Tape automated bonding package for a semiconductor chip employing corner member cross-slots

A semiconductor package (80) is provided that serves to support a semiconductor chip (12). A radial slot (54) is formed in an inner ring (26). Cross-slots (64) and (66) are formed in a corner member (38) of polyimide film (22). The slots (54), (64) and (66) serve to allow independent expansion of various portions of the polyimide film (22) and prevent breakage of contact leads (14), (16), (18) and (20) due to the differences in the thermal coefficient of expansion of the semiconductor material and the polyimide film material.

TECHNICAL FIELD OF THE INVENTION 
This invention relates in general to the field of electronic devices and 
more particularly to an improved tape automated bonding package for a 
semiconductor chip and a method of manufacture. 
BACKGROUND OF THE INVENTION 
One method of packaging integrated circuit chips formed on semiconductor 
chips is through the use of a polyimide film similar to photographic film 
that is used as a base for the interconnect wires which are routed from 
other circuitry to the bond pads on the semiconductor chip. The polyimide 
films may comprise, for example, Upilex or Kapton. A chip is initially 
placed in an inner opening in the film and interconnects are routed from 
the bond pads on the chip to test pads on the periphery of the film. The 
inner opening is surrounded by an inner polyimide ring. Four outer 
openings surround the inner polyimide ring. The interconnects are routed 
from the chip over the inner ring and then over the outer openings to the 
periphery of the film. The inner ring is coupled to the periphery of the 
film by four corner members of the polyimide film. After testing, the 
polyimide film and the interconnects are cut outside of the outer openings 
and the combination of the film, the interconnects and the chip is mounted 
to a circuit board so that the chip may be used for its intended purpose. 
The leads that are routed from the chip over the film are extremely thin 
and fragile. The chips are required to operate in environments with 
dramatically changing temperature. For example, some chips are tested in 
the temperature range on the order of -65.degree. C. to 150.degree. C. The 
difference in thermal coefficient of expansion between the film and the 
semiconductor material such as silicon which is used to form the 
integrated circuit chip creates stresses on the leads passing from the 
chip over the film. This stress can be great enough to cause delamination 
between the leads and the film and in catastrophic cases, breaking of the 
leads. 
For smaller die sizes, the spacing between the integrated circuit chip and 
the inner ring of polyimide film can be increased to reduce the stress on 
the leads. However, as die sizes increase, this approach becomes 
impractical. Accordingly, a need has arisen for a new form of tape 
automated bonding packaging which eliminates the problems with lead 
breakage and delamination caused by differences in the thermal coefficient 
of expansion between the semiconductor material and the film material. 
SUMMARY OF THE INVENTION 
In accordance with the teachings of the present invention, a tape automated 
bonding package and method of construction are provided that substantially 
eliminate or reduce disadvantages associated with prior packaging systems. 
According to one embodiment of the present invention, a packaged integrated 
circuit is provided that comprises a semiconductor chip coupled to a 
plurality of interconnects extending outward from the bond pads on the 
semiconductor chip. The package device further comprises an inner ring of 
polyimide film coupled to the interconnects and surrounding the 
semiconductor chip. The inner ring of polyimide film is connected to an 
outer ring of polyimide film by corner members of polyimide film. The 
outer ring of polyimide film surrounds the inner ring. The inner ring 
comprises radial expansion slots extending from proximate the corners of 
the semiconductor chip to proximate the corner members of polyimide films. 
The radial slots allow the four sides of the inner ring of polyimide film 
to expand and contract relatively independent of one another. 
According to another embodiment of the present invention, the corner 
connecting members of polyimide film comprise cross-slots formed in the 
edges of the corner members. The cross-slots allow the inner ring of 
polyimide material to expand relatively independent of the outer ring of 
polyimide material.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a schematic illustration of a tape automated bonded package 10 
which serves to package a semiconductor chip 12. Semiconductor chip 12 is 
surrounded by four groups of interconnecting leads 14, 16, 18 and 20. 
Interconnecting leads 14, 16, 18 and 20 are disposed on a surface of a 
sheet of polyimide film 22. Polyimide film 22 may comprise Upilex, Kapton, 
or other suitable polyimide film. Interconnecting leads 14, 16, 18 and 20 
comprise strips of metal such as gold-plated copper which are defined and 
formed on the surface of polyimide film 22 using photolithographic 
processes. One end of each of the interconnects 14, 16, 18 and 20 
terminates at and are electrically connected to a bond pad on the surface 
of semiconductor chip 12. 
Semiconductor chip 12 resides in an inner opening 24 in polyimide film 22. 
Inner opening 24 is defined by an inner ring 26 of polyimide film 
surrounding semiconductor chip 12. Inner ring 26 comprises four sides 28, 
30, 32 and 34. As shown in FIG. 1, side 28 of inner ring 26 serves to 
support a portion of interconnect leads 14. Similarly, side 30 supports a 
portion of interconnect lead 16; side 32 supports a portion of 
interconnect lead 18; and side 34 supports a portion of interconnect leads 
20. Inner ring 26 is supported by an outer body 36 of polyimide film 22. 
Inner ring 26 is connected to outer body 36 through four corner members 
38, 40, 42 and 44. 
FIG. 1 illustrates package 10 in test mode where each of the interconnects 
14, 16, 18 and 20 couple a bond pad on semiconductor chip 12 to a 
plurality of test pads around the periphery of polyimide film 22. After 
the semiconductor chip 12 is tested, the polyimide film 22 and the 
interconnects 14, 16, 18 and 20 will be cut immediately outside of 
openings 46, 48, 50 and 52, separating inner ring 26 from outer body 36 as 
shown in FIG. 1. The semiconductor chip 12 and the remaining interconnects 
14, 16, 18 and 20 will then be coupled to circuitry on a circuit board 
using the portion of interconnects passing over openings 46, 48, 50 and 
52. 
The thermal coefficient of expansion of the silicon material which may be 
used to form semiconductor chip 12 is on the order of two to three parts 
per million per degree centigrade. In contrast, the thermal coefficient of 
expansion of the polyimide film 22 is on the order of 18 parts per million 
per degree centigrade. As such, during radical changes in temperature 
sometimes encountered in the operating environment of semiconductor chip 
12, polyimide film 22 and semiconductor chip 12 can expand and contract at 
significantly different rates. This expansion differential places stress 
on contact leads 14, 16, 18 and 20. In some instances, semiconductor chip 
12 is tested to operate over a temperature range from -65.degree. C. to 
100.degree. C. During these temperature changes, the contact leads 14, 16, 
18 and 20 can delaminate from polyimide film 22 and in the most severe 
cases, certain leads, especially near the corners of semiconductor chip 
12, can break. 
According to the teachings of the present invention, the expansion of the 
polyimide film 22 and especially the expansion of the inner ring 26 is 
prevented from effecting the contact leads by including radial slots 54, 
56, 58 and 60 in the inner ring proximate the corners of the semiconductor 
chip 12 and the corner connecting members 38, 40, 42 and 44. As shown in 
FIG. 1, radial slot 54 extends partly through inner ring 26 between side 
piece 28 and side piece 30 of inner ring 26. Similarly, radial slot 56 
extends partly through inner ring 26 between side piece 30 and side piece 
32. Radial slot 58 extends partly through inner ring 26 between side piece 
32 and side piece 34 and, finally, radial slot 60 extends partly through 
inner ring 26 between side piece 34 and side piece 28. Radial slots 54, 
56, 58 and 60 operate to isolate the expansion and contraction of the four 
sides 28, 30, 32 and 34 of the inner ring 26 and, as such, prevent stress 
on the contact leads 14, 16, 18 and 20. 
Referring to FIG. 2, a tape automated bonding package 62 for semiconductor 
chip 12 is shown. Package 62 contains identical elements to package 10 
described with reference to FIG. 1. Particularly, package 62 comprises 
corner members 38, 40, 42 and 44 which serve to connect inner ring 26 to 
outer body 36 of polyimide film 22. As shown in FIG. 2, corner member 38 
comprises cross-slot 64 and cross-slot 66 which extend from opposite sides 
of corner member 38 partly into corner member 38. Similarly, corner member 
40 comprises identical cross-slots 68 and 70. Corner member 42 comprises 
cross-slots 72 and 74. Finally, corner member 42 comprises cross-slots 76 
and 78. Cross-slots 64 through 78 serve to isolate the expansion and 
contraction of the inner ring 26 from the expansion and contraction of the 
outer body 36 of polyimide film 22. 
FIG. 3 is an enlarged view of one corner of a package 80 constructed 
according to the teachings of the present invention. FIG. 3 illustrates 
one corner of semiconductor chip 12 which is once again surrounded by 
inner ring 26. Package 80 utilizes both cross-slots 64 and 66 in corner 
member 38 and radial slot 54 between side 28 and side 30 of inner ring 26. 
The combination of both techniques described respectively in FIG. 1 and 
FIG. 2 serve to completely isolate the expansion and contraction of the 
inner ring and the outer area 36 of polyimide film 22. FIG. 3 only 
illustrates one corner of the package 80 for reasons of clarity. It should 
be understood that similar structures may be formed on each corner of 
semiconductor chip 12. 
An important technical advantage of the present invention inheres in the 
fact that it allows for the differences in the rate of expansions between 
the semiconductor material used to form semiconductor chip 12 and the 
material used for form the portions of the polyimide film 22 used to 
support the semiconductor chip 12. The radial slots and cross-slots formed 
proximate the corners of the semiconductor chip 12 allow for the various 
portions of the polyimide film 22 and semiconductor chip 12 to remain 
isolated and to expand and contract independently. This independence 
prevents stress from being translated to the fragile contact leads and 
prevents delamination or breakage of the leads. 
Although the present invention has been described in detail, it should be 
understood that various changes, alterations and substitutions may be made 
to the teachings herein without departing from the spirit and scope of the 
present invention which is solely defined by the appended claims.