Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly alloy coating
Reexamination Certificate
1999-11-04
2003-01-21
Nguyen, Nam (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly alloy coating
C205S253000, C205S254000
Reexamination Certificate
active
06508927
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tin-copper alloy electroplating bath and a plating process therewith, the tin-copper alloy electroplating being useful as a substitute for tin-lead alloy (solder) plating.
2. Description of the Related Arts
It has been common practice to perform tin plating or tin-lead alloy plating, prior to soldering, on such parts of electronic machines and equipment as chips, quartz crystal oscillators, bumps, connector pins, lead frames, hoops, lead pins of packages, and printed circuit boards.
In the production of printed circuit boards, tin plating or tin-lead alloy plating film has been widely used as an etching resist film.
Stricter regulations are being enforced which restrict the use of lead for environmental protection. This has aroused a demand for lead-free plating baths which will supersede tin-lead alloy plating baths. This demand is not met by simple tin plating baths because tin deposit would deteriorate in solderability and would cause crystalline whiskers to occur in the plating film.
Attempts have been made to develop new kinds of plating with a tin alloy.
Tin-copper alloy plating is attracting attention. The conventional tin-copper alloy plating baths deposit a tin-copper alloy containing copper more than 50 wt %. The plating bath for tin-copper alloy is a strong alkaline bath which uses alkali cyanide or alkali pyrophosphate as a complexing agent, or a simple bath which is based on sulfuric acid and contains no complexing agent. The former is disclosed in Japanese Patent Laid-open No. 27590/1996. These plating baths, however, do not serve as a substitute for tin plating baths or tin-lead alloy plating baths applied to electronic parts and printed circuit boards. This is because they do not form tin-copper alloy plating film containing 0.01-10 wt % of copper required when applied to electronic parts and printed circuit boards. In addition, the plating bath should be neutral or acidic if it is to be applied to printed circuit boards or the like covered with an organic resist film which is liable to peel off in an alkaline plating bath. Although simple baths based on sulfuric acid are strongly acidic, they have the disadvantage of causing soluble tin or tin-copper alloy anodes to liberate tin from their surface and deposit copper on their surface when not energized. This makes it difficult to control the plating bath adequately. In addition, these plating baths readily precipitate tin compounds and hence lack long-term stability.
SUMMARY OF THE INVENTION
The present invention was completed in view of the foregoing. It is an object of the present invention to provide a tin-copper alloy electroplating bath as a substitute for the conventional tin-lead alloy plating bath. This tin-copper alloy electroplating bath imparts good solderability to various parts to be soldered or forms plating film of tin-copper alloy which serves as an etching resist. It is another object of the present invention to provide a process for plating with the tin-copper alloy electroplating bath.
The tin-copper alloy electroplating bath of the first aspect of the present invention comprises a water-soluble tin salt, a water-soluble copper salt, an inorganic or organic acid or a water-soluble salt thereof, and one or more compounds selected from thioamide compounds and thiol compounds.
The tin-copper alloy electroplating bath of the second aspect of the present invention comprises a water-soluble tin salt, a water-soluble copper salt, one or more compounds selected from carboxylic acids, lactone compounds, condensed phosphoric acids, phosphonic acids and water-soluble salts thereof, one or more compounds selected from thioamide compounds and thiol compounds, and an inorganic or organic acid or a water-soluble salt thereof other than carboxylic acids, lactone compounds, condensed phosphoric acids, phosphonic acids and water-soluble salts thereof.
The tin-copper alloy electroplating bath of the present invention gives plating film as a substitute for tin or tin-lead alloy plating film which is used for soldering or as an etching resist. It can be applied to any parts constituting electronic machines and equipment, such as chips, quartz crystal oscillators, bumps, connector pins, lead frames, hoops, lead pins of packages, and printed circuit boards, which need lead-free soldering.
The tin-copper alloy electroplating bath of the present invention permits a broad range of cathode current density and gives satisfactory plating film of tin-copper alloy when used in barrel plating, rack plating, or rackless plating (jet or flow high-speed plating). It can be applied to electronic parts made up of conducting materials having insulating materials such as ceramics, lead glass, plastics and ferrite incorporated therein without adverse effect such as corrosion, deformation, and degradation on insulating materials. It does not cause displacement deposition or precede deposition of copper to occur on the soluble anode of tin or tin-copper alloy or on the plating film. This is advantageous to plating operation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be described in more detail in the following.
According to the present invention, the tin-copper alloy electroplating bath contains a water-soluble tin salt, a water-soluble copper salt, an inorganic or organic acid or a water-soluble salt thereof, and one or more compounds selected from thioamide compounds and thiol compounds.
The tin salt may be either stannous salt or stannic salt. The stannous salt [Sn (II) salt] includes, for example, stannous organosulfonate (such as stannous methanesulfonate), stannous sulfate, stannous chloride, stannous bromide, stannous iodide, stannous oxide, stannous phosphate, stannous pyrophosphate, stannous acetate, stannous citrate, stannous gluconate, stannous tartrate, stannous lactate, stannous succinate, stannous sulfamate, stannous borofluoride, stannous formate, and stannous silicofluoride. The stannic salt [Sn (IV) salt] includes, for example, sodium stannate and potassium stannate.
The copper salt may be either cuprous salt or cupric salt. The cuprous salt [copper (I) salt] includes, for example, cuprous oxide, cuprous cyanide, cuprous chloride, cuprous bromide, cuprous iodide and cuprous thiocyanate. The cupric salt [copper (II) salt] includes, for example, cupric organosulfonate (such as cupric methanesulfonate), cupric sulfate, cupric chloride, cupric bromide, cupric iodide, cupric oxide, cupric phosphate, cupric pyrophosphate, cupric acetate, cupric citrate, cupric gluconate, cupric tartrate, cupric lactate, cupric succinate, cupric sulfamate, cupric borofluoride, cupric formate, and cupric silicofluoride.
The content of tin salt in the plating bath should preferably be 1-99 g/L, particularly 5-59 g/L in terms of tin, and the content of copper salt in the plating bath should preferably be 0.001-99 g/L, particularly 0.01-54 g/L in terms of copper. For obtaining a tin-copper alloy deposit containing 0.01-30 wt % of copper, the content of tin salt should preferably be 1-99 g/L, particularly 5-59 g/L in terms of tin and the content of copper salt should preferably be 0.001-30 g/L, particularly 0.01-18 g/L in terms of copper.
Examples of the inorganic or organic acid include sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, fluoroboric acid, phosphoric acid, sulfamic acid, sulfonic acid such as aliphatic sulfonic acid and aromatic sulfonic acid, carboxylic acid such as aliphatic saturated carboxylic acid, aromatic carboxylic acid, and aminocarboxylic acid, condensed phosphoric acid and phosphonic acid.
Examples of the aliphatic or aromatic sulfonic acid include substituted or unsubstituted alkanesulfonic acid, hydroxyalkanesulfonic acid, benzenesulfonic acid, and naphthalenesulfonic acid. The unsubstituted alkanesulfonic acid may be one which is represented by C
n
H
2n+1
SO
3
H (where n is 1-5, preferably 1 or 2).
The unsubstituted hydroxyalkanesulfonic acid may be
Oka Teruya
Okada Tetsurou
Tsubokura Hideyuki
Tsujimoto Masanobu
Yanada Isamu
C. Uyemura & Co., Ltd.
Nguyen Nam
Nicolas Wesley A.
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