Composition for microetching copper or copper alloy

A microetching composition for copper or copper alloys comprising, (a) nitric acid or sulfuric acid, or both, (b) ferric nitrate or ferric sulfate, or both, (c) at least one component selected from a group consisting of unsaturated carboxylic acids, salts of unsaturated carboxylic acid, and anhydrides of unsaturated carboxylic acid, and (d) water. The composition can produce a copper or copper alloy surface exhibiting excellent adhesion to resins such as prepregs and resists and superior solderability. The composition is suitable for the manufacture of printed wiring boards with highly integrated fine line patterns.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a microetching composition useful for 
treating surfaces of copper or copper alloys (the copper or copper alloys 
may be hereinafter collectively called "copper"). 
2. Description of the Background Art 
In the manufacture of printed wiring boards, copper surfaces are polished 
prior to coating such surfaces with an etching resist or a solder resist 
to improve adhesion of these resists to the copper surfaces. Mechanical 
cleaning using a buffing or scrubbing machine, or chemical cleaning, known 
as microetching, are used for roughening the copper surfaces. Microetching 
is more popular for treating substrates with fine line patterns. The 
copper surface is etched as deeply as 1-5 .mu.m by the microetching 
treatment. This depth of etching is calculated from the weight of copper 
decreased by etching, the specific gravity, and the surface area of the 
copper. 
The microetching is also applied to remove oxidized films from the surface 
of copper prior to a solder leveling process or prior to mounting 
electronic parts in order to improve solderability. An aqueous solution 
containing sulfuric acid and hydrogen peroxide as major components or an 
aqueous solution containing persulfate as a major component is used for 
the microetching. 
As the circuit density of printed wiring boards become higher, conventional 
heat curable solder resists are being replaced by UV curable solder 
resists which are superior in forming fine line patterns. The 
characteristics of the UV curable solder resists in adhering to copper 
surfaces, however, are weaker than those of conventional solder resists. 
The copper surfaces obtained by conventional microetching therefore 
exhibit insufficient adhesion to these UV curable solder resists. Resist 
films may be peeled or may swell during the subsequent steps of gold 
plating, solder leveling, or electronic part mounting. 
The solderability of copper surfaces obtained by conventional microetching 
is also insufficient for the solder leveling process for printing wiring 
boards which has an increasing number of pads for surface mount devices. 
Soldering failures sometimes occur. 
Therefore, development of a microetching agent which can produce roughened 
surfaces on copper or copper alloy with adequately deep irregularities 
exhibiting excellent adhesion of solder resists and the like has been 
desired. 
The inventors of the present invention have undertaken extensive studies 
and found that the addition of an unsaturated carboxylic acid, a salt 
thereof, or an anhydride thereof to a microetching agent comprising nitric 
acid or sulfuric acid and ferric nitrate or ferric sulfate, can achieve 
this object. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a 
microetching composition for copper or copper alloys comprising, 
(a) nitric acid or sulfuric acid, or both, 
(b) ferric nitrate or ferric sulfate, or both, 
(c) at least one component selected from a group consisting of unsaturated 
carboxylic acids, salts of unsaturated carboxylic acid, and anhydrides of 
unsaturated carboxylic acid, and 
(d) water. 
Other objects, features and advantages of the invention will hereinafter 
become more readily apparent from the following description. 
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
Either sulfuric acid or nitric acid, or both, may be used as the counter 
ion for dissolved copper. The amount of the acid, such as nitric acid, in 
the composition is in the range of 0.5 to 30% by weight (% by weight is 
hereinafter simply referred to as %), preferably 3 to 15%. If less than 
0.5%, the absolute amount of the acid to the amount of the dissolved 
copper is insufficient, permitting only a limited amount of copper to be 
dissolved, although the microetching composition has capability of 
oxidizing copper surface. The amount exceeding 30%, on the other hand, 
does not give any additional effect proportionate to the increased amount 
of the acid and is thus uneconomical. 
Ferric nitrate or ferric sulfate is used in the present invention to 
increase the etching speed. The amount of ferric nitrate or ferric sulfate 
to be added to the composition is in the range of 0.5 to 30%, and 
preferably 3 to 15%. If less than 0.5%, the required etching speed cannot 
be obtained; if more than 30%, production of noxious compounds, such as 
nitrogen oxide (when ferric nitrate is used), may be accelerated. 
An unsaturated carboxylic acid, a salt of unsaturated carboxylic acid, or 
an anhydride of unsaturated carboxylic acid is added to the composition of 
the present invention to produce etching with deep irregularities on the 
surface of the copper. As the unsaturated carboxylic acid, water soluble 
unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, 
crotonic acid, isocrotonic acid, maleic acid, fumaric acid, citraconic 
acid, itaconic acid, propiolic acid, tetrolic acid, and acetylene 
dicarboxylic acid, can be used. As the salts of these acids, sodium salt 
or potassium salt can be used. Maleic anhydride, itaconic anhydride, 
citraconic anhydride, and the like are given as examples of the anhydride 
of carboxylic acid used in the present invention. 
These unsaturated carboxylic acids, salts, or anhydrides may be used either 
individually or in combinations of two or more in any optional proportion. 
The amount of these components incorporated into the composition of the 
present invention is in the range of 0.1 to 20%, preferably 1 to 10%. If 
this amount is less than 0. 1%, the capability of the composition to 
produce adequately roughened copper surface is insufficient. It is 
difficult to dissolve these components in water if the amount is more than 
20%. In addition, the amount exceeding 20% does not give any additional 
effect proportionate to the increased amount and is thus uneconomical. 
In addition to the above essential components, the microetching composition 
of this embodiment may be formulated with various other additives as 
required. 
The microetching composition of the present invention can be prepared by 
adding the above-mentioned components in the proportions described above 
to water (d) and blending the mixture. There are no specific limitations 
to the method of addition. The components may be added either all at one 
time or separately in any arbitrary order. 
There are no specific limitations to the method for using the microetching 
composition of the present invention. Examples of such a method include a 
method of spraying the composition onto the surfaces of copper or copper 
alloy to be treated, a method of immersing the copper or copper alloy in 
the composition, and the like. 
The microetching composition of the present invention can be widely used 
for chemical cleaning or the like of copper or copper alloys. The 
resulting surfaces of the copper or copper alloy have adequate 
irregularities with deep convex and concave portions so that they can 
exhibit not only excellent adhesion to resins, such as prepregs, solder 
resists, dry film resists, and electrodeposition resists, but also 
superior solderability. Because of this, the microetching composition is 
particularly useful for the manufacture of various printed-wiring boards, 
including those for semiconductor packages, such as pin grid array (PGA) 
packages or ball grid array (BGA) packages. Further, in the manufacture of 
multi-layered printed-wiring boards, the use of the microetching 
composition for roughening the copper surfaces of inner layers produces 
surfaces which exhibit not only excellent adhesion to prepregs, but also a 
superb effect in preventing formation of pink rings. In addition, the 
microetching composition is effective for the surface treatment of lead 
frames used for integrated circuit 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 
Examples 1-6 and Comparative Examples 1-6 
Microetching compositions of the present invention and comparative 
microetching compositions were prepared by mixing the components listed in 
Tables 1 and 2. The microetching compositions obtained were sprayed on the 
surface of copper-clad laminates for printed-wiring boards (FR-4) at 
30.degree. C. for 10 seconds to produce roughened surfaces. A solder 
resist, PSR-4000.TM. (manufactured by Taiyo Ink Co., Ltd.) was coated onto 
the treated surfaces, irradiated with light, developed, and post-cured. 
The cured solder resist on the copper-clad laminate was cut into 1 
mm.times.1 mm squares, dipped in a 3.5% aqueous solution of hydrochloric 
acid at room temperature (about 20.degree. C.) for 10 minutes, washed with 
water, and dried according to JIS K 5400 8.5.2. Further, the peeling test 
according to the JIS K 5400 8.5.2 was carried out using a cellophane tape 
to evaluate the adhesion characteristics by observing the peeled off 
solder resist squares by the naked eye. The results were classified 
according to the following standard. 
.circleincircle. No solder resist whatsoever was attached to the cellophane 
tape. 
.smallcircle. A small number of solder resists were attached to the 
cellophane tape. 
X A great number of resists were attached over a wide area of the 
cellophane tape. 
The results are shown in Tables 1 and 2. 
TABLE 1 
______________________________________ 
Component Weight % Results 
______________________________________ 
Example 1 HNO.sub.3 (67.5%) 
5 
Fe(NO.sub.3).sub.3.9H.sub.2 O 
15 .largecircle. 
Acrylic acid 3 
Water 77 
Example 2 HNO.sub.3 (67.5%) 
15 
Fe(NO.sub.3).sub.3.9H.sub.2 O 
5 .largecircle. 
Maleic acid 10 
Water 70 
Example 3 HNO.sub.3 (67.5%) 
10 
Fe(NO.sub.3).sub.3.9H.sub.2 O 
12 .circleincircle. 
Itaconic acid 3 
Water 75 
Example 4 HNO.sub.3 (67.5%) 
12 
Fe(NO.sub.3).sub.3.9H.sub.2 O 
10 .largecircle. 
Disodium fumarate 
5 
Water 73 
Example 5 HNO.sub.3 (67.5%) 
12 
Fe(NO.sub.3).sub.3.9H.sub.2 O 
12 .largecircle. 
Maleic anhydride 
5 
Water 71 
Example 6 H.sub.2 SO.sub.4 (62.5%) 
8 
Fe.sub.2 (SO.sub.4).sub.3.nH.sub.2 O 
10 .largecircle. 
Maleic anhydride 
5 
Water 77 
______________________________________ 
TABLE 2 
______________________________________ 
Component Weight % Results 
______________________________________ 
Comparative 
Sulfuric acid 10 
Example 1 35% H.sub.2 O.sub.2 
5 X 
Water 85 
Comparative 
Sodium persulfate 
10 
Example 2 Sulfuric acid 1 X 
Water 89 
Comparative 
HNO.sub.3 (67.5%) 
15 
Example 3 Fe(NO.sub.3).sub.3.9H.sub.2 O 
15 X 
Water 70 
Comparative 
HNO.sub.3 (67.5%) 
12 
Example 4 Fe(NO.sub.3).sub.3.9H.sub.2 O 
12 X 
Malonic acid 5 
Water 71 
Comparative 
HNO.sub.3 (67.5%) 
12 
Example 5 Fe(NO.sub.3).sub.3.9H.sub.2 O 
12 X 
Succinic anhydride 
3 
Water 73 
Comparative 
H.sub.2 SO.sub.4 (62.5%) 
8 
Example 6 Fe.sub.2 (SO.sub.4).sub.3.nH.sub.2 O 
10 X 
Water 82 
______________________________________ 
A surface exhibiting not only excellent adhesion to resins such as prepregs 
and resists, but also superior solderability can be obtained by treating 
the surface of copper or a copper alloy with the microetching composition 
of the present invention. Because the resulting surface is less glossy 
than that obtained using conventional microetching compositions, this 
microetching composition has the effect of improving resolution when used 
as the base for a photosensitive resin and of decreasing errors in the 
inspection of printed wiring boards using an automatic optical inspector 
(AOI). The microetching composition of the present invention is thus 
useful for the manufacture of printed wiring boards as the patterns are 
increasingly miniaturized and the circuit density becomes higher. 
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.