Selectively plating apparatus for forming an annular coated area

The invention involves a selectively plating apparatus for forming an annular area. The apparatus is particularly characterized by including the inner and outer mask members which cooperate to define the annular areas to be coated. It enables the automatic operation for forming the annular coated areas and is very effective for the mass production of, for example, lead frames.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a selectively plating apparatus for forming an 
annular coated area. 
2. Description of the Prior Art 
FIG. 1 shows a lead frame. It is only the free ends b of inner leads a and 
islands c that are plated with gold, silver, etc. A known apparatus for 
the partial plating of those portions includes a mask member 21 having an 
opening 21a so sized as to enclose each group of the ends b of inner leads 
a and the corresponding island c and a mask support 22 having a hole 22a 
aligned with the opening 21a of the mask 21. The apparatus is shown in 
FIG. 2. When a lead frame 23 is plated, it is placed on the mask 21 so 
that the ends b of the inner leads a and the island c may be aligned with 
the opening 21a. A plating solution is received under pressure from a pump 
and jetted out through a pressure vessel 27 and a nozzle 24 against the 
lead frame 23 which is held against the mask member 21 by a pressing plate 
26. A sheet of rubber 25 is disposed between the lead frame 23 and the 
pressing plate 26. The pressure vessel 27 is used for supplying the 
plating solution uniformly to the area to be plated. An anode is connected 
to the plating solution, and a cathode to the lead frame, though they are 
not shown. 
If the lead frame is of the type in which an IC element is bonded by an 
adhesive, however, no plating is required for the island c, but it is 
sufficient to form an annular coated area around the island c, i.e., only 
the ends b of the inner leads a which are required for wire bonding. Such 
a lead frame can be plated by the apparatus of FIG. 2 if the island c on 
which an IC element is mounted is masked. This, however, presents a great 
deal of difficulty especially when a large number of lead frames must be 
plated on a mass production basis. Moreover, it is highly desirable to 
plate only the ends of the inner leads in order to save gold and silver. 
SUMMARY OF THE INVENTION 
Under these circumstances, it is an object of this invention to provide an 
annularly plating apparatus which is suitable for automatic operation and 
thereby enables mass production. 
This object is attained by an apparatus which comprises a pressure vessel 
for supplying a plating solution under pressure uniformly from a pump to 
the material to be coated, a member for supporting the pressure vessel, 
the member having an opening, a baffle provided in the opening of the 
supporting member for maintaining the uniform supply of the plating 
solution up the opening, an upper member mounted on the pressure vessel 
supporting member and having a hole for supplying the plating solution and 
a plurality of holes for discharging the plating solution, the upper 
member being adapted to position an insoluble anode in a location suitable 
for plating the material to be coated, a mask supporting member mounted on 
the upper member and having a substantially annular array of slits for 
jetting out the plating solution, a groove for causing the plating 
solution to flow substantially radially outwardly from the slits and a 
plurality of holes for discharging the plating solution, an outer mask 
member provided on the mask supporting member and defining the outer 
contour of the substantially annular area to be coated, and a plurality of 
inner mask members provided on the mask supporting member and each 
defining the inner contour of the substantially annular area to be coated. 
The material to be plated, e.g a lead frame, is positioned on the inner and 
outer mask members and a pressing plate having a bottom lined with rubber 
is placed on the lead frame to hold it against the mask members. The pump 
is driven to supply the plating solution through the pressure vessel and 
its supporting member and an electric current is supplied across the anode 
and a cathode, which is defined by the lead frame. This invention does not 
require any additional masking of the islands on which the IC elements are 
mounted, but enables the mass production of lead frames having annularly 
coated areas. The plating solution which has impinged against the lead 
frame is returned through the groove and the holes into its reservoir. 
The apparatus of this invention is particularly characterized by including 
the inner and outer mask members which cooperate to define the annular 
areas to be coated. It enables the automatic operation for forming the 
annular coated areas and is very effective for the mass production of, for 
example, lead frames.

DETAILED DESCRIPTION OF THE INVENTION 
An annular partial plating apparatus embodying this invention is shown in 
FIGS. 3 to 5. It includes an outer mask member 1 formed from silicone 
rubber and containing a reinforcing core 1.sub.1. It also includes a 
plurality of inner mask members 2 each formed from silicone rubber, 
containing a reinforcing core 2.sub.1, and having a plurality of 
positioning pins 2.sub.2, as shown in FIGS. 6(A) and 6(B). The reinforcing 
core 2.sub.1 has a threaded hole 2.sub.3 in which a screw is received for 
securing the inner mask member 2 to a mask supporting member 3. The pins 
2.sub.2 are aligned with positioning holes 4 (FIG. 4). The outer mask 
member 1 and each inner mask member 2 define therebetween a substantially 
annular opening 2' in which the ends b of the inner leads of a lead frame 
(FIG. 1) can be located. The mask members 1 and 2 are supported on the 
mask supporting member 3. The mask supporting member 3 has a plurality of 
slits 5 disposed in a substantially annular array along each opening 2' 
for supplying a plating solution thereinto, a groove 6 for causing the 
plating solution to flow substantially radially outwardly from each slit 5 
and a plurality of holes 7 for discharging the plating solution from the 
groove 6. The positioning holes 4 are provided in the mask supporting 
member 3 for positioning each inner mask member 2. The mask supporting 
member 3 also has a plurality of holes 8 each receiving the screw for 
securing one of the inner mask members 2. An upper member 9 is disposed 
under the mask supporting member 3. The upper member 9 has a plurality of 
holes 10 for supplying the plating solution into the slits 5 and a 
plurality of holes 11 for discharging the plating solution from the 
discharge holes 7 of the mask supporting member 3. 
The upper member 9 also has a groove 13 in the form of a grid. An insoluble 
anode 12 in the form of a wire, e.g. of platinum, is provided in the 
groove 13 under each slit 5 so that it may face the area of the lead frame 
to be plated. The anode wire 12 extends along all of the slits 5 to ensure 
the formation of an annularly coated area having a uniform coating 
thickness. The upper member 9 is supported on a supporting member 14 
having an opening 15 for supplying the plating solution to the slits 5 and 
provided with a baffle 16 for maintaining the uniform supply of the 
solution through the opening 15. A pressure vessel 17 is disposed under 
the supporting member 14 for supplying the plating solution at a uniform 
pressure from a pump to the material to be coated. 
The lead frame 18 to be plated is positioned on the outer and inner mask 
members 1 and 2 and a pressing plate 20 having a bottom lined with a sheet 
of rubber 19 is placed on the lead frame 18 to press it against the mask 
members 1 and 2, as shown in FIG. 5. The plating solution is supplied by 
the pump into the hole 10 of the upper member 9 and an electric current is 
applied across the anode wire 12 and the lead frame 18 which defines a 
cathode. The solution which has impinged against the lead frame 18 is 
returned through the groove 6 and the holes 7 and 11 into its reservoir 
not shown. It is not necessary to provide any special mask for the islands 
each time the plating operation is performed, since the islands on which 
the IC elements are mounted are automatically masked by the inner mask 
members 2. 
In the apparatus as hereinabove described, the platinum wire 12 defining an 
insoluble anode is disposed in the groove 13 of the upper member 9 below 
the slits 5. The lead frames 18 are, however, available in a wide variety 
of designs which differ to some extent from one another in the number of 
the lead frames to be produced from one sheet, the dimensions of the 
islands and the dimensions of the area to be plated. Therefore, it has 
been necessary to prepare a combination of the mask members 1 and 2, the 
mask supporting member 3 and the upper member 9 for each lead frame 
design. If the mask members 1 and 2 are bonded to the supporting member 3 
to form an integral mask combination, it is necessary to prepare any such 
mask combination for each lead frame design. It is, however, not always 
necessary to provide any upper member 9 for each such mask combination. 
Therefore, if the upper member 9 is of the type which can be used for all 
the mask combinations, it is advantageously possible to reduce the number 
of the parts which must be kept in stock, and thereby the cost thereof. An 
embodiment of this invention which is based on this concept is shown in 
FIGS. 7(A) and 7(B). 
The apparatus shown in FIGS. 7(A) and 7(B) includes an upper member 9 
having a hole 10 for supplying a plating solution below the slits 5, and 
provided with a shoulder at the upper end of the hole 10. An insoluble 
anode plate 21 is supported on the shoulder and has a plurality of 
apertures 22 each located below one of the openings 2' between the mask 
members 1 and 2. The anode plate 21 is easy to position or remove. It is 
sufficient to change the anode plate 21 to one which suits the lead frame 
18 to be plated. There is no necessity of changing the upper member 9 as a 
whole. 
The anode plate 21 is preferably formed from platinum or a platinum alloy, 
as platinum or a platinum alloy is easy to work. The holes 22 of the anode 
plate 21 need be sufficiently large to enable the appropriate supply of 
the plating solution to the slits 5. If they are too large, however, they 
present difficulty in the application of an electric current. Therefore, 
it is appropriate to select the shape and size of the holes 22 which suit 
the outer periphery of the slits 5. 
Each inner mask member 2 is in the form of a square of which each side has 
a length of only about 5 to 10 mm. The inner mask members 2 are elastic. 
Therefore, the bonding of each inner mask member 2 in its right position 
is a very difficult job and requires a jig which is not easy to prepare. 
If there is any inner mask member 2 that has not been correctly 
positioned, the opening or clearance between the inner mask member 2 and 
the outer mask member 1 lacks uniformity in width. As a result, it is 
likely that the end of one or more inner leads may be partly masked, or 
that the plating solution may fail to be supplied uniformly and not be 
able to form a coated film having a uniform thickness. 
A modified inner mask member is, therefore, shown in FIGS. 8(A) to 8(C). 
The inner mask member 23 comprises an elastic body, such as of silicone 
rubber, covering a core 24. The core 24 has a threaded hole 25 in which a 
screw 27 can be threadedly engaged for securing the inner mask member 23 
to a mask supporting member 3, as shown in FIG. 8(C). The inner mask 
member 23 is easy to produce if the core 24 in which the screw 27 is 
engaged is placed in a mold, and if silicone rubber, for example, is 
poured into the mold and solidified. The inner mask member 23 has a 
rectangular projection 26 at its bottom, as shown in FIG. 8(B), while the 
mask supporting member 3 has a recess in which the projection 26 can be 
fitted. The projection 26 and the recess facilitate the correct 
positioning of the inner mask member 23 as shown in FIG. 8(A). The 
projection 26 may be of any other shape if it prevents the rotation of the 
mask member 23. The mask supporting member 3 has a hole 3a through which 
the screw 27 extends into the threaded hole 25 of the core 24 to hold the 
core 24 against the mask supporting member 3 to secure the inner mask 
member 23 in position.