Semiconductor device having a lead frame

Abstract: Along the column of bonding pad (1), bonding terminal portions (2c), (3c), (4a), (5a) of bus bars (2), (3) and signal lines (4), (5) are arranged; principal wiring portions (2a), (3a) are made to extend in a 3-dimensional crossing configuration with respect to the signal lines and they are connected to the bonding terminal portion of the bus bars, forming the IC package of the LOC type. Between the various bonding terminal portions and the various bonding pads, there exists no main wiring portion of the bus bar. Consequently, bonding wires (6), (7), (8), (9) do not straddle the bus bar principal wiring portion. As a result, when the bonding wire is not elevated, the bonding wire still does not make contact with the bus bar principal wiring portion to cause short circuit; as a result, the reliability is high and the device becomes thinner.

Description: FIELD OF THE INVENTION This invention concerns a semiconductor device. In particular, this invention concerns a package with the LOC (Lead On Chip) structure. BACKGROUND OF THE INVENTION In the prior art, there is the LOC configuration with a lead frame set on the IC chip as a package for sealing the IC chip. This can be explained with reference to Figures 10 and 11. As shown in Figure 10, the LOC-structure DRAM (dynamic RAM) has multiple bonding pads 1 set on a straight line at the central portion of IC chip 10. On the two sides of the pad column are power-source lines 42, 43, known as bus bars, that form the lead frame, for LOC and are made of iron-nickel alloy, copper alloy or copper, as well as multiple signal lines (lead frame) 44, 45. Bus bars 42, 43 are connected to power source Vss or Vcc. On the other hand, signal lines 44, 45 are used for addresses A0 through A10 as well as CAS, RAS or other signals. Connection between each pad 1 and each line is performed by means of bonding wires 6, 7 on one side (the left side) of the bonding-pad column; it is performed by means of bonding wires 8, 9 on the other side (the right side). As shown explicitly in Figure 11, wires 7, 9, which connect signal lines 44, 45 to pad 1 stride over bus bars 42, 43, respectively. Consequently, when wires 7 and 9 are not sufficiently high, they may be in contact with bus bars 42, 43, and there is the danger that a short-circuit will formed between the signal lines and the bus bars. In order to prevent this problem, the height of wires 7, 9 must be sufficiently large. This, however, hampers the effort to reduce the thickness of the resin-mold package. As shown in Figure 12, on IC chip 10, bonding pads RP are set in one column on each of the left and right sides. On the two sides of each pad column, signal lines 3A1 and bus bars 3A2 are set. Connection by bonding wire W is performed for each pad column by means of signal lines on one side and by means of bus bars on the other side. Consequently, the wires no longer stride the bus bars as described in the above, and the short-circuit between the signal lines and the bus bars can be entirely avoided for this lead frame. However, for the package shown in Figure 12, signal lines 3A1 can be set only on one side with respect to a pad column; hence, the efficiency is poor, and the layout is also limited. In addition, as the pin number is increased, the pitch distance among the signal lines becomes smaller, and there is little tolerance. EP-A-0 425 775 discloses a plastics-encapsulated semiconductor package in which connecting lead frame members are deposited over the surface of the device together with a covering ground plane. In particular, a lead frame having a plurality of conductors is attached to a major active surface of a semiconductor chip via a ground plane in the form of a multilayered structure containing an insulated, integral, uniform ground plane positioned between the lead frame and the chip and adhesively and insulatively joined to both of them. Wires connect terminals on the major active surface of the semiconductor chip to the ground plane and to selective lead frame conductors. EP-A-0 272 187 discloses a plastics package for high frequency semiconductor devices including an internal ground plane connected to a ground ring formed on the packaged semiconductor device. The ground plane includes a plurality of bumps which project upward between adjacent lead fingers of a lead frame. A ground frame on the semiconductor die is connected to the bumps, and the signal bonding pads connected to the lead fingers by wire or tape bonding. The document PATENT ABSTRACTS OF JAPAN (045), (E-1162) and JP-A3 250 654 disclose a resin-sealed semiconductor device and lead frame in which to prevent cracking of resin from ocurring at the upper end of an inner lead, sealing resin is placed at least partially between an insulating film and the inner lead. An object of this invention is to provide a package-structure semiconductor device, in which a short-circuit between signal lines and bus bars can be prevented, the thickness of the package can be reduced, and the signal lines can be set easily, with the connection made at a high efficiency. The present invention provides a semiconductor device comprising: a semiconductor substrate having a surface on which an integrated circuit is provided, a plurality of bonding pads disposed on the surface of said semiconductor substrate at a central location thereon and arranged in a nearly columnar shape, first and second bus bars on the surface of said semiconductor substrate and respectively disposed on opposite sides of the nearly columnar arrangement of bonding pads, each of said bus bars having a plurality of wire bonding terminals and including a base wiring portion extending in a straight line in spaced parallel relation to said arrangement of bonding pads, first and second pluralities of elongated leads on the surface of said semiconductor substrate and having inner lead portions respectively disposed on opposite sides of said arrangement of bonding pads and outer lead portions integral with the respective inner lead portions and extending outwardly from said semiconductor substrate, first insulating means interposed between said first and second bus bars and the surface of said semiconductor substrate and between said first and second pluralities of elongated leads and the surface of said semiconductor substrate, a first group of individual connector wires connected to respective ones of said bonding pads at one end and to respective wire bonding terminals of said first and second bus bars at the other end thereof, and a second group of individual connector wires connected to respective others of said bonding pads at one end and to respective inner lead portions of said first and second pluralities of elongated leads at the other end thereof; characterized in that each of said bus bars includes a plurality of branch portions integral with and extending inwardly from said base wiring portion toward said arrangement of bonding pads, said plurality of branch portions being in substantially perpendicular relation to said base wiring portion, a plurality of bonding terminal portions integral with and corresponding to said plurality of branch portions, each of said bonding terminal portions including a wire bonding terminal of said plurality of wire bonding terminals, the leads of each of said first and second pluralities of elongated leads extending across the base wiring portion of the bus bar corresponding thereto, second insulating means interposed between the crossing leads of each of said first and second pluralities of elongated leads and the base wiring portion of the bus bar corresponding thereto for electrically insulating said leads from said base wiring portion, the wire bonding terminal of each of said bonding terminal portions extending inwardly from said base wiring portion toward said arrangement of bonding pads and in offset relation to the branch portion corresponding thereto, and said first and second groups of individual connector wires being arranged such that none of the connector wires cross over the respective bus bar corresponding thereto in being connected between respective bonding pads and wire bonding terminals with respect to the first group of connector wires and between bonding pads and respective inner lead portions of said first and second pluralities of elongated leads with respect to the second group of connector wires. The illustrated embodiments of the invention shown in the accompanying drawings include the following features: the multiple bonding pads connected to the bonding-terminal portion of the lead frame are set in a nearly columnar shape on the circuit-forming plane of the semiconductor chip; the aforementioned bonding-terminal portion for the multiple signal lines of the lead frame and the bonding-terminal portion for the multiple power-source lines are bonded via an electrical insulator on the aforementioned semiconductor chip in the vicinity of and along the aforementioned bonding-pad column; the principal portion of the aforementioned power-source line extends in a 3-dimensional crossed configuration for electrical insulation from the aforementioned signal line, the aforementioned principal portion of the aforementioned power-source line and the bonding-terminal portion of the aforementioned power-source line are formed continuously in an integrated manner; the aforementioned various bonding-terminal portions and the aforementioned bonding pads are electrically connected. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an enlarged partial oblique view illustrating the main portion of the IC package with the LOC structure in an embodiment of this invention. Figure 2 is a plan view illustrating the aforementioned main portion. Figure 3 is a cross-sectional view cut along line III-III in Figure 2. Figure 4 is a cross-sectional view cut along line IV-IV in Figure 2. Figure 5 is a plan view of the main portion in the state before the bus bar is folded in the embodiment illustrated in Figures 1-4. Figure 6 is a cross-sectional view cut along line VI-VI in Figure 5. Figure 7 is an enlarged partial cross-sectional view illustrating a modified example on the base of the example shown in Figures 1-6. Figure 8 is a partial plan view illustrating the main portion of the IC package with the LOC structure in another embodiment of this invention. Figure 9 is an enlarged partial oblique view illustrating the main portion of the IC package with the LOC structure in yet another embodiment of this invention. Figure 10 is a plan view illustrating the main portion of the IC package with the LOC structure in a conventional example. Figure 11 is a cross-sectional view cut along XI-XI line in Figure 10. Figure 12 is a plan view illustrating a portion of the lead frame with the LOC structure in another conventional example. In reference numerals as shown in the drawings: 1, bonding pad 2, 3, 12, 22, 23, 32, 33, bus bar (power source line) 2a, 3a, 12a, 22a, 23a, 32a, 33a, principal wiring portion 2b, 3b, 12b, 22b, 23b, 32b, 33b, branched portion 2c, 3c, 4a, Sa, 12c, 22c, 23c, 24a, 25a, 32c, 33c, bonding terminal portion 2d, 3d, 4b, 5b, 22d, 23d, 24b, 25b, 32d, 33d, lead portion 4, 5, 24, 25, signal line 4c, step portion 6, 7, 8, 9, bonding wire 10, IC chip 11, insulating double-side tape 15, insulating tape or insulating paste 16, groove of signal line 19, fixture for folding 26, bump electrode CL 1 , CL 2 , central line DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, embodiments of this invention will be explained in detail with reference to the accompanying drawings. Figures 1-6 show a first embodiment of this invention, applied to DRAM. The package in this embodiment has the LOC configuration explained above. As shown in Figure 2, multiple bonding pads 1 are set in a column on a straight line. With the column of bonding pad 1 taken as central line CL 1 , the configuration shown in the figure is symmetric for the right and left sides, with bus bar 2 (for Vss) set on the left side, and with bus bar 3 (for Vcc) set on the right side. Bus bar 2 (the same for bus bar 3) consists of a straight-line shaped wiring portion 2a, branched portion 2b (3b), bonding-terminal portion 2C (3C), and lead portion 2d, which is connected to the end of the bonding terminal and is lead outside the IC package. Using insulating double-sided tape 11, bonding-terminal portion 2C of bus bar 2 and bonding terminal 4a of signal line 4 are bonded on the upper surface of IC chip 10. In this figure, 4b represents the lead portion of signal line 4 to the outside of the IC chip. The same state also exists for bus bar 3 and signal line 5 on the side of bus bar 3. For the IC package, the configuration is symmetric for the upper and lower sides with reference to CL 2 as the center line. Broken line 12 on the periphery represents the resin-sealing area in case of molding. The bonding operation between the bus bars and signal lines is performed as follows. Bonding-terminal portion 2C of bus bar 2 and bonding terminal 4a of signal line 4 are connected to bonding pad 1 via bonding wires 6, 7. Similarly, bonding-terminal portion 3C of bus bar 3 and bonding-terminal portion 5a of signal line 5 are connected to bonding pad 1 by means of bonding wires 8, 9, respectively. Bonding wires 6 and 7 as well 8 and 9, are set on either the left or right side of center line CL 1 . As shown in Figure 3, the cross-sectional view cut along line III-III in Figure 2, and Figure 4, the cross-sectional view cut along line IV-IV in Figure 2, all of the wires do not stride the wiring as bonding pad 1 is connected to bonding-terminal portion 2C, 4a, 3C, or 5a. Consequently, there is no need to increase the height of wires 6, 7, 8, and 9, and there is no danger of a short-circuit. In this example, attention should be given to the shape of the bus bar. As can be seen from Figure 2, the enlarged obligue view of area I defined by the broken line is shown in Figure 1, where branch portion 2b of bus bar 2 is mechanically bent by 180° from the upper side to the left, and the upper and lower portions are overlapped with distance d between them. The thickness t 1 of bus bar 2 and signal line 4 of the lead frame for the LOC is 5 mil or 8 mil. When t 1 is 5 mil, distance d is 3 mil; when t 1 is 8 mil, distance d becomes [not given in original]. Here, 1 mil represents 25.4 µm. Consequently, principal wiring portion 2a of bus bar 2 is arranged at the distance d without contacting signal line 4. The thickness of the principal wiring portion of bus bar 2a, and the sum of the thickness t 2 of distance d and signal line 4, becomes 13 mil when t 1 is 5 mil. In the prior art shown in Figure 11, the loop apex of bonding wires 7, 9 for the signal equipment and striding for the bus bar has a height of 24 mil from the circuit-forming surface of the IC chip. On the other hand, in this invention, as pointed out in the above, when the thickness of the lead frame sheet is 5 mil, and the thickness of the insulating double-sided tape 11 is 3 mil, the height of the apex of the bus bar from the circuit-forming surface of the IC chip becomes 16 mil. That is, the thickness of the resin-mold package can be significantly reduced. As shown in Figures 1, 3, and 4, in order to reliably prevent the contact of bus bar 2a with signal-line lead portion 4b, the lower surface of principal wiring portion of bus bar 2a is bonded with an insulating tape or insulating paste 15. Distance d, the gap between principal wiring portion 2a and IC chip 10, the gap between bonding-terminal portions 2c, 4a and IC chip 10, and other gaps are filled with the sealing resin in the latter molding operation. The same operation as above is performed for bus bar 3 as well. The bending of branch portion 2b of bus bar 2 is performed as shown in Figure 5. The lead frame formed into a flat plate shape with a prescribed pattern is arranged on base (20) as shown in Figure 5 and Figure 6, the cross-sectional view cut along VI-VI line in Figure 5. Then, a plate-shaped fixture (19) with its cross-section finished to semicircular profile on one side is arranged with the aforementioned side in agreement with the bus bar bending position, and it is used to fix lead portions (2d), (4b) of bus bar (2) and signal line (4). In the figure, the portion of the bus bar before bending is represented by a broken line. Then, with fixture (19) arranged to fix bus bar (2) and signal line (4) on base (20), branched portion (2b) and principal wiring portion (2a) are bent by 180° as indicated by the arrow so that they come into contact with the upper surface of fixture (19). In this way, bus bar (2) assumes the shape represented by the solid line. As shown in Figures 1-4, the lead frame processed by the aforementioned method has its bonding terminal portions (2c), (4a) bonded on the upper surface of IC chip (10) by means of insulating double-side tape (11). Before the bonding operation, an insulating tape or insulating paste (15) is applied to bus bar principal wiring portion (2a). For bus bar (3), too, the same molding operation is performed as above. The processing of the bus bar does not require welding or other special techniques. Since it can be performed by using a simple fixture, a low cost is realized. Figure 7 is a cross-sectional view of the enlarged portion of the example with a smaller t 2 dimension in Figure 3 in the same way as to Figure 4. Figure 7 has a larger enlargement rate than Figure 4. In this example, suppose the plate used for the LOC lead frame has a thickness of 5 mil, for the bus bar portion, bus bars (2a), (2b), (2c) used in the aforementioned example are made thinner than the other portions by partial etching beforehand, and, with a thickness of 3 mil, are used as bus bar (12). For a portion of signal line (4), pre-etching is performed to form a groove (16), a portion of bus bar branched portion (12b) is bent so that principal wiring portion (12a) is located on groove (16). Then, a portion of the lower side of principal wiring portion (12a) and the insulating tape or insulating paste (15) bonded with it are made to enter groove (16), and the insulating tape or insulating paste (15) comes into contact with the bottom surface of groove (16). In this way, dimension t 3 between the upper surface of bus bar principal wiring portion (12a) and the lower surface of signal line (4) becomes 9 mil, smaller than dimension t 2 in the preceding example. Figure 8 illustrates another embodiment as a modification of the example shown in Figures 1-6. In this example, branched portions (32b), (33b) of bus bars (32), (33) are shorter than branched portion (2b) shown in Figure 2. Principal wiring portions (32a), (33a) are rather located nearer the side of bonding pad (1) than located on the plane curving portion of signal line (4), (5). In this way, the stability of principal wiring portions (32a), (33a) before sealing using resin is higher than that in the example shown in Figure 2. In this figure, (5b), (32d), and (33d) represent the lead portions. Other features are identical to those in Figures 1-6. Figure 9 shows another application example with further modification made on the example shown in Figures 1-6. In this example, principal wiring portion (2a) of bus bar (2) is bonded on IC chip (10) by means of an insulating double-side tape (11), and the portion in contact with bonding terminal portion (4a) of lead portion (4b) of signal line (4) is bent at two locations to arrange a step portion (4c). Lead portion (4b) is arranged on bus bar principal wiring portion (2a) with no electrical contact with it. In order to prevent this contact, it is preferred that an insulating tape or insulating paste be inserted. In this way, the bus bar and the signal line lead portions (2d), (4b) are located at the same height with respect to IC chip (10). Consequently, when the package is sealed by resin and molded, no difference is formed for the level for leading out from the package. This is identical to the aforementioned examples. Others are identical to those in the examples shown in Figures 1-6. For bus bar branched portion (2b), instead of bending for 180°, lead portion (2d) is arranged extending to the upper-right side from principal wiring portion (2a), and a same step portion as that of step portion (4c) of the signal line is placed in lead portion (2d). Also, the step portion may be not formed at lead portion (2d), instead, adjustment is made for dimension t 2 in Figure 4 or dimension t 3 in Figure 7 by selecting the radius of curvature of bending. In the above, this invention was explained with reference to respective embodiments. However, other modified versions are also allowed as long as the technical ideas of this invention are observed. For example, the package of this invention is not limited to the DRAM (16 mega [sic; megabit], 64 mega, etc), it may also be used in various other devices. In the semiconductor device of this invention, the bonding terminal portion of the power source line and the bonding terminal portion of the signal line are arranged along the column of the bonding pad; the principal portion of the aforementioned power source line extends with a 3-dimensional crossing configuration with respect to the aforementioned signal line with electrical insulation, and it is connected to the bonding terminal portion of the aforementioned power source line; consequently, between the aforementioned bonding terminal portion and the aforementioned bonding pad, there exists only the bonding wiring used to connect them. Consequently, even when the aforementioned bonding wire loop used for connection is not elevated, the bonding wire is still not in contact with the power source line principal portion, and hence no short circuit takes place. As a result, the reliability is high, and the device can be made thin.

Claims: A semiconductor device comprising: a semiconductor substrate (10) having a surface on which an integrated circuit is provided, a plurality of bonding pads (1) disposed on the surface of said semiconductor substrate at a central location thereon and arranged in a nearly columnar shape, first and second bus bars (2, 3; 32a, 33a) on the surface of said semiconductor substrate and respectively disposed on opposite sides of the nearly columnar arrangement of bonding pads, each of said bus bars having a plurality of wire bonding terminals and including a base wiring portion (2a, 3a; 32a, 33a) extending in a straight line in spaced parallel relation to said arrangement of bonding pads, first and second pluralities of elongated leads (4, 5) on the surface of said semiconductor substrate and having inner lead portions respectively disposed on opposite sides of said arrangement of bonding pads and outer lead portions integral with the respective inner lead portions and extending outwardly from said semiconductor substrate, first insulating means (11) interposed between said first and second bus bars and the surface of said semiconductor substrate and between said first and second pluralities of elongated leads and the surface of said semiconductor substrate, a first group of individual connector wires (6, 8) connected to respective ones of said bonding pads at one end and to respective wire bonding terminals of said first and second bus bars at the other end thereof, and a second group of individual connector wires (7, 9) connected to respective others of said bonding pads at one end and to respective inner lead portions of said first and second pluralities of elongated leads at the other end thereof; characterized in that each of said bus bars includes a plurality of branch portions (2b, 3b; 32b, 33b) integral with and extending inwardly from said base wiring portion toward said arrangement of bonding pads, said plurality of branch portions being in substantially perpendicular relation to said base wiring portiont (2a, 3a, 32a, 33a), a plurality of bonding terminal portions (2c, 3c; 32c, 33c) integral with and corresponding to said plurality of branch portions, each of said bonding terminal portions including a wire bonding terminal of said plurality of wire bonding terminals, the leads of each of said first and second pluralities of elongated leads extending across the base wiring portion of the bus bar corresponding thereto, second insulating means (15) interposed between the crossing leads of each of said first and second pluralities of elongated leads and the base wiring portion of the bus bar corresponding thereto for electrically insulating said leads from said base wiring portion, the wire bonding terminal of each of said bonding terminal portions extending inwardly from said base wiring portion toward said arrangement of bonding pads and in offset relation to the branch portion corresponding thereto, and said first and second groups of individual connector wires being arranged such that none of the connector wires cross over the respective bus bar corresponding thereto in being connected between respective bonding pads and wire bonding terminals with respect to the first group of connector wires and between bonding pads and respective inner lead portions of said first and second pluralities of elongated leads with respect to the second group of connector wires. A semiconductor device as set forth in Claim 1, further characterized in that each of said bonding terminal portions (2c) of said first and second bus bars is folded back beneath the branch portion (2b) corresponding thereto in providing the wire bonding terminal extending inwardly from the base wiring portion (2a) toward said arrangement of bonding pads and in offset relation to the branch portion corresponding thereto.- A semiconductor device as set forth ln Claim 1 or Claim 2, further characterized in that said second insulation means comprises an insulating tape (15) applied to the respective base wiring portions (2a) of said first and second bus bars on the surface thereof proximate to the crossing leads of said first and second pluralities of elongated leads. A semiconductor device as set forth in any of Claims 1 to 3, further characterized in that said leads (4, 5) of said first and second pluralities of elongated leads are arranged to extend beneath the base wiring portion of the respective one of said first and second bus bars corresponding thereto. A semiconductor device as set forth in Claim 4, further characterized in that said inner lead portions of said first and second pluralities of elongated leads are respectively provided with grooves (16), the base wiring portions (12a) of said first and second bus bars being respectively at least partially received in a groove of a corresponding inner lead portion, and said second insulating means (15) being interposed between said base wiring portions of said first and second bus bars and the bottoms of the respective grooves in said inner lead portions in which said base wiring portions of said first and second bus bars are received. A semiconductor device as set forth in either of Claims 1 or 2, further characterized in that the leads (4, 5) of said first and second pluralities of elongated leads extend over the respective base wiring portions (2a) of the first and second bus bars corresponding thereto. A semiconductor device as set forth in Claim 7, further characterized in that the inner lead portions of said first and second pluralities of elongated leads are respectively offset from the remainder of the leads corresponding thereto by a step portion (4c), said inner lead portions being disposed in coplanar relation with respect to said wire bonding terminals of the bonding terminal portions of said first and second bus bars, and the portions of said leads of each of said first and second pluralities of elongated leads other than the inner portions being disposed at an elevated level with respect thereto.

Inventors: MAEDA TAKAYUKI, MAEDA, TAKAYUKI
Applicants: TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS INCORPORATED
Application year: 1993
Main classification: H01L23
IPC codes: H01L23