Composition for treating copper or copper alloys

A composition suitable for the treatment of surfaces of copper and copper alloys is disclosed. It comprises, (a) a cupric complex of an azole compound, (b) an organic acid having a boiling point or a decomposition point of 230.degree. C or lower, (c) a difficultly volatile complexing agent, (d) a complexing agent having a complexing power which is weaker than that of the azole compound, and (e) water. The treatment of copper or copper alloys with the composition produces abraded surface with moderate irregularities, thereby ensuring better adhesion of various resists thereto and increased solderability. The composition is particularly useful for the manufacture of printed-wiring boards.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a composition for the treatment of 
surfaces of copper or copper alloys which is useful in removing rust and 
in roughening the surfaces of these materials. 
2. Description of the Background Art 
A treatment called microetching which consists of chemically abrading 
copper surfaces is performed in the manufacture of printed-wiring boards 
for promoting adhesion of etching resists and solder resists and for 
improving the soldering performances when electronic components are fixed 
to the wiring boards. The microetching consists of chemically abrading the 
surfaces of copper using an aqueous solution comprising sulfuric acid and 
hydrogen peroxide or an aqueous solution comprising a persulfate, as major 
components. 
The treatment using an etching agent comprising sulfuric acid and hydrogen 
peroxide or a persulfate, as major components, however, may cause 
corrosion of the wiring circuit and, in the worst case, may break the 
circuit, if the components in the etching agent remain in the substrate 
due to insufficient washing. These conventional etching agents produce 
mists during the treatment operation, which may pollute the working 
environment. 
Therefore, there has been a desire for the development of a composition for 
the treatment of surfaces of copper and copper alloys, which does not 
cause corrosion of the circuit, does not involve a risk of the circuit 
breakage, and does not accompany the production of mists and noxious 
gases, thereby improving the circumstances where the printed-wiring boards 
are manufactured. 
As a result of extensive studies, the present inventors have found that a 
combination a cupric complex of azole compound, specific organic acid, and 
specific complexing compounds can provide a surface treating agent which 
satisfies these requirements. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a composition 
for the treatment of surfaces of copper and copper alloys which comprises, 
(a) a cupric complex of azole compound, (b) an organic acid having a 
boiling point or a decomposition point of 230.degree. C. or lower, a 
difficultly volatile complexing agent, (c) a complexing agent having a 
complexing power which is weaker than the complexing power of the azole 
compound, and (d) water. 
These and other objects, features, and advantages of the present invention 
will become more apparent from the following description of the preferred 
embodiments taken in conjunction with the accompanying drawings. 
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
The cupric complex of azole compound, which is component (a) of the 
composition of the present invention, acts as an oxidizing agent which 
oxidizes metallic copper or the like. Among various cupric complexes which 
possess oxidizing effects, the cupric complexes of an azole compound are 
effective for the surface treating composition of the present invention to 
exhibit a suitable etching rate. Diazole compounds, triazole compounds, 
tetrazole compounds, and derivatives of these are included in the azole 
compounds which can be used for forming the cupric complex in the present 
invention. Among these, preferred in view of costs, availability, and the 
like are imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 
2-phenylimidazole, 2-undecylimidazole, and benzimidazole. 
These cupric complexes of azole compound may be used either singly or in 
combination as component (a) in the composition of the present invention. 
The amount of component (a) incorporated in the composition of the present 
invention can be suitably determined taking the aimed oxidizing effect and 
other factors into consideration, typically from the range of 1-5% by 
weight. If this amount is less than 1% by weight, the oxidizing power is 
too small for the composition to exhibit a sufficient etching effect. 
In the preparation of the composition of the present invention, either the 
cupric complex of azole compound can be used as component (a) or a copper 
(II) source and an azole compound may be separately added to form a cupric 
complex in the composition. As the source of copper (II), copper (II) 
hydroxide or copper (II) salts of an organic acid which is described below 
are preferred. 
The organic acid having a boiling point or a decomposition point of 
230.degree. C. or lower, which is the component (b), is added to the 
composition of the present invention in order to dissolve the copper which 
is oxidized by the cupric complex of azole compound. When electronic 
components are fixed to printed-wiring boards by soldering, typically at 
temperatures of 200.degree.-260.degree. C., it must be removed by 
volatilization or decomposition, so as not to affect the reliability of 
the product. Specific examples of the organic acid include saturated 
aliphatic acids, such as formic acid, acetic acid, propionic acid, butyric 
acid, valeric acid, and caproic acid; unsaturated aliphatic acid, such as 
acrylic acid, crotonic acid, and isocrotonic acid; saturated aliphatic 
dicarboxylic acids, such as oxalic acid, malonic acid, succinic acid, 
glutaric acid, adipic acid, and pimelic acid; unsaturated aliphatic 
dicarboxylic acids, such as maleic acid; and aromatic dicarboxylic acids, 
such as benzoic acid and phthalic acid. 
These organic acids may be used either singly or in combination as 
component (b) in the composition of the present invention. 
The component (b) may be incorporated in the composition of the present 
invention in an amount of about 5-30% by weight. If the amount is too 
small, the composition cannot sufficiently dissolve copper, producing only 
unacceptable surface conditions of the copper or copper alloy. If the 
amount of the organic acid is too large, the copper dissolving stability 
is impaired. 
The difficultly volatile complexing agent, component (c) of the present 
invention, is defined as a complexing agent which can volatilize only with 
difficulty. It plays a role of stably maintaining the copper which has 
been dissolved by the organic acid and has an advantage of not polluting 
the working environments. Specific examples of the difficultly volatile 
complexing agent include aliphatic amines, such as butyl amine, amyl 
amine, hexyl amine, dipropyl amine, diisopropyl amine, dibutyl amine, 
triethyl amine, and tripropyl amine; aromatic amines such as aniline; 
alkanol amines, such as monoethanolamine, diethanolamine, triethanolamine, 
and isopropanolamine; and amino acids, such as glycine, alanine, arginine, 
and asparagine. Among these, alkanol amines are particularly preferred, 
because they have an effect of increasing solderability when the 
printed-wiring boards treated with the composition of the present 
invention are soldered. 
These complexing agents may be used either singly or in combination as 
component (c) in the composition of the present invention. The amount of 
component (c) to be incorporated in the composition of the present 
invention is preferably 1% by weight or more, and usually less than 20% by 
weight. Because the difficultly volatile complexing agent is consumed as 
copper or the like is dissolved in the course of the surface treatment 
using the composition of the present invention, it must be appropriately 
supplied such that the above prescribed amount is always contained in 
order to achieve a stable surface treatment operation. 
For ensuring stable dissolution of copper, the difficultly volatile 
complexing agent used in the present invention should have a complexing 
power stronger than that of the azole compounds. With the use of this 
difficultly volatile complex alone, however, a sufficient etching rate 
cannot be achieved due to decrease in oxidizing power of the azole complex 
compound. Because of this and in order to achieve a desired etching rate, 
another complexing agent which has a complexing power weaker than that of 
the azole compound is incorporated to the composition of the present 
invention, as component (d). The types of the complexing agent used as the 
component (d) depend on the types of the azole compound used. Some 
examples are ammonia, pyridine, acetylhistidine, xantone, 
2-(2-ethyl)pyridine, and the like. 
These complexing agents may be used as component (d) either singly or in 
combination in the composition of the present invention. 
The amount of component (d) cannot be generically specified, because it may 
be varied depending of the types of other components and the cost of the 
complexing agent. Such an amount is typically 0.5-10% by weight in the 
composition of the present invention. 
These components (a) to (d) are dissolved in water, component (e), to 
prepare the composition of the present invention. Water purified by 
distillation or ion-exchanged water is used as component (e). 
It is desirable that the composition has a pH in a range of 6-8, measured 
at 40.degree. C. If the composition has a pH outside this range, sodium 
hydroxide, ammonia, or an organic acid may be further added so as to 
adjust the pH within this range. The above-mentioned organic acids used as 
component (b) can be preferably used as the acid for this purpose. In this 
instance, the amount of ammonia or the organic acid added should not 
exceed the amounts prescribed for preparing the composition of the present 
invention. If the pH is smaller than 6, the oxidation does not take place 
smoothly, retarding the rate of etching; if it is greater than 8, the rate 
of oxidation is too high so that the surface conditions of the products 
may be impaired. 
Other additives conventionally known in the art may be added to the 
composition of the present invention so long as the effects of the present 
invention are not adversely affected. 
The composition of the present invention may be applied to the surface of 
the copper or copper alloy for the treatment of the surface by using a 
method such as spraying or soaking. When the soaking method is employed, 
air is preferably bubbled into the composition in order to oxidize copper 
(I) produced by etching into cooper (II). 
The composition for surface treatment of the present invention can be 
widely applied to the chemical abrasion or the like of copper or copper 
alloys. Because the abraded surface is provided with moderate 
irregularities, the adhesion of various resists thereto is increased and 
solderability is also improved. The composition is particularly useful for 
the manufacture of printed-wiring boards.

Other features of the invention will become apparent in the course of the 
following description of the exemplary embodiments which are given for 
illustration of the invention and are not intended to be limiting thereof. 
EXAMPLES 
Example 1-4 
Compositions 1-4 were prepared by mixing components shown in Table 1 and 
adjusting the pH to 6.5. 
Substrates for printed-wiring boards with both side laminated with 
copper-clad (FR-4), each having a size of 150 mm.times.70 mm.times.1.6 mm, 
and 1000 throughholes, were used for the test. One side of the substrates 
was covered with a solder resist and the substrates were soaked in the 
compositions at 25.degree. C. for 1 minute. The odor produced by the 
soaking and the conditions of the surface not covered with the solder 
resist after the substrate was removed from the composition were examined. 
The etching amount was measured. The results are given in Table 1. The 
substrates were then heated at 230.degree. C. for 3 minutes without 
washing with water. After allowing to stand the substrates in a thermostat 
at 80.degree. C. and 90% RH for 30 days, the rate of conductivity break 
through throughholes was determined by measuring the resistance in the 
throughholes, The conductivity was deemed to have been broken, if the 
resistance of the throughhole exceeded 1 ohm, and the percentage of such 
throughholes were taken as a measure of the rate of conductivity breakage. 
The results are shown in Table 1. 
Comparative Examples 1-3 
Comparative Compositions 1-3 were prepared by mixing components shown in 
Table 2. The same tests as in Examples 1-4 were carried out in order to 
evaluate the performances of these comparative compositions. The results 
are shown in Table 2. 
TABLE 1 
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Conductivity Etching 
Example 
Component (wt %) breakage (%) 
Finished conditions 
Odor amount 
__________________________________________________________________________ 
(.mu.m) 
1 2-Methylimidazole.copper (II) complex (3) 
0 There were irregularities 
Slight acetic 
0.28 
Acetic acid (5) suitable for lamination 
acid odor, but 
Aniline (3) and soldering 
with no problem 
Pyridine (1) 
Ion-exchanged water (88) 
2 2-Methylimidazole.copper (II) complex (3) 
0 There were irregularities 
No odor 0.42 
Oxalic acid (5) suitable for lamination 
Aniline (3) and soldering 
Pyridine (1) 
Ion-exchanged water (88) 
3 2-Methylimidazole.copper (II) complex (3) 
0 There were irregularities 
Slight acetic 
0.33 
Acetic acid (5) suitable for lamination 
acid odor, but 
Diethanolamine (3) and soldering 
with no problem 
Pyridine (1) 
Ion-exchanged water (88) 
4 Imidazole.copper (II) complex (3) 
0 There were irregularities 
Slight acetic 
0.56 
Acetic acid (5) suitable for lamination 
acid odor, but 
Aniline (3) and soldering 
with no problem 
Pyridine (1) 
Ion-exchanged water (88) 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Comparative Conductivity Etching 
Example 
Component (wt %) 
breakage (%) 
Finished conditions 
Odor amount (.mu.m) 
__________________________________________________________________________ 
1 Sulfuric acid (10) 
32.4 There were irregularities 
Irritative odor 
0.82 
Hydrogen peroxide (5) 
suitable for lamination 
Ion-exchanged water (85) 
and soldering 
2 Sodium persulfate (10) 
21.4 There were irregularities 
Irritative odor 
0.63 
Sulfuric acid (1) suitable for lamination 
Ion-exchanged water (89) 
and soldering 
3 Sulfuric acid (10) 
29.7 No effects other than rust 
No odor 0.011 
Ion-exchanged water (90) 
prevention. The surfaces 
remained smooth. 
__________________________________________________________________________ 
Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that within the scope of the appended claims, the invention may 
be practiced otherwise than as specifically described herein. 
Japanese Patent Application No. 100121/1993 filed on Apr. 5, 1993 is hereby 
incorporated by reference.