Patent Grant
6856007
The present application relates to the art of packaging microelectronic elements such as semiconductor chips.
Semiconductor chips or dies commonly are provided in packages which facilitate handling of the chip during manufacture and mounting of the chip on an external substrate such as a circuit board or other circuit panel. For example, certain packaged semiconductor chips sold under the registered trademark μBGA® by Tessera, Inc., assignee of the present application, incorporate a dielectric element having terminals. The terminals are connected to contacts on the die itself. In particularly preferred arrangements, the connections between the terminals and the die are formed by flexible leads and the dielectric element, its mounting to the die or both are arranged so that the terminals remain moveable with respect to the chip. For example, where the dielectric element overlies a surface of the chip, a layer of a compliant material may be provided between the dielectric element and the chip. The packaged chip can be mounted to a circuit board or other underlying circuit panel by soldering or otherwise bonding the terminals on the dielectric element to contact pads on the circuit board. Because the terminals on the dielectric element can move relative to the chip, the assembly can compensate for differential thermal expansion and contraction of the chip and the circuit board during thermal cycling in service, in storage and during manufacturing processes.
Assemblies of this type are described, for example, in U.S. Pat. Nos. 5,148,265; 5,148,266; and 5,679,977. In certain embodiments, the leads can be formed partially or wholly as elongated metallic strips extending from the terminals along the dielectric element. These strips can be connected to the contacts on the chip by wire bonds, so that the wire bonds and strips cooperatively constitute composite leads. In other embodiments, the strips themselves can be connected directly to the terminals. Certain methods of forming strip-like leads and connecting numerous strip-like leads to numerous contacts on a die are described in U.S. Pat. Nos. 6,054,756; 5,915,752; 5,787,581; 5,536,909; 5,390,844; 5,491,302; 5,821,609; and 6,081,035, the disclosures of which are incorporated by reference herein.
The aforementioned structures, in their preferred embodiments, provide packaged chips with numerous advantageous including the aforementioned ability to compensate for differential thermal expansion and hence high reliability; compatibility with surface-mounting techniques for assembling components to a circuit board and the ability to accommodate numerous connections to the chip in a compact assembly. Some of these packages occupy an area of the circuit board just slightly larger than the area of the chip itself. Certain preferred packages of this type provide short, strip-like leads which minimize self-inductance in the leads and hence provide good high-frequency signal propagation. Moreover, certain packages according to this design can provide good heat dissipation from the chip. These packages have been widely adopted for semiconductor chips in numerous applications.
However, despite these advancements in the art, still further improvement and optimization would be desirable. Chips used for generating or processing radio frequency (“RF”) signals, commonly referred to as “RF chips,” are used in numerous devices including cellular telephones and wireless data communication devices. RF chips typically generate substantial amounts of heat. Although RF chips typically have only a moderate number of input/output connections, and hence require only a moderate number of connections to the circuit board, these connections should be made with low-inductance leads having controlled, predictable impendence at the frequencies handled by the chip. The packages for RF chips should be compact and economical. Moreover, it would be desirable to provide packages which are particularly well suited to RF chips using the same production equipment and techniques used with other package designs as, for example, the μBGA® chips.
One aspect of the present invention provides a semiconductor chip assembly. A semiconductor chip assembly according to this aspect of the invention desirably includes a packaged semiconductor chip incorporating a semiconductor die having a front surface, a rear surface and contacts exposed at the front surface. The packaged semiconductor chip also includes a chip carrier having inner and outer surfaces. The inner surface of the chip carrier faces toward the front surface of the die. The chip carrier also has a plurality of terminals and a thermally conductor, preferably formed from a metallic material, exposed at the outer surface of the chip carrier. The thermal conductor has a relatively large area, substantially larger than the area of each individual terminal. The thermal conductor may have an area of at least 10 times, and desirably at least 20 times, the area of a single terminal. The thermal conductor is at least partially aligned with the die. The terminals on the chip carrier optionally may be movable with respect to the die. The thermal conductor optionally may be movable with respect to the die. An encapsulant layer may be provided between the die and the chip carrier, and between the die and the thermal conductor.
The circuit panel has contact pads and has a thermal conductor mounting. The pads and thermal conductor mounting typically are metallic. The packaged chip is disposed on the circuit panel so that the outer surface of the chip carrier faces toward the circuit panel. The terminals of the chip carrier are bonded to the contact pads of the circuit panel. Most desirably, the thermal conductor of the chip carrier is also bonded to the thermal conductor mounting of the circuit panel, and this bond preferably is a metallurgical bond. As used in the disclosure, the term “metallurgical bond” refers to a connection between elements formed substantially or entirely from one or more metals or alloys. The thermal conductor and the bond between the thermal conductor and the thermal conductor mounting on the circuit panel provide a low thermal resistance cooling path between the packaged chip and the circuit panel. Moreover, the thermal conductor can attenuate undesired RF emissions from the chip and/or RF signals impinging on the chip from other portions of the circuit, and can also be referred to as a “shield.” Most desirably, the thermal conductor mounting of the circuit panel is connected to a ground or power voltage source and the thermal conductor is electrically connected to one or more ground or power contacts on the die by thermal conductor leads similar to those used to connect the other contacts with the terminals. Thus, the thermal conductor can act as a very large ground or power terminal. Because the thermal conductor has a substantial horizontal extent, the thermal conductor can also act as a ground or power distribution bus; in this case, the thermal conductor is electrically connected to numerous ground contacts or numerous power contacts at widely spaced locations on the die. In a variant of this approach, the thermal conductor may serve as a clock terminal and/or clock distribution bus, in which case the thermal conductor mount on the circuit panel is connected to a clock signal bus so that the clock signal is routed between the clock signal bus and the clock contacts of the chip.
In certain embodiments, the packaged chip may include a metallic heat spreader or “can” having a main or top wall structure overlying the rear surface of the chip so that a portion of the heat spreader faces upwardly, away from the circuit panel when the packaged chip is assembled to the circuit panel. The heat spreader desirably has a side wall projecting from the main portion of the heat spreader towards the front surface of the die. This wall desirably terminates in a horizontal surface or flange. In the assembly, the horizontal surface or flange of the heat spreader desirably is metallurgically bonded to a spreader mounting on the circuit panel. The spreader facilitates heat transfer from the packaged chip into the surroundings, away from the circuit panel. Where the spreader is bonded to the circuit panel, the spreader can also facilitate transfer of heat from the packaged chip into the circuit panel. The spreader can also serve as an RF shield, as a ground connection to the rear surface of the chip, or both. In an alternative arrangement, the side wall structure is bonded to a metallic feature on the chip carrier, which in turn is bonded to a mating feature of the circuit panel.
Yet another aspect of the invention provides packaged chips having features as discussed above in connection with the assembly.
A still further aspect of the invention provides connection components suitable for use in fabricating the packaged chips. Connection components according to this aspect of the invention most preferably include a dielectric layer having an inner surface and an outer surface, a metallic thermal conductor occupying at least a part of the dielectric layer, and terminals on the dielectric layer. The thermal conductor has an area substantially larger than the area of each individual terminal. The terminals and the thermal conductor are exposed at the outer surface of the dielectric layer. For example, the terminals and the thermal conductor may overlie the outer surface. Alternatively, the terminals and the thermal conductor may be disposed on the inner surface and openings in the dielectric layer may be provided in alignment with the terminals and the thermal conductor. The connection component desirably includes terminal leads electrically and physically connected to the terminals and most preferably includes one or more thermal conductor leads electrically and physically connected to the thermal conductor. The terminals, leads and thermal conductor are arranged so that when the leads are connected to the contacts on the die the thermal conductor overlies the front surface of the die. For example, the thermal conductor may be disposed in a central region of the dielectric layer, and at least some of the terminals may be disposed in a peripheral region of the dielectric layer surrounding the central region.
Most desirably, the terminals, lead and thermal conductor are all formed in a single metallization layer as, for example, by etching a single layer of metal. In one preferred arrangement, the leads extend across gaps in the dielectric layer so that the leads can be engaged with contacts on the chip during formation of a chip package by advancing a bonding tool into the gap so as to force the leads into engagement with the contacts on the chip. Most desirably, each lead includes a connection section which will be engaged with a contact on the chip and a frangible section weaker than the connection section. The frangible sections of the terminal leads may be disposed between the connection sections of these leads and the thermal conductor. Thus, prior to assembly with the chip, the terminals and terminal leads are electrically connected in common by the thermal conductor. However, when the frangible sections of the terminal leads are broken, the terminal leads are electrically disconnected from the thermal conductor. This allows use of the thermal conductor as a commoning bus during fabrication of the leads as, for example, in electroplating or etching operations.
A further aspect of the invention provides a packaged semiconductor chip. The packaged chip according to this aspect of the invention desirably includes a first semiconductor chip having an upwardly-facing front face, a downwardly-facing rear face, edges bounding said faces and contacts exposed at said front surface, said first semiconductor chip including active components. A connecting element including passive components such as resistors and capacitors is electrically connected to at least some of the contacts of the first chip. The connecting element overlies the front face of the first chip and projects outwardly beyond the edges of the first chip. A chip carrier is disposed below the rear surface of the first chip. The chip carrier has a bottom surface facing downwardly away from the first chip and has a plurality of terminals exposed at the bottom surface, at least some of such terminals being electrically connected to at least some of the contacts of the first chip through said connecting element. Most preferably, the connecting element is a second chip incorporating the passive elements, also referred to as a “passive chip.” The chip carrier may include a thermal conductor as discussed above, and may also include a spreader or enclosure having a top wall overlying the rear surface of the connecting element or passive chip. As discussed above, these features provide further enhanced thermal dissipation and electromagnetic shielding.
In a packaged chip according to a further aspect of the invention, the position and orientation of the first chip and the connecting element or passive chip are reversed, so that the first chip lies above the passive chip. In this arrangement, the front surface of the first or active chip faces downwardly and confronts the upwardly-facing surface of the second or passive chip. The rear surface of the passive chip faces downwardly, toward the chip carrier. Chip assemblies according to this aspect of the present invention may also include thermal conductors and spreaders as discussed above.
Yet another aspect of the present invention provides packaged modules including two separate microelectronic circuits a pair of separate radio frequency amplification circuits. A packaged module according to this aspect of the invention includes a carrier having top and bottom surfaces and having terminals exposed at the bottom surface. A first microelectronic unit or assemblage including one or more chips is mounted to the carrier and overlies a first region of the top surface. A second microelectronic unit or assemblage is also mounted to the carrier and overlies a second region of the chip carrier. The module according to this aspect of the invention most preferably includes a metallic enclosure having top wall structure extending above the microelectronic units or assemblages and side wall structure extending downwardly from the top wall structure to the vicinity of the carrier. The enclosure also desirably has a medial wall extending to the vicinity of said carrier between the first and second regions. The enclosure, and particularly the medial wall structure, electromagnetically shields the first and second microelectronic units or assemblages from one another. Moreover, the enclosure desirably is in thermal communication with the chip or chips included in the microelectronic units or assemblages. The preferred modules according to this aspect of the invention can be used, for example, to provide a surface-mountable RF amplification unit which incorporates a pair of separate radio frequency amplification circuits.
A further aspect of the invention provides a packaged surface acoustic wave or “SAW” device. The packaged device according to this aspect of the invention includes a SAW chip having an acoustically active region on its front surface. The SAW chip desirably is mounted front-face-down on a chip carrier having an inner surface and an outer surface so that the active region of the SAW chip front surface is aligned with a hole in the chip carrier. The front surface is sealingly connected to the chip carrier around the periphery of the hole, so that the active region of the SAW chip is maintained free of encapsulants and contaminants. Preferred structures according to this aspect of the invention can provide a thin, surface-mountable packaged SAW device at low cost.
Yet another aspect of the invention provides A packaged semiconductor chip assembly including a first semiconductor chip incorporating one or more active components together with a passive chip incorporating one or more passive components selected from the group consisting of resistors and capacitors. The packaged chip according to this aspect of the invention also includes a chip carrier having terminals thereon. The chips are secured to said chip carrier, and at least some of said terminals being connected to at least one of said chips. The packaged chip according to this aspect of the invention desirably includes at least one inductor defined at least in part by features on said chip carrier, said at least one inductor being connected to at least one of said chips. As further explained below, the use of a passive chip to provide at least some of the resistors and capacitors affords significant savings in space and cost as compared to the use of discrete passive components, whereas formation of the inductor at least in part on the chip carrier allows the use of thick, low-resistance windings in the inductor to provide inductors with a high quality factor or “Q.” The structural features of the foregoing aspects of the invention can be combined with one another or used separately.
Still further aspects of the invention provide particular structures for inductors usable in the foregoing aspects of the invention and in other applications.
Additional aspects of the invention provide methods of mounting chips to circuit panels. Methods according to this aspect of the invention desirably use packaged chips or modules and circuit panels as discussed above. In a method according to this aspect of the invention, the terminals are bonded to the contact pads and the thermal conductor is bonded to the thermal conductor mounting in a single operation. Most preferably, the terminals and thermal conductor are soldered or otherwise metallurgically bonded to the contact pads and to the thermal conductor mounting. Preferably, the contact pads and the thermal conductor carry layers of solder before the packaged chip is assembled to the circuit panel. Alternatively, the solder may be provided on the contact pads and on the thermal conductor mounting of the circuit panel. In either case, the solder connections can be relatively thin layers of solder as, for example, 25-50 microns thick. Stated another way, the connection between the packaged chip and the circuit panel may be a “land grid array” rather than a ball grid array. The ability to use thin solder connections further enhances the electrical performance of the completed assembly, and minimizes the height of the assembly. Moreover, there is typically no need for a layer of dielectric material or “underfill” surrounding the solder connections between the connection component and the circuit panel. This simplifies the connection procedure. Where a heat spreader is to be bonded to a spreader mounting on the circuit board, the spreader desirably is provided in place on the chip package before the chip package is assembled to the circuit panel, and the spreader is bonded to the circuit panel in the same bonding operation used to bond the terminals and thermal conductor.
Still other objects, features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments set forth below, taken in conjunction with the accompanying drawings.
A few of the leads are thermal conductor leads 30. The thermal conductor leads are similar to the terminal leads except that the connection sections of the thermal conductor leads are connected directly to thermal conductor 20, without an intervening frangible section. The end of the connection section of each thermal conductor lead 30 remote from thermal conductor 20 is connected to a “dummy” terminal 22a by a frangible section 32. Thus, the frangible sections of the thermal conductor leads are disposed adjacent the outer edges of the bond windows 24, remote from thermal conductor 20.
The terminals, leads and thermal conductor form an electrically continuous structure. Thus, the leads can be plated or otherwise subjected to processes requiring electrical current without the need for any additional electrical commoning element. Preferably, the thermal conductor, leads and terminals are formed from a single layer of copper or copper alloy about 10-30 microns thick, more preferably about 15-20 microns thick, on the dielectric layer. A photoresist can be applied and patterned using conventional techniques so that regions of the copper or copper alloy layer can be selectively removed so as to leave the terminals, thermal conductor and leads in place. This process typically is performed prior to formation of the bond windows. The bond windows can be formed by etching the dielectric or by exposing the dielectric to radiation such as laser radiation. The fabrication procedure for the chip carrier can be essentially as shown and described in the patents incorporated by reference. Also, although the frangible sections 28 and 32 are illustrated in
In fabrication of the package semiconductor chip, a die 14 is juxtaposed with the chip carrier so that the front surface 35 of the die faces toward the chip carrier and so that contacts 34 on the die are substantially aligned with the bond windows and with the connection sections of the terminal leads. Desirably, the arrangement of the leads is selected so that ground contacts on the die are aligned with the thermal conductor leads. In one manufacturing process, the dielectric is supported temporarily above the front or contact bearing surface of the die by a porous layer formed from a plurality of compliant elements or “nubbins” 36 (FIG. 1). As described in U.S. Pat. Nos. 5,706,174; 5,659,952; and 6,169,328, the disclosures of which are incorporated by reference herein, the nubbins typically are provided on the inner surface of the dielectric which faces toward the die. The connection sections of leads 26 and 30 may be bonded to the contacts by advancing a tool such as an ultrasonic or thermosonic bonding tool into the bond windows 24 so as to displace each connection section toward the die. This action breaks the frangible sections of the leads. Thus, the terminal leads 26 remain connected to terminals 22, and these terminals are disconnected from the thermal conductor. The thermal conductor leads 30 are disconnected from the associated dummy terminals 22a but remain connected to thermal conductor 20. Thus, at the end of the bonding process, the signal contacts 34 on the die are connected to the terminals whereas the ground contacts 34a are connected to the thermal conductor. The thermal conductor also serves as an anchor or support to facilitate breakage of the frangible sections associated with the terminal leads.
Following connection of the leads, the assembly is encapsulated by injecting a flowable, typically liquid encapsulant 40 between the die and the dielectric layer of the connection component. The encapsulant desirably also covers the edges 46 of the die, but does not cover the rear surface of the die. Techniques for applying an encapsulant are disclosed, for example, in U.S. Pat. Nos. 5,766,987; 6,049,972; and 6,046,076, the disclosures of which are also incorporated by reference herein. Typically, several connection components are provided as sections of a single dielectric layer tape, which incorporates several sets of terminals and several thermal conductors as aforesaid. Several chips are assembled to the various sets of terminals, and encapsulated, whereupon the tape is severed to provide individual packaged chips.
Other manufacturing processes can be employed. For example, the die can be attached to the connection component by a preformed pad of an adhesive material or “die attach” disposed between the front face 35 of the die and the connection component. Such a pad can be provided as a part of the connection component, or applied during the assembly operation. In another technique, die attach material is provided between the front face of the die and the connection component by dispensing a mass of uncured, flowable die attach onto the connection component or onto the die before assembling the die to the connection component.
After encapsulation, the packaged semiconductor chip has the configuration shown in FIG. 1. As best seen in that figure, the connection sections of the leads 26, 30 are bent toward the die and in contact with the contacts 34, 34a of the die. The encapsulant layer extends between the die and the dielectric element. In this embodiment, the terminals and thermal conductor are disposed on the bottom or outer surface 42 of the dielectric (the surface facing downwardly, away from the die in
In this embodiment, the terminals are disposed outside of the lateral edges 46 of the die. Stated another way, the terminals “fan out” from the die. Because the encapsulant is not directly loaded in shear between a terminal overlying the surface of the die and the die itself, substantial movability of the terminals can be achieved even with an encapsulant having a substantial shear modulus and a substantial modulus of elasticity. Typical encapsulants such as silicone gels tend to have coefficients of thermal expansion (“CTE”) substantially greater than that of the die and substantially greater than that of a circuit board to which the packaged chip will be mounted. In a fan-out structure, the fatigue stresses imposed on the leads during thermal cycling arise to some extent from the expansion of the encapsulant itself. Therefore, it is desirable to minimize the CTE of the encapsulant. For common encapsulants, there is an inverse relationship between CTE and modulus of elasticity. Thus, an encapsulant having lower CTE normally will have higher modulus of elasticity and higher shear modulus. Accordingly, the encapsulant 40 used in this embodiment desirably has a coefficient of thermal expansion less than about 200×106/° C. and more desirably less than about 100×106/° C. The encapsulant in this embodiment preferably has a modulus of elasticity between 0.5 GPa and 3 GPa, as measured at room temperature. It is desirable to minimize variation in the properties of the encapsulant with temperature as, for example, in the range of temperatures from −65° C. to +125° C. As the thermal conductor 20 overlies the front or contact-bearing surface 35 of the die, that portion of the encapsulant disposed between the thermal conductor and the die will be in direct shear between the die and the thermal conductor due to differential thermal expansion and contraction of these elements. However, strain in this portion of the encapsulant is limited because the entire thermal conductor lies close to the center of the die. Moreover, the bond between the thermal conductor 20 and the thermal conductor mounting of the circuit panel 12, discussed further below, covers a substantial area and thus has substantial strength and fatigue resistance. For this reason as well, stress on this bond due to thermal effects tends to be less critical than stress on the bonds between the terminals and the contact pads.
The packaged semiconductor chip is provided with thin layers of solder 50 on the terminals 22, 22a and with a thin layer of solder 52 on thermal conductor 20. Such thin layers can be applied by application of solder paste and subsequent volatilization of the organic carrier from the paste or by wave-soldering or dip-soldering techniques. Desirably, the solder layers are less than about 75 microns thick, most preferably between 25 and 50 microns thick. The solder layers can be applied before severing the tape to form individual packaged chips.
In an assembly technique according to a further aspect of the invention, the packaged semiconductor chip is assembled to a circuit board or other circuit panel 12 as shown in FIG. 1. In a single operation, using conventional surface-mounting soldering techniques, the terminals are soldered to the contact pads 54 of the circuit board, whereas the thermal conductor 20 is soldered to the thermal conductor mounting 56 of the circuit board. Most preferably, the bond between the thermal conductor and the thermal conductor mounting covers substantially the entire surface area of the thermal conductor, as, for example, at least about 80% of the thermal conductor surface area. Only a small fraction of the circuit board is illustrated. The contact pads 54 of the circuit board are connected by surface or internal connections of circuit panel 12 to appropriate signal-carrying traces and other electrical features of the circuit board, whereas the thermal conductor mounting 56 desirably is connected to a source of ground potential or other constant potential. Thus, after soldering the die is electrically connected to the appropriate signal connections of the circuit board through the terminals 22 and signal leads 26, whereas the die is connected to ground through the thermal conductor leads 30, thermal conductor 20 and thermal conductor mounting 56. The entire structure is quite thin. Typically, the entire structure is less than about 0.8 mm thick and more preferably less than 0.6 mm thick. In one example, the dielectric layer of the chip carrier is about 25-75 μm thick, and most desirably about 50 μm thick. The terminals, leads and thermal conductor are about 10-25 μm thick, and desirably about 18 μm thick, whereas the solder lands used to connect the structure to the circuit board are about 25-50 μm thick. In this embodiment, the encapsulant layer between the front face of the chip and the inner surface of the chip carrier is about 50-75 μm thick. The front face of the chip lies about 180 μm above the face of the circuit board when the assembly is mounted on the circuit board. These thicknesses are merely illustrative.
The thermal conductor 20 and the metallic bond between the thermal conductor and the thermal conductor mounting of the circuit board provide a thermally conductive heat transfer path from the die into the circuit board and also provide electrical shielding between the die and the circuit board. The entire structure is rugged and reliable. Inter alia, the bond between the thermal conductor and the thermal conductor mounting mechanically secures the packaged chip in place.
The packaged chip illustrated in diagrammatic sectional view in
Also, in the embodiment of
In the embodiment of
The packaged chip shown in
In the embodiment of
Other forms of leads can be employed. For example, as disclosed in U.S. Pat. No. 6,228,686, the disclosure of which is hereby incorporated by reference herein, a sheet-like element may include a main region and lead region which are partially segregated from the main region by slots extending around each lead region. The slot extending around each particular lead region is interrupted at a fixed end of the lead so that the fixed end remains attached to the main region of the sheet. The connection component diagrammatically depicted in
In the embodiments discussed above with reference to
Numerous further variations and combinations of the features discussed above can be utilized without departing from the present invention. For example, leads of the types shown in
A packaged semiconductor module according to a further embodiment of the invention (
The first electronic assemblage 602 overlies the top surface 638 of the chip carrier in the first region. The first or active chip 614 is connected by terminal lead 626 to the terminals 622 of the first set, and is also in thermal communication with the first thermal conductor 620. The relationship between the first chip 614 and the, first terminals 622 and first thermal conductor 620 may be similar to those discussed above. For example, an encapsulant 641 having a relatively high thermal conductivity may be used to provide intimate thermal communication between the front or contact-bearing surface of first chip 614 (the surface facing downwardly in
Chips 606 and 608, constituting second assemblage 604 are mounted in essentially the same way and overlie the second region 633 of the chip carrier.
The module according to
The enclosure 671 provides mechanical protection and reinforcement to the packaged module. Moreover, the enclosure cooperates with thermal conductors 620, 621 and other metallic components of the chip carrier to provide electromagnetic shielding for the components in both assemblages 602 and 604. Additionally, the medial wall structure 675, in cooperation with central ground strip 662, provides effective electromagnetic shielding between the two assemblages. Thus, assemblage 602 is effectively isolated from assemblage 604. This arrangement can be used to provide such isolation for any type of electronic circuits. It is especially useful in the case where multiple electronic assemblages must be provided in a compact unit. Merely by way of example, modules according to this aspect of the invention can be used in elements of RF transmitting and receiving circuits of cellular telephones. In such a dual-band radio frequency power amplifier, one assemblage 602 provides a radio frequency power amplifier operating in a first frequency band, whereas another assemblage 604 provides a radio frequency power amplifier operating in another frequency band. Both assemblages can operate independently, without cross-talk or interference, even though the components of both assemblages tend to emit substantial amounts of electromagnetic interference. In a variant of the structure shown in
However, in the case where each unit includes passive components in addition to the active chip, fabrication of at least some of the passive components in each assemblage in an integrated chip, such as passive chips 615 and 608, makes the module considerably more compact than it would be if the passive components were provided as separate, discrete elements. Resistors and capacitors, in particular, can be fabricated readily in a chip. The materials and processing techniques to make the passive chips 608 and 615 may be different from those used to make the active chips 606 and 614. For example, the passive chips may be formed on materials such as glass rather than on silicon. In another example, the active chips may be formed in whole or in part from compound semiconductors such as III-V semiconductors or II-VI semiconductors, whereas the passive chips may be silicon-based chips. Thus, RF power amplifier chips formed from gallium arsenide and related semiconductors can be used in conjunction with silicon-based passive chips. In another example, the second or passive chips can be made with a larger minimum feature size or “line width” than the active chips, or vice-versa. Additionally, active chips originally made for use with discrete external passive components can be used in conjunction with the passive chips. Thus, compactness similar to that achievable by incorporating the passive components in the active chip itself can be achieved without the expense and difficulty of modifying the active chip itself.
Most preferably, at least some of the inductors used in the circuit are formed at least in part by the chip carrier or by the chip carrier in conjunction with leads and other structures extending to one or both of the chips. Although inductors can be fabricated in a passive or active chip, it is difficult to make inductors with high inductance and, particularly, with a high quality of factor or Q. The chip carrier typically is a “thick-film” structure, having metal layers more than about 2 μm thick, typically more than about 4 μm thick, and most preferably more than about 10 μm thick. Such thick layers commonly are formed by processes such as lamination of metal layers to a dielectric, plating or screen printing. Inductors formed at least in part in the chip carrier can employ large, thick, low-resistance conductors and can provide high inductance values with resistance far lower than that achievable in a thin film structure. Thus, it is desirable to provide at least some of the inductors incorporated in the circuit as structures defined in part or in whole by elements of the chip carrier, by leads extending between the chip carrier and a chip or both.
As depicted in
As schematically illustrated in
As shown in
As best seen in
In the embodiment depicted in
An inductor according to a further embodiment of the invention (
A component usable in a further embodiment of the invention is depicted in fragmentary view in FIG. 18. The component according to this embodiment includes a substrate 850 incorporating a dielectric layer. The substrate desirably is generally planar or sheet-like. A plurality of conductive elements 852 are arrayed along a path 854. The substrate has bond windows 856 and 858 disposed on opposite sides of path 854. Each conductive element includes a first lead portion 860 aligned with bond window 856 on one side of the path, a second lead portion 862 aligned with the bond window 858 on the opposite side of path 854 and a trace portion 864 extending along the substrate between the lead portions. The ends of the lead portions remote from path 854 and remote from the trace portions 864 optionally may be connected to anchors 866, 868 by frangible portions 870, 872 as depicted in FIG. 18.
To form the indictor, the component is assembled with a chip, substrate or other element 880 (
A module in accordance with a further embodiment of the invention (
Chip carrier 918 has a hole 901 extending into the chip carrier from the inner surface 902. A metallic ring 904 is formed on the inner surface and surrounds hole 901. The metallic ring may be formed integrally with other metallic features on the inner surface, or may be separate therefrom. During manufacture, the front face 935 of chip 914 is juxtaposed with the inner surface of the chip carrier and is bonded to the chip carrier at ring 904. Thus, hole 901 provides a gas-filled cavity in alignment with the active surface region 902. The substrate does not contact the active surface region 902. A bonding material 903 desirably is provided between the inner surface of the chip carrier and the front face 935 of chip 914. For example, the bonding material may be a so-called “dry pad,” i.e., a pre-formed pad of a die attach material. The die attach material 903 is provided with a pre-formed hole prior to placing the die attach material between the front face of the chip and the chip carrier extending entirely around hole 901. The die attach material forms a seal between the front face of the chip and the inner surface of the chip carrier. During a subsequent stage of manufacture, encapsulant 917 is applied. The seal between the front face 935 of the chip and the inner surface of the chip carrier prevents entry of the encapsulant into hole 901. Alternatively or additionally, if chip 914 is provided with a ring-shaped metallic bond pad on its front face, the bond pad may be metallurgically bonded to ring 904 so as to form a similar seal extending entirely around hole 901 and active surface region 902.
Hole 901 desirably is closed or “blind,” so that the hole does not communicate with the bottom or outer surface 942 of the substrate. Hole 901 may be formed by any suitable technique used to for making blind vias in dielectric substrates. Desirably, hole 901 is partially filled with a metallic material. Thus, the hole 901 may have metallic via liner 907 extending along the wall of the hole. The via liner may join with a metallic element 909 on the outer or bottom surface of the substrate. This metallic element serves to close the hole. Moreover, metallic element 909 can be bonded by a solder mass 909, or other metallurgical bonding element, to a contact pad on the circuit panel. The via liner 907 thus serves as a heat-conducting element, so as to abstract heat from chip 914.
Structures according to this arrangement provide a gas-filled space in contact with the acoustic region of the surface acoustic wave chip, but also provide the other advantages achieved by mounting a chip in a package having a relatively thin chip carrier. Thus, the entire assembly can be substantially as compact as a unit which does not incorporate a surface acoustic wave device. Moreover, the structure is compatible from the manufacturing techniques used to make packaged chips and modules according to other embodiments of the invention, and the resulting packaged chip can be handled and mounted in the same manner as any other surface-mountable device. In the embodiments of
A packaged chip assembly according to yet another embodiment of the invention (
The second or passive chip projects outwardly in horizontal directions generally parallel to the plane of chip carrier 1018 beyond the edges 1021 of the active chip. The passive chip has outer contacts 1023 disposed beyond the edges of the active chip, and has conductors 1025 connected to these outer contacts. Conductors 1025 may connect directly with contacts 1019 and, hence, directly with contacts 1035 of the active chip. The passive chip also incorporates passive components, desirably resistors and capacitors, symbolized by a resistor 1027. As will be appreciated, a number of passive components may be incorporated within the passive chip. Also, some or all of the outer contacts 1023 of the passive chip may be connected to or through such passive components. If the package includes additional discrete components (not shown) or additional chips (not shown), the connections between outer contacts 1023 and inner contacts 1019 may include these elements.
The contact-bearing surface 1017 of the passive chip faces downwardly, toward the chip carrier or substrate 108. Thus, the outer contacts 1023 of the passive chip may be readily connected to the terminals 1022 of the chip carrier by leads 1026 similar to those discussed above. Moreover, because the rear surface 1044 of the active chip confronts the thermal conductor 1020, the rear surface of the active chip may be closely coupled to the thermal conductor so as to provide excellent heat transfer from the active chip to the thermal conductor and through the thermal conductor to the circuit panel. For example, the rear surface of the active chip may be coupled by a layer of solder or other metallic bonding material to the thermal conductor. As discussed above, the thermal conductor itself desirably is coupled to the thermal conductor mounting pad of the circuit panel by a large mass of solder or other metallic bonding material 1052. Additionally, the passive chip is coupled to enclosure 1070, as by a thin layer of die-bonding material or encapsulant having high heat conductivity, so that both the passive chip and the active chip can be cooled by heat transfer to enclosure 1070. Here again, inductors can be provided in the chip carrier itself or by structures such as those discussed above, including portions formed in the chip carrier and portions extending between the chip carrier and the passive chip.
An assembly according to yet another embodiment of the invention (
In the embodiment of
As these and other variations and combinations of the features set forth above can be utilized, the foregoing description of the preferred embodiment should be taken by way of illustration rather than by limitation of the invention.
The present application claims benefit of U.S. Provisional Patent Application No. 60/315,408, filed Aug. 28, 2001, the disclosure of which is hereby incorporated by reference herein.
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