WO2013072812A1

WO2013072812A1 - Led spring clamp & retainer

Info

Publication number: WO2013072812A1
Application number: PCT/IB2012/056223
Authority: WO
Inventors: Franklin Jospeh WALL; William David Collins; Walter Daeschner; Kathleen Anne Hartnett; Robert Andrew Zona
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-11-14
Filing date: 2012-11-07
Publication date: 2013-05-23

Abstract

Tension-providing clamps (110) are used to attach a light emitting assembly (150) to a submount (190). When the clamps (110) are tensioned against the light emitting assembly (150), the mechanical integrity of the combination is assured, while at the same time, because the clamps do not bond the assembly to the mount, per se, the thermally induced mechanical stress between the assembly and the submount is substantially reduced. The tension introduced by the clamp (110) may also be used to provide a tension-coupling of external terminals (120) to pads (260) on the assembly, thereby eliminating the need to subject the assembly to high soldering temperatures.

Description

LED SPRING CLAMP & RETAINER

FIELD OF THE INVENTION

[0001] This invention relates to the field of light emitting devices (LEDs), and in particular to a clamp and retainer that facilitates efficient mounting of LED assemblies on submounts, such as heat sinks.

BACKGROUND OF THE INVENTION

[0002] The ever increasing efficiency of solid-state light emitting devices (LEDs) has led to their use in a variety of applications, and this growing market has created a highly competitive environment. Techniques that improve or simplify the manufacturing and assembly processes associated with the production of light emitting devices can often significantly affect a vendor's profit margin.

[0003] The manufacture and assembly of a light emitting device typically comprises creating multiple semiconductor, insulation, and conductor layers on a substrate to create a light emitting assembly, including conductor pads that are used to connect the created light emitting assembly to an external power source. This assembly may include multiple light emitting device elements to produce particular combinations of colors, or to produce a desired luminance level, or to achieve some other lighting or optical effect. Such an assembly is typically mounted on a submount that provides mechanical support and facilitates the dissipation of the heat produced by the light emitting device. The submount will generally include terminals that are connected to the aforementioned conducting pads, the terminals being configured to plug into, or otherwise attach to a larger mounting element, such as a printed circuit board, a lamp structure, and so on.

[0004] The attachment of the light emitting assembly to a submount requires both electrical and mechanical integrity. An epoxy or other adhesive may be used to bond the assembly to the submount to provide the mechanical integrity, and solder is typically used to couple the terminals to the pads on the assembly to provide the electrical integrity; in some cases, solder provides both the mechanical and electrical integrity. These bonding and/or soldering processes are fairly complex, and introduce a number of potential problems. [0005] When materials of a different nature are bonded together, and subsequently subjected to high temperatures, the differences between the coefficients of thermal expansion (CTE) of the different materials may introduce a mechanical stress that can lead to fractures in one or both of the materials. If the fracture, or other thermally induced fault, occurs in a conducting layer, the operation of the light emitting device could fail prematurely.

[0006] The aforementioned soldering process also introduces thermally induced mechanical stress as the pads and terminals are heated to the proper soldering temperature. In some processes, wave soldering, or reflow soldering is used, wherein the entire assembly is subjected to the high soldering temperature. In addition to failures caused by the soldering process itself, the resultant solder joints are often the primary source of field failures due to what is commonly referred to as 'solder fatigue'.

SUMMARY OF THE INVENTION

[0007] It would be advantageous to be able to mount a light emitting assembly to a submount without the need to solder the pads on the assembly to terminals for external connections. It would also be advantageous to reduce the mechanical stress that is introduced by thermal changes.

[0008] To better address one or more of these concerns, in an embodiment of this invention, tension-providing clamps are used to attach a light emitting assembly to a submount. When the clamps are tensioned against the light emitting assembly, the mechanical integrity of the combination is assured, while at the same time, because the clamps do not bond the assembly to the mount, per se, the thermally induced mechanical stress between the assembly and the submount is substantially reduced. The tension introduced by the clamp may also be used to provide a tension-coupling of external terminals to pads on the assembly, thereby eliminating the need to subject the assembly to high soldering temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein:

FIGs. 1A-1B illustrate an example 'snap-on' clamp for mounting a light emitting assembly to a submount.

FIGs. 2A-2C illustrate an example 'screw-down' clamp for mounting a light emitting assembly to a submount.

FIG. 3 illustrates an alternative example clamp that sandwiches terminals between the assembly and the submount.

FIGs. 4A-4B illustrate an alternative example clamp that includes PC board terminals and anti- rotation elements.

FIGs. 5A-5B illustrate an alternative example clamp that includes a set of plug terminals and other features.

FIGs. 6A-6B illustrate an alternative example clamp that includes pin terminals and other features. FIGs. 7A-7B illustrate an alternative example clamp that includes a molded base and other features.

FIGs. 8A-8B illustrate an alternative example clamp that includes multiple fastening elements and other features.

[0010] Throughout the drawings, the same reference numerals indicate similar or

corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention.

DETAILED DESCRIPTION

[0011] In the following description, for purposes of explanation rather than limitation, specific details are set forth such as the particular architecture, interfaces, techniques, etc., in order to provide a thorough understanding of the concepts of the invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments, which depart from these specific details. In like manner, the text of this description is directed to the example embodiments as illustrated in the Figures, and is not intended to limit the claimed invention beyond the limits expressly included in the claims. For purposes of simplicity and clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

[0012] FIGs. 1A-1B illustrate an example 'snap-on' clamp 100 for mounting a light emitting assembly to a submount. In this embodiment, opposing clamp elements 1 10 are situated such that they may apply tension at a peripheral area of a light emitting assembly 150. In this manner, the clamp 100 does not interfere with the light that is emitted from the assembly 150. In principle, the clamp 100 forms a frame within which light is output from the light emitting assembly 150. This frame may completely enclose the assembly 150, or it may only cover part of a periphery of the combination of the assembly 150.

[0013] The clamp elements 1 10 apply a coupling tension between the assembly 150 and the submount 190 by clipping into grooves 195 on the submount 190. The clamp elements 1 10 are configured to flex outward as the clamp 100 is pressed atop the assembly 150, then snap into the grooves 195. Optionally, to assure that the clamp elements 110 remain secured to the mount 190 as the combination undergoes mechanical deformations with age, a ring element 130 may be situated so as to retain the clamp elements 110 within the groove 195. Also optionally, stress relief features, such as a groove 105 in the band element 115 between the clamp elements 110, may be provided to limit the maximum tension that is applied across the assembly 150. [0014] To allow coupling of the light emitting assembly 150 to an external source of power, a terminal element 120 is also provided. In this example, the terminal element 120 includes two electrodes 122A and 122B that are configured to be coupled to connection pads on the assembly 150 (e.g. pads 260 of FIG. 2C), and two pins 121A 121B that facilitate coupling to the external source of power. Pins 121 A and 12 IB may be members of electrodes 122 A and 122B

respectively. The tension provided by the clamps 110 towards the submount 1 10 provides a tension coupling of these electrodes to the connection pads on the assembly 150. Although two electrodes and two pins are shown, the use of any number of electrodes and pins are

contemplated, as detailed further below, and included within the scope of the invention.

[0015] Because the mechanical integrity of the combination of the light emitting assembly 150 and the mount 190 is provided by the tension produced by the clamp 100, rather than a true bonding between the assembly 150 and mount 190, each of these elements 150, 190 is able to thermally expand or contract in a manner that accommodates thermal expansion and contraction among the elements in the assembly.

[0016] In like manner, because the electrical integrity of the combination of the light emitting assembly 150 and the mount 190 is provided by the tension produced by the clamp 100, rather than by soldering the assembly 150 to the mount 190, the light emitting assembly 150 is not subjected to the heat required to establish such a soldered connection. Techniques for enabling a durable coupling between elements under tension-coupling are common in the art, including the use of, for example, gold plating on the electrodes 122 and pads 260 (FIG. 2C) to avoid the formation of an oxidation layer on either. In like manner, using a common material for the electrodes 122 and pads 260 and keeping these elements together under tension also serves to preserve the connection over time. One of skill in the art will recognize that additional steps may be taken to assure long-term reliability, including, for example, the use of a conductive epoxy or localized welding. [0017] FIGs. 2A-2C illustrate an example 'screw-down' clamp 200 for mounting a light emitting assembly 150 to a submount 290, using principles similar to those used in the 'snap-on' clamp 100. In this embodiment, each clamp elements 210 includes a slot 211 for receiving a screw 230 or other fastening element for coupling the clamp 200 to the submount 290. For the purposes of this disclosure, the slot 21 1 may be either open or closed, and may be oval, round, or any other shape that permits engagement with the screw 230. When the screw 230 is secured to the mount 290, the clamp elements 210 are configured to exert a coupling tension between the light emitting assembly 150 and the submount 290. As noted above, this coupling tension also provides a tension-coupled electrical connection between the electrodes 122 A and 122B on the clamp 200 and the pads 260 on the light emitting assembly 150. Pins 121A 121B that facilitate coupling to the external source of power are arranged in a similar manner to that of clamp 100 in FIGs. 1A- 1B.

[0018] As illustrated in FIG. 2A, the clamp 200 may also include a tab 212 or other feature that serves to limit rotation of the clamp 200, and consequently a rotation of the assembly 150, as the screw(s) 230 are torqued to couple the assembly 150 to the submount 290. Such features may also facilitate accurate placement of the light emitting assembly 150 relative to reference features of the submount 290. The use of another fastener in place of screw 230 e.g. a "Christmas tree" fastener is contemplated and included within the scope of the invention.

[0019] FIG. 3 illustrates an alternative example clamp 300 that sandwiches electrodes 322 between a light emitting assembly 350 and a submount 390 (or, with respect to the embodiment of FIGs. 1A-1B, to a submount 190). In this embodiment, these electrodes 322 are part of a terminal element (not shown) that serves to couple the light emitting assembly 350 to an external source of power. One of skill in the art will recognize that filler material or a filler element may also be situated between the assembly 350 and the submount 390 to avoid the creation of excessive stress points at the electrodes 322. [0020] In this example embodiment, the electrodes 322 (and corresponding terminal element) may be mechanically coupled to the structure that provides the clamping tension, to facilitate ease of assembly, or may be part of an independent element. One of skill in the art will also recognize that the submount 390 may be sculptured so as to receive these electrodes in a recessed area, thereby avoiding the 'extra' height imposed by these sandwiched electrodes 322.

[0021] FIGs. 4A-4B illustrate an alternative example clamp that includes a terminal element 420 that includes PC board terminals 421A, 421B and 'screw-down' clamp elements 210 with anti-rotation elements 212. The terminals 421A, 421B may also be connected directly to wires, without a PC board. In the example of FIG. 4B, a structural support 425 is provided to assure that the tension provided by the clamp elements 210 is adequately coupled to the electrodes 422.

[0022] FIGs. 5A-5B illustrate an alternative example clamp 500 that includes a terminal element 520 that includes a set of plug terminals 521. As illustrated in FIG. 5B, the clamp 500 may be embodied as an enclosing structure that serves to farther protect the light emitting assembly 150 and other elements from the environment.

[0023] FIGs. 6A-6B illustrate an alternative example clamp 600 that includes a terminal element 620 that includes pin terminals 621 that facilitate coupling of the combination to 'push in' receptacles, such as found in the base of lamp structures.

[0024] FIGs. 7A-7B illustrate an alternative example clamp 700 that includes a molded base 730 wherein the structure of the base 730 provides a tension producing region 710 that couples the light emitting assembly 150 to a submount (not shown) via electrodes 722.

[0025] FIGs. 8A-8B illustrate an alternative example clamp that includes multiple fastening elements 810, 815 that serve to provide a tension coupling between the light emitting assembly 150 and a submount (not shown). In this embodiment, the electrodes 822 are situated at an opposite side of the light emitting assembly 150, so that when tension is applied to fastening element 815, the electrodes 822 are assured to be under tension. [0026] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

[0027] For example, it is possible to operate the invention in an embodiment wherein the clamping elements are part of the terminal element. Using FIG. 6A as an example, electrodes 622 are illustrated as the connection to pads (not shown) on the light emitting assembly 150. One of skill in the art would recognize, in view of this disclosure, that each of the clamp elements 610 may be insulated from each other and coupled to a corresponding plug pin 621 , and that the pads on the assembly 150 may be located beneath these clamp elements 610. In such an embodiment, the clamp elements serve as the electrodes for coupling external connections directly to the pads on the assembly 150. One of skill in the art would also recognize that only one of the clamps may serve as an electrode, or that both clamps may serve as a common electrode.

[0028] One of skill in the art will also recognize that although the example embodiments illustrate only two electrodes, the principles of this invention are not limited to a two-electrode embodiment. In like manner, the terminal element need not provide a distinguishable pin or plug for coupling to each electrode; for example, the frame of the clamp may form a common ground with the submount, and the mounting of the submount to the next mount element may create the electrical connection to the corresponding pad on the assembly.

[0029] One of skill in the art will also recognize that the clamp elements need not be symmetric, or even similar. For example, one of the clamp elements may be similar to clamp element 110 in FIGs. 1 A-1B, and shaped to engage a recess or other feature of the submount, while the other clamp element may be similar to clamp element 210 in FIGs. 2A-2C, with a slot 21 1 for receiving a screw after the first clamp is engaged. In like manner, although two or more clamp elements are illustrated in the figures, one of skill in the art will recognize that the submount and/or the light emitting assembly may be configured such that a single clamp element may provide sufficient tension to provide the required mechanical and electrical integrity. For example, the submount may include a lip or ledge under which the assembly is placed, and the clamp element may fasten to the submount opposite this lip. Such an embodiment is particularly suitable if the pads on the assembly are proximate to the clamp element, and, if sufficiently proximate, may not require the aforementioned lip or ledge in the submount. [0030] These and other system configuration and optimization features will be evident to one of ordinary skill in the art in view of this disclosure, and are included within the spirit and scope of the following claims.

[0031] In interpreting these claims, it should be understood that:

a) the word "comprising" does not exclude the presence of other elements or acts than those listed in a given claim;

b) the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements;

c) any reference signs in the claims do not limit their scope;

d) several "means" may be represented by the same item or hardware or software implemented structure or function;

e) any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise;

f) no specific sequence of acts is intended to be required unless specifically indicated; and g) the term "plurality of an element includes two or more of the claimed element, and does not imply any particular range of number of elements; that is, a plurality of elements can be as few as two elements, and can include an immeasurable number of elements.

Claims

CLAIMS We claim:

1. A retainer comprising:

a frame that is configured so as to lie atop at least a portion of a perimeter area of a light emitting surface of a light emitting assembly, the frame including:

at least one clamp element that is configured to be attached to a submount, thereby clamping the light emitting assembly to the submount via tension at one or more portions of the perimeter area, and

a terminal element that includes one or more electrodes that are configured to be tension coupled to one or more pads on the light emitting assembly when the clamp element is attached to the submount, the terminal structure being configured to facilitate external electrical connection to the light emitting assembly.

2. The retainer of claim 1, wherein the terminal element is situated between the at least one clamp element and another clamp element.

3. The retainer of claim 1, wherein the clamp element forms one of the one or more electrodes of the terminal element.

4. The retainer of claim 1, wherein the frame is in a form of a ring that encompasses the light emitting assembly.

5. The retainer of claim 1, wherein the clamp element includes a top portion that lies atop the perimeter area, a side portion that extends down from the top portion, and a bottom portion that extends from the side portion, the bottom portion of the clamp being designed to engage a recess in the submount under tension.

6. The retainer of claim 5, including a ring element that is sized to retain the bottom portion of the clamp within the recess.

7. The retainer of claim 1, wherein the clamp element includes a slot that facilitates screwing the clamp element to the submount.

8. The retainer of claim 1, wherein the frame includes one or more elements that inhibit rotation of the frame relative to the submount.

9. The retainer of claim 1, wherein the frame includes one or more features that limit a maximum tension applied to the light emitting assembly by the at least two clamp elements.

10. The retainer of claim 1, wherein the frame includes one or more features that facilitate accurate positioning of the light emitting assembly on the submount.

11. A light emitting device comprising:

a light emitting assembly,

a submount, and

a retainer comprising:

a frame that is configured so as to lie atop at least a portion of a perimeter area of a light emitting surface of the light emitting assembly, the frame including:

at least one clamp element that is configured to be attached to the submount, thereby clamping the light emitting assembly to the submount via tension at one or more portions of the perimeter area, and

a terminal element that includes at least one electrode that is configured to be tension coupled to at least one pad on the light emitting assembly when the clamp element is attached to the submount, the terminal structure being configured to facilitate external electrical connection to the light emitting assembly.

12. The device of claim 11, wherein the submount includes a heat sink.

13. The device of claim 11 , wherein the terminal element is situated between the at least one clamp element and another clamp element.

14. The device of claim 11, wherein the clamp element forms the at least one electrode of the terminal element.

15. The device of claim 11 , wherein the clamp element includes a top portion that lies atop the perimeter area, a side portion that extends down from the top portion, and a bottom portion that extends from the side portion, the bottom portion of the clamp being designed to engage a recess in the submount under tension.

16. The device of claim 11, including a ring element that is sized to retain the bottom portion of the clamp within the recess.

17. The device of claim 11, wherein the clamp element is screwed to the submount.

18. The device of claim 11 , wherein the frame is in a form of a ring that encompasses the light emitting assembly.

19. The device of claim 11, including a conductive epoxy that couples the at least one electrode to the at least one pad.