JP2613336B2 - Method for forming aramid substrate printed circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an aramid substrate printed circuit board, and more particularly to a method for processing a circuit board using a resin board reinforced with aramid fiber as a substrate.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a printed circuit, a drill, a router, or the like is used for drilling, counterboring (forming a concave portion), or outer shape processing by a mechanical process. It has also been applied to circuit boards. However, recently, with the increase in the density of the circuit board, the diameter of the drill has become smaller, and a surface that cannot be dealt with by conventional machining, such as the necessity of fine outer shape processing and counterboring processing, has appeared.

[0003] Against this background, techniques for applying laser processing to printed circuit boards have been developed, and carbon dioxide lasers, YAG lasers, excimer lasers, and the like have been applied to drilling and external processing of printed circuit boards. For the application of lasers to printed circuit boards, see "Electronic Materials" 19
It is described in detail in the October 1991 issue, pages 120 to 125 (issued by the Industrial Research Council).

However, when laser processing is applied to a normal glass / epoxy laminate, the inner wall or cut surface of the hole is roughened with a carbon dioxide gas laser or a YAG laser, so that a clean surface cannot be obtained, and when an excimer laser is applied. Epoxy resins are decomposed and scattered, but glass fibers remain in nests, making it difficult to completely drill or cut.

An organic material can be generally processed by an excimer laser, and its application to a polyimide film is introduced in the above-mentioned article "Electronic Materials". Laminates made of aramid fiber base material (woven or paper made of aramid fibers impregnated with resin such as epoxy or polyimide) can also be processed by excimer laser, but the processed surface (the inner wall of the hole or the cut surface) ) Is roughened due to melting, carbonization, decomposition, etc. (FIG. 1). For this reason, a problem occurs in a wiring process and an assembly process such as subsequent plating, and for example, sufficient through-hole reliability cannot be maintained.
There was such a problem.

[0006] Therefore, there has been a demand for a processing method which can be easily processed by a laser and has a clean and smooth processing surface.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a clean and smooth processing method which can be easily processed by a laser and can be sufficiently used as a printed circuit board, and to provide a low-cost and highly reliable printed circuit board. It is in.

[0008]

That is, the present invention is a method for forming an aramid substrate printed circuit board, which comprises processing with an excimer laser and then treating in a heated aqueous solution of potassium permanganate.

In the present invention, aramid (aromatic polyamide) is composed of a repeating unit represented by the following formula (I) and / or (II).

[0010]

Embedded image

[0011]

Embedded image In the above formula, Ar ₁ , Ar ₂ , and Ar ₃ are substituted or unsubstituted aromatic rings, and are selected from the following groups.

[0012]

Embedded image However, X is the following divalent group.

[0013]

Embedded image

The substituents on the aromatic ring of Ar ₁ , Ar ₂ and Ar ₃ include an alkyl group having 1 to 3 carbon atoms, a halogen atom and a phenyl group. In the aromatic polyamide of the repeating unit (I), 15 to 30 mol% of Ar ₁ is

[0015]

Embedded image And / or

[0016]

Embedded image And the rest are

[0017]

Embedded image And / or

[0018]

Embedded image And / or

[0019]

Embedded image

A linear or parallel axis-bonded aromatic residue (however, a part of the hydrogen atom directly bonded to the aromatic ring may be substituted with a halogen atom, a methyl group or a methoxy group) A high modulus wholly aromatic polyamide copolymer fiber obtained by sufficiently stretching the copolymer to be oriented highly and highly is particularly preferable.

The single yarn fiber of the aromatic polyamide fiber of the present invention is 0.1 to 10 denier, preferably 0.3 to 5 denier. If the denier is less than 0.1 denier, there are many difficulties in the yarn-making technology (such as breakage and generation of fluff). On the other hand, if it exceeds 10 denier, it becomes impractical in terms of mechanical properties.

The aromatic polyamide fiber can take various forms. For example, it may be a base material in the form of a sheet such as a woven fabric, a long-fiber nonwoven fabric, a short-fiber nonwoven fabric, or paper, or may be a base material in the form of a short fiber simply dispersed in an epoxy resin. In the form of nonwoven fabric or paper, the aromatic polyamide fibers may be in the form of either short fibers or fibril-like pulp, or may be a mixture of any combination thereof.

In the case of short fibers, the fiber length is preferably from 1 to 60 mm, more preferably from 2 to 50 mm. When the fiber length is less than 1 mm, the mechanical properties of the obtained nonwoven fabric or paper are reduced. On the other hand, if the fiber length exceeds 60 mm, the distribution of short fibers in the obtained nonwoven fabric or paper becomes poor, and the mechanical properties are also lowered. Pulp in which short fibers are fibrillated by mechanical shearing force can be obtained to short fibers having a fineness that is difficult to produce, and particularly in paper, the distribution of short fibers can be further improved to improve the formation. In general, paper is a form in which the epoxy resin has good impregnation and uniform formation and performance can be obtained.

In the present invention, the impregnated resin of the laminate is a resin (curable resin) or a thermoplastic resin which is cured by heat and / or light. In the case of a resin that is cured by heat, a resin or a compound or a composition thereof capable of increasing the molecular weight or cross-linking by a chemical reaction caused by heating. The reaction caused by heating is a radical reaction,
Examples include an ionic reaction, an addition reaction, a condensation reaction, a substitution reaction, a hydrogen abstraction reaction, and an oxidation reaction.

Specific examples of the resin, compound or composition thereof include phenol resin, furan resin, xylene resin, formaldehyde / ketone resin, urea resin, melamine resin, aniline resin, sulfonamide resin, epoxy resin, Polyimide resin, triallyl cyanurate resin, diallyl phthalate resin, polybutadiene resin, bismaleimide resin and mixtures thereof, for example, epoxy resin / acrylonitrile-butadiene copolymer composition, epoxy resin / polyamide resin, epoxy resin / polyimide resin , Phenolic resin /
A polyvinyl butyral resin can be used. Of these, epoxy resins and polyimide resins are most commonly used, and are particularly preferably used because of good workability.

The base material and the resin may contain an inorganic filler such as silica, alumina, and titanium oxide within a range not to impair the purpose of the present invention.

The aramid laminate thus obtained may be formed into a circuit board by a conventional subtractive method, or may be formed by an additive method or a circuit transfer method (a circuit is previously formed on a metal plate or the like, and a prepreg is formed). The circuit board may be formed by, for example, a method of transferring a circuit by pressing.

In any method, an excimer laser is used for drilling, counterboring, and cutting instead of conventional machining. These processing steps may be performed before the circuit formation, or may be performed later depending on the circuit formation method. In the ordinary subtractive method, drilling is usually performed before forming a circuit.

The oscillation source of the excimer laser is Ar
F, KrF, XeCl, or the like is used, and as a mask method, a mask image method, a contact mask method, a conformal mask method, or the like can be used.

The processing conditions of the excimer laser, that is, energy density, irradiation time, scanning speed, etc.
It is appropriately selected according to the thickness of the processing target, the type of the resin, and the like.

Drilling with an excimer laser, counterbore,
After processing such as cutting, these processed surfaces are cleaned and etched with potassium permanganate in order to form a smooth surface.

In the etching, the aramid substrate laminate is treated in a heated potassium permanganate aqueous solution. The concentration of potassium permanganate is preferably at least 20 g / l, more preferably at least 30 g / l. Processing temperature is 60
C. or higher, more preferably 80.degree. C. or higher.

As another method for forming an aramid-based printed circuit board, prior to treatment with potassium permanganate, treatment is performed with an alkaline aqueous solution containing a solvent in advance. As the treatment solvent, at least one solvent selected from the group consisting of glycol ether, n-methylpyrrolidone, dimethylsulfoxide, and dimethylformamide is preferable. Furthermore, it is preferable to neutralize with an aqueous acid solution after treating with potassium permanganate.

[0034]

According to the method for forming a printed circuit board according to the present invention, a circuit board having a high density and excellent reliability can be formed at a low cost by punching, counterboring, cutting and the like on the circuit board. Can be manufactured. In particular, it can be used for a high-density circuit board having a large number of through holes and via holes, a minute counterbore for mounting minute components, and cutting around a high-density circuit in which a circuit extends to the periphery of the circuit board.

In particular, the workability and reliability of the aramid fiber-based copper-clad laminate having low expansion and hardly causing migration can be further improved.

[0036]

EXAMPLE A wholly aromatic polyetheramide (polyparaphenylene 3,4) prepared by copolymerizing 100 mol% of high-purity terephthalic acid chloride, 50 mol% of paraphenylenediamine, and 50 mol% of 3,4'-diaminodiphenyl ether. '-Diaminodiphenyl ether terephthalamide) was wet-spun and a fiber having a denier of 1.5 denier was prepared by changing the spinning conditions to reduce the equilibrium moisture content, the amount of sodium contained, the amount of extracted sodium, and the amount of extracted chlorine. The obtained wholly aromatic polyetheramide fiber was cut into a length of 3 mm, which was dispersed in water to make a paper weighing 55 g / m ² . A water-dispersed epoxy resin composition was used as a binder, added by a spray method after papermaking, and dried.
The amount of the binder attached was about 5% by weight. The paper was hot-pressed at 200 kg / cm and 5 m / min using a pair of metal roll calenders having a metal roll having a surface temperature of 190 ° C.

Next, 80 parts by weight of a glycidyl etherified product of a polycondensate of bisphenol A and formaldehyde (epoxy equivalent 208), 20 parts by weight of a bisphenol A type epoxy resin (epoxy equivalent 187) and 30 parts by weight of tetrabromobisphenol A The reaction was carried out in the presence of 0.03 parts by weight of imidazole to give an epoxy equivalent of 34.
2. An epoxy resin a-1 having a bromine content of 23% by weight was obtained.

Next, a curing agent b-1 which is a polycondensate of bisphenol A and formaldehyde was obtained.

56 parts by weight of the epoxy resin a-1 was added to a brominated bisphenol A type epoxy resin (epoxy equivalent: 47).
29 parts by weight), and 24 parts by weight of the curing agent b-1. To the epoxy resin composition consisting of 0.04 parts by weight of 2-ethyl-4-methylimidazole was added methyl ethyl ketone / A mixed solvent of ethylene glycol monomethyl ether (mixing ratio by weight: 1/1) was added to prepare a varnish having a nonvolatile content of 60% by weight and a bromo content of 22.5% by weight (relative to the solid content).

The varnish is impregnated into the above-mentioned paper-like material, and
After drying at 0 ° C. for 3 minutes, a prepreg having an epoxy resin composition solid content of 70% by weight was obtained. Next, two 35 μm-thick electrolytic copper foils and five prepregs were laminated and pressed with a hot press at 170 ° C. and 40 kg / cm ² for 1 hour to prepare a copper-clad laminate. The volume ratio of the epoxy resin composition in the laminate was about 60%, and the thickness of the resin layer was 0.5 mm. When the coefficient of thermal expansion of the resin layer was measured by TMA (thermodynamic analyzer), it was 6 ppm / ° C.

The laminate thus obtained (FIG. 3A)
Coated with photosensitive resist on both sides (Fig. 3B)
After that, only one side is exposed to ultraviolet rays and then developed with an alkali to develop an opening having a diameter of 0.1 mm (a substrate having a resist-coated portion (FIG. 3C) having 1,000 pieces (width 4.5).
cm, length 10 cm)). While the resist was coated on the entire back surface, cupric chloride was sprayed from the front surface to etch the copper foil exposed at the opening (FIG. 3D). The resist on the front surface was completely peeled off with alkali, and the back surface was left as it was.

A KrF excimer laser (wavelength: 248 nm, energy density: 1.6 J / cm ² ) was applied to the surface of the laminate having the opening portion of the copper foil thus obtained.
Is squeezed with a lens to a width of about 100 μm and a length of 5 cm.
Scanning was performed at a speed of cm / min. The excimer laser caused abrasion, and the resin layer in the opening portion of the copper foil was etched (FIG. 3E), but the wall surface was covered with the molten material, and the carbide was adhered.

Further, in order to etch the copper foil on the back surface,
After coating the etching resist on the copper foil on the surface again, ferric chloride was sprayed on the surface to etch the copper foil in the portion perforated with a laser (FIG. 3F), and then the resist on both surfaces was peeled off with alkali. (FIG. 3G).

Further, the inner wall of the hole was treated under the following conditions. [Pretreatment] Treatment agent Deionized water 80% by volume Diethylene glycol 10% by volume Caustic soda (added until the pH of the aqueous solution becomes 1.0) Treatment conditions 70 ° C, 5 minutes

[Potassium permanganate treatment] Treatment agent Deionized water Potassium permanganate 50 g / l Treatment conditions 70 ° C, 5 minutes

[Neutralization] Treatment agent Deionized water Concentrated sulfuric acid (added until the pH of the aqueous solution becomes 1.0 or less) Treatment conditions 45 ° C., 3 minutes

On the inner wall of the obtained hole, both the melt and the carbide were etched cleanly, and the fiber and the resin were clearly separated. This situation is shown in FIG. 1 (before processing) and FIG. 2 (after processing). Further, the obtained perforated plate was plated through an ordinary plating process to a thickness of about 20 μm (FIG. 3H), and a circuit for through-hole reliability was formed by etching, and then subjected to a thermal shock test. The test method was MIL-P-551.
Ten methods (-65 ° C, 15 minutes and 150 ° C, 15 minutes) were followed. The number of thermal shocks leading to disconnection was 1500 times.

[Brief description of the drawings]

FIG. 1 is a side cross-sectional view of an aramid-based printed circuit board drilled with an excimer laser and before being treated with a heated aqueous potassium permanganate solution.

FIG. 2 is a cross-sectional side view of an aramid-based printed circuit board after being treated with a heated potassium permanganate aqueous solution drilled with an excimer laser.

FIG. 3 is a schematic view (side sectional view) at each stage when an aramid-based printed circuit board is formed by the method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 Copper foil 3 Resist A Schematic diagram of copper-clad aramid substrate printed circuit board B Schematic diagram of printed circuit board developed after coating with resist C Schematic diagram of printed circuit board etched with copper foil D Printed circuit board after laser processing Schematic diagram E Schematic diagram of printed circuit board with resin layer etched F Coating etching resist on the surface again,
Schematic diagram of printed circuit board with copper foil etched on the back side G Schematic diagram of printed circuit board with resist stripped H Schematic diagram of printed circuit board with through-hole plating after treatment with heated potassium permanganate aqueous solution

Claims (3)

(57) [Claims] 1. A method for forming an aramid substrate printed circuit board, comprising: processing with an excimer laser, followed by treatment in a heated aqueous solution of potassium permanganate. 2. A method for forming an aramid-based printed circuit board, comprising: drilling, cutting or counterboring with an excimer laser and treating in a heated potassium permanganate aqueous solution. 3. A method for forming an aramid substrate printed circuit board, comprising: processing with an excimer laser, treating with an alkaline aqueous solution containing a solvent, and then treating in a heated aqueous solution of potassium permanganate.