Thermal management plate

A thermal management plate designed to take advantage of the thermally conductive path provided as an integral part of printed circuit board component assemblies. The plate is a shelf-like unit providing both thermal management of electronic assemblies and a mounting arrangement for assemblies. Manufactured of high conductive material, the unit includes a printed circuit board assembly locator, a thermal path and a series of finned surfaces on the front and rear to dissipate heat generated by components.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to cooling of the electronic or 
telecommunications equipment and more particularly to a thermal management 
plate useful for mounting printed circuit board assemblies as well as 
providing heat dissipation. 
2. Background Art 
Historically, telecommunications and similar electronic equipment has been 
free convection cooled. Although the amount of heat that can be dissipated 
is relatively low, this has been acceptable because power dissipation 
densities typically were very low. 
With increased power densities, forced convection (fan) cooling was 
introduced. Though satisfactory equipment cooling is provided by the 
forced convection method, this method has a number of drawbacks. These 
drawbacks include cost, being added in the form of fans, their necessary 
mounting hardware and the required failure detection circuitry that must 
be provided. The reliability of fans must be considered and accordingly 
appropriate maintenance techniques must be developed. Beacuse of the 
questionable reliability of fan devices, fan failure detection and alarm 
equipment must be provided if system degradation can result if and when a 
fan failure occurs. Finally, in many instances, acoustic noise is 
generated by the fan type devices and in many office environments such 
noise may be considered objectionable. 
With the rapid expansion of miniaturization techniques in the electronics 
field, electronic systems have been constructed utilizing smaller and 
smaller components. While these components are smaller they individually 
dissipate more power than many of the larger components previously 
utilized. Thus, a desirable trend is to form the assembly of the printed 
circuit board and its related components with an arrangement that mounts 
and interconnects these components to provide a thermally conductive plane 
as an integral part of the unit. Accordingly it is the object of the 
present invention to provide a thermal management plate that allows the 
thermal coefficient of expansion of the component and its mountings to be 
matched as well as to improve local thermal management at a high power 
density device by conducting heat away from it. 
SUMMARY OF THE INVENTION 
The thermal management plate of the present invention is designed to take 
advantage of the thermally conductive path provided as an integral part of 
many printed circuit board component assemblies. Such printed wiring cards 
on which the components are mounted contain a conductive heat transfer 
surface--aluminum or copper sheet or plate. Through its use, heat is 
carried from the assemblies to the thermal management plate and via 
conduction heat transfer to the exterior of the basic electronics 
enclosure enclosing all of the printed circuit boards, where it is 
dissipated via convection and radiation heat transfer. The thermal 
management plate of the present invention offers the reliability of free 
convection heat transfer in that it is a "benign" approach requiring no 
power and with no associated failure rates that must be considered in this 
design. 
A part of the present invention of the thermal management plate is a 
shelf-like unit that provides both for thermal management of electronic 
assemblies and a mounting arrangement for them. The thermal management 
plate is made of high conductivity materials and includes a series of 
finned surfaces to dissipate heat generated by the components. 
In actual practice, printed circuit board assemblies are positioned between 
two thermal management plates. It will be obvious, therefore, that a given 
printed circuit board assembly is thermally conducting to two plates and 
the dissipation to the outside environment occurs at the four finned areas 
that protrude through the system enclosure. Because adjacent printed 
circuit board assemblies share common thermal management plates, the 
tendency will be to create an iso-thermal condition through conductive 
coupling. If the distance between the printed circuit board assembly and 
the outside of the enclosure is relatively large, or the thermal 
conductivity of the thermal management plate is not sufficient to conduct 
the heat to the fins, heat pipes may be incorporated in the thermal 
management plate structure. This arrangement would allow the amount of 
metal utilized in the thermal management plate to be reduced, thus 
lowering costs and weight without sacrificing thermal management.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, the thermal management plate 1 of the present 
invention is a shelf-like unit providing both for thermal management of 
electronic assemblies and as well as a mounting arrangement for them. In 
this manner it functions similar to a card file. The thermal management 
plate of the present invention may be manufactured of high conductive 
material, such as aluminum, and provides both locator and thermal paths 
for printed circuit board assemblies. 
A series of finned surfaces 2 and 3 located at the front and rear, 
respectively, are provided to dissipate heat generated by the components 
mounted on the associated printed circuit board assemblies for which the 
thermal management plate 1 provides mounting. 
Also included in the thermal management plate 1 are a plurality of printed 
circuit board assembly locator and thermal path connectors, such as 4, an 
optional latching groove, such as 5, may also be included as well as 
thermal insulators 6 and 7. 
In practice, printed circuit board assemblies, such as 21, 22, and 23, are 
positioned between thermal management plates, such as 1 and 11. Obviously, 
therefore, a given, printed circuit board assembly, such as 22, is shown 
as thermally conducting to two plates (1 and 11) and the heat dissipation 
to the outside environment occurs at the four finned areas 8, 9, 18 and 
19, respectively. Because adjacent printed circuit board assemblies share 
common thermal management plates, the tendency would be to create an 
iso-thermal condition through conductive coupling. Thus, if the distance 
between the printed circuit board assembly and the outside of the 
enclosure is relatively large, or the thermal conductivity of the thermal 
management plate is insufficient to conduct heat to the fins, it may be 
useful to insert heat pipes 12 that may be incorporated into the thermal 
management plate structure, base plates. This would permit the amount of 
metal used in the thermal management plate to be reduced thus reducing 
cost and weight without sacrificing the necessary thermal management. 
The thermal management plate of the present invention relies on forming a 
good conductive coupling between the printed circuit board assembly and 
the thermal management plate as may be seen by reference to FIG. 3. In 
FIG. 3, a portion of a thermal management plate 31 is shown with two 
printed circuit board assemblies 33 and 34 mounted thereon. To ensure good 
conductive coupling, the printed circuit board assemblies, such as 33 and 
34, rest against a combination locator and thermal path unit, such as 35 
and 36, respectively, on one surface only. This arrangement is unlike 
conventional card guides that are designed to loosely entrap a printed 
circuit board assembly. The surface of engagement between a printed 
circuit board assembly 33 and the locator and thermal conductive path unit 
35 is critical, but ensured by having the locator have a machined surface 
that represents a reference plane. By establishing a reference plane to 
the surface of the printed circuit board assembly connector, good 
conductive contact between the printed circuit board assemblies is 
guaranteed regardless of the thickness of the printed circuit board 
assembly. These are shown by the indicies t.sub.1 and t.sub.2 in FIG. 3. 
Through the application of a force F, the surface of the printed circuit 
board assembly, such as 33 and 34, is driven against the associated 
locator, such as 35 and 36, establishing a major heat conductive path Q2 
in the upper and lower plates. Additional a minor path Q1 is also 
established by the printed circuit board assembly by virtue of its resting 
on the lower plate portion of the thermal management plate 31. The 
distance between printed circuit board assembly locators, such as P, is 
chosen to allow force F to be applied and to allow at the same time 
minimum printed circuit board assembly spacing. For example, if the 
minimum of printed circuit board assembly spacing is 0.500", P may be 
chosen at 0.250" to allow printed circuit board assembly spacings of any 
0.250" multiple. 
Referring now to FIGS. 4, 5 and 6, a variety of mechanical means may be 
used to force the printed circuit board assembly against its associated 
locator. A self-locking wedge approach, as shown in FIG. 4, provides a 
number of advantages when used to provide this force. The wedges, such as 
41 and 42, mounted directly on the printed circuit board assembly card 40 
and a permit a limited sliding motion with respect to the printed circuit 
board assembly. The taper on the wedge is matched by the taper on the 
printed circuit board locator, as is present in wedges 51, ect., as shown 
in FIG. 5. Thus, after the printed circuit board assembly is inserted into 
its associated backplane connector, the wedges are slid to engage both an 
unused printed circuit board assembly locator, such as 51, and the card. 
The resulting wedging action creates an intimate contact between the 
printed circuit board assembly and the locator it shares a reference plane 
with. If the sliding wedge is formed from a thermally conductive material, 
another heat path is then created between the thermal management plate 
locator it is wedging against and the printed circuit board assembly, as 
shown as Q3 in FIG. 3. The taper of the wedge is chosen so that the wedge 
is self-locking and acts as a lock to the printed circuit board assembly. 
An alternate version of locator construction is shown in FIG. 6 in which 
the locator taper is affected by a number of contact ridges of varying 
heights arranged in a wedge-like configuration. 
An enclosure in which the thermal management plates in accordance with the 
present invention are mounted is shown in FIG. 7. The enclosure 70 is 
designed to allow finned areas, such as 73, 74, 75, 76 and 77, to extend 
through the enclosure door 71. In this manner heat can be dissipated to 
the surrounding environment by convection and radiation heat transfer. It 
may be possible because of particular engineering requirements that the 
configuration of the thermal management plate extending from the front of 
the enclosure may be different from that of the rear. It may be desirable 
to configure the thermal management plate so the greatest temperatures 
appear at the rear where the finned areas can be much larger because the 
printed circuit board assemblies do not have to be inserted passed them 
and the front is relatively cool with a minimum appearance impact. 
Reference to FIG. 8 shows a similar enclosure 80 with doors 81 and 82 in 
the open positions and by way of openings, such as 83, 84, 85, 86, 87 and 
88. The finned areas of thermal management plates, such as 93, 94, 95, 96, 
97 (when doors 81 and 82 are closed) project through the respective 
openings. 
From the foregoing it will be apparent that benign, high reliability 
conduction, convection and radiation heat transfer means are provided by 
the present invention to cool electronic components. Because of the 
included design, assemblies of various thicknesses can be easily 
accommodated. Selective electromagnetic induction shielding can also be 
provided to reduce the cost of such shielding. It should also be noted 
that through the use of heat pipes in the plate and a rear enclosure door 
containing liquid cooling tubes, a zoned, heat dissipation assembly could 
be obtained where conductivity problems are even greater than those 
envisioned by the basic concept, can be solved. 
While but a single embodiment of the present invention has been shown it 
will be obvious to those skilled in the art that numerous modifications 
may be made without departing from the spirit of the present invention 
which shall be limited only by the scope of the claims appended hereto.