Lead frame including deformable plates

A lead frame for a semiconductor chip has a plurality of supporting plates connecting to each other by a plurality of readily deformable plates so that a predetermined gap exists between adjacent supporting plates. When the semiconductor chip and the supporting plates are heated when fixing the semiconductor chip to the supporting plates by melting a conductive adhesive, less stress is induced in the semiconductor chip due to uneven thermal expansion between the chip and the supporting plates since a reduced area of the chip is fixed to the supporting plates.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a lead frame which provides lead wires for an 
electronic part such as an intergrated circuit (IC) and which serves as a 
frame in the process of manufacturing the electronic part. 
2. Description of the Prior Art 
In assembling semiconductor devices such as transistors and integrated 
circuits, the semiconductor devices are often assembled successively on a 
lead frame having a metal ribbon with a plurality of metal wires formed by 
blanking. The lead frame includes portions on which semiconductor chips 
are fixedly set, portions used for wire bonding, and portions which are 
used as external lead wires when the semiconductor devices have been 
assembled. 
FIG. 1 is a plane view of a conventional lead frame showing only a part of 
the lead frame which supports one semiconductor device. The lead frame is 
for a resin mold type semiconductor device. The lead frame has a square 
chip fixing plate 2 on which a semiconductor chip 1 is fixedly placed. A 
rectangular connecting frame plate 3 has one side which extends 
perpendicularly from the centers of two opposed sides of the chip fixing 
plate 2. A plurality of external connection electrode plates 4 are also 
provided and each electrode plate 4 has a lead wire connecting portion 4a 
which is used for wire bonding and a lead wire portion 4b. The lead wire 
connecting portions 4a confront the chip fixing plate 2 and the lead wire 
portion 4b is connected to the connecting frame plate 3. 
When a semiconductor device is fixed to the lead frame described above, the 
semiconductor chip 1 is fixedly set on the chip fixing plate 2 and bonding 
pads 1a on the semiconductor chip 1 are connected to the lead wire 
connecting portions 4a with thin conductors 5 by bonding. Thereafter, the 
entire region indicated by the two-dot chain line in FIG. 1 identified by 
reference number 19 is molded with resin and then the lead frame is cut 
along the two-dot chain lines in FIG. 1 identified by reference number 20 
to remove the part of the connecting frame plate 3 which becomes 
unnecessary after the semiconductor device has been molded in place. This 
forms a resin mold type semiconductor device. 
When the semiconductor chip 1 is fixiedly set on the chip fixing plate 2 of 
the lead frame, both the chip 1 and plate 2 are flat as shown in FIG. 
2(A). However, since the thermal coefficient of expansion of the chip 1 is 
different from that of the plate 2, when the temperature is raised in the 
resin molding operation, the semiconductor chip 1 and the chip fixing 
plate 2 become deformed as shown in FIG. 2(B). As a result of this 
deformation, stresses are set up in the semiconductor chip 1 and the chip 
fixing plate 2. If a large semiconductor chip is to be fixed to the lead 
plate, a rather large area is used for fixing the semiconductor chip 1 to 
the chip fixing plate 2 which produces rather large temperature induced 
stresses. As the size of the semiconductor chip increases, so do the 
stresses. Accordingly, when the semiconductor chip 1 is 1.times.1 
cm.sup.2, it is sometimes cracked because the termperature induced 
stresses exceed a value allowable for the chip 1. 
SUMMARY OF THE INVENTION 
Accordingly, an object of this invention is to provide a lead frame in 
which stress caused by temperature increases is made small so that even if 
a large chip is fixed to the lead frame the large chip will not crack. 
The lead frame according to the present invention has a chip fixing plate 
which comprises a plurality of readily deformable plates and a plurality 
of supporting plates. The plurality of supporting plates are coupled to 
one another by the readily deformable plates which results in less stress 
being induced in the chip upon heating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 3 is a diagram showing one embodiment of a lead frame according to the 
present invention. A chip fixing plate 2 is shown in FIG. 3 as well as a 
part of a connecting frame plate 3. The remaining part of the connecting 
frame plate 3 and electrode plates 4 are not shown in FIG. 3 because they 
are similar in configuration to those shown in FIG. 1. The chip fixing 
plate 2 comprises four supporting plates 6, 7, 8 and 9 which have a 
substantially rectangular or square shape and four readily deformable 
plates 10, 11, 12 and 13 which are each belt-shaped. The supporting plate 
6 is adjacent to the supporting plate 7 with a predetermined gap being 
provided therebetween, the supporting plate 7 is adjacent to the 
supporting plate 8 with the predetermined gap being provided therebetween 
also, and so on. Each readily deformable plate is bent at the central 
portions thereof and two adjacent supporting plates are connected to each 
other through one readily deformable plate. The supporting plates and the 
readily deformable plates are integral with each other to form the chip 
fixing plate 2. The chip fixing plate 2 preferably is provided by 
blanking. 
With the lead frame described above, a semiconductor device can be secured 
to the lead frame in the same manner as it is when the semiconductor 
device is secured to the conventional lead frame shown in FIG. 1. That is, 
the semiconductor chip 1 is fixedly set at a position indicated by the 
dotted line in FIG. 3 by a method in which gold-silicon entectic, 
electrically conductive adhesive or other suitable material is used. Prior 
to fixedly setting the semiconductor chip 1, the chip 1 and the chip 
fixing plate 2 are flat as shown in FIG. 4(A). However, when the lead 
frame according to the present invention, and in particular the supporting 
plates 6 and 7 thereof along with the semiconductor chip 1, are deformed 
by the temperature rise which is caused by the resin molding, stresses are 
set up in the supporting plates 6 and 7 and the semiconductor chip 1 
causing the deformation showin in FIG. 4(B). Since the area of the 
semiconductor chip which is used to fix it to the supporting plates 6 and 
7 is smaller than that of the semiconductor chip 1 which is used to fix it 
to the chip fixing plate 2 in the conventional lead frame, the stresses 
set up in the semiconductor chip 1 in the vicinity of the supporting 
plates 6 and 7 are smaller than those which are created when the 
conventional lead frame is used. The stresses set up in the semiconductor 
chip 1 in the vicinity of the remaining supporting plates 8 and 9 are 
similar to the stresses set up in the vicinity of the supporting plates 6 
and 7. 
As the gap between the supporting plates 6 and 7 increases, the bend angle 
of the bent portion of the readily deformable plate 10 is changed from the 
configuration indicated by the solid line in FIG. 4(C) to that indicated 
by the dotted line in this figure. This deformation occurs in the other 
readily deformable plates 11, 12 and 13 as the gaps between the supporting 
plates 7 and 8, 8 and 9, and 6 and 9 are increased respectively due to 
heating. The deformation is caused even if external forces which are 
exerted on the gaps between the supporting plates 6 and 7, 7 and 8, 8 and 
9, and 9 and 6 to increase or decrease the gaps are small. The area of the 
semiconductor chip 1 which is fixed to each of the readily deformable 
plates 10 through 13 is very small and the semiconductor chip 1 is weakly 
coupled mechanically to each of the readily deformable plates 10 through 
13. Therefore. in the vicinities of the gaps between the supporting plates 
6 and 7, 7 and 8, 8 and 9 and 9 and 6, the semiconductor chip 1 expands 
substantially freely with its intrinsic thermal expansion coefficient as 
the temperature rises. Thus, the external force exerted on the chip 1 is 
very small and the stress set up in the chip 1 is also very small. 
Accordingly, with the above-described example of the lead frame according 
to the invention, the stress set up in the semiconductor chip 1 due to the 
temperature rise is small and cracking or the like of the chip 1 is 
prevented. 
FIG. 5 is a plane view showing a part of another embodiment of the lead 
frame according to the present invention. In this embodiment, a readily 
deformable plate 10 has a zigzag shape, that is, it is bent at three 
points. Readily deformable plates 11, 12 and 13 (not shown) are similar in 
configuration to the readily deformable plate 10. The other plates are 
similar to those in FIG. 3. This embodiment functions like the embodiment 
of FIG. 3 when heated. 
FIG. 6 is a plane view showing a part of a third embodiment of the lead 
frame according to the present invention. The lead frame has a chip fixing 
plate 2 comprising eight substantially triangular supporting plates 14 
through 21 and readily deformable plates 22 through 29 which are 
substantially similar in configuration to plates 10 through 13 in FIG. 3. 
The supporting plates 14 through 21 are adjacent to one another with a 
predetermined gap being provided therebetween and the adjacent supporting 
plates are coupled to one another through the readily deformable plates 22 
through 29, respectively. The other plates of the lead frame are similar 
to those in FIG. 1. In this third embodiment the area of the semiconductor 
chip 1 which is used to fix the latter 1 to the supporting plates 14 
through 21 is smaller than that of the semiconductor chip 1 which is used 
to fix it to the supporting plates 6 through 9 in the first embodiment 
shown in FIG. 3. Therefore, the stress set up in the chip 1 is further 
reduced. 
As is apparent from the above description, the lead frame of the invention 
can reduce the stress which is set up in a semiconductor chip fixed 
thereto when the temperature rises. Therefore, a large area chip can be 
fixed to the lead frame.