Semiconductor integrated circuit packages

A lead frame for mounting a semiconductor chip in an integrated circuit package incorporates a deformation absorbing member as an integral part of the paddle support arm so that the initial, desired physical and electrical characteristics are unaltered after a forming operation such as paddle downsetting.

TECHNICAL FIELD 
This invention relates generally to packages for semiconductor integrated 
circuits. 
BACKGROUND OF THE INVENTION 
An essential part of semiconductor integrated circuit manufacture resides 
in the placing of the integrated circuit chip into a package so that the 
chip can be conveniently contacted electrically as well as mounted in a 
physically secure manner. The chip itself is mounted on a lead frame which 
has a plurality of fingers for electrical connections and a paddle for 
physical support. The paddle is connected physically to an external 
mounting frame by paddle support arms. Electrical contacts are made 
through wires bonded to the fingers and to the paddle. 
Although the package could be assembled using a lead frame in which the 
paddle remains in the same plane as do the fingers, it has often been 
found desirable to assemble a package using a lead frame in which the 
paddle has been depressed, i.e., made lower, with respect to the external 
mounting frame and fingers. It has been found that this configuration 
reduces the number of edge shorts between the electrical contact wires and 
the chip. It also allows a balanced flow condition during molding. As will 
be readily appreciated by those skilled in the art, the depressed 
positioning will necessarily lead to a physical deformation of the paddle 
support arms during the forming process because the lead frame is 
initially a flat metal piece. The deformation will generally be in the 
form of a necking down, i.e., a constriction of paddle support arms in the 
transverse axial direction. 
As feature sizes in integrated circuits continue to decrease and the scale 
of integration continues to increase, package designers must make more 
interconnects in an amount of space that is, at best, equal to that 
previously available. The only expedient way this may be accomplished is 
to decrease the width of the fingers and paddle support arms to permit 
placement of more fingers in either the same or a smaller area. 
Consequently, the combined effect of the constriction and decreased 
feature size may lead to problems such as loss of physical integrity and 
distortion of the paddle support arms. If these arms are also used for 
electrical connections, there may be undesirable changes in the electrical 
characteristics as well. 
SUMMARY OF THE INVENTION 
A semiconductor integrated circuit package is described which as a 
semiconductor integrated circuit chip and a lead frame, on which said chip 
is mounted, having a plurality of fingers, a paddle and a plurality of 
paddle support arms with the paddle support arms having a deformation 
absorbing member. The lead frame is formed so that the paddle is in a 
depressed position with respect to the external mounting frame .Iadd.and 
to at least a portion of the fingers. .Iaddend.The deformation absorbing 
member is designed to maintain the desired mechanical characteristics 
after forming. It may also retain the desired electrical characteristics 
if the arms are used for electrical connections. In one embodiment, the 
deformation absorbing member is an annular member which contracts in a 
direction transverse to the load direction. In another embodiment, the 
deformation absorbing member is a T bar. The paddle is supported by the 
paddle support arms which terminate in a T before contacting the external 
mounting frame. The legs of the T. perpendicular to the paddle support arm 
axis, are designed to deflect and absorb the deformation that results from 
the metal forming process of depressing the paddle. In all embodiments, 
the deformation absorbing member localizes the deformation which occurs 
during the mounting step producing the deformation.

DETAILED DESCRIPTION 
A side view of an exemplary integrated circuit package is depicted in FIG. 
1. Depicted are semiconductor chip 1 which is mounted on paddle 3 by means 
of epoxy material 5. Paddle 3 is part of the lead frame which also has a 
plurality of fingers 7 and paddle support arms 9 for physical support. The 
fingers 7 are connected to the external mounting frame 13. There are 
electrical connections 15 between the chip and the fingers 7. As can be 
seen, the paddle 3 is positioned lower than the external mounting frame 13 
because the paddle support arms have been deformed. .Iadd.It can also be 
seen that the paddle is positioned lower than the lead frame fingers; 
i.e., it is depressed with respect to at least a portion of the lead frame 
fingers. .Iaddend.This arrangement is desirable because it facilitates 
making, e.g., the electrical connections as previously discussed. The 
paddle support arms are bent to accommodate the vertical mismatch and each 
has a deformation absorbing member which localizes the deformation to the 
vicinity of that member. 
FIG. 2 is a top view of the single site depicted in FIG. 1 of a typical 
lead frame. Depicted are a lead frame site comprising an external mounting 
frame 13, a paddle 3, a plurality of fingers 7, and a plurality of paddle 
support arms 9 extending from the paddle. Each paddle support arm has a 
deformation absorbing member 11. For reasons of clarity, not all fingers 
are depicted. In the embodiment depicted in FIG. 2, the deformation 
absorbing member 11 comprises an annular member, i.e., a member with 
expanded dimensions in the direction perpendicular to the major axis of 
the paddle support arm. The annular member is depicted as being circular 
although other shapes, e.g., oval, can be used. 
During the forming operation, i.e., as the paddle is depressed with respect 
to the external mounting frame, .Iadd.and to at least a portion of the 
lead frame fingers, .Iaddend.the deformation absorbing member constricts 
in the direction perpendicular to the axis of motion. However, due to the 
size and shape of the deformation absorbing member, the desired electrical 
and physical characteristics are maintained after the forming operation as 
the paddle support arm does not form a necked down region. Thus, it is 
essential that the deformation absorbing member compensate for the axial 
motion along the paddle support arm. Further steps required for packaging 
need not be desired in detail as they are well known to those skilled in 
the art. 
FIG. 3 illustrates another embodiment of a paddle support arm 11 having a 
deformation absorbing member which comprises a T bar with the two ends of 
the T mounted to the external mounting frame .Iadd.and to at least a 
portion of the fingers.Iaddend.. During the forming operation, the paddle 
support arms move radially inward causing the ends of the T to deflect 
about the mounting axis in the direction shown by the arrows. 
Other embodiments are contemplated, and two embodiments are depicted in 
FIGS. 4 and 5. In FIG. 4 the deformation absorbing member comprises an S 
bend while in FIG. 5 it comprises a wrinkle. FIG. 6 shows the wrinkle 
along line A-A' in FIG. 5.