Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1999-03-25
2001-04-03
Valentine, Donald R. (Department: 1741)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S275100
Reexamination Certificate
active
06210548
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for removing Au or Ag plating films deposited on the surface of an area for which plating is not necessary, from a leadframe depositing the plating films.
2. Description of Related Art
As one of systems for mounting semiconductor chips on a leadframe, a so-called wire bonding system is known in which each of the semiconductor chips is bonded to each of the die pads of the leadframe and is connected by bonding wires with the tips of inner leads.
An example of the leadframe used in this system is shown in
FIGS. 1A and 1B
. In order to facilitate a bonding with the bonding wires and improve its reliability, a leadframe
1
, as shown in
FIG. 1A
, has plating films
2
of precious metal, such as Au or Ag, deposited on the surfaces of parts (indicated by hatching), such as a die pad
1
a
and the tips of inner leads
1
b
, for which plating is necessary. If the deposition of the plating films is extended unnecessarily, a greater amount of precious metal, such as Au or Ag, than is necessary will be used, and thus cost is raised. Moreover, if the Au or Ag plating films protrude from a mold area (an area in which an IC is covered with resin), the effect of the hermetical seal of molding will be lost or molding resin will be peeled off. This causes various obstacles to a semiconductor mounting process. Consequently, all the products depositing the plating films outside areas for which plating is necessary are treated as rejects. In this way, when the plating films are deposited outside the areas for which plating is necessary, production efficiency is impaired. The positioning accuracy of the plating films is thus important in plating the leadframe.
In general, the plating films are deposited in such a way that, for example, a rubber pad is pressed against the surface of the area of the leadframe for which plating is not necessary and an Au or Ag plating liquid is sprayed on the leadframe. In this case, the plating liquid penetrates into clearance between the rubber pad and the leadframe, and films may be deposited by the plating liquid on the surface of the area for which plating is not necessary. The plating films deposited on the surface of this area are less in thickness than those deposited on the surface of an area for which plating is necessary.
Thus, as shown in
FIG. 1B
, when the Au or Ag plating films
2
are also deposited on the surface of an area A of the leadframe
1
for which plating is not necessary, an apparatus for removing films, such as that shown in
FIG. 2
, is used to eliminate unwanted plating films. Specifically, the leadframe
1
is passed between insoluble anode rollers R so as to function as anodes, and an insoluble cathode plate P is used for electrolysis through a film removing liquid L such as a cyanic solution.
This electrolytic treatment is carried out in accordance with the thicknesses of the plating films deposited on the surface of the area for which plating is not necessary, over the entire surface including the area for which plating, such as Au or Ag, is necessary, so that the plating films are dissolved and removed.
With such a technique of removing the plating films, however, the plating films in the area for which plating is necessary are removed by a predetermined thickness, and thus the thicknesses of the Au or Ag plating films themselves must be previously increased. Consequently, time required for plating is extended unnecessarily and production efficiency is impaired accordingly, with a resulting increase in cost.
Furthermore, the use of this technique shows a tendency that the plating films deposited inside the area for which plating is necessary are excessively removed or the plating films outside this area cannot be completely removed. In this way, it is very difficult and cumbersome to adjust only necessary plating films to desired thicknesses so that they are kept constant.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an apparatus for partially removing plating films of a leadframe which is capable of easily removing the plating films deposited outside an area for which plating is necessary, without readjusting the thicknesses of plating films deposited inside this area, and is also capable of improving the entire work efficiency of plating treatment of the leadframe and of reducing cost.
In order to achieve this object, the apparatus for partially removing plating films of a leadframe according to the present invention includes a mask member having annular openings configured to coincide with the predetermined areas of the leadframe for which plating films are not required; a mask supporting means having outflow channels communicating with the annular openings to introduce a film removing liquid outside the annular openings, film removing liquid outflow holes communicating with the outflow channels to introduce the film removing liquid downwardly, film removing liquid inflow channels for feeding the film removing liquid to the annular openings, and an insoluble cathode wire housing groove for incorporating an insoluble cathode wire therein, communicating with the film removing liquid inflow channels; a mechanism for supplying a power to continuously run the insoluble cathode wire; and a mechanism for masking and dismasking the upper surface of the leadframe placed at a predetermined position of the mask supporting member.
More specifically, the apparatus of the present Invention Includes a mask member having annular openings configured to coincide with the predetermined areas of the leadframe for which plating films are not required; a mask supporting member provided with guide grooves communicating with the annular openings to introduce a film removing liquid outside the annular openings, first film removing liquid outflow holes communicating with both sides of each of the guide grooves to Introduce the film removing liquid downwardly, and a first opening communicating with the first film removing liquid outflow holes and with fine groves extending outside the first film removing liquid outflow holes and the guide grooves; a first lower member placed beneath the mask supporting member to configure the outflow channels of the film removing liquid on the upper surface thereof, in association with the fine grooves of the mask supporting member, having a wire housing groove for incorporating an insoluble cathode wire therein, communicating with the first opening of the mask supporting member, a first film removing liquid jet hole of slit shape, communicating with the wire housing groove, and second film removing liquid outflow holes communicating with the outflow channels of the film removing liquid, introducing the film removing liquid downwardly; a second lower member having a second opening communicating with the first film removing liquid Jet hole and third film removing liquid outflow holes communicating with the second film removing liquid outflow holes, introducing the film removing liquid downwardly; a third lower member having a third opening communicating with the second opening, second film removing liquid Jet holes staggered, communicating with the third opening, and fourth film removing liquid outflow holes communicating with the third film removing liquid outflow holes, introducing the film removing liquid downwardly; a mechanism for supplying a power to continuously run the insoluble cathode wire; and a mechanism for masking and dismasking the upper surface of the leadframe placed at a predetermined position of the mask supporting member, with a rubber part constructed to coincide with each of predetermined areas in which plating films are required, by actuating a cylinder vertically.
This and other objects as well as the features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiment when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4110190 (1978-08-01), Visser
patent: 4202739 (19
Kobayashi Takashi
Maetani Kazuo
Wada Keisuke
Fish & Richardson P.C.
Sumitomo Metal & Mining Co., Ltd.
Valentine Donald R.
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