Compositions – Etching or brightening compositions – Inorganic acid containing
Reexamination Certificate
1999-06-08
2003-12-23
Gulakowski, Randy (Department: 1746)
Compositions
Etching or brightening compositions
Inorganic acid containing
C252S079100, C252S079200, C252S079300, C510S295000, C510S367000, C510S375000, C216S096000, C216S100000, C216S103000, C216S105000, C216S106000, C216S107000, C134S002000, C134S003000
Reexamination Certificate
active
06666987
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a liquid etchant used for etching of a copper foil or a copper plate and a method for etchant for acicularly roughening a surface of copper and a method for etching a surface of copper to roughen the surface.
A multi-layer printed board is typically constructed by laminating an inner layer material, an outer layer material and prepregs on each other. In general, manufacturing of such a raw multi-layer printed board thus constructed is carried out by roughening a surface of a copper conductive pattern layer of the inner layer material and then laminating the outer layer material made of resin, a film, an ink or the like on the roughened conductive pattern of the inner layer material to prepare a laminate. Then, the laminate is formed with through-holes and then subjected to electro-plating.
Roughening of the copper conductive pattern layer is conventionally carried out according to any one of three methods. A first method is to form a layer of oxide such as cuprous oxide or cupric oxide on the surface of the copper conductive pattern layer. A second method is to reduce such an oxide layer to copper metal while keeping a shape of the oxide layer unchanged. A third method is to form a metallic copper layer increased in particle diameter on the surface of the copper conductive pattern layer by electroless copper plating.
Unfortunately, the first method, when copper oxide exposed on an inner surface of each of the through-holes is immersed or dipped in an acidic liquid such as a plating solution, causes the exposed copper oxide to be dissolved in the acidic liquid, leading to a defect called a pink ring. The second method requires to use an expensive reducing agent after formation of the oxide, to thereby cause not only an increase in number of steps in the manufacturing but an increase in manufacturing cost. Also, the third method likewise causes an increase in number of steps in the manufacturing.
In view of the foregoing, the assignee proposed etching techniques of subjecting a surface of copper to etching using an liquid etchant containing an oxo acid, an azole (in particular, benzotriazole) and a halide, as disclosed in Japanese Patent Application Laid-Open Publication No. 96088/1998. The proposed techniques permit a copper conductive pattern to be provided with a roughened surface increased in acid resistance while keeping the number of steps from being increased, to thereby solve the problems encountered by the first to third methods described above.
However, the proposed techniques necessarily require to combine benzotriazole with a halide. Also, the halide must be added in an amount of about 100 mg/l, to thereby stabilize a dissolving rate or etching rate of copper. This causes the etching rate to be reduced to a level as low as 0.5 &mgr;m/min. Thus, the proposed techniques require a considerable period of time as long as about 4 to 6 minutes for formation of the roughened surface, leading to a failure in exhibiting increased productivity.
More particularly, the proposed techniques cause the etching rate with respect to a chlorine ion concentration to exhibit such characteristics as shown in FIG.
5
. The etching rate is drastically increased or varied when the chlorine ion concentration is reduced to a level below 40 mg/l, so that it is highly difficult to keep the etching rate at a constant level. Thus, the proposed techniques require to adjust the chlorine ion concentration at a level of about 100 mg/l in order to stabilize the etching rate. Unfortunately, this leads to a reduction in the etching rate.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing disadvantages of the prior art.
Accordingly, it is an object of the present invention to provide a liquid etchant which is capable of forming a copper conductive pattern layer or the like with a roughened surface increased in acid resistance in a short period of time.
It is another object of the present invention to provide a method for roughening a surface of copper for production of a printed circuit board using such a liquid etchant while keeping the number of steps from being increased.
In accordance with one aspect of the present invention, a liquid etchant is provided. The liquid etchant includes a main component containing at least one acid selected from the group consisting of oxo acids represented by one of the following chemical formulae:
XO
m
(OH)
n
and H
n
XO
(m+n)
wherein X is a central atom, m is an integer of 0 or more, and n is an integer of 1 or more and derivatives thereof and at least one compound selected from the group consisting of peroxides and derivatives thereof. The central atom X may be S, P, N and the like. Also, the liquid etchant includes an auxiliary component containing at least one tetrazole.
Also, in accordance with this aspect of the present invention, a liquid etchant is provided. The liquid etchant includes a main component containing at least one acid selected from the group consisting of oxo acids represented by one of the following chemical formulae:
XO
m
(OH)
n
and H
n
XO
(m+n)
wherein X is a central atom, m is an integer of 0 or more, and n is an integer of 1 or more and derivatives thereof and at least one compound selected from the group consisting of peroxides and derivatives thereof. The central atom X may be S, P, N and the like. Also, the liquid etchant includes an auxiliary component containing at least one azole selected from the group consisting of 1,2,3-azoles which have three or more nitrogen atoms arranged in succession in a five-membered N-heterocycle thereof.
In a preferred embodiment of the present invention, the 1,2,3-azoles are represented by one of the following chemical formulae:
wherein R is selected from the group consisting of hydrogen, methyl, amino, carboxyl, mercapto radicals and the like.
In a preferred embodiment of the present invention, the auxiliary component contains at least one halide selected from the group consisting of chlorides, fluorides and bromides. The halide may be a chloride which is contained in the liquid etchant so that a chlorine ion concentration is 50 mg/l or less. Alternatively, the halide may be a fluoride which is contained in the liquid etchant so that a fluorine ion concentration is 50 g/l or less. The halide may also be a bromide which is contained in the liquid etchant so that a bromine ion concentration is 0.1 g/l or less.
In a preferred embodiment of the present invention, the auxiliary component further contains a second azole.
In a preferred embodiment of the present invention, the m in the chemical formulae representing the oxo acids is 2 or more.
In a preferred embodiment of the present invention, the (m+n) in the chemical formulae representing the oxo acids is 4 or more.
In accordance with another aspect of the present invention, a method for roughening a copper surface is provided. The method includes the step of subjecting the copper surface to etching using any one of liquid etchants described above so that the copper surface is provided with acicular projections.
In the present invention, the oxo acids and their derivatives are typically represented by sulfuric acid (H
2
SO
4
). However, they are not limited to sulfuric acid. They may include nitric acid (HNO
3
), boric acid (H
3
BO
3
), perchloric acid (HClO
4
), chloric acid (HClO
3
),phosphoric acid (H
3
PO
4
), 2-hydroxyethane-1-sulfonic acid (HOC
2
H
4
SO
3
H), hydroxybenzenesulfonic acid (HOC
6
H
4
SO
3
H), methanesulfonic acid (CH
3
SO
3
H), nitrobenzenesulfonic acid (NO
2
C
6
H
4
SO
3
H), aminosulfonic acid (NH
2
SO
3
H) and the like.
The peroxides are typically represented by hydrogen peroxide (H
2
O
2
), and the peroxide derivatives may include peroxo acids and their salts. Hydrogen peroxide, peroxomono acid or its salt is suitable for this purpose. More specifically, the peroxomono acids include peroxomonosulfuric acid (H
2
SO
5
), peroxochromic acid (H
3
CrO
8
), peroxonitric acid (HNO
4
), peroxoboric acids (HBO
3
, HBO
4
, HBO
5
), peroxomonopho
Morikawa Yoshihiko
Senbiki Kazunori
Yamazaki Nobuhiro
Ebara Densan Ltd.
Gulakowski Randy
Kornakov M.
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