Patent Publication Number: US-6707136-B2

Title: Multi-layer lead frame for a semiconductor device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 09/941,020, filed Aug. 28, 2001, now U.S. Pat. No. 6,515,353, issued Feb. 4, 2003, which is a continuation of application Ser. No. 09/633,415, filed Aug. 7, 2000, now U.S. Pat. No. 6,307,255, issued Oct. 23, 2001, which is a continuation of application Ser. No. 09/371,681, filed Aug. 10, 1999, now U.S. Pat. No. 6,124,630, issued Sep. 26, 2000, which is a continuation of application Ser. No. 09/002,161, filed Dec. 31, 1997, now U.S. Pat. No. 5,965,936, issued Oct. 12, 1999, which is a continuation of application Ser. No. 08/811,343, filed Mar. 4, 1997, now U.S. Pat. No. 5,734,198, issued Mar. 31, 1998, which is a continuation of application Ser. No. 08/711,668, filed Sep. 4, 1996, abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to a semiconductor lead package system and, more particularly, to a multilayer lead frame for decoupling the power supply to an integrated circuit chip. 
     2. State of the Art 
     A semiconductor integrated circuit (IC) packaged device (part) generally includes an IC chip (die) being connected to inner leads of a lead frame by wire bonds. The chip, wire bonds, and inner leads are completely encapsulated for protection with a substance, such as plastic. Outer leads communicate with the inner leads of the lead frame, but the outer leads typically remain exposed for mounting of the packaged device to external circuitry, such as a printed circuit board. 
     In a conventional IC packaged device, a semiconductor die is placed on and bonded to a center die paddle of a lead frame for support. Inner lead fingers of the lead frame are disposed proximate to the paddle but do not contact or communicate with the paddle. Rather, wire bonds communicate between contact pads (terminals) on the die and the inner lead fingers of the lead frame by spanning the gap between the die and the fingers. The wire bonds allow for the transmission of the electrical signals between the die and the lead frame. 
     The recent production of three (3) volt IC chips has created the need for better power supply stability when testing and using the parts. Small spikes, glitches, bounces, noise, or the like (collectively “distortions”) on the power supply are more likely to cause failure in these 3-volt parts than in five (5) volt parts which have a better margin of error for power supply distortions. Namely, a given distortion at 3 volts is a higher percentage of the overall voltage than that at 5 volts. 
     In an effort to resolve potential failure from voltage distortions, decoupling capacitors have been mounted externally to the part on a board, or mounted on a handler during testing, in order to ensure a cleaner voltage supply to the part. However, for best decoupling, a capacitor must be mounted as close to the part as possible. But in an effort to mount a capacitor close to a part, other drawbacks usually arise. For example, a capacitor can be embodied on a die, but this takes up valuable and limited die space. Also, when testing a part in a handler, it is difficult to mount a capacitor close enough to the part to provide a reasonable amount of decoupling. 
     Thus, in an attempt to provide power supply decoupling, and also to improve heat dissipation and electrical performance, it has been known to use a multilayer lead frame wherein one of power supply and ground connections is supplied through a first layer, and the other of power supply and ground connections is supplied through a second layer. For example, U.S. Pat. No. 4,891,687 issued to Mallik et al. on Jan. 2, 1990, discloses a multilayer IC package. However, this disclosure requires the use of two conductive plates overlaying each other for power and ground, respectively, and a separate lead frame overlaying the plates for wire bonding. As such, the solution is undesirably complex. Namely, two separate layers of adhesive must bond the two plates and lead frame, one plate must have a center portion punched out for placement of the die and for wire bonding the die with the plates, and special tabs must be placed in precise locations on the plates for electrically connecting the plates with lead fingers of the lead frame. 
     Similarly, U.S. Pat. No. 4,965,654, issued to Karner et al. on Oct. 23, 1990, discloses a semiconductor package with a ground plane. However, in this case, the adaptation is only for a Lead Over Chip (LOC) implementation, and there are not two separate plates for power supply and ground connections, but rather only a ground plane and a lead frame overlaying the ground plane. Consequently, the decoupling capacitive effect is not as complete. Furthermore, the ground plane is actually two separate plates overlaying the die and proximate the bonding pads. This is necessary in order to allow for wire bonding of the lead fingers with the centrally located pads on the die. Moreover, the ground plane has special, small, cut-away portions on a surface for wire bonding with the die. 
     Given the foregoing problems associated with existing art and techniques, objects of the present invention are to provide a semiconductor lead package system that provides good decoupling of a power supply to a semiconductor die with a simplified multilayer lead frame. 
     BRIEF SUMMARY OF THE INVENTION 
     According to principles of the present invention in its preferred embodiment, a multilayer lead frame for decoupling a power supply to a semiconductor die includes overlaying first and second lead frame bodies having an insulator disposed therebetween and at least one main lead finger extending from each body. The bodies act as a capacitor to decouple the power supply to the die. One of the bodies and a respective finger provides one of power supply and ground connections for wire bonding with the die, and the other of the bodies provides the other of power supply and ground connections for wire bonding with the die. 
     According to further principles of the present invention, the first body includes a die paddle for supporting the die, and the second body includes a plate. The paddle overlays the plate with the insulator disposed in between the paddle and plate, thereby providing an electrical decoupling effect therebetween upon supplying power and ground connections respectively. 
     According to further principles of the present invention, a method of decoupling a power supply is disclosed for a semiconductor die using a multilayer lead frame as disclosed herein. The method comprises the steps of (1) supplying one of a power signal and a ground connection to the die through the first main lead finger extending from one of the paddle and plate, and wherein a wire bond communicates between the first main lead finger and one of a power and ground terminals of the die, and (2) supplying the other of the power signal and ground connection to the die through the second main lead finger extending from the other of the paddle and plate, and wherein a wire bond communicates between the second main lead finger and the other of the power and ground terminals of the die. 
     The aforementioned principles of the present invention provide an improved multilayer lead frame for decoupling a power supply to a semiconductor die. Other objects, advantages, and capabilities of the present invention will become more apparent as the description proceeds. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a perspective view of an exploded representation of one embodiment of the present invention showing the spacial relationship between an IC chip and the present invention multilayer lead frame. 
     FIG. 2 is a plan view of an alternate embodiment of the present invention multilayer lead frame. 
     FIG. 3 is a cross-section view of a packaged IC device embodying the multilayer lead frame of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a perspective view of an exploded representation of one embodiment of the present invention showing the spacial relationship between an IC chip (die)  10  and the present invention multilayer lead frame  20 . Lead frame  20  comprises first conducting lead frame body  25  having a die paddle  30  for supporting the die, and at least one first main lead finger  35  communicating with the paddle. Lead frame  20  further comprises a second conducting lead frame body  40  having a plate  45  and at least one second main lead finger  50  communicating with the plate. In the preferred embodiment, each main lead finger  35  and  50  is formed as a part of the paddle and plate, respectively, extending therefrom. Paddle  30  overlays plate  45  (or it could be said plate  45  overlays paddle  30 ), and insulator  55  is disposed therebetween. 
     One of paddle  30  and plate  45 , and respective main lead finger  35  and  50 , provides one of power supply and ground connections for wire bonding with one of power and ground terminals  85  and  90  of die  10 . The other of the paddle and plate, and respective communicating main lead finger, provides the other of power supply and ground connections for wire bonding with the respective power and ground terminals  85  and  90  of the die. 
     Die  10  is supportable on a first planar surface  60  of paddle  30 , and a second planar surface  65  (not visible) of the paddle, opposite the first planar surface, overlays plate  45  with insulator  55  disposed therebetween. 
     In its preferred embodiment, paddle  30  is of a shape and dimension substantially similar to die  10 . Namely, a circumferential dimension of paddle  30  is of a dimension substantially similar to a circumferential dimension of die  10 . Likewise, plate  45  and insulator  55  are of a shape and dimension substantially similar to paddle  30 . 
     Also in its preferred embodiment, insulator  55  is a double-sided thermosetting or thermoplastic adhesive coated polyimide film (tape), such as that sold under the trade name duPont Kapton®, or a sprayed-on polyimide or other highly dielectric material. Insulator  55  adheres paddle  30  to plate  45  and protects them from electrically shorting with each other. 
     First body  25  further includes, optionally, one or more signal lead fingers  70 , each having a tip disposed proximate to and separate from paddle  30  for wire bonding signal leads with bonding pads (terminals)  80  of die  10 . Likewise, second body  40  further includes, optionally, one or more signal lead fingers  75 , each also having a tip disposed proximate to and separate from plate  45  for wire bonding signal leads with terminals  80  of die  10 . Signal lead fingers  70  and  75  are termed “optional” because either first body  25  or second body  40  may have signal lead fingers in a mutually exclusive manner, or both may have signal lead fingers concurrently in any manner deemed best suited for a particular die used in conjunction with the lead frame. See FIG. 2 for further alternate embodiment details. 
     It should be noted here that lead finger bar supports  95  are not pertinent to the invention other than for supporting the lead fingers as part of the lead frame prior to being clipped off upon encapsulation of the die as is well known in the art. Also, although not shown in the drawing, it is understood by those of ordinary skill in the art that an insulator may be disposed between paddle  30  and die  10  as appropriate, depending on the type of die being used. 
     In reference to an example for this embodiment of the invention, assume first main lead finger  35  of paddle  30  is designated to receive a power supply, and terminal  85  of die  10  is designated as a power supply terminal. Assume also that second main lead finger  50  of plate  45  is designated as a ground connection finger, and terminal  90  is a ground connection terminal for die  10 . In this example, first main lead finger  35  would be wire bonded to power terminal  85  of die  10 , and second main lead finger  50  would be wire bonded to ground terminal  90  of die  10 . Any other signal connections are properly wire bonded between terminals  80  of die  10  and lead fingers  70  and  75  of either lead frame body, respectively. This configuration allows the paddle and plate to act as a capacitor to decouple the power supply to the die, ensuring a more clean and stable voltage signal supply to the die. 
     This example configuration also demonstrates the simplicity of the present invention in providing a clean power supply to a die. Namely, (1) a separate lead frame does not overlay the paddle and plate for wire bonding as in the prior art; (2) no special punched out portions need to be created in the paddle or plate for placement of the die as in the prior art; (3) no special tabs need to be placed in precise locations on the paddle and plate for electrically connecting such with lead fingers of the lead frame as in the prior art; and (4) no special notched portions need to be placed on the paddle and plate for wire bonding with the lead fingers as in the prior art. 
     Referring now to FIG. 2, a plan view of an alternate embodiment of the present invention multilayer lead frame is depicted. Although shown separately in this drawing, first lead frame body  102  includes paddle  105  which overlays plate  110  of second lead frame body  112  according to principles of the present invention, and an insulator is disposed therebetween (not shown). First main lead finger  115  extends from paddle  105  for supplying one of power and ground connections, and second main lead finger  120  extends from plate  110  for supplying the other of power and ground connections. In this embodiment, all of the signal lead fingers  125  are disposed proximate to paddle  105  as part of first lead frame body  102 , rather than some being disposed proximate to plate  110  as part of second body  112 . 
     Although FIGS. 1 and 2 depict two examples of how the paddle and plate are shaped, and how and where the main lead fingers could extend from the paddle and plate, and how and where the signal lead fingers could be disposed proximate to the paddle and plate, it is obvious that any number of shapes and configurations could be used, and any number of lead fingers could be employed, in coordination with the die that is to be wire bonded with the lead frame. For example, in FIG. 2, main lead fingers  115  and  120  could connect at any location around the periphery of the respective paddle and plate  105  and  110 . Specifically, the location of one of signal lead fingers  125  could be designated as the location for the connection of main lead finger  115 . Likewise, first lead frame body  102  is currently referenced with paddle  105  for supporting the die and overlaying plate  110 , and second body  112  is referenced with plate  110 . However, if second body  112  were to overlay first lead frame body  102 , then reference  110  would be considered the paddle for supporting the die, and reference  105  would be considered the plate. 
     FIG. 3 is a cross-section view of a packaged IC device  130  embodying the multilayer lead frame of the present invention. Die paddle  135  supports die  140  and overlays plate  145  with insulator  150  disposed therebetween. 
     One of paddle  135  and plate  145  provides one of power supply and ground connections for wire bonding with one of power and ground terminals of die  140 . The other of the paddle and plate provides the other of power supply and ground connections for wire bonding with the respective power and ground terminals of the die. 
     Wire bonds  155  and  157  communicate between terminals  160  and  165  of die  140  and main lead fingers  170  and  175 , respectively. Although not distinguishable from this view, one of terminals  160  and  165  may be a power terminal, and the other may be a ground terminal. Likewise, although not distinguishable from this view, one of lead fingers  170  and  175  may provide the power supply, and the other may provide the ground connection for die  140 . Signal lead fingers which are disposed only proximate the paddle and plate for wire bonding are not visible from this view as they are disposed “behind” main lead fingers  170  and  175 . 
     Die  140  is supportable on a first planar surface  180  of paddle  135 , and a second planar surface  185 , opposite the first planar surface of the paddle, overlays plate  145  with insulator  150  disposed therebetween. Insulator  150  adheres paddle  135  to plate  145  and protects them from electrically shorting with each other. 
     While a preferred embodiment of the invention has been disclosed, various modes of carrying out the principles disclosed herein are contemplated as being within the scope of the following claims. Therefore, it is understood that the scope of the invention is not to be limited except as otherwise set forth in the claims.