Patent Application
20100090229
This application claims the priority benefit under 35 U.S.C. §119 of Japanese Patent Application No. 2008-264439 filed on Oct. 10, 2008, which is hereby incorporated in its entirety by reference.
The presently disclosed subject matter relates to a semiconductor light emitting apparatus including a plurality of semiconductor light emitting devices, and in particular, to a semiconductor light emitting apparatus including a wavelength conversion layer containing a phosphor material or the like.
Based on recent developments in the area of high-powered and high-intensity light emitting diodes (LEDs), white LEDs have gradually been used as light sources for vehicle headlights, general lighting fixtures, street lamps, traffic lamps, and various illumination apparatuses. Such a white LED can include, for example, a blue LED and a wavelength conversion layer containing a phosphor material or the like. The blue LED can emit blue light, and part of the blue light is wavelength converted by the wavelength conversion material in the wavelength conversion layer to become yellow light (or yellowish orange light). This yellow light is mixed with the original blue light so that white light is obtained.
Known methods for forming a phosphor-containing layer which covers over the side and/or top surfaces of an LED chip include a stencil printing method, a screen printing method using a metal mask, a suspension coating method and other methods, for example, disclosed in Japanese Patent Application Laid-Open Nos. 2002-185048, 2006-313886, and 2003-526212, respectively. Furthermore, Japanese Patent Application Laid-Open No. 2001-244507 discloses a structure in which a phosphor layer is formed only on the top surface of an LED chip by a gas-phase growth method such as a vapor deposition method, a sputtering method, or the like. Japanese Patent Application Laid-Open No. 2005-109434 discloses a structure in which two light emitting elements are arranged side by side between which a resin is filled, and a wavelength conversion member is formed by a screen printing method or a stencil printing method so as to cover the entire top surface of the two light emitting elements.
Some illumination apparatuses, such as vehicle headlights, may be required to have a front luminous intensity distribution having a sharp difference at the interface between the light emitting area and the surrounding non-light emitting area (outer environment). When a white LED is used as a light source for such an illumination apparatus, the LED should have a configuration that can emit light from the top surface of the LED in the front direction with high directivity while the light emitted in the oblique or horizontal directions should be prevented.
The LEDs as disclosed in Japanese Patent Application Laid-Open Nos. 2002-185048, 2006-313886, and 2003-526212 include a phosphor-containing layer that covers the side and top faces of the LED chip. In this configuration, the light can be emitted not only from the top surface of LED in the front direction but also from the side faces thereof in the horizontal or obliquely downward directions. Some of such light can be reflected by the substrate or other members to be directed in the front direction. Accordingly, the front luminous intensity distribution may have a gradually decreased distribution near the periphery of the LED. The LEDs as disclosed in Japanese Patent Application Laid-Open Nos. 2001-244507 and 2005-109434 have the phosphor-containing resin layer provided on the top surface thereof, and the layer has a rectangular end surface perpendicular to the top surface. In this configuration, light can be emitted from the end surface of the phosphor-containing resin layer in the horizontal or obliquely downward directions, and then can be directed in the front direction by the reflection from the substrate or other members. Accordingly, this configuration also provides a front luminous intensity distribution having a gradually decreased distribution near the periphery of the LED.
Furthermore, when a plurality of LED chips are to be arrayed in line to form a single LED light emitting apparatus, the formation of the phosphor-containing layer on the individual LED chip by printing or similar methods as disclosed in Japanese Patent Application Laid-Open Nos. 2002-185048, 2006-313886, 2003-526212 and 2001-244507 may have the following problems. That is, the phosphor-containing layer may have a distribution unevenness of the contained phosphor particles, resulting in light color unevenness of the arrayed LED light emitting apparatuses. This may be caused by the local light intensity decrease between the adjacent LED chips.
The presently disclosed subject matter was devised in view of these and other issues, characteristics and problems and in association with the conventional art. According to one aspect of the presently disclosed subject matter, a light emitting apparatus can include a plurality of light emitting elements arranged in an array and a wavelength conversion layer configured to wavelength convert part of light emitted from the light emitting elements. The light emitting apparatus can have a front luminous intensity distribution having a sharp difference at the interface between a light emitting area and a surrounding non-light emitting area (outer environment) so as to suppress or prevent light color unevenness.
According to another aspect of the presently disclosed subject matter, a semiconductor light emitting apparatus can include: a substrate; a plurality of light emitting elements each having a top surface as a light emitting surface and disposed on the substrate with a predetermined gap interposed between the adjacent light emitting elements; bridge portions each disposed at the respective gaps between the adjacent light emitting elements so as to connect the light emitting elements; and a wavelength conversion layer disposed over the top surfaces of the plurality of the light emitting elements and the bridge portions entirely. The wavelength conversion layer can have a thickness that is decreased at least around its peripheral area and can be gradually thinned to the end portion. The thickness of the wavelength conversion layer covering the elements and the like entirely can be decreased toward the end portion, and accordingly, the light emitted horizontally or toward the substrate from the wavelength conversion layer can be reduced. In addition to this, the wavelength conversion layer covering the plurality of the light emitting elements as a unit can reduce the occurrence of the light color unevenness.
In the above configuration, the wavelength conversion layer can have a top surface to be formed as a convex curved surface in the front direction. This configuration can flatten the luminous intensity distribution at the positions of the LED elements, thereby reducing the luminous intensity unevenness.
In the above configuration, the wavelength conversion layer can be devoid of an end surface that is substantially perpendicular to the main plane including the top surface. For example, all surfaces of the wavelength conversion layer that are exposed away from the light emitting element and that ultimately end and are in contact with the light emitting element can extend from a plane containing the top surface of the light emitting element at an angle other than substantially ninety degrees.
The wavelength conversion layer can include a wavelength conversion material and a resin containing the wavelength conversion material dispersed therein (for example, a resin to which phosphor particles are added and dispersed).
The bridge portion can have a width and a length that are equal to or more than the size of the gap between the adjacent light emitting elements, and can have longitudinal ends that are disposed on the same plane as the top surface of the light emitting element. This configuration can maintain, even at the bridge portion, the surface tension of the mixed liquid material that serves as the wavelength conversion layer after it has been dropped onto the light emitting element and the bridge portion. The maintained surface tension can ensure the correct configuration for the wavelength conversion layer when it is coated over the entire surface of the plurality of light emitting elements. The bridge portion, for example, can also be described as having longitudinal ends that are the outermost peripheral portion of the bridge portion (when viewed in a light emitting direction of the apparatus) and that lie within a plane containing the top surface of the light emitting element(s).
In this configuration, the bridge portion and the substrate can form a space therebetween, with the space being vacant. This configuration can help the ends of the bridge portion to be disposed on the same plane as the top surface of the light emitting element.
The bridge portion can have a shape having inclined surfaces from its apex toward the top surface of the light emitting element along the longitudinal direction of the gap. The inclined surfaces of the bridge portion can reflect the light from the light emitting element so that the reflected light can be directed in the front direction (upward), thereby increasing the luminous intensity.
In the above configuration, the bridge portion can be composed of a filler having a light reflecting property and a resin containing the filler therein.
According to still another aspect of the presently disclosed subject matter, a method for producing such a semiconductor light emitting apparatus can include: disposing a plurality of light emitting elements, each having a top surface as a light emitting surface, on a substrate with a predetermined gap interposed between the adjacent light emitting elements; disposing bridge portions at the gaps between the adjacent light emitting elements; and forming a wavelength conversion layer disposed over the top surfaces of the plurality of the light emitting elements and the bridge portions entirely, wherein the wavelength conversion layer can have a thickness decreased at least around a peripheral area thereof and gradually thinned to an end portion thereof.
The act of forming the wavelength conversion layer can include, for example, a step of dropping a material mixed liquid for the wavelength conversion layer onto the bridge portions and the plurality of the light emitting elements to form a coating film over the entire surfaces of the bridge portions and the light emitting elements with the coating film being convex maintained by its surface tension, and curing the coating film.
The act of disposing the bridge portions can include disposing the bridge portions each having a width and a length that are equal to or more than the size of the gap between the adjacent light emitting elements, so that longitudinal ends of the bridge portions are disposed on the same plane as the top surface of the light emitting element.
For example, the act of disposing the bridge portions can be achieved by extruding a thixotropic resin material from a nozzle with a predetermined opening diameter so as to fill the gap between the light emitting elements therewith, and curing the material.
The act of disposing the bridge portions can include the steps of extruding a thixotropic resin material from a nozzle with a predetermined opening diameter so as to form the resin material disposed at the gap between the light emitting elements, with the extruded material having inclined surfaces from its apex toward the top surface of the light emitting element along the longitudinal direction of the gap, and curing the resin material.
The act of disposing the bridge portions also can include disposing the thixotropic resin material only above the gap between the adjacent light emitting elements so as to form a vacant space between the substrate and the bridge portion. This configuration can help the ends of the bridge portion to be disposed on the same plane as the top surface of the light emitting element with ease.
The method can include, before forming the wavelength conversion layer, connecting electrodes formed on the light emitting elements to wirings formed on the substrate by wire bonding. As the wire bonding operation is performed before the material for the wavelength conversion layer adheres to the electrodes, the electrical reliability can be improved.
According to the presently disclosed subject matter, there can be provided a semiconductor light emitting apparatus including a plurality of light emitting elements arranged in array and a wavelength conversion layer for wavelength converting part of the light emitted from the light emitting elements, thereby providing a front luminous intensity distribution having a sharp difference at the interface between the light emitting area and the surrounding non-light emitting area (outer environment) as well as the suppressed light color unevenness.
These and other characteristics, features, and advantages of the presently disclosed subject matter will become clear from the following description with reference to the accompanying drawings, wherein:
A description will now be made below to semiconductor light emitting apparatuses of the presently disclosed subject matter with reference to the accompanying drawings in accordance with exemplary embodiments.
It should be noted that the present exemplary embodiments will deal with, as non-limiting examples, the cases of white light emitting apparatuses where a plurality of blue light emitting elements (blue LEDs) are arranged in line and a wavelength conversion layer containing a phosphor as a wavelength conversion material are used in combination. Herein, the phosphor can wavelength convert blue light which acts as an excitation light to yellowish orange light that is to be emitted, thereby producing white light by the mixture of blue light and yellowish orange light. It should be noted that the color combination and the color of the finally emitted light are not limited to the following exemplary embodiments, and the presently disclosed subject matter can employ various combinations of color achieved by various combinations of semiconductor light emitting elements and wavelength conversion materials.
It should also be noted that the main emission direction of light is defined as an upper direction or front direction, and based on this the down and horizontal directions and so on are defined accordingly.
Each of the four light emitting elements 102 can be formed of an LED chip having a top surface as a light emitting surface for emitting blue light in the front direction (upward direction). The wavelength conversion layer 103 can be formed of a resin layer in which phosphor particles as a wavelength conversion material are dispersed. The phosphor particles can wavelength convert blue light as excitation light to emit yellowish orange fluorescence light. The phosphor particles can be YAG type phosphor particles as an example. The light emitting element 102 can have electrodes (wire bonding pads) 107 formed on the top surface. The four light emitting elements 102 can be disposed so that the electrodes 107 having the same polarity face upward. Then, the electrodes 107 can be wire bonded on the substrate 101 by bonding wires 108. Not-shown paired electrodes with respect to the electrodes 107 on the top surface can be formed on the other surfaces of the four light emitting elements 102. The paired electrodes can be electrically connected to an electrode pattern formed on the substrate 101. The wavelength conversion layer 103 can be disposed so that the electrodes 107 and the bonding wires 108 can be embedded therein in part.
The four light emitting elements 102 can emit blue light in the front direction (upper direction) and then the blue light can pass through the wavelength conversion layer 103 provided on the top surfaces of the elements. Part of the blue light can excite the phosphor contained in the wavelength conversion layer 103 so that the phosphor can emit yellowish orange fluorescence light. The blue light having passed through the wavelength conversion layer 103 and the generated yellowish orange fluorescence light can be mixed together so that white light can be projected from the wavelength conversion layer 103 upward.
The wavelength conversion layer 103 can have a thickness as shown in
In the present exemplary embodiment, the top surface of the wavelength conversion layer 103 can be formed in a convex curved surface in the front direction. Accordingly, the wavelength conversion layer 103 can have a continuous curved surface from the center to the ends covering the connected light emitting elements 102 entirely. In other words, the wavelength conversion layer 103 can avoid having any end faces perpendicular to the main plane, and can have a continuously variable thickness from the center toward both the ends with the center portion being a topmost (i.e., apex) portion. This configuration can prevent light emitted from the wavelength conversion layer 103 from being directed laterally or toward the substrate 101. The light emitted from the wavelength conversion layer 103 upward can be controlled to show the luminous intensity distribution being flattened at the positions of the LED elements.
It should be noted that the thickness of the wavelength conversion layer 103 does not need to be decreased (e.g., tapered) in its entirety, but can be decreased (e.g., tapered) at least around the peripheral area of the wavelength layer 103. Accordingly, the surface of the wavelength conversion layer 103 at the center area may be completely flat (e.g., parallel to the top surface of the light emitting element).
The wavelength conversion layer 103 can be formed as a single layer over the four light emitting elements 102. When compared with the case where the four light emitting elements 102 each have the wavelength conversion layer 103, the wavelength conversion layer 103 can have a phosphor particle distribution with less localization of the phosphor particles, thereby preventing the light color unevenness and the luminous intensity unevenness.
The wavelength conversion layer 103 can be formed as a single layer over the entire surface of the connected four light emitting elements 102. As a result, the upper surface of the wavelength conversion layer 103 can be rectangular with four corners. In contrast, if the four light emitting elements 102 each have a wavelength conversion layer, the number of corners is 16 (4 by 4). Accordingly, the configuration of the presently disclosed subject matter can reduce the number of corners. When the thickness of a wavelength conversion layer is decreased (e.g., tapered) at the peripheral areas and also at the corners, the light emitted there can have a bluish white color because of a reduced amount of phosphor existing there. The configuration of the presently disclosed subject matter can employ the single wavelength conversion layer for covering the four light emitting elements 102 entirely, and the number of corners can be reduced, thereby suppressing the light color unevenness.
The method for forming the wavelength conversion layer 103 with such a shape is not specifically limited, and any method(s) suitable for this purpose can be employed. One method used for the present exemplary embodiment can include preparing a mixed liquid material for the wavelength conversion layer 103, dropping the mixed liquid material onto the four light emitting elements 102 connected via the bridge portions 105 while keeping its convex shape due to the surface tension, and curing it as it is. As a result, the wavelength conversion layer 103 can be easily formed with a shape of having a gradually decreasing thickness toward the peripheral areas.
In order to form the wavelength conversion layer 103 utilizing the surface tension of the mixed liquid material, the bridge portion 105 can be shaped to have certain end shapes by maintaining the surface tension of the mixed liquid material on the bridge portions 105 after it has been dropped onto the light emitting elements 102. For example, the bridge portion 105 can have a circular cross section as shown in
After the convex shape of the mixed liquid material is completed, the coating film 123 of the mixed liquid material can be formed as shown in
In contrast, as shown in
The shape of the bridge portion 105 is not limited to the shapes shown in
The method for producing the bridge portion 105 can be a method of disposing a separately prepared member at an appropriate position, a method of directly coating a material between the light emitting elements 102, or other methods. In the exemplary embodiment, a method of coating or printing a resin material for the bridge portion directly between the light emitting elements 102 while the resin material is controlled in fluidity can be used. This method can form the bridge portion 105 with its ends 121 or bottom sides 122a of the end surfaces 122 being disposed on the same plane as the top surface of the ends of the light emitting element 102. Examples of the method for forming the bridge portion 105 can include, but are not limited to, a dispenser coating process, a screen printing process, a stencil printing process, and the like.
A description will now be made to the method for manufacturing a semiconductor light emitting apparatus of the present exemplary embodiment. Herein, the shape of the bridge portion 105 is exemplified as to have a circular cross section and rounded ends 121 as shown in
The light emitting elements 102 can be prepared in advance, as illustrated in
The thin film semiconductor light emitting layer 1021 can be formed to have a smaller size than the conductor opaque substrate 1022. This is because, when the light emitting elements 102 are separated from a wafer including a plurality of elements 102 by dicing or scribing, the cleavage of the semiconductor light emitting layer 1021 and the associated damage at the interface can be prevented. Accordingly, a non-emission portion with a constant width “a” can exist on the top surface of the substrate 1022 and around the outer peripheral area of the light emitting layer 1021 as shown in
The substrate 101 may be a ceramic substrate having an electrode wiring pattern formed in advance on its surface. As shown in
Then, the bridge portions 105 can be formed between the light emitting elements 102. The material for the bridge portion 105 can be selected from materials having heat resistance and stress resistance, such as, but not limited to, thermosetting resins, RTV rubbers, and the like. The bridge portion 105 can be formed so as to linearly fit the gap between the adjacent light emitting elements 102, thereby allowing the entire side surfaces of the four light emitting elements 102 to be continuous. Examples of the thermosetting resins for use as the material for the bridge portion 105 can include, but are not limited to, silicone resins, epoxy resins, phenol resins, polyimide resins, melamine resins, and the like. In addition, the resin material can be mixed with a filler such as, but not limited to, titanium oxide, alumina, or the like to impart a light reflecting property to the bridge portion 105. This can enhance the light utilization efficiency.
When employing a thermosetting resin, the bridge portion 105 can be formed by a dispenser coating process, a screen printing process or a stencil printing process. When it is formed by a dispenser coating process, the wire bonding process can be carried out before the formation of the bridge portion 105. This method can allow the wire bonding to be performed before the thermosetting resin material for the bridge portion 105 adheres to the electrode (wire bonding pad) 107. This can eliminate a need for a masking and the like for the electrode 107. Furthermore, this can improve the reliability of the bonding portions.
On the other hand, when it is formed by a screen or stencil printing process, a mask alignment process for printing can be taken into consideration and the wire bonding process can be performed before the formation of the bridge portion. The printing process can be carried out while the thermosetting resin material for the bridge portion 105 is prevented from adhering to the electrode 107. Depending on the position of the electrode 107, the bridge portion formation process and the wire bonding process can be performed in any arbitrary order.
The width of the bridge portion 105 can be adjusted to be wider than the gap between the adjacent light emitting elements 102 and smaller than the gap between the elements 102 plus twice the width “a” of the non-emission portion of the element 102 (see
Furthermore, the bridge portion 105 can be formed so that the longitudinal ends 121 of the bridge portion 105 are disposed on the same plane as the top surface of the light emitting elements 102.
In order to form such a controlled end position and a width of the bridge portion 105, it may be necessary to control the fluidity of the resin material for the bridge portion 105. Specifically, the resin material can be mixed with a material for increasing the viscosity or imparting thixotropy (i.e., using thixotropic material, such as silica or alumina nano-particles), thereby allowing the resin material to have thixotropy for maintaining its shape for a long period of time after coating or printing. When the bridge portion 105 is formed by a dispenser coating process, a material having appropriate thixotropy can be extruded with the use of a nozzle having a predetermined diameter while the dropping amount is controlled. This process can provide a coating film having ends disposed at appropriate positions and having an advantageous width. Specifically, the bridge portion 105 can be formed as a cylindrical resin material coating as shown in
Specifically, the nozzle diameter can be set to the value equal to or greater than the gap between the adjacent light emitting elements 102 and smaller than the gap between the elements 102 plus twice the width “a” of the non-emission portion of the element 102 (see
As the bridge portion 105 is formed so that the ends coincide with the top surface of the elements 102, a space can be formed between the bridge portion 105 and the substrate 101 below the bridge portion 105 as shown in
Next, the wavelength conversion layer 103 can be formed (see
The wavelength conversion layer 103 can be formed without any end surface perpendicular to the main plane but has thinned peripheral areas. Accordingly, the semiconductor light emitting apparatus of the present exemplary embodiment can have a front luminous intensity distribution having a sharp difference between the light emitting area and the surrounding non-light emitting area. Furthermore, as the wavelength conversion layer 103 can be formed as a single layer as a whole, the phosphor concentration above the respective light emitting elements can be evened with less light color unevenness and luminous intensity unevenness. In addition to this, as the wavelength conversion layer 103 can be limited to four corners over the area of the four light emitting elements 102, the wavelength conversion layer 103 can be prevented from having light color unevenness and luminous intensity unevenness due to a lot of corners.
With reference to
The bridge portion 105 having the shape as shown in
The semiconductor light emitting apparatus of the present exemplary embodiment, the bridge portion 105 can have the inclined surfaces along its longitudinal direction as shown in
When the resin material for the bridge portion 105 includes a reflecting material (filler) mixed therein, it can be advantageous because the reflection effect can be improved. Examples of the reflecting material can include, but are not limited to, titanium oxide, alumina, and the like.
When the wavelength conversion layer 103 is formed, the mixed liquid material can be coated over the entire surface covering the four light emitting elements 102 and the outermost pads 117 so that the convex shape of the coated liquid can be kept due to the generated surface tension. Accordingly, the single wavelength conversion layer 103 can be formed with the thickness “b” at the ends of the outermost light emitting elements 102 being thicker when compared with the case of no outermost pad 117. This means the difference in thickness of the wavelength conversion layer above the four light emitting elements can be reduced when compared with the case of no outermost pad 117. This configuration can thus reduce the light color unevenness occurring when the light is emitted through the wavelength conversion layer with different phosphor concentrations.
The height of the outermost pad 117 can be the same as that of the light emitting element 102. The ends and the outer peripheral areas of the light emitting elements 102 and the outermost pads 117 can be positioned on the same plane, so that the surface tension of the liquid material for the wavelength conversion layer can be kept. The width of the outermost pad 117 in the arranged direction can be equal to, or less than, the width of the light emitting element 102, and also can be equal to, or more than one half the width. If the width of the outermost pad 117 is less than one half of the width, it might not be possible to maintain the surface tension of the liquid for the wavelength conversion layer. If it is more than the width of the light emitting element, the entire size of the apparatus may be too large. The upper surface of the outermost pad 117 can be rectangular or semi-circular. A semi-circular shape with the linear side adjacent to the light emitting element 102 can keep the surface tension of the liquid for the wavelength conversion layer.
Materials of the outermost pad 117 can include, but are not limited to, a metal material, a ceramic material, a resin material or the like. Among them, metal with reflective silver plating or alumina can be advantageous in certain applications because the pad can reflect the light from the light emitting element upward (in the front direction).
As described above, a semiconductor light emitting apparatus made in accordance with the principles of the presently disclosed subject matter can include the bridge portions between the light emitting elements to connect the plurality of the light emitting elements, thereby facilitating the formation of the single wavelength conversion layer with a predetermined shape. Accordingly, it is possible to provide a light emitting apparatus with a novel light emission shape that is formed by connecting the elements in a unit.
It should be noted that the present exemplary embodiments have dealt with the cases in which the four light emitting elements are connected in line. The presently disclosed subject matter, however, is not limited to these exemplary embodiments. The light emitting elements can be arranged two by two, three by three, a letter L-shaped arrangement, a rectangular connected arrangement, or the like. In each of the embodiments the bridge portions can be formed between adjacent elements.
It should be noted that the present exemplary embodiments have dealt with the cases in which the bridge members are formed by arranging a thixotropic resin material between the adjacent light emitting elements 102 by a dispenser coating process or a printing process, and then curing the resin material. The presently disclosed subject matter, however, is not limited to these processes. For example, the bridge portions 105 can be separately produced to have a predetermined shape, and then the already produced bridge portions 105 can be mounted between the light emitting elements 102.
The bridge portions 105 can be produced by any suitable methods including, but not limited to, injection molding, laser processing, etching and the like. In this case, the bridge portion 105 can be produced to include a bridge main body 105a and a chip-insertion spacer 105b. The chip-insertion spacer 105b can support the bridge main body 105a and can be inserted into the predetermined gap between the light emitting elements 102. This configuration can ensure the fixing of the bridge portion 105. The length of the chip-insertion spacer 105b can be shorter than the main body 105a. Accordingly, there is no chip-insertion spacer just below the end surface 122 of the main body 105a so as to expose the bottom side 122a of the end surface 122. The shape of the bridge main body 105a can be any desired shape including, but not limited to, a rectangular prism, a triangular prism, a semi-cylindrical shape and the like, as shown in
As shown in
As described above, the effects of the semiconductor light emitting apparatus made in accordance with the principles of the presently disclosed subject matter can include:
(1) A plurality of light emitting elements that can be connected with the bridge portions disposed between the elements, and accordingly, a single wavelength conversion layer can be formed over them with a predetermined shape, thereby achieving the sharp difference of a front luminous intensity distribution between the light emitting area and the surrounding non-light emitting area (outer environment);
(2) A wavelength conversion layer can be formed in a continuous fashion over the light emitting elements, the surface concavity and convexity can be leveled during coating, meaning that the wavelength conversion layer can be shaped depending on the coating amount and the resulting layer can have a uniform phosphor concentration above the respective light emitting elements so that any light color unevenness and luminous intensity unevenness can be improved;
(3) The wavelength conversion layer can have a continuous surface by the provision of the bridge portions, and it is therefore possible to provide a light emitting apparatus with a novel light emission shape by the integrally formed wavelength conversion layer over the plurality of light emitting elements; and
(4) When the wavelength conversion layer is formed by a dispenser coating method, the wire bonding process can be performed before coating and masking for electrodes (wire bonding pads) may not be required, thereby preventing the electrode contamination and providing improved reliability.
The semiconductor light emitting apparatus of the present exemplary embodiments can be used as light sources for use in vehicle headlights, general lighting fixtures, street lamps, and various light emitting apparatuses.
As an Example, the semiconductor light emitting element having the configuration as described with reference to
Specifically, a ceramic substrate 101 having a wiring pattern formed thereon in advance was prepared. Four light emitting elements 102 were arranged in line on the ceramic substrate 101, and were fixed with a bonding material. The gap between the adjacent light emitting elements 102 was one tenth of the width L of the light emitting element in the arranging direction. A resin material for the bridge portion 105 was prepared by mixing a silicone resin with 15% of silica fine particles (Aerosil 380 manufactured by Nippon Aerosil Co., Ltd.) for imparting thixotropy to the material, and dispersing titanium oxide particles having a particle size of 0.2 to 0.4 μm as a reflecting filler in the resin. This resin material was dropped in between the light emitting elements 102 while the dropped amount thereof was controlled with the use of a nozzle having an elliptic opening shape with an opening diameter of 0.05 mm×0.15 mm. Then, the resin material was heated at 150° C. for 120 minutes for curing. By doing so, the bridge portions 105 were formed so as to be disposed on the substantially same plane as the top surface of the element at its ends as shown in
Then, respective ends of the wires 108 were bonded to the electrodes (wire bonding pads) 107 and the wiring pattern on the substrate 101, respectively, for electrical connection therebetween.
A liquid material for the wavelength conversion layer 103 was prepared by mixing a silicone resin with YAG phosphor particles having a particle size of 15 μm (in an amount ratio of 23%). Then, a nozzle of a dispenser for the liquid material was scanned over the four light emitting elements 102 connected with the bridge portions 105 to drop the mixed liquid material over the four light emitting elements 102. The dropped mixed liquid material was configured to have a convex surface due to its surface tension so that a single coating film was formed to cover the four light emitting elements 102 entirely. The coating film was subjected to heat treatment at 50° C. for 90 minutes, and then again heat treatment at 150° C. for 120 minutes. As a result, the coating film was cured to complete the semiconductor light emitting apparatus of the present example.
As Comparative Example 1, another semiconductor light emitting apparatus was produced without a bridge portion 105 as used in the example above, and resin layers containing phosphor particles separately were formed on respective top surfaces of the light emitting elements 102 by printing instead of the single wavelength conversion layer 103. In Comparative Example 1, the semiconductor light emitting apparatus had one electrode 107 formed on its top surface. As the wavelength conversion layer provided by printing was formed on each light emitting element, when the elements were arranged, the independent four wavelength conversion layers were disposed at regular intervals in line. The formed wavelength conversion layer had a constant thickness due to the printing method employed, and it had end surfaces perpendicular to the top surface of the element.
As Comparative Example 2, another semiconductor light emitting apparatus was produced as shown in
As shown in the luminous intensity distribution of the semiconductor light emitting apparatus of the Comparative Example 1 (
The semiconductor light emitting apparatus of Comparative Example 2 had independent domed phosphor layers 903 on the respective elements. Accordingly, the luminous intensity distribution of the semiconductor light emitting apparatus of Comparative Example 2 shown in
It will be apparent to those skilled in the art that various modifications and variations can be made in the presently disclosed subject matter without departing from the spirit or scope of the presently disclosed subject matter. Thus, it is intended that the presently disclosed subject matter cover the modifications and variations of the presently disclosed subject matter provided they come within the scope of the appended claims and their equivalents. All related art references described above are hereby incorporated in their entirety by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-264439 | Oct 2008 | JP | national |
