Inner-digitized bond fingers on bus bars of semiconductor device package

[0002] This application is a divisional of application Ser. No. 08/980,151, filed Nov. 26, 1997, now issued as U.S. Pat. No. 6,144,089.

[0003] 1. Field of the Invention

[0004] The present invention relates to semiconductor device packages. More particularly, the present invention relates to inner-digitized bond fingers on bus bars of lead frames in semiconductor device packages.

[0005] 2. State of the Art

[0006] The advancement of microprocessing technology has resulted in decreases in the physical dimensions of semiconductor devices such as integrated circuit dies or chips. Such dimensional decreases require coresponding decreases in the dimensions of semiconductor device packages, including a reduction in the size of lead frames and leads used in such packages.

[0007] In many semiconductor devices, a lead called a “bus bar” is used to distribute operating voltages to several contact areas on the semiconductor device, and to provide a ground bus to individual contact areas. For example, a bus bar can serve as an inner lead for providing a power supply voltage (Vcc) and a reference voltage (Vss) or a ground to the semiconductor chip. The bus bar can be connected to any point on the chip by short distance wire bonding to supply a voltage. This allows the bus bar to be effectively employed to reduce noise and increase processing speed.

[0008] Semiconductor device packages having a lead-on-chip structure have been developed to meet the demand that packaging for chips be smaller and thinner. A bus bar is used in a lead-on-chip structure to accommodate a number of wires in a limited space, and the bus bar is positioned on the chip.

[0009] A packaged semiconductor device is disclosed in U.S. Pat. No. 5,229,329 to Chai et al., in which a lead-on-chip lead frame having a first array and a second array of opposing lead fingers is utilized in the device. A pair of power supply bus bars lies between the opposing lead fingers, with an insulator covering the face of the bus bars.

[0010] In another lead-on-chip semiconductor device disclosed in U.S. Pat. No. 5,532,189 to Kiyono, recessed bus bar regions are provided in an elongated bus bar to accommodate location of bonding wires which couple the chip pads and associated inner leads. Fillets are formed of insulative adhesive material up about the bus bar region sides to thereby engage the bonding wires to prevent contact between the wires and the bus bar.

[0011] In conventional lead-on-chip semiconductor device packages with a bus bar, the bonding wires attached to leads and the chip are required to jump over the bus bar, resulting in a relatively higher wire loop and longer wire. Adjacent bonding wires attached to the bus bar and the chip have a relatively shorter wire loop height and length. Thus, the respective bonding wires attached to the bus bars and to the leads have different loop heights and lengths, resulting in more complexity in manufacturing the device.

[0012] In U.S. Pat. No. 5,592,020 to Nakao et al., a conventional semiconductor device package (not lead-on-chip) is disclosed in which a chip is mounted on a bed of a lead frame, and leads such as a pair of bus bars have alternating offset projections off the chip. In one embodiment, an elongated portion of one of the bus bars, excluding the projections on the bus bar, is pushed downward away from bonding wires attached to the chip. While the alternating offset projections on the bus bars provide for more uniformity in wire length in this conventional package, the wire lengths are still relatively longer, since the bus bars have to be spread out off the chip to form the offset projections, thereby reducing the speed of the chip.

[0013] Accordingly, there is a need for improved bus bar structures that overcome or avoid the above problems in semiconductor devices.

[0014] The present invention is directed to a semiconductor device package such as a lead-over-chip (LOC) integrated circuit package in which at least one pair of bus bar structures on a lead frame in the device has inner-digitized bond fingers for wire bonding to a semiconductor die or chip. The inner-digitized bond fingers provide for substantial uniformity in wire loop height and length for bond wires attached to the bus bars and the chip. This allows for easier manufacture and inspection of an LOC semiconductor device.

[0015] In one aspect of the invention, a semiconductor device package includes a lead frame with a plurality of lead members positioned in an array on a first plane along a vertical axis of the lead frame and a semiconductor die secured to the lead frame. At least one pair of bus bars is connected to the lead frame and positioned over the semiconductor die, with a portion of the bus bars positioned over the semiconductor die including a plurality of inner-digitized bond fingers. The inner-digitized bond fingers are formed from a series of alternating projections and recesses on each bus bar. A first plurality of connection members such as bond wires electrically couples the lead members to the semiconductor die. A second plurality of connection members electrically couples the inner-digitized bond fingers of the bus bars to the semiconductor die. The second plurality of connection members preferably has a substantially uniform loop height and length.

[0016] An encapsulating material is formed around the semiconductor die, the bus bars, the connection members, and an inner portion of the lead frame to provide a protective covering for the semiconductor device. The portions of the bus bars over the semiconductor die can be offset along the vertical axis from an outer surface of the semiconductor die, or the portions of the bus bars over the semiconductor die can be adjoined to the outer surface of the semiconductor die.

[0017] In one preferred embodiment, a semiconductor device package according to the present invention having a lead-over-chip structure includes a lead frame with a plurality of lead fingers positioned in an array. A semiconductor die is secured to the lead frame, with the semiconductor die including first and second pluralities of bond pads. A first bus bar operatively connected to the lead frame traverses over the semiconductor die and includes a plurality of alternating projections and recesses. A second bus bar operatively connected to the lead frame traverses over the semiconductor die adjacent the first bus bar, with the second bus bar also including a plurality of alternating projections and recesses. Each of the projections of the second bus bar extends into a corresponding one of the recesses of the first bus bar, while each of the projections of the first bus bar extends into a corresponding one of the recesses of the second bus bar, thereby forming inner-digitized bond fingers. A first plurality of bond wires electrically couples the first bus bar to the semiconductor die, with each of the first plurality of bond wires being connected to one of the projections of the first bus bar and one of the first plurality of bond pads on the semiconductor die. A second plurality of bond wires electrically couples the second bus bar to the semiconductor die, with each of the second plurality of bond wires traversing the first bus bar to be connected to one of the projections of the second bus bar and one of the second plurality of bond pads on the semiconductor die.

[0018] The present invention provides many advantages and benefits in forming a semiconductor device package. The inner-digitized bond fingers on the bus bars in the present invention result in a reduced number of wire groups having different looping parameters, since there is consistency in the wire trajectory and loop height and length of bond wires attached to the bus bars over the die. This allows the wire bonding program to be simpler with respect to set-up and operation, allows line production to run smoother, and provides increased performance to the chip. In addition, production line yield at the wire bond is improved because the bonding target zones on the inner-digitized bond fingers are all at a similar distance from the bond pads. The present invention also provides improved production line yield during encapsulation of a semiconductor device.

[0019] In another aspect of the invention, a method for fabricating a semiconductor device package includes forming a lead frame with a plurality of lead members such as lead fingers positioned in an array on a first plane along a vertical axis of the lead frame. At least one pair of bus bars is formed on the lead frame, with a portion of the bus bars including a plurality of inner-digitized bond fingers. A semiconductor die is secured to the lead frame such that the pair of bus bars is positioned over the semiconductor die. A first plurality of bond wires is attached to the semiconductor die and the lead members. A second plurality of bond wires is attached to the semiconductor die and the inner-digitized bond fingers of the bus bars, such that the second plurality of bond wires has a substantially uniform loop height and length. The above components are then encapsulated with a protective material.

[0020] Other aspects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.

[0021] In order to understand the manner in which the above-recited and other advantages of the invention are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0022] FIG. 1 is a plan view of a semiconductor device package according to one embodiment of the present invention; and

[0023] FIG. 2 is a plan view of a semiconductor device package according to another embodiment of the invention.

[0024] The present invention is directed to a semiconductor device package such as a lead-over-chip integrated circuit package in which at least one pair of bus bar structures on a lead frame in the device has inner-digitized bond fingers for wire bonding to a semiconductor die or chip. The term “inner-digitized” as used herein in conjunction with bond fingers on a pair of bus bars means that the bond fingers on each bus bar form alternating offset projections defining adjacent recesses that accept corresponding projections from the other bus bar to form at least one interlaced bond finger region along the pair of bus bars. The inner digitized bond fingers on the bus bars of the present invention enhance wire bonding performance and throughput during manufacture of a semiconductor device. The bus bars are connected to lead fingers that extend off the chip.

[0025] Referring to FIG. 1, a semiconductor device package 10 according to one embodiment of the present invention is depicted. The package 10 has a lead-over-chip (LOC) structure and includes a lead frame 12 formed of a conductive metal. The lead frame 12 has a plurality of external connections in the form of lead members or fingers 14, which later serve as pins for connecting the semiconductor device.

[0026] An integrated circuit semiconductor chip or die 16 is secured to lead frame 12 by a conventional attaching means such as a suitable adhesive. The semiconductor die 16 can be any integrated circuit device. The semiconductor die 16 has a plurality of interconnection pads on an active surface thereof such as bond pads 18, 19aand 19b, which are disposed along the outer edges of semiconductor die 16 along three sides. The bond pads are configured for electrical connection to lead fingers 14 and to bus bars by connection members such as bond wires, as discussed in more detail below.

[0027] A first pair of bus bars 20aand 20btraverses over semiconductor die 16 and is electrically connected respectively to lead fingers 21aand 21bthat come off semiconductor die 16. The bus bars are formed as part of the lead frame conductive material and provide ground voltage (Vss) or positive voltage (Vcc) to semiconductor die 16. As shown in FIG. 1, a low potential Vss (e.g., ground potential) is applied to lead fingers 21aconnected to bus bar 20a, while a high potential Vcc is applied to lead fingers 21bconnected to bus bar 20b.

[0028] Portions of bus bars 20aand 20btraversing over semiconductor die 16 include a plurality of inner-digitized bond fingers 22aand 22bformed by a series of alternating recesses and projections on each of bus bars 20aand 20b. The projections and recesses forming the bond fingers 22aon bus bar 20aengage respectively with the recesses and projections forming bond fingers 22bon bus bar 20bas shown in FIG. 1. Thus, each of the projections of bus bar 20aextends into a corresponding one of the recesses of bus bar 20b, and each of the projections of bus bar 20bextends into a corresponding one of the recesses of bus bar 20a. The bond fingers 22aand 22bof bus bars 20aand 20binclude bonding zones thereon for attachment of bond wires as discussed below. The inner-digitized configuration of bond fingers 22aand 22ballows the bond wire lengths to be substantially uniform for both of bus bars 20aand 20b.

[0029] The portions of bus bars 20aand 20bpositioned over semiconductor die 16 can be offset such as by being upset along a vertical or z-axis from an outer surface of semiconductor die 16. Changing the z-axis height of the bus bars balances out the flow of the molding compound during encapsulation of the device. As shown in FIG. 1, each of bus bars 20aand 20bis connected to four separate leads in the form of lead fingers 21aand 21b, respectively. This adds strength to the lead frame structure, which is important during encapsulation of the device with a molding compound. Alternatively, the portions of bus bars 20aand 20bover semiconductor die 16 can be adjoined to the outer surface of semiconductor die 16, with an appropriate insulation material (not shown) used therebetween.

[0030] FIG. 1 also depicts a second pair of bus bars 24aand 24bthat traverses across semiconductor die 16. The bus bars 24aand 24bdo not have inner digitized bond fingers. Leads at opposite ends of package 10 in the form of lead fingers 25aand 25bare attached to each end of bus bars 24aand 24b, providing added strength to the bus bar structures.

[0031] An encapsulating material 26 such as a molding compound of a plastic material is formed around the semiconductor die, the bus bars, the bond wires, and an inner portion of the lead frame to provide a protective covering such as a plastic body for these components. A molding compound such as a plastic epoxy can be utilized as the encapsulating material. Low stress molding techniques known to those skilled in the art are used in encapsulating the device. With the bus bars running across the semiconductor die, it is important to anchor down the bus bars at both ends so the bus bars do not move around during encapsulation with a molding compound.

[0032] The portions of lead fingers 14 disposed in encapsulating material 26 are referred to as “inner leads,” while the portions of lead fingers 14 that extend out of material 26 are referred to as “outer leads.” The outer leads extending outside of material 26 later serve as external pins for connecting the semiconductor device.

[0033] Each inner lead portion of lead fingers 14 is provided with a bonding area 15 where a bond wire is to be attached. It is preferred, where possible, that the width of the inner lead at bonding area 15 be wider than the other portion of a lead finger 14 to ensure proper wire bonding.

[0034] A conventional wire bonding process can be used to couple various bond wires to the semiconductor die and to the lead fingers and bus bars. For example, one end of a bond wire is connected to a bond pad on the semiconductor die, while the other end of the bond wire is attached to the bonding area of a lead finger. Other bond wires are connected to different bond pads and to bonding zones on the bus bars.

[0035] As shown in FIG. 1, a first plurality of bond wires 28 electrically couples lead fingers 14 to a first plurality of bond pads 18 of semiconductor die 16. For example, one end of a bond wire 28 is attached to a lead finger 14 at bonding area 15 and the other end of bond wire 28 is attached to a corresponding bond pad 18 along the edge of semiconductor die 16.

[0036] A plurality of bond wires 29aand 29belectrically couples the bond fingers 22aand 22bof bus bars 20aand 20bto a plurality of selected bond pads 19aand 19bon semiconductor die 16. For example, one end of a bond wire 29ais connected to a corresponding bond pad 19a. The other end of bond wire 29ais connected to a bonding zone of a bond finger 22aof bus bar 20a. The bond wires 29bare connected in a similar manner to bond pads 19band to bonding zones on bond fingers 22bof bus bar 20b. Multiple bond wire contacts are made to the bus bars to more efficiently distribute voltage to the chip.

[0037] In forming the semiconductor device package of the invention, it is important that the bonding zones on the bond fingers of the bus bars be as close to directly in front of a corresponding bond pad on the semiconductor die as possible. It is also important that adjacent bond wires not touch each other in order to prevent shorting. In one preferred encoding the trajectories of the bond wires attached between the bond pads and the bond fingers are about 30° or less with respect to a line perpendicular to the edge of the die adjacent to the bond pads. Thus, a bond wire trajectory of 0° would be perpendicular to the edge of the die. The trajectory angle can be greater as long as the trajectory of a particular bond wire does not interfere with another bond wire.

[0038] Referring to FIG. 2, a semiconductor device package 40 according to another embodiment of the present invention is depicted. The package 40 has a lead-over-chip structure and includes a lead frame 42 with a plurality of lead fingers 44. A semiconductor die 46 is secured to lead frame 42 by a conventional attaching means. The semiconductor die 46 has a plurality of bond pads 48 and 49a-49fdisposed along the outer edges of three sides thereof. The bond pads are configured for electrical connection to lead fingers 44 and to bus bars by bond wires, as discussed in more detail below.

[0039] Three pairs of bus bars traverse over various portions of semiconductor die 46 as shown in FIG. 2. A first pair of bus bars 50aand 50btraverses over a portion of semiconductor die 46 at one end thereof and is connected respectively to lead fingers 51aand 51bthat come off semiconductor die 46. A second pair of bus bars 50cand 50dtraverses over a portion of semiconductor die 46 at the opposite end thereof from bus bars 50aand 50b, and is connected respectively to lead fingers 5cand 51d. A third pair of bus bars 50eand 50ftraverses over the entire length of semiconductor die 46 and is connected respectively to lead fingers 51eand 51fdisposed at opposite ends of lead frame 42. As illustrated in FIG. 2, a low potential Vss (e.g., ground potential) is applied to lead fingers 51a, 51cand 51econnected to bus bars 50a, 50cand 50e, while a high potential Vcc is applied to lead fingers 51b, 51dand 51fconnected to bus bars 50b, 50dand 50f.

[0040] The portions of the bus bar pairs traversing over semiconductor die 46 include a plurality of inner-digitized bond fingers formed by a series of alternating recesses and projections on each bus bar. For example, projections and recesses form bond fingers 52aon bus bar 50a, which engage respectively with recesses and projections forming bond fingers 52bon bus bar 50bas shown in FIG. 2. Projections and recesses also form bond fingers 52con bus bar 50c, which engage respectively with recesses and projections forming bond fingers 52don bus bar 50d. In addition, projections and recesses also form bond fingers 52eon bus bar 50e, which engage respectively with recesses and projections forming bond fingers 52fon bus bar 50f. The bond fingers of the bus bars include bonding zones thereon for attachment of bond wires as discussed below.

[0041] The portions of the bus bars positioned over semiconductor die 46 can be offset such as by being upset along a vertical or z-axis from an outer surface of semiconductor die 46. Alternatively, the portions of the bus bars over semiconductor die 46 can be adjoined to the outer surface of semiconductor die 46, with an appropriate insulation material (not shown) used therebetween.

[0042] An encapsulating material 56 such as a molding compound of a plastic material is formed around the semiconductor die, the bus bars, the bond wires, and an inner portion of the lead frame to provide a protective covering for these components in the embodiment of FIG. 2. The outer leads extending outside of material 56 later serve as external pins for connecting the semiconductor device. Each inner lead portion of lead fingers 44 is provided with a bonding area 45 where a bond wire is to be attached. It is preferred, where possible, that the width of the inner lead at bonding area 45 be wider than the other portion of a lead finger 44 to ensure proper wire bonding.

[0043] As shown in FIG. 2, a first plurality of bond wires 58 electrically couples lead fingers 44 to a first plurality of bond pads 48 of semiconductor die 46. For example, one end of a bond wire 58 is attached to a lead finger 44 at bonding area 45 and the other end of bond wire 58 is attached to a corresponding bond pad 48 along the edge of semiconductor die 46.

[0044] A plurality of other bond wires electrically couples the bond fingers of the bus bars to a plurality of selected bond pads on semiconductor die 46. For example, one end of a bond wire 59ais connected to a corresponding bond pad 49a. The other end of bond wire 59ais connected to a bonding zone of bond finger 52aof bus bar 50a. The bond wires 59bare connected in a similar manner to bond pads 49band bonding zones on bond fingers 52bof bus bar 50b. Additional bond wires 59c, 59d, 59eand 59fconnect bus bars 50c, 50d, 50eand 50fto selected bond pads 49c, 49d, 49eand 49fon semiconductor die 46 as depicted in FIG. 2.

[0045] The above-described embodiments of the invention utilize a hybrid lead frame in which some leads are off the semiconductor die, and some leads attached to bus bars are over the die. With the bus bars placed over the die, the whole area of the die can be utilized. This allows leads to not be crowded so it is possible to inner-digitize the bus bars over the die. All of the bond wires that are on the die can have one wire group set of parameters and all the wires that are off the die can have a different wire group set of parameters, thereby more easily facilitating manufacture of the semiconductor device. For example, the leads that are off the die can have bonding areas that are lower than the bond pads on the semiconductor die. Thus, the bond wires attached to leads off the die are going to have different parameters than bond wires attached to the bus bars over the die.

[0046] The present invention provides for general uniformity in the trajectory of bond wires in a group, which means that every wire in a particular group has the same or similar loop height and length. The loop height is defined as the vertical distance from the surface of the die to the highest point of the wire. The loop length is the distance the wire travels from a bond pad on the semiconductor die to a bonding zone on a bus bar or a lead finger. The present invention allows consistent loop shapes and lengths within a particular wire group, as well as fewer wire groups.

[0047] Although the present invention has been described with respect to lead-over-chip assemblies, the present invention can also be applied to conventional semiconductor packages in which bus bars are being jumped over by bond wires.

[0048] In a method for fabricating a semiconductor device package according to the present invention, a lead frame is formed with a plurality of lead fingers positioned in an array on a first plane along a vertical axis of the lead frame. At least one pair of bus bars is formed on the lead frame, with a portion of the bus bars including a plurality of inner-digitized bond fingers. A semiconductor die having first and second pluralities of bond pads thereon is secured to the lead frame such that the pair of bus bars is positioned over the semiconductor die. A first plurality of bond wires is attached to the first plurality of bond pads on the semiconductor die and to the lead fingers. A second plurality of bond wires is attached to the second plurality of bond pads on the semiconductor die and to the inner-digitized bond fingers of the bus bars, such that the second plurality of bond wires has a substantially uniform loop height and length. The above components including the semiconductor die, the bus bars, the first and second pluralities of bond wires, and an inner portion of the lead frame are then encapsulated with a protective material such as an epoxy material.

[0049] In a method for producing a lead frame for use in a semiconductor device package having a lead-over-chip structure according to the present invention, a plurality of lead fingers is formed in an array on a first plane along a vertical axis of the lead frame. A first bus bar is formed with a plurality of alternating projections and recesses and is configured to traverse over a semiconductor die. A second bus bar is formed adjacent to the first bus bar, with the second bus bar also including a plurality of alternating projections and recesses. In the assembled lead frame, each of the projections of the second bus bar extends into a corresponding one of the recesses of the first bus bar and each of the projections of the first bus bar extends into a corresponding one of the recesses of the second bus bar.

[0050] The present invention provides many advantages and benefits in forming a semiconductor device package over prior technology. The inner-digitized bond fingers on the bus bars in the present invention result in a reduced number of wire groups having different looping parameters, since there is consistency in the wire trajectory and loop height and length of bond wires attached to the bus bars over the die. This allows the wire bonding program to be simpler with respect to set-up and operation, allows line production to run smoother, and provides increased performance to the chip. Otherwise, if there is a varying degree of wire loop trajectories and loop heights such as in the prior art, it is more difficult for the wire bonding program to be set-up and operated.

[0051] In addition, production line yield at the wire bond is improved because the bonding target zones on the inner-digitized bond fingers are all at a similar distance from the bond pads. The wire bonder machine utilized during production runs smoother if all bond wire lengths are about the same. The present invention also provides improved production line yield during encapsulation of a semiconductor device. By having consistent wire looping, the process window is wider and allows for easier molding because there is more room to move within the process window without affecting the product.

[0052] The inner-digitized bond fingers of the bus bars according to the present invention are also advantageous in that by allowing for uniformity of bond wire loops in length, height and trajectory, inspection for defects of a manufactured product is facilitated. A uniform bond wire loop scheme allows for easy detection of a poorly formed loop that may lead to yield reduction if not detected. Consistency and uniformity of the wires allow inspection of a manufactured product to be made more easily, since it is easier to identify a bad or sagging wire if one exists in relation to a uniform group of wires. Such inspection can be by individual visual inspection or by an optical device that recognizes differences in placement of the wires.

[0053] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.