CN100470117C - Method and device for light-emitting diode light-emitting panel - Google Patents

Abstract

A light-emitting diode light-emitting board, comprising a highly thermally conductive substrate (for example, a metal-clad PCB), a plurality of light-emitting diode semiconductor devices mechanically connected to the substrate, fixed on the substrate and surrounding at least a part of the periphery of the above-mentioned light-emitting diode devices A bank, a substantially transparent polymeric encapsulant (eg, optical grade silicone) over the plurality of LED devices and bounded by the peripheral bank. In one embodiment, the luminescent panel includes a reflector (eg, a generally conical reflector) secured to the substrate to form the peripheral bank. In another embodiment, optical components (eg, lenses, filters, etc.) are optically attached to the polymer encapsulant on the LED device.

Description

Method and device for light-emitting diode light-emitting panel

technical field

The present application relates generally to lighting products, and in particular to luminous panels with light emitting diodes (Light Emitting Diodes).

Background technique

For many years, light emitting diodes (LEDs) have been used for relatively low power indicator lights, digital displays, and the like. In recent years, however, the brightness and power of individual LEDs have improved considerably, making them available in 1- and 5-watt devices.

Although small in size, LEDs have high efficacy and average lifespan compared to traditional lighting products. For example, a typical incandescent bulb has an efficacy of 10-12 lumens per watt and lasts approximately 1,000 to 2,000 hours; a common fluorescent tube has an efficacy of 40-80 lumens per watt and lasts for 10,000 to 20,000 hours; The halogen bulb has an efficacy of 20 lumens per watt and lasts 2000 to 3000 hours. In contrast, red-orange LEDs can emit 55 lumens per watt and have an average lifespan of 100,000 hours.

Despite the vastly improved efficacy and significant energy savings of LEDs, existing systems are still unable to take advantage of the desirable properties of LEDs and produce replacements for standard lighting products used in commercial and consumer applications. This is mainly due to the inherent limitations of existing luminescent panels.

For example, commercial high-energy light-emitting diode devices generate a large amount of heat, on the order of 50 W/cm ² . For reliability and longer lifetime, it is very important to keep the temperature of LEDs low. Existing known systems cannot compactly assemble multiple LEDs while maintaining the necessary heat transfer performance.

Similarly, LED dies are best protected by some coating, but standard semiconductor passivation cannot be used to reliably protect a row of multiple LED dies due to temperature excursions, especially in large assemblies. Thermal stress can cause shear line bonding, cracked die bonding, and other reliability problems.

Also, attempts to mix multiple colored LEDs to produce white light are not ideal, because even if the LED devices are packed together in close proximity (still limited by thermal transport reasons), the light produced by such a system cannot be very bright. Mixed well, the result is uneven spots of individual colors rather than a uniform projection of white light. Similarly, currently produced synthetic semiconductor light-emitting diode colors cannot efficiently generate a certain wavelength (eg, yellow light at 575nm). Mixing active red and green LEDs is a good idea.

Accordingly, there is a need for an LED light panel assembly that overcomes these and other limitations of the prior art.

Contents of the invention

In general, the present invention provides a novel, multi-chip-on-board (MCOB) light-emitting board, which includes a high thermal conductivity substrate, several light-emitting diode semiconductor devices mechanically connected to the substrate, fixed on the substrate and An outer dike surrounding at least a portion of the LED device, and a substantially transparent polymeric encapsulant (eg, optical grade silicone) positioned over the LED device and bounded by the outer dike.

According to one embodiment of the invention, the highly thermally conductive substrate comprises a metal clad printed circuit board (PCB).

According to various embodiments of the present invention, the electrical connection structure of the light emitting diode devices is series connection, parallel connection, or a combination thereof.

According to another embodiment of the present invention, the luminescent panel comprises a reflector (eg, a substantially conical reflector) fixed on the substrate to form a peripheral bank.

According to another embodiment of the present invention, optical components (eg, lenses, filters, etc.) are optically attached to the polymer encapsulant on the LED device.

Thus, the present invention provides a high-efficiency LED light-emitting panel widely applicable to lighting devices.

Brief description of the drawings

A more complete understanding of the invention may be obtained by reference to the detailed description taken in conjunction with the accompanying drawings, in which like reference numerals represent like elements throughout, and:

1 is an isometric view of a light-emitting panel according to an embodiment of the present invention, the light-emitting panel has a plurality of surface-connected light-emitting diode chips connected in parallel and in series;

2 is a top view of a light-emitting panel according to another embodiment of the present invention, the light-emitting panel has a plurality of wire-bonded light-emitting diode chips connected in parallel and in series; wherein each light-emitting diode chip includes two bonding pads;

3 is a top view of a light-emitting panel according to another embodiment of the present invention, the light-emitting panel has a plurality of parallel-connected wire-bonded light-emitting diode chips;

4 is a top view of a light-emitting panel according to another embodiment of the present invention, the light-emitting panel has a plurality of wire-bonded light-emitting diode chips connected in parallel and in series; wherein each light-emitting diode chip includes a bonding pad;

Figure 5 is a partial isometric view of an exemplary light emitting board including a light emitting diode circuit die on a metal clad, high thermal conductivity PCB substrate;

Figure 6 is an isometric view of a luminous panel including an inner dike and a peripheral dike;

7A and 7B are top and side views, respectively, of a light emitting panel including peripheral and inner dikes filled with encapsulant material;

Figure 8 is an isometric view of a luminous panel including reflectors and inner dikes;

9A and 9B are a top view and a side view of the luminous panel in FIG. 8, respectively;

10A and 10B are top and side views, respectively, of a light emitting panel with exemplary lenses;

Fig. 11 is a graph showing the spectrum of white light at different temperatures.

Detailed ways

The following description is only a description of exemplary embodiments of the present invention, and does not limit the scope, usage or structure of the present invention in any way. Rather, the following description provides a convenient description for implementing various embodiments of the invention. It will be apparent that various changes may be made in the function and arrangement of elements described in these embodiments without departing from the scope of the invention.

overview

In general, an LED light panel according to the present invention comprises a highly thermally conductive substrate (e.g., a metal-clad PCB), a plurality of LED (LED) semiconductor devices mechanically connected to the substrate, fixed on A peripheral bank on the substrate and surrounding at least a portion (preferably all) of the LED devices, and a substantially transparent polymer encapsulant (e.g., an optical grade) disposed on the plurality of LED devices and bounded by the peripheral bank Silicone). In one embodiment, the luminescent panel includes reflectors (e.g., generally conical reflectors) affixed to the substrate to form peripheral banks and help direct and focus light and/or mix light from two or more different colors. light emitting diode device. In other embodiments, one or more optical elements, such as filters, lenses, etc., are affixed to the encapsulant coating, as described further below.

LED Connectivity

Referring to FIG. 1 , which shows an exemplary electrical topology employed in the present invention, a luminescent panel 100 includes a plurality of light emitting diode devices 104 connected to a highly thermally conductive substrate (or simply "substrate") 102 (in this disclosure). In one embodiment, a surface-attached light-emitting diode chip). In this embodiment, the substrate 102 includes a conductive trace pattern 106 electrically or mechanically connected to the plurality of LED devices 104 .

Trace pattern 106 is configured to interface with an AC or DC power source depending on the application. For example, in the illustrated embodiment, a DC V ₊ terminal 108 and a V ₀ terminal 110 are provided. In some cases, these terminals are generally referred to as "inputs".

The LED devices 104 are electrically connected to each other by any suitable means. As shown in FIG. 1, for example, the light emitting diode device 104 may be a circuit to connect groups of individual devices in series, where the groups themselves are connected in parallel with respect to the input. In the illustrated embodiment, seven parallel columns are themselves connected in parallel across terminals 108 and 110, and each column includes five LED devices connected in series. Alternatively, referring to FIG. 3 , a plurality of LED devices 104 (in this embodiment, 49 wire-bonded chips) are connected in series with terminals 110 and 108 .

In general, notwithstanding the embodiments shown above, the present invention encompasses any number of LED arrangements in any suitable electrical arrangement (series, parallel or combinations thereof) and in any suitable geometry. For example, the LED devices may be positioned in a rectilinear pattern (eg, a square or rectangular array), a circular or curved pattern, a random or random pattern, or any combination thereof. Additionally, LED devices may be provided in multiple regions, with each region having a different pattern and a different number of devices.

The number of LED devices 104 used in a device can be selected based on a number of design variables including, for example, characteristics of the power source (AC to DC conversion, effective DC voltage, real power, etc.), characteristics of the LED device itself (e.g., forward voltage ( _Vf , power rating, etc.), desired color scheme (described below), properties of substrate 102 (eg, thermal conductivity, geometry, etc.), and properties of use and external thermal conditions.

In one embodiment, the light emitting diode devices are connected in series or in parallel such that all combined positive voltages of the light emitting diode devices match the electrical input. For example, in domestic applications in the US and Canada, 120VAC must be rectified to 162V DC by a power converter before being input to the LEDs. Generally speaking, depending on the V _f of each LED, 40 to 80 LED devices can be connected in series to accept 162V rectified DC input. Typical red and amber LED devices are known to have a rated Vf of about 1.8 to 2.5V, and green and blue LEDs have a rated _Vf of about 3.0 to 4.5V. In order to apply a lower voltage, such as 12V DC or 24V DC MR-16, in order to obtain the required light output and match the input voltage, it is necessary to connect the LED chips in series or parallel. Outside of the United States and Canada, the household power supply in most countries is 220V or 230V, so 80 to 160 light-emitting diode chips need to be connected in series to match the rectified DC.

By matching the combined positive voltage and the voltage of the input power supply, the power supply to the light-emitting panel can be simplified, so that there is no need to connect a bulky, complex voltage step-up or step-down rectifier, or a switching power supply to the system; simple, An efficient AC to DC rectification circuit is sufficient. This allows light panels to be incorporated into compact assemblies—for example, a light bulb assembly that plugs into a standard light bulb socket.

LED device

Any suitable light emitting diode device 104 may be used in conjunction with the present invention, including single die, chip scale package, conventional package, surface mount device (SMD), or any other now known or future developed LED device. In the embodiment described in connection with FIG. 1, for example, the light emitting diode device 104 comprises a surface mount device having electrical contacts mounted directly to the surface of the trace pattern 106, such as a "flip-chip chip)” or on dies with solder bumps.

Alternatively, referring to FIG. 2, the LED device may include LED chips 204 coupled (by soldering, epoxy bonding, etc.) to respective PCB pads 206, wherein each die 204 has at least two bond pads. , for providing electrical connection through wire bonding interconnector 202 . Alternatively, an intermediate PCB pad 208 may be used to facilitate wire bonding between individual dies. This embodiment shows seven dies in series forming seven groups of parallel dies; however, as described above, the invention is not limited thereto and may include any number of dies connected in series, parallel or mixed.

FIG. 5 shows an isometric partial cross-sectional view of a single LED device shown in FIG. 2 . As shown, substrate 102 includes a highly thermally conductive base 504 overlaid with a highly thermally conductive, electrically insulating material 502 . Individual PCB traces 208 and 206 are placed on layer 502 , and light emitting diode die 204 is bonded to PCB trace 206 . Wire bonds (not shown) are used to interconnect die 204 and adjacent dies (eg, using intermediate traces 208 ).

Fig. 4 also shows another embodiment of the present invention. According to this design, a single LED circuit die 204 is connected (via a solder bond or other conductive coupling) to a PCB pad 206 . A single wire bond interconnect 202 is then used to couple the PCB pad 206 to the bonding area of the adjacent die. That is, each LED die 204 includes a single connection pad, and the backside of the die serves as a second electrical contact.

Light emitting diode device 104 is fabricated from one or more suitable semiconductor materials including, for example, GaAsP, GaP, AlGaAs, AlGaInP, GaInN, and the like. The selected dimensions of the LED device 104 can be determined using various design parameters. In one embodiment, light emitting diode device 104 is a 300×300 square micron die approximately 100 microns thick. Those skilled in the art will realize that the present invention is not limited thereto.

It is known that each light emitting diode device has a particular color corresponding to a particular wavelength (or frequency). One aspect of the invention relates to the ability to use multiple light emitting diodes of different colors to produce a desired color of emitted light. Typically, a set of LED devices mounted on a substrate includes x red LEDs, y green LEDs, and Z blue LEDs, where the x:y:z ratio is chosen to achieve a specific correlated color temperature (CCT) white light.

In general, any number of LED colors can be used in any desired ratio. A typical incandescent bulb produces light with a CCT of 2700K (warm white light), and a fluorescent bulb produces light of about 5000KCCT. Thus, typically more red and yellow light-emitting diodes are required to obtain 2700K light, and more blue light-emitting diodes are required for 5000K light. In order to obtain a high color rendering index (CRI) (ColorRendering Index), the light source must White light is emitted with a spectrum covering almost the entire range of visible light (380nm to 770nm wavelength) so that dark red, reddish, amber, greenish, dark green, light blue and dark blue colors appear in the mix.

In order to achieve these objects, the invention allows the use of light-emitting diode arrangements with different wavelengths in the light-emitting panel. In one embodiment, for example, to obtain light at 3200K, the mixing ratio (relative to the number of LEDs) of R(620nm):Y(590nm):G(525nm):B(465nm) is 6:2:5 :1. According to another embodiment, the mixing ratio of R:Y:G:B is 7:3:7:2 for obtaining 3900K light. In another example, a ratio of 10:3:10:4 was used to obtain light at 5000 K. The spectra for each of the above three examples are represented in FIG. 11 .

It will be appreciated that the listed mixing ratios are determined by the brightness of the chips as well as their wavelengths. Accordingly, the invention is not limited by the number of types of light emitting diodes that can be used to create a desired light output.

In addition to white light, the present invention can also use similar color mixing techniques to generate light of a specific color. That is, while multiple single-color LEDs can often be used to produce a desired color, in some cases LEDs of two or more colors can be combined to form a composite color.

More specifically, due to the material properties of LED compound semiconductors, efficacy at certain wavelengths is not desired. For example, no conventional compound semiconductor material efficiently emits yellow light at 575nm. This wavelength, 575nm, is located in the performance valley between AlGaInP and CaInN semiconductors. However, by mixing LED devices fabricated from these two materials, it is possible to produce yellow light with the desired efficacy.

base

Substrate 102 includes any structure capable of providing mechanical support to LED device 104 while providing desired thermal characteristics—ie, by helping to dissipate all or part of the heat generated by LED device 104 . In this regard, substrate 102 is preferably a highly thermally conductive substrate.

As used herein, the term "high thermal conductivity substrate" refers to a substrate having an effective thermal conductivity greater than 1 W/°K-m, preferably greater than about 3 W/°K-m. The geometry and material of the substrate 102 may thus vary depending on its application. In one embodiment, the substrate 102 includes a metal clad PCB, such as a Thermagon T-Lam or Bergquist thermal clad substrate. These metal-clad PCBs can be fabricated using conventional FR-4 PCB processes and are therefore relatively cost-effective. Other suitable substrates include various hybrid ceramic substrates and enamelled metal substrates. Additionally, reflection of light from the substrate can be enhanced by applying a white mask over the substrate and silvering the trace circuitry.

sealant layer

Preferably, a substantially transparent polymeric encapsulant is disposed over the light emitting diode device and then suitably cured to provide a protective layer. In a preferred embodiment, the encapsulant comprises optical grade silicone. The properties of the encapsulant can be selected to achieve other optical properties, for example by filtering out light generated by the light emitting diode device. At the same time, the protective encapsulant layer is flexible enough to withstand thermal excursions experienced by the component without degrading the die, leads, and other components.

Figures 6, 7A and 7B show different views of an embodiment of the invention wherein the encapsulant covering the LED device is adapted to be defined by a dike structure. More specifically, the light emitting panel 100 of FIG. 6 includes a peripheral bank 602 that surrounds at least a portion of the light emitting diode die 204 . In a preferred embodiment, the embankment 602 generally has a substantially rectangular, square, hexagonal, circular, octagonal or elliptical structure surrounding the entire array of LED dies 204 . Peripheral bank 602 is adapted to be attached to substrate 102 using an adhesive or other suitable attachment method. A circular dike is preferred for optical reasons.

As shown, the encapsulant material is preferably deposited on LED die 204 such that it fills the space formed by peripheral bank 602 . That is, referring to the cross-section (section A-A) shown in FIG. 7B , the encapsulant material 606 fills the top surface of the peripheral bank 602 . Additionally, peripheral bank 602 is preferably made of a substantially transparent material, such as a transparent plastic (eg, polycarbonate) material. Its transparency allows light emission around the edges of the luminescent panel.

In an alternative embodiment, a second, inner dike 604 is located near the center of the LED die 204 . The inner dike 604 serves to confine the sealant and is preferably a transparent material. The presence of inner dike 604 allows connections to be made through the center of the circuit board.

reflective ring

According to another embodiment, the light emitting panel comprises a reflective ring substantially surrounding the light emitting diode arrangement, which helps to focus and/or direct the light generated by the system.

Referring to FIG. 8, an exemplary reflector 802 is suitably attached to the substrate 102 of the light-emitting panel in such a manner that all of the LED dies 204 are located on the base of the reflector. In the illustrated embodiment, the reflector 802 is generally conical. However, it will be appreciated that the reflector 802 may be parabolic, angular, or have any other desired shape and size. As shown, the reflector 802 acts as a peripheral bank by confining the encapsulant.

In order for the reflector 802 to direct and focus the light generated by the LED die 204, the texture and material of the reflector 802 preferably have a high reflectivity. In this regard, the reflector 802 preferably generally has a generally smooth, polished , mirror-like inner surface.

In applications where substantially white light (or other specific color) is to be used and LEDs of two or more colors are used in combination to produce that color, it is preferred that the inner surface of reflector 802 serve to scatter the light generated by the LED devices , thus providing optimal color mixing, even though the efficiency or focus of the luminous panel would thus be slightly reduced (due to light scattering). Therefore, in applications where two or more color LEDs are used, the inner surface of the reflector 802 is preferably treated by an appropriate process and in an appropriate ratio. For example, the reflector 802 may be faceted, sandblasted, chemically roughened, or otherwise treated to provide a desired scattering rate. Additionally, the texture or facets can be random, regular, random or a combination thereof.

other optical components

According to another embodiment of the invention, one or more optical elements are arranged on the surface of the encapsulant to provide a desired optical effect with respect to the light emitted by the light emitting diode arrangement. These optical elements themselves can be hard glass or plastic, and since the encapsulant layer acts as a protective surface, the elements do not cause damage to the LED device. Suitable optical elements include, for example, various lenses (concave, convex, planar, "bubble" lenses, Fresnel lenses, etc.) and various filters (polarizing filters, color filters film, etc.).

Figures 10A, 10B and 10C show top, cross-sectional and isometric views of a light emitting panel with "bubble" lenses according to one embodiment of the present invention. More lens bubbles 102 include a planar side connected to the encapsulant 606 and a bubble side that includes a plurality of raised regions 1004 . In the illustrated embodiment, the bubble lens 102 includes a 4x4 grid of such bubbles. Any number and size of such lens features are contemplated by the present invention.

in conclusion

Briefly, the present invention provides a novel, highly efficient multi-chip LED-on-board lighting board that can be used in any imaginable lighting application, now known or developed in the future. For example, such light panels can be used in devices that use light bulbs that can be installed in standard household devices (standard screw-in bulbs, fluorescent lamps, halogen lamps, etc.), automotive applications (tail lights, headlights, blinkers, etc.), portable lighting devices and traffic control devices (traffic signals, etc.). In addition, the claimed luminescent panels may be used in devices of a specific color or range of colors, including white light of any desired color temperature. The content of this application is not intended to limit the scope of applications in which the invention may be used.

Other advantages and structural details of the present invention are apparent from the accompanying drawings and will be well understood by those skilled in the art. The present invention has been described above in terms of specific exemplary embodiments. However, many changes, combinations and modifications can be made to the exemplary embodiments without departing from the scope of the present invention.

Claims (21)

1. A luminescent panel, comprising: High thermal conductivity substrate; a plurality of light emitting diode devices mechanically connected to said substrate, said light emitting diode devices being electrically connected to each other in a circuit having first and second terminals for receiving an input voltage; a peripheral bank secured to the substrate and surrounding at least a portion of the LED device; a transparent polymeric encapsulant over said plurality of light emitting diode devices and bounded by said peripheral bank, and The inner embankment located in the middle of the above-mentioned base. 2. The light-emitting panel according to claim 1, wherein said plurality of light-emitting diodes comprises a first light-emitting diode with a first color and a second light-emitting diode with a second color, and said reflective ring has a surface structure , the surface structure disperses the light generated by the first and second light emitting diodes, so as to mix the light of the first color and the second color. 3. The light-emitting panel according to claim 1, wherein the base is connected to the reflective ring. 4. The luminescent panel according to claim 3, wherein a part of said reflective ring is used as said peripheral bank. 5. A luminescent panel, comprising: High thermal conductivity substrate; a plurality of light emitting diode devices mechanically connected to said substrate, said light emitting diode devices being electrically connected to each other in a circuit having first and second terminals for receiving an input voltage; a peripheral bank secured to the substrate and surrounding at least a portion of the LED device; a transparent polymeric encapsulant on said plurality of light emitting diode devices and bounded by a peripheral bank, wherein said substrate is attached to a reflective ring, a portion of said reflective ring serving as said peripheral bank, Wherein, the above-mentioned plurality of light-emitting diode devices include a first light-emitting diode with a first color and a second light-emitting diode with a second color, and the above-mentioned reflective ring has a surface structure, and the surface structure is dispersed by the first and second light-emitting diodes. The light generated so as to mix the above-mentioned light of the first color and the light of the second color. 6. A light-emitting diode light-emitting panel, comprising: Substrates for printed circuit boards with metal cladding; a plurality of light emitting diode devices mechanically connected to said substrate, said light emitting diode devices being electrically connected to each other in a circuit having first and second terminals for receiving an input voltage; a reflective ring secured to the substrate and surrounding at least a portion of the LED device; a transparent polymeric encapsulant on said plurality of light emitting diode devices and bounded by a reflective ring, Said plurality of light emitting diode means comprises a first light emitting diode having a first color and a second light emitting diode having a second color, said reflective ring having a surface structure which disperses light produced by said first and second light emitting diodes light to mix the light of the first color and the second color. 7. The light-emitting panel according to any one of claims 1, 5 or 6, characterized in that the light-emitting diode devices are electrically connected in series. 8. The light-emitting panel according to any one of claims 1, 5 or 6, characterized in that the above-mentioned light-emitting diode devices are electrically connected in parallel. 9. The light-emitting panel according to any one of claims 1, 5 or 6, characterized in that the above-mentioned light-emitting diode devices are divided into different series-connected groups of light-emitting diode devices, and these device groups are connected in parallel. 10. The light-emitting panel according to any one of claims 1 and 5, characterized in that the substrate with high thermal conductivity comprises a metal-clad printed circuit board. 11. The light-emitting panel according to any one of claims 1, 5 or 6, characterized in that the above-mentioned sealant comprises optical grade silicone resin. 12. The light-emitting panel according to any one of claims 1 and 5, wherein the sealant flows on the top surface of the peripheral bank, and the peripheral bank is transparent. 13. The luminescent panel according to claim 5 or 6, further comprising an inner dike located in the middle of the base. 14. The luminescent panel according to any one of claims 1, 5 or 6, further comprising an optical component on said polymer encapsulant. 15. The luminescent panel according to claim 14, wherein said optical component comprises a lens. 16. The light-emitting panel according to claim 15, wherein the lens is selected from concave lenses, convex lenses or flat lenses. 17. The luminescent panel according to claim 14, wherein said optical component comprises a filter. 18. The light-emitting panel according to any one of claims 1, 5 or 6, characterized in that the above-mentioned plurality of light-emitting diode devices includes a ratio of a single light-emitting diode of a specific color to be selected in order to obtain a color with a desired specific correlated color temperature ( CCT) white light. 19. The light-emitting panel according to claim 18, wherein the CCT is between 2000K and 10000K. 20. A luminescent panel as claimed in any one of claims 1, 5 or 6, characterized in that said plurality of LEDs comprises a ratio of individual LEDs of a specific color to be selected in order to obtain a specific color. 21. The luminous panel according to any one of claims 3, 5 or 6, characterized in that the reflective ring includes a reflective plating layer and a structure for mixing light.

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