Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal coating
Reexamination Certificate
2001-09-05
2004-11-02
Wong, Edna (Department: 1753)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal coating
C205S196000, C106S001210, C106S001280
Reexamination Certificate
active
06811674
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a palladium plating solution for electroplating. More particularly, the present invention relates to a palladium plating solution which can form a plated surface having good adhesion to resin.
2. Background Art
Palladium plating solutions have hitherto been put to practical use in plating of electrical and electronic components. In recent years, the use of palladium plating solutions is also desired in the field of lead frames. Semiconductor devices using lead frames are generally produced by mounting a semiconductor chip on a lead frame, wire bonding the semiconductor chip in its electrode to the lead frame in its inner lead, covering the circumference of the semiconductor and the wire bonded portion by mold resin, and then cutting off the outer frame of the lead frame. In this case, the front end of the inner lead is previously plated with silver for good wire bonding purposes. Further, the surface of the outer lead is solder plated after the construction of the semiconductor device.
Since, however, solder contains lead, there is a fear of posing problems including the influence of the solder on environment. For this reason, the use of palladium plating as an alternative to solder plating for outer leads of lead frames has drawn attention. Further, the use of palladium plating as an alternative to silver plating for inner leads has also drawn attention.
When palladium plating solutions are used in lead frame applications, in general, excellent adhesion to mold resin, wettability by solder after heat history, ductility, wire bondability, reliability in solder joining, migration resistance, corrosion resistance, and other properties are required of plating solutions.
In particular, when palladium plating solutions are used in lead frame applications, the adhesion to mold resin is important. For this reason, improving the adhesion of palladium plating solutions to mold resin has been desired.
Regarding means for improving the adhesion between palladium plating formed using a palladium plating solution (that is, plated surface) and mold resin, for example, Japanese Patent Laid-Open No. 077594/2000 discloses a method wherein a lead frame material is etched with an acid to form suitable concaves and convexes on the surface of a nickel plating as a substrate, whereby the adhesion between the palladium plating and the mold resin is enhanced by anchor effect attained by the concaves and convexes on the surface of the nickel plating. In this method, however, in addition to the step of plating, the step of previously performing etching should be provided. Therefore, this method is also unsatisfactory from the viewpoints of troublesome treatment and treatment cost. Further, when applications other than lead frames are taken into consideration, roughening of the surface by etching is not always favorable.
On the other hand, unlike plating using palladium plating solutions, regarding plating using copper plating solutions, for example, Japanese Patent Laid-Open No. 096284/2000 discloses that the precipitation of acicular crystal on the surface of plating can improve the adhesion of the plating to resin. So far as the present inventor know, however, the formation of acicular crystals on the surface of a plating in palladium plating has not been reported. Copper plating and palladium plating are utterly different from each other in properties, plating conditions, and mode of use.
SUMMARY OF THE INVENTION
The present inventor have found that, when a palladium plating solution comprising at least a specific amount of a soluble palladium salt and a specific amount of sulfamic acid or its salt and substantially free from a brightening agent is prepared and is used for palladium plating, a palladium plating having an acicular crystal on its surface can be formed. The present invention has been made based on such finding.
Accordingly, it is an object of the present invention to provide a palladium plating solution that can form a palladium plating having on its surface an acicular crystal which has excellent adhesion to resin.
According to one aspect of the present invention, there is provided a palladium plating solution comprising at least 1 to 60 g/L, in terms of the amount of palladium, of a soluble palladium salt and 0.1 to 300 g/L of a sulfamic acid or its salt, said palladium plating solution being substantially free from a brightening agent.
According to another aspect of the present invention, there is provided a method for palladium plating, comprising the steps of: providing a plating bath using the above palladium plating solution; and then electroplating a substrate in the plating bath under conditions of bath temperature 30 to 70° C. and cathode current density 0.2 to 20 A/dm
2
to form, on the substrate, a plating having on its surface an acicular crystal.
According to a further aspect of the present invention, there is provided a palladium-plated product produced by electroplating a substrate using the above palladium plating solution.
Plating treatment using the palladium plating solution according to the present invention can form a plating having on its surface an acicular crystal. The formation of this plating can be expected to offer anchor effect. Therefore, the plating has better adhesion to resin than a plating having a glossy surface. In this case, in general, the appearance of the plating is substantially dull because the acicular crystal microscopically constitutes the surface of the plating. Further, plated products produced by a combination of the formed plating with resin have good adhesion between the plating and the resin and thus can maintain stable properties for a long period of time. Further, the palladium plating solution according to the present invention has excellent service life and good current efficiency. Therefore, the palladium plating solution according to the present invention can be suitably used as a plating solution for lead frames.
DETAILED DESCRIPTION OF THE INVENTION
Palladium Plating Solution
The palladium plating solution according to the present invention comprises at least a specific amount of a soluble palladium salt and a specific amount of sulfamic acid or its salt and is substantially free from a brightening agent. The palladium plating solution is generally used in electroplating.
Here “brightening agent” refers to an additive, which is added to plating solutions, for imparting a gloss to the plated face. In general, the brightening agent refers to inorganic and organic additives which can level the surface of a plating. The brightening agent referred to herein is any brightening agent commonly used in the art, and examples thereof include: the so-called primary brightening agents, such as saccharin, sodium benzenesulfonate, benzenesulfonamide, phenolsulfonic acid, and methylenebis(naphthalene)sulfonic acid; and the so-called secondary brightening agents, such as 2-butyne-1,4-diol, benzaldehyde-O-sodium sulfonate, 2-butene-1,4-diol, and allyl sulfonate.
By virtue of a specific composition, the plating solution according to the present invention can form a plating having on its surface an acicular crystal, and the presence of the acicular crystal on the surface of the plating renders the appearance of the plating substantially dull. Therefore, that the plating solution is substantially free from a brightening agent is considered advantageous in the formation of a dull surface, i.e., a surface constituted by an acicular crystal. Accordingly, the plating solution according to the present invention is also characterized in that the plating solution is substantially free from a brightening agent. Here “substantially free from a brightening agent” of course embraces that the plating solution does not contain the above brightening agent, and also embraces that the plating solution contains the brightening agent in such an amount that cannot function as a brightening agent.
Preferably, the palladium plating solution according to the present invention furthe
Ladas & Parry
Matsuda Sangyo Co., Ltd.
Wong Edna
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