JPH11135917A - Manufacture of printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make irregularities of a copper foil surface small and uniformly smoothe and reduce pattern damage due to polishing scratch, by etching a copper foil surface by etchant formed by adding disodium hydrogen phosphate or trisodium phosphate 12 hydrate to sulfuric acid-hydrogen peroxide etchant. SOLUTION: A plating resist layer 2 is formed in a part excepting a portion which becomes a conductor on a laminated insulation substrate 1 with adhesive. The portion which becomes the conductor is subjected to roughening treatment and a surface conductor 3 is formed by electroless copper plating. Etching is carried out by using a composition wherein either of disodium hydrogenphosphate (Na2 HPO4 ) or trisodium phosphate 12 hydrate (Na3 PO4 .12H2 O) is added to sulfuric acid-hydrogen peroxide etchant. As a result, etching rate is stabilized and a copper foil surface of uniform and small irregularities can be obtained. Proper concentration of disodium hydrogen phosphate, etc., added to sulfuric acid-hydrogen peroxide etchant is 80 to 120 g/l.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a printed wiring board formed by an additive method.

[0002]

2. Description of the Related Art Conventionally, in a printed wiring board formed by an additive method, through holes such as a component mounting hole and a via hole are formed in an insulating substrate with an adhesive, and a portion other than a portion serving as a conductor is formed by a plating resist. In general, a conductor is formed by plating a portion to be a conductor.

[0003] Printed wiring boards by the additive method are:
It is characterized in that a conductor layer is simultaneously formed on the inner wall of a surface layer circuit conductor and a through hole (hereinafter, referred to as a through hole) by electroless copper plating. However, a conductor surface formed by the above-described electroless copper plating (hereinafter, referred to as a copper foil surface)
Varies depending on the state of the plating solution and the deposition rate of the plating. The surface of such a copper foil is smoothed by physical mechanical polishing to ensure the smoothness of the surface. As a method of this mechanical polishing, for example, when the roughness of the copper foil surface after plating is relatively small, sufficient mechanical smoothness with a low polishing power can be obtained, but when the roughness is large, a strong polishing power is obtained. Change mechanical polishing by changing polishing direction, buff grain size and buff pressure.
I've been there four times.

[0004]

In the above-mentioned conventional mechanical polishing, when the surface of the copper foil has small irregularities, sufficient surface smoothness can be obtained even with relatively weak mechanical polishing. However, when the roughness is large, mechanical polishing with a strong polishing force is performed, so that many deep polishing scratches are generated, and in some cases, the fine wire pattern or the copper foil is damaged. Such defects are caused by a chip-on-board (hereinafter, referred to as COB) wiring board or a ball grid array (hereinafter, referred to as BGA) wiring board which requires fine wiring patterns and smoothness of a copper foil surface. Such a surface mount board poses a serious problem in connection reliability, quality assurance, defect rate, productivity, and the like. In the present invention, in order to solve the above-mentioned conventional problems, even if the copper foil surface has large irregularities, scratches due to polishing are small and a copper foil surface having a small depth can be obtained.
It is an object of the present invention to provide a method of manufacturing a printed wiring board in which the connection reliability between a high-density printed wiring board such as an OB wiring board and a BGA wiring board and a silicon chip is improved.

[0005]

In order to achieve the above object, a method for manufacturing a printed wiring board according to the present invention comprises the steps of: forming a hole in an insulating substrate with an adhesive; A step of forming a plating resist layer on a part other than a part to be a conductor by ink or a dry film, a step of roughening a part to be a conductor and applying plating, and the conductor (copper foil) formed by plating The present invention provides a method for manufacturing a printed wiring board by an additive method including a step of slightly etching the surface and a step of mechanical polishing thereafter. However, even if the copper foil surface has large irregularities, etching after plating reduces the irregularities on the copper foil surface.Sufficient surface smoothness can be obtained by simply polishing this surface with a weaker than conventional mechanical polishing power. Property is obtained.

[0006]

FIG. 1 is a block diagram showing an embodiment of the present invention.
It will be described based on. FIG. 1 is a cross-sectional view illustrating a method for manufacturing a printed wiring board according to the present invention. As shown in FIG. 1, the insulating substrate with adhesive 1 uses ACL-E-168 (trade name of Hitachi Chemical Co., Ltd.), and the insulating substrate with adhesive 1 has through holes such as component mounting holes and via holes. 5
Drill holes. The insulating substrate 1 with the adhesive is laminated using a plating solution of SR-3000 (trade name of Hitachi Chemical Co., Ltd.) which is a dry film resistant to plating solution. Next, after overlaying a negative film at a predetermined position on the laminated insulating substrate 1 with an adhesive, exposing the film with a printing machine, developing and performing UV curing, a plating resist layer 2 is formed on a portion other than a portion to be a conductor. To form Next, a portion to be a conductor is subjected to a roughening treatment, and a surface conductor 3 and a through-hole plating layer 4 are formed by electroless copper plating.

FIG. 2 is an enlarged sectional view of a portion of the surface conductor 3 of FIG. 1 formed by the electroless copper plating. As shown in FIG. 2A, the surface of the copper foil as the surface conductor 3 has irregularities in the plated copper crystal depending on the state of the plating solution, the deposition rate of the plating, and the local stirring state of the plating solution. The formed surface roughness is about 4 to 6 μm. The surface of the copper foil having large irregularities as shown in FIG.
When slightly etched with an etching solution to about 8 μm, the surface roughness of the copper foil surface becomes 2 to 2 μm as shown in FIG.
The surface conductor 3 has small irregularities of about 3 μm. further,
As shown in FIG. 2 (c), the surface is adjusted by physical mechanical polishing to further reduce the unevenness of the copper foil surface and to make the surface roughness of the copper foil surface as smooth as about 0.8 to 1.5 μm. be able to.

The above-mentioned etching solution is generally sulfuric acid (H
_Although an etching solution containing ₂ SO ₄ ) -hydrogen peroxide (H ₂ O ₂ ) as a main component is used, the processing speed of the etching solution changes due to dissolution of copper, and the etching solution becomes unstable. This sulfuric acid (H
₂ SO ₄ ) -hydrogen peroxide (H ₂ O ₂ ) in an etchant, disodium hydrogen phosphate (Na ₂ HPO ₄ ) or trisodium phosphate dodecahydrate (Na ₃ PO ₄ .12H ₂ O) ), The etching rate is stable, and a uniform copper foil surface with small irregularities can be obtained. This is because the etching rate of sulfuric acid-hydrogen peroxide is about 5μ.
m / min, but for phosphate systems such as disodium hydrogen phosphate and trisodium phosphate dodecahydrate
Since the etching rate is as low as m / min, the convexities on the copper foil surface are slowly etched and smoothed, so that subsequent mechanical polishing can be weakly applied with a fine buff and the smoothness of the copper foil surface can be improved. improves. The disodium hydrogen phosphate or trisodium phosphate dodecahydrate to be added to the sulfuric acid-hydrogen peroxide etching solution is 80 to 120 g /
The concentration of 1 is good.

In order to improve the connection reliability of a COB wiring board, a BGA wiring board, and wire bonding, which require a fine wiring pattern or a high smoothness of the copper foil surface, only the step of etching the copper foil surface requires: Oils and fats, resins that have insufficient surface roughness and cannot be removed chemically
A mechanical polishing step is also performed to remove fibrous impurities and the like. However, mechanical polishing may be performed before the etching step. In the case of a normal surface-mounted substrate, only the etching with an etching solution of sulfuric acid-hydrogen peroxide containing the above-mentioned disodium hydrogen phosphate or trisodium phosphate dodecahydrate, followed by physical mechanical polishing May be omitted.

Sulfuric acid (H ₂ SO ₄ ) -hydrogen peroxide (H ₂ O ₂ )
Disodium hydrogen phosphate (Na ₂ HP
O ₄ ), trisodium phosphate dodecahydrate (Na ₃ PO _4.
Table 1 shows the amount of etching when treated with an etching solution having a composition containing 12H ₂ O) and the result of the connection reliability of wire bonding after gold plating. As is clear from this table, a uniform etching surface is obtained by adding disodium hydrogen phosphate or trisodium phosphate dodecahydrate to the composition of the etching solution, and the smoothness of the copper foil surface is reduced by sulfuric acid. The surface roughness is improved to about 1/4 to 1/8 as compared with a hydrogen peroxide-based etchant, and is excellent. Furthermore, in order to improve the connection reliability of wire bonding, mechanical polishing can be weakly applied, and the smoothness and flatness of the copper foil surface can be increased.

[0011]

[Table 1] Processing conditions # 1 to # 3: Etching at 35 ° C. for 60 seconds, then mechanical polishing once

[0012]

According to the present invention, when the unevenness of the copper foil surface after the conventional electroless copper plating is large, work management such as polishing direction, buff grain size, buff pressure, and number of times of polishing is complicated. By etching the copper foil surface with an etching solution obtained by adding a phosphoric acid-based disodium hydrogen phosphate and a trisodium phosphate decahydrate to a sulfuric acid-hydrogen peroxide-based etching solution, the copper foil surface is increased. Unevenness can be smoothed uniformly small. Therefore, not only the pattern damage and the defect rate due to deep polishing scratches are reduced and the productivity is improved, but also the CO 2
It is possible to improve the connection reliability and quality assurance of surface mounting components and wire bonding of high-density printed wiring boards such as B wiring boards and BGA wiring boards.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a printed wiring board according to the present invention.

FIG. 2 is an enlarged cross-sectional view of a copper foil surface of a printed wiring board for explaining the present invention. (A) is an expanded sectional view of the copper foil surface after electroless copper plating. (B) is an enlarged sectional view of the state where (a) was etched. (C) is an enlarged sectional view of a state where the copper foil surface of (b) is further mechanically polished.

[Explanation of symbols]

1 ... insulating substrate with adhesive, 2 ... plating resist layer,
3 ... surface conductor, 4 ... through-hole plating layer, 5 ... through-hole.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyoshi Yokoyama 1065 Kushita, Ninomiya-cho, Haga-gun, Tochigi Pref.

Claims (2)

[Claims] A step of forming a hole in an insulating substrate with an adhesive; a step of forming a plating resist layer; a step of plating a portion to be a conductor; a step of slightly etching the surface of the conductor; A method of manufacturing a printed wiring board by an additive method. 2. The method of manufacturing a printed wiring board according to claim 1, wherein said sulfuric acid-hydrogen peroxide etchant is disodium hydrogen phosphate (Na ₂ HP).
O ₄ ), trisodium phosphate dodecahydrate (Na ₃ PO _4.
Method for manufacturing a printed wiring board according to additive process which comprises using an etching liquid containing any one of 12H ₂ O).