WO2006121487A2

WO2006121487A2 - Circuit module with thermal casing systems and methods

Info

Publication number: WO2006121487A2
Application number: PCT/US2006/007004
Authority: WO
Inventors: James Douglas Wehrly, Jr.; James Wilder; Mark Wolfe; Paul Goodwin
Original assignee: Staktek Group L.P.
Priority date: 2005-05-06
Filing date: 2006-02-28
Publication date: 2006-11-16
Also published as: US20060090102A1; WO2006121487A3; US7446410B2

Abstract

Flexible circuitry is populated with integrated circuitry (ICs) disposed along one or both of major sides. Contacts are distributed along the flexible circuitry to provide connection between the module and an application environment. The populated flexible circuitry is disposed about an edge of a rigid substrate preferably devised from thermally-conductive materials and one or more thermal spreaders are disposed in thermal contact with at least some of the constituent integrated circuitry of the module. Optionally, as an additional thermal management feature, the module may include a high thermal conductivity thermal sink or area that is disposed proximal to higher thermal energy IC devices. In preferred embodiments, extensions from the substrate body or substrate core encourage reduced thermal variations amongst the ICs of the module while providing an enlarged surface for shedding thermal energy from the module.

Description

Circuit Module with Thermal Casing Systems and Methods

Field:

[001] 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 with features directed to reducing thermal loading.

Background:

[002] 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, systems that employ DIMMs provide limited profile space for such devices and conventional DIMM-based solutions have typically provided only a moderate amount of memory expansion.

[003] 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.

[004] 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. [005] 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. The additional connection may, however, cause flawed signal integrity for the data signals passing from the DIMM to the daughter card while the additional thickness of the daughter card(s) increases the profile of the module.

[006] Multiple die packages (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. [007] 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. 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.

[008] 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 a multilayer DIMM that has less than desirable thermal characteristics. In particular, when an advanced memory buffer (AMB) is employed in an FB-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 .

[009] What is needed, therefore, are methods and structures for providing high capacity circuit boards in thermally-efficient, reliable designs that perform well at higher frequencies but are not too large, yet can be made at reasonable cost with commonly available and readily managed materials.

Summary:

Flexible circuitry is populated with integrated circuitry (ICs) disposed along one or both major sides of the flexible circuitry. Contacts are distributed along the flexible circuitry to provide connection between the module and an application environment. The populated ό

flexible circuitry is supported by a rigid substrate, about which it is disposed in preferred embodiments, thus placing the integrated circuitry on one or both sides of the substrate with one or more layers of integrated circuitry on one or both sides of the substrate. The substrate is preferably devised from thermally-conductive materials and one or more thermal spreaders are disposed in thermal contact or connection with at least some of the constituent integrated circuitry of the module. Optionally, as an additional thermal management feature, the module may include a high thermal conductivity thermal sink or area that is disposed proximal to higher thermal energy IC devices. In preferred embodiments, extensions from the substrate body encourage reduced thermal variations amongst the ICs of the module while providing an enlarged surface for shedding thermal energy from the module.

Brief Description of the Drawings:

[0010] Fig. 1 depicts a perspective view of a module devised in accordance with a preferred embodiment of the present invention. [0011] Fig. 2 is an enlarged view of the area marked "A" in Fig. 1.

[0012] Fig. 3 is a cross-sectional depiction of a preferred embodiment taken along a perspective line that corresponds to line B-B of Fig. 1.

[0013] Fig. 4 is a cross-sectional view of a preferred embodiment taken along a perspective line that corresponds to line C-C of Fig. 1. [0014] Fig. 5 is a depiction of a substrate employed in a preferred embodiment of the present invention.

[0015] Fig. 6 illustrates a substrate employed with an alternative embodiment of the present invention in which an area of the substrate is deformed to provide an indentation.

[0016] Fig. 7 depicts one side of a flex circuit employed in a preferred embodiment of the present invention.

[0017] Fig. 8 depicts another side of the flex circuit depicted in Fig. 7.

[0018] Fig. 9 is a view of a preferred embodiment before thermal spreaders devised in accordance with a preferred embodiment of the present invention are included in the module.

A cutaway area D is provided to enhance illustration of certain features. [0019] Fig. 10 is an enlarged depiction of the area identified with "D" in Fig. 9.

[0020] Fig. 11 is a cross-sectional depiction of the area near an end of a substrate as employed in a preferred embodiment of the present invention.

[0021] Fig. 12 is an exploded cross-sectional view of a flex circuit employed in a preferred embodiment of the present invention. [0022] Fig. 13 is a cross-sectional view of another preferred embodiment devised in accordance with the invention.

[0023] Fig. 14 is an enlarged perspective view of the preferred embodiment of Fig. 13 devised in accordance with the present invention. [0024] Fig. 15 is another cross-sectional view of another preferred embodiment devised in accordance with the invention.

[0025] Fig. 16 is an enlarged perspective view of the preferred embodiment of Fig. 15 devised in accordance with the present invention.

[0026] Fig. 17 is another cross-sectional view of another preferred embodiment devised in accordance with the invention.

Detailed Description of Preferred Embodiments:

[0027] Figs. 1 and 2 depict a module 10 devised in accordance with a preferred embodiment of the present invention. The depictions illustrate module 10 having substrate 14 about which is disposed flex circuit 12 populated with ICs 18 which are, in a preferred embodiment, integrated circuitry in CSP packages. Some alternative embodiments will have separate flex circuit on each side of substrate 14. Substrate 14 is shown with an optional extension 16T which, in this embodiment, is integral with the body 14B of substrate 14. [0028] Optional extension 16T may be devised in a variety of configurations and need not extend laterally from the main axis of substrate 14 in both directions. For example, extension 16T may extend from substrate 14 in only one direction and need not project perpendicular from the body 14B of substrate 14.

[0029] Preferably, substrate 14 is comprised of thermally conductive material. Metallic materials are preferred choices. For example, aluminum like many other metallic materials, is thermally conductive and may be readily manipulated for configuration as substrate 14. Materials such as FR4 may be employed, but if non-metallic materials are employed, other non-metallic materials that are thermally conductive are preferred over FR4. Carbon-based materials and certain plastics, for example, are known to readily conduct thermal energy and, as alternatives to metallic materials, such materials may be employed to advantage in preferred embodiments in accordance with the present invention where metallic materials are not available or wanted.

[0030] In the depicted embodiment, thermal spreaders 13₁ and 13₂ are thermally connected to ICs 18 and substrate 14. Thermal spreaders 13i and 13₂ are comprised of thermally conductive material with higher conductivity metallic materials being preferred. Aluminum is a preferred choice for thermal spreaders in this embodiment due to its amenability to fabrication and relatively high thermal conductivity. Those of skill will recognize, however, that use of copper and copper alloys for thermal spreaders \3_\ and 13₂ will typically provide even greater thermal benefits although at typically a higher cost. Thermal spreaders D₁ and 13₂ are preferably thermally connected to ICs 18 (or other ICs where accessible) with thermal adhesive.

[0031] ICs 18 are partially shown in Fig. 2 with portions of profiles that represent just some of the many profiles that may be exhibited by ICs 18. ICs 18 on flexible circuit 12 are, in this preferred embodiment, CSP 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. [0032] Embodiments of the present invention may be employed with 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 in the exemplar Figs.

[0033] Multiple integrated circuit die may be included in a package depicted as a single IC 18. While in this embodiment memory ICs are used to provide a memory expansion board or module, various embodiments may include a variety of integrated circuits and other components and may be directed principally to functions other than or in addition to memory. Such variety may include processors - whether general purpose or function specific such as graphics, FPGA 's, RF transceiver circuitry, and digital logic as a list of non-limiting examples, while primary module functions may include, as a non limiting list of examples, memory, graphics, communications, and computing to name just a few examples. Some modules in accordance with a preferred embodiment will exhibit plural CSPs of a first type, such as memory CSPs, for example, and will have at least one CSP of a second type, such as a microprocessor, graphics processor or buffer or, more particularly, an AMB, for example. Other modules will exhibit ICs of only a first type such as memory CSPs, for example, while other modules may exhibit many types of ICs such as, for example, memory ICs, logic ICs, and one or more buffer ICs.

[0034] Fig. 3 is a cross-sectional depiction of an exemplar module 10 taken along a line corresponding to B-B of Fig. 1. ICs 18 are shown as being thermally connected to thermal spreaders 13i and 13₂. The thermal connection between thermal spreaders 13i and 13₂ and ICs 18 can be effectuated by direct contact or through an intermediate substance, particularly one that encourages thermal conduction. An example of such a substance is indicated in Fig. 3 with reference 30 representative of a thermal adhesive. Thermal adhesive is also preferred between ICs 18 and substrate 14 as shown. Optional flex support 14FS supports flex circuit 12 in its transition from end 16A of substrate 14 toward the ICs.

[0035] Those of skill will also note that Fig. 3 may be also representative of a cross-sectional view through an exemplar module 10 along a line corresponding to C-C of Fig. 1 as well as line B-B in those instances where module 10 consists primarily of ICs 18 along its entire length. For example, if no larger IC such as an AMB is employed, a typical memory module 10 comprising constituent CSP ICs 18 along its length may have a cross-sectional aspect that may be represented by the depiction of Fig. 3 when flex circuit 12 is populated on both sides while thermal spreaders 13i and 13₂ are disposed adjacent and thermally connected to ICs 18B which are populated on side 8 of flex circuit 12 as further shown in Fig. 7. Reference to Fig. 7 illustrates that the ICs 18B represented as being thermally connected to thermal spreaders 13₁ and 13₂ are disposed in two ranks separated by contacts 20.

[0036] It should be recognized that optional substrate extension 16T enables a thermal conduction path for thermal energy to flow from inner ICs 18 A (shown proximal to substrate 14 in Fig. 3) into thermal spreaders 13i and 13₂ through the thermal connection shown extant between substrate 14 and thermal spreaders 13j and 13₂ effectuated by substrate extension 16T in thermal connection with thermal spreader extensions H₁A and 13₂A, respectively.

[0037] Fig. 4 is a cross-sectional view of an exemplar module 10 that employs a larger IC 19 such as an AMB 19 with the view of Fig. 4 being taken along a line that corresponds to C-C of Fig. 1. Fig. 4 shows a substrate 14 with a window 250 through which an optional thermal sink 14TS is accessible. Thermal sink 14TS is comprised, in this preferred embodiment, from metallic material of high thermal conductivity such as, for example, copper or copper alloy and has, in this preferred embodiment, a central portion 14TC that is a copper field substantially larger than and preferably in thermal contact with IC 19 which, in this preferred embodiment, is an AMB. AMB die 19D is in contact with area 14TC of thermal sink 14TS either directly, or through thermally conductive adhesive or a thermally conductive gasket material, for example. Thermal contact with a part of circuit 19 should be considered thermal contact with circuit 19.

[0038] In this preferred embodiment, central portion 14TC of thermal sink 14TS is raised above the periphery of thermal sink 14TS and additionally provides an indentation into which may be introduced at least a portion of AMB circuit 19 such as, for example, AMB die 19D, to assist in realization of a low profile for module 10. Neither thermal sink 14TS nor an indentation are required, however, to practice the invention. In the preferred depicted embodiment, thermal sink 14TS is disposed over a window 250 through substrate 14. AMB circuit 19, which is mounted on the "inside" of flex circuit 12, is disposed, at least in part, into window 250 from the "back" side of substrate 14 to realize thermal contact with thermal sink 14TS to provide a conduit to reduce thermal energy loading of AMB circuit 19. [0039] Thermal sink 14TS need not cover the entirety of window 250. In other embodiments, for example, thermal sink 14TS may merely be across the window 250 or thermal sink 14TS may be set into window 250 instead of over or across the opening of window 250. Thermal sink 14TS is typically a separate piece of metal from substrate 14 but, after appreciating this specification, those of skill will recognize that, in alternative instances, thermal sink 14TS may be integral with substrate 14 or a particular portion of substrate 14 may be constructed to be a thermal sink 14TS in accordance with the teachings herein. For example, substrate 14 may be comprised of aluminum, while a thermal sink area 14TS of substrate 14 may be comprised of copper yet substrate 14 and thermal sink 14TS are of a single piece. In a variation of the integral thermal sink-substrate embodiment, the thermal sink could be attached to the substrate without a window and thus be preferentially accessible only on one side of substrate 14. Construction expense will be more likely to militate against such construction but the principles of the invention encompass such constructions. Consequently, a window in substrate 14 is not required to practice some embodiments of the invention. Therefore, a thermal sink 14TS should be considered to be an area or element integral with or attached to a substrate 14 and the material from which that thermal sink is composed exhibits greater thermal conductivity than the material of the substrate. To continue the example, substrate 14 may be aluminum while thermal sink 14TS is comprised of copper. [0040] Substrate 14 has first and second lateral sides identified as Si and S₂. Flex 12 is wrapped about perimeter edge 16A of substrate 14. Some alternative embodiments may employ individual flex circuits on each side of substrate 14. As will be further shown, AMB circuit 19 is mounted on inner side 9 of flex circuit 12. When flex circuit 12 is disposed about substrate 14, AMB circuit 19 is introduced, at least in part, into window 250 with AMB die 19D being disposed, preferably, in thermal contact with thermal sink 14TS of substrate 14. That thermal contact is preferably through thermally conductive adhesive 30 but, in an alternative embodiment, another preferred construction may place AMB die 19D in direct physical contact with thermal sink 14TS to realize the thermal contact or connection between AMB circuit 19 and thermal sink 14TS. Other thermal conduction enhancing materials may also be used in place of, or addition to thermal adhesive 30 such as for example, thermal grease or a thermal gasket.

[0041] hi Figs. 3 and 4, thermal spreaders 13i and 13₂ exhibit optional thermal spreader extensions D₁A and 13₂A which, as previously described, provide a thermal conduction path for thermal energy from the inner ICs 18 A. They also, as shown, in cooperation with extension 16T, form a thermally conductive enclosure 11 over module 10. Thermal spreader extensions are not required as a part of thermal spreaders 13i and 13₂, but where employed as those of skill will recognize, they may provide thermal or structural advantages. [0042] In Fig. 5 a depicted substrate 14 is shown as having an integral thermal sink 14TS. The different materials used for the thermal sink 14TS as opposed to the substrate in general which result in the different thermal conductivity characteristics between substrate 14 and thermal sink 14TS are represented by the different hatching of the Fig. 5. For example, thermal sink 14TS in this depiction 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 thermal sink 14TS. Flex support 14FS is also shown in Fig. 5 and is typically comprised of the same material as substrate 14.

[0043] Despite the advantages of using a thermal sink with module 10, for cost reasons, amongst other rationales, some may wish to construct modules with low profiles lacking the conductivity differential of that feature. In that case, Fig. 6 illustrates a substrate employed with another alternative embodiment of the present invention in which an area of the substrate is deformed to provide an indentation but no thermal sink 14TS is employed. Thus, embodiments that employ substrates such as that depicted in Fig. 6 will not have a thermal sink, but may rely on thermal connection or contact between substrate 14 and IC 19 to dissipate heat generated by IC 19 where IC 19 has been mounted on inner side 9 of flex circuit 12 as shown later. As those of skill will note, indentation 14IN is not required but provides low profile advantages.

[0044] Consequently, an exemplar embodiment that employed a substrate such as that shown in Fig. 6 and does not exhibit a thermal sink 14TS would look very much like the embodiment shown in Fig. 4 except that the structure labeled 14TS would not be separate from substrate 14 and would be a part of substrate 14 and composed from the same material. Further, no window 250 would be present since no opening in substrate 14 would be needed. IC 19 would preferably be in thermal contact with substrate 14.

[0045] Where a window 250 in substrate 250 is employed, at least a part of thermal sink 14TS should be accessible through window 250 from the "other" side of substrate 14. AMB circuit 19 or other high heat IC 19 and, in particular, AMB die 19D, may be disposed in or across or over window 250 and preferably, will be introduced into an indentation of thermal sink 14TS and disposed in thermal contact with thermal sink 14TS and, more preferably, with the central core 14TC of thermal sink 14TS (where a central core has been optionally included in thermal sink 14TS) either with direct contact or through thermal adhesives or glues. Other embodiments may include additional windows where other high heat circuits are employed on module 10. Still other embodiments may insert some or all of ICs 18 into cutout areas in substrate 14 as described in detail in U.S. Pat. App. No. 11/005,992 which has been incorporated by reference herein. [0046] In a preferred embodiment, thermal sink 14TS covers window 250 on one side of substrate 14 while AMB circuit 19 is disposed, at least in part, into window 250 to realize contact between thermal sink 14TS and AMB circuit 19 and particularly AMB die 19D either directly or as mediated through a thermally-conductive adhesive or glue. [0047] Fig. 7 depicts a first side 8 of flex circuit 12 ("flex", "flex circuitry", "flexible circuit") used in constructing a module according to an embodiment of the present invention. Flex circuit 12 is preferably made from one or more conductive layers supported by one or more flexible substrate layers as further described with reference to later Fig 12. The construction of flex circuitry is known in the art. The entirety of the flex circuit 12 may be flexible or, as those of skill in the art will recognize, the flexible circuit structure 12 may be made flexible in certain areas to allow conformability to required shapes or bends, and rigid in other areas to provide rigid and planar mounting surfaces. Preferred flex circuit 12 has openings 17 for use in aligning flex circuit 12 to substrate 14 during assembly.

[0048] The depiction of Fig. 7 shows flex circuit 12 as having first and second fields or ranks of ICs 18 with contacts 20 being disposed between said ranks or fields of ICs 18. After flex circuit is assembled with substrate 14, those of skill will recognize that contacts 20 may appear on one or both sides of module 10 depending on the mechanical contact interface particulars of the application. Other embodiments may employ flex circuitry that exhibits contacts closer to an edge of the flex circuit. [0049] Flex circuit 12 may also referenced by its perimeter edges, two of which are typically long (PE_longi and PEi_{ong 2}) and two of which are typically shorter (PE_shorti and PE_Sh_Ort₂) although flex circuit 12 may come in a variety of shapes including square. Contact arrays such as array HA are disposed beneath ICs 18 and IC 19, where employed, and are comprised of array contacts 11C. An exemplar contact array 1 IA is shown as is exemplar IC 18 to be mounted at contact array 1 IA as depicted.

[0050] A first rank, group or plurality of ICs 18 is shown on side 8 of flex circuit 12 and is identified as IC_R1 and a second rank, group or plurality of CSPs on side 8 is identified as IC_R2. Those of skill will recognize that the identified pluralities of CSPs are, when disposed in the configurations depicted, typically described as "ranks". Between the ranks IC_R2 and IC_R2, flex circuit 12 bears a plurality of module contacts allocated in this embodiment into two rows (C_R1 and CR₂) of module contacts 20. When flex circuit 12 is folded about substrate 14 as earlier depicted, side 9 which is depicted in later Fig. 8, is closer to the substrate 14 about which flex circuit 12 is disposed than is side 8 and thus, ICs 18A which are identified in the cross- sectional view of Fig. 3, for example, are populated along the inner side 9 of flex circuit 12 while those ICs 18B identified in Fig. 3 are populated along the outer side 8 of flex circuit 12. Other embodiments may have other numbers of ranks and combinations of plural CSPs connected to create the module of the present invention. [0051] Fig. 7 depicts an exemplar conductive trace 21 connecting row C_R2 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. 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. [0052] Fig. 8 shows side 9 of flex circuit 12 depicting the other side of the flex circuit shown in Fig. 7 as may be employed in a preferred embodiment. Side 9 of flex circuit 12 is shown as being populated with multiple CSPs 18 and AMB circuit 19. Side 9 includes fields Fl and F2 that each include at least one mounting contact array site for CSPs and, in the depicted case, include multiple contact arrays. Each of fields Fl and F2 include, in the depicted preferred embodiment, two pluralities of ICs in this embodiment. Other embodiments may have other arrangements and constituent ICs and, in some cases, may have ICs on only one side of flex circuit 12. Other embodiments may also have fewer or greater numbers of ranks or pluralities of ICs in each field or on a side of a flex circuit. [0053] Fig. 9 is a view of a preferred embodiment before thermal spreaders devised in accordance with a preferred embodiment of the present invention are appended about the module. A cutaway area D is provided to enhance illustration of certain features. [0054] Flex circuit 12 is cutaway in area "D" to illustrate internal preferred features of module 10. Area "D" is shown in greater enlargement in later Fig. 10. Within area D are seen thermal sink 14TS and beyond the cutaway section of thermal sink 14TS, there is shown a part of a circuit 19 which, in the depicted preferred embodiment, is an AMB employed in FB-DIMM circuitry. AMB circuit 19 includes AMB die 19D and contacts 19C.

[0055] Fig. 10 is an enlarged depiction of the area D identified in Fig. 9 of an exemplar module 10 depicting in partial cutaway, details concerning the relationship between a high heat IC 19 such as an AMB 19 and substrate 14 in a preferred embodiment. This view provides insight that would otherwise be blocked from view if thermal spreaders 13i and 13₂ were included in the depiction. AMB circuit 19 is shown through window 250 through substrate 14. Preferably, AMB circuit 19 is mounted on what will become the internal side 9 of flex circuit 12 relative to module 10 and is, therefore, inserted into window 250 from the "rear" relative to the perspective shown in Fig. 10. Those of skill will recognize, particularly with reference to Fig. 10, that a portion of flex circuit 12 has been removed to expose thermal sink 14TS and a part of 14TS has also been cutaway.

[0056] Fig. 11 depicts an enlarged view of the area near end or edge 16A of an exemplar module 10. While a rounded configuration is shown, edge 16A may take on other shapes devised to mate with various connectors or sockets. The form and function of various edge card connectors are well know in the art. In many preferred embodiments, flex 12 is wrapped around edge 16A of substrate 14 and may be laminated or adhesively connected to substrate 14 with adhesive 30. The depicted adhesive 30 and flex 12 may vary in thickness and are not drawn to scale to simplify the drawing. The depicted substrate 14 has a thickness such that when assembled with the flex 12 and adhesive 30, the thickness measured between module contacts 20 falls in the range specified for the mating connector. In some other embodiments, flex circuit 12 may be implemented with two flex circuits 12A and 12B instead of one wrapped about end 16 A. For example, a flex circuit 12A may be disposed on one side of module 10 while another flex circuit 12B may be disposed on another side of module 10. Adhesive 30 is employed to attached flex circuit 12 to substrate 14 and contacts 20 are disposed on each side of module 10. In other embodiments, contacts 20 need not be on both sides of module 10 and may be exhibited on only one side in configurations.

[0057] Fig. 12 is an exploded depiction of a flex circuit 12 cross-section according to one preferred embodiment of the present invention. The depicted flex circuit 12 has four conductive layers 1201-1204 and seven insulative layers 1205-1211. The numbers of layers described are merely those used in one preferred embodiment and other numbers of layers and arrangements of layers may be employed. Even a single conductive layer flex circuit 12 may be employed in some embodiments, but flex circuits with more than one conductive layer prove to be more adaptable to more complex embodiments of the invention.

[0058] Top conductive layer 1201 and the other conductive layers are preferably made of a conductive metal such as, for example, copper or alloy 110. In this arrangement, conductive layers 1201, 1202, and 1204 express signal traces 1212 that make various connections by use of flex circuit 12. These layers may also express conductive planes for ground, power or reference voltages.

[0059] In this embodiment, inner conductive layer 1202 expresses traces connecting to and among various ICs. The function of any one of the depicted conductive layers may be interchanged in function with others of the conductive layers. Inner conductive layer 1203 expresses a ground plane, which may be split to provide VDD return for pre-register address signals. Inner conductive layer 1203 may further express other planes and traces. In this embodiment, floods or planes at bottom conductive layer 1204 provides VREF and ground in addition to the depicted traces.

[0060] Insulative layers 1205 and 1211 are, in this embodiment, dielectric solder mask layers which may be deposited on the adjacent conductive layers for example. Other embodiments may not have such adhesive dielectric layers. Insulating layers 1206, 1208, and 1210 are preferably flexible dielectric substrate layers made of polyimide. However, any suitable flexible circuitry may be employed in the present invention and the depiction of Fig. 12 should be understood to be merely exemplary of one of the more complex flexible circuit structures that may be employed as flex circuit 12. [0061] Fig. 13 depicts another preferred embodiment in accordance with the present invention. The depicted module 10 includes thermal spreaders 13i and 13₂ configured with plural extensions 13E which reside above substrate extension 16T and project inwardly. As those of skill will recognize, plural spreader extensions will encourage thermal shedding from the module. Fig. 14 provides a perspective view of a module 10 shown in cross-section in prior Fig. 13.

[0062] Fig. 15 depicts another preferred embodiment in accordance with the present invention. The module 10 depicted in Fig. 15 exhibits plural spreader extensions above substrate extension 16T but unlike the plural spreader extensions depicted in Fig. 13, the spreader extensions 13E exhibited by the module 10 depicted in Fig. 15 project outwardly. Fig. 16 depicts a perspective view of a module 10 with plural thermal spreader extensions that project outwardly above substrate extension 16T. [0063] Fig. 17 depicts an exemplar module 10 that exhibits multiple radiative projects from thermal spreaders D₁ and 13₂ to provide even more surface area for thermal shedding from module 10.

[0064] One advantageous methodology for efficiently assembling an embodiment of a module 10 depicted herein is as follows. In a preferred method of assembling a preferred module assembly 10, flex circuit 12 is placed flat and both sides populated according to circuit board assembly techniques known in the art. Flex circuit 12 is then folded about end 16A of substrate 14. Flex 12 may be laminated or otherwise attached to substrate 14. Adhesives are employed to secure thermal conduction between outer ICs 18B and thermal spreaders D₁ and 13₂ while additional thermally conductive adhesive may be employed between substrate extension 16T and thermal spreader extensions D₁A and 13₂A where such structures are employed in module 10.

[0065] 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.

Claims

Claims:

1. A circuit module comprising: a rigid substrate having two opposing lateral sides and an edge; a flex circuit having a first side which has plural contacts adapted for connection to a circuit board socket and first-flex-side first and second ranks of plural memory ICs between which are disposed the plural contacts, and the flex circuit having a second side which has second-flex-side first and second ranks of plural memory ICs, the flex circuit being disposed about the edge of the rigid substrate to dispose the second-flex-side first and second ranks of plural memory ICs adjacent to the rigid substrate; a first thermal spreader adjacent to and thermally connected to the first-flex-side first rank of plural memory ICs and a second thermal spreader adjacent to and thermally connected to the first-flex-side second rank of plural memory ICs.

2. The circuit module of claim 1 in which the rigid substrate is comprised of thermally conductive material.

3. The circuit module of claim 1 in which the rigid substrate exhibits a substrate extension and the first and second thermal spreaders each exhibit a thermal path extension which cooperates with the substrate extension to provide a thermal conduction path from the second- flex-side first and second ranks of plural ICs to the first and second thermal spreaders, respectively.

4. The circuit module of claims 1, 2, or 3 in which an IC having a function other than memory is populated on the second side of the flex circuit.

5. The circuit module of claim 4 in which the IC having a function other than memory is an AMB.

6. The circuit module of claims 2, 3, or 5 in which the first and second thermal spreaders each have at least one added extension in addition to the thermal path extension.

7. The circuit module of claim 1 in which the rigid substrate and the thermal spreaders are comprised of metallic thermally conductive material.

8. The circuit module of claim 1 in which the rigid substrate is comprised of aluminum.

9. The circuit module of claim 7 in which the rigid substrate exhibits an extension.

10. The circuit module of claim 1 in which the rigid substrate and the thermal spreaders are comprised of aluminum.

11. A circuit module comprising: (a) a rigid substrate having two opposing lateral sides and an edge and a thermal sink accessible on at least one of the two opposing lateral sides of the substrate; and

(b) a flex circuit having first and second sides, the first side of the flex circuit having plural contacts adapted for connection to a circuit board socket and at least the first of the first and second sides of the flex circuit being populated with plural memory CSPs with the second major side of the flex circuit being populated with at least an AMB, the flex circuit being disposed about the edge of the rigid substrate to dispose the AMB in thermal contact with the thermal sink;

(c) at least one thermal spreader which is thermally connected to and adjacent to at least some of the plural memory CSPs.

12. The circuit module of claim 11 in which the rigid substrate is comprised of thermally conductive material.

13. The circuit module of claim 11 or 12 in which the substrate exhibits at least one extension.

14. The circuit module of claim 11 or 12 in which the rigid substrate is comprised of aluminum.

15. The circuit module of claim 11 in which at least a portion of the thermal sink provides an indentation into which, at least in part, a portion of the AMB is introduced.

16. The circuit module of claim 11 in which the thermal contact is realized through thermally conductive adhesive.

17. The circuit module of claim 11 in which both the first and second sides of the flex circuit are populated with plural memory CSPs.

18. The circuit module of claim 11 in which the thermal sink is comprised of copper.

19. The circuit module of claim 11 in which the thermal sink is comprised of non-metallic material that is thermally-conductive.

20. The circuit module of claim 11 in which the rigid substrate exhibits a window through which the thermal sink is accessible.

21. The circuit module of claim 11 in which the thermal sink is across a window of the rigid substrate.

22. The circuit module of claim 11 in which the thermal sink covers a window of the rigid substrate.

23. The circuit module of claim 11 in which an extension of the substrate and an extension of the at least one thermal spreader provide a thermal conduction path between the substrate and the at least some of the plural ICs to which the at least one thermal spreader is thermally connected.

24. A circuit module comprising: (a) a rigid substrate comprised of thermally conductive material and having first and second opposing lateral sides and an edge, the rigid substrate having a window through the substrate;

(b) first and second thermal spreaders;

(c) a thermal sink, at least a part of which is accessible in the window through the substrate;

(d) a flex circuit having first and second sides, the first side of the flex circuit having plural contacts adapted for connection to a circuit board socket and the first and second sides of the flex circuit being populated with plural CSPs of a first type with the second major side of the flex circuit being populated with at least one CSP of a second type, the flex circuit being disposed about the edge of the rigid substrate to dispose the at least one CSP of the second type in thermal contact with the thermal sink and the first thermal spreader being disposed adjacent to and in thermal connection with at least a selected first one of the plural CSPs of the first type and the second thermal spreader being disposed adjacent to and in thermal connection with at least a selected second one of the plural CSPs of the first type.

25. The circuit module of claim 24 in which the rigid substrate is comprised of thermally conductive material.

26. The circuit module of claim 24 in which the thermal sink is configured with an indentation into which, at least in part, a portion of the at least one CSP of the second type is introduced.

27. The circuit module of claim 24 in which the substrate is comprised of aluminum and the first and second thermal spreaders are comprised of aluminum and the substrate exhibits an extension.

28. The circuit module of claim 24 in which the rigid substrate is comprised of metallic thermally-conductive material.

29. The circuit module of claim 24 in which the thermal sink is comprised of copper.

30. The circuit module of claim 24 further comprising at least one alignment hole in the flex circuit for use in aligning the flex circuit with the substrate during assembly.

31. The circuit module of claim 24 in which the flex circuit is comprised of more than one conductive layer.

32. The circuit module of claim 24 in which the flex circuit is comprised for four conductive layers.

33. The circuit module of claim 27 in which the substrate exhibits a substrate extension and the first and second thermal spreaders are thermally connected to the substrate extension.

34. A circuit module comprising: a rigid substrate have first and second lateral sides and an edge; a flex circuit populated with plural ICs and having a set of contacts for insertion in a circuit board edge connector, the flex circuit being disposed about the edge of the substrate to place the flex circuit on each side of the rigid substrate; and first and second thermal spreaders disposed in thermal connection with and adjacent to selected ones of the plural ICs.

35. The circuit module of claim 34 in which the rigid substrate is comprised of thermally conductive material.

36. The circuit module of claim 35 in which the rigid substrate exhibits a substrate extension which forms a part of a thermal path between the rigid substrate and the selected ones of the plural ICs which are adjacent to the first or second thermal spreaders.

37. The circuit module of claim 34 in which the flex circuit is comprised of more than one conductive layer.

38. The circuit module of claim 34 in which the rigid substrate has at least one extension.

39. A circuit module comprising:

(a) a rigid substrate having two opposing lateral sides and an edge and an extension;

(b) a flex circuit having plural contacts adapted for connection to a circuit board socket, the flex circuit being populated with plural CSPs of a first type and at least one CSP of a second type, the flex circuit being disposed about the edge of the rigid substrate to dispose the at least one CSP of the second type in thermal contact with the rigid substrate; and

(c) first and second thermal spreaders each of which is adjacent to at selected ones of the plural CSPs of the first type.