JP2000061679A - Method for forming through hole by laser beam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a small-diameter through hole on many copper-coated sheets at one time precisely, speedily and directly only by high output gaseous CO2 laser beam. SOLUTION: An oxide metallic treatment is applied onto a copper-coated sheet having copper layers of at least two or more layers, these sheets of 2-10 sheets are stacked, and the surface of the copper foil is directly irradiated with laser beams by using energy selected from 20-60 mj/pulse enough to remove the copper foil through the pulse oscillation of gaseous CO2 laser beam, thereby forming the through hole. As a result, a through hole can be formed at high speed, enabling a printed circuit board to be obtained which has a high connecting reliability of the hole wall and an improved cost performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a plurality of through holes at the same time in a copper clad plate having at least two copper layers instead of a mechanical drill. That is, without etching the surface copper foil in advance, the energy selected from the high-power carbon dioxide gas laser is placed on a plurality of copper-clad plates that have been treated with a metal oxide, and the carbon dioxide laser is directly radiated from above to penetrate the copper clad plate. Regarding the method of making holes. The printed wiring board using the copper clad board obtained by this drilling is mainly used for small semiconductor plastic packages.

[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 slow. However, there is a problem in productivity, reliability, etc. Furthermore, using a negative film in advance on the upper and lower copper foils to make holes of the same size by a predetermined method, and when trying to form through holes that penetrate the upper and lower sides with a carbon dioxide laser, the positions of the upper and lower holes will be Gaps occur,
There were drawbacks such as difficulty in forming lands. The thermosetting resin copper-clad laminate of the glass cloth substrate has a problem in that, when the output of the carbon dioxide gas laser is small, it is difficult to process the glass and fluff remains on the hole wall. Moreover, it was not possible to simultaneously punch a plurality of copper clad plates.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above problems and stacks a large number of copper-clad plates whose surfaces are treated with an oxide metal with energy selected from a high-power carbon dioxide laser. Provided is a method for forming a small-diameter hole at high speed with high reliability of the hole wall.

[0004]

[Means for Solving the Problems] Using an energy selected from the energy of 20 to 60 mJ / pulse, which is sufficient to remove a copper foil with a carbon dioxide gas laser, the metal oxide treatment is performed with a copper oxide pulse by pulse oscillation of the carbon dioxide gas laser. By stacking 2 to 10 copper clad plates on the foil surface and forming through holes for through holes, a large number of small diameter through holes for through holes could be formed with high efficiency. After that, both surfaces of the copper foil are planarly etched to partially remove the original thickness of the copper foil by etching, thereby simultaneously removing the copper foil burr protruding in the hole to remove the copper foil around the hole. By forming the through-hole plating holes in which the copper foil on both sides remains, the copper foil positions of the upper and lower holes do not shift, lands can be formed, and the through holes can be formed without bending up and down. Since the foil becomes thinner, it is possible to create a high-density printed wiring board without the occurrence of defects such as shorts and pattern breaks in the circuit formation of the fine wire of the front and back copper foil obtained by plating up with the subsequent metal plating. I was able to. In addition, the processing speed was remarkably faster than that obtained with a drill, the productivity was good, and the economy was excellent. After the through holes are formed, the surface can be mechanically polished in addition to the method of etching with a chemical solution, but etching with a chemical solution is preferable from the viewpoint of removing burrs and forming a fine pattern. The holes may be formed not only on the double-sided copper-clad laminate, but also on a multilayer board or a single-sided board obtained by using the same resin composition.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a copper-clad plate which has been subjected to at least a metal oxide treatment with a direct laser using only an energy selected from a high-power carbon dioxide gas laser is used for 2-1.
After stacking 0 sheets, a required pulse (shot) of a carbon dioxide laser is radiated from above to form through holes for through holes, particularly small-diameter holes. The perforated printed wiring board is used for mounting a semiconductor chip.

The double-sided copper clad board used in the present invention includes:
Although not particularly limited, for example, a double-sided copper clad plate having a glass cloth as a base material, a thermosetting resin composition mixed with an inorganic insulating filler, and having a homogeneous structure is preferably used. Besides,
Copper clad board with film copper foil such as polyimide film,
An organic fiber-based copper clad plate or the like may be used. A copper clad plate having a single copper layer can be similarly drilled. The thickness of the copper clad plate is not particularly limited, but is preferably 0.05 to 1.0 mm.

The substrate is not particularly limited, but as the inorganic fiber, a generally known glass woven fabric or nonwoven fabric can be used. Specifically, the glass fibers are E, S, D, N
Examples thereof include glass. The glass content is not particularly limited, but is generally 30 to 85 wt%. As an organic fiber,
For example, woven or non-woven fabric of wholly aromatic polyamide fiber, liquid crystal polyester fiber or the like is used. In addition, the polyimide film may be used as a base material and a resin layer may be attached to one surface or both surfaces of the polyimide film.

As the resin of the thermosetting resin composition used in the present invention, generally known thermosetting resins are used. Specific examples thereof include epoxy resins, polyfunctional cyanate ester resins, polyfunctional maleimide-cyanate ester resins, polyfunctional maleimide resins, and unsaturated group-containing polyphenylene ether resins. One kind or two or more kinds. Are used in combination. A thermosetting resin composition with a glass transition temperature of 150 ° C or higher is preferable from the viewpoint of through-hole shape during processing with high-power carbon dioxide laser irradiation. Moisture resistance, migration resistance, electrical characteristics after moisture absorption, etc. From this point of view, a polyfunctional cyanate ester resin composition is preferable.

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. To give a concrete example, 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) sulfone, tris (4-cyanatophenyl) phosphite, tris (4-cyanatophenyl) phosphate, and cyanates obtained by reaction of novolac with cyanogen halide. .

In addition to these, Japanese Examined Patent Publications 41-1928 and 43-18
468, same 44-4791, same 45-11712, same 46-41112, same 4
The polyfunctional cyanate ester compounds described in 7-26853 and JP-A-51-63149 can also be used. Moreover, the molecular weight of the polyazine having a triazine ring formed by trimerization of the cyanato group of these polyfunctional cyanate ester compounds is 400
~ 6,000 prepolymers are 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 and the like. 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. 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.

Although these thermosetting resins can be used alone, it is preferable to use them in combination in consideration of the balance of properties.

Various additives may be added to the thermosetting resin composition of the present invention, if desired, within the range in which 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-methylpentene, polystyrene, AS resin, ABS resin, MBS resin, styrene-isoprene rubber, polyethylene-propylene copolymer, 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 exemplified and used appropriately. In addition, various other additives such as known organic fillers, thickeners, lubricants, defoamers, dispersants, leveling agents, photosensitizers, flame retardants, brighteners, polymerization inhibitors, thixotropic agents, etc. The agents are used in an appropriate combination 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 and economical efficiency. 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.

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 thereof include wollastonite, natural mica, synthetic mica, kaolin, magnesia, alumina and perlite. The addition amount is 10 to 60 wt%, preferably 15 to 50 wt%.

Further, it is preferable to add a black dye or pigment to the resin so that the light is not dispersed by the irradiation of the carbon dioxide laser. The particle diameter is preferably 1 μm or less for uniform dispersion. As the type of dye and pigment, generally known insulating materials can be used. The addition amount is preferably 0.1 to 10 wt%. Further, glass fibers whose surface is dyed black can also be used.

A generally known copper foil can be used as the outermost copper foil. Preferably, an electrolytic copper foil or the like having a thickness of 3 to 18 μm is used. As the inner layer copper foil, an electrolytic copper foil having a thickness of 5 to 18 μm is preferably used.

The substrate-reinforced copper-clad laminate is prepared by first impregnating the above-mentioned substrate with the thermosetting resin composition and drying to obtain B stage,
Create a prepreg. 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. The cross-section of this copper-clad laminate has a resin other than glass and an inorganic filler uniformly dispersed, and when laser-drilled, the holes are uniformly formed. Also,
The blacker one is that the laser light is not dispersed and there is no unevenness on the hole wall, and it is more uniform.

As the metal oxide treatment for treating the surface of the copper foil in the present invention, generally known ones can be used, and specific examples thereof include black or brown copper oxide treatment.

The copper foil surface of the copper clad plate, which is directly irradiated with the carbon dioxide laser, is subjected to a metal oxide treatment, and a total of 2-1 is applied.
0 sheets are piled up and a carbon dioxide laser is directly irradiated to make a hole.

When a carbon dioxide laser is irradiated with an energy selected from an output of 20 to 60 mJ / pulse, preferably 22 to 50 mJ / pulse to form a through hole, burrs are generated around the hole. Therefore, after carbon dioxide laser irradiation,
By etching both surfaces of the copper foil in a plane and removing a part of the thickness of the original metal foil, the burr is also removed at the same time, and the obtained copper foil is suitable for forming a fine pattern. A through hole for through-hole plating is formed, which is suitable for a high-density printed wiring board and has copper foil on both sides around the hole.

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,
02-25090, 02-59337, 02-60189, 02-16
6789, same 03-25995, same 03-60183, same 03-94491, same
According to the method disclosed in JP-A-04-199592 and JP-A-04-263488 for dissolving and removing a metal surface with a chemical (referred to as the SUEP method). In this case, the etching rate is generally 0.02-1.
Perform at 0 μm / sec.

The carbon dioxide laser is in the infrared wavelength range.
Wavelengths of 9.3 to 10.6 μm are commonly used. Output is 20 ~
It is used at 60 mJ / pulse, preferably 22 to 50 mJ / pulse.

[0027]

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,
Add 100 parts of bis (4-maleimidophenyl) methane to 150 ° C.
Was melted and reacted for 4 hours with stirring to obtain a prepolymer. This was dissolved in a mixed solvent of methyl ethyl ketone and dimethylformamide. Bisphenol A
Type epoxy resin (trade name: Epicoat 1001, manufactured by Yuka Shell Epoxy Co., Ltd.) 400 parts, cresol novolac type epoxy resin (trade name: ESCN-220F, Sumitomo Chemical Co., Ltd.)
(Manufactured by Mfg. Co., Ltd.) was added and uniformly mixed. Furthermore, 0.4 parts of zinc octylate was added as a catalyst, dissolved and mixed, and to this was added 500 parts of inorganic insulating filler (trade name: BST200, average particle size 0.4 μm, manufactured by Nippon Talc Co., Ltd.), epoxy silane cup. A varnish A was obtained by adding 4 parts of a ring agent and 2 parts of a black pigment and stirring and mixing them uniformly. This varnish is 100 μm thick
This was impregnated with the glass woven fabric of Example 1 and dried at 150 ° C. to prepare a prepreg (prepreg B) having a gelling time (at 170 ° C.) of 120 seconds and a glass cloth content of 57% by weight. Electrolytic copper foil with a thickness of 12 μm is placed above and below the above four prepreg B sheets,
Laminate molding was performed for 2 hours under vacuum at 20 ° C., 20 kgf / cm ² , 30 mmHg or less to obtain a double-sided copper-clad laminate C having an insulating layer thickness of 400 μm. Black copper oxide treatment was applied to the surface of this copper clad laminate and
Stack the sets, and from above, with a spacing of 300 μm and a hole diameter of 100
Direct carbon dioxide laser with 900 μm holes, output 40 mJ
/ Pulse was applied for 20 pulses (shots), and 70 blocks of through holes for through holes were opened. After removing the copper oxide film on the surface with a 5% hydrochloric acid aqueous solution, the copper foil burr around the holes was dissolved and removed by the SUEP method, and at the same time, the copper foil on the surface was also dissolved to 5 μm. Copper plating of 15 μm (total thickness: 20 μm) was applied to this plate by a conventional method. All the copper foil for land around this hole remained. The circuit (line / line
Space = 200/50 μm), solder lands, etc. are formed, and at least semiconductor chips, bonding pads, solder ball pads are covered with a plating resist, nickel and gold plating is applied, and a printed wiring board is created. did. Table 1 shows the evaluation results of this printed wiring board.

Example 2 1400 parts of epoxy resin (trade name: Epikote 5045), 600 parts of epoxy resin (trade name: ESCN220F), 70 parts of dicyandiamide, 2 parts of 2-ethyl-4-methylimidazole are mixed with methyl ethyl ketone and dimethylformamide. A varnish D was obtained by dissolving in a solvent, further adding 800 parts of the inorganic insulating filler of Example 1, and forcibly stirring to uniformly disperse. This was impregnated in a glass woven cloth having a thickness of 100 μm and dried to prepare a prepreg (prepreg E) having a gel time of 150 seconds and a glass cloth content of 55 wt%. Use one piece of this prepreg E,
Place 12μm electrolytic copper foil on both sides, 190 ℃, 20kgf / cm ² ,
A double-sided copper-clad laminate F was prepared by laminate molding for 2 hours under a vacuum of 30 mmHg or less. The insulating layer had a thickness of 100 μm. On this double-sided copper-clad laminate F, black copper oxide treatment was carried out, 8 sets of these were superposed, and through-holes for through holes were opened with 27 pulses (shots) at a carbon dioxide gas laser output of 40 mJ / pulse. After that, the same processing was performed to prepare a printed wiring board. The evaluation results are shown in Table 1.

Comparative Example 1 Using the double-sided copper-clad laminate of Example 1, a hole was similarly formed by a carbon dioxide laser without surface metal oxide treatment, but no hole was formed.

Comparative Example 2 In Example 2, Epicoat 5045 was used as the epoxy resin.
Using 2,000 parts of each, and using the other double-sided copper clad laminates made in the same way, arrange sheets on the copper foil surface in the same manner, stack 8 sets of this, and use carbon dioxide laser with output of 17 mJ / pulse It was irradiated with 40 shots and a through hole for through hole was opened. In this hole wall, glass fibers were found in the hole, and the hole shape was not a perfect circle but an elliptical shape. Similarly, the printed wiring board was prepared by washing with warm water, without performing the SUEP treatment, and only by mechanical polishing. The evaluation results are shown in Table 1.

Comparative Example 3 Using the double-sided copper-clad laminate of Example 1, the sheets were stacked and the diameter was 100
Using a mechanical drill of μm, holes were similarly drilled at 300 μ intervals at a rotation speed of 100,000 rpm and a feed rate of 1 m / min. Mechanical polishing was performed, copper plating was similarly performed to 15 μm without performing the SUEP treatment, circuits were formed on the front and back sides, and the same processing was performed to form a printed wiring board. Two drill breaks occurred on the way. The evaluation results are shown in Table 1.

Comparative Example 4 900 holes each having a hole diameter of 100 μm were formed by etching the copper foil on the surface of the copper foil of the double-sided copper-clad laminate of Example 1 at intervals of 300 μm. Similarly, on the back side, make a hole with a hole diameter of 100 μm at the same position
900 holes, 1 block 900 blocks, 70 blocks, 63,0 in total
Three sets of copper clad laminates with holes of 00 were piled up, and a carbon dioxide gas laser was applied from the surface for 19 pulses (shots) at an output of 40 mJ / pulse to form through holes for through holes. Thereafter, in the same manner as in Comparative Example 3, copper plating was applied to 15 μm only by mechanical polishing, circuits were formed on the front and back surfaces, and a printed wiring board was similarly prepared. The evaluation results are shown in Table 1.

<Measurement method> 1) Displacement of front and back hole positions and drilling time A hole having a hole diameter of 100 μm and
70 blocks (63,000 holes in total) were created as holes / blocks. The time required to drill 63,000 holes / sheet and the maximum deviation of the front and back hole positions when the holes were drilled with a carbon dioxide laser and a mechanical drill were shown. 2) Broken circuit pattern and short circuit In the examples and comparative examples, a plate without holes was similarly prepared, and a comb-shaped pattern of line / space = 50/50 μm was prepared, and then 200 patterns after etching with a magnifying glass. Was visually observed, and the total number of pattern breaks and short patterns was shown in the molecule. 3) Glass transition temperature It was measured by the DMA method. 4) Through-hole / heat cycle test A land diameter of 200 μm was created in each through-hole, 900 holes were connected alternately on the front and back sides, and 1 cycle was performed at 260 ° C / solder / immersion 30 seconds → room temperature / 5 minutes, and 200 cycles were performed. The maximum rate of change in resistance was shown. 5) Hole shape The cross section of the hole and the shape from above were observed. 6) A copper foil missing diameter around the land was created to have a diameter of 200 μm, and the lack of the copper foil between the land copper foil in the hole and the through hole was observed and evaluated.

Table 1 Item Example Comparative Example 1 2 2 3 4 Displacement of front and back hole positions (μm) 0 0 0 0 25 Hole shape Almost circular Almost circular Elliptical circular Almost circular hole Inner straight line Straight inner wall straight line Almost straight line Convex large Hole size Top, bottom, top, bottom When going to the bottom, the top and bottom plates are almost the same Approximately the same Approximately the same stepwise smaller Same as going to the bottom plate The hole diameter becomes smaller and the shape becomes irregular There is no copper foil around the land None None None None Yes Pattern breaks and shorts (number) 0/200 0/200 55/200 55/200 57/100 Glass transition temperature (℃) 235 160 139 234 235 Through hole heat cycle test (%) 2.8 4.9 28.3 2.6 10.9 hole Drilling time (minutes) 19 11 16 630 −

[0033]

[Effects of the Invention] By using energy selected from a high output of 20 to 60 mJ / pulse, which is sufficient to remove carbon dioxide laser of copper foil, by pulse oscillation of carbon dioxide laser,
A method of forming through-holes in a large number of copper clad plates, which is preferably made of glass cloth as a base material and mixed with an insulative dye or pigment to be blackened, and thermosetting at a glass transition temperature of 150 ° C or higher. Resin, mixed with an insulating inorganic filler, in the cross section of the laminate, using a glass cloth substrate copper clad laminate having a uniform proportion of the inorganic filler and the resin in the thermosetting resin composition, The surface of the copper foil to be irradiated with the carbon dioxide gas laser is treated with metal oxide, and a total of 2 to 10 sheets of this are laminated, and the energy selected from the carbon dioxide gas laser of 20 to 60 mJ / pulse is directly radiated on the copper foil to form a through hole. By forming the holes, the hole positions on the front and back sides did not deviate, the hole walls were well opened, and the through holes having excellent connection reliability could be obtained. In addition, the processing speed is much faster than drilling, and the productivity can be greatly improved.

[Brief description of drawings]

FIG. 1 is a process diagram of drilling through holes [(1) and (2)] using a carbon dioxide gas laser of Examples 1 and 2, deburring [(3)] using SUEP, and copper plating [(4)].

FIG. 2 is a similar process drawing of a carbon dioxide gas laser of Comparative Example 4. However, do not use SUEP.

[Explanation of symbols]

a metal oxide treatment layer b copper foil c glass cloth base material thermosetting resin layer d through hole through hole drilled by carbon dioxide laser e generated burr f through hole through hole drilled part with copper foil gap between front and back g Plated misalignment through hole

Continued front page    (72) Inventor Yasuo Tanaka             6-1, 1-1 Shinjuku, Katsushika-ku, Tokyo Mitsubishi tile             The chemical company Tokyo factory F-term (reference) 4E068 AF01 AF02 CF03 DA11                 5E339 AB02 AD03 AE01 BC02 BE11                       GG10

Claims (2)

[Claims] 1. A copper having at least two copper layers by pulse oscillation of a carbon dioxide laser using energy selected from 20 to 60 mJ / pulse sufficient to remove the copper foil with the carbon dioxide laser. In the method of forming a large number of through-holes on the stretched plate at the same time, at least the surface of the copper foil irradiated with the carbon dioxide gas laser is subjected to a metal oxide treatment, and a total of 2 to 10 pieces of the metal oxide treatment are arranged. A method for forming holes in which a gas laser is irradiated with necessary pulses to simultaneously form through holes in a large number of copper clad plates. 2. Both surfaces of the perforated copper clad plate are planarly etched to partially remove the thickness of the original copper foil, and at the same time, the copper foil burr protruding into the hole is removed by etching. The method for forming a hole according to claim 1, comprising: