Patent Description:
In a broad range of applications, printed wiring boards (PWBs) are used to support and interconnect electronic components. Individual electronic components as well as electronic modules, which include electronic components packaged together, as electronic modules. A stiffener is a frame that is used to provide mechanical support to a PWB. Generally, a stiffener should provide the necessary structural support without adding too much weight. <CIT> relates to a mounting structure for a Large Scale Integrated Circuit chip.

In one embodiment, an electronic assembly is defined in claim <NUM> and includes a printed wiring board (PWB), and a stiffener secured to the PWB. The stiffener includes one or more tray sections. One or more electronic modules is secured respectively to the one or more tray sections of the stiffener.

Additionally or alternatively, in this or other embodiments wedge locks secure the stiffener based on compressive force.

Additionally or alternatively, in this or other embodiments a first wedge lock mounting rail supports a first set of the wedge locks, and a second wedge lock mounting rail supports a second set of the wedge locks.

Additionally or alternatively, in this or other embodiments a first edge of the stiffener forms the first wedge lock mounting rail, and a second edge of the stiffener forms the second wedge lock mounting rail.

Additionally or alternatively, in this or other embodiments a material of the stiffener is aluminum alloy.

Additionally or alternatively, in this or other embodiments screws affix the one or more electronic modules respectively to the one or more tray sections of the stiffener.

Additionally or alternatively, in this or other embodiments screws affix the stiffener to the PWB.

Additionally or alternatively, in this or other embodiments an adhesive film adheres the stiffener to the PWB.

Additionally or alternatively, in this or other embodiments one or more thermal pads are disposed between each of the one or more electronic modules and respective ones of the one or more tray sections of the stiffener.

In another embodiment a method of assembling an electronic assembly is defined in claim <NUM> and includes fabricating a stiffener with one or more tray sections, and securing the stiffener to a printed wiring board (PWB). One or more electronic modules is respectively secured to the one or more tray sections of the stiffener.

Additionally or alternatively, in this or other embodiments wedge locks are arranged to secure the stiffener based on compressive force.

Additionally or alternatively, in this or other embodiments the first wedge lock mounting rail is formed from a first edge of the stiffener, and the second wedge lock mounting rail is formed from a second edge of the stiffener.

Additionally or alternatively, in this or other embodiments the stiffener is fabricated from aluminum alloy.

Additionally or alternatively, in this or other embodiments the one or more electronic modules is respectively affixed to the one or more tray sections of the stiffener using screws.

Additionally or alternatively, in this or other embodiments the stiffener is affixed to the PWB using screws.

Additionally or alternatively, in this or other embodiments the stiffener is adhered to the PWB using an adhesive film.

As previously noted, PWBs support and interconnect electronic components individually or packaged together in an electronic module. Generally, some electronic components (e.g., resistors, capacitors) may dissipate less heat than others (e.g., diodes, magnetics) and may dissipate much less heat than electronic modules (e.g., direct current (DC)-DC converters, transistors, metal oxide field effect transistors (MOSFETs), silicon carbide MOSFETs (SiCFETs)) that house many components. Embodiments detailed herein relate to a conductive thermal management architecture employing a stiffener of a PWB. The exemplary electronic modules that are discussed for explanatory purposes are DC-DC converters. However, conductive heat transfer facilitated by the architecture detailed herein is equally applicable to other electronic modules and individual electronic components. Exemplary applications of these embodiments include deep space, underwater-based, and ground-based applications. The heat dissipation requirement, rather than the specific application, drives the use of the PWB assembly according to one or more embodiments.

<FIG> is an exploded view of a PWB assembly <NUM> according to one or more embodiments. Six electronic modules <NUM> sit on six thermal pads <NUM>. The six thermal pads <NUM> fit on tray sections <NUM> of a stiffener <NUM>. The stiffener <NUM> is adhered to the PWB <NUM> by an adhesive film <NUM>. Edges of the stiffener <NUM> act as wedge lock mounting rails <NUM> for wedge locks <NUM> (<FIG>). Heat generated by the electronic modules <NUM> flows through the thermal pads <NUM> to the tray sections <NUM> and eventually flows to the wedge lock mounting rails <NUM>, which act as heat sinks.

While six electronic modules <NUM> and corresponding thermal pads <NUM> and tray sections <NUM> are shown for explanatory purposes, the PWB assembly <NUM> is scalable. That is, the size of the tray sections <NUM>, their number, and their location may be changed. Generally, relatively high heat-dissipating electronic components (e.g., diodes, magnetics) and electronic modules <NUM> are placed closer to the wedge lock mounting rails <NUM> to improve heat flow while lower heat-dissipating electronic components (e.g., resistors, capacitors) may be placed closer to the center of the PWB <NUM> and farther from the wedge lock mounting rails <NUM>. In addition, lower heat-dissipating electronic components may be placed directly on the PWB <NUM> rather than on a tray section <NUM>. In the exemplary case of the electronic modules <NUM> being DC-DC converters, the six exemplary DC-DC converters dissipate a total of <NUM> watts. Thermal analysis may be performed to verify that temperature requirements for a particular application are met by a given arrangement within a PWB assembly <NUM>.

<FIG> show two sides of the stiffener <NUM> according to an exemplary embodiment. In the exemplary embodiment, the stiffener <NUM> includes six tray sections <NUM>. <FIG> shows one side of the stiffener <NUM> referred to, for explanatory purposes, as an upper side <NUM>. The view of <FIG> indicates that the tray sections <NUM> are recessed to accommodate the electronic modules <NUM>. Exemplary dimensions of the tray section <NUM> to accommodate a DC-DC converter may be on the order of <NUM> inches for the length L, <NUM> inches for the width W, and <NUM> inches for the depth D. The tray section <NUM> may have a thickness on the order of <NUM> inches. The heat dissipation capability of the tray section <NUM> is not proportional to its thickness. The dimensions of the entire stiffener <NUM> may be on the order of <NUM> inches long and <NUM> inches wide in the exemplary case of accommodating six electronic modules <NUM>. The stiffener <NUM> includes holes <NUM> that are used to secure the stiffener <NUM> to a PWB <NUM>. Each tray section <NUM> is shown to include a hole <NUM> at each of the four corners to secure an electronic module <NUM> (<FIG>) to the tray section <NUM>. Each tray section <NUM> also includes gaps <NUM> to accommodate wires and pins. For example jumper wires from the module <NUM> can be passed through the gaps <NUM> and soldered to the PWB <NUM>.

<FIG> shows a side of the stiffener <NUM> opposite the upper side <NUM> that is referred to, for explanatory purposes, as a lower side <NUM>. The lower side <NUM> of the stiffener <NUM> is the side that is adhered to the PWB <NUM> by the adhesive film <NUM>. Each tray section <NUM> may be machined such that the stiffener <NUM> is a single metallic structure. Because the tray sections <NUM> are integral parts of the stiffener <NUM>, thermal interface resistance is eliminated between each tray section <NUM> and the stiffener <NUM>. Elimination of the thermal interface resistance facilitates dissipation of higher heat than if the tray sections <NUM> were not part of the stiffener <NUM> (i.e., if there were thermal interface resistance). The material used for the stiffener <NUM> may be aluminum alloy, for example, because of the heat conduction properties and relatively light weight (e.g., compared with copper). Series <NUM>, <NUM>, and <NUM> aluminum alloy may be used according to exemplary embodiments. The stiffener <NUM> serves a structural function in addition to a thermal one. Based on the specific application and related specifications for the PWB assembly <NUM>, the stiffener <NUM> must provide sufficient support to comply with vibration and pyroshock requirements. Structural analysis may be performed to ensure that the PWB assembly <NUM> meets structural requirements for a particular application.

<FIG> shows thermal pads <NUM> covering tray sections <NUM> of the stiffener <NUM> according to one or more embodiments. The thermal pads <NUM> are sized the same as the tray sections <NUM> of the stiffener <NUM> and are be placed on the tray sections <NUM> rather than being fastened or adhered. The thickness of the thermal pads <NUM> may be on the order of <NUM> inches, for example. The surface of the module <NUM> that would contact the tray section <NUM> directly, as well as the surface of the tray section <NUM> itself, are not entirely smooth. Thus, without the thermal pad <NUM> between each module <NUM> and the corresponding tray section <NUM>, there would be an imperfect contact and, consequently, reduced heat flow between the module <NUM> and the tray section <NUM>. The thermal pads <NUM> reduce thermal interface resistance and thereby increase the heat dissipation capability of the PWB assembly <NUM>.

<FIG> shows modules <NUM> on the thermal pads <NUM> shown in <FIG>. Each exemplary module <NUM> is a DC-DC converter whose pins <NUM> extend into the gaps <NUM> on either side of each tray section <NUM> of the stiffener <NUM>. Cross-sections A-A and B-B are respectively detailed in <FIG> is a cross-sectional view through A-A as indicated in <FIG>. The gap <NUM> on each side of the tray section <NUM> and the pins <NUM> in the gaps <NUM> are visible. The thermal pad <NUM> between the module <NUM> and the tray section <NUM> of the stiffener <NUM> is also visible in the view shown in <FIG> is a cross-sectional view through B-B as indicated in <FIG>. As <FIG> indicates, the cross-section B-B aligns with the holes <NUM> used to secure the module <NUM> to the stiffener <NUM>. These are visible on either side of the module <NUM> in <FIG>. A cross-section of the wedge lock mounting rail <NUM> is also visible in <FIG>.

<FIG> show two different views of the PWB assembly <NUM> according to one or more embodiments. <FIG> shows an isometric view of the PWB assembly <NUM>. The wedge locks <NUM> are installed by applying torque on a wedge lock screw (not shown). The torque subjects the wedge locks <NUM> to both axial and normal force. The normal force is transferred to the stiffener <NUM> as a compressive force that ensures that the stiffener <NUM> is held firmly in place in a chassis of an electronic box, for example. The wedge locks <NUM> are supported by the wedge lock mounting rails <NUM> shown in <FIG>. <FIG> is a top-down view of the PWB assembly <NUM>. The screws <NUM> that fit in the holes <NUM> (<FIG>) to affix the electronic modules <NUM> to the stiffener <NUM> are visible. The screws <NUM> that fit in the holes <NUM> (<FIG>) to affix the stiffener <NUM> to the PWB <NUM> are also visible. The cross-section C-C indicated in <FIG> is shown in <FIG>.

<FIG> is a side view of the PWB assembly <NUM> according to one or more embodiments. An expanded view of a portion of the side view is also shown. The side view shows the wedge lock mounting rail <NUM> below the wedge locks <NUM>. This wedge lock mounting rail <NUM> is a portion of the stiffener <NUM> that extends as an edge as shown in <FIG>. As previously noted, compressive force exerted by the wedge locks <NUM> hold the stiffener <NUM> firmly in place on the PWB <NUM>. The adhesive film <NUM> between the stiffener <NUM> and the PWB <NUM>, as well as the screws <NUM> (<FIG>) also ensure attachment of the stiffener <NUM> and PWB <NUM>.

<FIG> is a cross-sectional view of the PWB assembly <NUM> through C-C as indicated in <FIG>. Arrows are used to indicate the heat transfer that takes place in the PWB assembly <NUM> according to one or more embodiments. Heat emitted by the electronic module <NUM> flows into the tray section <NUM> of the stiffener <NUM>. As previously noted, the thermal pad <NUM> reduces thermal interface resistance between the electronic module <NUM> and the tray section <NUM> and, thereby, increases heat dissipation. The heat directed into the tray section <NUM> of the stiffener <NUM> is then directed to the edge of the stiffener <NUM>, the wedge lock mounting rail <NUM>. Thus, the wedge lock mounting rail <NUM> serves as a heat sink for the heat source (i.e., electronic module <NUM>). The temperature of the wedge lock mounting rail <NUM> is controlled by a convective heat sink, a radiative heat sink, or both, for example.

Claim 1:
An electronic assembly comprising:
a printed wiring board, PWB (<NUM>);
a stiffener (<NUM>) secured to the PWB, wherein the stiffener includes one or more tray sections (<NUM>) formed as integral parts of the stiffener (<NUM>) and with gaps (<NUM>) on two sides of each of the one or more tray sections (<NUM>); and
one or more electronic modules (<NUM>) secured respectively onto the one or more tray sections of the stiffener.