COPPER-CONTAINING ARTICLES WITH A CORROSION INHIBITOR COATING AND METHODS OF PRODUCING THE COATING

Abstract: Corrosion inhibition of copper-containing metals. The treatment of copper-containing bodies with 5-methyl benzimidazole yields excellent protection from oxidation and/or corrosion of the treated copper-containing body. Additionally, this treatment does not interfere with a subsequent soldering of the copper-containing body.

Description: COPPER-CONTAINING ARTICLES WITH A CORROSION INHIBITOR COATING AND METHODS OF PRODUCING THE COATING Background of the Invention 1. Field of the Invention This invention relates to corrosion inhibition of copper-containing articles. 2. Art Background Copper is a very important material for use in a vast number of applications. Not only is copper used for its aesthetic appearance in ornamental objects, but additionally the electronics industry heavily relies upon copper for its electrical conductivity properties. Whether copper is used in ornaments or in the high technology products, oxidation or corrosion of this metal seriously degrades its usefulness for the desired application. A variety of treatments have been developed to prevent oxidation and corrosion with their associated adverse effects. The difficulties in finding a suitable oxidation and corrosion inhibitor are particularly great in the electronics industry. The treatment must not * only produce effective oxidation and corrosion inhibition, but also the treatment must not interfere with subsequent fabrication procedures such as soldering of the treated copper surface. Additionally, since corrosion or oxidation severely degrades electrical properties, an effective oxidation or corrosion inhibitor must be operative over an extended period of time. Many compounds have been employed for corrosion or oxidation inhibition. For example, benzotriazole (BTA) has been used extensively in the electronics industry to produce a corrosion and oxidation—free surface that is amenable to subsequent soldering. Although BTA has been found to be quite useful, it is always desirable, if possible, to find and utilize inhibitors that have even greater lifetimes provided they also have the necessary properties for related operations such as soldering. In this regard, a variety of compounds have been tested as inhibitors. (See J. B. Cotton, Proc. 2nd International Congress of Metallic Corrosion, page 590, New York (1963), and J. B. Cotton and I. R. Scholes, British Corrosion Journal, _2, page 1 (1967).) However, despite a substantial effort, BTA is still considered the best inhibitor. Summary of the invention The treatment of copper or other metals such as copper (containing) alloys with 5-methyl benzimidazole (MBA) yields excellent oxidation and corrosion inhibition. Additionally, this treatment does not interfere with the subsequent soldering of treated copper. The results of aging tests particularly in humid environments indicate that MBA is significantly more effective than BTA. Detailed Description FIG. 1 relates to parameters utilized in the subject invention and FIG. 2 illustrates a use of the subject invention. Brief Description of the Drawing The effect of the MBA is not dependent on any particular pretreatment of the metal to be treated, e.g., the copper. However, it is generally desirable to clean the metal, e.g., copper, prior to the treatment with the MBA to allow the greatest interaction between the MBA and the copper surface. It is established from surface chemical analysis that the corrosion inhibition effect of the MBA results from a film composed of a composition produced by a chemical interaction between the MBA and the protected metal, e.g., the copper. This interaction is somewhat diminished if surface contamination is present. Conventional techniques for removing contamination, such as treatment with an organic solvent to remove oil or similar contamination, and treatment with aqueous acid solution to remove excess oxide or other inorganic contamination is O-.'PI typically employed. In a preferred embodiment, the metal is treated by immersion in a warm solution of the MBA. Although it is not essential that the solution be warmed, enhanced interaction between the MBA and the metal occurs when the temperature employed is in the range of 20 to 80 degrees C, preferably 45 to 65 degrees C. Additionally, the form of solution, i.e., aqueous or non-aqueous, is not essential. However, it is most convenient to use an aqueous solution. The concentration of the solution and the time of immersion in this solution determines the amount of MBA which reacts with and remains on the metal to inhibit corrosion and/or oxidation. It is generally desirable to form between the MBA and the metal an interaction layer which has a thickness in the range of 5 to 60nm. (Films thicker than 60nπ do not generally yield an additional amount of protection chat is needed for most applications, and thus although not precluded are not typically advantageous. Thinner layers yield shortened inhibition periods.) Generally, treatment times in the range of 0.5 to 4 minutes for solution concentrations in the range of 10~^ to 10 -1 M afford the preferred degree of interaction layer formation. After treatment, the sample is removed from the solution, rinsed in warm deionized H 2 0, and allowed to dry. If it is desired to subsequently solder a portion of the treated metal, no further processing is necessary. It is possible to solder in the normal manner directly on the treated metal. The following examples are illustrative of the use of the MBA as an inhibitor and also compare its inhibition efficacy to other inhibitors. Additionally, suitable parameters for processing copper containing metals are illustrated. Example 1_ Highly conductive (poly) crystalline copper squares (1cm x lcm) were cleaned by first degreasing with benzene. The samples were then air-dried and immersed in aqueous (50 volume percent) nitric acid for 20 seconds. After the nitric acid treatment:, the samples were thoroughly rinsed in deionized water. hile still wet from the water rinse the copper samples were immersed in a 0.02M aqueous solution which was maintained at 60 degrees C. The copper squares remained immersed for 3 minutes and stirring was maintained during the immersion period. (The samples were rinsed in 60 degrees C water after treatment.) A variety.of-compounds were used to produce the 0.02M solution and they are listed in Table I as follows: O PI " " TABLE I Name Structure Time of Initial Tarnish Benzimidazole Hours 10 Benzotriazole 15 2-Methyl Benzimidazole CII. 6 Hours TABLE I (Continued) Name Structure Time of Initial Tarnis 5,6-Dimeth.yl Benzimidazole 6 Hours lo 2,5,6-Trimethyl Benzimidazole 15 2-Phenyl Benzimidazole 20 Hours 20 Cu-O/Cu (Copper with, no ^2 Hours azole treatment) The treated samples were exposed to an environment of hydrogen sulfide gas by suspending the squares above a polysulfide reagent in a partially evacuated desiccator at 25 degrees C. (The polysulfide reagent was prepared by first making a saturated aqueous solution of sodium sulfide. An excess (more than 250g per liter) of flowers of sulfur was added to the saturated solution. After standing 24 hours, the solution was filtered and diluted with water to a specific gravity of 1.142 (at room temperature) . The samples in this environment were then periodically visually checked for the first signs of discoloration indicating tarnishing. The time when this initial tarnishing was observed for each type of copper treatment is given in Table 1. Example 2_ Optically flat copper substrates were degreased and treated as described in Example 1 with an aqueous solutions of MBA. Various temperatures and concentrations of the aqueous solution containing the MBA were employed. The thickness of the resulting film produced on the copper samples for a given immersion time in the solution was monitored using an ellipsometer to measure thickness. The results obtained are shown in FIG. 1. Example 3_ A phosphor bronze copper alloy (Copper Development Association No. 510) lead obtained from North American Specialty Company, Flushing, New York was treated with a 0.02M MBA solution for 0.5 minutes at 25 degrees C. (The shape of this lead, 20, which contains a solder slug, 22, is shown in FIG. 2.) The lead, 20 was then soldered to a printed circuit board, 24, by condensation soldering. [A description of condensation soldering is found in G. M. Wengen and R. L. Mahajan, Insulation/Circuits, 25, page 133 (1979)]. The same procedure was followed with a lead that had not been treated with the MBA solution. The untreated lead showed patches where the soldering did not adhere. The treated lead was uniformly coated with the solder.

Claims: AMENDED CLAIMS (received by the International Bureau on 22 December 1982 (22.12.82)) " " 1. (Amended) An article comprising of copper- containing metal having thereon a protective coating of an oxidation inhibitor comprising 5-methyl benzimidazole, 5 CHARACTERIZED IN THAT said protective coating is at least 5nm in thickness. 2. An article according to claim 1, CHARACTERIZED IN THAT 10 the protective coatinσ ranges from 5 to 60nm in thickness. 3. (Amended) The process for protecting a copper- containing metal against corrosion, which comprises contacting said metal with a solution of an oxidation 15 inhibitor containing 5-methyl benzimidazole to form a protective coatinq, CHARACTERIZED BY forming said protective coating in a thickness of at least 5nm. 20 4. The process according to claim 3, CHARACTERIZED BY forming a film of the inhibitor in a thickness ranging from 5 to 60 nπi. 5. The process according to claim 3, 25 CHARACTERIZED BY producing said coating by treating said metal with an aqueous solution of 5-methyl benzimidazole. 6. The process according to claim 5, CHARACTERIZED BY 30 the aqueous solution being at a temperature ranging from 20 to 80 degrees C. 7. The process according to claim 6 , CHARACTERIZED IN THAT said temperature ranges from 45 to 65 degrees C. 35 8. The process according to claim 3, CHARACTERIZED IN THAT said metal comprises a copper alloy.

Inventors: HOBBINS NORRIS DALE, ROBERTS RONALD FREDERICK, HOBBINS, NORRIS, DALE, ROBERTS, RONALD, FREDERICK
Applicants: WESTERN ELECTRIC CO, WESTERN ELECTRIC COMPANY, INC.
Application year: 1982
Main classification: C23F11
IPC codes: C23F11, H05K3