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  Non-cyanogen type electrolytic solution for plating goldRelated Patent Categories: Electrolysis: Processes, Compositions Used Therein, And Methods Of Preparing The Compositions, Electrolytic Coating (process, Composition And Method Of Preparing Composition), Depositing Predominantly Single Metal Coating, Gold, Utilizing Organic Compound-containing BathThe Patent Description & Claims data below is from USPTO Patent Application 20070029206. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of U.S. patent application Ser. No. 10/661,533 filed Sep. 15, 2003, and claims priorty thereto. This application also claims priority to Japanese application no. 2002-284821 filed Sep. 30, 2002, and Japanese application no. 2003-033101 filed Feb. 12, 2003, the contents being incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to an electrolytic solution and, more specifically, to a noncyanogen type electrolytic solution for plating gold, containing a gold salt as a supply source of gold and a non-cyanogen type compound. [0004] 2. Description of the Related Art [0005] A plated gold film is excellent in electric characteristic, corrosiveness, soldering ability or others. Accordingly, when a circuit board used in a semiconductor device or the like is produced, copper patterns formed on a surface of the circuit board are subjected to electrolytic gold plating. [0006] This electrolytic gold plating is usually carried out in an electrolytic plating solution containing a cyanogen compound. [0007] In this regard, if it is desired that only a predetermined part of the patterns formed on the surface of the circuit board is subjected to gold plating, the circuit board, the part which not to be plated with gold being covered with resist, is dipped into a gold-plating electrolytic solution. [0008] However, when an electrolytic solution added with a cyanogen compound is used as a bath for gold plating, cyanogen ions corrode the resist to separate the latter from the surface of the circuit board. Thereby, the gold-plating electrolytic solution may enter a gap between the circuit board and the resist to form a gold film on a part of the circuit board which is not to be plated with gold. [0009] Accordingly, when gold is plated to a predetermined portion of micro-patterns formed on the circuit board, gold is also plated to other portions not to be plated due to the entry of the gold-plating solution into the gap between the surface of the circuit board and the resist, which may cause a short-circuit between the micro-patterns. [0010] To solve this problem, there has been proposed a non-cyanogen type electrolytic solution, containing a gold salt, as a supply source of gold, and a non-cyanogen type acetylcysteine as a complexing agent (see Japanese Unexamined Patent Publication No. 10-317183; pages 4 to 5). [0011] According to the non-cyanogen type gold-plating electrolytic solution disclosed in the above-mentioned patent publication, it is possible to plate, with gold, only a predetermined portion of micro-patterns formed in a circuit board, the solution being less toxic and easily treatable as well as not being corrosive, due to cyanogen ions, to a resist coated on the circuit board because no cyanogen compound is added thereto. Thus, it is possible to plate gold on a predetermined portion of the micro-patterns formed on the circuit board. [0012] However, it has been found that the gold-plating film obtained by using the non-cyanogen type gold-plating electrolytic solution disclosed in the above-mentioned patent publication is black in appearance and the gold-plating electrolytic solution bath lacks stability. SUMMARY OF THE INVENTION [0013] In view of the above-mentioned problems, an object of the present invention is to provide a non-cyanogen type gold-plating electrolytic solution capable of providing a gold-plating having golden luster and a good stability. [0014] The present inventors has studied to solve the above-mentioned problems and found that when the electrolytic gold plating is carried by using a gold-plating electrolytic solution bath added with 2-aminoethanethiol as a compound for forming a complex compound with gold, the resultant gold-plating exhibits an appearance having golden luster and the stability of the gold-plating electrolytic solution bath is favorable. Thus, the present invention has been made. [0015] That is, according to the present invention, there is provided a non-cyanogen type electrolytic solution for plating gold, containing gold salt, as a supply source of gold, and a non-cyanogen type compound, wherein the electrolytic plating solution is added with one selected from a group of thiouracil; 2-aminoethanethiol; N-methylthiourea; 3-amino-5-mercapto-1,2,4-triazole; 4,6-dihydroxy-2-mercaptopyrimidine; and mercapto-nicotinate; as a compound forming a complexing compound with gold. [0016] In the present invention, chloroaurate or gold sulfite may be favorably used as a gold salt. [0017] In the present invention, the non-cyanogen type compound preferably has a deposition potential in a range from -0.4 to -0.8 Vvs.SCE. The non-cyanogen type compound is preferably thiouracil or 2-aminoethane thiol. The hydrogen ion concentration pH of the non-cyanogen type compound is 12 to 5, and more preferably is 8 to 5. [0018] According to another aspect of the present invention, there is provided a gold plating method using a non-cyanogen type electrolytic solution, containing gold salt as a supply source of gold and added with a non-cyanogen type compound, wherein the electrolytic plating solution is added with one selected from a group of thiouracil; 2-aminoethanethiol; N-methylthiourea, 3-amino-5-mercapto-1,2,4-triazole; 4,6-dihydroxy-2-mercaptopyrimidine; and mercapto-nicotinate; as a compound forming a complexing compound with gold. [0019] The gold plating is preferably carried out in a condition of a current density of 0.5 A/dm.sup.2 or less. DETAILED DESCRIPTION OF THIS INVENTION [0020] The non-cyanogen type gold-plating electrolytic solution according to the present invention is one using a gold salt as a supply source of gold and added with a non-cyanogen type compound. Continue reading... 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