Abstract:
A lamp assembly including at least two light emitting diodes (LEDs) attached to an electrically non-conductive housing by at least two beads of electrically conductive epoxy. The electrically conductive epoxy beads are disposed in at least two grooves formed in the housing, for providing at least two voltage rails for connecting the LEDs to a driving circuitry.

Description:
FIELD OF INVENTION 
   The invention relates to the field of lamps, and in particular a LED lamp assembly with an integrated circuit. 
   BACKGROUND OF INVENTION 
   Light emitting diodes (LEDs) are gradually replacing incandescent light bulbs in many automotive applications. For example, it is attractive to use LEDs for automotive exterior lighting applications such as brake, turn or other signal lamps due to the long life and high luminance provided the latest generation of LEDs. LEDs also enable the lamp housing to have a narrower or shallower profile, which can be advantageous in many applications. 
   In order to provide luminance levels comparable to incandescent lamps, a series or plurality of LEDs must often be used in a lamp thus increasing the complexity and cost of manufacture. For example, the conventional manufacturing practice is to mount the LEDs on a printed circuit board (PCB), which in turn is mounted in a lamp housing. The problem with this practice is that it typically requires the use of sophisticated soldering machinery or techniques, and the resultant PCBs are typically limited in form factor since PCBs are generally flat (complexly shaped PCBs being considerably more expensive to procure). However, the luminaire housing, such as an automotive turn signal, may be a complex shape and thus a PCB-based LED lamp may not be the most optimal design choice. 
   Examples of LED arrays mounted on PCBs or other substrates can be found in U.S. Pat. Nos. 4,742,432; 4,966,862; 5,119,174; 5,331,512; 6,299,337;and 6,346,777. 
   An alternative method of constructing LED arrays employs a foldable metal substrate onto which the LEDs can be solderlessly connected using a clinching machine. The metal substrate features flexible joints between rows of LED bus bars that allow the substrate to be formed to a complex shape. Such systems are disclosed in U.S. Pat. No. 5,404,282 and U.S. Pat. No. 5,519,596. A commercially available system similar to that disclosed in U.S. Pat. No. 5,519,596 is marketed in association with the SnapLED™ brand by Lumileds Lighting of San Jose, CA. This system requires machinery for the creation of a metallic substrate and tooling for clinching the LEDs to the metallic substrate (or the outsourcing thereof), as well as tooling for stamping the metallic substrate into the desired final form. 
   A more economical approach is desired to minimize the cost and/or complexity for assembling LED arrays, especially for use in complexly shaped luminaire housings such as may be found in automotive exterior lighting applications. 
   SUMMARY OF INVENTION 
   According to one aspect of the invention, a lamp is provided which includes an electrically non-conductive housing. One or more light emitting diodes (LEDs) are attached to the housing by one or more beads of electrically conductive epoxy. The LEDs can also optionally be mechanically attached to the housing. The electrically conductive epoxy provides one or more voltage rails for connecting the LEDs to a driving circuitry. 
   In the preferred embodiment, at least two grooves are formed in the housing. A platform formed or present between two walls provides a snap for mechanically attaching the LEDs to the housing. One of the grooves is intended for placement of LED cathodes therein and the other groove is intended for placement of LED anodes therein. A bead of the electrically conductive epoxy is deposited in each of the grooves so as to provide a voltage rail to power the LEDs. 
   According to another aspect of the invention, a method of constructing a lamp assembly is provided. An electrically non-conductive housing is provided. One or more light emitting diodes (LEDs) are mechanically attached to One or more beads of electrically conductive epoxy are deposited on the housing so as to fasten the LEDs to the housing and connect the LEDs to a driving circuit. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The foregoing and other aspects of the invention will become more apparent from the following description of illustrative embodiments thereof and the accompanying drawings, which illustrate, by way of example only, the principles of the invention. In the drawings: 
       FIG. 1  is a perspective view of a lamp according to the preferred embodiment; 
       FIG. 2  is a sectional view of the lamp taken along line A-A in  FIG. 1 ; 
       FIG. 3  is a sectional view of the lamp taken along line B-B in  FIG. 1 ; 
       FIG. 4  is a detailed perspective view of a portion of the lamp in  FIG. 1 ; and 
       FIG. 5  is a sectional view of a lamp according to an alternative embodiment of the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  shows an LED-based lamp  10  comprising a lamp housing assembly  12  onto which a lens (not shown) may be mounted along the perimeter of the housing. The housing  12  is preferably constructed from a non-electrically conductive plastic material such as polyvinyl chloride (PVC), polyethylene terephthalate (PET) or acrylonitrile butadiene styrene (ABS) and may be manufactured via well known molding techniques, as known in the art per se. In the illustrated example, the housing  12  is curvilinear in shape (as seen best in  FIG. 2 ) but it should be understood that the housing  12  may be molded to much more complex shapes, determined by styling criteria. Other types of non-conductive materials may be employed for the housing, but as will be discussed shortly, a material which is somewhat resilient is most preferred. 
   The housing  12  includes at least one channel  15  formed therein which features two independent grooves  16   a  and  16   b . Cross-sectional profiles of the preferred housing  12  along lines A-A and B-B in  FIG. 1  are shown in  FIGS. 2 and 3 , and a detailed perspective view of the housing  12  is shown in  FIG. 4 . As seen in these drawings, the channel  15  includes inner walls  20   a  and  20   b  and outer walls  22   a  and  22   b . A ridge or platform  18  is formed between the inner walls  20   a ,  20   b  in the junction. On this platform, a plurality of snaps are provided, each comprising two posts  23   a ,  23   b . Each post  23   a ,  23   b  includes a small notch  24  therein and the top portion of the post  23   a ,  23   b  above the notches  24  is slightly tapered or chamfered. 
   An LED  30 , such as a SuperFlux™ model manufactured by Lumileds of San Jose, CA. (which is shown in isolation in  FIG. 3 ) is mechanically mounted onto the posts  23   a ,  23   b , in or over the channel  15 . The posts  23   a ,  23   b  and notches  24  are dimensioned such that cathode lead(s) or pins (s)  32  of the LED  30  extend into one of the grooves  16   a ,  16   b  (as illustrated, groove  16   a ) and anode lead(s) or pin(s)  34  extend into the other groove (as illustrated, groove  16   b ). The body of the LED  30  is supported by the posts  23   a ,  23   b , the spacing of which is closely matched to the dimensions of the LED body so as to provide a snap fit. The LED  30  is preferably forcibly inserted so as to deflect the posts  23   a ,  23   b  until the LED body nestles into the notches  24  formed therein. The posts  23   a ,  23   b  are preferably formed from a resilient organic material such as PVC, PET or ABS plastic so that once the LED  30  is inserted it cannot back out of the posts  23   a ,  23   b  unless they are deflected apart. The lamp  10  is unlikely to encounter such forces under normal operating conditions and thus the preferred embodiment provides a snap mechanism for mechanically attaching the LEDs  30  to the housing  12 . 
   In addition to the snap, a bead of electrically conductive epoxy  28  is used to bond the cathode  32  and anode  34  leads of the LED  30  to the channel  15  and hence the housing  12 . The epoxy  28  is also thermally conductive, and thus serves to both electrically connect together all of the cathode  32  or anode  34  leads of the LEDs  30  mounted in the same groove  16   a  or  16   b , and provides a heat sink for carrying heat away from the LED  30 . By mounting the LED  30  on the posts  23   a ,  23   b , the grooves  16   a ,  16   b  can be made relatively wide and deep to provide sufficient heat dissipation and electrical conduction for many applications. Examples of suitable epoxies include TIGA 920H™, TIGA 951™, and TIGA 901 silver conductive epoxies marketed by Resin Technology Group LLC, of S. Easton, Mass.; Bolger C-14F™ epoxy marketed by Tech Film Services Inc. of Billerica, Mass.; and Metaduct™ epoxies marketed by Mereco Technologies Group of West Warwick, R.I. These epoxies are flexible, deformable, functional over a wide range of operating temperatures, and can be laid over a complex topography via manual or automated means. 
   In the preferred embodiment, the beads of electrically conductive epoxy  28  are laid by a robot as is well known in the art. The above mentioned epoxies have some viscosity prior to curing, and thus the epoxy  28  can fill the groove  16   a  or  16   b  to ensconce the cathode  32  or anode  34  leads. Furthermore, the manipulator or working tip of the robot can be angled to reach underneath the LED body near the cathode  32  or anode  34  leads in order to deposit the epoxy  28  proximate thereto. 
   In the illustrated embodiment, when filled with the electrically conductive epoxy  28 , groove  16   b  functions as a ground rail that electrically connects the cathode leads  32  of the series of LEDs  30  mounted therein. Groove  16   a , when filled with the electrically conductive epoxy  28 , functions as a positive voltage rail for connecting the anode leads  34  of the series of LEDs  30  mounted therein. The illustrated lamp  10  includes a third groove  16   c  which cooperates with groove  16   b  for mounting the anode leads  34  of another series of LEDs  30  associated with a second electrical circuit. In this region of the housing  12 , grooves  16   b  and  16   c . Numerous other patterns can be employed for mounting one or more series of LEDs, the number of LEDs in each channel being limited only by the electrical and thermal conduction limits of the particular epoxy being used. 
   A PCB  40  carrying LED control and driving circuitry is mounted to the housing  12  as well known in the art. The PCB  40  includes terminations (not explicitly shown) for electrically connecting the beads of electrically conductive epoxy  28  to the driving circuitry. 
   In an alternative manufacturing process, it is possible to first lay down the beads of electrically conductive epoxy  28  using a glue robot and the use of a second robot to mount the LEDs  30  in the channel  15 . This is possible due to the time typically required for the epoxy  28  to cure, which often exceeds 10 minutes. This will ensure a continuous bead of the electrically conductive epoxy  28  in each groove  16   a ,  16   b ,  16   c  underneath each LED  30 . It may also be possible to avoid the use of the mechanical attachments, if the epoxy  28  is sufficiently cured to retain the LED  30  in position when inserted therein. 
   In a still further manufacturing process, it may be desirable to lay down a first layer of electrically conductive epoxy in each groove, followed by a flexible metallic strip in each groove, followed by a second layer of electrically conductive epoxy in each groove. The LEDs may be mounted in the channel before or after the deposit of the second epoxy layer. 
   By mounting the LEDs  30  directly onto the flexible housing using a ductile epoxy, the lamp housing  12  remains somewhat flexible which is advantageous when installing the lamp housing  12  onto the vehicle. 
   An alternative embodiment of the invention is shown in cross sectional view in  FIG. 5 . In this embodiment, a channel  215  formed in the housing  12  includes planar inner walls  220   a  and  220   b  and planar outer walls  222   a  and  222   b , the outer walls  222   a ,  222   b  being taller than the inner walls  220   a ,  220   b . Independent grooves  216   a  and  216   b  are located between the inner  220   a ,  220   b  and outer  222   a ,  222   b  walls, as shown. A ridge or platform  218  is formed between the inner walls  220   a ,  220   b , which are slightly tapered or chamfered. The outer walls  222   a ,  222   b include small notches  224  therein and the top portions of the outer walls  222   a ,  222   b  above the notches  224  are also slightly tapered or chamfered. In this embodiment, the spacing between the outer walls  222   a ,  222   b  of the channel  215  and the size of each notch  224  is closely matched to the dimensions of the LED body so as to provide a snap fit. If desired, the body of the LED  30  can also be supported by the platform  218 . 
   The illustrated embodiments have shown the use of a snap for mechanically attaching the LEDs to the housing, but a variety of other mechanisms such as detents, index keys, latches or other such mechanisms can be used to mechanically attach the LEDs to the housing. The mechanical attachment means preferably locks the LED to the housing but in alternative embodiments it does not need to immovably lock the LEDs to the housing since the epoxy provides an additional means for immovably locking the LEDs in place. 
   Those skilled in the art will appreciate that a variety of modifications may be made to the preferred embodiments without departing from the spirit of the invention.