Patent Application
20080029774
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims and drawings where:
Throughout this disclosure, reference is made to some terms which may or may not be exactly defined in popular dictionaries as they are defined here. To provide a more precise disclosure, the following terms are presented with a view to clarity so that the true breadth and scope may be more readily appreciated. Although every attempt is made to be precise and thorough, it is a necessary condition that not all meanings associated with each term can be completely set forth. Accordingly, each term is intended to also include its common meaning which may be derived from general usage within the pertinent arts or by dictionary meaning. Where the presented definition is in conflict with a dictionary or arts definition, one must use the context of use and liberal discretion to arrive at an intended meaning. One will be well advised to error on the side of attaching broader meanings to terms used in order to fully appreciate the depth of the teaching and to understand all the intended variations.
Herein throughout this disclosure, we use the term ‘optically cooperative material’ meaning optical media which interacts with light passing therethrough. Generally at least partly transparent, these media are sometimes and preferably arranged as a suspension of matter in a binder agent. The materials cooperate with and promote optical conduction while at the same time imparting some influence on beams passing therethrough.
A dispersant is any physical body which operates on incident light to cause a change in its propagation direction. This may be via reflection, refraction, diffraction or any combination of these.
A wavelength shifting medium is a material which operates on incident light to produce a change in its wavelength. Generally a phosphor absorbs light of a high energy and re-emits light at a lower energy—i.e. the process is lossy.
The term ‘mounting pad’ may merely refer to a position on a substrate to which a semiconductor may be affixed. It may also include a mechanical bonding agent and electrical support such as electrical contacts. However, a mounting pad primarily refers to the location to which a semiconductor belongs.
In accordance with each of preferred embodiments of these inventions, there is provided semiconductor optical sources having output with a high degree of angular uniformity. It will be appreciated that each of embodiments described include apparatus and the apparatus of one preferred embodiment may be different than the apparatus of another embodiment.
Typical semiconductor light sources are generally referred to as ‘LED’s or light emitting diodes. While special cases include semiconductor lasers, in general we consider diode source whether or not stimulated emission is included. When considering these sources, one may refer to them as an ‘LED’. However the name seems to only include the diode but not the supporting package in contrast to its common use. By ‘LED’, it is meant in the arts that the semiconductor chip, its electrical supports and mechanical supports are included. Thus, LED includes the diode semiconductor and the supporting package and systems.
Special LED packages and those included here are comprised primarily of two major elements including a lens cover and a substrate. A substrate is used to mechanically and electrically couple a semiconductor die or ‘chip’ in a fashion whereby it operates to produce light when energized. A lens cover is included to provide optical coupling from the semiconductor chip, or plurality of chips, into an output beam. In addition to these two important elements, certain LED packages designed with particular performance properties in mind may also include such elements as phosphors which operate to change the system wavelength and dispersants to spread light into an optical beam having good angular uniformity. Phosphors can be used to change a portion of high energy photons into lower energy photons of longer wavelengths. In this way, one can arrive at a system with broadband outputs. Further, dispersants can be used to cause highest intensity light on axis to be coupled into off axis directions thereby evening the intensity for various small angles. Thus, it can be said that some high performance LED systems are comprised of a semiconductor die (at least one), a substrate, a lens cover, phosphors and dispersants. It is implied that these are accompanied by electrical and mechanical support systems as well.
It is an important aspect of these inventions that these lens covers and substrates cooperate together and jointly form an enclosed cavity. When a lens cover is pushed to and joined with a substrate via any of various coupling means, an enclosed space remains between them. This space is intentionally formed to accommodate the semiconductor die, its mechanical and electrical couplings, phosphor wavelength shifting media and dispersants. The size and shape of such cavities are carefully designed with a view to supporting a particular optical output.
A first version of these inventions may be understood in view of the diagram of
The cavity may be filled with an optically active or ‘optically cooperative’ material. An optically active material might be one which emits light such as a photophosphor type material. In contrast, an ‘optically cooperative’ material might be one which is not necessarily optically active but still operates to interact with optical beams propagating therethrough.
The optically cooperative material or materials may be injected into the cavity such that it comes into close proximity or entirely covers and surrounds a semiconductor die 6. In preferred versions, optically active material is injected to completely fill the cavity. In this way, good thermal conduction provides a heat escape path from the semiconductor to both the lens cover and substrate to improve cooling characteristics of the system. In addition, well placed material in accordance with this description also assures good optical homogeneity.
The optically cooperative material(s) may be injected into the cavity after the lens cover and substrate are brought together and joined to form the enclosed cavity. These optically cooperative materials may be injected through filling ports 7 and 8. One or more fill ports may be provided as needed in various important locations on the substrate. Either of these ports might also operate an ‘exhaust’ or ‘exit’ port as well. When material is being injected via a first port, the other port permits air and excess material to escape.
In review, it is important to note that a substrate having ports therein is joined with a lens cover to form an enclosed cavity of prescribed shape. The molded shape of the under surface of the lens cover provides definition as to the cavity shape and size.
To more fully appreciate details of these inventions, figure two is provided to illustrate injection of an optically cooperative material in a viscous form. Lens cover 21 includes a shaped undersurface which provides an enclosed cavity when the lens cover is joined with and coupled to substrate 22. A semiconductor light emitting device 23 is affixed to the substrate and mechanically and electrically coupled therewith. An injection tool 24, or simple syringe, permits a fine needle 25 to address the filling port whereby viscous material 26 may be pushed from inside the injection tool into the cavity. As the optically cooperative material 27 enters the enclosed cavity and begins to fill it including taking up the precise shape of the cavity, it also pushes air 28 such that the air and any excess material exits the cavity at port 29.
It is meaningful to note that since the viscous optically cooperative material takes up the shape of the cavity precisely, the spatial distribution of the optical material of a final device is dictated by the shape of the cavity and more precisely the undersurface of the lens cover. Thus, since one can effect the spatial distribution of optically cooperative material via the design of the undersurface of the lens cover, this design ultimately effects that beam shape and characteristics. For example, if the optical material is a dispersant material, then more or less dispersant can be applied to various angles with respect to the system axis and thus permit a controlled application of dispersant and result in a beam having ideal divergence characteristics.
Some preferred embodiments include a simple configuration where light emitted from a semiconductor diode passes through a first optically cooperative material, and then thereafter in the optical train, passes through a second optically cooperative material. The first optical material may be delivered and provided to envelope and cover the semiconductor. The second optical material may be provided to envelope the combination of the semiconductor and first optical material to effect a ‘nested’ system of elements. Light emitted from the semiconductor necessarily passes through the first optically cooperative material and interacts therewith. After, the light passes from the first optical material and into the second. As it further passes through the second optically active material it is subject to further interaction therewith that material which may be different than the first. That is to say the optical effect imparted to the beam may be different to the effect provided by the first. In this way, the system may be characterized as multi-layered where each layer is comprised of a different composition. One of such configurations is illustrated in the drawing presented here as
A lens cover 31 is formed of hard plastic or polymer material in a molding process which imparts a lensing type smooth top surface 32 and an undersurface 33 which may have particular shape such as spherical or other desired configuration. It is of considerable importance that the undersurface form a partially enclosed cavity space; or a region characterized as ‘concave’. It is not necessary that the surface be rectilinear or spherical; but rather it may in fact be a compound and complex system of curves joined together to form a concavity without natural geometric description. The lens cover also includes a seating surface 34 which permits it to be joined to and coupled with substrate 35 which may be substantially flat.
In preferred versions, the substrate top surface is smooth and flat and is joined to a cooperating seat similarly smooth and flat. However, in other versions it is anticipated that cooperating mechanical interlock surfaces might operate to join these elements together. In either case, when a lens cover element and a substrate are joined together, a substantially enclosed cavity is formed therebetween. The space is suitable for receiving therein one or more semiconductor elements and optically cooperative materials. In particular, a light emitting diode 36 may be mounted and electrically coupled to the substrate at a semiconductor mounting pad fashioned at the top surface of the substrate.
A mounting pad may provide electrical and/or mechanical support and coupling between a substrate and a semiconductor chip. However for purposes of this disclosure, a mounting pad may be merely a location on the substrate without any particular specification as to electrical or mechanical mounting. A mounting pad suggests the place where a semiconductor die may be joined to a substrate. This is important because the location of filling ports in relation to those mounting pads can dictate the final position and distribution of injected optical materials.
In addition, an optical material such as a wavelength shifting material 37 including phosphor, or an optical material such as a colloid 38 comprising a dispersant agent may fill the cavity space. Combinations of these are fully anticipated and are the subject of some preferred embodiments. Fill ports 39 may be suitably located in the substrate whereby fluid materials injected therethrough form shaped volumes of optical materials inside the cavity space. In one example, a first material is injected through the fill port close to the semiconductor or mounting pad. That material may form an envelope about the semiconductor and completely surround it. It may thereafter cure to a state where it is stable and tends not to move with regard to position or shape. A second fill port may be used to inject a different optically cooperative material. Similarly, this material may cure to form a hardened element of desired shape and location. In this way, light emitted by the semiconductor is subject to passing through both types of optically cooperative material before leaving the device through the lens cover top surface. The optical output of the system is improved because wavelengths emitted may be broadband and the beam shape including angular divergence and uniformity may be controlled to desired states. Thus, these systems anticipate multi-layer and multi-composition configurations.
It is easy to appreciate configurations possible when considering the diagram of
In certain versions, it is desirable to include as part of the package a special provision which aids in assembly. It has no material effect on the optical operation of the device after it is fully assembled and operational; however during assembly, it aids to position and form a portion of the optically cooperative material. Specifically, it deflects material injected at a certain fill port toward a preferred position/location. It is desirable to cover and completely surround a semiconductor die with material such that it forms an envelope thereabout. Since a fill port must be displaced from the chip and its mounting pad at the substrate, it is preferred to direct injected material so that it migrates away from the fill port and toward the semiconductor geometric center or sometimes the system axis. This is more easily understood in view of the drawing of
Special preferred versions are illustrated in
The term ‘dispersant bodies’ is chosen with care as many different type of physical bodies/structures can serve well to disperse light. Further, various forms of these bodies may be particularly well suited for integration with some of systems taught herein. Dispersant bodies may be either from the group including: crystalline structures, granular matter, inhomogeneous matter, and air bubbles or oil drops for example. It is noted that use of air bubbles and oil drops instead of mechanical dispersant is a good possibility. These could be injected or generated in binding materials by application of ultrasonic energy. It is possible to regulate by frequency and intensity of ultrasonic energy the concentration and size of air or oil beads. In this way, one may adjust appropriate size and concentration of air and oil beads for effective scattering of emitting light. High concentration of air or oil beads doesn't appreciably influence the viscosity of binder material. It is also possible to vary the refractive index of oil beads by using of different oils and correspondingly to vary the average refractive index for the mixture of air and oil beads. In preferred versions, the sizes of beads are of the order of light scattering wavelength; for UV/blue chips λ˜0.3÷0.5 μm. Preferably the mean particle sizes are less than about 5 μm and more than about 0.03 μm.
In general, the bigger the phosphor grains are, the higher will be the resulting wavelength conversion efficiency (see Patent Application US20050035365 A, Dec. 10, 2005). However, for big phosphor grains (more than 10 μm) there is a problem related with active precipitation (deposition) of the grains in the binder materials that makes worse the optical quality of the system. When using air bubbles as dispersant, air bubbles will partially cover the surface of phosphor grains and provide a ‘floating-up’ effect for big phosphor grains that prevents precipitation in the binder material. At the same time, large free spaces between big phosphor grains prevent phosphor packing and loss emitted light. In preferred versions, these free spaces are filled by air and oil beads or mixture of air and oil beads and other dispersant that provide more effective use of light.
In most general terms, apparatus of these inventions may precisely be described as including: semiconductor light sources comprising at least one semiconductor light emitter in combination with an opto-mechanical package with a substrate and lens cover element forming therebetween an enclosed cavity filled with optically cooperative material(s) including a dispersant agent. Further, in some versions these semiconductor light sources with optically cooperative materials are arranged as colloids including a binder media and granular matter held therein. Granular matter is distributed and suspended in the binder to prevent migration about the holding medium such that the material density remains constant. These binders may be described as either: gel; epoxy; resin; polymer; the like; and mixtures thereof. These optically cooperative materials include both wavelength shifting media such as an optically pumped phosphor and light dispersant bodies which provide a dispersion action via either diffraction, refraction, or reflection optical mechanisms. In some special version, light dispersant bodies are merely well distributed air bubbles or tiny oil drops; and sometimes these air bubbles are affixed to the surfaces of phosphor grains.
Of significant importance are the packages' filling ports provided in substrates. In addition, a substrate may also include one or more exit ports. Also, deflection element(s) may be integrated with a substrate to better position material in relation to a semiconductor chip and mounting pad to which it is affixed.
It is an important embodiment that these optically cooperative materials includes arrangements of at least two distinct volumes. In some cases, a first volume is arranged as wavelength shifting media and a second volume is arranged as a dispersant agent. The spatial distribution of these being important to the effect they have on light passing therethrough. These combinations of distinct volumes are arranged to fill and occupy the space of cavities formed between the lens cover and the substrate. In certain versions, wavelength shifting media is enclosed by a dispersant agent. Some substrates include a one-to-one correspondence between filling ports and semiconductor mounting pads. Optically cooperative material can be arranged into a plurality of discrete orbs, a ‘blob’ including phosphor, each forming an association with a particular semiconductor light emitter as it completely surrounds and envelops any of the semiconductor light emitters.
In special versions, a lens cover is arranged with an undersurface forming two distinct axially symmetric and concentric cavities, and a cooperating substrate has at least two fill ports, one each associated with and coupled to each of these separate cavities. In these special versions, it is sometimes preferred that the centrally disposed cavity be filled with phosphor, and the peripheral cavity be filled with dispersant.
One will now fully appreciate how packages for light emitting semiconductors may be arranged to include means in support of output beam dispersion and wavelength shifting functionalities. Although present inventions have been described in considerable detail with clear and concise language and with reference to certain preferred versions thereof including best modes anticipated by the inventors, other versions are possible. Therefore, the spirit and scope of the invention should not be limited by the description of the preferred versions contained therein, but rather by the claims appended hereto.
