Fluid cooled thermal management technique for a high-density composite focal plane array

A fluid cooled thermal management technique for a high-density composite focal plane array (CPFA) is disclosed. In one embodiment, a high density CFPA assembly includes a plurality of imaging dies mounted on a front surface of a printed wiring board (PWB) and a base plate. The base plate has a substantially matched coefficient of thermal expansion (CTE) to that of the high density CFPA. Further, the high density CFPA is disposed on a front side of the base plate. Furthermore, the base plate has a plurality of integral serpentine fluid flow channels configured to receive and circulate fluid and further configured such that the heat generated by the CFPA is transferred via conduction into the base plate and to the integral serpentine fluid flow channels and to the circulating fluid to dissipate the generated heat.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application claims rights under 35 USC §119(e) from U.S. application Ser. No. 61/532,279 filed Sep. 8, 2011, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical sensors, more specifically to thermal management of optical sensors.

2. Brief Description of Related Art

One of the most difficult challenges posed by high resolution imaging equipment is management of the thermal output of the many electronic components, especially the large amount of localized energy generated by the required high density of focal plane arrays (FPAs). As technology advances, the power dissipated per FPA tends to increase, as well as the number of FPAs in each optical sensor. However, in order for optical sensors and their component FPAs to function properly, the environment must be maintained below a maximum temperature. Given the high number of FPAs and their dense packaging, thermal management continues to be an increasingly important and difficult aspect of high resolution imaging.

Traditional thermal management techniques use circulated cooling air and heat sinks, usually constructed of a suitable metal, to dissipate thermal energy generated by optical sensors. Most of the existing techniques for thermal management of high resolution imaging systems including composite focal plane arrays (CFPAs) use a structure comprising an interposer positioned between the printed circuit (PC) boards, wherein at least one outer edge of the interposer is capped by a semiconductor material, such as aluminum nitride. Typically, in these techniques, a heat sink is positioned adjacent to this end-cap, in a flow path of the circulating air. However, the thermal dissipation potential of these traditional techniques has largely been maximized, and modern imaging systems exceed even this maximized dissipation capability.

SUMMARY OF THE INVENTION

A fluid cooled thermal management technique for a high-density composite focal plane array (CPFA) is disclosed. According to an embodiment of the present subject matter, a high density CFPA assembly includes a plurality of imaging dies mounted on a front surface of a printed wiring board (PWB) and a base plate. Further, the high density CFPA is disposed on a front side of the base plate. The base plate has a substantially matched coefficient of thermal expansion (CTE) to that of the high density CFPA. Furthermore, the base plate has a plurality of integral serpentine fluid flow channels configured to receive and circulate fluid and further configured such that the heat generated by the CFPA is transferred via conduction into the base plate and to the integral serpentine fluid flow channels and to the circulating fluid to dissipate the generated heat.

In addition, the high density CFPA assembly includes a back plane disposed on a back side of the base plate. The back plane is configured to receive the signal lines routed through the thickness of the PWB and then through the signal exit channels. Moreover, the high density CFPA assembly includes a fluid circulation pump fluidly coupled to the plurality of integral serpentine fluid flow channels in the base plate. Also, the high density CFPA assembly includes a fluid-to-metal-to-air heat exchanger fluidly coupled to the plurality of integral serpentine fluid flow channels in the base plate. The fluid circulation pump is configured to pump the fluid via the plurality of fluid flow channels and the fluid-to-metal-to-air heat exchanger is configured to receive the fluid from the plurality of integral serpentine fluid flow channels and to dissipate the heat.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiments described herein in detail for illustrative purposes are subject to many variations in structure and design.

The terms “printed wiring board (PWB)” and “printed circuit board (PCB)” are used interchangeably throughout the document.

FIG. 1is a cross sectional view of a fluid cooled high-density composite focal plane array (CFPA) assembly100, according to an embodiment of the present subject matter. Particularly,FIG. 1illustrates the high-density CFPA assembly100includes a high-density CFPA102, a base plate104, a PWB106and a back plane110. For example, the high-density CFPA102is an optically flat imaging plane. The high-density CFPA102is disposed on a front side of the base plate104. In one embodiment, coefficient of thermal expansion (CTE) of the base plate104is substantially matched to that of the high-density CFPA102. Further, the PWB106is a ceramic PWB and the base plate104is a ceramic base plate. The ceramic PWB and the ceramic base plate have substantially similar CTE.

Further as shown inFIG. 1, the high-density CFPA102includes a plurality of imaging dies mounted on a front surface of the PWB106. Exemplary imaging dies is silicon based high density CFPA. For example, the plurality of imaging dies and the PWB106have substantially similar CTEs. Furthermore, the base plate104includes a plurality of integral serpentine fluid flow channels112. In addition, the high-density CFPA102includes a plurality of signal lines108routed through the thickness of the PWB106to the back surface that is disposed across from the mounted front side of the imaging dies. Also, the back plane110is disposed on a back side of the base plate104. In one embodiment, the base plate104including the fluid flow channels112is configured to receive and circulate fluid and further configured such that the heat generated by the high-density CFPA102is transferred via conduction into the base plate104and to the integral serpentine fluid flow channels112and to the circulating fluid to dissipate the generated heat. This is explained in more detail with reference toFIG. 3.

Referring now toFIG. 2, which is a cross sectional isometric view200of the fluid cooled high-density CFPA102, such as the one shown inFIG. 1, according to an embodiment of the present subject matter. Particularly,FIG. 2illustrates the high-density CFPA102, the base plate104, the PWB106, the fluid flow channels112and a plurality of signal exit channels202. As shown, the base plate104includes the plurality of signal exit channels202. The plurality of signal exit channels202are configured to route the plurality of signal lines108, shown inFIG. 1, coming through the thickness of the PWB106and the back surface of the PWB106. Further, the back plane110is configured to receive the signal lines108routed through the thickness of the PWB106and then through the signal exit channels202.

Referring now toFIG. 3, which illustrates an example block diagram300of a thermal management system for the fluid cooled high-density CFPA102, such as the one shown inFIG. 1. Particularly,FIG. 3illustrates the high-density CFPA102, the base plate104, the PWB106, a fluid circulation pump302, a fluid-to-metal-to-air heat exchanger304, and a fluid path306. As shown, the fluid circulation pump302is fluidly coupled to the plurality of integral serpentine fluid flow channels112, shown inFIGS. 1 and 2, in the base plate104by the fluid path306. Further, the fluid-to-metal-to-air heat exchanger304is fluidly coupled to the plurality of integral serpentine fluid flow channels112in the base plate104by the fluid path306. Furthermore, the fluid circulation pump302is coupled to the fluid-to-metal-to-air heat exchanger304by the fluid path306. In one embodiment, the fluid-to-metal-to-air heat exchanger304is a radiator designed to dissipate heat from the fluid via a convection air flow.

In operation, the fluid circulation pump302is configured to pump the fluid via the plurality of fluid flow channels112to absorb the heat dissipated by the high-density CFPA102. The heat generated by the high-density CFPA102is transferred via conduction into the base plate104and to the integral serpentine fluid flow channels112and to the circulating fluid to dissipate the generated heat. Exemplary properties of the fluid include material compatibility with the base plate104, anti-freeze, substantially high boiling temperature, and high thermal conductivity/carrying capability. Further, the fluid-to-metal-to-air heat exchanger304is configured to receive the fluid from the plurality of integral serpentine fluid flow channels112and to dissipate the heat. The arrows310indicates the cool air passing through the fluid-to-metal-to-air heat exchanger304and the arrows308indicates hot air dissipated from the fluid-to-metal-to-air heat exchanger304. In one example implementation, a thermal imaging camera includes the fluid cooled high-density CFPA assembly100, shown inFIG. 1.