside was prepared. The number of penetrations was counted and expressed in%. 2) Glass transition temperature: Measured by the DMA method of JIS C6481. 3) Blind via hole / heat cycle test: A land diameter of 250 μm was created for each blind via hole, 900 holes were connected alternately on the front and back sides, and one cycle was 200 ° C at 260 ° C, solder, immersion for 30 seconds → room temperature for 5 minutes. The cycle was performed and the maximum rate of change in resistance was shown. 4) Migration resistance: In each of the Examples and Comparative Examples, blind via holes were opened in parallel in two rows so that the distance between the hole walls was 150 μm, 1000 holes were formed in each row, and a land diameter of 250 μm was produced on the front and back sides. Connected and arranged in 2 rows, 85 ℃ ・ 85
% RH / 50VDC was applied and the insulation resistance value was measured.

[0025]

The present invention has at least two copper layers,
When a blind via hole is formed by directly irradiating one energy selected from pulse energy of 5 to 60 mJ directly on the copper surface of a copper clad laminate having a thin surface copper foil, a protective metal plate is provided on the back surface of the copper clad laminate. By arranging and punching a thin copper foil of 3 to 5 μm, a blind via hole with excellent hole reliability could be formed without penetrating the copper foil on the back surface.

[Brief description of drawings]

FIG. 1 is a process diagram of forming a blind via hole according to the first embodiment.

FIG. 2 is a process diagram of forming a blind via hole in Comparative Example 1.

[Explanation of symbols]

a surface cobalt alloy treated copper foil b laminated plate c protective metal plate d blind via hole made by carbon dioxide laser e residual resin layer f blind via hole copper plated after desmear treatment g circuit h backside copper foil i with holes Blind via hole with holes in the backside copper foil j Blind via hole with holes in the backside copper foil plated with copper after desmearing

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Claims (2)

[Claims] 1. A copper foil is processed from the surface of a double-sided copper-clad plate in which a thin copper foil with a reinforcing metal plate and a thickness of 3 to 5 μm is stretched on at least one outer surface of a blind via hole bottom portion of the outermost layer. Sufficient pulse energy One carbon dioxide laser energy selected from 5 to 60 mJ is directly irradiated by pulse oscillation to form blind via holes in at least two or more layers of copper clad plate, and then the reinforcing metal plate on the back surface is peeled and removed. A method for forming blind via holes by a carbon dioxide laser, which is characterized by the above. 2. The method for forming blind via holes according to claim 1, wherein the thin copper foil is a thin copper foil with a reinforcing metal plate, the shiny surface of which is treated with nickel, cobalt, or an alloy thereof.