Integrated Circuit and Lead Frame Assembly

1. Field of the Invention

The present invention relates to integrated circuit and lead frame assemblies and more particularly, to such assemblies which are implemented in a tape automated bonding (TAB) process.

2. Description of the Related Art

Tape automated bonding (TAB) is a technique for connecting conductive leads to the electrical contacts on an integrated circuit chip, known as a die. When such leads are so connected, they can be used to interconnect the integrated circuit with additional circuitry. Typically a strip of film is divided into a plurality of adjacent rectangular segments, each of which has a plurality of conductive leads etched thereon. The leads in each segment are referred to as a lead frame. A die mounted on a central portion of each lead frame is electrically connected to the inner ends of the leads in the frame in a known manner. When so assembled, the film or tape upon which the die are mounted may be wound onto reels prior to additional processing, testing and the like. After final testing, the tape is cut into individual TAB segments, each of which contains a die and an associated lead frame.

Typically the leads are arranged so that the inner extremities thereof define a predetermined rectangular pattern which corresponds to a substantially identical pattern of contacts or bumps on the integrated circuit die to which each of the leads is connected. The outer extremity of each lead may thus be used to connect the integrated circuit to other components. TAB bonding is limited in the number of leads which can be routed to an integrated circuit (IC) due to processes in fabricating the TAB tape which limit the spacing of the leads. This is a particular problem on some integrated circuits which can require as many as 250 or more leads. It would be desirable to increase the number of lead connections which can be made to an integrated circuit.

An integrated circuit assembly comprises an integrated circuit having first and second sets of contact pads mounted thereon. A first lead frame comprises a substantially planar array of leads and has the inner extremities thereof connected to the first set of contact pads. In the central portion of the lead frame an opening is defined by the inner extremities of the leads. A second lead frame has a plurality of leads which extend through the opening and which are connected to the second set of contact pads.

A method of creating such an assembly is also provided.

It is a general object of the present invention to provide an integrated circuit and lead frame assembly which provides an increase in the number of lead connections which can be made to an integrated circuit.

It is a more specific object of the present invention to provide such an assembly in which two TAB lead frames are connected to an integrated circuit.

The foregoing and other objects, features and advantages of the invention will become more readily apparent from the following detailed description of a preferred embodiment which proceeds with reference to the drawings.

FIG. 1 is a plan view of an integrated circuit constructed in accordance with the present invention.

FIG. 2 is a plan view of a first lead frame connected to the integrated circuit of FIG. 1.

FIG. 3 is a plan view of a second lead frame connected to the structure illustrated in FIG. 2.

FIG. 4 is a cross-sectional view taken along 3--3 in FIG. 3.

Indicated generally at 10 in FIG. 1 is an integrated circuit die which makes up a portion of the preferred embodiment of the present invention. The die includes a body 12 which incorporates a silicon wafer (not visible) having the integrated circuit fabricated therein in a known manner. The body includes an upper surface 14 which is coated with a passivation layer to protect the integrated circuit.

A first set of contact pads 16 comprise a plurality of bumps, like bumps 18, 20, 22, 24, which are formed in a square adjacent the perimeter of die 10. A second set of contact pads, indicated generally at 26, includes a plurality of bumps, like bumps 28, 30, 32, which are formed in a square concentric with the square formed by the contact pads in first set 16.

The bumps in each of sets 16, 26 comprise gold posts which extend above passivation surface 14 approximately 1 mil to provide a mechanical stand-off from surface 14 for connecting leads thereto. Each of the bumps is electrically connected to internal regions of the integrated circuit in die 10. Die 10, including the bumps formed thereon, is fabricated utilizing a well known process. It is to appreciated that the present invention may also be implemented with an unbumped die.

In FIG. 2, die 10 is shown interconnected with a first lead frame 34. The lead frame is supported on a square, substantially planar base 36 having a central square opening 38 therethrough. Base 36 is made from a polyimide film. Polyester or glass-reinforced epoxy films are equally suitable as a material for base 36. Lead frame 34 includes a plurality of conductive leads, like leads 39, 40, 41, 42, 44, 45, which are connected to and supported by base 36. The leads, like leads 39-45, extend over the outer edge of base 36 as shown. Some of the leads extend inwardly to a bump, like lead 41 extends to bump 20, on die 10. Others of the leads, like lead 42, extend inwardly part way to the edge of opening 38 in base 36. The short leads, like leads 40, 42 are referred to herein as traces. The long leads, like leads 41, 44, 45, include inner ends which are connected to the bumps and which form an opening in the lead frame formed by the long leads.

Turning now to FIG. 3, indicated generally at 53 is an integrated circuit and lead frame assembly constructed in accordance with the present invention. Included therein is a second lead frame 54 which is shown laid over the structure illustrated in FIG. 2. Assembly 53 includes a planar base 56 having a central opening 58 therethrough. As with base 36, base 56 comprises a polyimide film which is substantially square and concentric with square opening 58. Base 56 supports a plurality of conductive leads, like leads 60, 62, 64. Each of the leads includes an inner and outer end, like inner end 66 and outer end 68 (in FIG. 4) on lead 60. An outer extremity 70 of lead 60 is connected to trace 40 on lead frame 34 directly therebeneath. The manner of making the connection is conventional and can comprise a solder connection or one made with conductive epoxy.

Each of the leads on second lead frame 54 includes an inner end which extends over opening 58 and which is connected to one of the bumps which form the contact pads in second set 26, like end 66 is connected to bump 28. Each of the outer lead ends on second lead frame 54 extends over the outer edge thereof and is connected to one of the traces on first lead frame 34, like outer end 68 of lead 60 is connected to trace 40. Since bases 36, 56 are substantially planar and are parallel to one another, the outer and inner ends of the leads in second lead frame 54 include bends which extend downwardly from the lead frame to connect with the bumps. Each of the bumps in both sets 16, 26 is thus electrically connected to a different lead over one of slots 48, 50, 52, 54. The outer ends of the leads mounted on base 36 are bent as shown in FIG. 4 to facilitate attachment to a circuit board.

In constructing assembly 53, die 10 is first fabricated, in a known manner, to produce gold bumps in a first set 16 and a second set 26, best illustrated in FIG. 1. Lead frames 34, 54 and the bases 36, 56, respectively, are also manufactured using known TAB processes. Lead frame 34 is connected to die 10 by positioning the two components as illustrated in FIG. 4 with the inner ends of the leads over the first set 16 of bumps. Thereafter, the inner lead ends are gang bonded to the bumps using known gang bonding technology. As previously mentioned, the present invention can be also implemented with unbumped die and single-point bonding. With lead frame 34 and die 10 so connected to one another, lead frame 54 is positioned relative to the die and first lead frame as shown in FIG. 4. The inner ends of the leads on lead frame 54 are then connected to the bumps in set 26, via, e.g., gang bonding or single-point bonding. The outer leads on frame 54 are connected to traces, like traces 40, 42 on lead frame 34, by soldering or with conductive epoxy. Other techniques, such as single-point bonding or laser welding may be equally well used.

An integrated circuit and lead frame assembly is thus provided which increases the number of leads which can be connected to an integrated circuit.

Having illustrated and described the principle of my invention in a preferred embodiment thereof, it should be readily apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles.