Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With reflector – opaque mask – or optical element integral...
Reexamination Certificate
2002-02-11
2003-04-01
Wilson, Allan R. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With reflector, opaque mask, or optical element integral...
C257S099000, C257S100000
Reexamination Certificate
active
06541800
ABSTRACT:
FIELD
The embodiments relate generally to packaging for use in manufacturing light emitting diodes (LED), and the like, that may provide greater light output and increased reliability. One aspect of the embodiments may be to produce an optically efficient LED that can generate a higher degree of illumination per unit area than is currently available in the art. Another aspect of the embodiments may be to provide a means of mechanically attaching the device to a light fixture or printed circuit board. Another aspect of the embodiments may be to provide an improved package for LEDs and a method for packaging multiple LEDs on strips, which better facilitates automated manufacturing methods for assemblies utilizing the LEDs. Another aspect of the embodiments may be to provide a means of producing a white light. Another aspect of the embodiments may be to provide a means of mounting multiple LED dice.
PRIOR ART
The art of manufacturing the light emitting component of LEDs is widely described in the art and well known to those so skilled. Furthermore, the art of producing white LEDs is well known and described in the art. Pertinent patents include: U.S. Pat. No. 5,813,752 issued to Singer et al. on Sep. 29, 1998, entitled “UV/Blue LED-Phosphorus Device With Short Wave Pass, Long Wave Pass Band Pass and Peroit Filters,” which describes the use of a layered blue/UV LED semiconductor having a top layer of phosphor and filters for producing white light; U.S. Pat. Nos. 5,998,928 and 6,060,440 issued to Shimizu et al. on Dec. 7, 1999 and May 20, 2000, respectively and each entitled “Light Emitting Device Having A Nitride Compound Semiconductor And A Phosphor Containing A Garnet Fluorescent Material,” which describe the design of white LEDs that utilize blue LEDs to excite a layer of phosphor material comprising garnet fluorescent materials activated with cerium and/or including the use of dispersing materials surrounding the phosphor containing components to diffuse the resulting illumination.
The structural makeup of various LED packages are also disclosed in the commercial data sheets of a number of LED manufacturers, see for example, the technical data sheets for Super Flux LEDs, by LumiLeds (a joint venture between Philips Lighting and Agilent Technology); SnapLED 150 LEDs, by LumiLeds; Six LED High Mount Stop Light Array, by LumiLeds; Luxeon Star, by LumiLeds; Shark Series, High Flux LED Illuminators, by Opto Technology, Inc.
BACKGROUND
A light emitting diode (LED) is a compact semiconductor device that generates light of various colors when a current is passed through it. The color depends primarily upon the chemical composition of the light emitting component, or chip, of the LED die. LEDs exhibit various advantages over filament based lighting devices such as longer life, lower power requirements, good initial drive characteristics, high resistance to vibration and high tolerance to repeated power switching. Because of these favorable characteristics LEDs are widely used in such applications as indicators and lower power lighting applications.
Recently LEDs for red, green and blue (RGB) having high luminance and efficiencies have been developed and employed in large screen LED displays. This type of LED display can be operated with less power and has favorable characteristics as being lightweight and exhibiting long life. The application for use of LEDs as alternative light sources is burgeoning.
Even in light of its positive characteristics, since the device is not 100% efficient at generating light from the supplied electrical current, a great deal of heat can be produced by the LED chip. Therefore, heat sinks are employed to dissipate heat generated by the LED, usually provided through the metal lead frame of the LED itself. If the heat is not adequately dissipated, stress is imposed on various internal components of the LED due to differing coefficients of thermal expansion. Some manufacturers have produced more powerful LEDs having large heat sinks but at a trade-off. First, if a LED with a large heat sink is soldered using conventional methods (i.e. wave solder, reflow solder), the heat from the soldering process is transferred to the LED chip, which may cause failure of the LED. Second, if the LED is soldered using non-conventional techniques (i.e. bar soldering or laser soldering), this must generally be performed by the LED manufacturer due to the heat sensitive nature of the process. Therefore, the LED manufacturer provides a high flux LED as a “board level” component. Unfortunately, such a configuration may not accommodate the physical space requirements of the intended end product design.
In addition, optical coupling of the LED to an associated lens is inefficient. Generally, an LED consists of a semiconductor chip potted into place on a substrate using an optically clear epoxy. This direct interface of the chip (index of refraction n≈3.40) to the epoxy (n≈1.56) creates a dramatic index of refraction gradient between the two materials. As light travels from a medium of high index of refraction to low index of refraction, Fresnel losses are experienced due to the inability of the light to escape the package caused by internal reflection. Therefore, a material or a layer of material that minimizes the transition in index of refraction will decrease the Fresnel losses that would otherwise occur. By substituting the clear epoxy with one or more layers of an optical gel or fluid (hereinafter, collectively referred to as a “gel”) having an index of refraction value midway between the LED chip material and the epoxy, photon extraction, and thus light output, will be enhanced.
Furthermore, because the epoxy used to encapsulate the conventional LED chip is generally rigid when fully cured, thermal expansion can cause a degree of shear and tensile stress on the bond(s) between the wire and LED chip. By encapsulating the chip and wire bond in a gel instead of an epoxy, the wire bonds are enabled some movement within the gel under normal operating conditions, thereby lessening the shear and stresses between the chip and the wire bonding.
Finally, when incorporated into various product applications, LEDs (in their numerous package designs) are generally designed to be assembled onto a printed circuit board and secured using a soldering process. However, since the LED package of the present invention can be assembled using an alternative mechanical process (i.e., pin & socket, laser-welding, etc.), the use of LEDs is more flexible for automated manufacturing processes, utilizes less board space than previously required and can accommodate a wider variety of product applications. Mechanical attachment of the LED package of the present embodiments will greatly reduce or even eliminate altogether the heat to which the LED chip is exposed during the LED assembly process, thereby eliminating a major source of component failure. In addition, the LED is provided with an integral metal lead frame providing substantial greater heat sinking than that provided by conventional LEDs coupled to an epoxy printed circuit board.
SUMMARY
One embodiment provides a system comprising an LED package. The LED package comprises an annular anode and a cathode coupled to the annular anode. The LED package also comprises an LED die coupled to the cathode and the annular anode and a lens coupled to the annular anode. The LED package also comprises a viscous material located in a cavity defined by the lens, the cathode, and the annular anode.
Another embodiment provides a system comprising a mounting device and an LED package. The LED package comprises an annular lead frame with a central opening, a heat sink coupled to the lead frame adjacent the central opening, an LED die coupled to the heat sink and via wire bonding to the lead frame, and a lens coupled to the lead frame. The lens comprises protrusions that are utilized to mechanically secure the LED package to the mounting device. The LED package further comprises silicone material located in a cavity defined by the lens, the heat sink, and the lea
Barnett Thomas J.
Tillinghast Sean P.
Eley James R.
Thompson Hine LLP
Weldon Technologies, Inc.
Wilson Allan R.
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