Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
1998-12-07
2001-02-27
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S321200, C361S321500
Reexamination Certificate
active
06195248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic component having a tin alloy plating film, and more particularly to an electronic component having a lead-free tin alloy plating film.
2. Description of the Related Art
Tin alloy plating films have been used in various electronic components.
FIG. 1
shows a conventional laminated ceramic capacitor
5
as one example of such electronic components. The laminated ceramic capacitor
5
comprises a laminated ceramic body
3
in which dielectric layers
1
and internal electrodes
2
are alternately stacked and a pair of external electrodes
4
are electrically connected to the internal electrodes
2
. Each of the external electrodes
4
includes a Ag electrode
4
a
as a foundation layer, a Ni electrode
4
b
provided on Ag electrode
4
a
as an intermediate layer and a Sn electrode or a Sn—Pb alloy electrode
4
c
provided on the Ni electrode
4
b
as an outermost layer.
The Ag electrode
4
a
is formed for electrical connection to an internal electrode, and the Ni electrode
4
b
is formed to prevent corroding of the Ag at the time of soldering or the generation of whiskers. The Sn electrode or Sn—Pb alloy electrode
4
c
is formed in order to promote the wettability of solder at the time of soldering.
The conventional electronic components represented by the laminated ceramic capacitor
5
have the following problems when the Sn electrode or Sn—Pb alloy electrode is formed. Sn plating films are likely to generate whiskers. On the other hand, the Sn—Pb alloy electrode includes Pb which is a regulated substance, and is therefore necessary to be replaced in view of environmental problems.
In addition, when the Sn or Sn—Pb alloy outermost electrode is formed by electrolytic plating the Ni electrode is usually formed in advance by electrolytic plating. However, the Ni plating liquid sometimes contaminates the Sn or Sn—Pb plating bath adversely. This results in degradation of the adhesive strength of the plating film and the poor quality of the obtained plating film.
In order to solve this problem, it is necessary to perform a cleaning process after the Ni plating process, thereby preventing residual Ni plating liquid from being brought into the plating bath of the Sn or Sn—Pb. In addition to this countermeasure, it might be necessary to renew the plating bath of Sn or Sn—Pb more frequently based on the number of uses of the plating bath. As a result, the number of process steps and production controls are increased. This results in an increase of the production cost.
For the forgoing reasons, there is a need for an electronic components having a plating film which includes no Pb, causes no whiskers and prevents corrosion of Ag at the time of soldering, as well as promotes wettability of solder.
SUMMARY OF THE INVENTION
The present invention is directed to an electronic component that satisfies the aforementioned need. The electronic component comprises: a body; a metal film formed on the body; and a tin alloy plating film formed on the metal film, where the tin alloy plating film comprises Sn and one or more additive metal selected from the group consisting of Bi, Ni, Ag, Zn and Co.
The metal film preferably comprises one of Ag and Cu. The content ratio of the additive metal is preferably within the range of about 0.5 to 20 wt %.
The additive metal may be Bi. In this case, the content ratio of Bi is preferably within the range of about 1 to 20 wt % and more preferably within the range of about 5 to 20 wt %.
The additive metal may be Ni. In this case, the content ratio of Ni is preferably within the range of about 0.5 to 10 wt %, and more preferably within the range of about 1 to 2 wt %.
The additive metal may be Ag. Here, the content ratio of Ag is preferably within the range of about 1 to 20 wt %, and more preferably within the range of about 5 to 10 wt %.
The additive metal may be Zn and the content ratio of Zn is preferably within the range of about 1 to 20 wt %, and more preferably within the range of about 5 to 8 wt %.
The additive metal may be Co. In this case, the content ratio of Co is preferably within the range of about 0.5 to 10 wt %, and more preferably within the range of about 1 to 2 wt %.
The body is preferably made of dielectric ceramic, piezoelectric ceramic, semiconductor ceramic, magnetic ceramic and insulating ceramic. The body may include a plurality of ceramic layers made of the selected material and a plurality of internal electrodes alternately stacked with each other and the metal film is electrically connected to the internal electrodes.
According to the present invention, there is provided an electronic component comprising a lead-free tin alloy plating film which prevents generation of whiskers and silver corrosion as well as maintaining a wettability in the solder of conventional Sn plating or Sn—Pb alloy plating. The lead-free tin alloy plating film further makes a Ni electrode interface layer unnecessary.
Therefore, no cleaning process is necessary before forming the tin alloy plating film, and the life time of the tin alloy plating bath also can be prolonged. Accordingly, the production cost of the electronic components can be reduced and the through put can be increased.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
REFERENCES:
patent: 4618912 (1986-10-01), Sakabe et al.
patent: 5347423 (1994-09-01), deNeuf et al.
patent: 5426560 (1995-06-01), Amaya et al.
patent: 5852542 (1998-12-01), Wada et al.
patent: 5995360 (1999-11-01), Hata et al.
patent: 6008981 (1999-12-01), Harada et al.
Endo Masanori
Fujii Yukiko
Kunishi Tatsuo
Tokuda Yu
Dinkins Anthony
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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