Abstract:
LED mounting arrangements are described which provide flexibility for LED users to mount a first LED having different physical, electrical, thermal, or other characteristic footprints from those for a second LED on a mounting pad designed for the second LED. With such arrangements, migration from one LED to another can be facilitated without the need for redesigning the printed circuit board for a lighting application. Flexibility is thereby provided to LED customers.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to improvements in the field of mounting arrangements for light emitting devices, and, in particular, to methods and apparatus for improving the flexibility of light emitting device mounting arrangements. 
       BACKGROUND OF THE INVENTION 
       [0002]      FIGS. 1A ,  1 B,  1 C and  1 D illustrate a standard LED packaging arrangement, such as that employed by the XLamp® 7090 XR-E series of LED products manufactured by Cree, Incorporated, and how that packaged LED lamp may be suitable mounted on a larger printed circuit board (PCB). As seen in  FIG. 1A , a packaged LED lamp  100  comprises a lens  102 , a reflector  104  and a mounting substrate  106 . The arrangement  100  may also be referred to as an LED, LED lamp or a lamp. As seen in  FIG. 1B , an LED chip  108  is electrically connected by bond wires  110  and  112  to electrical contact strips  114  and  116 , respectively, on the substrate  106  which may suitably be a printed circuit board (PCB), such as a flame resistant 4 (FR4) board. When power is applied through the contacts  114  and  116 , chip  108  emits light. The chip  108  is shown as having two top contacts for a chip having a horizontal arrangement. However, alternative LED chips and chip mounting arrangements are possible where the LED has a horizontal or vertical orientation or is flip chip mounted, as would be understood by one of ordinary skill in the art. In the arrangement shown, reflector  104  helps direct the emitted light upwards and the lens  102  focuses the emitted light. The chip  108  is thermally mounted on top surface  18  of substrate  106  with a thermal bonding paste  FIG. 1C  shows a bottom surface  120  of the substrate  110  and electrical contacts  114  and  116  along with representative dimensions for the XLamp® 7090 XR-E series of LED products. It will be recognized that 9.0 mm is slightly smaller than 1 cm and is about ⅓ of an inch. As a result, it can be seen that the XLamp® LED products and other similar products have a small form factor compared to typical incandescent bulbs.  FIG. 1D  shows a solder pad  120  for mounting the packaged LED lamp  100  to a larger PCB, such as the one shown in  FIG. 2 . 
         [0003]      FIG. 2  shows a PCB  201  for an LED flashlight demonstrator  200 . The PCB  201  on its top surface has a battery mount  202  with a battery  203 , circuitry  204 , a push button on/off switch  205  and an LED solder mounting pad  206  corresponding to the pad  120  of  FIG. 1D . Electrical connections of the various components on the top surface of PCB  201  are made by electrical traces on the bottom surface of PCB  201  in a known fashion. In a typical approach to manufacturing a product, such as a flashlight employing an LED, a customer designs a printed circuit board, such as board  201 , for an LED from a particular manufacturer. The LED customer having procured an inventory of such boards will be locked in to selecting an LED having contacts which can be mounted on the mounting pad on the board, such as pad  206 , shown in  FIG. 2 . If that customer wants to switch to a different LED having a different contact arrangement, then that customer has to wait until the inventory of PCBs is used up or bear the cost of disposing of the remaining boards, redesigning a new board compatible with the new LED, and the cost of obtaining the new boards, or the like. 
       SUMMARY OF THE INVENTION 
       [0004]    Among its several aspects, the present invention recognizes that more flexible and cost effective mounting arrangements are desirable to address such problems, as well as others. For example, hobbyists may want to try different LEDs. A large scale manufacturer may know that a better LED will become available from the LED supplier within the next six months. For example, a production schedule may be in place for a smaller, brighter LED that uses less power. In such a cases the manufacturer may not want to be locked in to the older LED until an existing inventory of PCBs is used up, or may want to have the flexibility of using the older proven LED until a new LED has successfully passed beta testing. 
         [0005]    To such ends, the present invention provides a low cost and flexible mounting arrangement which provides a migration path for a coming upgrade. This arrangement can also be employed to support side by side testing of competitive LEDs and the needs of hobbyists and others desiring greater flexibility as discussed in greater detail below. 
         [0006]    One aspect of the present invention addresses a footprint adapter or converter for light emitting devices, such as LEDs and the like. The adapter may be suitably embodied on a flame resistant (FR) 4 board which allows a second light emitting device with a different physical, different thermal, different electrical, or some other different characteristics, or a combination of different footprint characteristics to be used in place of a first light emitting device at relatively low cost as addressed further below. Thus, for example, an existing PCB can be retrofit with a new and different LED. 
         [0007]    In another aspect, a light emitting device footprint adapter is provided comprising a mounting substrate having a top surface with first mounting contacts for mounting a first light emitting device; the substrate having a bottom surface with mounting contacts for mounting the substrate on a mounting surface having second mounting contacts for a second light emitting device having a different footprint than the first light emitting device; and connections through the mounting substrate connecting the first mounting contacts of the top surface with the second mounting contacts of the bottom surface. 
         [0008]    In another aspect, a method is provided for utilizing a light emitting device footprint adapter to enable replacement of a first light emitting device having a mounting arrangement with a second light emitting device having an incompatible mounting arrangement. The method may suitably comprise mounting the second light emitting device on a top mounting surface of an adapter, the top mounting surface having mounting contacts for mounting the second light emitting device, the adapter having a bottom mounting surface with compatible mounting contacts for mounting the adapter on the mounting pad for the first device; mounting the bottom mounting surface of the adapter on the mounting pad for the first light emitting device; and connecting the mounting contacts for mounting the second light emitting device to the compatible mounting contacts for mounting the adapter through the adapter. 
         [0009]    These and other advantages and aspects of the present invention will be apparent from the drawings and Detailed Description which follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIGS. 1A ,  1 B and  1 C show a top perspective, a top, and a bottom view, respectively, of a typical prior art mounting arrangement for mounting an LED on a flame resistant (FR)  4  board; and  FIG. 1D  shows a printed circuit board (PCB) solder pad for mounting the LED lamp package of  FIGS. 1A-1C  to a larger PCB board for a particular application; 
           [0011]      FIG. 2  shows an example of a PCB board for a flashlight application demonstrator employing the solder pad of  FIG. 1D ; 
           [0012]      FIGS. 3A and 3B  show an example of a footprint adapter in accordance with the present invention for mounting a Cree® XLamp® XP-E LED on a printed circuit board with a solder pad for a Cree® XLamp® XR-E LED; 
           [0013]      FIGS. 4A ,  4 B and  4 C show examples of footprint adapters in accordance with the present invention for mounting a Cree® XLamp® MC-E LED on a printed circuit board with a solder pad for the XR-E LED; 
           [0014]      FIGS. 5A ,  5 B and  5 C illustrate a perspective and bottom view of a Luxeon® Rebel LED, and  FIG. 5C  shows a footprint adapter in accordance with the present invention for mounting the Rebel LED on an XR-E LED solder pad; 
           [0015]      FIG. 6  shows a top view of a footprint adapter in accordance with the present invention for mounting a Nichia® NS6 LED on an XR-E LED solder pad; 
           [0016]      FIGS. 7A and 7B  show top and bottom views of a footprint adapter in accordance with the present invention for mounting a Luxeon® K2 LED on a XR-E LED solder pad; 
           [0017]      FIGS. 8A-8C  illustrate further footprint adapters in accordance with the present invention; and 
           [0018]      FIG. 9  shows a process of using a footprint adapter in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Where an LED lamp or some other type of light emitting device is to be replaced by another having the same physical dimensions, the same electrical contact pattern, and similar thermal characteristics, no mounting issues may be presented. However, where a smaller or larger physical device is present, a different electrical contact or driving arrangement, and different thermal dissipation requirements, all three, or some combination thereof are presented, the present invention recognizes that end users having committed to a particular printed circuit board (PCB) need an alternative to using up the boards with less efficient or effective LEDs or junking an existing inventory of PCBs. 
         [0020]    Such a circumstance can arise even with a single LED supplier, such as Cree Incorporated which recently announced Cree® XLamp® XP-E LEDs in a package with an 80% smaller physical size than the Cree® XLamp® XR-E LED. Additionally, the Cree® XLamp® MC-E LED while having a similar physical size to the XR-E LED has a very different electrical contact arrangement as will be discussed further below. With multiple LED suppliers in the mix, the variety of physical sizes, electrical contact arrangements, thermal dissipation requirements, and the like can be large. Among its several aspects, the present invention addresses cost effective techniques for customer migration from one LED to another consistent with the different physical, electrical and thermal footprints of these various devices. 
         [0021]    To such ends,  FIGS. 3A and 3B  show a top and bottom view, respectively, of a physical size, electrical, and thermal footprint adapter  300  according to the present invention which supports the migration of a manufacturer from the XR-E lamp of  FIG. 1A  to the XP-E lamp as discussed further below. In one embodiment, the footprint adapter  300  may be suitably embodied using an FR 4 board as a mounting substrate as discussed further below. In this embodiment, the physical dimensions of board  300  correspond to those shown in  FIG. 1C . As shown in  FIG. 3A , the top of board  300  has a standard solder pad cross-hatched portion  310  for the XP-B lamp modified to include extending arm portions  312  and  314 . The bottom of board  300  shown in  FIG. 3B  has the standard electrical and thermal contacts  322 ,  324  and  326 , respectively for the UR-E lamp. These contacts correspond to those shown in  FIG. 1C . In addition to standard solder pad  310  and extended arm portions  312  and  314 , there are a number of vias or holes  316 - 321  drilled through the FR4 board  300 . These vias allow solder to flow from top surface  330  to bottom surface  340  so that electrical and thermal contact are made through the adapter as follows. Via  316  when filled with solder makes electrical contact between extended arm  312  and electrical contact  322 . Similarly, via  317  makes electrical contact between extended arm  314  and electrical contact. Vias  318 - 321  make thermal contact between central thermal portion of solder pad  310  and thermal pad  326 . While  FIG. 3A  shows an exemplary solder pad and via arrangement, it will be recognized that other arrangements may be devised consistent with the present teachings and the electrical and thermal connections desired for a particular application. 
         [0022]    As one example of the use of footprint adapter  300 , if a manufacturer of LED flashlights has been using boards like board  200  with the XR-E lamp and wants to retrofit those boards with the XP-E lamp which has an 80% smaller package footprint, the footprint adapter  300  allows that manufacturer to do so. Footprint adapter  300  adapts for the smaller physical size and the different electrical and thermal mounting characteristics comprising the different footprint of the XP-E. 
         [0023]      FIGS. 4A ,  4 B and  4 C show top views of electrical and thermal footprint adapters  400 ,  450  and  480  according to the present invention which support the migration of a manufacturer from the XR-E lamp of  FIG. 1A  to the MC-E lamp as discussed further below. Bottom views are not shown as they correspond to that seen in  FIG. 3B . With the addition of appropriate active electrical drive circuitry if necessary, the availability of the adapters  400 ,  450  and  480  gives a manufacturer the ability to utilize an XR-E lamp for one application (no adapter), the MC-E lamp wired for parallel operation for another application (adapter  400 ), the MC-E lamp wired for series operation for a third application (adapter  450 ) and the MC-E lamp wired for two chips in series and two chips in parallel (adapter  480 ). 
         [0024]    The physical dimensions of adapters  400 ,  450  and  480  correspond to those shown in  FIG. 1C . As shown in  FIG. 4A , the top of adapter  400  has a standard solder pad cross-hatched portion  410  for the MC-E lamp. The MC-E lamp has four LED chips with a pair of contacts for each. In  FIG. 4A , the standard solder pad has been modified to include extending arm portions  412  and  414 . The bottom of the adapter  400  not shown has the same standard electrical and thermal contacts for the XR-E lamp, like contacts  322 ,  324 , and  326  shown in  FIG. 3B . In addition to standard solder pad  410  and extended arm portions  412  and  414 , there are a number of vias or holes, such as vias  416 ,  418  and  420  drilled through the adapter  400  which may be embodied in an FR4 board as discussed above. These vias allow solder to flow from top surface  430  to the bottom surface so that electrical and thermal contacts are made as follows. Via  412  when filled with solder makes electrical contact between its corresponding arm  412  and an electrical contact, like contact  322 , on the bottom of adapter  400 . Similarly, via  420  makes electrical contact between its corresponding arm  414  and an electrical contact, like contact  324 , on the bottom of adapter  400 . Vias, such as via  418 , make thermal contact between central thermal portion of solder pad  410  and a thermal pad, like pad  326 , on the bottom of adapter  400 . 
         [0025]    As shown in  FIG. 4B , the top  470  of adapter  450  has a standard solder pad cross-hatched portion  460  for the MC-E lamp modified to include extending arm portions  462  and  464 , as well as, contact connectors  472 ,  474  and  476  to support serial operation. The bottom of adapter  450  not shown has standard electrical and thermal contacts such as the contacts  322 ,  324  and  326  shown in  FIG. 3B  for the XR-E lamp. In addition to the standard solder pad  460 , the extended arm portions  462  and  464 , and the contact connectors  472 ,  474  and  476 , there are a number of vias or holes, such as vias  466 ,  468  and  470 , drilled through the adapter  450  which may be embodied as an FR4 board as discussed herein. These vias allow solder to flow from top surface  470  to bottom surface like surface  340  so that electrical and thermal connections through adapter  450  contact are made as follows. Via  466  when filled with solder makes electrical contact between arm  462  and an electrical contact, such as contact  322  of  FIG. 3B . Similarly, via  470  makes electrical contact between arm  464  and a corresponding electrical contact like contact  324 . Via  468  makes thermal contact between central thermal portion of solder pad  460  and a thermal pad like pad  326 . 
         [0026]    As shown in  FIG. 4C , the top  490  of adapter  480  has a standard solder pad cross-hatched portion for the MC-E lamp modified to include extending arm portions  482 ,  483 ,  484  and  485  supporting parallel operation of to chips of the MC-E lamp. Extending arm portions  486  and  488 , as well as contact connector  489 , support serial operation of the other two chips of the MCE-lamp. The bottom of adapter  480  not shown has standard electrical and thermal contacts such as the contacts  322 ,  324  and  326  shown in  FIG. 3B  for the XR-E lamp. In addition to the standard solder pad  492 , the extended arm portions and the contact connector, there are a number of vias or holes, such as vias  491 ,  493 ,  494 ,  495 ,  496 ,  497 ,  498  and  499 , drilled through the adapter  480  which may be embodied as an FR4 board as discussed herein. These vias allow solder to flow from top surface  490  to bottom surface like surface  340  so that electrical and thermal connections through adapter  480  contact are made. 
         [0027]      FIGS. 5A and 5B  illustrate a perspective view and bottom view of a prior art Luxeon® Rebel LED  500 , respectively. As seen in  FIG. 5B , a thermal pad  510  and two electrical contact pads  520  and  530  are found on the bottom of an adapter  540 . Exemplary dimensions in millimeters for the pads  510 ,  520  and  530  are shown in  FIG. 5B . By comparing these dimensions with those seen in  FIG. 1C , it is seen that the LED  500  is physically, electrically and thermally incompatible with the standard mounting pad seen in  FIG. 1D . 
         [0028]      FIG. 5C  shows a top view of a footprint adapter  550  according to the present invention which allows a customer to mount a Rebel LED  500  on a PCB, such as the PCB  200  of  FIG. 2  having a solder pad for an XR-E LED, such as LED  100 . As seen in  FIG. 5C , the top of adapter  550  has a standard Rebel solder pad  560  which has been modified to include additional extended arm portions  562  and  563  which are shown cross hatched. A number of vias, such as vias  566 ,  568  and  570  allow solder to flow from top surface  580  of adapter  550  to electrical and thermal contacts as discussed further below. Via  566  connects extended arm  566  and its respective contact to an electrical contact, like contact  322  of  FIG. 3B , on the bottom of adapter  550 . Via  568  connects extended arm  568  and its respective contact to an electrical contact, like contact  324  of  FIG. 3B , on the bottom of adapter  550 . Via  570  connects the thermal pad, like pad  326  of  FIG. 3B , on the bottom of adapter  550 . 
         [0029]      FIG. 6  shows a top view of an adapter  600  according to the present invention which supports the migration of a manufacturer from the XR-E lamp of  FIG. 1A  to a Nichia® NS6 lamp as discussed further below. The physical dimensions of board  600  correspond to those shown in  FIG. 1C . As shown in  FIG. 6 , the top of adapter  600  has a standard solder pad cross-hatched portion  610  for the NS6 lamp. The bottom of adapter  600  has standard electrical and thermal contacts like the contacts  322 ,  324  and  326  of  FIG. 3B  for the XR-E lamp. In addition to standard solder pad  610 , there are a number of vias or holes, such as vias  616 ,  618 ,  620  drilled through the adapter  600 . These vias allow solder to flow from top surface  630  to the bottom surface so that electrical and thermal contact are made as follows. Via  616  when filled with solder makes electrical contact between its corresponding electrical contact and an electrical contact, like contact  322  of  FIG. 3B . Similarly, via  618  makes electrical contact between its corresponding electrical contact and an electrical contact like electrical contact  324 . Vias, such as via  618  make thermal contact between the corresponding thermal portion of solder pad  610  and a thermal pad, like thermal pad  326 . While  FIG. 6  shows an exemplary solder pad and via arrangement, it will be recognized that other arrangements may be devised consistent with the present teachings and the electrical and thermal connections desired for a particular application. 
         [0030]      FIGS. 7A and 7B  show top and bottom views, respectively, of an adapter  700  according to the present invention which supports the migration of a manufacturer from the XR-E lamp of  FIG. 1A  to the Luxeon® K2 lamp as discussed further below. The physical dimensions of 14.0 mm×10.0 m for adapter  700  correspond to those shown of a typical solder pad layout for the Luxeon® K2 lamp. Top surface  702  of adapter  700  has conductive pads  704 ,  706 ,  708 ,  710  and  712 . A solder mask area  714  is shown cross-hatched. Dashed line  714  is an outline showing where the Luxeon® K2 package is mounted. The electrical wing pinouts of the K2 lamp connect to the conductive pads  704 ,  706 ,  708  and  710 . As seen in  FIG. 7B , the bottom  722  of adapter  700  has the standard electrical and thermal contacts  722 ,  724  and  726 , respectively, for the XR-E lamp with the same dimensions for the contacts as seen in  FIG. 1C . The board  700 , however, is substantially larger than board  118 , for example. As such, so long as a PCB board like board  200  has sufficient landing area for board  700 , the board  700  can be used with standard pad  206 , for example. 
         [0031]    In addition to standard electrical contacts  722  and  724 , there are extender connections  723  and  725  to connect electrical contacts  722  and  706  and  725  and  708 , respectively, by way of vias  732  and  734  filled with solder. Additional vias  736  filled with solder provide thermal connection between the thermal contacts  726  and  712 . While  FIGS. 7A and 7B  show an exemplary solder pad and via arrangement, it will be recognized that other arrangements may be devised consistent with the present teachings and the electrical and thermal connections desired for a particular application. 
         [0032]      FIGS. 8A-8C  illustrate further footprint adapters  810 ,  840  and  870 , respectively, in accordance with the present invention.  FIGS. 8A and 8B  show adapters  810  and  840  with current adjusting resistors  815  and  845 , respectively for adapting to an LED or LEDs with a different electrical footprint. More specifically,  FIG. 8A  shows an arrangement for adapting to two LEDs connected in series where each LED has the same resistance as the LED which they are going to replace. In this arrangement, a current balancing resistor  815  is added in parallel with the contacts  816  and  818  for the two series connected LEDs. As was the case in  FIGS. 3A and 3B , vias connect these contacts to electrical contacts on the bottom of the board. 
         [0033]      FIG. 8B  shows an arrangement for adapting to two LEDs connected in parallel where again each LED has the same resistance as the LED which are they are going to replace. In this arrangement, a current limiting resistor  845  is added in series as shown in  FIG. 8B . It will be recognized that the resistors of  815  and  845  of  FIGS. 8A and 8B  are exemplary of electrical components and circuits more generally if such are needed to adapt with existing circuitry and supplies of current and voltage of a board, such as the board  201  of  FIG. 2 . 
         [0034]    Finally,  FIG. 5C  illustrates an adapter  870  for an LED having greater thermal dissipation requirements than the LED which it is replacing in which a heat sink  875  is mounted on a portion of a solder pad  880  for the LED. 
         [0035]      FIG. 9  illustrates an exemplary process  900  of utilizing a light emitting device footprint adapter according to the present invention to enable a first light emitting device customer to employ a second light emitting device in place of a first light emitting device using an incompatible mounting pad arrangement customized for the first light emitting device. Initially, it is determined that it is desired to employ a second light emitting device in place of a first light emitting device having a different mounting pad arrangement. In step  902 , the second light emitting device is mounted on a top mounting surface of an adapter. The top mounting surface of the adapter has mounting contacts for mounting the second light emitting device. A bottom surface of the adapter has mounting contacts compatible with the mount pad arrangement customized for a first light emitting device. In step  904 , the bottom surface of the adapter with the second light emitting device mounted on its top surface is mounted on the mounting pad customized for the first light emitting device. In one suitable approach to such mounting, surface mount techniques are employed. In step  906 , the first mounting contacts are connected through the adapter on the top surface and the second mounting contacts on the bottom surface of the adapter. 
         [0036]    While the present invention has been disclosed in the context of various aspects of presently preferred embodiments, it will be recognized that the invention may be suitably applied to other environments consistent with the claims which follow. By way of example, while the present invention has been disclosed primarily in the context of exemplary LEDs and mounting arrangements, it will be recognized that the present teachings may be readily adapted to other LEDs and mounting arrangements, as well as, other lighting emitting devices, such as other light emitting semiconductor or solid state devices, such as laser diodes, and optoelectronic device chips, such as phototransistors and the like, by way of example. Further, while presently preferred materials and arrangements of exemplary numbers of LEDs are described herein with examples of solder pads and vias, other materials and arrangements may be adapted to particular lighting environments.