Patent Application
20140264393
Embodiments of the invention generally relate to light engines comprising flexed printed circuit boards and methods pertaining to the same.
Conventional light fixtures use light emitting diodes (“LEDs”) or other suitable light sources. Because LEDs and other light sources give off thermal energy, luminaire housings with heat sinks are sometimes incorporated into the light fixture to facilitate heat dissipation from the light sources. Such heat dissipation can result both from conduction of heat from the light sources via the heat sink material as well as convection of heat from the heat sink to the air circulating through and around the heat sink.
When LEDs are used as the light source, a printed circuit board (“PCB”) is typically populated with LEDs that are wired to the PCB. During assembly of the light fixture, the PCB (with LEDs mounted thereon) is typically fastened to the heat sink using either multiple screws or other suitable fasteners.
The terms “invention,” “the invention,” “this invention” and “the present invention” used in this patent are intended to refer broadly to all of the subject matter of this patent and the patent claims below. Statements containing these terms should not be understood to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. Embodiments of the invention covered by this patent are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to the entire specification of this patent, all drawings and each claim.
In certain embodiments there is provided a light engine with a heat sink having a curved recessed cavity that receives a flexed PCB bearing a plurality of LEDs. Once released, the elastic PCB has a tendency to attempt to return to its flat state. Flanges or other suitable mechanisms along the ends of the cavity, however, restrain the edges of the PCB and prevent the PCB from returning to its flat state. In this way, the PCB is securely retained within the cavity by its own forces. Moreover, the inability of the PCB to return to its natural state causes the PCB to bear against the curved surface of the cavity to increase its thermal contact with the underside of the cavity. Upon activation of the light source, the PCB heats up from the heat generated by the LEDs and expands, further biasing the PCB against the cavity of the heat sink and increasing the thermal conductivity between the two components.
A full and enabling disclosure including the best mode of practicing the appended claims and directed to one of ordinary skill in the art is set forth more particularly in the remainder of the specification. The specification makes reference to the following appended figures, in which use of like reference numerals in different features is intended to illustrate like or analogous components.
The subject matter of embodiments of the present invention is described here with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described.
Cavity 14 may have a generally rectilinear, single-axis concave shape such that cavity 14 has a slightly curved upper surface 15. As one non-limiting example, cavity 14 may be recessed such that the general mid-point of cavity 14 is recessed approximately 0.200 inches as compared with the ends of the cavity. In some embodiments, cavity 14 includes one or more flanges 16 that extend at least partially along two opposing generally straight ends 13 of cavity 14. Each flange 16 serves as an edge-constraint along each generally straight end 13. In other embodiments, instead of flanges 16, other suitable mechanisms are used to restrain the edges 20 of PCB 18 within cavity 14 and prevent PCB from returning to its natural flat state as described in detail below.
In some embodiments, PCB 18 is a substantially rigid board that elastically deforms. In other words, when flexed below its yield point, PCB 18 attempts to recover and return to its naturally flat state (as opposed to plastic deformation where the board would be permanently deformed with no ability to return to its original shape). In some embodiments, PCB 18 is a metal core board or made of another suitable material. PCB 18 may be covered by a flexible dielectric material that enables the board to flex slightly without cracking components on the board or causing the components to lose connectivity with the board. In some cases, the dielectric layer is both stretchable and flexible/bendable so that it can elastically deform so as to prevent the dielectric layer from both cracking and delaminating during the deformation process. One non-limiting example of such a resilient dielectric layer is sold by Dupont™ under the tradename CooLam™.
As shown in
Because PCB 18 is held tightly against the curved upper surface 15 of cavity 14 by its own internal forces, thermal conductivity between PCB 18 and heat sink 12 is increased, which leads to greater heat dissipation. Moreover, as PCB 18 heats from the heat generated by the LEDs or other light source, PCB 18 expands. However, PCB 18 is constrained by the edges of cavity 14, and thus, upon such expansion, is only able to elastically deform even further towards curved upper surface 15. Thus, PCB 18 is retained even more tightly within, and biased more securely against, cavity 14 when the LEDs are in use and such contact is the most critical.
In some embodiments, as shown in
Moreover, a lens sheet 26 may be overlaid on PCB 18. If used, lens sheet 26 may be injection-molded plastic or other suitable material and may have a plurality of lenses 19 that align with LEDs 22 of PCB 18. Lens sheet 26 may be transparent or semi-transparent. If used, lens sheet 26 may be molded into the same shape and general curvature as the flexed PCB 18. Lens sheet 26 may then be overlaid onto PCB 18 and positioned within cavity 14. Like PCB 18, the edges of lens sheet 26 will be tightly edge-constrained by flanges 16 of cavity 14. Moreover, because lens sheet 26 is plastic or other suitable material that expands as it heats, a tight fit between PCB 18 and lens sheet 26 is achieved as discussed above with respect to PCB 18. Optionally, a suitable perimeter sealing device or method may be used to further constrain lens sheet 26 within cavity 14. One non-limiting example is a resilient O-ring that may be inserted into a groove around the outside of the lens sheet (not pictured) and used to further secure the lens sheet within cavity 14. If desired, lens sheet 26 may also be mechanically fastened to heat sink 12 to aid with retention. Because lens sheet 26 is tightly restrained within cavity 14, it is less likely that lenses 19 will shift relative to LEDs 22.
Embodiments of the light engine 10 disclosed herein may be incorporated into any light fixture or luminaire.
Also disclosed is a method of mounting a PCB such as PCB 18 into a heat sink such as heat sink 12 as described above and a method of using the light engine 10. In one embodiment, a PCB 18 is mounted as described above and the LEDs 22 are powered on. As the LEDs 22 on the PCB 18 heat up, the PCB 18 heats up and expands and continues to attempt to return to its flat state due to its elastic deformation. Because the PCB 18 is constrained around its edges 20 by flanges 16, the PCB's only permitted movement is to arch more against cavity 14. As described above, as it arches more, the PCB 18 bears more tightly against the surface 15 of cavity 14 (or against thermal pad 24 if one is used), thus increasing thermal efficiency, both in contact pressure and path length.
As the LEDs 22 heat up, the lens sheet 26, if used, also expands due to the material properties of the lens sheet 26. Like the PCB 18, the lens sheet 26 is constrained around its perimeter and is thus only permitted to press itself more tightly against the PCB 18. To counteract any stresses built in the lens sheet, the lens sheet 26 optionally may be designed with movement-absorbing features such as corrugations or other suitable ways of lowering stresses below the elastic limit of the material of the lens sheet 26.
Because separate mechanical fasteners are not required to secure the PCB 18 to the heat sink 12, the raw material, tooling and assembly costs of the light engine 10 are reduced. Moreover, connecting a PCB to a heat sink using mechanical fasteners makes the process much more time intensive, so the above assembly and methods decrease the time and expense associated with assembling the PCB 18 within the heat sink 12. Similarly, because the lens sheet 26 is restrained within cavity 14 of heat sink 12 without the need for mechanical fasteners, material and assembly costs are reduced. Moreover, the tight connection between the lens sheet 26 and the heat sink cavity 14 helps ensure that the lenses 19 do not move relative to LEDs 22. In addition, the tight seal between the lens sheet 26 and the PCB 18 helps protect the PCB 18 and the LEDs 22 against the environment in a reliable and consistent fashion.
The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of the present invention. Further modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of the invention. Different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and subcombinations are useful and may be employed without reference to other features and subcombinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications can be made without departing from the scope of the claims below.
