Surface-treating agents for copper and copper alloy

Abstract: An aqueous solution containing 0.1 g/l or more of piperidine or a derivative, 100 - 500 g/l of sulfuric acid, 10 - 50 g/l of hydrogen peroxide and 0.5 g/l or more of phosphoric acid is used for treating the surface of copper or copper alloy used in manufacturing of printed circuit.

Description: Background of the Invention This invention relates to surface-treating agents for copper and copper alloy which are used in the manufacture of printed circuits. Recently, printed circuits have become increasingly important in the assembly of electronic circuits. They have steadily and step by step overcome technical obstacles produced by the development of smaller, lighter and more multifunctional electronic instruments. With the progress of automation of the assembly of electronic instruments, lines of the print circuit have become finer, the holes smaller in diameter, and the system more multilayered. In addition, technical improvement of the formation of so-called high density circuits is increasingly desirable. In association with the development of high density printed circuits, steps for applying various platings such as electroless copper plating subsequent to various processing of the copper-plated laminate have increased. Thus, a so-called soft etching step for: (1) the removal of the anticorrosive film and the oxide film remaining on the surface of the copper foil of the copper-plated laminate; (2) roughing the copper surface to activate the cooper surface and to improve the adherence of the plating; and (3) removal of the flaws formed on the processed surface, etc., plays an important role. Furthermore, due to the development of finer patterns of printed circuit, mechanical or pumice polishing heretofore employed has become technically difficult, and substitution of the polishing with chemical cleaning is desired. Heretofore, ammonium persulfate or sodium persulfate is used as the soft etching agent. Ammonium persulfate, however, is defective in that copper ammonium complex is formed during neutralization due to the co-existence of ammonium ions in the effluent, and copper in the wastewater cannot be removed. Sodium persulfate requires various measures to improve its performance which is inferior to that of ammonium persulfate. In addition, there are such disadvantages as short life, frequent bathings and a high manufacturing cost when the etching solution comprises ammonium persulfate or sodium persulfate. The application of soft etching with an acid aqueous solution of hydrogen peroxide has been attempted in order to overcome these disadvantages. However, the prior-art acid aqueous solutions of hydrogen peroxide meet with the following problems: (1) a two-step treatment, involving a soaking aftertreatment with diluted sulfuric acid or diluted hydrochloric acid, is required due to the formation of an oxide film on the copper surface after soft etching; (2) the rate of copper dissolution is apt to be influenced by the change of hydrogen peroxide concentration in the etching solution so that the finish of the copper surface is not uniform; and (3) the adherence of the plating is inferior as compared with soft etching ammonium persulfate. Polishing with an acid hydrogen-peroxide system has been proposed as a chemical polishing substitution for the mechanical polishing as mentioned above. In general, however, this process needs a two-step treatment in which an oxide film is first formed with hydrogen peroxide and sulfuric acid and then the oxide film is removed with a dilute aqueous solution of an acid. Improved one-step chemical polishing methods by addition of phosphoric acid and an amine are proposed in Japanese Patent Publication Nos. 32339/1978 and 32340/1978. These methods are not adaptable to use in the high-density printed circuit because they are not economical due to the high hydrogenperoxide concentration, 5% - 60%. Even the addition of phosphoric acid and an amine cannot lead to complete removal of the oxide film. US 3756957 described a solution for the chemical dissolution treatment of metallic materials. The solution comprises sulphuric acid, hydrogen peroxide and at least one organic compound which may be cyclohexylimine. The organic compound acts to suppress the decomposition reaction of hydrogen peroxide. Summary of the Invention It is the object of the invention is to overcome the above mentioned problems. As a result of studies in order to improve the methods as mentioned above we have found that addition of an adequate amount of piperidine or a derivative thereof to an aqueous solution of hydrogen peroxide consisting essentially of hydrogen peroxide, sulfuric acid and phosphoric acid achieves such improvements. Thus, the invention is directed-to a surface-treating agent for copper and copper alloy comprising: an aqueous acid solution containing 100 - 500 g/l of sulfuric acid, 10 - 50 g/l of hydrogen peroxide and at least 0.5 g/l of phosphoric acid; and at least 0.1 g/l of piperidine or a derivative thereof. The piperidine derivative preferably has the formula wherein Y = CH₃, CH₂OH or COOR wherein R represents hydrogen, methyl or ethyl, and n = 1 - 5. More preferably, n is 1 or 2. Detailed Description of the Invention The copper or copper alloy treated with the surface-treating agent of the invention forms no oxide film on the surface with a result that aftertreatment of removing the oxide film needed in the prior-art methods can be omitted as well as excellent performance such as superior adherence of the plating and wettability and brightness of the solder is produced. Phosphoric acid is effective in inhibition the formation of the oxide film when added in an amount of 0.5 g/l or more. An amount in the range between 2 and 5 g/l is particulary preferred. The addition of 5 g/l or more is also effective, and no upper limit is required to be set. However, large amounts are unfavourable in economical consideration. Although addition of 0.5 g/l or more of phosphoric acid is effective in inhibiting the formation of the oxide film, use of an aqueous solution of hydrogen peroxide composed only of sulfuric acid, hydrogen peroxide and phosphoric acid does not obviate the need for an oxide film-removing step. The first feature of the invention is based upon the finding that piperidines produce the surprising result of completely inhibiting the oxide film. Moveover, the result is not produced by the combination of piperdine with sulfuric acid and hydrogen peroxide but first developed by the further addition of phosphoric acid. The piperidine or a derivative thereof is added in an amount of 0.1 g/l or more. Addition of an amount less than 0.1 g/l is unfavourable because the oxide film will then be formed. The preferred amount for the addition is in the range between 0.1 and 5 g/l. The addition of an amount more than 5 g/l is unfavorable because the surface finish of the copper or copper alloy will occasionally lose brightness. Particular examples of the piperidine or its derivative include piperidine, 2-pipecoline, 3-pipecoline, 4-pipecoline, 2,6-lupetidine, 3,5-lupetidine, 3-piperidinemethanol, pipecolic acid, isonipecotic acid, methyl isonipecotate, ethyl isonipecotate and the like. They can be used either alone or in combination of two or more. The surface-treating agent of the invention may contain other appropriate additives as required. Particular examples of the additive include alcohols, phenols, glycol ethers and the like known as a stabilizer for hydrogen peroxide. The surface-treating agent of the invention. is not adversely affected by the addition by these additives. The surface-treating agent of the invention is also characterized by its applicability to a wide range of the steps for manufacturing printed circuits; These areas follows: (1) Primary copper-plating pretreatment, (2) secondary copper-plating pretreatment, (3) pretreatment for the photo printing, (4) pretreatment for solder resist printing, (5) pretreatment for the solder coating step, (6) finishing treatment and (7) chemical treatment substitution for mechanical polishing. The liquid temperature in using the surface-treating agent of the invention is generally 50°C or below and preferably in the range between 30 and 40°C. A temperature above 50°C is unfavorable because extensive decomposition 5 of the hydrogen peroxide will cause difficulty in controlling the liquid. The surface-treating agent may be applied by any known means such as soaking or spraying. The invention will be described with reference to the examples below but is not intended to be limited thereto. Example 1 Surface-treating agents were prepared by adding a piperidine as an additive to an aqueous solution composed of 200 g/l of sulfuric acid, 35 g/l of hydrogen peroxide. and 2 g/l of phosphoric acid. Test pieces were prepared by cutting a glass-epoxy copper-plated laminate with a thickness of the copper of 35 µ into pieces of a size of 5 cm x 5 cm. In a beaker was placed 400 ml of the surface-treating agent thus prepared, in which was soaked the test piece for 2 min. while keeping the temperature at 35°C. Immediately after the soaking the test piece was washed with water and air dried. The presence or absence of the oxide film on and finish of the copper surface were examined. The same tests were run with addition of a substance other than piperidines for comparison. The results are shown in Table-1. Finish of the surface: Smooth and bright o ○ Slightly bright ○ Poor finish and discolored X Example 2 Surface-treating agents were prepared from an aqueous solution composed of 200 g/l of sulfuric acid and 35 g/l of hydrogen peroxide in the presence or absence of piperidine and phosphoric acid added. The copper surface after the same surface treatment as in Example 1 was evaluated. The results are shown in Table-2. Example 3 Surface-treating agents were prepared from an aqueous solution containing sulfuric acid and hydrogen peroxide in varied concentrations by adding 2 g/l of phosphoric acid and 1 g/l of piperidine. Surface treatment was carried out by the same procedures as in Example 1, and states of the oxide film on the surface and the finish were collectively evaluated. The results are shown in Table-3. Evaluation of the copper surface Good: Smooth and bright, no oxide film Fair: Somewhat inferior brightness, no oxide film Poor: Poor finish, some oxide film Example 4 A surface-treating agent was prepared from an aqueous solution composed of 200 g/l of sulfuric acid, 35 g/l of hydrogen peroxide, 2 g/l of phosphoric acid and 2 g/l of pipecoline in which 5 g/l of monobutyl cellosolve (*) was added as a stabilizer. In the solution was soaked a glass-epoxy copper-plated laminate which had been defatted at 35°C for 2 min. immediately followed by washing with water and drying. The resulting copper surface was good without oxide film formed. Without the addition of pipecoline there remained oxide film on the treated copper surface. The surfaces were subjected to electroless copper plating to 3 µ and then to copper electroplating to 35 µ, washed with water and dried. The product from the pipecoline addition was superior in adherence strength to the product treated without the pipecoline addition. Example 5 A surface-treating agent was prepared from an aqueous solution composed of 200 g/l of sulfuric acid, 35 g/l of hydrogen peroxide, 2 g/l of phosphoric acid and 2 g/l of piperidine in which 5 g/l of monobutyl cellosolve was added as a stabilizer. In the solution was soaked a glass-epoxy copper-plated laminate which had been defatted at 30°C for 1 min. immediately followed by washing with water, catalyst treatment and accelerator treatment. The surfaces were subjected to electroless copper plating to 0.3 µ and then to copper electroplating to 25 µ. The adherence was examined by the burner lignition test to find that it was equivalent to that of the product from the treatment with 150 g/l of ammonium persulfate. The formulae of exemplary piperidine derivates for use in surface-treating agents according to the invention are as follows:

Claims: A surface-treating agent for copper and copper alloy comprising an aqueous acid solution containing 100 - 500 g/l of sulfuric acid, 10 - 50 g/l of hydrogen peroxide, at least 0.5 g/l of phosphoric acid and at least 0.1 g/l of piperidine or a derivative thereof. A surface-treating agent according to Claim 1 wherein said piperidine derivative has the formula wherein Y = CH₃, CH₂OH or COOR wherein R represents hydrogen, methyl or ethyl, and n = 1 - 5. A surface-treating agent according to Claim 2 wherein n is 1 or 2. A surface-treating agent according to Claim 2 wherein said piperidine derivative is 2-pipecoline, 3-pipecoline, 4-pipecoline, 2,6-lupetidine, 3,5-lupetidine, 3-piperidinemethanol, pipecolic acid, isonipecotic acid, methyl isonipecotate or ethyl isonipecotate. A surface-treating agent according to any preceding claim wherein content of the piperidine or derivative thereof is 0.1 - 5 g/l.

Inventors: HIRAI AKIRA, ITANI KATSUTOSHI, KIMURA TOSHIYA, NAKAJIMA SHIGEKI, OHNUKI HIDEBUMI, WAKASHIMA KOICHI, HIRAI, AKIRA, ITANI, KATSUTOSHI, KIMURA, TOSHIYA, NAKAJIMA, SHIGEKI, OHNUKI, HIDEBUMI, WAKASHIMA, KOICHI
Applicants: TOKAI ELECTRO CHEMICAL CO, TOKAI DENKA KOGYO KABUSHIKI KAISHA
Application year: 1990
Main classification: C23F3
IPC codes: C23G1, H05K3, C23F1, C23F3