Patent Description:
This application relates to the field of electronics, and particularly thermal management and cooling of chip assemblies utilizing heat distribution devices, such as cold plates. Such heat distribution devices can be utilized within a microelectronic assembly to aid in the reduction of heat generated by microelectronic elements with the assembly, as well as heat generated by components external to the assembly.

In addition to industry standard chip packages, the exploration of special purpose silicon is expected to result in high power heat sources in servers. This technology may also be applied to graphics processing units ("GPUs") and custom application-specific integrated circuits ("ASICs"). Further, services such as imaging and artificial intelligence ("AI") will likely require large computer resources at a high density, with many servers in close proximity to one another. Data centers around the globe are being mandated to simultaneously increase energy efficiency, consolidate operations and reduce costs. These trends indicate that high performance cooling technologies that scale well with cooling cost and energy are needed, while enabling cooling for high density electronics.

Heat distribution devices are commonly used to cool and regulate the temperature of microelectronic elements, in a microelectronic assembly. Such heat distribution devices can include heat sinks, water blocks, cold plates, and the combination of one or more of these and other devices.

The coefficient of thermal expansion ("CTE") mismatch between the heat distribution device and other components in the chip assembly can stress the assembly when any one of these components expands at a different rate than other components due to temperature changes that occur during manufacture or use of the chip assembly. In typical assemblies, a one piece heat distribution device comprised of a single thermally conductive material can overlie the rear surface of the chip and also extend toward and be attached to the substrate. Due to the CTE mismatches between the substrate, the heat distribution device, and chip, cycling of the chip assembly through one or more reflow processes and operation of the chip assembly can further cause warpage of the substrate and/or chip, as well as other mechanical failure within the assembly.

<CIT> discloses an integrated circuit package with enhanced thermal conduction.

<CIT> describes an integrated heat spreader with configurable heat fins.

<CIT> recites a semiconductor microcooler.

<CIT> discloses a cooling structure for electronic boards.

The present application provides for a method of manufacturing a chip assembly according to claim <NUM>.

Aspects of the disclosure disclose chip assemblies that incorporate heat distribution devices, such as cold plates, that are bonded to chips using high thermally conductive materials and optimized methods of manufacture. Additionally, structures and methods disclosed herein allow for greater control of bond line thickness, which is essential for controlling heat generated by high power devices.

Heat generated by individual chips can further result in hot spots created at central portions of a chip, which can be difficult to access, especially when multiple chips are provided in an array. Aspects of the disclosure address the increased heat by the thinning of one or more portions of a chip and/or modifying the structure of the heat distribution device to accommodate the change in size of the chip. In one example, the bottom surface of the heat distribution device is adapted to accommodate the differing thicknesses of one or more chips that may have been thinned. The heat distribution device may include one or more protrusions extending from its bottom surface that can overlie and be in closer proximity to a chip that may be thinner than adjacent chips. This can improve the effectiveness of the heat distribution device. In another example, the die or chip can be thinned by providing a plurality of cavities in the rear surface of the die or chip. The cavities can be filled with high thermally conductive ("K") material for enhanced heat distribution. In another example, the plurality of cavities remain open and can be occupied by extended heat fins from a cold plate.

The material or combination of materials selected to manufacture the cold plate can further enhance the thermal conductivity and performance of a heat distribution device within a chip assembly. According to another aspect of the disclosure, an ultra-high thermally conductive material can be selected to form one or more portions of the heat distribution device. For example, the base or the fins of a heat distribution device may be formed from an ultra-high thermally conductive material, such as silver diamond.

A stiffener and a heat distribution device that extend across rear surfaces of the microelectronic element may be used in the chip assembly to enhance thermal conductivity and warpage control. This configuration can replace a one-piece and u-shaped heat distribution device that both extends around and along the rear surface of the chip assembly, that is directly attached to the substrate, and that is made from a single material, such as only copper. This configuration can similarly be used in place of a two-piece structures formed from the same material. Further, use of a select combination of materials for the heat distribution device and stiffener, alone or in combination with selected adhesives, can further optimize the thermal conductivity and warpage control within the chip assembly. For example, the adhesive used to join stiffener with substrate may have a modulus of elasticity that differs from the modulus of elasticity of a second adhesive used to join the stiffener with the heat distribution device. In one example, selection of silver-diamond (e.g., AgD) as a high thermally conductive material for the heat distribution device, and copper (e.g., Cu, Cu-OFE, CuOHF) for the stiffener can achieve enhanced thermal conductivity and warpage control. Better bond-line thickness control of the thermal interface materials can also be achieved using such combination. Additionally, use of copper to form the stiffener saves on the cost of forming a monolithic heat distribution device formed entirely of high-cost silver diamond material or other ultra-high conductive material.

It is to be appreciated that examples of microelectronic elements can include microelectronic chips, semiconductor chips, non-semiconductor chips, MEMs, ASICs, and the like. Further the discussion of the heat distribution devices herein will often be made in reference to a "chip(s)," but it is to be appreciated that the heat distribution devices disclosed herein are not limited to use with a chip, or any particular type of chip, and can encompass any microelectronic element or device that can benefit from a heat distribution device.

<FIG> illustrates a schematic cross-sectional view of a microelectronic element assembly <NUM> according to aspects of the disclosure. In this example, assembly <NUM> is supported by a printed circuit board <NUM>, as well as a substrate <NUM> that overlies printed circuit board <NUM>. The active front surfaces 142A, 142B, 142C of respective chips 140A, 140B, 140C may face toward and be joined in a ball grid array to substrate <NUM>. Metallization (not shown) can also be provided on rear surfaces 144A, 144B, 144C of chips 140A, 140B, 140C. Chips 140A, 140B, 140C may be electrically interconnected with substrate <NUM> through an interposer <NUM>, but as will be shown in other examples herein, an interposer is not required. Bonding material, such as solder balls 127B, may be used to electrically interconnect chips 140A, 140B, 140C with interposer <NUM>, and bonding material, such as solder balls 127A, may be used to electrically interconnect and join interposer <NUM> with substrate <NUM>. A cold plate <NUM> overlies rear surfaces 144A, 144B, 144C of respective chips 140A, 140B, 140C, and a stiffener <NUM> extends between bottom surface <NUM> of base <NUM> of cold plate <NUM> and top surface <NUM> of substrate <NUM>. Bottom surface <NUM> of substrate <NUM> may be joined to another device, such as a printed circuit board <NUM>, through another set of solder balls 127C.

Cold plate <NUM> may include two components: a cold plate base <NUM> and a cold plate lid <NUM> that are joined together. With reference to <FIG> and <FIG>, an example base <NUM> and lid <NUM> are shown. Base <NUM> may include a bottom surface <NUM> and an opposed top surface <NUM>. Similarly, lid <NUM> may include a bottom surface <NUM>, and an opposed top surface <NUM> from which an inlet 176A and two outlets 176B may extend. In other examples, the configuration of inlets and outlets can vary, such as there being two outlets directly adjacent to one another, or two inlets and one outlet, or any desired configuration of inlets and outlets. Base <NUM> and lid <NUM> may be manufactured using molding, machining, and similar processes.

Base <NUM> may include a plurality of thermally conductive fins <NUM>, which help to facilitate cooling of assembly <NUM>, as well as a recess 168A extending around fins <NUM>. Fins may be longitudinal structures extending away from a surface of the base, such as those known in the art. The fins may be integrally formed with the base or may be attached to the base by soldering, adhesive or the like. In this example, fins <NUM> are integrally formed with the base.

Lid <NUM> overlies base <NUM>, such that bottom surface <NUM> of lid <NUM> is directly adjacent top surface <NUM> of base <NUM>. Although not required and as shown in <FIG>, O-rings <NUM> may be provided within recess 168A so as to form a seal between base <NUM> and lid <NUM>. When joined together, base <NUM> and lid <NUM> enable fluids and gases to pass into cold plate <NUM> through inlet 176A, and out of cold plate <NUM> through outlets 176B. Additional O-rings <NUM> (<FIG>) may also be provided adjacent inlets 176A and outlets 176B to provide a seal between inlet 176A and outlets 176B and the components which may be connected to them.

Base <NUM> and lid <NUM> may be formed from known heat dissipating materials, such as aluminum, copper, silver, and metal alloys. In this example, base <NUM> and lid <NUM> are formed from the same material, but in other examples, and as will be discussed in more detail below, the material comprising the base and the lid may differ.

With reference to <FIG> and <FIG>, a stiffener ring, such as stiffener <NUM> may extend circumferentially around chips 140A, 140B, and 140C. Stiffener <NUM> includes a bottom surface <NUM>, an opposed top surface <NUM>, and an aperture <NUM> extending through the top and bottom surfaces <NUM>,<NUM>. The bottom surface <NUM> of stiffener <NUM> can be attached to the top surface <NUM> of substrate <NUM>, and the top surface <NUM> of stiffener <NUM> can be attached to the bottom surface <NUM> of cold plate base <NUM> with a bonding material (not shown), such as an adhesive. Aperture <NUM> may be generally central with respect to an outer perimeter of stiffener <NUM>, though in other examples the position of aperture <NUM> may be adjusted. For example, the size and shape and position of aperture <NUM> may be adapted based on circuitry of the underlying substrate <NUM> to be exposed through aperture <NUM> or the arrangement of chips 140A, 140B, 140C and interposer <NUM> within aperture <NUM>.

Stiffener <NUM> can be comprised of various materials. In one example, stiffener is formed from copper and is later plated with electroless nickel (or similar metal to promote adhesion) to substrate <NUM>.

The stiffener can be further modified to provide ridges <NUM>-<NUM> extending along at least one edge of stiffener <NUM>-<NUM>. For example, <FIG> illustrate ridges <NUM>-<NUM> extending around all four edges of stiffener <NUM>-<NUM>, as well as partially between top surface <NUM>-<NUM> and opposed bottom surface <NUM>-<NUM>. The ridges <NUM>-<NUM> allow for gas egress during the reflow process. The stiffener <NUM>-<NUM> can instead include apertures that extend fully through the thickness of the stiffener along at least one edge of the stiffer. For example, <FIG> illustrates apertures <NUM>-<NUM> extending around all four edges of stiffener <NUM>-<NUM>, and between the top and bottom surfaces <NUM>-<NUM>, <NUM>-<NUM>, although any number of apertures can extend around one or more edges.

With reference back to <FIG>, a thermal interface material ("TIM") with high thermal conductivity ("k") may be used to join or couple cold plate <NUM> directly to chips 140A, 140B, and 140C. In this example, bottom surface <NUM> of base <NUM> of cold plate <NUM> is directly joined to rear surfaces 144A, 144B, 144C of respective chips 140A, 140B, 140C through use of TIM <NUM>. TIM <NUM> may be a high k TIM, which can also be a low melting temperature metal, including metal or graphite, such as Nano Ag or Indium, but other high k TIM materials may be implemented. Thus, direct soldering is one example for directly joining cold plate <NUM> to chips 140A, 140B, 140C. Additionally, in some implementations, it may be desired to use an ultra-high K material for TIM, as will be discussed herein. However, the methods and structures disclosed herein can also be utilized with a low k TIM, with reduced levels of thermal conductivity.

TIM may be provided in any desired form, such as liquid, solid, semi-solid, and the like. For example, a TIM can be applied in liquid form, which will later cure and remain as a soft elastomer. In other examples, TIM can be a grease, film, or solder.

Interposer <NUM> may be a conventional interposer configured to provide an electrical interface routing between bond pads <NUM> of chips 140A-140C and contacts <NUM> disposed at the surface of the substrate <NUM> to which chips 140A-140C are attached. It is to be appreciated that throughout the disclosure, contacts at the surface, disposed at the surface, or exposed at the surface of the substrate is understood to mean having a surface exposed for an electrical interconnection. The contact itself may be partially above or below the surface of the substrate, may be fully disposed at the top surface of the substrate, or any configuration of contacts that allows for an electrical interconnection. Interposer <NUM> may include contacts <NUM> at its top surface <NUM>, contacts <NUM> at its bottom surface <NUM>, and conductive vias (not shown) extending between the top and bottom surfaces. Bond pads <NUM> of the chips 140A-<NUM> C may be directly joined and soldered to contacts at the interposer in a ball grid array pattern. Bond pads of chips 140A-140C will be conductively connected to contacts on substrate <NUM> through the conductive vias.

Interposer may be bonded to a printed circuit board <NUM> using an array of solder balls 127C. Solder balls may be first applied to either interposer <NUM> or contacts of printed circuit board <NUM>. The printed circuit board may be any known circuit board adapted for use alone or in connection with another device. In some examples, the printed circuit board may be a server tray.

<FIG> is another example assembly <NUM> which is identical to <FIG>, except that it further includes springs <NUM> overlying stiffener <NUM>. As shown, assembly <NUM> includes a substrate <NUM> and chips 240A, 240B, and 240C electrically connected with the substrate <NUM> through interposer <NUM>, all of which are attached to a printed circuit board <NUM>. A cold plate <NUM> is provided within the assembly to distribute heat generated by chips 240A, 240B, 240C. Cold plate <NUM> further includes a base <NUM> and a lid <NUM>. Base <NUM> may include a recess <NUM> and fins <NUM> provided within recess <NUM>. Base <NUM> may directly overlie and be attached to rear surfaces 244A, 244B, 244C of chips 240A, 240B, 240C through a TIM <NUM>, such as high K TIMs and other TIMs previously discussed herein. Base <NUM> may also directly overlie stiffener <NUM> and springs <NUM>.

Springs <NUM> may be positioned between bottom surface <NUM> of base <NUM> and top surface <NUM> of stiffener <NUM>. As shown in <FIG>, posts <NUM> may be positioned at corners of stiffener <NUM> and extend away from top surface <NUM> of stiffener <NUM>. Springs <NUM> may be wrapped around posts <NUM>. Springs <NUM> can provide additional compression force to the substrate to minimize warpage of the assembly, as well as to enable greater control over bond line thickness of TIM <NUM>.

<FIG> provides another example assembly <NUM> according to aspects of the disclosure. Assembly <NUM> is similar to the prior examples to the extent that the assembly generally includes a substrate <NUM>, a stiffener <NUM>, an interposer <NUM>, and a cold plate <NUM>, all of which can overlie and be electrically interconnected printed circuit board <NUM>. The cold plate further includes a base <NUM> with fins <NUM>; and a lid <NUM> that includes at least one inlet. In this example, a single inlet 376A and two outlets 376B are provided. Additionally a thermal TIM <NUM>, including high K TIM previously discussed herein, can be used to join cold plate base <NUM> to chips 340A, 340B, 340C. Assembly <NUM> differs from the prior examples due to the arrangement of cold plate <NUM>. As shown, cold plate <NUM> only overlies chips 340A, 340B, 340C and does not overlie stiffener <NUM>. Top surface <NUM> of stiffener <NUM> instead remains exposed, since it no longer supports cold plate <NUM>. In this arrangement, the weight of stiffener <NUM> alone becomes one of the primary forces maintaining warpage control over substrate <NUM> and printed circuit board <NUM> of assembly <NUM>.

<FIG> illustrate another example assembly <NUM>. <FIG> illustrates a perspective view of assembly <NUM> and <FIG> illustrates a cross-sectional view. This assembly <NUM> is similar to the previously disclosed assemblies, except that the microelectronic element is directly attached to the substrate without an interposer and a bolster plate <NUM> underlies a printed circuit board <NUM>. As seen in <FIG>, an exploded perspective view of a subassembly <NUM>-A of assembly <NUM> without the printed circuit board and bolster plate <NUM> is illustrated. Subassembly <NUM>-A (also shown in <FIG>) can include a plurality of chips, a stiffener <NUM>, a TIM <NUM>, a cold plate <NUM> (which in this example includes a base <NUM> with fins <NUM> and a lid <NUM>), and an O-ring <NUM>, such as the examples previously disclosed herein, although numerous variations of the examples provided herein may be utilized. TIM can include at least a high K TIM or an ultra-high K TIM, as previously discussed herein. In this example, four chips are provided in a face-down position, but any number of chips may be implemented. As shown in <FIG>, cold plate base <NUM> and cold plate lid <NUM> are joined together by screws <NUM>. Bottom surface <NUM> of base <NUM> is joined to rear surfaces 444A-E of respective chips 440A-440E with a TIM <NUM>, such as disclosed herein. Chips 440A-440E are joined directly to substrate <NUM>. Although not shown, bond pads on chips 440A-440E may be joined to contacts on substrate <NUM> through solder connections, such as a ball grid array. Stiffener <NUM> overlies substrate <NUM>. Chips 440A-440E and a portion of bottom surface <NUM> of base <NUM> are positioned within aperture <NUM> of stiffener <NUM>. In this example, base <NUM> overlies stiffener <NUM>, but is not directly attached to stiffener <NUM>. A gap G (<FIG>) exists between bottom surface <NUM> of base <NUM> and top surface <NUM> of stiffener <NUM>, such that cold plate <NUM> does not apply a direct compression force onto stiffener <NUM>.

<FIG> illustrate another example arrangement for stiffener <NUM>, substrate <NUM>, and chips 440A-440E within aperture <NUM> of stiffener <NUM>, which can be implemented into any one of the aforementioned assemblies. As shown, a shim <NUM> may be provided within aperture <NUM> of stiffener <NUM>. Shim <NUM> can extend around the outermost edge surfaces of chips 440A-440E. As shown in <FIG>, the enlarged perspective view, stiffener ring <NUM> can be attached to substrate <NUM>. As shown, chips 440A-440E are directly attached to substrate <NUM>.

<FIG> illustrates another example assembly <NUM>'. This assembly is otherwise identical to assembly <NUM>, except that the cold plate base and stiffener are formed as a single monolithic cold plate base and stiffener unit. Referring first to <FIG>, an example monolithic cold plate and stiffener unit <NUM> is shown. Monolithic cold plate and stiffener unit <NUM> includes a main body <NUM>' with fins <NUM>' and rigid stiffener legs <NUM>'. A recess <NUM>' is provided between stiffener legs <NUM>'. With reference back to <FIG>, chips 440A', 440B', 440C', can be coupled or attached to interposer <NUM>', such as, for example, a silicon interposer, and substrate <NUM>', all of which can be coupled or attached to a printed circuit board <NUM>'. Monolithic cold plate and stiffener unit <NUM> can then be attached to top surface <NUM>' of substrate <NUM>'. For example, a TIM <NUM>' can be used to attach monolithic unit <NUM>' to rear surfaces 444A', 444B', and 444C' of chips 440A', 440B', 440C'. The TIM can be any TIM, including a high-K TIM or an ultra-high K TIM. Additionally, an adhesive or the like can be used to attach bottom surface <NUM>' of stiffener legs <NUM>' to top surface <NUM>' of substrate <NUM>'. Chips 440A', 440B', 440C', interposer <NUM>' will be positioned within recess <NUM>'. Once monolithic cold plate and stiffener unit <NUM> is in place, cold plate lid <NUM>' may then be attached to and overlie monolithic cold plate and stiffener unit <NUM>. In other examples, cold plate lid <NUM>' can be pre-attached to monolithic cold plate and stiffener unit <NUM>, and then the two components may be attached to the rest of the assembly. Similarly, lid <NUM> can be integrally formed along with the stiffener and cold plate lid to form a monolithic unit comprised of a combination of the lid, stiffener, and cold plate.

Such configuration can provide added warpage benefits due to the additional structural rigidity of stiffener <NUM>' created by the addition of base <NUM>'. This allows for cold plate assembly to be completed at a package level, such that few or no additional thermal process steps are required at the printed circuit board level.

Various methods aimed at achieving high thermal conductivity and heat distribution within a package, including controlling bond line thickness and the number of times reflow occurs, can be implemented when manufacturing any one of the aforementioned example assemblies, as well as variations thereof.

<FIG> illustrate one example method for manufacturing the assembly <NUM> shown in <FIG>. As shown in <FIG>, an interposer <NUM> may be joined with substrate <NUM>. Interposer <NUM> can include contacts <NUM> at its bottom surface <NUM> that can be aligned with contacts <NUM> exposed at top surface <NUM> of substrate <NUM>. Solder balls 527A may be provided on either substrate <NUM> or interposer <NUM>. As shown in <FIG>, microelectronic elements, such as chips 540A, 540B, 540C may be joined to interposer <NUM> using solder balls 527B. Chips 540A, 540B, 540C include bond pads <NUM> that can be aligned with contacts <NUM> at top surface <NUM> of interposer <NUM>. Solder balls 527B can be pre-attached to either bond pads <NUM> of chips 540A, 540B, 540C or contacts <NUM> of interposer <NUM>. The package can then be reflowed to secure the bond connections between chips 540A, 540B, 540C and interposer <NUM>, as well as interposer <NUM> and substrate <NUM>. Alternatively, a first reflow process can occur to reflow solder balls 527A and join interposer <NUM> and substrate <NUM>. A second reflow process may then occur to reflow solder balls 527B to bond chips 540A, 540B, 540C, <NUM> with interposer <NUM>.

In <FIG>, a stiffener <NUM> may be attached to top surface <NUM> of substrate <NUM>. An adhesive (not shown) can be used to join stiffener <NUM> to substrate <NUM>. Stiffener <NUM> can extend circumferentially around chips 540A, 540B, 540C and interposer <NUM>. The combination of stiffener <NUM>, substrate <NUM>, and interposer <NUM> can be sputter coated with a combination of metals, such as titanium, NiV, and gold. In one example, three materials with the following thicknesses can be applied as follows: 1000A Ti, 3500A NiV, and 1000A Au. In other examples, one or more of these same or different materials may be applied with the same or different thicknesses. This can help to promote the chemical bond between the package and the TIM material. In other examples, stiffener <NUM> can be omitted.

The resulting subassembly shown in <FIG> is an in-process unit <NUM>-<NUM> that can be manufactured by, for example, an outsourced semiconductor assembly and test (OSAT) market company. This arrangement of first assembling in-process unit <NUM>-<NUM> can allow for an OSAT manufacturer or the like to manufacture and supply a bare die package to a contract manufacturer or the like, who can incorporate in-process unit <NUM>-<NUM> into a specific device or application.

Turning now to <FIG>, in-process unit <NUM>-<NUM> can be attached to a printed circuit board <NUM> or the like. As shown, contacts <NUM> at bottom surface <NUM> of substrate <NUM> can be aligned with contacts <NUM> exposed at the top surface <NUM> of printed circuit board <NUM>. Solder balls 527C in a grid array can be used to attach substrate <NUM> to printed circuit board <NUM>. The package can be reflowed at this stage to create a bonded connection. Solder balls 527C may be comprised of a high melting point solder. In one example, the solder may have a reflow temperature of <NUM>° C, but in other examples the temperature may be higher or lower. Additionally, different types of solder or different bonding materials may be utilized.

As shown in <FIG>, a TIM <NUM>, may be applied to rear surfaces of chips 540A-540B, 540C. TIM can be any high k TIM material disclosed herein, or alternatively any known TIM. TIM may be applied using various methods. In the example where TIM is a paste, TIM may be directly applied to rear surfaces 544A, 544B, 544C of chips, which will later cure and harden. In another example, TIM can be pre-reattached to a cold plate, such as cold plate base <NUM>, either by reflowing TIM <NUM> (before secondary reflow to chip). TIM <NUM> can alternatively be attached to cold plate <NUM> through an adhesive or similar material that can secure TIM <NUM> in place prior to reflow.

With reference to <FIG>, base <NUM> of cold plate <NUM> may be attached to rear surfaces 544A, 544B, 544C of chips 540A, 540B, 540C, as well as top surface <NUM> of stiffener <NUM>. A TIM <NUM>, such as a high-K or ultra-high-K TIM may be positioned between cold plate base <NUM> and rear surfaces 544A, 544B, 544C. TIM <NUM> can help to dissipate heat generated by chips 540A, 540B, and 540C. Once base <NUM> is positioned over rear surfaces and stiffener, the TIM may be reflowed to ensure a connection between cold plate and chips 540A, 540B, 540C. In some examples, a TIM may be selected that has a reflow temperature that is lower than a reflow temperature of the bonding material used to join the in-process unit to the printed circuit board. This can also be beneficial since the bonding material, for example solder balls 527C, between the printed circuit board <NUM> and the substrate <NUM> is not reflowed when the TIM is reflowed.

As shown in <FIG>, an O-ring <NUM> can optionally be provided within a recess (not shown) of cold plate base <NUM> of cold plate <NUM>, so as to accommodate lid <NUM>. <FIG> illustrates the final assembly <NUM>. Lid <NUM>, including inlet 576A and outlets 576B, may be attached to base <NUM> using various forms of attachment. In one example, lid <NUM> may be screwed together with base <NUM>, but any known means of attachments may be utilized. In another example, lid <NUM> and base <NUM> can first be joined together, and then attached to the in-process unit <NUM>-<NUM> as a completed cold plate assembly.

<FIG> illustrates the addition of piping <NUM> that can allow for cooling of the chip assembly. In this regard, the piping may route cooling fluid only to a single chip assembly <NUM>, or may be joined to one or more other chip assemblies (as will be discussed in later example embodiments shown in <FIG>). As shown, piping <NUM> can be directly connected to inlet 576A. Additionally, piping <NUM> is connected to outlets 576B. During operation, this allows for the flow of water or other liquids through piping <NUM> into inlet 576A and cold plate <NUM>, and then out of outlets 576B on opposed sides of inlet 576A.

It is to be noted that first preparing the in-process unit <NUM>-<NUM>, as discussed above, and then subsequently attaching the cold plate base with a TIM having a lower reflow temperature than the reflow temperature of the bonding material bonding the in-process unit <NUM>-<NUM> to the printed circuit board can allow for the omission of one or more reflow processes. This process prevents the TIM material from having to go through extra reflow steps, which can provide for good reliability.

In another example, the cold plate can alternatively be assembled as part of the in-process unit prior to the in-process unit being mounted and bonded to the printed circuit board. For example, as shown in <FIG>, cold plate base <NUM>-<NUM> is pre-assembled as part of the in-process unit <NUM>-1A. Thereafter, in-process unit <NUM>-1A can be mounted to a printed circuit board and the lid (not shown) may be joined to the base <NUM>. In such example, the TIM used to join the cold plate base <NUM>-<NUM> to the rear surfaces 544A, 544B, 544C of chips 540A-<NUM>, 540B01, 540C-<NUM> and stiffener <NUM>-<NUM> may be one that is not impacted by the reflow process for joining the in-process unit <NUM>-1A to the board. For example, a TIM that has higher reflow temperature than the bonding material used to bond the chip to the board may be selected.

Referring to <FIG>, a method of manufacturing a chip assembly, such as chip assembly <NUM> (<FIG>) is shown. The method of manufacture is otherwise identical to the method discussed in <FIG>, except for the addition of a spring. As in the prior example, <FIG> illustrate assembly of chips 640A, 640B, 640C to interposer <NUM>, and the assembly of the chips 640A, 640B, 640C and interposer <NUM> to substrate <NUM>. As previously mentioned, reflow to allow for joinder of chips 640A, 640B, 640C, interposer <NUM>, and substrate <NUM> can occur in either one step (once chips, interposer, and substrate are aligned with one another) or two steps (first solder reflow interposer to substrate, and then reflow interposer to chips). Additionally, chips may instead first be attached to interposer <NUM>, and then the chips 640A, 640B, 640C together with interposer <NUM> may be attached to substrate <NUM>.

Referring to <FIG>, a stiffener <NUM> may be provided on a top surface of substrate <NUM>, as well as around the chips 640A, 640B, 640C and interposer <NUM>. Posts <NUM> can be integrally formed with stiffener <NUM> or subsequently added to the top surface of stiffener <NUM>. (See, e.g., <FIG>. ) As shown in <FIG>, a biasing mechanism, such as springs <NUM>, may be added to posts <NUM>. This results in an in-process unit <NUM>-<NUM>.

Turning now to <FIG>, in-process unit <NUM>-<NUM> can be attached to a printed circuit board <NUM> or the like. As shown, contacts <NUM> at bottom surface <NUM> of substrate <NUM> can be aligned with contacts <NUM> at the top surface <NUM> of printed circuit board <NUM>. Solder balls 627C arranged in a grid array can be used to attach substrate <NUM> to printed circuit board <NUM>. The package and solder can be reflowed to form the bonded connection.

As shown in <FIG>, TIM <NUM> may be applied to rear surfaces 644A, 644B, 644C of respective chips 640A, 640B, 640C. TIM <NUM> can be any TIM material disclosed herein or any known TIM. TIM may be applied using various methods. In the example where high K TIM is a paste, TIM may be deposited directly onto rear surfaces of chips 640A, 640B, 640C, which will later cure and harden.

With reference to <FIG>, base <NUM> of cold plate, including fins <NUM> may be attached to the in-process unit <NUM>-<NUM> and printed circuit board. In particular, base <NUM> may be attached to rear surfaces 644A, 644B, 644C of chips 640A, 640B, 640C, as well as top surface <NUM> of stiffener <NUM>, including springs <NUM>. In this example, TIM <NUM> may be positioned between cold plate base <NUM> and rear surfaces 644A, 644B, 644C. TIM will help to dissipate heat generated by chips 640A, 640B, and 640C. Once base <NUM> is positioned over one or more rear surfaces 644A, 644B, 644C and stiffener <NUM>, the TIM may be reflowed to ensure a connection between cold plate <NUM> and chips 640A, 640B, 640C. Springs <NUM> can help to ensure a compression force against stiffener <NUM> and substrate <NUM> by the weight of base <NUM> and lid <NUM>. O-ring <NUM> can also be provided within a recess (not shown) in base <NUM>.

<FIG> illustrates the final assembly <NUM>. Lid <NUM> may be attached to base <NUM> using various forms of attachment. In one example, lid <NUM> may be screwed together with base <NUM>, but in other examples, an adhesive or other bonding material can be utilized. Loop and piping can be further added to the assembly <NUM>, as disclosed herein.

In one example method of assembly, the in-process unit <NUM>-<NUM>, as shown in <FIG>, can be prepared by one manufacturer, such as an OSAT manufacturer or the like. In process unit <NUM>-<NUM> can then be further packaged by a second contactor or the like who will then perform the remaining steps in <FIG>. Alternatively, all of the steps <FIG> can be formed by one entity. In still other examples, chips may first be joined to interposer <NUM>, and then the combination of interposer and chips 640A-640C may be joined to substrate <NUM>.

<FIG> illustrate various methods of attaching TIM material to form assemblies described herein at the server tray level, as well as variations thereof. <FIG> illustrates an in-process unit <NUM>-<NUM>, which is identical to the in-process unit shown in <FIG>. As previously discussed, in-process unit <NUM>-<NUM> can include a substrate <NUM>, interposer <NUM>, and chips 740A, 740B, 740C attached to interposer <NUM>. Stiffener ring <NUM> can extend circumferentially around chips 740A-740C and interposer <NUM>. In other examples, as previously discussed, in-process units can include different features. For example, interposer <NUM> and/or stiffener <NUM> may be omitted. Omission of interposer <NUM> will allow for direct connection of chips 740A, 740B, 740C to substrate <NUM>.

After formation of in-process unit <NUM>-<NUM>, package metallization can be performed. In process unit <NUM>-<NUM> can be sputter coated with a combination of metals, including, for example, titanium NIV, and gold. This will help to promote a chemical bond between the in-process unit <NUM>-<NUM> and the TIM <NUM> (as will be discussed in more detail below).

Multiple in-process units <NUM>-<NUM> can be applied to a printed circuit board, such as a server tray <NUM>. In one example, as shown in <FIG>, after metallization, each in-process unit <NUM>-<NUM> may be reballed for solder, and then reflowed to attach and bond each in-process unit <NUM>-<NUM> to server tray <NUM>.

The next phase of the process, as previously discussed, is to attach the cold plates to each of the respective in-process units <NUM>-<NUM>. <FIG> illustrates an exploded view of an example completed assembly <NUM> to facilitate the discussion. In one example, TIM <NUM>, such as a high K TIM disclosed herein, may be directly applied to rear surfaces 744A, 744B, 744C of chips 740A, 740B, 740C, and then cold plate <NUM> (which in this example can include cold plate base <NUM> and cold plate lid <NUM>) can be attached to in-process unit <NUM>-<NUM>. In another example, TIM <NUM> can instead be pre-reattached to cold plate base <NUM> by reflowing TIM <NUM> (before secondary reflow to chip) or alternatively, attaching TIM <NUM> to cold plate base <NUM> through an adhesive or similar material that can secure TIM <NUM> in place prior to reflow. Other methods can also be implemented. Some example methods of attachment will be discussed in more detail below.

TIM can be provided on one or more of the rear surfaces 744A. 744B, 744C of respective chips 740A, 740B, 740C using different methods. <FIG> illustrates server tray <NUM> showing two example compression methods and example structures (<NUM>,<NUM>) for attaching a cold plate to the in-process unit <NUM>-<NUM>.

In one example <NUM>, a weight <NUM> may be applied over the in-process unit <NUM>-<NUM> (or any unit undergoing reflow), which will allow for the weight of gravity to provide a compressive force onto TIM <NUM> (<FIG>) during reflow. As shown in the enlarged views of <FIG>, which shows weight <NUM> in transparent form for illustration and discussion purposes, and <FIG>, weight <NUM> may be a solid monolithic block of material. Weight <NUM> may alternatively be formed from multiple portions joined together and/or include portions that are not solid. The weight can take on a variety of shapes, sizes and configurations. In one example, weight <NUM> includes a top surface 759A, which in this example is shown as a continuously planar surface, but in other examples, the top surface 759A may vary. An opposed bottom surface 759B of weight <NUM> can further include an extended portion EP centrally located along the bottom surface 759B. The extended portion EP may extend beyond two lower portions LP. The extended portion EP may be substantially planar so as to allow for a uniform force or pressure to be applied to the in-process unit <NUM>-<NUM>. In other examples, the extended portion EP may be omitted, such that the resulting bottom surface of weight <NUM> may be a continuous and substantially planar surface. In still other examples, the extended portion EP may not extend across an entire rear surface of the in-process unit <NUM>-<NUM> and may instead by configured so that it overlies only portions of the in-process unit. The weight <NUM> can be comprised of a variety of materials, but in one example, weight <NUM> is formed from stainless steel. Weight <NUM> can be any designated or desired amount of weight, but in one example, the weight is <NUM>. In other examples, the weight may be greater than or less than <NUM>. Weight <NUM> may include recesses 750A configured to receive bores or studs 750B that may be provided on and extend away from the cold plate. The bores or studs 750B can guide weight <NUM> to ensure proper placement of weight <NUM> over the in-process unit <NUM>-<NUM>. Additionally, as better seen in <FIG>, a fixture <NUM> can also be provided directly adjacent the base of weight <NUM> and in-process unit <NUM>-<NUM>. The fixture <NUM> can include recesses <NUM> adapted to receive spacers or bolts on the tray <NUM>.

The weight may be removable or mechanically attached to the circuit board. For example, the weight may be directly attached to the circuit board with a mechanical fastener (not shown), such as screws or bolts. Additionally or alternatively, the weight may be coupled or attached to a secondary fixture that can control movement and positioning of the weight. In such an example, the secondary fixture can position the weight to overlie the chip assembly and then apply pressure to the weight and the chip assembly during the reflow process.

At the conclusion of the reflow process, the weight may be removed.

Utilizing a weight <NUM> to secure the high k TIM to rear surfaces 744A, 744B, 744C of the chips 740A-740C can help provide even load distribution, large thermal mass, and consistent load during reflow. Weight <NUM> can then be removed at the conclusion of reflow.

In another example <NUM>, with reference to <FIG> and <FIG>, a compression plate <NUM> with spring connections <NUM> can be used to help provide a compressive force during reflow. As best shown in the enlarged view of <FIG>, a compression plate <NUM> is a plate that overlies and exerts a force on an in-process unit, such as in-process unit <NUM>-<NUM>. Compression plate <NUM> may be a rigid plate that is machined to provide a desired thread offset. Compression plate <NUM> may take on a variety of shapes and sizes provided compression plate <NUM> can apply a compressive force onto the in-process unit <NUM>-<NUM>. Four spring assemblies may be positioned at each of the four corners of the compression plate <NUM>. Springs <NUM> can help to accommodate differences in force. Compression plate <NUM> may similarly include apertures 750B-<NUM> configured to receive bores or posts 750A-<NUM> that will place compression plate <NUM> into the proper position overlying the in-process chip assembly, and also prevent compression plate <NUM> from moving in a lateral direction.

With reference to <FIG> (as well as reference back to <FIG>) , a schematic top view of four chip assemblies <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D mounted on a printed circuit board, such as server tray <NUM>-<NUM>, is shown. The configuration of assemblies <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D can be identical to the chip assembly <NUM> shown in <FIG>, except that the printed circuit board is instead a larger circuit board, such as server tray <NUM>-<NUM>, and is configured to accommodate multiple rows and columns of chips assemblies <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D. As shown, each cold plate lid 570A, 570B, 570C, 570D includes an inlet and a pair of outlets. For example, cold plate lid 570A includes inlet <NUM>-A-A and outlets 576B-A on opposite sides of inlet <NUM>-A-A. In this example, only four chips assemblies are shown, but any number of chip assemblies may be used and may be arranged on server tray <NUM>-<NUM>.

When configuring the chip assemblies <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D, in one example, the cold plate base of each of the chip assemblies <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D may first be bonded (not shown) to the respective chip assemblies or in-process units that are attached to the server tray <NUM>-<NUM>. In one example, final assembly of the cold plate lids can occur sequentially. For example, cold plate lid 570A can first be attached to the cold plate base (not shown) within assembly <NUM>-A. Cold plate lid 570B can then be attached to the cold plate base (not shown) of assembly <NUM>-B; cold plate lid 570C can then be attached to the respective cold plate base (not shown) within assembly <NUM>-C; and finally, cold plate lid 570D can then be attached to its respective cold plate base (not shown) within assembly <NUM>-D. The order of assembly can, of course, vary. Alternatively, two or more of the cold plate lids 570A, 570B, 570C, 570D can be attached at the same time. In still other examples, the cold plate lids 570A, 570B, 570C, 570D can be attached in any order.

Once the respective cold plate lids are attached, they can be connected together in a plumbing and cooling loop. With reference to the schematic view of <FIG>, cold plate lids 570A, 570B, 570C, 570D can be connected together via a continuous piping loop or cooling loop <NUM>, which allows for fluid, such as water, to flow through the cold plate system. For example, with reference to assembly <NUM>-A, loop <NUM> is first connected to inlet 576A-A, which will allow fluid, such as water, to flow into the cold plate of assembly 570A and then exit assembly 570A through outlets 576B-A on opposed sides of inlet 576A-A. This same pattern of loops <NUM> will continue through each remaining assembly <NUM>-B, <NUM>-C, and <NUM>-D. An example three-dimensional side view of loops <NUM> overlying assemblies <NUM>-C and <NUM>-D is illustrated in <FIG>.

In another example shown in <FIG>, prior to attaching cold plate lids 570A, 570B, 570C, 570D to their respective cold plate bases, the cooling loop <NUM> can first be attached to each of the cold plate lids 570A, 570B, 570C, 570D. This allows for formation of a cooling loop unit 582A, comprising cold plate lids 570A, 570B, 570C, 570D and cooling loop <NUM>, that can then be attached to the respective cold plate bases <NUM>. Once the entire pre-connected loop assembly <NUM> is formed, pre-connected loop and the cold plate lids 570A, 570B, 570C, 570D can be directly attached to respective cold plate bases to complete the respective chip assemblies.

In still another example, instead of first attaching cold plate bases to TIM and rear surfaces of chips, cold plate bases and cold plate lids 570A, 570B, 570C, 570D can first be joined together, along with a pre-assembled cold plate loop <NUM>. Once assembled, the combination cold plate base, cold plate lid, and cold plate loop can be directly attached to the rear of chips 540A-540D as a single unit.

Additional three-dimensional (3D) views and examples of cooling loop assemblies are shown in <FIG>, <FIG>, and <FIG>. These figures illustrate components of a system prior to reflow and attachment of the cold plate lid to the in-process unit. In particular, the assembly illustrates components of the cold plate and cooling loop assembly, as well as the compression device prior to soldering of the cold plate base to the assembly. In each example, the example in-process units, such as previously discussed herein, are shown already being soldered to a circuit board (see, e.g., <FIG>), such as a server tray assembly. <FIG> illustrate example methods of assembly where the cold plate base will be assembled and attached to the in-process unit and circuit board. In some examples, the cold plate base may be bonded to the in-process unit and circuit board using a high thermally conductive material prior to attachment of the cold plate lid and cooling loop. Alternatively, the cold plate base may be attached to either or both the cold plate lid and/or cooling loop, prior to being bonded to the in-process unit and circuit board. For ease of discussion, the same reference numerals will be used to discuss the same components throughout each of <FIG>, <FIG>, and <FIG>.

<FIG> provides an example exploded view showing components of a system prior to reflow and attachment of the cold plate to the in-process unit. In this example, each cold plate base is first bonded (not shown) to the in-process unit, including chip, and circuit board, with the use of any thermally conductive material, including a solder; thereafter, the cold plate lid may be assembled to the cold plate base and chips; and the cooling loop may then be assembled to each respective cold plate lids.

As previously discussed herein, a cold plate base may first be bonded to an in-process unit. For example, a high thermally conductive material, such as solder or the like, can be used to attach each cold plate base <NUM> to each of the respective in-process units <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D, which can result from direct attachment of the cold plate base <NUM> to the rear surfaces of chips (not shown) of each in-process unit <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D. Bonding can occur using any desirable material. In one example, a high thermally conductive material or ultra-high thermally conductive material, such as those discussed or to be discussed herein, may be utilized. Thereafter, the rest of the cold plate assembly can be mounted to the base. For example, each cold plate lid <NUM> may be attached to base <NUM> overlying each respective in-process unit <NUM>-A through <NUM>-D, along with a compression plate assembly <NUM>, which further includes compression plate <NUM>, springs <NUM>, and openings <NUM> to accommodate connections to the cooling loop <NUM>). Thereafter, a cooling loop <NUM> may be attached. As shown, the cooling loop <NUM> can include a flexible hose 882A and an interconnection and sealing pipe and fitting <NUM>, such as British Standard Pipe Parallel ("BSPP") thread fittings with an o-ring face seal. Enlarged view of an example fitting <NUM> is also shown. Other fittings, configurations, and the like can be utilized in connection with this manufacturing process.

<FIG> is identical to <FIG>, except for the method and order of assembling the components. <FIG> provides for another example where a cold plate base <NUM> is first bonded (not shown) to each of the respective in-process units <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D, and then respective cold plate lids <NUM>, cooling loop <NUM>, and compression plate assembly <NUM> (which includes compression plate <NUM> and springs <NUM>) are attached thereafter. In this example, however, cooling loop <NUM> can first be pre-attached directly to the inlets and outlets of cold plate lids <NUM> to form a subassembly <NUM> that includes lid <NUM>, cooling loop assembly <NUM>, and compression plate assembly <NUM>. Subassembly <NUM> can then be directly attached to each cold plate base <NUM>, which is already attached to the respective in-process units <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D. Alternatively, in an otherwise identical configuration to <FIG> and <FIG>, <FIG> illustrates an example which utilizes a barb fitting 883B, instead of a BSPP fitting. The remaining components can be identical to the prior example, as shown by the similar numbering. In still other examples, different types of fittings may be utilized to form a connection between the cooling loop and the inlets and outlets of the cold plate.

<FIG> is another example where each cold plate bases <NUM> is first bonded to the in-process units <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D. A subassembly, including cold plate lid <NUM>, compression assembly <NUM>, and cooling loop <NUM> may be first and separately attached together as a modular unit or subassembly <NUM>, which is then attached as a completed subassembly <NUM> to cold plate base <NUM>. This example is otherwise similar to <FIG> to the extent that the lid <NUM> and cooling loop <NUM> are pre-assembled together prior to attachment to cold plate base <NUM>. However, in this example, cooling loop <NUM> is brazed to cold plate lid <NUM> (along with compression assembly <NUM>), and then joined to cold plate base <NUM>. In other examples, cooling loop <NUM> may be attached to cold plate lid <NUM> using various alternative methods and configurations.

<FIG> illustrates an example where the cold plate lid <NUM>, cold plate base <NUM>, and compression assembly <NUM> are first joined together as a subassembly <NUM>. As in the previous examples, this can optionally include assembly of o-ring <NUM>. Each subassembly <NUM> can then be bonded to the in-process unit <NUM>-C and tray <NUM> using a thermally conductive interface material, including the use of solder to solder the subassembly <NUM> to each of the in-process units <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D. In one example, as previously discussed, each base <NUM> of each subassembly <NUM> can be bonded to the respective in-process units <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D using a high thermally conductive interface material, as previously discussed herein. Thereafter, cooling and plumbing loop <NUM> may be attached to lid <NUM>. In other examples, the cold plate may be a single unitary cold plate that is not separately formed with both a lid and base.

<FIG> is identical to the example of <FIG>, except that in the subassembly 850B, an o-ring is not utilized in connection with the joinder of the cold plate base <NUM> and lid <NUM>. Instead, the cold plate base <NUM>, cold plate lid <NUM>, and compression assembly <NUM> are brazed together without the use of an o-ring. Once joined together, each subassembly <NUM> can then be joined to each respective in-process unit <NUM>-A, <NUM>-B, <NUM>-C, <NUM>-D, as previously discussed. Cooling loop <NUM> can then be joined to subassembly <NUM>.

<FIG> illustrates an example exploded view where the entire cooling loop <NUM>, cold plate assembly <NUM> (including cold plate lid <NUM> and cold plate base <NUM>), and compression plate assembly <NUM> are pre-attached together to form a completed cooling unit <NUM>. In this example, cooling loop <NUM> is brazed to the cold plate lid so as to form a completed cooling unit <NUM>, although other forms of connection are contemplated within the scope of this disclosure. Then, the cooling loop <NUM> and each of the cold plate bases may be attached and bonded to each of the respective in-process units <NUM>-A, <NUM>-B, <NUM>-D, <NUM>-C, <NUM>-D.

It is to be appreciated that in these examples, differing types of in-process units and components may be attached to the circuit board <NUM>.

As an alternative to the methods and structures described above and to be described below, or in addition to the methods and structures described above or to be discussed below, forming the cold plate from select materials can improve heat distribution. For example, selecting an ultra-high thermally conductive (k) material to comprise the cold plate can provide optimal results. In some examples, an ultra-high thermally conductive (k) material with a coefficient of thermal expansion ("CTE") that matches the silicon in the semiconductor chips can be used to manufacture the cold plate or portions of the cold plate. In other examples, selection of a material having a thermal conductivity greater than copper (<NUM> W/mk at <NUM> C) can help to provide optimal heat distribution. For example, silver diamond (AgD) (<NUM> W/mK), which has a significantly greater thermal conductivity than the thermal conductivity of copper (<NUM> W/mk), is one example of an ultra-high thermally conductive (k) material. In other examples, other ultra-high thermally conductive materials having a thermal conductivity greater than copper (<NUM> W/mk) can be utilized. The selection of an ultra-high thermally conductive material to comprise the cold plate, alone or in combination with TIM and/or the structures, such as those disclosed herein, can help to provide optimal heat distribution in a chip assembly.

For ease of discussion, reference will be made to the example chip assembly of <FIG>, in which cold plate <NUM> is attached to chips 140A, 140B, 140C through TIM <NUM>. But it is to be appreciated that the selection of materials for the components is not limited to the structure of <FIG> or any one of the other figures disclosed herein. For example, a cold plate may be a monolithic cold plate base and lid combined together; cold plate base may not include fins, and fewer than three chips or more than three chips can be utilized within a chip package.

In one example, cold plate base <NUM> is formed from an ultra-high k thermally conductive material that has a CTE matching at least one of the semiconductor chips 140A, 140B, 140C. The high k material enables greater thermal performance through heat spreading. This same material can be used to manufacture fins <NUM> of base <NUM> of cold plate. To attach base <NUM> of cold plate <NUM> to chips 140A-140C, as previously discussed, base <NUM> of cold plate <NUM> can be attached to the rear of chips 140A, 140B, 140C with a TIM, such as grease, solder, or other materials.

In another example, cold plate base <NUM> may be comprised of an ultra-high thermally conductive material. In some examples, the ultra-high thermally conductive material may have a thermal conductivity greater than copper (<NUM> W/mk at <NUM>° C). Such materials can comprise AgD or any other ultra-high K material or combinations of materials. Fins <NUM> and lid <NUM> may be formed of a different material having a lower thermal conductivity than the ultra-high thermally conductive material forming cold plate base <NUM>. In some examples, the fins <NUM> may be soldered, plated, or 3D printed onto base <NUM>. To attach cold plate base <NUM> to chips 140A-140C, as previously discussed, base <NUM> of cold plate <NUM> can be attached to the rear of chips 140A, 140B, 140C with a TIM, such as grease, solder, or other materials.

In another example, cold plate base <NUM> and fins <NUM> are formed from the same ultra-high k thermally conductive material. In some examples, the ultra-high thermally conductive material may have a thermal conductivity greater than copper (<NUM> W/mk at <NUM>° C). Such materials can comprise AgD or any other ultra-high K material or combinations of materials. For example, base <NUM> and fins <NUM> may be an integral unit. Lid <NUM> may instead be formed from a different material. To attach cold plate base <NUM> to chips 140A-140C, as previously discussed, cold plate base <NUM> can be attached to the rear of chips 140A, 140B, 140C with a TIM, such as grease, solder, or other materials.

Simulations were conducted in which TIM thickness used to attach cold plate to chips 140A-140C was varied, as well as the materials forming the cold plate base and cold plate fins. Optimal results were achieved using an ultra-high k or thermally conductive cold plate base formed from silver diamond, bonded to chips 140A, 140B, 140C with a TIM <NUM> having a thickness of <NUM> microns. Such configuration can support a chip heat flux of <NUM> W/mm<NUM> at <NUM> degree Celsius junction temperature. Other examples and combinations using silver diamond as the material forming at least a portion of the cold plate are shown in the chart of <FIG>.

<FIG> shows a comparison between using copper (high K) as the base plate, as compared to silver diamond (ultra-high K), which has a thermal conductivity significantly greater than copper in combination with different TIM materials and thicknesses and thermal conductivities. As shown, a heat distribution device having a cold plate base and cold plate fins formed from silver diamond can achieve the greatest heat flux of <NUM> w/mm2. Additional examples and variations are also contemplated within the scope of the disclosure. Further, it is to be appreciated that in certain applications, it may be sufficient to vary the materials forming the cold plate base, fins, and lid, without the use of an ultra-high thermally conductive material, and simply rely on, for example, high-k materials, such as copper, to form the base.

Die thinning and modification of the cold plate and cold plate fins can provide for greater control over heat distribution. <FIG> illustrates a schematic view of a portion of a package <NUM>. Package <NUM> can include a printed circuit board <NUM>, substrate <NUM>, silicon interposer <NUM>, three chips 1040A, 1040B, 1040C, and a cold plate base <NUM> joined to the respective rear surfaces 1044A, 1044B, 1044C of chips 1040A, 1040B, 1040C by a TIM <NUM>. The package can further include a stiffener, as further discussed. In this example, three chips are shown adjacent one another. A central chip 1040B is positioned between at least two directly adjacent chips 1040A, 1040C positioned on opposed sides of the central chip 1040B. Central chip 1040B may be thinned, such that chip 1040B has a thickness T1 that is less than the thickness of one or more directly adjacent chips. In this example, central chip 1040B has at thickness T1 that is less than the thickness T2 of both directly adjacent chips 1040A, 1040C. This creates a difference in height between chips 1040A, 1040C and chip 1040B, as well as a recessed area A directly above chip 1040B. Die thinning can be accomplished by grinding, etching, milling or any known methods of die thinning. Die thinning reduces the thermal resistance within silicon of chip 1040B. In some examples, central chip 1040B may be an ASIC chip and the directly adjacent chips 1040A, 1040B may have the same or different function. In other examples, central chip 1040B is another type of chip.

To accommodate the change in thickness of chip 1040B due to die thinning, the structure of cold plate base <NUM> can be modified. As shown, bottom surface <NUM> of base <NUM> is not planar, but includes a step or protrusion P that extends into the recessed area A above chip 1040B so as to fill the open space created by the thinning of die 1040B. Cold plate base <NUM> therefore includes at least one protrusion P. Additionally, fins <NUM> have a length L1 that is greater than a length L2 of the fins <NUM> in cold plate base <NUM> that overlie chips 1040A and 1040C. In such example, the elongated fins may have a length L1 between <NUM> and <NUM>, which can be optimized based on the cooling requirements of the chip, but in other examples, length L1 can vary. In the example shown, the elongated fins extend upwardly from a recessed portion R of the top surface 1060A of base <NUM>. Base <NUM> can be joined to rear surfaces of chips 1040A, 1040B, 1040C by a thermally conductive interface material <NUM>, including a low melting point metal, as previously discussed herein.

<FIG> is another example chip assembly <NUM>-<NUM> similar to <FIG>, except that the structure of example fins <NUM>-<NUM> of cold plate base <NUM>-<NUM> differs. As shown, chip 1040B is positioned between chips 1040A, 1040C. Chip 1040B has been thinned so that the overall thickness of chip 1040B is less than the thickness of directly adjacent chips 1040A, 1040C. All of the fins <NUM>-<NUM> of cold plate base <NUM>-<NUM> have a substantially equal length L3, as all fins <NUM>-<NUM> extend from a continuously planar interior surface <NUM> of cold plate base <NUM>-<NUM>. Bottom surface <NUM>-<NUM> of cold plate base <NUM>-<NUM> will have a similar stepped profile, as bottom surface <NUM> of cold plate base <NUM>-<NUM> of <FIG>.

<FIG> illustrates another example chip assembly <NUM>-<NUM> that is similar to <FIG>, except that bottom surface <NUM>-<NUM> of cold plate base <NUM>-<NUM> includes a recessed portion R, which creates two protrusions P-1A and P-1B. In this example, instead of the middle chip 1040B-<NUM> having a thickness that is less than the thickness of the two adjacent chips, middle chip 1040B-<NUM> instead has a thickness that is greater than the two adjacent and outermost chips 1040A-<NUM>, 1040C-<NUM>. Cold plate <NUM>-<NUM> accommodates the change in thickness of the chips by including a recessed portion R in a central portion of bottom surface <NUM>-<NUM>. This allows for chip 1040B-<NUM> to extend into recessed portion R, and for protrusions P-1A and P-1B to overlie thinned chips 1040A-<NUM> and 1040C-<NUM>. Cold plate base <NUM>-<NUM> may be attached to chips 1040A-<NUM>, 1040B-<NUM>, 1040C-<NUM> through use of a TIM <NUM>.

<FIG> illustrates an example subassembly <NUM> of a chip package including substrate <NUM>, an interposer <NUM>, and chips 1140A, 1140B, 1140C mounted on a printed circuit board <NUM>. Instead of thinning the overall height of chip 1140B, chip 1140B includes cavities <NUM> directly within chip 1140B. Cavities <NUM> can be formed using any known methods, including milling, etching, and the like.

In one example, to better distribute heat from the chip, cavities <NUM> can be filled with a conductive material for heat distribution, such as the assembly 1100A shown in <FIG>. In some examples, a high or ultra-high thermally conductive material <NUM> can fill the cavities <NUM>. An example of such material can include copper, but other materials may also be utilized. The high or ultra-high thermally conductive material <NUM> may have a top surface <NUM> that is aligned or flush with the rear surface 1144B of chip 1140B. In other examples, top surface <NUM> of material <NUM> may be recessed below rear surface 1144B of chip 1140B, or extend beyond rear surface 1144B of chip 1140B, as discussed below.

In another example chip assembly 1100B shown in <FIG>, top surface <NUM>-<NUM> of material <NUM>-<NUM> extends beyond rear surface 1144B of chip 1140B-<NUM> to form protrusions or chip fins <NUM>. Chip fins <NUM> can help to distribute heat away from chip 1140B-<NUM> and the overall chip assembly 1100B. A high or ultra-high thermally conductive material <NUM>-<NUM> can be deposited into cavities <NUM>-<NUM>. Chip fins <NUM> can be formed in various ways. In one example, the fins can be formed by a subtractive process, such as etching/laser followed by an additive process like plating, physical vapor deposition and printing and the like. Other methods of manufacture may also be utilized.

<FIG> provides another example chip subassembly <NUM>, which is similar in structure to the prior example subassembly of <FIG>, except that instead of multiple cavities, a single and central cavity <NUM> is provided at the central portion of chip 1240B. This is intended to address the amount of heat generated at the center of chip 1240B, which is typically highest at the center of the chip. Additionally, the location of chip 1240B between two directly adjacent chips 1240A, 1240C, makes it even more difficult to dissipate heat at the center of chip 1240B. Thinning of chip 1240B can help to decrease the amount of heat generated.

In this example, instead of filling cavity <NUM> with thermally conductive material, a cold plate base <NUM> can be attached and bonded to rear surfaces 1244A, 1244B, 1244C of chips 1240A, 1240B, 1240C with a TIM <NUM>. As shown in <FIG>, base <NUM> can include a stepped and non-planar bottom surface <NUM>. The stepped or protrusion P of base <NUM> can protrude directly into cavity <NUM>. It is to be appreciated that although base <NUM> does not include fins, fins can be provided in other examples. Similarly, any one of the cold plates described herein can omit fins. Further, central cavity <NUM> can instead be filled with a thermally conductive material, such as, for example, a high or ultra-high thermally conductive material.

Enhanced heat distribution within a chip assembly, in combination with enhanced warpage control, may be further achieved by coordinating the selection of the material or combination of materials forming the heat distribution device and the selection of the material or combination of materials forming the stiffener. In an example chip assembly that includes a heat distribution device overlying at least a portion of the stiffener, the thermal conductivity of the material forming the heat distribution device may be higher than the thermal conductivity of the material forming the stiffener, but the coefficient of thermal expansion of the material forming the heat distribution device may be lower than the coefficient of thermal expansion of the material forming the stiffener. This combination can allow for use of a high thermally conductive material as the heat spreader, even though the material may have a comparatively low coefficient of thermal expansion ("CTE"). To compensate for the low CTE of the high thermally conductive material, a stiffener formed of a material with a higher CTE can be used. For example, an ultra-high thermally conductive material, such as silver diamond (e.g., AgD) previously discussed herein or any form of silver diamond, may be selected as the material forming the heat distribution device, whereas copper (e.g., Cu-OFE) or any form of copper may be selected as the material forming the stiffener. In other examples, different combinations of materials may be selected, as discussed below. The arrangement of the components within the assembly, combined with the selection of materials can optimize heat distribution and warp control of the substrate and microelectronic device.

Turning to <FIG>, an example microelectronic device assembly <NUM> is illustrated. The assembly may include at least a substrate <NUM> supporting the assembly <NUM>, a stiffener element <NUM>, at least one microelectronic element or chip <NUM>, and a heat distribution device <NUM>. Chip <NUM> can be a semiconductor chip and may be arranged so that the active front surface <NUM> faces toward and can be joined or bonded in a ball grid array to substrate <NUM>. Although only a single chip is shown in the figure, multiple chips may be present within assembly <NUM>. Substrate <NUM> may be a traditional single layer or multi-layer substrate formed from a non-conductive dielectric material, such as glass epoxy, silicon, polyimide, polytetrafluorethylene, fiberglass-epoxy laminate. Bonding material, such as solder balls <NUM>, may be used to electrically interconnect chip <NUM> with substrate <NUM>.

A stiffener element may extend around chip <NUM> and overlie substrate <NUM>. An adhesive 2038A may join the bottom surface <NUM> of stiffener element <NUM> to top surface <NUM> of substrate <NUM>. As previously discussed, an example stiffener element <NUM> can be a stiffener ring that extends circumferentially around chip <NUM>. Stiffener element <NUM> may be circular, rectangular, or any other desired shape. As shown, stiffener element <NUM> can include a bottom surface <NUM>, an opposed top surface <NUM>, an outer edge surface <NUM> extending between the bottom and top surfaces <NUM>, <NUM>, an opposed interior edge surface <NUM> extending between the bottom and top surfaces <NUM>, <NUM>, and an aperture <NUM> extending through the top and bottom surfaces <NUM>, <NUM>. Aperture <NUM> may be generally central with respect to an outer perimeter of stiffener <NUM>, though in other examples the position of aperture <NUM> may be adjusted. For example, the size and shape and position of aperture <NUM> may be adapted based on circuitry of the underlying substrate <NUM> to be exposed through aperture <NUM> or the arrangement of chip within aperture <NUM>.

Heat distribution device <NUM> may extend over at least portions of stiffener <NUM> and chip <NUM>. In this example, heat distribution device <NUM> is a single monolithic element having a planar bottom surface <NUM> and a planar top surface <NUM>. Example heat distribution devices <NUM> can include a cold plate or heat spreader, and may further include thermally conductive fins or other features (not shown). An adhesive 2038B can be used to attach heat distribution device <NUM> to stiffener element <NUM>. As shown, a second adhesive 2038B joins bottom surface <NUM> of heat distribution device <NUM> to top surface <NUM> of stiffener <NUM>. Heat distribution device <NUM> may include a bottom surface <NUM>, a top surface <NUM>, and outermost edge surfaces <NUM> extending between the bottom and top surfaces <NUM>, <NUM>. In this example, both outermost edges <NUM> of heat distribution device <NUM> are aligned with the outermost edges <NUM> of stiffener element <NUM>. In other examples, including those to be described below, one or both edges <NUM> are not aligned with outermost edges <NUM>.

A thermal interface material ("TIM") with at least a high thermal conductivity ("k") may be used to join heat distribution device <NUM> directly to chip <NUM>. In this example, bottom surface <NUM> of cold plate <NUM> is directly joined to rear surfaces <NUM> of chip <NUM> through use of TIM <NUM>. TIM <NUM> may be a high k TIM, which can also be a low melting temperature metal, including metal or graphite, such as Nano Ag or Indium, but other high k TIM materials may be implemented. The methods and structures disclosed herein can also be utilized with a low k TIM, with reduced levels of thermal conductivity.

TIM <NUM> may be provided in any desired form, such as liquid, solid, semi-solid, and the like. For example, a TIM can be applied in liquid form, which will later cure and remain as a soft elastomer. In other examples, TIM can be a grease, film, or solder.

In some examples, the first adhesive 2038A joining bottom surface of stiffener <NUM> to substrate <NUM> may be different than the second adhesive 2038B joining stiffener <NUM> to heat distribution device <NUM>. For example, the first adhesive 2038A can optionally possess characteristics that differ from the second adhesive 2038B. As will be discussed below, selection of the adhesive, alone or in combination with the selection of material forming stiffener element <NUM> can further help to compensate for a CTE mismatch in the overall system, including any CTE mismatch between the heat distribution device <NUM> and the substrate <NUM> and/or stiffener element <NUM>.

The first adhesive 2038A may have a higher resistance to elastic deformation and a higher modulus of elasticity than the modulus of elasticity of a second adhesive 2038B. In some examples, first adhesive 2038A may have a modulus of elasticity ranging from 10MPa to 100MPa. In other examples, the modulus of elasticity of first adhesive 2038A can be less than 10MPa or greater than <NUM> MPa. First adhesive 2038A may be in the form of a paste, but can also take on other forms. The second adhesive 2030B may differ and have a second modulus of elasticity ranging from <NUM>. 1MPa to <NUM> MPa. In other examples, the modulus of elasticity of second adhesive 2038B can be less than <NUM> MPa or greater than <NUM> MPa. The second adhesive may be in form of a liquid or film, but in other examples, the second adhesive can take on other forms. Thus, while there is a slight overlap in the exemplary ranges of the modulus of elasticity of the first and second adhesives 2038A and 2038B, in examples where the modulus of elasticity of the first and second adhesives is intended to differ, an exemplary embodiment will be one where the modulus of elasticity of the first adhesive 2038A is selected that is greater than the modulus of elasticity of the second adhesive 2038B. In other examples, the same or similar modulus of elasticity may be selected for the first and second adhesives 2038A and 2038B, so as to rely on the properties selected for the stiffener <NUM> and heat distribution device <NUM>, alone or in combination with other components of the package, to minimize warping of the chip package.

The differing adhesives can further help to achieve enhanced warpage control and compensate for a CTE mismatch between a stiffener and heat spreader and/or substrate or other components within the assembly. In some examples, as long as the first modulus of elasticity is greater than the second modulus of elasticity, the selected modulus of elasticity can be within or outside of the example ranges noted above. In this example, having the first adhesive in the form of a paste, as compared to a second adhesive in the form of liquid, this combination can further assist with CTE mismatch in the assembly, depending on the materials selected for the stiffener and heat spreader. In other examples, the second adhesive 2038B may have a greater modulus of elasticity than the first adhesive 2038A. In still other examples, depending on the materials selected for the heat spreader <NUM> and stiffener element <NUM>, the first and second adhesives 2038A and 2038B may be the same or substantially the same, or have respective modulus of elasticities that do not significantly differ.

The first and second adhesives may be dielectric or insulating adhesives. For example, the first and second adhesives may be epoxies, or other types of materials. The selective adhesives may be thermally conductive or non-conductive, and have high reliability to both thermal cycling and mechanical shock and vibration.

To allow for enhanced heat distribution within the assembly, as well as enhanced warpage control to prevent warpage of the chip and/or substrate and other mechanical failure, the materials forming the heat distribution device <NUM> and the stiffener element <NUM> can additionally or alternatively be coordinated to compensate for one another. The heat distribution device <NUM> (and TIM <NUM>) can control heat distribution within assembly <NUM>, thereby making a heat distribution device formed from a high thermally conductive material desirable. The stiffener element <NUM> can control warpage of substrate <NUM> and components within the assembly making a stiffener element <NUM> formed from a material having a high CTE desirable. Additionally, stiffener element <NUM>, in combination with first adhesive 2038A having a higher modulus of elasticity than the modulus of elasticity of the second adhesive 2038B, can further provide greater warpage control of substrate <NUM> and components within the assembly. In one example, the material or combination of materials forming heat distribution device <NUM> can differ from the material or combination of materials forming stiffener <NUM>. For example, the thermal conductivity of the material forming the heat distribution device <NUM> may be higher than the thermal conductivity of the material forming stiffener element <NUM>, but the CTE of the material forming heat distribution device <NUM> may be lower than the CTE of the material forming stiffener element <NUM>. In some examples, the thermal conductivity of the material forming heat distribution device <NUM> can be at least <NUM> percent greater than the thermal conductivity of the material forming stiffener element <NUM>. Additionally, the CTE of the material forming stiffener <NUM> may be at least <NUM> percent greater than the CTE of the material forming heat distribution device <NUM>. In still other examples, the CTE of stiffener element may be at least two times greater than the CTE of the heat distribution device <NUM>.

The below Table <NUM> lists the CTE and thermal conductivity of several common materials.

Materials identified on this chart indicate that a stiffener element <NUM> formed from copper, which will help to control warpage, can be paired with a heat distribution device <NUM> formed from silver diamond (e.g., AgD) the combination of which will help to achieve the highest thermally conductive assembly <NUM>. Further, in combination with a first adhesive 2038A which joins the stiffener element to the substrate, and the second adhesive 2038B which joins the stiffener element to the heat distribution device <NUM>, stiffener <NUM> can also help to compensate for CTE mismatch of the heat distribution device and stiffener element and the substrate <NUM>. As noted from Table <NUM> above, silver diamond has one of the highest thermal conductivities at 900Wm/K, but the lowest CTE of <NUM> ppm/K. While silver diamond is highly effective at distributing or transferring heat, its ability to control warpage is low. Thus, while it may be desirable to select silver diamond due to its high thermally conductive properties, depending on the application and structure of the assembly, use of silver diamond alone could result in possible warpage of the substrate and other mechanical failures within the assembly. Selection of a material that has a greater CTE than silver diamond in at least the structures disclosed herein can better help to control warpage. In one example, a Copper material (e.g., Cu, CuOFE) with a CTE of <NUM> ppm/K and a thermal conductivity of <NUM> w/mK can be selected. The high CTE of copper can offset the low CTE of silver diamond. Further, copper possesses one of the highest thermal conductivities of the remaining components on the chart and has the added advantage of distributing heat within the chip assembly <NUM>. Thus, the combination of a copper stiffener element <NUM> and silver diamond heat distribution device <NUM> can help to achieve optimal thermal conductivity and warpage control in a chip package. Other combinations of material are also contemplated within the scope of this disclosure, examples of which are discussed in more detail below.

With reference to <FIG>, results from testing chip assemblies are shown in a chart. The chart illustrates how use of a silver diamond heat distribution device and a copper stiffener can achieve optimal results, as compared to a monolithic heat distribution device. The monolithic heat distribution device may be formed from a single material and combine the structure of the heat distribution device and stiffener into one integral heat distribution device within the assembly. The chart highlights the resulting warpage of a substrate due to CTE mismatch between the substrate and the heat distribution device /stiffener. In particular, the chart shows warpage results of a substrate A1 in a chip assembly attached to a heat distribution device A2 formed entirely of either copper or silver diamond. Similarly, the warpage results of a substrate B1 within an assembly B, in which a heat distribution device B2 is formed of silver diamond, and a separate stiffener B3 is formed from copper are shown.

At room temperature of <NUM>° C, the warpage of a substrate A1 in assembly A that results from use of an "u-shaped" all copper heat distribution device A2 is approximately <NUM> microns. The warpage of a substrate A1 in assembly A that results from use of a "u-shaped" all silver diamond heat distribution device A2 is approximately <NUM> microns. The warpage of a substrate B1 in assembly B that results from use of a combined planar silver diamond heat distribution device B2, in combination with a copper stiffener B3, and first and second adhesives B1A and B1B is approximately <NUM> microns. In this simulation, first adhesive 2038A has a modulus of elasticity that is greater than the modulus of elasticity of the second adhesive 2038B. Similar results at a high temperature of <NUM>° C show the similarity in warpage of the substrate B2 in an assembly B utilizing a silver diamond heat distribution device B2 and copper stiffener B3, as compared to warpage of a substrate A1 in an assembly A utilizing an all copper and "u-shaped" heat distribution device.

These test results reveal several improvements that result from the use of such a combined silver diamond heat distribution device and copper stiffener. The combined silver diamond heat distribution device <NUM> with copper stiffener <NUM> demonstrates warpage properties that are similar to an all copper heat distribution device. This is advantageous because the enhanced warpage control is possible with the silver diamond/Copper combination, while still allowing for the greatly enhanced thermally conductive properties of the silver diamond heat distribution device. Further, as a pure metal, copper already possesses one of the highest thermally conductive properties, making copper a desirable material to further assist with thermal conductivity in the assembly.

Cost can be reduced by use of the combination silver diamond heat distribution device and copper stiffener. Silver diamond is an expensive material. Using copper as the material forming stiffener element <NUM>, in place of a traditional "u-shaped" all silver diamond heat distribution device (such as heat distribution device A1; <FIG>), allows for a reduction in the material volume of silver diamond necessary to form the components. This in turn, minimizes the overall cost.

Ease of manufacturing is also realized by the silver diamond and copper combination. By using a planar heat distribution device <NUM>, instead of a "u-shaped" heat distribution device, it is easier to attach heat distribution device <NUM> to chip <NUM>. Better bond line thickness control of the TIM <NUM> between chip <NUM> and heat distribution device <NUM> can be achieved. For example, consistent bond line thickness of <NUM> and <NUM> microns can be obtained.

Additional combinations of materials can be considered to achieve both enhanced warpage control and thermal conductivity. Optimal results can be obtained by considering combinations of materials, in which thermal conductivity of the materials is at least the same or greater than copper. For example, while silver diamond may be preferred due to its internal properties of being one of the highest thermally conductive materials, it may be possible to obtain optimal warpage and thermal conductivity by selection of a copper material for stiffener, and a Copper Diamond or Aluminum Diamond material for the heat distribution devices. In still other examples, different materials can be selected for the stiffener to compensate for differences in thermal expansion of the package. For example, when it is desired to offset a low CTE of the material forming the heat spreader and to help maintain warpage control of the substrate and overall package, a stiffener can be selected with a high CTE that can either match or exceed the CTE of the material forming the heat spreader. The can help to compensate for a low CTE of the material forming the heat spreader. Additionally, the stiffener, in combination with the first and second adhesives, can help make up for CTE mismatch. Other combinations of materials achieving similar results can also be obtained based on aspects of the disclosure, including metal alloys or combinations of other materials not listed here.

Another example structure, according to aspects of the disclosure, is configured to achieve optimal heat distribution and warpage control. As shown in <FIG>, microelectronic device assembly <NUM> includes a substrate <NUM> supporting the assembly <NUM>, a stiffener element <NUM>, at least one microelectronic element or chip <NUM>, and a heat distribution device <NUM>. A first adhesive 2138A joins a bottom surface <NUM> of stiffener <NUM> to the top surface <NUM> of substrate <NUM>. A second adhesive 2138B joins a top surface <NUM> of stiffener <NUM> to the bottom surface <NUM> of heat distribution device <NUM>.

The components in assembly <NUM> possess the same characteristics as assembly <NUM> in <FIG>, differing only in the configuration of the heat distribution device <NUM>, relative to the other components in the assembly. As shown, outermost edges <NUM> of heat distribution device <NUM> are laterally spaced a distance 2168A and 2168B away from edge <NUM> of stiffener element <NUM>. In this example, distance 2168A and 2168B are the same, but in other examples the distances 2168A and 2168B may differ. In still another example, only one edge <NUM> of the heat distribution device <NUM> may be laterally spaced away from the outer edge <NUM> of stiffener <NUM> and the other edge <NUM> of the heat distribution device may be aligned with edge <NUM> of stiffener element <NUM>.

Turning to <FIG> according to aspects of the disclosure, an example microelectronic device assembly <NUM> includes a substrate <NUM> supporting the assembly <NUM>, a stiffener element <NUM>, at least one microelectronic element or chip <NUM>, a TIM <NUM>, and a heat distribution device <NUM>. A first adhesive 2238A can join a bottom surface <NUM> of stiffener <NUM> to the top surface <NUM> of substrate <NUM>. A second adhesive 2238B can join and bond a top surface <NUM> of stiffener <NUM> to the bottom surface <NUM> of heat distribution device <NUM>. As in the previous embodiment, the components in assembly <NUM> possess the same characteristics as assembly <NUM> in <FIG>, differing only in the height of chip <NUM> and the configuration of the heat distribution device <NUM>, relative to the other components in the assembly. As shown, chip <NUM> may be thinned by grinding, etching, milling or any known methods of die thinning. As a result, chip <NUM> has a height H10 that is less than a height H12 of stiffener <NUM>. To compensate for this difference in height, heat distribution device <NUM> may include a central portion <NUM> that extends away from primary bottom surface <NUM> of heat distribution device. The central portion <NUM> is sized to completely cover and extend across rear surface <NUM> of chip <NUM>, but in other examples, only a portion of bottom surface <NUM> may be covered. Edges <NUM> of heat distribution device <NUM> may be aligned with edge <NUM> of stiffener <NUM>. In other examples, one or more heat distribution devices <NUM> may be laterally offset from edge <NUM> of stiffener element <NUM>.

<FIG> provide another example microelectronic device assembly <NUM> according to aspects of the disclosure. The device assembly includes a substrate <NUM> supporting the assembly <NUM>, a stiffener element <NUM>, at least one microelectronic element or chip <NUM> and a heat distribution device <NUM>. The chip <NUM> may have a rear surface <NUM>. A first adhesive 2338A can join a bottom surface <NUM> of stiffener <NUM> to the top surface <NUM> of substrate <NUM>. A second adhesive 2338B can join a top surface <NUM> of stiffener <NUM> to the bottom surface <NUM> of heat distribution device <NUM>.

The components in assembly <NUM> possess the same characteristics as assembly <NUM> in <FIG>, differing only in the configuration of the heat distribution device <NUM>, relative to the other components in the assembly.

Heat distribution device <NUM> includes a top surface <NUM>, a bottom surface <NUM>, and an interior peripheral edge <NUM> extending between the top surface <NUM> and bottom surface <NUM>. Interior peripheral edge extends around an aperture 2339A. Another aperture 2339B extends through the top and bottom surfaces <NUM>, <NUM> and is defined by interior peripheral edge <NUM>. Interior peripheral edge <NUM> of heat distribution device <NUM> extends beyond interior edge <NUM> of stiffener element <NUM>, such that in a top plan view, such as shown in <FIG>, only microelectronic element <NUM> and substrate <NUM> are visible through aperture <NUM>. Stiffener element <NUM> is not visible from a top plan view. Further, aperture 2339A and aperture 2339B are aligned with one another.

Enhanced heat distribution, in combination with enhanced warpage control, may be further achieved by coordinating the selection of the material or combination of materials forming the heat distribution device, in combination with the selection of the material or combination of materials forming the stiffener in any of the additional chip assemblies disclosed in <FIG>, as well as any of the assemblies previously disclosed herein. As discussed, the thermal conductivity of the material forming any one of the heat distribution device in these examples may be higher than the thermal conductivity of the material forming the stiffener, but the coefficient of thermal expansion of the material forming the heat distribution device may be lower than the coefficient of thermal expansion of the material forming stiffener. This can allow for optimal heat distribution and warpage control in the package. In one example, optimal results can be achieved by use of a silver diamond material to form heat distribution device and a copper material to form the stiffener, but other combinations are available according to aspects of the disclosure.

To summarize the foregoing, according to a first aspect of the disclosure, a method of manufacturing a chip assembly comprises joining an in-process unit to a printed circuit board, the in-process unit comprising: a substrate having an active surface, a passive surface, and contacts exposed at the active surface; an interposer electrically connected to the substrate; a plurality of semiconductor chips overlying the substrate and electrically connected to the substrate through the interposer, and a stiffener overlying the substrate and having an aperture extending therethrough, the plurality of semiconductor chips being positioned within the aperture; reflowing a bonding material disposed between and electrically connecting the in-process unit with the printed circuit board, the bonding material having a first reflow temperature; and then joining a heat distribution device to the plurality of semiconductor chips using a thermal interface material ("TIM") having a second reflow temperature that is lower than the first reflow temperature; and/or.

According to a second aspect of the disclosure, a microelectronic assembly comprises: a substrate having an active surface, a passive surface, and contacts exposed at the active surface; a plurality of semiconductor chips overlying the substrate; a heat distribution device, the heat distribution device including a base, thermally conductive fins extending upwardly from the base, and a lid overlying and at least partially enclosing the plurality of thermally conductive fins within the base, wherein at least the base is formed from a first material having a first thermal conductivity greater than <NUM> W/m2, and wherein at least one of the lid and the plurality of thermally conductive fins is formed from a second material having a second thermal conductivity of less than <NUM> W/m2 or less; a thermal interface material ("TIM") disposed between the heat distribution device and the plurality of semiconductor chips, wherein the coefficients of thermal expansion of at least one of the plurality of semiconductor chips and the base are substantially similar or identical; and a printed circuit board electrically connected to the substrate; and/or.

According to a third aspect of the disclosure, a microelectronic device assembly comprises: a substrate; and a plurality of microelectronic elements connected to the substrate, the plurality of microelectronic elements having an active surface facing toward the substrate and a passive surface facing away from the substrate, wherein one or more cavities extend through at least one surface of the plurality of microelectronic elements, and wherein the one or more cavities are filled with a thermally conductive material to dissipate heat from the plurality of microelectronic elements; and/or.

According to a fourth aspect of the disclosure, a chip assembly comprises: a substrate; a plurality of semiconductor chips electrically connected to the substrate, each of the plurality of semiconductor chips having an active surface facing toward the substrate and a passive surface facing away from the substrate; and, a heat distribution device joined to the plurality of semiconductor chips, the heat distribution device including a plurality of thermally conductive fins, wherein a first fin length of at least some of the plurality of thermally conductive fins is greater than a second fin length of remaining fins of the plurality of thermally conductive fins, wherein a first height of at least one of the plurality of semiconductor chips is less than a second height of the others of the plurality of semiconductor chips, and wherein the at least some of the plurality of thermally conductive fins have a first fin length overlying the plurality of semiconductor chips having the first height; and/or.

According to a fifth aspect of the disclosure, a method of assembling a cooling loop assembly to an in-process unit comprises: joining a plurality of in-process units to a circuit board, each in-process unit including: a substrate; at least one microelectronic element electrically connected to the substrate, the microelectronic element having an active front surface facing toward the substrate and an opposed rear surface facing away from the substrate;, joining a plurality of heat distribution devices to corresponding ones of the plurality of in-process units, each of the plurality of heat distribution devices including an inlet and an outlet; and bonding a cooling loop assembly to the inlet and outlet of each of the plurality of heat distribution devices, the cooling loop assembly including a network of fluid lines connected to each inlet and each outlet; and/or.

According to the sixth aspect of the disclosure, a microelectronic device assembly comprises: a substrate; a microelectronic element electrically connected to the substrate, the microelectronic element having an active surface facing toward the substrate and a rear surface facing away from the substrate, a stiffener element overlying the substrate and extending around the microelectronic element, the stiffener element comprised of a first material having a first coefficient of thermal expansion ("CTE"); and a heat distribution device overlying the rear surface of the microelectronic element and a surface of the stiffener element facing toward the heat distribution device, the heat distribution device comprised of a second material having a second CTE; and wherein the first material is different than the second material, wherein the first CTE of the first material of the stiffener element is greater than the second CTE of the second material of the heat distribution device; and/or.

Claim 1:
A method of manufacturing a chip assembly comprising:
joining an in-process unit to a printed circuit board (<NUM>), the in-process unit comprising:
a substrate (<NUM>) having an active surface, a passive surface, and contacts exposed at the active surface;
an interposer (<NUM>) electrically connected to the substrate;
a plurality of semiconductor chips (140A, 140B, 140C) overlying the substrate and electrically connected to the substrate through the interposer, and
a stiffener (<NUM>) overlying the substrate and having an aperture extending therethrough, the plurality of semiconductor chips being positioned within the aperture;
reflowing a bonding material (<NUM>) disposed between and electrically connecting the in-process unit with the printed circuit board, the bonding material having a first reflow temperature; and then joining a heat distribution device (<NUM>, <NUM>) to the plurality of semiconductor chips using a thermal interface material ("TIM") (<NUM>) having a second reflow temperature that is lower than the first reflow temperature.