Compositions – Etching or brightening compositions
Reexamination Certificate
2000-11-09
2002-07-30
Utech, Benjamin L. (Department: 1765)
Compositions
Etching or brightening compositions
C252S079300, C252S079400
Reexamination Certificate
active
06426020
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an etchant for copper or copper alloys useful in the manufacture of printed circuit boards and the like.
2. Description of the Background Art
Microetching is performed in the production of printed circuit boards to remove contamination and oxides from the surface of copper and to obtain an active copper surface. Microetching is an operation of slightly etching a surface, usually less than 5 &mgr;m in depth. Microetching is performed as a pretreatment for lamination or coating of resins such as an etching resist, solder resist, insulating layer, a pretreatment for electroless plating or electroplating, a pretreatment for soldering, and the like. In particular, when resins are laminated or coated, microetching is performed to produce a roughened surface exhibiting improved adhesion with the resins.
Conventionally, persulfate-based microetching compositions, sulfuric acid-hydrogen peroxide-type microetching compositions, and the like are used as microetching compositions.
However, conventional persulfate-based microetcing compositions have drawbacks such as a low etching rate and fluctuation in the etching rate due to unstable properties of etching solutions caused by decomposition of persulfate compounds. Another problem is related to metals other than copper, such as a tin lead alloy (solder), nickel, and gold, used in printed circuit boards. When microetching such a printed circuit board, the tin lead alloy or nickel may also be etched or discolored.
Sulfuric acid-hydrogen peroxide type microetching compositions also have such problems as instability of etching solutions due to decomposition of hydrogen peroxide which results in fluctuation in the etching rate, discoloration of metals other than copper, and the like.
An alkaline etchant containing copper ammonium complex ion as a major component is used in a circuit patterning step in the process of photoetching. This alkaline etchant also exhibits instability in the liquid composition, namely the etching rate tends to fluctuate. An additional problem with this etchant is a strong ammonia odor which impairs working environmental conditions.
Japanese Patent Publication No. 55-15512 discloses a neutral etchant containing a copper (II) ion source such as copper (II) chloride and a complexing agent such as monoethanolamine, and an alkaline etchant prepared by further adding an ammonium salt such as ammonium chloride. However, this neutral etchant exhibits a low etching rate and the alkaline etchant imparts an ammonia odor.
Japanese Patent Application Laid-open No. 6-17266 discloses a surface treating composition containing a copper (II) ion source such as copper (II) chloride and an alkanolamine, which the applicant claims is useful in removing gray or black films formed on a lead frame surface etched using an aqueous solution of iron (II) chloride or the like. However, this surface treating composition cannot be used as an etchant because of a low copper etch rate.
Japanese Patent Application Laid-open No. 7-292483 discloses a surface treating composition which is an aqueous solution containing a copper (II) complex of an azole compound, an organic acid, and a halide ion, and optionally alkanolamine. However, the amount of alkanolamine in this surface treating composition must not be in excess of the equivalent amount of the organic acid. If alkanolamine in excess of the amount of the organic acid is added, the copper etching rate is retarded.
Therefore, an object of the present invention is to provide an etchant in which the above problems in conventional etchants have been overcome, namely, the present invention provides an etchant free from problems such as instability of the liquid composition and unpleasant odor, and exhibiting a high etching rate.
Another object of the present invention is to provide an etchant exhibiting only very slight corrosion even if a small amount of residue is left on the surface, and capable of producing a roughened surface when used for microetching.
The inventors of the present invention have conducted extensive studies and have been successful in solving the above-described problems in the prior art by using the following etchant.
SUMMARY OF THE INVENTION
Specifically, the above object is solved in the present invention by an etchant for copper or copper alloys comprising 5-50wt % (hereinafter simply indicated by “%”) of an alkanolamine, a copper ion source in the amount of 0.2-10% as copper, a halide ion source in the amount of 0.005-10% as halogen, 0.1-30% of an aliphatic carboxylic acid, and the balance water, wherein the molar ratio of the alkanolamine to one mol of the aliphatic carboxylic acid is two or more.
In a preferred embodiment of the above etchant, the copper ion source is a copper (II) ion source, the amount of the halide ion source is 0.005-5wt % as a halogen, the amount of the aliphatic carboxylic acid is 2-30 wt %, and the etchant has a pH in the range of 7.5 to 11.5.
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
The alkanolamine is a component acting as a complexing agent to dissolve copper. A low molecular weight alkanolamine having a molecular weight of 500 or less is preferable, because such a low molecular weight alkanolamine produces a low viscosity etching solution which ensures uniform etching and is suitable for etching to form fine circuit patterns.
As specific examples of such an alkanolamine, monoethanolamine and its derivatives such as N-methylethanolamine, N-ethylethanolamine, N-butylethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-dibutylethanolamine, 2-(2-hydroxy)ethoxyethanolamine; diethanolamine and its derivatives such as N-methyldiethanolamine and N-butyldiethanolamine; triethanolamine, propanolamine, iso-propanolamine, and hydroxy ethylpiperazine, as well as derivatives of these may be given.
The concentration of alkanolamines is 5-50%, and preferably 10-30%. If the concentration of alkanolamines is less than 5%, the etching rate becomes low; if more than 50%, the viscosity of the etchant increases. When a copper complex of an alkanolamine, which is hereinafter discussed, is used as a copper ion source, an alkanolamine in the amount of 5% or more is added in addition to the alkanolamine forming the copper complex. In this instance, the upper limit of 50% for alkanolamines in the etchant must be observed.
In addition, the ratio of the alkanolamine to one mol of the aliphatic carboxylic acid, which is discussed later, is two mols or more. If this ratio is less than two mols, the etching rate is retarded.
The copper ion source is a component which forms a complex with the above-described alkanolamine and acts as an oxidant of copper. As the copper ion source, the above-mentioned copper complexes of alkanolamine, copper hydroxide, copper complexes of aliphatic carboxylic acid which are discussed later, copper halides such as copper chloride and copper bromide, copper carbonate, copper sulfate, copper oxide, and the like can be given. The copper ion sources may be either the compounds which generate the copper (I) ion or the compounds which generate the copper (II) ion. When the concentration of halide ion described later is less than 5%, the compounds generating the copper (II) ion are preferred due to their capability of dissolving copper in a stable manner.
The concentration of the copper ion sources is 0.2-10% as copper, and preferably 1-6% as copper. If the concentration is less than 0.2%, the etching rate becomes low. The etching rate also becomes low when the concentration is more than 10%. When a copper halide is used as the copper ion source, the copper halide should be added in such an amount that the concentration of the halide ion does not exceed 10%.
The halide ion sources increase copper solubility in the etchant, copper dissolution stability, and the etching rate. In addition, the halide ion
Arimura Maki
Kuriyama Masayo
Okada Masao
MEC Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tran Binh X
Utech Benjamin L.
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