Outer tape automated bonding semiconductor package

Abstract: A semiconductor package (10) for protecting a semiconductor chip (32) such as a Very Large Scale Integration chip and connecting it to an electrical circuit is disclosed. The chip is bonded to a section of Tape Automated Bonding, (TAB), tape (20) which contains a number of leads (22) thereover, each lead has an inner lead section (24) bonded to the chip and an outer lead section (26) that extends beyond the outer perimeter of the tape, for connecting to the circuit. The chip is enclosed in a housing (18) which subtends an area slightly larger than the chip itself. The inner lead sections project from the TAB tape into the housing and are bonded to the chip. A metal layer (54) under the TAB tape is connected to a number of the leads. After the semiconductor package of this invention is assembled, the outer leads are attached to the associated circuit so as to connect the chip to the circuit. The metal layer serves as a reference plane so the leads connected thereto supply a voltage that does not vary to sub-circuits on the chip.

Description: This invention relates generally to the field of packaging for integrated circuit chips, and more particularly to tape automated bonding packaging. Packaging is one of the final steps in the process of manufacturing integrated semiconductor circuit components or chips. In packaging, a fabricated semiconductor chip is mounted in a protective housing. After packaging, the assembled component is subjected to final testing and then connected to an electronic circuit. Currently, many semiconductor chips are contained in plastic packages. These packages are provided with reinforced metal leads for electrically connecting the chip to the printed circuit board which contains the circuit in which the chip is to be included. Within the package, one end of each lead is connected to a specific bonding point on the chip, usually by an intermediate lead; the other end of the lead, which extends outside of the package, is attached to a connection on the printing circuit board. Recently, advances in semiconductor manufacturing technology have made the fabrication of Very Large Scale Integration (VLSI) chips possible. VLSI chips comprise a large number of individual circuit components that are fabricated together on a single, very small chip. VLSI chips are able to perform a large number of electrical functions, and perform them more rapidly, then was previously possible. To date, it has been difficult to provide suitable packaging for VLSI chips. In part, this is because each chip requires a large number of connections to external circuit elements. Many VLSI chips have 100 to over 300 bonding points each of which must be connected to a lead for connection to external circuit elements. Another consideration in the use of a VLSI chip is the need to provide common voltages to a number of different locations on the chip. For instance, a chip that comprises a number of individual transistors, such as C-MOS type transistors, may require a common drain voltage supplied by an external power supply that is applied to the drain terminals of all the transistors, and a common source voltage also provided by an external power supply applied to the source terminals of all the transistors. Typically the drain voltage is positive with respect to a common reference or ground voltage, and the source voltage is typically at the same level as the ground voltage. The common voltages need to be supplied to the chip so the individual components all operate with respect to a common power level. Normally, common voltages are supplied to the components on the chip by providing sets of leads, each set designed to carry the same voltage, to different bond points on the chip. Providing a VLSI chip with a common voltage at a number of locations has, to date, been a difficult task. In a VLSI package, the leads which are connected to the chip are spaced closely together. Moreover, some of the leads supply voltages such as signal voltages that fluctuate rapidly as electronic functions are performed on them by the chip and the other circuit components. This causes the magnetic field normally developed around these leads to vary, which in turn causes an inductive current to flow in adjacent leads. Whenever a sufficiently large inductive current is developed in a common voltage lead, the voltage it is carrying changes. This problem may be intensified because in a VLSI chip such as a digital logic chips voltages may fluctuate rapidly; this rapid change intensifies the development of a magnetic field and the associated inductive current flow. As a result, the voltage supplied to one or more components on the VLSI chip may vary so greatly as to cause the chip to malfunction. There have been some attempts at providing packages for VLSI chips that are designed to minimize the problems associated with the development of inductive current flow. One such package is a multi-layered ceramic package. This package includes layers of conductors separated by layers of dielectric ceramic that are pressed together. A cavity is formed in the layers, and the chip is mounted in the cavity. Wire bonds are used to connect the bond points on the chip to the individual conductors on the top layer of conductors. Individual wire bonds or reinforced metal leads are used to provide an electrical connection to the printed circuit board the chip is attached to. Selected top-layer conductors, which carry common voltages, are connected to common intermediate-layer conductors. The intermediate-layer conductors function as reference voltage planes which insure the common voltages supplied through the top-layer conductors attached thereto does not appreciably vary. However, there are a number of limitations associated with multi-layer ceramic packages. The size of these packages tends to be extremely large in order to accommodate the interconnections needed between the conductor layers. Moreover, a multi-layered ceramic package designed to contain a VLSI chip is expensive to manufacture. In some instances, the cost of the multi-layered ceramic package may significantly exceed the cost of fabricating the chip. GB-A-215748 shows an integrated circuit package comprising a plurality of conductive leads supported by frames of electrically insulating material and interconnecting bond points on a semiconductor chip with external conductive elements. The chip is enclosed by a housing. EP-A-0223699 gives an indication as to existing TAB tape manufacture and technology making use of vias between conductive layers to achieve ground planes for tape bonded devices. The invention is defined by claim 1 and provides a new and improved semiconductor chip package that occupies a minimal amount of space, is easy to assemble, and economic to manufacture, and which minimizes inductive voltages that can disrupt the voltage over the common power supply leads in the semiconductor chip assembly. An advantage of this semiconductor package is that it connects directly to the external circuitry without the use of an additional level of reinforced leads between the chip and the external circuitry. This eliminates the need to provide a large package for the chip that would obviate the advantage gained by miniaturization. Moreover, this significantly reduces the complexity of providing the chip package, and substantially reduces the cost of its manufacture. The conductive film serves as reference planes for the common voltages. Since the common voltage leads each are connected to the conductive layer, the voltage across each lead to their respective bond points on the chip are identical. In other words, the conductive film minimizes the affect of inductive voltage flux in the common voltage leads so each such lead provides a constant common voltage to the chip component it is connected to. The above and further advantages of this invention may be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: Figure 1 is a perspective view of a TAB semiconductor package attached to a printed circuit board containing an electronic circuit for the purposes of explaining the present invention, Figure 2 is an exploded view, from the base of the housing, showing disassembled TAB semiconductor components for the purpose of explaining the present invention, Figure 3 is a cross-section view of the TAB semiconductor package of figure 2. Figure 4 is a perspective view of an alternative embodiment of the TAB semiconductor package of figures 1 to 3, Figure 5 is a top view of an embodiment of metal film used with the TAB semiconductor package of this invention. Figure 1 illustrates a Tape Automated Bonding (TAB) semiconductor package 10, attached to a printed circuit board 12. Adjacent the TAB semiconductor package 10 are conventional plastic semiconductor packages 14 and other components 16 that are part of the electronic circuit assembled on the printed circuit board 12. Referring to Figures 2 and 3, the TAB semiconductor package 10 is shown in greater detail. The TAB semiconductor package 10 includes a housing 18, containing a semiconductor chip 32, which is attached to a section of TAB tape 20 that surrounds the housing. The chip 32 and housing 18 subassembly is housed in a center opening 46 formed in the TAB tape 20. A number of conductive leads 22 are plated on the surface of the TAB tape 20. Each lead 22 has an inner lead portion 24 that extends into the center opening 46 and is attached to a bond point on the chip within the housing 18, and an outer lead portion 26 attached to a contact pad 28 on the printed circuit board. The contact pads 28 are connected to conductors 30 on the printed circuit board 12 to electrically connect the chip to the appropriate external circuit components. The chip 32 is contained inside the housing 18 formed of plastic or ceramic which comprises a base 34 on which the chip is seated and a cover 36 which extends over the base and defines a space 40 large enough so the chip may be housed therein. The cover 36 includes rim 38 which defines the perimeter of space 40. The leads 22 are formed on the TAB tape 20 according to standard TAB practice. The TAB tape may be a film 42 of polymide, Kapton, or other suitable insulating dielectric. The outer leads 26 each extend out from the outer perimeter of the TAB film 42. An outer support ring 44, also formed of polymide, is spaced away from the TAB film 42, and is secured over the ends of the outer lead portions 26. The outer support ring 44 secures the outer lead sections 26 so they do not curl or cross, or otherwise become out of registration with the contact pads 28 during bonding thereto. A more detailed explanation of the use of the outer support ring 44 to secure the outer lead portions prior to and during bonding to the contact pads is set forth in EP-A-0259222. The inner lead portions 24 each extend into the center lead opening 46 perpendicularly with respect to the inner perimeter of the TAB film 42. An inner support ring 48 that is spaced interiorly away from the inner perimeter of the TAB film 42 prevents the inner lead portions 24 from curling, crossing or otherwise becoming out of registration. The inner lead portions extend inwardly from the inner support ring 48 to provide end sections 52. The TAB tape 42, inner support ring 48 and inner lead portions 28 are dimensioned to provide film-free sections 50 of the inner lead portions 24 approximately equal to the width of the rim 38 of cover 36. The chip 32, rim 38, space 40, and inner support ring 48 are dimensioned so the chip is centered in the space and there is sufficient area between the chip and the rim to accommodate the inner support ring. A layer 54 of conductive metal film is bonded to the underside of the TAB film 42. The metal film layer 54 extends underneath all of the TAB film 42, and may also extend under the outer support ring 44 and the inner support ring 48. Vias 56 extend through the TAB film 42 to electrically connect selected leads 22a to the metal film 54. In one specific embodiment of this invention, the leads 22a that are connected to the metal film 54 are connected by a plurality of vias 56 that are spaced apart from each other. The TAB semiconductor package 10 is assembled by first bonding the chip 32 to the TAB tape 20 in accordance with standard tape automated bonding practice. The chip 32 is bonded to the TAB tape 20 inside the center opening 46 and within the area defined by the inner perimeter of the inner support ring 48; the inner lead's end sections 52 are connected to bond points on the chip 32. After tape bonding, the chip 32 is enclosed within the protective housing 18. The base 34 is placed under the chip 32 and the cover 36 placed over the base. Epoxy, or other suitable adhesive, is used to seal the cover 36 and base together at the top surface of cover rim 38. The tape bonded chip subassembly is positioned so the TAB film and conductive film-free sections 50 of the inner leads 24 are positioned between the rim 38 and the cover 36 and the adhesive is applied between them. The TAB semiconductor package 10 may be assembled by automated equipment. The TAB tape 20 may be provided with conventional excisable test pads (not illustrated), for testing of the assembled package 10. After assembly and testing, the TAB semiconductor package may be installed on the printed circuit board 12. As seen in Figure 3, the package 10 is mounted on the printed circuit board so the base 34 of the housing 18 and the leads are adjacent the printed circuit board 12, and the cover 36 of the housing and the metal film 54 are exposed. The outer leads 26 may then be attached to the printed circuit board contact pads 28. The TAB semiconductor package 10 protects the chip 32. Furthermore, the TAB 20 of this package 10 can have 400 or more leads 22 etched on it. The package 10 can thus be used to protect and attach a Very Large Scale Integration semiconductor chip directly to a printed circuit board 12. The package 10 does not require reinforced metal leads to electrically connect the chip 32 to the circuit board 12 to which it attaches. This eliminates the need to provide lead assemblies, and an associated housing, that encompass a large amount of space. Moreover, since there is no need to provide an intricate lead assembly and an associated housing, this package 10 is very economical to manufacture. The metal film 54 below the TAB tape 20 serves as reference planes for the leads 22a connected to it by the vias 56. This reduces the magnetic fields that can be developed around the leads 22a by the other leads which carry rapidly changing voltages, such as signal voltages, thereby minimizing the inductive current flow and varying voltages that may develop therein. Thus, the leads 22a are used to provide an identical supply or reference voltage to the several sub-circuits on the chip 32 that will not too substantially vary between the sub-circuits thereon. For a C-MOS chip it would thus be desirable to connect leads 22a to the metal film 54 that supplies the reference and source voltages to the components on the chip. The metal film would thus serve as a reference plane for these voltages to minimize their variance. Moreover, the drain voltage tends to vary inversely with any changes in the reference voltage. Magnetic fields produced by change in the reference and drain voltages would thus be complementary and tend to cancel each other out. The net effect would be to minimize the development of magnetic fields and accompanying voltage variations in the leads carrying voltages both to and from the chip. An alternative embodiment of figures 1 to 3 is depicted in Figure 4. Figure 4 illustrates a package assembly 60 wherein the chips are enclosed within separate housings 18 attached to a single section of TAB tape 62. Etched on the TAB tape are a number of leads 22 which connect the chips to contact pads 28 on the printed circuit board 12, and a number of other leads extending between the housings 18 to interconnect the chips, shown in phantom. The package assembly 60 may have one section of metal film disposed under the entire TAB tape 62 to provide a reference plane for both chips, or two sections of metal film spaced apart, one adjacent each chip, to provide separate reference planes. Extension to more than two chips are readily apparent. In an embodiment in accordance with the present invention, Figure 5 depicts a layer of metal film 70 that is used with the TAB tape 20 for the film 54 (Figure 2). The metal film 70 comprises alternating side portions 72 and corner portions 74 that are separated from each other by approximately 1 to 2 mils (1 mil = 25.4µm). The leads 22, shown in phantom, are arranged so that different sets of leads 22a are electrically connected to an individual side portion 72 or corner portion 74. Thus, the individual side portions 72 and corner portions 74 can function as separate reference planes for different voltages supplied to the chip. Alternatively, some chips, such as those having emitter-coupled logic may have another form of reference plane attached to the TAB tape 20 and leads 22. In the illustrations the chip 32, the inner support ring 48, the TAB film 42, and the outer support ring 44 are shown as having a rectangular profile. This is only one way the elements of the semiconductor package of this invention may be formed. Alternatively, these elements may have other forms, including nonlinear ones. It may be desirable to attach a heat sink assembly to the top of the cover to provide a means to dissipate heat generated by the chip away therefrom.

Claims: A semiconductor package (10) for protecting one or more semiconductor chips (32), each of the chips (32) having bond points for electrical connection to external conductive elements, said package comprising: a separate housing (18) enclosing each of the chips; and a section of tape automated bonding tape (20) comprising: a section of tape film (42) comprising an electrical insulating dielectric material surrounding at least a portion of each housing; and a plurality of conductive leads (22) on said tape film, each of said conductive leads having an inner lead portion (24) that extends into said housing and is connected to one of the chip bond points, and an outer lead portion (26) that extends beyond the outer perimeter of said tape film for bonding to said external conductive elements (30), whereby each chip bond point is electrically connected to one of the external conductive elements by said conductive lead; and in which a metal film (70) is affixed to said tape film (42) opposite the surface of said tape film carrying said leads (22) said metal film comprising alternating side portions (72) and corner portions (74) separated from each other and functioning as separate reference planes for different voltages supplied to each chip; and a selected number of said leads (22a) which are used to provide a plurality of reference voltages to said one or more semiconductor chips are each connected by vias (56) to a respective one of said portions (72,74) of the metal film (70) such that each of said selected leads (22a) connected to a respective portion (72,74) will carry an identical voltage to a plurality of bond points on each chip regardless of any signal induced on to any of said selected leads (22a) by conductive leads (22) adjacent to said selected leads (22a). The semiconductor package of claim 1 further including an inner support ring (48) disposed around said inner lead portions (24), and spaced away from said tape film (42) so as to form a film-free section (50) of said inner lead portions. The semiconductor package of claim 1 wherein said inner support ring (48) is spaced away from the ends of said inner lead portions (24). The semiconductor package of claim 1 further including said housing (18) comprising a cover (36) forming a space (40) wherein the chip is contained, and a base (34) attached to said cover. The semiconductor package of claim 2 further including: a) said housing (18) comprising a cover (36) with a protruding rim (38) defining a space (40) wherein the chip is contained, and a base (34) attached to said rim; and b) said tape film (42) and said inner support ring (48) are dimensioned so that said film-free sections (50) of said inner lead portions (24) subtend at least the area defined by said cover rim (38). The semiconductor package of claim 1 wherein an outer support ring (44) is disposed over the ends of said outer lead portions (26), and said outer support ring is spaced away from said tape film. The semiconductor package of claim 1 wherein said selected leads (22a) are connected to said portions (72,74) by a plurality of vias (56) that are spaced apart from each other.

Inventors: BROWN KENNETH M, HANNEMANN ROBERT J, HANSEN STEPHEN P, BROWN, KENNETH M., HANNEMANN, ROBERT J., HANSEN, STEPHEN P.
Applicants: DIGITAL EQUIPMENT CORP, DIGITAL EQUIPMENT CORPORATION
Application year: 1988
Main classification: H01L23
IPC codes: H01L21, H01L23