Process for manufacturing a multi-layer lead frame having a ground plane and a power supply plane

A process for manufacturing a multi-layer semiconductor lead frame comprising the step of adhering a lead frame strip to a metal power supply plane strip and a metal ground plane strip.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a lead frame, more particularly to a multi-layer 
lead frame having at least one metal plate or plane, hereinafter referred 
to as "metal plane" which is used for a semiconductor device. This 
invention also relates to a process for manufacturing such a multi-layer 
lead frame. 
2. Related Art 
A plastic package, whose speed and heat-radiation characteristics are as 
good as those of a ceramic package, has recently been developed. In 
addition, in place of a conventional single-layer lead frame, a 
multi-layer plastic lead frame for a semiconductor device has also been 
developed. 
Such a multi-layer lead frame comprises at least one metal plane connected 
via an insulative layer to the bottom surfaces of inner leads. Using such 
a multi-layer lead frame, it will be possible to mount a relatively 
power-consumable semiconductor chip on the metal plane, due to a good heat 
radiation capacity of the metal plane. Also, the metal plane can be used 
as a ground layer or a power supply layer to improve the electrical 
characteristics of the semiconductor device. 
FIG. 10 shows a conventionally known multi-layer lead frame which comprises 
three layers, i.e., a signal layer (i.e., lead frame 12) and two metal 
planes, i.e., a power supplying metal plane 14 and a ground metal plane 
16, which are laminated via insulative tape 17a and 17b made of 
heat-resistant material made of, such as a polyimide. 
Using such a multi-layer lead frame, it would be possible to prevent a 
so-called cross talk which might be generated between signal lines and 
also possible to reduce the capacitance between the lines or inductance. 
As shown in FIG. 10, in order to manufacture the abovementioned multi-layer 
lead frame, at the first stage, a lead frame 12, a power supplying metal 
plane 14, a ground metal plane 16, and insulative tape pieces 17a and 17b 
each having respective surfaces providing with adhesive layers must 
individually be made. Then, these individual pieces must be positioned by 
using a special instrument (not shown), such as an image reader, and then 
heat-pressed to laminate and adhere them together. 
However, in the above mentioned manufacturing process, it has been very 
troublesome and laborious work to position and laminate the five layers 
including the insulative tape pieces 17a and 17b by using the image 
reader. It also requires a lot of time and, therefore, an effective 
production rate would not be expected. In addition, after these pieces are 
gripped by the gripping means and laminated, when the pieces are released 
or disengaged from the gripping means, the laminated pieces might be moved 
slightly and, therefore, a precise laminated multi-layer lead frame might 
not be obtained. 
The multi-layer lead frame should originally have a good quality for 
multi-pin and, therefore, inner leads thereof are usually very dense. 
Thus, even a slight abberation might cause a disconnection between the 
terminals of the power supply plane 14 and ground plane 16 and the 
corresponding inner leads of the lead frame 10. 
In addition, an insulative sheet must be punched to form the insulative 
tape pieces 17a and 17b. Such a punching process requires a relatively 
laborious work. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a multi-layer lead frame 
and a process for manufacturing the same, in which an insulative tape 
piece is no longer required and, therefore, it is possible to reduce the 
time to make the same. 
Another object of the present invention is to provide a multi-layer lead 
frame and a process for manufacturing the same, in which positioning of 
the planes can be conducted precisely and effectively. 
According to the present invention, there is provided a multi-layer lead 
frame for a semiconductor device comprising: a lead frame body made of a 
metal strip; and at least one metal plane, which is independent by itself 
from said lead frame body, said metal plane being adhered to said lead 
frame body by means of a coated adhesive film, without using any 
insulative tape piece. 
According to another aspect of the present invention, there is provided a 
multi-layer lead frame for a semiconductor device comprising: a lead frame 
body made of a metal strip; and at least one metal plane, which is 
independent by itself from said lead frame body, but said metal plane 
being adhered to said lead frame body by means of two layers consisting of 
a coated adhesive film and a coated insulative resin film, without using 
any insulative tape piece. 
According to a still another aspect of the present invention, there is 
provided a process for manufacturing a multi-layer lead frame for a 
semiconductor device comprising a lead frame body and at least one metal 
plane being adhered to said lead frame body by means of an adhesive 
material, said process comprising the following steps of: forming a lead 
frame strip and at least one metal plane strip, said lead frame strip 
comprising a plurality of said lead frame bases sequentially arranged and 
continuously connected to each other, and said metal plane strip 
comprising a plurality of said metal planes sequentially arranged and 
continuously connected to each other; coating at least one of said lead 
frame strip and said metal plane strip with an adhesive material in 
accordance with a predetermined adhesion pattern; positioning said metal 
plane strip with respect to said lead frame strip; and, adhering said at 
least one metal plane of said metal plane strip to said at least one lead 
frame body of said lead frame strip via said adhesive material. 
Thus, in the present invention, the multi-layer lead frame can be 
effectively and precisely manufactured, since the positioning of the lead 
frame strip and the metal plane strip can be easily arranged. Also, 
coating these planes with an adhesive material or an insulative resin can 
be easily and precisely performed, by using a masking, for example. 
Therefore, the positions of the metal plane with respect to the lead frame 
and the patterns of the adhesive material and/or the insulative resin can 
be precisely defined and controlled.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, wherein FIG. 1 shows a preferred embodiment 
of a multi-layer lead frame according to the present invention. The 
multi-layer lead frame generally indicated by a reference numeral 10 
comprises a lead frame 12 and two metal planes, i.e., a power supplying 
metal plane 14 and a ground metal plane 16, which are affixed to the lead 
frame 12 via thermosetting insulative adhesive resins 18a and 18b, 
respectively. 
The multi-layer lead frame 10 can be manufactured by a process as described 
below with reference to FIG. 2, wherein A is a line of process for 
manufacturing a lead frame strip 20, B is a line of process for 
manufacturing a power supply plane strip 22, and C is a line of process 
for manufacturing a ground plane strip 24. The process line B intersects 
perpendicularly at Al with the process line A and, at the downstream of 
the intersection Al, the process line C intersects perpendicularly at A2 
with the process line A. 
In the process line A, a metal strip is forwardly fed through several metal 
molds (not shown). Along these molds the metal strip is formed in a 
conventionally known manner. Thus, as schematically shown in FIG. 3, 
obtained is a lead frame strip 20 comprising a support frame 25 and a 
plurality of lead frames 12 longitudinally, sequentially and continuously 
arranged and connected to each other by means of connecting portions. The 
support frame 25 is provided with a plurality of regularly arranged guide 
holes 26 which cooperate with guide means (not shown) for feeding this 
lead frame strip 20 forwardly through the metal molds. 
In the process line B, another metal strip is first intermittently coated 
with an adhesive made of thermosetting resin in accordance with a 
predetermined adhesion pattern defined between the lead frame 12 and the 
power supply plane 14. The metal strip is then fed to a low-temperature 
dryer (not shown), where the coated adhesive is dried and becomes a coated 
film 18a. Then, the metal strip is fed forwardly through the metal molds. 
In these metal molds, the metal strip is formed as schematically shown in 
FIG. 4. The above results in a power supply plane strip 22 comprising a 
plurality of power supply planes 14 longitudinally, sequentially and 
continuously arranged and connected to each other by means of connecting 
portions 27. The connecting portions 27 are provided with regularly 
arranged positioning guide holes 28. A reference numeral 29 indicates 
terminals protruded from the power supply plane 14. A reference numeral 18 
indicates a pattern of the adhesive film. 
In the same manner as the above, in the process line C, still another metal 
strip is first intermittently coated with an adhesive made of 
thermosetting resin in accordance with a predetermined adhesive pattern 
defined between the power supply plane 14 and the ground plane 16. The 
metal strip is then dried, so that the adhesive becomes a coated film 18b. 
Then, the metal strip is fed forwardly through the metal molds. In these 
metal molds, the metal strip is formed as schematically shown in FIG. 5 
and obtained is a ground plane strip 24 comprising a plurality of ground 
planes 16 longitudinally, sequentially and continuously arranged and 
connected to each other by means of connecting portions 30. The ground 
plane strip 24 is also provided with positioning guide holes 31 and 
terminals 32. 
The above-mentioned power supply plane strip 22 is divided into an 
individual power supply plane 14 at the intersection Al (FIG. 1) of the 
process line A. The divided power supply plane 14 is then positioned at a 
predetermined position on the lead frame 12 and provisionally adhered 
thereto by means of the adhesion film 18a. 
FIG. 6 shows an example of the heat-press apparatus which comprises a 
cutting punch 35, a die 36, and a heater block 37. When the power supply 
plane strip 22 is positioned by means of the above-mentioned positioning 
guide holes 28 at a predetermined position above the lead frame 12 and fed 
to a position between the cutting punch 35 and the die 36, the cutting 
punch 35 is lowered to cut the connecting portions 27, so that the power 
supply plane strip 22 is cut into the individual power supply plane 14, 
which is then heat-pressed against the lead frame 12 provisionally heated 
by the heater block 37. The heat-pressing in this process is sufficient to 
soften the adhesive film 18a, but not to completely harden the adhesive 
film 18a. 
The pressing surface of the cutting punch 35 is provided with some suction 
holes (not shown) communicated to any vacuum means (not shown) for sucking 
to hold the power supply plane 14 and simultaneously to press the same 
against the lead frame 12. Thus, the power supply plane 14 is stably held 
against the lead frame 12 of the lead frame strip 20. 
The lead frame strip 20, to which the power supply plane 14 is adhered, is 
further fed forwardly and, at the intersection A2 of the process line C, 
the ground plane 16 is then provisionally adhered to the power supply 
plane 14 by means of the adhesion film 18b in the same manner as mentioned 
above. That is to say, when the lead frame strip 20 and the ground plane 
strip 24 are positioned to each other by means of the respective guide 
holes 26 and 31 and fed forwardly to the intersection A2 of the process 
line C, the cutting punch (not shown) is lowered to cut into the 
individual ground plane 16, which is then heat-pressed against the power 
supply plane 14 on the lead frame 12 provisionally heated by the heater 
block to soften to provisionally adhere the ground plane 16 against the 
power supply plane 14. 
Thus, the lead frame strip 20, to which the power supply plane 14 and the 
ground plane strip 16 are laminated, is further fed forwardly along the 
process line A. The lead strip 20 is further heated and pressed by upper 
and lower heater blocks 41a and 41b and thus the adhesive films or layers 
18a and 18b are suitably thermoset to obtain a multi-layer lead frame 10. 
The respective terminals 29 and 32 of the power supply plane 14 and the 
ground plane strip 16 are connected to the corresponding leads of the lead 
frame 10 by a spot welding or the like. 
Although, in the above-mentioned embodiment, the adhesive film 18a for 
adhering the power supply plane 14 to the lead frame 12 is provided on the 
power supply plane 14, such an adhesive film 18a may be provided on the 
lead frame strip 20. 
Otherwise, the power supply plane 14 may be provided on its respective 
surfaces with adhesive films for adhering the same to the lead frame 12, 
as well as to the ground plane 16. 
FIG. 7 shows another embodiment of a laminating process according to the 
present invention. In this embodiment, the power supply plane strip 22 and 
the ground plane strip 24 are not cut into individual planes, but these 
strips are themselves positioned with respect to each other by any 
positioning means, such as, pilot pins and superimposed onto the lead 
frame strip 20, so that they are heat-pressed together by means of upper 
and lower heater blocks 41a and 41b to thermoset the adhesive films 18. 
The connecting portions 27 and 30 of the power supply plane strip 22 and 
the ground plane strip 24 are thereafter cut into individual planes. These 
connecting portions 27 and 30 may be provided at the base thereof with 
V-shaped notches or the like extending to the direction of thickness so as 
to easily cut these connecting portions. 
FIG. 8 shows another embodiment of a multi-layer lead frame 10 having a 
lead frame 12, a power supply plane 14, and a ground plane 16. In this 
embodiment, however, the respective planes are adhered to each other by 
means of two insulative layers comprising an adhesive film 18 made of a 
thermosetting resin as in the previous embodiment and another insulative 
resin film 19, which is an insulative liquid resin coated and dried. 
According to this embodiment, since the two insulative layers 18 and 19 are 
served to keep a predetermined thickness between the respective planes, an 
insulation efficiency can still be improved. It should not be understood 
that the adhesive film 18 and the insulative resin film 19 are limited to 
be provided between the lead frame 12 and the power supply plane 14, and 
between the power supply plane 14 and the ground plane 16. 
FIG. 9 shows another embodiment of a manufacturing process of a multi-layer 
lead frame according to this invention. FIG. 9(a) shows a ground plane 
strip 24 which is formed on the process line C (FIG. 1). FIG. 9(b) shows a 
power supply plane strip 22 which is formed on the process line B (FIG. 
1). FIG. 9(c) shows a lead frame plane 20 which is formed on the process 
line A (FIG. 1), in the same manner as mentioned above. 
In this embodiment, however, the ground plane 16 is provided on its surface 
facing to the power supply plane 14 with an insulative resin film 19 and 
also provided on the opposite surface with an adhesive film 18 of 
thermosetting resin. Also, the power supply plane 14 is provided on its 
surface facing to the lead frame 12 with an insulative resin film 19 and 
provided on the opposite surface with an adhesive film 18 of thermosetting 
resin. 
The lead frame 12 and the respective planes 14 and 16 are then laminated 
and heat-pressed together. Thus, the adhesive film 18 is thermoset to 
obtain a laminated multi-layer lead frame. 
In this laminating process, the power supply plane strip 22 and the ground 
plane strip 24 may be first positioned and then cut into individual planes 
to be laminated, in the same manner as the previous embodiment shown in 
FIG. 6. Otherwise, the power supply plane strip 22 and the ground plane 
strip 24 may be positioned, laminated, and heat-pressed with respect to 
the lead frame 12, so that the adhesive films 18 are thermoset, and then 
divided into individual planes by the connecting portions. 
Although, in the above mentioned embodiments, the multi-layer lead frame 
comprises three layers, i.e., the lead frame 12, the power supply plane 14 
and the ground plane 16, this invention can also be applied to the other 
multi-layer lead frame comprising, such as, two layers, i.e., a lead frame 
and a single metal plane. In this case, the metal plane may be a power 
supply plane, a ground plane or a radiation/stage plane which is not 
electrically connected to the lead frame. 
A multi-layer lead frame according to the present invention may, of course, 
be comprised of four or more layers. 
It should be understood by those skilled in the art that the foregoing 
description relates to only preferred embodiments of the disclosed 
invention and that various changes and modifications may be made in the 
invention without departing form the sprit and scope thereof.