WO2008155368A1 - Method and device for improving optical led performance - Google Patents

Method and device for improving optical led performance Download PDF

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Publication number
WO2008155368A1
WO2008155368A1 PCT/EP2008/057738 EP2008057738W WO2008155368A1 WO 2008155368 A1 WO2008155368 A1 WO 2008155368A1 EP 2008057738 W EP2008057738 W EP 2008057738W WO 2008155368 A1 WO2008155368 A1 WO 2008155368A1
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WO
WIPO (PCT)
Prior art keywords
light emitting
emitting diode
light
led
encapsulant
Prior art date
Application number
PCT/EP2008/057738
Other languages
French (fr)
Inventor
Bruno Devos
Katrien Noyelle
Peter Gerets
Original Assignee
Barco N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Barco N.V. filed Critical Barco N.V.
Publication of WO2008155368A1 publication Critical patent/WO2008155368A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/58—Optical field-shaping elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/4805—Shape
    • H01L2224/4809—Loop shape
    • H01L2224/48091—Arched
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/481—Disposition
    • H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
    • H01L2224/48245—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic
    • H01L2224/48247—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic connecting the wire to a bond pad of the item
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/481—Disposition
    • H01L2224/48151—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive
    • H01L2224/48221—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked
    • H01L2224/48245—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic
    • H01L2224/48257—Connecting between a semiconductor or solid-state body and an item not being a semiconductor or solid-state body, e.g. chip-to-substrate, chip-to-passive the body and the item being stacked the item being metallic connecting the wire to a die pad of the item
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/73—Means for bonding being of different types provided for in two or more of groups H01L2224/10, H01L2224/18, H01L2224/26, H01L2224/34, H01L2224/42, H01L2224/50, H01L2224/63, H01L2224/71
    • H01L2224/732—Location after the connecting process
    • H01L2224/73251—Location after the connecting process on different surfaces
    • H01L2224/73265—Layer and wire connectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/15—Details of package parts other than the semiconductor or other solid state devices to be connected
    • H01L2924/181—Encapsulation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2933/00—Details relating to devices covered by the group H01L33/00 but not provided for in its subgroups
    • H01L2933/0091—Scattering means in or on the semiconductor body or semiconductor body package
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/44—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the coatings, e.g. passivation layer or anti-reflective coating
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/52—Encapsulations
    • H01L33/54—Encapsulations having a particular shape

Definitions

  • the present invention relates to light emitting diodes (LEDs) applied in direct light displays. More particularly, the present invention relates to optical properties of light emitting diodes, which optical properties influence the optical performance of the LED, and to means to improve the optical performance of the LED.
  • the present invention relates to a direct light display system comprising such LEDs, and to a method of fabricating such LEDs.
  • the LEDs may be of lamp type or of surface mounted device (SMD) type.
  • LEDs are typically sold in a packaged form that includes a LED die or light emitting diode chip mounted on a metal header.
  • the header can have a reflective cup in which the LED die is mounted, and electrical leads connected to the LED die.
  • Some packages also include a molded transparent resin that encapsulates the LED die.
  • the encapsulating resin can have either a nominally hemispherical front surface to partially collimate light emitted from the die, or a nominally flat surface, depending on whether the LED is of the lamp type or of the SMD type.
  • the reflective cup or silver-covered lead frame within the LED reflects incoming light and thus decays contrast.
  • the positioning of the LED dies determines the colour compound performance. The wider the LED dies are spatially separated, the more angular colour shift is present. LED dies are also getting smaller and more efficient. This, combined with the spatial separation, results in optical perception of separated light spots in stead of integrated light sources (colour compound).
  • the encapsulant of the LED (epoxy, silicone%) often reflects opaque, resulting in a greyish reflective aspect of the LEDs which results in a decaying contrast.
  • the present invention provides a method to improve the colour compound of a LED, by using an optical element such as a diffuser or diffusion material within the physical border of the LED, more specifically onto or in the encapsulant respectively.
  • This diffusion yields an integration effect of the light emanating from the LED chip.
  • This integration effect improves the perception of the LED chips as being separated, and improves viewing angle discoloration, because of the light integration effect.
  • the present invention provides a method to decrease internal reflection of the lead frames, the LED chips and the diffusing material in the encapsulant. In order to obtain this, light absorbing material is applied in the LED encapsulant. This will dramatically increase contrast ratio of the LED and thus of the total display in which these LEDs are used.
  • the present invention comprises embedding a polarizer in the body of a LED, for selecting a specific polarization of light being output from the LED.
  • the polarizer is placed between the encapsulant and the LED chip, and yields a very high increase of contrast ratio for the LED, because all reflections of the reflecting parts within the LED are eliminated by nature of the workings of the polarizer.
  • Figure 1 is a cross-sectional view of an SMD type LED package illustrating the physical border of the LED
  • Figure 2 is a cross-sectional view of a lamp type LED package illustrating the physical border of the LED
  • Figure 3 is a cross-sectional view of a SMD type LED with additional optical element and material within the physical border of the LED in accordance with embodiments of the present invention
  • Figure 4 is a cross-sectional view of a lamp type LED with additional optical element and material within the physical border of the LED in accordance with embodiments of the present invention
  • Figure 5 is a cross-sectional view of an array of lamp type LEDs in accordance with an embodiment of the present invention, provided with a shading grid illustrating avoiding cross talk of neighbouring LEDs;
  • Figure 6 is a cross-sectional view of a lamp type LED in accordance with an embodiment of the present invention, having a light absorbing film within the physical border of the LED;
  • Figure 7 is a cross-sectional view of a lamp type LED in accordance with an embodiment of the present invention, having a polarizing element within the physical border of the LED;
  • Figure 8 is a cross-sectional view of a lamp type LED in accordance with an embodiment of the present invention, having a layer of particles within the physical border of the LED.
  • the present invention provides a light emitting diode comprising a light emitting diode chip or LED die and a light transmissive material (an encapsulant) encapsulating the light emitting diode chip, the light transmissive material having an outer surface forming a physical border of the light emitting diode.
  • the light emitting diode according to this aspect of the present invention furthermore comprises at least one further optical element or material within the physical border of the light emitting diode.
  • the light transmissive material, or encapsulant may consist essentially of a single layer or may comprise multiple layers.
  • the light transmissive material can have an undulating surface in order to improve optical properties of the LED.
  • the light emitting diode may be for use in a direct light or direct view displays.
  • an optical element or material is added within the physical border 17 of a LED, thereby influencing the LED's optical properties.
  • “Within the physical border of the LED” means “within the containment of the LED outlines”.
  • the LED outlines are formed by the outer surface of the potting and filling encapsulant 16, which is at the bottom of the encapsulant bordering with lead frames 13 and package body 11 , at the upright sides of the encapsulant bordering with the sidewalls 12 of the LED package 10, and at the upper surface part of the encapsulant bordering with the environment.
  • the LED outlines 17 are formed by the outer surface of the encapsulant 16, having a bulged upper part (nominally hemispherical front surface) and a flat bottom.
  • the encapsulant 16 is surrounding the LED chip 14 and part of the terminal pins 18.
  • a combination of one or more such optical elements and/or one or more such optical materials within the physical border of the LED, both simultaneously influencing the LED's optical properties, is also an embodiment of the present invention - see Figure 4 for an example.
  • an optical film can be used as an example of such an optical element within the physical border 17 of the LED.
  • Said optical film is e.g.
  • an absorbing film sheet 24 attached to the inner surface of the encapsulant 16 and absorbing part of the light emitted by the LED chip 14 and impinging onto the absorbing film sheet 24.
  • the bottom part and/or bottom upstanding part of a lamp type LED encapsulant 16 can be covered with such an absorbing layer 24 in order to eliminate cross talk between neighbouring LEDs beneath a shading grid 25 as illustrated in Figure 5.
  • an optical element is e.g. a polarizer 21 , selecting and transmitting only light of one specific polarization direction.
  • the polarizer 21 selects and transmitting only light of one specific polarization direction.
  • the polarizer 21 may be placed in the encapsulant 16, above the LED chip 14, as illustrated in Figure 4 and Figure 7.
  • the polarizer 21 may be placed between the LED chip 14 and the encapsulant 16, touching with one side the LED chip 14 and being surrounded at all its other sides by the encapsulating material 16, as illustrated in Figure 3.
  • a micro-structured element can furthermore be placed between the encapsulant 16 and the LED chip 14.
  • a layer of optical particles 23 with or without surface relief structure can be added to the inner surface of the lamp type LED encapsulant 16, as illustrated in Figure 4 and Figure 8.
  • a significant amount of optical particles 22 can be mixed in advance with the encapsulant material before it is moulded to a fixed shape encapsulating the LED chip 14.
  • the optical particles may be light absorbing particles or light diffusing particles.
  • absorbing material can be added to or mixed with the encapsulant's material.
  • the added or mixed material is integrally formed with the encapsulant's basic material, such as epoxy or silicone.
  • the present invention provides an array of light emitting diodes according to an aspect of the present invention.
  • the array of light emitting diodes may form a display.
  • the display may be a direct view display.
  • the present invention provides a method to improve the colour compound of a LED, by using an optical element such as a diffuser or diffusion material within the physical border of the LED, more specifically onto or in the encapsulant 16.
  • the diffusion or diffusion material generates diffusion of the light generated by the LED chip, and yields an integration effect. This effect improves the perception of the LED chips as being separated.
  • the light integration improves viewing angle discoloration.
  • the present invention provides a method for decreasing internal reflection of the lead frames, the LED chips and the diffusing material in the encapsulant.
  • light absorbing material is applied in the LED encapsulant 16. This will increase contrast ratio of the LED and thus of the total display in which these LEDs are used.
  • a polarizer is embedded in the body of a LED.
  • the polarizer selects light of a specific polarization direction.
  • the polarizer may be placed between the encapsulant 16 and the LED chip 14. It yields a very high increase of contrast ratio for the LED, because reflections of reflecting parts within the LED may be eliminated by nature of the working principles of the polarizer.
  • Embodiments of the present invention distinguish from prior art LEDs in that optical elements or optical material are added within the physical border of the light emitting diode, rather than being applied to the outside thereof.
  • the present invention provides a method for manufacturing a light emitting diode.
  • the method comprises providing a light emitting diode chip, providing a light transmissive material encapsulating the light emitting diode chip, the light transmissive material having an outer surface forming a physical border of the light emitting diode, and providing at least one further optical element or material within the physical border of the light emitting diode.
  • the at least one further optical element or material may for example be a light absorbing element or material, a polarising element or material, or a light diffusing element or material.
  • Providing the light transmissive material encapsulating the light emitting diode may comprise dispensing curable encapsulating material onto a substrate that may include, for example, a LED die 14 mounted on a lead frame 13 on a package body 11.
  • the dispensed curable material may form a liquid mass having an unconstrained smooth outer surface.
  • Providing the light transmissive material encapsulating the light emitting diode then further includes curing the dispensed material to convert the liquid mass into a solid encapslant having an outer encapsulant surface, the outer encapsulant surface forming the outer border of the LED.

Abstract

The present invention relates to light emitting diodes, LKDs. In order to improve the properties of an LED assembly to yield improved. optical LED performance, an optical element or material such as a polarizer (21), a layer of light absorbing or light diffusing particles (23), or an absorbing filsm sheet (24) is added within the physical border of the LED.

Description

METHOD AND DEVICE FOR IMPROVING OPTICAL LED PERFORMANCE
Technical field of the invention
The present invention relates to light emitting diodes (LEDs) applied in direct light displays. More particularly, the present invention relates to optical properties of light emitting diodes, which optical properties influence the optical performance of the LED, and to means to improve the optical performance of the LED. The present invention relates to a direct light display system comprising such LEDs, and to a method of fabricating such LEDs. The LEDs may be of lamp type or of surface mounted device (SMD) type.
Background of the invention
LEDs are typically sold in a packaged form that includes a LED die or light emitting diode chip mounted on a metal header. The header can have a reflective cup in which the LED die is mounted, and electrical leads connected to the LED die. Some packages also include a molded transparent resin that encapsulates the LED die. The encapsulating resin can have either a nominally hemispherical front surface to partially collimate light emitted from the die, or a nominally flat surface, depending on whether the LED is of the lamp type or of the SMD type.
The reflective cup or silver-covered lead frame within the LED reflects incoming light and thus decays contrast. The positioning of the LED dies determines the colour compound performance. The wider the LED dies are spatially separated, the more angular colour shift is present. LED dies are also getting smaller and more efficient. This, combined with the spatial separation, results in optical perception of separated light spots in stead of integrated light sources (colour compound).
For these optical disadvantages, a number of measures can be taken.
The encapsulant of the LED (epoxy, silicone...) often reflects opaque, resulting in a greyish reflective aspect of the LEDs which results in a decaying contrast.
Description of the invention
It is an object of the present invention to provide LEDs with good optical properties.
The above objective is accomplished by a device and method as described in the attached claims.
In a first aspect, the present invention provides a method to improve the colour compound of a LED, by using an optical element such as a diffuser or diffusion material within the physical border of the LED, more specifically onto or in the encapsulant respectively. This diffusion yields an integration effect of the light emanating from the LED chip. This integration effect improves the perception of the LED chips as being separated, and improves viewing angle discoloration, because of the light integration effect.
In a second aspect, the present invention provides a method to decrease internal reflection of the lead frames, the LED chips and the diffusing material in the encapsulant. In order to obtain this, light absorbing material is applied in the LED encapsulant. This will dramatically increase contrast ratio of the LED and thus of the total display in which these LEDs are used.
In a third aspect, the present invention comprises embedding a polarizer in the body of a LED, for selecting a specific polarization of light being output from the LED. The polarizer is placed between the encapsulant and the LED chip, and yields a very high increase of contrast ratio for the LED, because all reflections of the reflecting parts within the LED are eliminated by nature of the workings of the polarizer.
The characteristics, features and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, which illustrate, by way of example only, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.
Brief description of the drawings
Figure 1 is a cross-sectional view of an SMD type LED package illustrating the physical border of the LED;
Figure 2 is a cross-sectional view of a lamp type LED package illustrating the physical border of the LED; Figure 3 is a cross-sectional view of a SMD type LED with additional optical element and material within the physical border of the LED in accordance with embodiments of the present invention;
Figure 4 is a cross-sectional view of a lamp type LED with additional optical element and material within the physical border of the LED in accordance with embodiments of the present invention;
Figure 5 is a cross-sectional view of an array of lamp type LEDs in accordance with an embodiment of the present invention, provided with a shading grid illustrating avoiding cross talk of neighbouring LEDs; Figure 6 is a cross-sectional view of a lamp type LED in accordance with an embodiment of the present invention, having a light absorbing film within the physical border of the LED;
Figure 7 is a cross-sectional view of a lamp type LED in accordance with an embodiment of the present invention, having a polarizing element within the physical border of the LED;
Figure 8 is a cross-sectional view of a lamp type LED in accordance with an embodiment of the present invention, having a layer of particles within the physical border of the LED.
In the different figures, the same reference signs refer to the same or analogous elements.
Description of embodiments of the present invention
The present invention will be described with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.
It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. In one aspect, the present invention provides a light emitting diode comprising a light emitting diode chip or LED die and a light transmissive material (an encapsulant) encapsulating the light emitting diode chip, the light transmissive material having an outer surface forming a physical border of the light emitting diode. The light emitting diode according to this aspect of the present invention furthermore comprises at least one further optical element or material within the physical border of the light emitting diode. The light transmissive material, or encapsulant, may consist essentially of a single layer or may comprise multiple layers. The light transmissive material can have an undulating surface in order to improve optical properties of the LED. The light emitting diode may be for use in a direct light or direct view displays.
Thus, according to this aspect, an optical element or material is added within the physical border 17 of a LED, thereby influencing the LED's optical properties. "Within the physical border of the LED" means "within the containment of the LED outlines". In case of an SMD type LED as illustrated in Figure 1 , the LED outlines are formed by the outer surface of the potting and filling encapsulant 16, which is at the bottom of the encapsulant bordering with lead frames 13 and package body 11 , at the upright sides of the encapsulant bordering with the sidewalls 12 of the LED package 10, and at the upper surface part of the encapsulant bordering with the environment. In case of a lamp type LED as illustrated in Figure 2, the LED outlines 17 are formed by the outer surface of the encapsulant 16, having a bulged upper part (nominally hemispherical front surface) and a flat bottom. The encapsulant 16 is surrounding the LED chip 14 and part of the terminal pins 18. A combination of one or more such optical elements and/or one or more such optical materials within the physical border of the LED, both simultaneously influencing the LED's optical properties, is also an embodiment of the present invention - see Figure 4 for an example. As an example of such an optical element within the physical border 17 of the LED, an optical film can be used. Said optical film is e.g. in Figure 4 and Figure 6 an absorbing film sheet 24, attached to the inner surface of the encapsulant 16 and absorbing part of the light emitted by the LED chip 14 and impinging onto the absorbing film sheet 24. In particular the bottom part and/or bottom upstanding part of a lamp type LED encapsulant 16 can be covered with such an absorbing layer 24 in order to eliminate cross talk between neighbouring LEDs beneath a shading grid 25 as illustrated in Figure 5.
Another example of an optical element is e.g. a polarizer 21 , selecting and transmitting only light of one specific polarization direction. The polarizer
21 may be placed in the encapsulant 16, above the LED chip 14, as illustrated in Figure 4 and Figure 7. In alternative embodimens, the polarizer 21 may be placed between the LED chip 14 and the encapsulant 16, touching with one side the LED chip 14 and being surrounded at all its other sides by the encapsulating material 16, as illustrated in Figure 3.
In order to guide the output beam of the LED chip 14 before it reaches the encapsulant 16, a micro-structured element can furthermore be placed between the encapsulant 16 and the LED chip 14.
As an example of optical material within the physical border of the LED, thereby influencing the LED's optical properties, a layer of optical particles 23 with or without surface relief structure can be added to the inner surface of the lamp type LED encapsulant 16, as illustrated in Figure 4 and Figure 8. Instead of a layer of optical particles, using SMD or lamp type LED, a significant amount of optical particles 22 can be mixed in advance with the encapsulant material before it is moulded to a fixed shape encapsulating the LED chip 14.
The optical particles may be light absorbing particles or light diffusing particles.
As another example of optical material within the physical border 17 of the LED, thereby influencing the LED's optical properties, absorbing material can be added to or mixed with the encapsulant's material. The added or mixed material is integrally formed with the encapsulant's basic material, such as epoxy or silicone.
In an aspect, the present invention provides an array of light emitting diodes according to an aspect of the present invention. The array of light emitting diodes may form a display. The display may be a direct view display.
In another aspect, the present invention provides a method to improve the colour compound of a LED, by using an optical element such as a diffuser or diffusion material within the physical border of the LED, more specifically onto or in the encapsulant 16. The diffusion or diffusion material generates diffusion of the light generated by the LED chip, and yields an integration effect. This effect improves the perception of the LED chips as being separated. The light integration improves viewing angle discoloration.
In yet another aspect, the present invention provides a method for decreasing internal reflection of the lead frames, the LED chips and the diffusing material in the encapsulant. In order to obtain this, light absorbing material is applied in the LED encapsulant 16. This will increase contrast ratio of the LED and thus of the total display in which these LEDs are used.
In still another aspect, a polarizer is embedded in the body of a LED. The polarizer selects light of a specific polarization direction. The polarizer may be placed between the encapsulant 16 and the LED chip 14. It yields a very high increase of contrast ratio for the LED, because reflections of reflecting parts within the LED may be eliminated by nature of the working principles of the polarizer. Embodiments of the present invention distinguish from prior art LEDs in that optical elements or optical material are added within the physical border of the light emitting diode, rather than being applied to the outside thereof.
In an aspect, the present invention provides a method for manufacturing a light emitting diode. The method comprises providing a light emitting diode chip, providing a light transmissive material encapsulating the light emitting diode chip, the light transmissive material having an outer surface forming a physical border of the light emitting diode, and providing at least one further optical element or material within the physical border of the light emitting diode. The at least one further optical element or material may for example be a light absorbing element or material, a polarising element or material, or a light diffusing element or material.
Providing the light transmissive material encapsulating the light emitting diode may comprise dispensing curable encapsulating material onto a substrate that may include, for example, a LED die 14 mounted on a lead frame 13 on a package body 11. The dispensed curable material may form a liquid mass having an unconstrained smooth outer surface. Providing the light transmissive material encapsulating the light emitting diode then further includes curing the dispensed material to convert the liquid mass into a solid encapslant having an outer encapsulant surface, the outer encapsulant surface forming the outer border of the LED.

Claims

1.- A light emitting diode comprising a light emitting diode chip and a light transmissive material encapsulating the light emitting diode chip, the light transmissive material having an outer surface forming a physical border of the light emitting diode, further comprising a light absorbing element or material within the physical border of the light emitting diode.
2.- A light emitting diode according to claim 1 , wherein the light emitting diode is of the lamp type.
3.- A light emitting diode according to claim 1 , wherein the light emitting diode is of the SMD type. 4. A light emitting diode according to any previous claim, wherein the light absorbing element or material is a film material. 5.- A light emitting diode according to any previous claim, wherein the light absorbing element is an optical film. 6.- A light emitting diode according to any previous claim, wherein the light absorbing element comprises a plurality of light absorbing particles. 7.- A light emitting diode according to claim 6, wherein the light absorbing particles are mixed with the light transmissive material encapsulating the light emitting diode chip. 8.- A light emitting diode according to claim 6, comprising a layer of light absorbing particles applied at the inner surface of the light transmissive material encapsulating the light emitting diode. 9.- A light emitting diode according to any of the previous claims, further comprising a light diffusing element. 10.- A light emitting diode according to claim 9, wherein the light diffusing element comprises a plurality of light diffusing particles. 11.- A light emitting diode according to any of the previous claims, further comprising a polarising element.
12.- An array of light emitting diodes as claimed in any of the previous claims. 13.- A direct view display system, comprising an array of light emitting diodes as in claim 12.
4.- A method for manufacturing a light emitting diode a light emitting diode chip, the method comprising providing a light transmissive material encapsulating the light emitting diode chip, the light transmissive material having an outer surface forming a physical border of the light emitting diode, and providing at least one further optical element or material within the physical border of the light emitting diode, the at least one further optical element or material being a light absorbing element or material.
PCT/EP2008/057738 2007-06-18 2008-06-18 Method and device for improving optical led performance WO2008155368A1 (en)

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