Patent Description:
Abbreviations appearing relatively infrequently in this document are defined upon initial usage, while abbreviations appearing more frequently in this document are defined below.

High power microelectronic modules, such as modules containing RF semiconductor die and other circuitry, are often prone to excess heat generation during module operation. In the absence of an adequate thermal solution for dissipating heat from the module, elevated local temperatures or "hot spots" can develop within the microelectronic module and detract from module performance. Existing thermal solutions implemented by manufacturers typically rely upon increasing the metal content within the module substrate in some manner; e.g., by forming bar vias within the body of the module substrate or by installing a prefabricated metal body, such as a Cu coin or slug, within a cavity formed in the module substrate. Such thermal solutions are generally effective at enhancing heat dissipation from microelectronic modules containing heat-generating devices, within limits. Nonetheless, there exists a continued demand within the microelectronic industry for still further enhancements in the heat dissipation capabilities of microelectronic modules. <CIT> describes a method of making interconnect substrate having routing circuitry connected to posts and terminals. <CIT> describes an open cavity leadless surface mountable package for high power RF applications.

According to a first aspect, there is provided a microelectronic module according to claim <NUM>. According to a second aspect, there is provided a method for fabricating a microelectronic module according to claim <NUM>.

At least one example of the present invention will hereinafter be described in conjunction with the following figures, wherein like numerals denote like elements, and:.

For simplicity and clarity of illustration, descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the exemplary and non-limiting embodiments of the invention described in the subsequent Detailed Description. It should further be understood that features or elements appearing in the accompanying figures are not necessarily drawn to scale unless otherwise stated. For example, the dimensions of certain elements or regions in the figures may be exaggerated relative to other elements or regions to improve understanding of embodiments of the invention.

The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. The term "exemplary," as appearing throughout this document, is synonymous with the term "example" and is utilized repeatedly below to emphasize that the following description provides only multiple non-limiting examples of the invention and should not be construed to restrict the scope of the invention, as set-out in the Claims, in any respect. Terms of orientation, such as "upper," "lower," and "underneath," as appearing throughout document, are defined with respect to the frontsides and the opposing backsides of the below-described module substrates.

The following definitions apply throughout this document. Those terms not expressly defined here or elsewhere in this document are assigned their ordinary meaning in the relevant technical field.

Heat spreader extension-a thermally-conductive structure contained in a thermal extension level (defined below), bonded to a substrate-embedded heat spreader (also defined below), and in thermal communication with the substrate-embedded heat spreader.

Metallic material-a material predominately composed of metallic constituents, by weight percentage.

Microelectronic device-any small scale device or component mounted to a module substrate and having electronic functionalities, whether passive or active in nature. A non-exhaustive list of microelectronic devices includes semiconductor die, sensors, RF antenna structures, RF or Electromagnetic Interference (EMI) shield structures, MEMS devices, and passive SMDs in the form of discrete resistors, inductors, diodes, and capacitors, such as chip caps.

Substrate-embedded heat spreader-a thermally-conductive structure, such as a monolithic body or composite structure, that aids in heat dissipation through a module substrate and that is substantially or wholly embedded in the module substrate.

Thermally-conductive-having a thermal conductivity exceeding <NUM> watts per meter-Kelvin (W/mK).

Thermal extension level-any number of thermally-conductive and, perhaps, electrically-conductive structures located adjacent the backside of a module substrate, generally distributed along a common plane, and including at least one structure (herein, a "heat spreader extension") in thermal communication with a substrate-embedded heat spreader, as defined above.

The following describes high thermal performance microelectronic modules including thermal extension levels, as well as methods for manufacturing high thermal performance microelectronic modules. As indicated by the term "high thermal performance," the below-described microelectronic modules contain unique structures or features enhancing thermal dissipation of excess heat generated by microelectronic devices, such as semiconductor (e.g., RF) die and other circuitry, contained within a given module. Such structures will typically include, at minimum, a heat spreader extension, which is contained in a thermal extension level located adjacent the backside of a module substrate and directly or indirectly bonded to the thermal extension level. In embodiments, the heat spreader extension may be bonded to a lower principal surface of a heat spreader, which is embedded within the module substrate and which has a surface substantially coplanar with the backside thereof. In certain implementations, the heat spreader extension may be directly bonded to the substrate-embedded heat spreader by, for example, forming the heat spreader extension from a plated material (e.g., plated Cu) deposited directly onto the exposed surface of the substrate-embedded heat spreader. Alternatively, the heat spreader extension may be provided as a prefabricated piece or part, such as a singulated piece of a leadframe or a discretely-placed component, which is bonded to the substrate-embedded heat spreader by a thermally-conductive material.

Through the inclusion of such a heat spreader extension, the thermal dissipation capabilities of the microelectronic module can be increased to promote conductive heat flow away from heat-generating device(s) contained within the module. Additionally, the heat spreader extension and the substrate-embedded heat spreader may cooperate or combine to form a highly conductive thermal conduit, which extends from an upper portion of the module substrate (perhaps from the substrate frontside), through the substrate body, through the heat spreader extension, and to a mount plane of the module. Excess heat generated during module operation may thus be conductively transferred from the heat-generating device(s) within the module, through the substrate-embedded heat spreader, through the heat spreader extension, and to a larger system substrate on which the microelectronic module is installed. Finally, the heat spreader extension and, more generally, the thermal extension level may be unencapsulated and directly exposed to the ambient environment to further promote convective transfer of excess heat from the module to the surrounding environment. For these reasons, the provision of such a heat spreader extension can favorably enhance thermal performance of the microelectronic module. Additionally, the heat spreader extension may be electrically active in at least some embodiments and, perhaps, may cooperate with the substrate-embedded heat spreader (and possibly other electrical routing features) to form an electrical grounding path through the module substrate and to microelectronic devices, such as semiconductor die bearing RF circuitry, mounted to the substrate frontside.

In certain implementations, the thermal extension level may include other structures or features in addition to the above-described heat spreader extension, such as a number of electrically-conductive contact bridges or "terminal extensions. " When included in the thermal extension layer, such terminal extensions may be joined to electrical terminals, such as contact pads, embedded in the module substrate. Opposite the substrate-embedded terminals, the terminal extensions may terminate along with the heat spreader extension at a common plane, which is referred to herein as "a module mount plane. " Such a structural configuration allows the high thermal performance microelectronic module to be mounted to a system substrate, and electrically interconnected with contact pads or other terminals provided on the system substrate, in essentially the same manner as are conventional microelectronic modules lacking thermal extension levels, thereby easing customer adoption. In other embodiments, the thermal extension level may not contain terminal extensions; e.g., as may be the case when a different interconnect approach, such as wirebonding, is utilized to supply power to, to electrically ground, and/or to permit signal communication with the microelectronic devices contained within the module. Examples of high thermal performance microelectronic modules having thermal extension levels and methods for manufacturing microelectronic modules will now be described in conjunction with <FIG>.

Turning now to <FIG>, there is shown a simplified cross-sectional view of a system substrate <NUM> (partially shown) to which a high thermal performance microelectronic module <NUM> is mounted, as illustrated accordance with an exemplary embodiment of the present invention. System substrate <NUM> is depicted in a generalized manner to emphasize that microelectronic module <NUM> can be utilized in conjunction with various types of system substrates, without limitation, providing that the selected system substrate is capable of supporting module <NUM> and, perhaps, serves as a heatsink to which heat extracted from module <NUM> can be conductively transferred. Substrate <NUM> usefully, but non-essentially includes interconnect lines, metal traces, contact or landing pads, and/or other electrically-conductive routing features (not shown) to which the terminals of module <NUM> can be interconnected. Again, only a limited portion of system substrate <NUM> is shown in <FIG>, with the non-illustrated portions of substrate <NUM> potentially supporting any number and type of additional microelectronic devices, modules, and other components.

As just stated, system substrate <NUM> can assume any form suitable for supporting microelectronic module <NUM>, such as a coreless substrate. In the illustrated example, system substrate <NUM> is realized as a multilayer PCB and is consequently referred to hereafter as "PCB <NUM>. " PCB <NUM> can include any practical number of patterned metal levels or wiring layers, which are hidden from view in <FIG> for illustrative clarity. Typically, PCB <NUM> will include at least one patterned metal layer or level formed on PCB frontside <NUM>, which defines interconnect lines (e.g., Cu traces), contact pads, and other such routing features. An additional metal level or wiring layer may be formed on the backside of PCB <NUM>, and any practical number of internal wiring layers may be formed within PCB <NUM> when composed of multiple layers or laminates. PCB <NUM> may also contain a number of plated vias, metal plugs, or similar electrically-conductive structures, which provide electrically-conductive paths entirely or partially through the thickness of PCB <NUM>; the term "thickness," as appearing herein, refers to a dimension measured along an axis orthogonal to the backside of module substrate <NUM> (e.g., a dimension extending between frontside <NUM> and the backside of the PCB <NUM>, or between frontside <NUM> and the backside of module <NUM>). In certain cases, PCB <NUM> may also be formed to include one or more thermally-conductive structures, which serve as a heatsink to which excess heat extracted from microelectronic module <NUM> is conductively transferred. This possibility is indicated in <FIG> by dashed region <NUM>, which generically represents a thermally-conductive structure (e.g., a via farm or a thermally-conductive slug, such as a coin composed of Cu or another thermally-conductive material) over which microelectronic module <NUM> may be mounted. Such a thermally-conductive structure (e.g., via farm or coin) may thus serve as both a heatsink for microelectronic module <NUM> and to provide electrical grounding of the devices within module <NUM> in at least some implementations.

Microelectronic module <NUM> contains a module substrate <NUM>, a thermal extension level <NUM>, and a number of microelectronic devices <NUM>, <NUM>. Microelectronic devices <NUM>, <NUM> are distributed at various locations across substrate frontside <NUM>. Microelectronic devices <NUM>, <NUM> can be electrically interconnected utilizing any type of interconnect features, which are not shown in <FIG> to avoid cluttering the drawing. Such interconnect structures will often assume the form of metallic (e.g., Cu) traces and pads formed on PCB frontside <NUM> utilizing lithography and metallization processes. Other types of interconnect features can be equivalently utilized, however, including wirebonding and/or three dimensionally printed metal traces (e.g., as may be printed utilizing ink containing metallic particles), which conformally extending along surfaces of substrate <NUM> and perhaps devices <NUM>, <NUM>. The particular manner in which microelectronic devices <NUM>, <NUM> are interconnected may vary depending upon the desired functionality of microelectronic module <NUM>, as will the type of devices <NUM>, <NUM> contained in module <NUM>. Generally, microelectronic devices <NUM>, <NUM> can include any number and type of semiconductor die (e.g., memory die or Application Specification Integrated Circuit (ASIC) die), MEMS devices, and SMDs, such as discrete or passive capacitors (e.g., chip caps), inductors, resistors, and diodes, to list but a few examples. In the depicted embodiment, and by way of non-limiting illustration, microelectronic devices <NUM> assume the form of circuit-bearing (e.g., RF) semiconductor die, while microelectronic devices <NUM> assume the form of passive SMDs, such as discrete capacitors, resistors, or inductors.

Referring now to <FIG> and <FIG> in combination with <FIG>, microelectronic module <NUM> will be described in greater detail. Addressing first substrate <NUM>, module substrate <NUM> can assume any form suitable for supporting microelectronic devices <NUM>, <NUM>, such as a PCB or a coreless substrate. Module substrate <NUM> usefully contains electrical routing features, such as electrically-conductive traces; however, this is not required in all embodiments. In the exemplary embodiment of <FIG>, specifically, module substrate <NUM> is realized as a multilayer PCB containing a number of internal wiring layers or metal levels. This may be most readily appreciated by reference to <FIG>, which is a cross-sectional view of module <NUM> taken along line <NUM>-<NUM> in <FIG>. Accordingly, module substrate <NUM> includes a dielectric body <NUM> and multiple metal levels or wiring layers <NUM> (also referred to herein as "electrical routing features"), which are contained within body <NUM>, spaced along the centerline of module <NUM> (parallel to the Y-axis identified by coordinate legend <NUM> in <FIG>), and interconnected by plated vias, metal plugs, or similar structures. Dielectric body <NUM> thus has a multi-layered construction in the illustrated embodiment. Dielectric body <NUM> may be composed of a resin, polymeric material (e.g., a polyimide or polytetrafluoroethylene (PTFE)), and various other dielectric materials.

One of microelectronic devices <NUM> mounted to frontside <NUM> of module substrate <NUM> is shown in <FIG>. Wirebonds <NUM> are further shown, which electrically couple the bond pads of the illustrated device <NUM> to corresponding contacts provided on substrate frontside <NUM>. As indicated in <FIG> by phantom line, the illustrated microelectronic device <NUM> and the other microelectronic devices <NUM>, <NUM> shown in <FIG> can be surrounded by some form of an enclosure <NUM> in at least some instances. In certain embodiments, enclosure <NUM> may assume the form of an overmolded body, which is composed of a mold compound (or other moldable dielectric material) injected over module substrate <NUM>. In other embodiments, enclosure <NUM> may assume the form of a box-like structure, which includes a peripheral sidewall enclosed by a lid or cover. The peripheral sidewall and lid may thus define an air cavity in which microelectronic devices <NUM>, <NUM> are located. In still other embodiments, enclosure <NUM> may assume a different form or may be omitted from microelectronic module <NUM>.

As further shown in <FIG>, a substrate-embedded heat spreader <NUM> is contained within dielectric body <NUM>. In certain embodiments, substrate-embedded heat spreader <NUM> can assume the form of a plated metal body or block, which is compiled on a layer-by-layer basis during the metallization processes utilized to successively form wiring layers <NUM>. Alternatively, substrate-embedded heat spreader <NUM> can assume the form of a prefabricated structure or discrete piece part, which is installed within a central cavity provided in module substrate <NUM> and secured in place by press-fit and/or utilizing a suitable bonding material. In this latter case, substrate-embedded heat spreader <NUM> may be fabricated to have a monolithic, composite, or layered construction. For example, in certain implementations, substrate-embedded heat spreader <NUM> may assume the form of a thermally-conductive piece (e.g., a metal slug) or an elongated thermal conduit (e.g., a heat pipe), which is affixed within the one or more cavities provided in substrate <NUM> utilizing a thermally-conductive bonding material, such as a sintered bond layer of the type described below. Further description of thermally-conductive structures suitable for usage as heat spreader <NUM> can be found in the following document, <CIT>.

Regardless the particular form assumed thereby, substrate-embedded heat spreader <NUM> will typically be composed of a material, or combination of materials, having a thermal conductivity exceeding that of dielectric body <NUM>. In many cases, substrate-embedded heat spreader <NUM> will be composed of a metallic material, such as Cu, aluminum (Al), or nickel (Ni), and alloys thereof. In other embodiments, and as briefly mentioned above, substrate-embedded heat spreader <NUM> may be fabricated from a composite material or a non-metallic material having relatively high thermal conductivities. Such materials include, but are not limited to, diamond polycarbonate materials, diamond-metal composites (e.g., diamond gold (Au), diamond silver (Ag), and diamond Cu), pyrolytic graphite, and materials containing allotropes of carbon, such as graphene and carbon nanotube-filled materials. In one specific, albeit non-limiting example, substrate-embedded heat spreader <NUM> is formed as a plated metal block having a volume equal to or greater than one half of the volume of module substrate <NUM>. In other embodiments, substrate-embedded heat spreader <NUM> may be formed or provided in a different manner and/or may have a volume less than one half that of substrate <NUM>.

As shown in <FIG> and <FIG>, microelectronic module <NUM> further includes a plurality of contact pads or terminals <NUM>, which are at least partially embedded in module substrate <NUM> and referred to hereafter as "substrate-embedded terminals <NUM>. " As with substrate-embedded heat spreader <NUM>, substrate-embedded terminals <NUM> are exposed at and/or substantially extend to or beyond substrate backside <NUM>. Substrate-embedded terminals <NUM> may have lower principal surfaces substantially coplanar with the lower principal surface or backside <NUM> of substrate-embedded heat spreader <NUM>. Substrate-embedded terminals <NUM> can be provided in various different manners, including as prefabricated conductive pieces that are placed in desired positions and enveloped by dielectric body <NUM> when formed utilizing an overmolding process. Alternatively, when module substrate <NUM> assumes the form of a multi-layer PCB, as shown, substrate-embedded terminals <NUM> may be formed during the metallization processes utilized to form the lower metal level or levels within module substrate <NUM>. In either case, substrate-embedded terminals <NUM> may be electrically coupled to microelectronic devices <NUM>, <NUM> through electrical routing features or wiring layers <NUM> contained in module substrate <NUM>. As best shown in <FIG> (described below), substrate-embedded terminals <NUM> may be distributed around a lower periphery of substrate-embedded heat spreader <NUM>, while being spatially offset therefrom and electrically isolated by intervening portions of dielectric body <NUM>. In other embodiments, the spatial distribution of substrate-embedded terminals <NUM> may vary, as may the shape and dimensions of terminals <NUM> and/or heat spreader <NUM>.

A patterned thermally-conductive bond layer <NUM> joins thermal extension level <NUM> to substrate-embedded heat spreader <NUM> and substrate-embedded terminals <NUM>. Thermally-conductive bond layer <NUM> may be deposited or otherwise applied in a pattern, which includes a heat spreader-contacting portion <NUM> and a number of terminal-contacting portions <NUM>. Heat spreader-contacting portion <NUM> bonds heat spreader extension <NUM> to lower principal surface or backside <NUM> of substrate-embedded heat spreader <NUM>, while terminal-contacting portions <NUM> bond terminal extensions <NUM> to substrate-embedded terminals <NUM>. Patterned thermally-conductive bond layer <NUM> need not attach all of structures contained in thermal extension level <NUM> to module substrate <NUM>, however. In some implementations, one or more of the structures contained in thermal extension level <NUM> may be imparted with a solder finish, which is reflowed to form the desired joints between components. This possibility is indicated in <FIG> in which terminal extensions <NUM> are depicted as solder-covered contacts, which are electrically and mechanically attached to a corresponding pair of substrate-embedded terminals <NUM> by solder reflow during the fabrication of microelectronic module <NUM>. Terminal extensions <NUM> may each assume the form of soldered-covered spherical contacts or balls, which each contain an inner (e.g., Cu or Au) core having a first thermal conductivity (represented in <FIG> by dashed circles <NUM>) and further contains an outer shell composed of a solder material having a second thermal conductivity less than the first thermal conductivity. In still other embodiments, all structures contained in thermal extension level <NUM> may be joined to module substrate <NUM> by solder reflow, whether applied as a paste or finish.

Thermally-conductive bond layer <NUM> can be composed of various materials providing a desired mechanical bond strength, while possessing a relatively high thermal conductivity; e.g., a thermal conductivity exceeding <NUM> W/mK. Additionally, when utilized to provide electrical connections, bond layer <NUM> also usefully has a relatively high electrical conductivity. Candidate materials include, but are not limited to, metal-filled (e.g., Cu-, Au-, and Ag-filled) epoxies, solder materials (e.g., deposited solder pastes), and other die attach materials having the aforementioned properties. In one group of embodiments, thermally-conductive bond layer <NUM> is formed from a sintered metallic material predominately composed of one or more metallic constituents, by weight percentage (wt%). Advantageously, when so composed, thermally-conductive bond layer <NUM> can achieve relatively high thermal conductivities and may be formed from a metal-particle containing precursor material utilizing a low temperature sintering process. Given these advantages, the following will primarily describe thermally-conductive bond layer <NUM> as "sintered bond layer <NUM>" hereafter. It is again emphasized, however, that this description is provided by way of non-limiting illustration only and that bond layer <NUM> can be composed of various other thermally-conductive bonding materials in alternative embodiments.

As noted above, sintered bond layer <NUM> may be predominately composed of at least one metal, as considered by wt%. In one embodiment, sintered bond layer <NUM> is predominately composed of Cu, Ag, Au, or a mixture thereof, again as considered by wt%. Sintered bond layer <NUM> may or may not contain organic materials. For example, in certain implementations, sintered bond layer <NUM> may be essentially free of organic materials; the term "essentially free," as appearing herein, defined as containing less than <NUM> wt% of organic materials. In other embodiments, sintered bond layer <NUM> may contain selected organic materials or fillers to tailor the properties of bond layer <NUM>. For example, in certain instances, sintered bond layer <NUM> may contain an epoxy or another organic material. In one implementation, sintered bond layer <NUM> is composed of a sintered metal (e.g., Ag) material having a thermal conductivity exceeding <NUM> W/mK and, perhaps, a thermal conductivity equal to or exceeding about <NUM> W/mK. Additionally, sintered bond layer <NUM> may be produced to have a desired porosity, which may range from <NUM>% to <NUM>% by volume in an embodiment. In another embodiment, sintered bond layer <NUM> may be formed to each have a porosity of less than <NUM>% by volume.

With continued reference to <FIG>, the respective lower surfaces of heat spreader extension <NUM> and terminal extensions <NUM>, <NUM> are substantially coplanar and, thus, co-terminate at a module mount plane <NUM> (<FIG>). Module mount plane <NUM> extends substantially parallel to substrate backside <NUM>, while being offset therefrom by a predetermined distance. Extensions <NUM>, <NUM>, <NUM> each project from a point adjacent module backside <NUM> to module mount plane <NUM>. Heat spreader extension <NUM> and terminal extensions <NUM>, <NUM> have substantially equivalent thicknesses, as measured along axes orthogonal to substrate backside <NUM>; that is, along axes parallel to the Y-axis of coordinate legend <NUM> (<FIG>). In embodiments, heat spreader extension <NUM> and terminal extensions <NUM>, <NUM> may each have a thickness range from about <NUM> to about <NUM>,<NUM> microns (µm) or, more preferably, from <NUM> to <NUM>,<NUM>. In other embodiments, extensions <NUM>, <NUM>, <NUM> may have thicknesses greater than or less than the aforementioned ranges, as discussed more fully below in conjunction with <FIG>. This notwithstanding, extensions <NUM>, <NUM>, <NUM> are not required to have equivalent thicknesses or to terminate at a common mount plane in all embodiments, and more complex mounting schemes can be complemented in which one or more of extensions <NUM>, <NUM>, <NUM> may project beyond module mount plane <NUM>, depending upon the interface between module <NUM> and system substrate <NUM> (<FIG>).

As briefly indicated above, heat spreader extension <NUM> can assume the form of any prefabricated structure or part having a relatively high thermal conductivity exceeding that of dielectric body <NUM>. In many cases, heat spreader extension <NUM> will possess a thermal conductivity substantially equivalent to or greater than that of substrate-embedded heat spreader <NUM>. Generally, heat spreader extension <NUM> can be composed of a metallic material, a non-metallic material, or a composite material having a relatively high thermal conductivity; e.g., a thermal conductivity approaching or exceeding <NUM> W/mK. Suitable metallic materials include Al, Cu, and Ni, as well as alloys thereof. Suitable non-metallic materials and composites include diamond polycarbonate materials, diamond-metal composites (e.g., diamond Au, diamond Ag, and diamond Cu), pyrolytic graphite, and materials containing allotropes of carbon, such as graphene and carbon nanotube-filled materials. In the embodiment shown in <FIG>, heat spreader extension <NUM> is provided as a prefabricated structure and, specifically, as a singulated piece of a leadframe. Terminal extensions <NUM> are likewise provided as singulated pieces of leadframe in the illustrated embodiment, further described below in conjunction with <FIG>. In other embodiments not forming part of the present invention, heat spreader extension <NUM> may not be provided as a singulated piece of a leadframe; and may, instead, assume the form of a discrete prefabricated part, such as a metallic slug or coin, as further described below.

Heat spreader extension <NUM> may be electrically active in at least some embodiments of microelectronic module <NUM>. In such embodiments, heat spreader extension <NUM> may combine with substrate-embedded heat spreader <NUM> and, perhaps, other electrically-conductive features of microelectronic module <NUM> (e.g., electrical routing features <NUM>) to allow power supply to, electrical grounding of, and/or signal communication with any number of microelectronic devices <NUM>, <NUM> (<FIG>). For example, an electrical grounding path may be provided from one or more of microelectronic devices <NUM>, <NUM>, through substrate-embedded heat spreader <NUM>, through central (heat spreader-contacting) portion <NUM> of sintered bond layer <NUM>, through heat spreader extension <NUM>, and to module mount plane <NUM> in embodiments. In this manner, one or more of microelectronic devices <NUM>, <NUM> may be electrically coupled to ground through a low resistivity electrical path, which is principally formed by substrate-embedded heat spreader <NUM> and heat spreader extension <NUM>. More specifically, in one non-limiting implementation, microelectronic devices <NUM> may assume the form of semiconductor die bearing RF circuitry, which is electrically coupled to an electrically-grounded feature of PCB <NUM> (e.g., thermally-conductive structure in dashed region <NUM> shown in <FIG>, as provided in the form of a via farm, an embedded coin, or a press-fit coin) through substrate-embedded heat spreader <NUM> and heat spreader extension <NUM>.

As shown most clearly in <FIG>, which shows the system substrate <NUM> and the thermal extension level <NUM> with the module substrate <NUM> removed, heat spreader extension <NUM> includes a central portion or main body <NUM>, which has planform dimensions generally corresponding to those of lower principal surface <NUM> (identified in <FIG>) of substrate-embedded heat spreader <NUM>. Heat spreader extension <NUM> also includes one or more peripheral projections or wings <NUM>, which project from main body <NUM> in lateral directions; that is, along the X-Z plane of coordinate legend <NUM> (<FIG>). Wings <NUM> extends beneath selected ones of substrate-embedded terminals <NUM> and, perhaps, may be placed in electrical and thermal communication therewith through terminal-contacting portions <NUM> of bond layer <NUM>. For example, in embodiments in which heat spreader extension <NUM> is electrically grounded, wings <NUM> may extend beneath, be bonded to, and electrically communicate with certain substrate-embedded terminals <NUM> that are likewise electrically grounded. Additionally or alternatively, one or more wings <NUM> of heat spreader extension <NUM> may extend beneath, and be bonded to, electrically inactive or "dummy" terminals included in substrate-embedded terminals <NUM>. Wings <NUM> are usefully formed to increase the overall heat spreading capabilities of heat spreader extension <NUM> and thereby further boost the heat dissipation capabilities of module <NUM>. Additionally, in embodiments according to the present invention, in which at least heat spreader extension <NUM> is provided as a singulated piece of a leadframe, wings <NUM> may be leveraged as spars or tie bars initially connecting main body <NUM> of extension <NUM> to the larger leadframe, as discussed more fully below in conjunction with <FIG>. In other embodiments not forming part of the present invetion, such as when heat spreader extension <NUM> is provided as a discretely-placed piece (rather than in leadframe format), heat spreader extension <NUM> may lack wings <NUM>.

The maximum thicknesses of substrate-embedded heat spreader <NUM> and heat spreader extension <NUM> are identified in <FIG> by double-headed arrows T<NUM> and T<NUM>, respectively. When provided as a prefabricated structure, heat spreader extension <NUM> may be imparted with a maximum thickness equal to or greater than that of substrate-embedded heat spreader <NUM> such that T<NUM> ≤ T<NUM> in certain instances. In other embodiments, heat spreader extension <NUM> may be thinner than heat spreader <NUM>. By way of non-limiting example, the maximum thickness of substrate-embedded heat spreader <NUM> (T<NUM>) may range between <NUM> and <NUM> millimeters (mils) in embodiments, while the maximum thickness of heat spreader extension <NUM> (T<NUM>) ranges between <NUM> and <NUM> mils. In yet other implementations, heat spreader <NUM> and/or heat spreader extension <NUM> may be thicker or thinner than the aforementioned ranges. Comparatively, the maximum thickness of module substrate <NUM> (identified in <FIG> by double-headed arrow T<NUM>) will typically be greater than or equal to that of heat spreader <NUM> (T<NUM>), depending upon whether heat spreader <NUM> extends through the entirety of substrate <NUM> to breach substrate frontside <NUM> and substrate backside <NUM>. Lastly, the thickness of sintered bond layer <NUM> (identified by double-headed arrow T<NUM>) may range between <NUM> and <NUM> in an exemplary embodiment.

The provision of heat spreader extension <NUM> and, more generally, of thermal extension level <NUM> may favorably increase the heat dissipation capabilities of microelectronic module <NUM> in a number of manners. First, heat spreader extension <NUM> increases the overall thermal dissipation capabilities of microelectronic module <NUM>, generally considered, to more uniformly distribute thermal gradients across module <NUM>. Second, and as previously noted, heat spreader extension <NUM> and substrate-embedded heat spreader <NUM> cooperate or combine to form a highly conductive thermal conduit extending from an upper portion of module substrate <NUM>, through dielectric body <NUM>, through heat spreader extension <NUM>, and to module mount plane <NUM>. Thus, when mounted to system substrate <NUM> (<FIG>), excess heat generated by microelectronic devices <NUM>, <NUM> (<FIG>) can be conductively transferred through substrate-embedded heat spreader <NUM>, through heat spreader extension <NUM>, and to substrate <NUM> to remove excess heat from module <NUM> in a highly efficient manner. Third, as shown in <FIG>, thermal extension level <NUM> may be left unencapsulated and directly exposed to the ambient environment to further promote convective transfer of excess heat from module <NUM>, particularly from heat spreader extension <NUM>, to the surrounding environment. Such convective heattransfer can be further promoted, if desired, by directing forced airflow through or otherwise cooling thermal extension level <NUM>. By more effectively removing or dissipating excess heat from module <NUM>, microelectronic devices <NUM>, <NUM> can be operated at higher power levels with little to no performance degradation. This is highly desirable, particularly when microelectronic devices <NUM>, <NUM> provide high power RF functionalities.

An exemplary fabrication process for manufacturing microelectronic module <NUM> shown in <FIG>, along with a plurality of identical modules, will now be described in conjunction with <FIG>. If desired, a multi-substrate panel may be processed to produce a number of microelectronic modules <NUM> in parallel for increased process efficiency. An example of such a multi-substrate panel <NUM> is shown in <FIG>, which illustrate the frontside and backside of panel <NUM>, respectively. In this example, multi-substrate panel <NUM> has a strip-like form factor and contains a plurality of module substrates <NUM>, which are physically connected at the present juncture of manufacture and arranged into two grids <NUM>. For ease of description, the following will focus on the processing of four interconnected module substrates <NUM> contained in dashed rectangle <NUM> appearing in each of <FIG>. It will be appreciated, however, that the below-described process steps will be performed globally across panel <NUM> for all interconnected module substrates <NUM> to yield a relatively large number of microelectronic modules <NUM>. Also, in other embodiments, the depicted microelectronic modules can be manufactured on an individual basis or utilizing a different fabrication approach. Furthermore, the below-described process steps are provided by way of non-limiting example only. In alternative implementations, the below-described process steps may be performed in alternative sequences, certain steps may be omitted, and various other process steps can be introduced into the fabrication process.

Referring to <FIG>, backsides <NUM> of four module substrates <NUM> included in multi-substrate panel <NUM> (<FIG>) are shown prior to attachment of thermal extension levels <NUM>. Here, it can be seen that the lower principal surfaces of substrate-embedded heat spreaders <NUM> and substrate-embedded terminals <NUM> are visible through the respective backsides <NUM> of interconnected substrates <NUM>. Additionally, a number of intersecting saw lanes <NUM> are identified in <FIG>. As discussed below, multi-substrate panel <NUM> and the below-described extension level leadframe may be cut or otherwise separated along saw lanes <NUM> during singulation to separate microelectronic modules <NUM>' into discrete units. In <FIG>, and also in <FIG>, the prime symbol (') is appended to those reference numerals designating structural elements or items in a non-completed or transitional state. For example, in each of <FIG>, the illustrated microelectronic modules are shown in a partially completed state and are thus identified utilizing reference numeral "<NUM>'.

Advancing to <FIG>, a bond layer precursor material <NUM>' (represented by dot stippling) is applied over the exposed surfaces of substrate-embedded heat spreaders <NUM> and substrate-embedded terminals <NUM>. In the illustrated example, bond layer precursor material <NUM>' is deposited onto panel <NUM> in a predetermined pattern including heat spreader-contacting portions <NUM>', which are deposited onto substrate-embedded heat spreaders <NUM>; and terminal-contacting portions <NUM>', which are deposited onto substrate-embedded terminals <NUM>. Bond layer precursor material <NUM>' may be composed of die attach epoxy, a solder paste, a die attach material, or another such material that can processed (e.g., via thermal or ultraviolet curing) to yield a thermally-conductive bond layer of the type discussed above. For example, in embodiments, bond layer precursor material <NUM>' can be applied in a dry state as, for example, a thin film or B-stage epoxy. Alternatively, in other embodiments, bond layer precursor material <NUM>' can be deposited in the desired pattern utilizing a wet state application process, such as screen printing or fine needle dispense. As still further possibility, bond layer precursor material <NUM>' may instead be applied to the appropriate surfaces of the below-described extension level leadframe by dipping, patterned dispensing (e.g., screen printing), as a dry film, or utilizing another approach; and then brought into contact with the exposed surfaces of substrate-embedded heat spreaders <NUM> and substrate-embedded terminals <NUM> when the leadframe is positioned against multi-substrate panel <NUM>, as described below.

Turning to <FIG>, an extension level leadframe <NUM> (partially shown) is next positioned over and against multi-substrate panel <NUM>. Extension level leadframe <NUM> contains a number of thermal extension levels <NUM>, which are interconnected by intervening frame-like structure referred to as "tie bars <NUM>. " Specifically, as indicated in <FIG>, tie bars <NUM> are physically connected to terminal extensions <NUM> and to heat spreader extensions <NUM> through the wings thereof prior to singulation of leadframe <NUM>. Extension level leadframe <NUM> may have various other form factors in further embodiments, depending upon the design of modules <NUM>'. Further, extension level leadframe <NUM> may be utilized to only provide a subset of the features included in thermal extension levels <NUM> in certain implementations. For example, as indicated in <FIG>, terminal extensions <NUM> (e.g., solder-covered balls) included in thermal extension level <NUM> may have a solder finish and be placed independently of leadframe <NUM>; e.g., utilizing a pick-and-place tool or fixture, such as a template having openings for receiving and positioning terminal extensions <NUM> and, perhaps, heat spreader extension <NUM>. Further, in embodiments in which bond layer precursor material <NUM>' is composed of a metal particle-containing precursor material, as described below, a common process may be utilized to reflow the solder finishes of extensions <NUM>, while also performing low temperature sintering of precursor material <NUM>'. In yet further embodiments, substrate-embedded heat spreaders <NUM> and substrate-embedded terminals <NUM> may likewise be provided as discretely placed pieces or parts, rather than provided as part of a larger leadframe.

After positioning of extension level leadframe <NUM> against bond layer precursor material <NUM>', precursor material <NUM>' may be subject to curing, as needed. As appearing herein, sintering processes are considered a type of "curing," as are other techniques (including solder reflow) involving the application of heat, pressure, and/or particular wavelengths of light utilized to process a material into its final form or composition. Thus, in embodiments in which bond layer precursor material <NUM>' is a metal particle-containing paste, a low temperature sintering process may be performed to transform precursor material <NUM>' into sintered bond layer <NUM>. An example of such a low temperature sintering process will be described below, and further discussions of such sintering processes can be found in the following documents, <CIT>.

As noted above, bond layer precursor material <NUM>' may be a sinter precursor material in embodiments. In such embodiments, the sinter precursor material can be applied in various different manners including both wet state and dry state application techniques. Suitable wet state application techniques include, but are not limited to, screen or stencil printing, doctor blading, spraying, dipping, and fine needle dispense techniques. When a wet state application technique is employed, a flowable or wet state coating precursor material is initially obtained by, for example, independent production or purchase from a third party supplier. In addition to metal particles (described below), the wet state coating precursor material contains other ingredients (e.g., a solvent and/or surfactant) to facilitate wet set application, to adjust the viscosity of the precursor material, to prevent premature agglomeration of the metal particles, or to serve other purposes. In one embodiment, the wet state coating precursor material contains metal particles in combination with a binder (e.g., an epoxy), a dispersant, and a thinner or liquid carrier. The volume of solvent or liquid carrier contained within the coating precursor material can be adjusted to tailor of the viscosity of the precursor material to the selected wet state application technique. For example, in embodiments wherein the precursor material is applied by screen printing or doctor blading, the coating precursor material may contain sufficient liquid to create a paste, slurry, or paint. After application of the wet state coating material, a drying process can be carried-out to remove excess liquid from the sinter precursor material, if so desired.

In further embodiments, the sinter precursor material can be applied utilizing a dry state application technique. For example, a film transfer process can be employed to apply the precursor material to the appropriate component surfaces. In this regard, a dry film may first be prepared by, for example, initially depositing (e.g., screen printing or otherwise dispensing) one or more sinter precursor material onto a temporary substrate or carrier, such as a plastic (e.g., polyethylene terephthalate) tape backing. The sinter precursor material may be applied to the carrier in a wet, flowable state and then heated or otherwise dried to yield a dry film, which is transferred to the appropriate package component surfaces. Heat, pressure, or both heat and pressure are then applied to adhere the metal particle-containing precursor layer (dry film) to the appropriate component surfaces. The carrier (e.g., tape backing) may then be removed by physical removal (e.g., peeling away) or by dissolution in a chemical solvent. This process may then be repeated to apply additional sinter precursor material to other component surfaces, as appropriate. In still further embodiments, one or more freestanding films may simply be positioned between the microelectronic module components during stacking or build-up (also considered "film transfer" in the context of this document).

The metal particles dispersed within the sinter precursor material can have any composition, shape, and size enabling the particles to form a substantially coherent adhesive layer pursuant to the below-described sintering process. In one embodiment, the sinter precursor material contains Au, Ag, or Cu particles, or a mixture thereof. In another embodiment, the metal particles contained within the precursor material consist essentially of Ag or Cu particles. The metal particles contained within the precursor material may or may not be coated with an organic material. For example, in some implementations, the metal particles may be coated with an organic dispersant, which prevents physical contact between the particles to inhibit premature agglomeration or particle sintering. When present, any such organic particle coating may be burned away or thermally decomposed, whether in whole or in part, during the below-described metal sintering process. In still further embodiments, other material systems amenable to low temperature sintering, whether currently known or later developed, may be utilized during the module fabrication process.

The metal particles contained within the precursor material can have any shape or combination of shapes including, but not limited to, spherical shapes, oblong shapes, and platelet or laminae shapes. The average dimensions of the metal particles will vary in conjunction with particle shape and process parameters. However, in general, the average maximum dimension of the metal particles (e.g., the diameter of the metal particles when spherical or the major axis of the metal particles when oblong) may be between about <NUM> and about <NUM> nanometers (nm) in an embodiment. In other embodiments, the metal particles may have average maximum dimension greater than or less than the aforementioned range. In certain implementations, a mixture of metal particles having average maximum dimensions in both the nanometer and micron range may be present within the precursor material. In other implementations, only nanoparticles (that is, particles having average maximum dimension between <NUM> and <NUM>) may be contained within the sinter precursor material. As a specific, albeit non-limiting example, the precursor material may contain at least one of Ag, Au, or Cu nanoparticles or micron-sized particles in an embodiment, with Ag or Cu nanoparticles preferred.

As noted above, a low temperature sintering process is performed to produce the desired metal sinter layers after application of the sinter precursor material. The low temperature sintering process can be carried-out under any process conditions suitable for transforming the sinter precursor material into metal sinter layers, noting that some diffusion may occur from the precursor material into contacting components of the microelectronic modules. The sinter bond process thus advantageously forms low stress, mechanically-robust, solid state metallurgical diffusion bonds at the bond joint interfaces. The sintering process may be performed with or without pressure, with or without heating (although some degree of elevated heat will typically be applied), and in any suitable atmosphere (e.g., open air or in the presence of an inert gas, such as nitrogen). As a point of emphasis, the sintering process is carried-out at maximum processing temperatures (TMAX) less than the melt point of the metal particles contained within the precursor material. Indeed, in many embodiments, TMAX will be significantly less than the melt point of the metal particles and, perhaps, less than one half the melt point of the particles considered on an absolute temperature scale (in Kelvin). Generally, TMAX will be greater than room temperature (considered <NUM> herein) and less than <NUM>. Comparatively, the melt point of Ag, Au, and Cu particles in a nanometer or micron size range will commonly range between approximately <NUM> to <NUM>. To provide a still further example, TMAX may be between approximately <NUM> and <NUM> in an embodiment. In still further embodiments, TMAX may be greater than or less than the aforementioned range, providing that TMAX (in conjunction with the other process parameters) is sufficient to induce sintering of the metal particles without liquefaction of the metal particles.

A multistage heating schedule can be employed during the sintering process. In this case, the multistage heating schedule may entail heating microelectronic modules <NUM>, in a partially fabricated state, to a first temperature (T<NUM>) less than TMAX for a first time period, gradually increasing or ramping-up the temperature process to TMAX, and then maintaining TMAX for a second time period. A cool down period may follow. In one embodiment, and by way of non-limiting example only, T<NUM> may range from approximately <NUM> to <NUM>, while TMAX is greater than T<NUM> and ranges from approximately <NUM> to <NUM>. As discussed below, the process parameters employed may or may not be controlled to fully decompose any organic material from the sinter precursor material during the sintering process.

In at least some implementations of the microelectronic module fabrication method, a controlled convergent pressure or compressive force is applied across the partially-fabricated microelectronic modules during the sintering process. When applied, the convergent pressure can be delivered as a substantially constant force or, instead, varied in accordance with a time-based or temperature-based schedule. Any suitable mechanism can be utilized to apply the desired convergent pressure including bulk weights, resilient bias devices (e.g., spring-loaded plungers or pins), clamps, hydraulic presses, and the like. The pressure applied may be selected based upon various factors including the desired final thickness of the metal sinter layers, the desired porosity of the metal sinter layers, and the composition of the sinter precursor material. In one embodiment, and by way of non-limiting example only, a maximum pressure (PMAX) ranging between about <NUM> and about <NUM> megapascal (Mpa) is applied during the sintering process. In other embodiments, PMAX may be greater than or less than the aforementioned range, if pressure is applied during the sintering process.

After bonding thermal extension levels <NUM> to module substrates <NUM>, singulation is performed to separate microelectronic modules <NUM>' into individual units. As indicated above, singulation may be carried-out by directing a suitable cutting tool (e.g., a dicing saw) along saw lanes <NUM> (<FIG> and <FIG>) to separate multi-substrate panel <NUM> into individual substrates <NUM> and to sever the connections between heat spreader extensions <NUM>, terminal extensions <NUM>, and tie bars <NUM>. This, in turn, results in the electrical isolation of heat spreader extensions <NUM> and terminal extensions <NUM>, which include spars extending to an outer periphery of each module <NUM>. Attachment and interconnection of microelectronic devices <NUM>, <NUM> (<FIG>) is advantageously performed prior to panel singulation, although this is not necessary in all embodiments. The end result is a plurality of completed microelectronic modules <NUM> similar or substantially identical to that shown in <FIG>, as previously described.

<FIG> is a cross-sectional view of a high thermal performance microelectronic module <NUM>, not forming part of the present invention but useful for understanding it. In many respects, microelectronic module <NUM> is similar to module <NUM> described above in conjunction with <FIG>. For example, as does microelectronic module <NUM>, high thermal performance microelectronic module <NUM> includes a module substrate <NUM> to which any number and type of microelectronic devices may be mounted and electrically interconnected with the routing features of module substrate <NUM>. In this regard, a microelectronic device <NUM>, such as a semiconductor die, may be attached to substrate <NUM> and electrically interconnected utilizing wirebonds <NUM>. Microelectronic module <NUM> may also contain any practical number and type of additional microelectronic devices, which are hidden from view in the cross-section of <FIG>. An enclosure <NUM> (e.g., an overmolded body or lidded container defining an air cavity) may further be provided to house microelectronic device <NUM> and any other devices contained in microelectronic module <NUM> in at least some implementations.

Module substrate <NUM> assumes the form of a PCB including a number of metal levels or wiring layers <NUM> contained in a dielectric body <NUM>. A substrate-embedded heat spreader <NUM> is again provided in a central portion of dielectric body <NUM>, as are a plurality of substrate-embedded terminals <NUM> spaced around a lower periphery of a heat spreader <NUM>. As was previously the case, a thermal extension level <NUM> is positioned adjacent and bonded to backside <NUM> of module substrate <NUM>. Specifically, thermal extension level <NUM> includes a heat spreader extension <NUM> bonded to the lower principal surface of substrate-embedded heat spreader <NUM>, which is substantially coplanar with backside <NUM> of module substrate <NUM>. Additionally, thermal extension level <NUM> includes terminal extensions <NUM>, which are bonded to the lower surfaces of substrate-embedded terminals <NUM>. Once again, extensions <NUM>, <NUM> have substantially equivalent thickness and extend from points adjacent substrate backside <NUM> to terminate at a module mount plane <NUM>.

In contrast to thermal extension level <NUM> of microelectronic module <NUM> (<FIG>), the structures of thermal extension level <NUM> are produced via deposition of a thermally-conductive material over the surfaces of substrate-embedded heat spreader <NUM> and substrate-embedded terminals <NUM> exposed at backside <NUM> of module substrate <NUM>. In one embodiment, an alloy consisting essentially of Cu, or containing Cu as a primary constituent, is plated over the exposed surfaces of heat spreader <NUM> and terminals <NUM>. The particular thickness to which extensions <NUM>, <NUM> are plated or are otherwise deposited will vary in embodiments, but may be range between <NUM> and <NUM> mils in one non-limiting example. Plated thermal extension level <NUM> may consequently increase the heat rejection capabilities of microelectronic module <NUM> in a manner analogous to that described above in conjunction with <FIG>. Furthermore, the aforementioned approaches can also be combined to yield still further embodiments of the high thermal performance microelectronic module. For example, in yet other embodiments, thermal extension level <NUM> may be produced by initially attaching prefabricated structures in the form of a heat spreader extension and/or terminal extensions to module substrate <NUM> and, afterwards, one or more plating layers may be formed thereover, if so desired. Conversely, thermal extension level <NUM> may be formed by first electrodepositing a patterned plating level, as shown in <FIG>, and then subsequently attaching one or more prefabricated structures to the newly-deposited plating layer utilizing a thermally-conductive bond layer in the manner previously described.

The foregoing has thus provided high thermal performance microelectronic modules including thermal extension levels, as well as methods for manufacturing high thermal performance microelectronic modules. As described above, the microelectronic modules contain unique structures or features enhancing thermal dissipation of excess heat generated by microelectronic devices, such as semiconductor (e.g., RF) die and other circuitry, contained within a given module. Such structures will generally include at least one heat spreader extension, which is contained in a thermal extension level located adjacent the backside of a module substrate and directly or indirectly bonded thereto. The provision of the heat spreader extension consequently increases the overall thermal dissipation capabilities of the microelectronic module. Further, the heat spreader extension and, more generally, the thermal extension level may be unencapsulated and thus directly exposed to the ambient environment to further promote convective transfer of excess heat from the module to the surrounding environment. This, in turn, allows, significant improvements in the overall thermal performance of the microelectronic module, with only modest increases in fabrication costs and module thicknesses.

Computer simulations were performed demonstrating improvements in thermal performance potentially achieved by embodiments of the high thermal performance microelectronic modules. The results of one such computer simulation are graphically set-forth in <FIG>, not forming part of the present invention but useful for understanding it. System thermal resistance is plotted along the abscissa (vertical axis) and presented as a percentage of reduction in the system-wide thermal resistance (measured in degrees Celsius over watts) as compared to a baseline heat flow metric through a conventional substrate containing bar vias (represented by trace <NUM>). PCB thickness is further plotted in <FIG> along the ordinate (horizonal axis) and ranges <NUM> to <NUM> mills in this example. As a first point of comparison, system thermal resistivity lowered by approximately <NUM>% to approximately <NUM>% were achieved for a heat spreader extension composed of Cu, having a thickness of <NUM> mil thickness, and attached to a substrate-embedded heat spreader by an Ag sinter layer (represented by trace <NUM>). Comparatively, as second, third, and fourth points, the exemplary simulations demonstrated reductions in system thermal resistance ranging from about <NUM>% to about <NUM>% were seen for the same heat spreader extension configuration, but having <NUM>, <NUM>, and <NUM> mil thickness, respectively. Thus, as can be seen, increases in heat spreader extension thickness exceeding about <NUM> mils provides relatively little reduction in system thermal resistivity. Accordingly, in an embodiment, the heat spreader extension and, more generally, the thermal extension level may be imparted with a thickness ranging from <NUM> to <NUM> mil inclusive and, more preferably, a thickness ranging from <NUM> mil to <NUM> mil inclusive. In other embodiments, the heat spreader extension and the thermal extension level may be thicker or thinner than the aforementioned ranges.

As noted above, the various structures contained in the thermal extension level can be provided as discrete, prefabricated components or may instead be deposited utilizing, for example, a plating process. When assuming the form of prefabricated components, the structures of the thermal extension level are conveniently, although not necessarily initially provided in leadframe form. It is also possible for the heat spreader extension to be provided in leadframe form, while the terminal extensions (if included in the thermal extension level) are provided as discrete pieces or structures. In this latter regard, the terminal extensions can be provided as discretely-placed pieces having any desired shape (e.g., rods, cubes or spheres) and that bonded to exposed surfaces of the substrate-embedded terminals utilizing a suitable electrically-conductive bonding material. For example, when the terminal extensions (and possibly the heat spreader extension) are provided as discrete structures, the terminal extensions may have a solderable surface (and, perhaps, solder plating), which is joined to the exposed surfaces of the substrate-embedded terminals by soldering. Placement of the terminal extensions can be streamlined utilizing a template having openings corresponding to the desired spatial arrangement of the terminal extensions, although individual placement of extensions can also be performed (e.g., utilizing a pick-and-place tool) if desired. In one approach (which is generically illustrated in <FIG>), terminal extensions <NUM> may be joined to substrate-embedded terminals or contact pads <NUM> by a layer portion <NUM> composed of solder, while heat spreader extension <NUM> is joined to substrate-embedded heat spreader <NUM> by layer portion <NUM> composed of a sintered (e.g., Ag) material. Such an approach provides temperature capability advantages (generally avoiding solder fatigue issues, which can limit maximum solder temperature) and improved thermal conductivity.

While at least one exemplary embodiment has been presented in the foregoing Detailed Description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing Detailed Description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.

Claim 1:
A microelectronic module (<NUM>), comprising:
a module substrate (<NUM>) having a substrate frontside (<NUM>) and a substrate backside (<NUM>);
a microelectronic device (<NUM>) mounted to the substrate frontside;
a substrate-embedded heat spreader (<NUM>) thermally coupled to the microelectronic device (<NUM>), at least partially contained within the module substrate, and having a lower surface parallel with the substrate backside; and
a thermal extension level (<NUM>) adjacent the substrate backside and extending away therefrom to terminate at a module mount plane (<NUM>), the thermal extension level (<NUM>) comprising a heat spreader extension (<NUM>) bonded to and in thermal communication with the substrate-embedded heat spreader (<NUM>); and
substrate-embedded terminals (<NUM>) contained in the module substrate (<NUM>) and having lower surfaces parallel with the substrate backside;
wherein the thermal extension level further comprises terminal extensions (<NUM>) comprising spars extending to an outer periphery of the module and bonded to the substrate-embedded terminals (<NUM>), the microelectronic device (<NUM>) electrically coupled to the terminal extensions (<NUM>) through the substrate-embedded terminals (<NUM>);
wherein the heat spreader extension (<NUM>) and at least one of the terminal extensions (<NUM>) comprise singulated portions of a leadframe (<NUM>), wherein the heat spreader extension (<NUM>) comprises a main body (<NUM>) underlying the substrate-embedded heat spreader, as taken along a first axis orthogonal to the substrate backside; and at least one wing (<NUM>) extending laterally from the main body (<NUM>) to cover at least one of the substrate-embedded terminals, as taken along a second axis orthogonal to the substrate backside; and the microelectronic module (<NUM>) further comprises a thermally-conductive bond layer (<NUM>) bonding the heat spreader extension (<NUM>) to the substrate-embedded heat spreader.