Abstract:
Flexible circuitry is populated with integrated circuitry (ICs) disposed along one or both major sides. Contacts distributed along the flexible circuitry provide connection between the module and an application environment. A rigid substrate configured with wings diverging from a central axis to create, preferably, a ‘V’-shaped structure provide supportive structure for the populated flex circuitry that is wrapped about an edge of the substrate.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 11/364,489, filed Feb. 27, 2006, and a continuation-in-part of U.S. patent application Ser. No. 11/283,355, filed Nov. 18, 2005, and a continuation-in-part of U.S. patent application Ser. No. 11/255,061, filed Oct. 19, 2005, and a continuation-in-part of U.S. patent application Ser. No. 10/934,027 filed Sep. 3, 2004. These four U.S. Patent Applications are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to systems and methods for creating high density circuit modules and, in particular, to systems and methods for creating such modules that provide high capacity with thermal management features.  
       BACKGROUND  
       [0003]     Memory expansion is one of the many fields where high density circuit module solutions provide space-saving advantages. For example, the well-known DIMM (Dual In-line Memory Module) has been used for years, in various forms, to provide memory expansion. A typical DIMM includes a conventional PCB (printed circuit board) with memory devices and supporting digital logic devices mounted on both sides. The DIMM is typically mounted in the host computer system by inserting a contact-bearing edge of the DIMM into a card edge connector. Typically, conventional DIMM-based solutions have typically provided only a moderate amount of memory expansion.  
         [0004]     As bus speeds have increased, fewer devices per channel can be reliably addressed with a DIMM-based solution. For example, 288 ICs or devices per channel may be addressed using the SDRAM-100 bus protocol with an unbuffered DIMM. Using the DDR-200 bus protocol, approximately 144 devices may be addressed per channel. With the DDR2-400 bus protocol, only 72 devices per channel may be addressed. This constraint has led to the development of the fully-buffered DIMM (FB-DIMM) with buffered C/A and data in which 288 devices per channel may be addressed. That buffering function is provided by what is typically identified as the Advanced Memory Buffer or AMB. With the FB-DIMM, not only has capacity increased, pin count has declined to approximately 69 signal pins from the approximately 240 pins previously required.  
         [0005]     The FB-DIMM circuit solution is expected to offer practical motherboard memory capacities of up to about 192 gigabytes with six channels and eight DIMMs per channel and two ranks per DIMM using one gigabyte DRAMs. This solution should also be adaptable to next generation technologies and should exhibit significant downward compatibility. The FB-DIMM solution does, however, generate significant thermal energy, particularly about the AMB.  
         [0006]     There are several known methods to improve the limited capacity of a DIMM or other circuit board. In one strategy, for example, small circuit boards (daughter cards) are connected to the DIMM to provide extra mounting space.  
         [0007]     In another strategy, multiple die package (MDP) can also be used to increase DIMM capacity. This scheme increases the capacity of the memory devices on the DIMM by including multiple semiconductor die in a single device package. The additional heat generated by the multiple die typically requires, however, additional cooling capabilities to operate at maximum operating speed. Further, the MDP scheme may exhibit increased costs because of increased yield loss from packaging together multiple die that are not fully pre-tested.  
         [0008]     Stacked packages are yet another way to increase module capacity. Capacity is increased by stacking packaged integrated circuits to create a high-density circuit module for mounting on the larger circuit board. In some techniques, flexible conductors are used to selectively interconnect packaged integrated circuits. Staktek Group L.P., the assignee of the present application, has developed numerous systems for aggregating CSP (chipscale packaged) devices in space saving topologies. The increased component height of some stacking techniques may, however, alter system requirements such as, for example, required cooling airflow or the minimum spacing around a circuit board on its host system.  
         [0009]     Typically, the known methods for improved memory module performance or enlarged capacity raise thermal management issues. For example, when a conventional packaged DRAM is mounted on a DIMM, the primary thermal path is through the balls of the package into the core of what is typically an epoxy based FR4 board that has less than desirable thermal characteristics. In particular, when an advanced memory buffer (AMB) is employed in an FM-DIMM, a significant amount of heat is generated. Consequently, the already marginal thermal shedding attributes of DIMM circuit modules is exacerbated in a typical FB-DIMM by the localized generation of heat by the AMB.  
         [0010]     Memory DIMMs, both buffered and unbuffered, are often employed on motherboards mounted in server racks with limited space. Large capacity memory devices often have dimensions that create addition height issues (in the longitudinal direction away from the mounting socket).  
         [0011]     What is needed, therefore, are methods and structures for providing high capacity circuit boards in thermally-efficient, reliable designs, that provide in some modes, the opportunity for concomitant reduction in module height.  
       SUMMARY  
       [0012]     Flexible circuitry is populated with integrated circuitry (ICs) disposed along one or both major sides. Contacts distributed along the flexible circuitry provide connection between the module and an application environment. A rigid substrate configured with wings diverging from a central axis to create, preferably, a ‘V’-shaped structure provide supportive structure for the populated flex circuitry that is wrapped about an edge of the substrate.  
         [0013]     In some embodiments, the wings are configured to include one or more extra heat dissipating surfaces while others may include added heat dissipating structures alone one or more external sides of the module. In some embodiments, the upper surfaces of ICs populated along a surface of the flex circuitry are in thermal contact with the wings of the substrate while, if present, ICs disposed along the other side of the flex circuitry exhibit upper surfaces disposed away from the ‘V’-shaped structure. Thermally conductive rigid side pieces may be attached to the rigid substrate and/or disposed in thermal contact with top surfaces of such oppositely-disposed ICs.  
         [0014]     Some embodiments are server systems that include multiple circuit modules. Air channels may be formed between such multiple circuit modules to direct cooling air flow and such channels may be formed by single or multiple rows of modules.  
     
    
     DESCRIPTION OF DRAWINGS  
       [0015]      FIG. 1  depicts an exemplary substrate as may be employed in an embodiment of the present invention.  
         [0016]      FIG. 2  is a perspective view of an exemplary substrate as may be employed in a preferred embodiment of a circuit module in accord with an embodiment.  
         [0017]      FIG. 3  depicts a layout view of a flex circuit populated with ICs upon the depicted side according to one embodiment.  
         [0018]      FIG. 4  depicts a layout view of a flex circuit depicting a second side of a flex circuit such as the flex circuitry shown in  FIG. 3  and, in this embodiment, populated with ICs and an AMB.  
         [0019]      FIG. 5  depicts an exemplary circuit module in accordance with the present invention.  
         [0020]      FIG. 6  depicts an exemplar substrate to which has been fitted a cooling attachment.  
         [0021]      FIG. 7  depicts an exemplar module in which a cooling structure has been mounted within a ‘V’ channel of the exemplary circuit module.  
         [0022]      FIG. 8  depicts an exemplar circuit module in accord with an embodiment.  
         [0023]      FIG. 9  depicts a perspective view of several circuit modules arranged to form cooling channels.  
         [0024]      FIG. 10  depicts an exemplary circuit module with ICs mounted in a ‘V’ channel of the module.  
     
    
     DETAILED DESCRIPTION  
       [0025]      FIG. 1  depicts an exemplary substrate  14  as may be employed in some embodiments of the present invention. Depicted substrate  14  includes flex circuit strain projections  16  to accommodate flexion of flexible circuitry  12  induced when populated flex circuitry  12  is disposed about edge  15  of substrate  14  and ICs populated along flex circuitry  12  are disposed along illustrated wings  14 A and  14 B of substrate  14 . As shown, wings  14 A and  14 B of substrate  14  diverge to form channel  13  between wings  14 A and  14 B. Those of skill will appreciate that although a “V” shape is efficient and provides advantages such as profile control and thermal improvements, wings  14 A and  14 B need not create a V shape and may diverge from a central portion of substrate  14  in other configurations in addition to or besides a “V”. Wings  14 A and  14 B also include optional radiative projections  14 R as shown in the depiction of this embodiment of substrate  14 .  
         [0026]      FIG. 2  is a perspective view of a preferred substrate  14  as may be employed in a preferred embodiment of a V core circuit module.  
         [0027]      FIG. 3  depicts a layout view of a flex circuit and ICs populated upon the depicted side according to one embodiment. Depicted is an exemplar conductive trace  21  connecting row ICR 2  of module contacts  20  to ICs  18 . Those of skill will understand that there are many such traces in a typical embodiment. Traces  21  may also connect to vias that may transit to other conductive layers of flex  12  in certain embodiments having more than one conductive layer. In a preferred embodiment, vias connect ICs  18  on side  9  of flex  12  to module contacts  20 . Rows of ICs IC R1  and IC R2  are mounted along respective IC-bearing portions of flex  12 . An example via is shown as reference  23 . Traces  21  may make other connections between the ICs on either side of flex  12  and may traverse the rows of module contacts  20  to interconnect ICs. Together the various traces and vias make interconnections needed to convey data and control signals amongst the various ICs and buffer circuits. Those of skill will understand that the present invention may be implemented with only a single row of module contacts  20  and may, in other embodiments, be implemented as a module bearing ICs on only one side of flex circuit  12 .  
         [0028]      FIG. 4  depicts side  9  of flex circuit  12  depicting a second side of the flex circuit shown in  FIG. 3  which, in the depicted embodiment, is populated with ICs and an AMB. Those of skill will recognize that flex circuitry  12  need not be populated with an AMB and that such circuits are merely one of many optional devices that may be populated along flex circuitry  12 .  
         [0029]     Consequently, side  9  of flex circuit  12  is shown as being populated with multiple CSPs  18  and AMB circuit  19 . Other embodiments may not be FB-DIMMS and may therefore have no AMB circuit  19 . Side  9  includes fields F 1  and F 2  that each include at least one mounting contact array site for CSPs and, in the depicted case, include multiple contact arrays. Each of fields F 1  and F 2  include, in the depicted preferred embodiment, two pluralities of ICs similar to those identified in earlier  FIG. 3  as IC R1  and IC R2 .  
         [0030]      FIG. 5  depicts an exemplar circuit module  100  that exhibits a V core. As shown, in V core module  100 , flex circuitry (flex circuit, flexible circuitry, flexible circuit)  12  is disposed about edge  15  of substrate  14 . One or more integrated circuits (ICs)  18  are mounted along sides  8  and  9  of flex circuitry  12 . In some embodiments, ICs  18  may be memory devices in chip scale packaging (CSP) packages. Some embodiments employ dual-die packaged ICs arranged on along increased-height wings  14 A and  14 B. This is advantageous because some dual packages may present one or more outer dimensions longer than typical single-die packages. The profiles shown for ICs  18  are, however, structures to indicate just some configurations of the many ICs that may be employed as ICs  18  in some embodiments. While some modules  100  may be employed as memory modules, other configurations of module  100  may have a primary function other that memory such as, for example, communications or graphics.  
         [0031]     In general, substrate  14  is formed in the shape of a ‘Y,’ with a central portion  14 C that branches into two wings  14 A and  14 B that deviate away from the centerline of portion  14 C in the shape of a ‘V.’ Other embodiments may have wings that diverge at other angles than that depicted and, in some cases, the wings may not form a V but a “U”. In some embodiments, the ‘Y’ shape of the substrate  14  may permit larger ICs  18  to be used while still meeting space specifications devised for traditional DIMMs. In some embodiments, substrate  14  may be made in whole or part of metal (e.g., copper, aluminum, iron, metal alloys) or other thermally conductive material, thereby conducting heat away from the ICs  18  to provide a cooling effect. Other constructions may be employed for substrate  14  such as, for example, a ‘Y’ outer profile and a solid or honeycombed interior, or a ‘U’ shaped interior channel, or rectangular channel  13 .  
         [0032]     In some embodiments, the ‘Y’ shape of substrate  14  may provide for comparatively greater surface area than is provided by a traditional DIMM. Preferably, convective surface area is greatly increased, on the order of 500%. Further, the depicted design provides convection cooling properties to the inner depicted sets of ICs  18  populated along inner side  9  of flex circuitry  12 , by being so disposed to have an individual heat conduction path through wings  14 A and  14 B to the depicted ‘V’ channel  13  convective cooling area. The ‘V’ channel  13  in the depicted embodiment allows air to flow into the center of the V core module  100  to provide a temperature regulating effect.  
         [0033]     An optional extensions  14 R are shown extending from wings  14 A and  14 B. In some embodiments, extensions  14 R may increase the surface area of the V core module  100  that may be used for temperature regulation. In some embodiments, extensions  14 R may provide a surface against which an insertion force may be applied.  
         [0034]     V core module  100  includes optional members  50 A and  50 B. Members  50 A- 50 B are mounted to V core module  100  by a mount  55 A and a mount  55 B, which may be constructed as clips, clamps, or other joining structures. Some embodiments may not include mounts but instead employ thermally conductive adhesive, pressure sensitive adhesive (PSA), metal bonds, or other suitable attachment schemes. In some embodiments, members  50 A and  50 B may be made of metal or other thermally conductive material, and/or include features that may provide additional surface area for regulating the temperature of V core module  100 . For example, members  50 A and  50 B may include fins that increase the surface area of members  50 A and  50 B that may be used for thermal management. Members  50 A and  50 B may be constructed of the same or different material from the remainder of substrate  14 . They may be copper, for example, while the main body of substrate  14  may be comprised of aluminum, to name just one example. Another example could be a plastic bodied substrate  14  and a copper-based members  50 A and  50 B. In some embodiments, mounts  55  may be made of metal or other thermally conductive material. Preferably mount  55  may provide a path that encourages the heat energy flow between substrate  14  and sides members  50 A and  50 B.  
         [0035]     Inner ICs  18 I preferably have their top surfaces  22  in thermal connection to respective wings  14 A and  14 B of substrate  14 , while the top surfaces  22  of outer (or external) ICs  18 E are preferably in thermal communication with members  50 A and  50 B. Such thermal connection may be enhanced by thermally conductive adhesive or thermal grease, for example.  
         [0036]     Those of skill in the art will recognize, after appreciating this disclosure, that substrate  14  may be comprised of more than one piece, but still exhibit the principles disclosed herein. The depicted embodiments dispose the populated area of flex circuit  12  on an outer surface of wings  14 A and  14 B, leaving all or a substantial area of ‘V’ channel  13  available for thermal management structures, such as fins or other temperature regulating features.  FIG. 6  depicts an exemplar substrate  14  to which has been fitted a cooling attachment  56  having radiative fingers  58  and, as shown, cooling attachment  56  is disposed in channel  13  into which it may be clipped or set. No flex circuitry is shown in  FIG. 6  to allow attention to be case unimpeded upon the substrate and cooling component  56 . In some embodiments, cooling component  56  may be made of metal or other thermally conductive material. For example, cooling component  56  may be made of aluminum, and heat energy may be conduced between V core module  100  and cooling component  56  to provide thermal management for V core module  100 . In some embodiments, cooling component  56  may be formed so a substantial amount of the surface of cooling component  56  may come into thermal contact with the sides of the ‘V’ trench. In some embodiments, cooling component  56  may include additional cooling features. For example, cooling component  56  may include fins  57  or other features that may collect or radiate thermal energy. In some embodiments, cooling component  56  may include a conduit as shown, for example, for use of fluids to enhance thermal shedding from module  100 . For example, cooling component  56  may be constructed as a heat sink to provide thermal management for V core module  100 . In some embodiments, cooling component  56  may include active cooling features, such as fans or thermoelectric devices (e.g., peltier junctions, p-junctions).  
         [0037]     In some embodiments, the thin construction of flex circuit  12  may allow flex circuit  12  to conform to the shape of substrate  14 . Further, thin flex circuit  12  construction provides a low flex circuit thermal impedance to allow the transfer of thermal energy through flex circuit  12 . Those of skill will also recognize that a variety of construction methods may be employed to maintain mechanical integrity of module  100 . Preferably, thermally conductive bonds such as metal bonding or thermally conductive epoxy secure flex circuit  12  in place.  
         [0038]     The ICs  18  depicted along flexible circuit  12  are shown as chip-scale packaged memory devices of small scale. For purposes of this disclosure, the term chip-scale or “CSP” shall refer to integrated circuitry of any function with an array package providing connection to one or more die through contacts (often embodied as “bumps” or “balls” for example) distributed across a major surface of the package or die. CSP does not refer to leaded devices that provide connection to an integrated circuit within the package through leads emergent from at least one side of the periphery of the package such as, for example, a TSOP.  
         [0039]     Various embodiments may employ leaded or CSP devices or other devices in both packaged and unpackaged forms but where the term CSP is used, the above definition for CSP should be adopted. Consequently, although CSP excludes leaded devices, references to CSP are to be broadly construed to include the large variety of array devices (and not to be limited to memory only) and whether die-sized or other size such as BGA and micro BGA as well as flip-chip. As those of skill will understand after appreciating this disclosure, some embodiments of the present invention may be devised to employ stacks of ICs each disposed where an IC  18  is indicated. Multiple integrated circuit die may be included in a package depicted as a single IC  18 .  
         [0040]     While in this embodiment, memory ICs are used to provide a memory expansion board or module, and various embodiments may include a variety of integrated circuits and other components. Such variety may include microprocessors, FPGAs, RF transceiver circuitry, digital logic, as a list of non-limiting examples, or other circuits or systems that may benefit from a high-density circuit board or module capacity. In some embodiments, V core module  100  may be a memory device, but the principles of the invention may be employed with a variety of devices such as, for example, a microprocessor or graphics processor employed in a circuit module while other embodiments will consist essentially of memory ICs only. In some embodiments, the ‘V’ channel  13  may provide a mounting area where additional features may be attached or inserted, examples of which being later shown here.  
         [0041]     For example, as shown in  FIG. 7 , a cooling conduit  60  may be mounted within the ‘V’ channel  13  for transporting fluids to remove heat energy from the V core module  100 . Conduit  60  provides a path through which a fluid (e.g., air, water, coolant, antifreeze, oil, Freon, nitrogen, helium, ammonia) may flow to add or remove heat energy from the conduit  60 , and, in turn, V core module  300 . In some embodiments, conduit  60  may formed as cylindrical tube, an elliptical tube, or other shaped single passageway. For example, conduit  60  may encompass substantially the entire cross-sectional area of channel  13 , thereby causing cooling component  60  to be formed as a three dimensional V-shaped member. In some embodiments, conduit  60  may be formed as a number of conduits such as, for example, two or more passageways that may allow coolant to flow through several paths within channel  13 . Conduit  60  may also appear in cross section as a honeycomb of fluid passageways.  
         [0042]      FIG. 8  depicts a perspective view of an exemplary V core module  100 . The V core module  100  includes a number of module contacts  20  disposed along each side of the V core module  100 . In some embodiments, contacts  20  need not be on both sides of the V core module  100  and may be exhibited on only one side the V core module  100 .  
         [0043]      FIG. 9  depicts a perspective view of an arrangement  000  of several V core modules  100  arranged to form cooling channels. In general, two or more V core modules  100  may be arranged in parallel to create channels between two neighboring V core modules  100  through which a fluid, such as air, may flow to provide thermal management for V core modules  100 .  
         [0044]     Arrangement  400  includes a substrate  910 . In some embodiments, substrate  910  may be a printed circuit board (e.g., a computer motherboard or other computer system, which may include a memory controller and/or microprocessor using the memory, for example, as server memory.). A number of V core modules  100  are mounted to substrate  910  by a number of mounts  920 . In some embodiments, the mounts  920  may be connectors that provide support for V core modules  100  and/or provide conductive pathways between V core modules  100  and substrate  910 . The mounts  920  are arranged on substrate  910  so V core modules  100  are mounted substantially parallel to each other, and spaced apart such that one, or a number of a cooling channel  930  is formed. For example, two V core modules  100  may be mounted next to each other so the upper right arm of the first V core module  100  is in close proximity to the upper left arm of the second V core module  100 , and channel  930  may be formed under the adjacent arms through which air may flow. Air, or other fluid, may thereby be directed through channels  930  to provide thermal management for the V core modules  100 . The arrows depicted in  FIG. 9  show exemplar cooling air flow. While two-directional flow is shown in adjacent channels, one-directional flow and any combination of flow direction with redirecting air ducts may be employed to achieve thermal management air flow along similar channels in various embodiments.  
         [0045]      FIG. 10  depicts an exemplary V core module  100  according to another embodiment having ICs mounted along the interior region of the ‘V’-shaped channel  13 . The V core module  100  depicted in  FIG. 10 , uses the space inside the ‘V’ channel  13  to mount additional ICs. The depicted embodiment has what are going to be identified as inner and outer ICs  19  along flex circuit  12  and which are disposed in channel  13  of substrate  14 . As the depicted embodiment illustrates, ICs  18  (both  18 I (inner) and  18 E (outer)) are also disposed along flex circuitry  12  and ICs  18 I are in thermal communication with wings  14 A and  14 B of substrate  14 .  
         [0046]     Flex circuitry  12  is preferably made from one or more conductive layers supported by one or more flexible substrate layers. As those of skill will recognize, flexible circuit  12  may be comprised of more than one individual flex circuit although there are substantial construction advantages to having a unitary flex circuitry along which are mounted the ICs. The construction of flex circuitry is known in the art.  
         [0047]     Although the present invention has been described in detail, it will be apparent to those skilled in the art that many embodiments taking a variety of specific forms and reflecting changes, substitutions and alterations can be made without departing from the spirit and scope of the invention. Therefore, the described embodiments illustrate but do not restrict the scope of the claims.