Lead frame for integrated circuit devices

A lead frame for an IC device includes a body element located at its center, the body element including recesses in its outer periphery in which the inner tips of the leads of the lead frame are fitted at predetermined positions. With such an arrangement, the leads are prevented from being deformed during steps of formation of the IC device.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to lead frames for integrated circuits, and 
more particularly to lead frames for glass-encapsulated integrated 
circuits. 
2. Prior Art 
Glass-encapsulated integrated circuits are conventionally assembled by 
stamping a strip of Alloy 42 into a lead frame having a plurality of 
leads, then attaching the lead frame to a ceramic substrate coated with 
glass, then fixing an IC (integrated circuit) chip to the assembly, and 
finally connecting the tips of the inner ends of the leads of the lead 
frame to electrodes of the IC chip with wires of aluminum, normally by an 
automatic bonder. It is important that the tips of the inner ends of the 
leads of the lead frame which is attached to the ceramic substrate be 
located in predetermined positions. If the tips are displaced out of 
position due to deformations, the aluminum wires will not be properly 
bonded to the displaced tips, and the resulting IC device will be useless. 
As shown in FIG. 1 of the accompanying drawings, an ordinary conventional 
lead frame has thin leads which extend toward the center of the frame and 
are supported only at their outer ends, provides a construction which is 
mechanically weak and susceptible to deformation. The leads can be easily 
deformed due to residual stresses created when the lead frame is stamped 
out of a raw material, or else due to rough handling during subsequent 
assembling operations. At the same time, as more and more electronic 
functions are performed by IC, the lead frame must have an increased 
number of leads which are increasingly thinner and longer and which are 
hence more easily subject to deformations. 
One way to reduce such deformations is disclosed in U.S. Pat. No. 4,137,546 
to J. M. Frusco. In this patent a lead frame is shown in which the tips of 
the inner ends of the leads are spaced apart at intervals by separate 
tabs. However, these tabs cannot perfectly prevent the leads from being 
deformed. More specifically, when one of the tabs is subjected to an 
external force, all of the leads that are connected to that tab will be 
deformed. In addition, the tabs must be broken off by being bent in a 
subsequent operation which, however, cannot be mechanically performed due 
to various difficulties. 
It is an object of the present invention to provide a lead frame having 
leads arranged to resist deformation so that aluminum wires can be 
reliably connected thereto by an automatic bonder. 
SUMMARY OF THE INVENTION 
According to the present invention, a lead frame for an integrated circuit 
is constructed to include a body element which has recesses in which are 
fitted at least two tips at the inner ends of the associated leads. 
Further objects, advantages and features of the present invention will 
become more fully apparent from a detailed consideration of the 
arrangement and construction of the constituent parts as set forth in the 
following specification taken together with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A conventional lead frame, as illustrated in FIG. 1, includes support 
strips 2 which support leads 1 at their outer ends, their inner ends 
extending inwardly toward the center of the lead frame (due to their being 
bent at an angle of about 90 degrees at a point along their length). Due 
to this mode of support, the inner ends of the leads 1 are positionally 
unstable and susceptible to deformation. As shown in FIG. 2, the inner 
ends of the leads are normally arranged in a predetermined spatial 
relation so as to form a space having a generally rectangular contour. 
When one of the leads is, however, deformed, its inner tip 3a will be 
displaced, e.g., to a position shown by the broken-line 3b, such that the 
inner tip will possibly touch an adjacent inner lead tip or else be 
directed upwardly. In this event, the wires of aluminum cannot be 
thereafter properly bonded to these tips by an automatic bonder, e.g., the 
wires as connected may be short-circuited. 
According to the present invention, a body element 5 is positioned at the 
center of the lead frame, the body element 5 including recesses 4 in its 
outer periphery in which are fitted the respective tips of the inner ends 
of the leads 1, the recesses 4 being spaced at predetermined intervals or 
pitches. 
It should be noted that lead frames are normally formed by a stamping press 
having progressive dies, and at an intermediate processing step the lead 
frames will have a configuration in which the inner lead tips and a 
centrally positioned body will be integral with each other. However, the 
inner lead tips and the body have heretofore been cut off along a broken 
line 6 as shown in FIG. 3 to provide the desired lead frame. 
The lead frame of the present invention, on the other hand, can be 
fabricated by severing the intermediate product along a contour which 
leaves the extended inner lead tips as shown by the solid line 7 in FIG. 
3, thus forming the body element 5 with the recesses 4 in its peripheral 
sides. 
More specifically, as illustrated in FIGS. 5 and 6, the body element 5 is 
first cut stamped out by an upper die 8 and is then lowered as it is 
sandwiched between the upper die 8 and a lower die 9. When the upper die 8 
is lifted, the severed body 5 is also raised back by the lower die 9 under 
the force of a spring 10 acting on the lower die into fitting engagement 
with the inner lead tips 3 to prevent their subsequent displacement. Such 
raising back of the blanked body element 5 is known as "pushback" in the 
art of stamping technology. By lightly striking the interfitting portions 
of the body element wherein the inner lead tips 3 are fitted in the 
recesses 4, the body element 5 can support the inner lead tips 3 with an 
increased degree of strength. 
The lead frame thus constructed is attached to a ceramic substrate 12 (see 
FIG. 4) coated with a layer of glass 11, which is melted and solidified to 
bond the lead frame to the ceramic substrate 12. As the body element 5 and 
the inner lead tips 3 are held in interfitting engagement with each other, 
the leads as they are attached to the ceramic substrate 12 will remain 
positionally and dimensionally the same as when they were stamped out. The 
body element 5 can be removed from the leads by being pulled out with a 
suitable tool inserted in a central hole 13 in the body element 5. Thus, 
the lead frame has positionally stable leads to which aluminum wires can 
be reliably bonded by an automatic bonder. 
The present invention is advantageous in that the inner lead tips can be 
positioned with a high precision, and hence no positional displacement 
between the inner lead tips and the aluminum wires will occur while being 
processed with an automatic bonder. There is no possibility of the leads 
being deformed between the step of manufacturing the lead frame to the 
step of attaching the latter to the ceramic substrate. Thus, the lead 
frame can be handled with ease in such processing steps. 
While the present invention has been described with reference to particular 
embodiments thereof, it will be understood that numerous modifications may 
be made by those skilled in the art without actually departing from the 
spirit and scope of the invention as defined in the appended claims.