LED device and method for manufacturing the same

A semiconductor light-emitting device and a method for manufacturing the same can include a soft silicon resin encapsulating an LED chip with a thin overcoat of microparticles located on the silicon resin to prevent dirt and dust from attaching to the silicon resin. The semiconductor light-emitting device can include a base board having at least one LED chip, a reflector fixed on the base board so as to enclose the LED chip, a soft silicon resin having a tacky surface disposed in the reflector, and an overcoat of microparticles on the silicon resin. Thus, manufacturing lead time can be reduced because the microparticles can attach to the silicon resin in a thin and single layer and a solidifying process for an extra layer on top of the silicon resin is not necessary. The overcoat of microparticles can prevent dirt and dust from attaching to the silicon resin, and can decrease optical variability in an inclined direction from an optical axis of the device.

This application claims the priority benefit under 35 U.S.C. §119 of Japanese Patent Application No. 2007-314603 filed on Dec. 5, 2007, which is hereby incorporated in its entirety by reference.

BACKGROUND

The presently disclosed subject matter relates to semiconductor light-emitting devices including an LED chip and to a manufacturing method for the same, and more particularly to reliable semiconductor light-emitting devices including a silicon resin for encapsulating the LED chip and to the manufacturing method for these devices.

2. Description of the Related Art

Various semiconductor light-emitting devices including an LED chip have been used for general lighting in recent years. One reason is that an LED chip may be a favorable light source with respect to energy savings and environmental concerns. In addition, semiconductor light-emitting devices including an LED chip can emit variously-colored light while the structure thereof can be thin and small in size. High power LED chips have been developed and have been used as a light source in keeping the above trend.

However, while high power LED chips have been used as a light source for light-emitting devices, an epoxy resin that has been generally used as an encapsulating resin for LEDs has become difficult to use for semiconductor light-emitting devices, especially for devices that require high reliability. This is sometimes due to stress caused by a difference of thermal expansion coefficients between the material for mounting the LED chip and the encapsulating resin that is composed of epoxy. In some cases, a semiconductor light-emitting device that includes the epoxy resin may be damaged by the above-referenced stress. In addition, an epoxy resin may deteriorate in terms of quality and function thereof due to ultraviolet rays emitted from an LED chip, especially from the high power LED chip that can emit a light of high intensity.

Thus, while high-power LED chips become more prevalently used as a light source for a semiconductor light-emitting device, a soft silicon resin has been more frequently employed as an encapsulating resin in these devices. A characteristic of the soft silicon resin is that it may not be damaged by the above-described stress and may not deteriorate in quality due to ultraviolet rays. A soft silicon resin can generally resolve or reduce the problems caused by the ultraviolet rays and the stress. However, certain other problems or concerns are present when using a soft silicon resin, such as the characteristic that dirt and dust may easily attach to a surface thereof during the manufacturing process for the light-emitting device. Dirt and dust and other debris are attracted to the silicon resin because the surface thereof might be tacky.

A conventional light-emitting device that may resolve the above-described problems, for example, is disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP2007-036030). According to Patent Document No. 1, and as shown inFIG. 6, a pair of lead frames23a,23bis insert-formed in a casing21that includes a cavity22for encapsulating an LED chip24with encapsulating resins described later. The pair of lead frames23a,23bis depicted on a bottom surface of the cavity22.

The LED chip24is mounted on the lead frame23avia a conductive material and has one electrode thereof that is electrically connected to the lead frame23avia one bonding wire25a. The other electrode of the LED chip24is electrically connected to the lead frame23bvia the other bonding wire25b. A first silicon resin26aincluding a phosphor28is disposed in the cavity22so as to encapsulate the LED chip24.

The phosphor28can absorb light emitted from the LED chip24and can convert the light into a different wavelength of light as compared to that of the light emitted directly from the LED chip24. Therefore, the light-emitting device including the LED chip24may emit variously-colored light according to the type, quality, kind, etc., of phosphor28located within the resin26a. The first silicon resin26aincluding the phosphor28may also protect the LED chip24from problems caused by dust, moisture, etc.

In this case, dirt and dust may attach to a surface of the first silicon resin26a. Accordingly, the surface of the first silicon resin26ais covered by a second silicon resin26bthat is configured with a hard silicon resin having a higher hardness as compared to the first silicon resin26a. Thus, the second silicon resin26bhaving a high hardness can prevent dirt and dust from attaching to a surface thereof, and therefore the light-emitting device can operate reliably and maintain predetermined optical characteristics.

However, the above-described light-emitting device requires a process for covering the surface of the first silicon resin26awith the second silicon resin26bduring manufacture. In addition, the light-emitting device requires both a process for at least partly solidifying the first silicon resin26abefore covering it with the second silicon resin26band a process for solidifying the second silicon resin26b. Thus, a manufacturing method for the light-emitting device may include certain problems or concerns, such as increased lead time for manufacturing the device as compared to that for manufacturing a conventional light-emitting device.

In addition, the second silicon resin26bmay be difficult to form in a thin and uniform layer in a short time with a simple manufacturing machine. Thus, the light-emitting device may be difficult to form in a thin manner while accomplishing predetermined optical characteristics in line with the trend of providing thinner devices. The conventional device may also include variability in terms of optical characteristics from product to product if a thickness of the second silicon resin26bcannot be made uniform in the overcoat and solidifying processes.

On the other hand, an inventor of the disclosed subject matter discovered that a microparticle such as silicon dioxide and the like can be useful as a luminescent material as disclosed in Patent Document No. 2 (Japanese Patent Application Laid Open JP2006-143861). A manufacturing method for the microparticle is also disclosed in detail in Patent Document No. 2.

The above-referenced Patent Documents are listed below, and are hereby incorporated with their English abstracts in their entireties.

1. Patent Document No. 1: Japanese Patent Application Laid Open JP2007-036030

2. Patent Document No. 2: Japanese Patent Application Laid Open JP2006-143861

The disclosed subject matter has been devised to consider the above and other problems, features, and characteristics. Thus, embodiments of the disclosed subject matter can include semiconductor light-emitting devices and associated manufacturing methods that do not cause and/or are designed to prevent some of the above-described problems, concerns, and characteristics related to a thin and uniform overcoat and the manufacturing lead time, etc. The disclosed subject matter can also include a light-emitting device that is configured to decrease optical variability caused by differences between a light-emitting color emitted from the optical axis thereof and a light-emitting color emitted in an inclined direction from the optical axis, and can reduce or change other associated problems, features, and characteristics of the conventional devices and methods.

SUMMARY

The presently disclosed subject matter has been devised in view of the above and other problems, features, and characteristics. Another aspect of the disclosed subject matter includes methods of manufacture that provide various semiconductor light-emitting devices including a thin and single layer overcoat and which can provide less lead time while using a simple manufacture machine with respect to conventional light-emitting devices and processes.

According to an aspect of the disclosed subject matter, a semiconductor light-emitting device can include: a base board having at least one pair of electrodes that is connected to electrode conductor patterns for receiving a power supply; at least one LED chip mounted on the at least one pair of electrodes, and also being electrically connected; a reflector being formed in a substantially tubular shape, and fixed on the base board so as to enclose the at least one LED chip; a soft silicon resin having a tacky surface disposed in the reflector; and microparticles configured to be disposed on substantially all the surface of silicon resin opposite the base board so as not to expose the silicon resin to the outside.

As a variation of the above-described exemplary semiconductor light-emitting device, the reflector can be eliminated. The semiconductor light-emitting device can include: the base board; the at least one LED chip; the silicon resin disposed on the pair of electrodes so as to encapsulate the at least one LED chip and bonding wire(s); and microparticles configured to be disposed in a dome-shape on substantially all the surface of silicon resin that does not face the base board so as not to expose the silicon resin to the outside.

In the above-described exemplary semiconductor light-emitting device, the silicon resin can include at least one of a diffuser, a phosphor material, colored particles using a dye, and a pigment, wherein the phosphor material, colored particles using a dye, and pigment are configured to selectively absorb light having a predetermined wavelength. The microparticles can be configured with SiO2, and also can include at least one of a particle of pigment, a particle of phosphor material and a colored particle using a dye.

According to the above-described exemplary semiconductor light-emitting device, the device can reduce a decrease of light intensity caused by dirt and dust attached on the light-emission surface thereof because the silicon resin can be prevented from accumulating dirt and dust thereon with the overcoat of microparticles. In addition, because the microparticles can accelerate mixing the light emitted from the LED chip with wavelength-converted light via the phosphor material, the device can reduce an optical variability that can otherwise be caused by differences between a light-emitting color emitted from an optical axis thereof and a light-emitting color emitted in an inclined direction from the optical axis.

Another aspect of the disclosed subject matter includes a method for manufacturing the above-described semiconductor light-emitting devices that can include: preparing a base board that includes at least one pair of electrodes, whereon at least one LED chip is electrically connected; encapsulating the at least one LED chip with a silicon resin having an tacky surface; solidifying the silicon resin; and spraying microparticles on substantially all surface of the silicon resin that does not expose to the outside.

In the above-described exemplary method for manufacturing the semiconductor light-emitting devices, the same or similar variations of the device can be employed as set forth above.

According to the above-described exemplary method for manufacturing semiconductor light-emitting devices, lead time can be reduced with respect to a conventional manufacturing method because the microparticles are not required to undergo a solidifying process. Furthermore, because the microparticles can attach to the silicon resin in a thin and single layer by spraying them on the tacky surface of the silicon resin, the overcoat can be formed in a short time with a simple manufacturing machine even if the overcoat is not a flat surface.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The first exemplary embodiment of the disclosed subject matter will now be described in detail with reference toFIG. 1.FIG. 1is a cross-sectional summary view of a first exemplary embodiment made in accordance with principles of the disclosed subject matter.

The semiconductor light-emitting device can include: a base board2having a pair of electrodes3a,3bexposed thereon; an LED chip4that is mounted on one electrode3aof the pair of electrodes via a conductive material. The LED chip can include a top and a bottom electrode connected to a respective one of the pair of electrodes3a,3bvia the conductive material and a bonding wire5, respectively. A reflector1can be formed in a substantially tubular shape with a cavity, and disposed on the base board so as to enclose the LED chip4. A silicon resin6can be disposed in the cavity formed by the reflector1and the base board2.

In this embodiment, the silicon resin6can be configured as a soft silicon resin having a tacky surface, and microparticles7such as SiO2and the like can be attached to substantially the entire surface of silicon resin opposite the base board2so as not to expose the silicon resin6to the outside. Thus, the light-emitting device can prevent dirt and dust from attaching to a light-emission surface thereof that is composed of the microparticle7formed on the silicon resin6. Each of the above-described components will now be described in detail.

The base board2can be made using high temperature conductive materials, such as a metal board that is provided with Au, Al, and the like with an insulating layer thereon or a ceramic substrate, such as Al2O3, AlN, SiC, Si3N4and ZrO2. The base board2can be formed with the pair of electrodes3a,3bon a surface thereof, and the pair of electrodes3a,3bcan be connected to electrode conductor patterns for receiving a power supply.

The reflector1can be composed of an opaque resin material, metal material, ceramic material and the like, and can be fixed at a predetermined position on the base board2via an adhesive material with a high temperature conductivity, or the like. The reflector1can define the cavity for exposing the pair of electrodes3a,3band can be configured for reflecting the light of an LED chip4. Thus, the reflector1can be made using high reflectivity materials for the LED chip4. Alternatively, an inner surface of the reflector1can be coated with a material with high reflectivity.

The reflector1can also be integrated with the base board2as one body. In the case when they are formed as one body, the base board2including the reflector1can be insert-formed with the pair of electrodes3a,3busing lead frames.

The LED chip4can include, for example, a blue LED chip composed of a GaN-based compound semiconductor, a red LED chip composed of GaAs-based compound semiconductor and the like for any purpose or specific application. The LED chip4can be mounted on the pair of electrodes3a,3bof the base board2in the cavity of the reflector1. The pair of electrodes3a,3bcan be electrically connected to both electrodes of the LED chip4via die bonding and wire bonding, respectively.

When the LED chip4is mounted on one electrode3aof the pair of electrodes via die bonding, a solder, a silver paste and the like can be used as an adhesive material that is electrically conductive. When an electrode of the LED chip4is electrically connected to the other electrode3bof the pair of electrodes via wire bonding, an Au wire and the like can be used as a conductive wire5. The LED chip4is not limited to one chip, and can also include a plurality of chips. Additionally, the LED chip can be mounted on the pair of electrodes via a sub mount.

The silicon resin6can be configured as a soft silicon resin having a tacky surface. The soft silicon resin can be an elastomeric resin and a gelled resin that have hardness within the range of substantially 30 to 80 in shore hardness A. A thermosetting silicon resin can also be used as the silicon resin6. The silicon resin6can include a diffuser such as TiO2, CaCO3and the like for efficiently emitting light to the outside.

Thus, the silicon resin6does not deteriorate very much in quality and function due to ultraviolet rays in the light emitted from the LED chip4, and can efficiently emit the light emitted from the LED chip4to the outside therethrough. In addition, the light-emitting device is configured to prevent damage due to stress caused by a difference of thermal expansion coefficients between the silicon resin6and the above-described materials for mounting the LED chip4because the silicon resin6can be configured as a soft silicon resin that can absorb the stress.

The microparticles7can be configured in various shapes and can include various materials such as phosphors. The microparticles7can be sized within a range of substantially 1 to 20 micrometer in mean particle size. In this case, because the microparticles7can be dispersed in a volatile solution and can be sprayed on the soft silicon resin, or because the microparticle7can be directly splayed by air on the soft silicon resin, the overcoat process of the microparticles7can be easier than a conventional process such as when the soft silicon resin is covered with a harder silicon resin, and also can be carried out by a simple manufacturing machine even if a surface of the silicon resin6is not flat.

In addition, the thickness of the overcoat formed on the silicon resin6can become thinner by using microparticles7that have a mean particle size of less than 10 micrometer. The microparticles7can include different materials, such as SiO2, Al2O3, B2O3, MgO, CaO, ZnO, AlN, TiO2, acrylic, polycarbonate and the like. For example, SiO2can be a favorable material in certain application and can maintain a strong attachment to the silicon resin6while also being a clear material having high transparence.

Furthermore, the microparticles7are not necessarily transparent, and can be composed of a colored material such as red, green and the like, that is, a pigment, a colored microparticle using a dye and a phosphor for selectively absorbing light emitted from the LED chip4and emitting a different colored light from that of the LED chip4. When both the above-described colored microparticle and a mixture microparticle mixed with a transparent material with a colored material can be used as the microparticles7, the microparticles7can provide a color correction for a colored light of the light-emitting device.

The microparticles7can attach to substantially the entire surface of silicon resin opposite the base board2so as not to expose the silicon resin6to the outside. The overcoat layer formed on the soft silicon resin is not necessarily a plurality of layers. For example, a single layer of microparticles can be formed on the soft silicon resin. Thus, because the thickness of the overcoat layer can be substantially the same thickness as the particle size of the microparticle, the overcoat layer can be formed as a thin single layer.

The reason that the microparticles7can attach to the soft silicon resin which has a tacky surface, but do not attach to each other is because the microparticles7can be formed of an incohesive material. Therefore, even when the microparticles may accumulate on the surface of the soft resin6, the single layer can be easily formed by blowing the excess microparticles7away with an air gun, etc.

A second exemplary embodiment of the disclosed subject matter will now be described with reference toFIG. 2. A semiconductor light-emitting device of the second exemplary embodiment is shown inFIG. 2, wherein the same or similar elements shown inFIG. 1are referenced by same reference numerals. The light-emitting device can be similar to the light-emitting device shown inFIG. 1. A difference between the semiconductor light-emitting devices ofFIG. 1andFIG. 2can be the absence of a reflector structure in the embodiment shown inFIG. 2.

In the second exemplary embodiment, a circuit board that is generally used for a surface mount device can also be used as the base board2similar to the first exemplary embodiment. When the silicon resin6is disposed on the base board2, the soft silicon resin can be directly disposed by a dispenser so as to encapsulate the LED chip4mounted on the pair of electrode3a,3b.

In this case, the shape of the silicon resin6can be formed using the variables of quantity, hardness and surface tension of the soft silicon resin to obtain a desired form. Therefore, because the process may be simple and can be carried out in a short time by a simple manufacturing machine, the process may be useful for use in manufacturing the above-described surface mount LED devices that are thin and small and are produced at low cost. However, the method may make it difficult to exactly form a same and consistent shape in many products.

When it is desired that the silicon resin6form a same and consistent shape in many products, a molding tool can be placed on the base board2and used to accurately and consistently dispose and shape the silicon resin6. When the silicon resin6is disposed in the cavity formed by the molding tool and the molding tool is removed after the silicon resin6is solidified, the silicon resin6can be formed in an exactly same shape consistently for many products in accordance with the cavity of the molding tool.

After the silicon resin6is formed, the above-described microparticles7can be splayed on the soft silicon resin or the soft silicon resin on the base board2can dipped into a bath of microparticles7. Thus, a single layer of microparticles7can be formed in a dome-shape on the entire surface of soft silicon resin6that does not face the base board2so as not to expose the silicon resin6to the outside. The microparticles7can also be softly blown with an air gun or the like, such that the overcoat layer can be perfectly formed in a thin single layer because excess microparticles7can be removed. Thus, the light-emitting device of the second exemplary embodiment can emit a wide range of light on the base board2.

Another exemplary embodiment of the disclosed subject matter will now be described with reference toFIG. 3.FIG. 3shows a semiconductor light-emitting device that can be configured similar to the semiconductor light-emitting device shown inFIG. 1. Thus, the same or similar elements inFIG. 3are referenced using the same reference numerals as those inFIG. 1. A difference between the semiconductor light-emitting devices ofFIG. 1andFIG. 3can be the inclusion of a phosphor8in the device shown inFIG. 3.

The phosphor8can absorb a predetermined wavelength of light emitted from the LED chip4, and can emit a different wavelength of light from that emitted from the LED chip4. For example, when the LED chip is a blue LED chip that emits a blue light with a peak wavelength of 450 nm, YAG: Ce, (Ca, Sr, Ba)2SiO4: Eu, and the like can be used as the phosphor8.

The phosphor8can be mixed with the silicon resin6, and the silicon resin6can be disposed along with the phosphor8in the cavity of the reflector1. When the LED chip4is provided with a power supply via the pair of electrodes3a,3b, the light-emitting device can emit a mixture light that includes light emitted from the LED chip3mixed with wavelength-converted light emitted via the phosphor8. Alternatively, the light-emitting device can be configured to emit only the wavelength-converted light using the LED chip4and the phosphor8. The silicon resin6can also include a pigment that can absorb light having a predetermined wavelength.

The above-described structure can include an overcoat of microparticles7on the silicon resin6as described in the first and second exemplary embodiments. Therefore, the light-emitting device can also prevent dirt and dust from attaching to the light-emission surface thereof. In addition, the microparticles7can accelerate the mixture of light emitted from the LED chip4with light that is wavelength-converted light emitted via the phosphor8.

As described above, conventional light-emitting devices including both an LED chip and a phosphor may exhibit a problem or feature such as optical variability that is caused by a difference between light-emitting color of light emitted from the optical axis thereof and light-emitting color of light emitted in an inclined direction from the optical axis. However, the microparticles7can reduce the optical variability because the microparticles7can accelerate mixing of light emitted from the LED chip4with wavelength-converted light emitted via the phosphor material8.

A manufacturing method for the above-described semiconductor devices will now be described in detail with reference toFIGS. 4A-D. The same or similar elements inFIGS. 4A-Dare used to reference the same or similar features as shown inFIGS. 1-3.

In process A shown inFIG. 4(A), an exemplary method for manufacturing semiconductor light-emitting devices can include: preparing or providing a base board2that includes at least one pair of electrodes3a,3b, whereon at least one LED chip4is mounted and is electrically connected; fixing a reflector1to the base board, the reflector being formed in a substantially tubular shape with a cavity so as to enclose the at least one LED chip4therein. In this case, the LED chip4can be electrically connected using a flip chip via die bonding and wire bonding.

In process B shown inFIG. 4(B), the method can include filling a silicon resin6in the cavity using a dispenser9so as to enclose the at least one LED chip4mounted on the at least one pair of electrodes3a,3bof the base board2.

In process C shown inFIG. 4(C), the method can include solidifying the silicon resin6. In this case, for instance, the silicon resin6can be solidified for four hours at 150 degrees centigrade. However, it should be noted that the surface of the silicon resin6can be solidified either before process D (described below), and/or the silicon resin6can be absolutely solidified after process D.

In process D shown inFIG. 4(D), the method can include spraying the microparticles7on the silicon resin6using a sprayer10. In this case, the microparticles7are dispersed in a volatile solution and can be sprayed on the silicon resin6. Moreover, the microparticles7can be directly sprayed by the sprayer10onto the resin6. If excess microparticles7are attached to or stacked on the silicon resin6, the overcoat layer can be formed as a thin and single layer by blowing the microparticles7with an air gun and/or the like.

According to the above-described manufacturing method, a hard silicon resin is not required to be disposed on the surface of silicon resin6. Therefore, both resins can be solidified at the same or different times with respect to each other. Thus, the manufacturing method can provide various semiconductor light-emitting devices in less lead time with respect to a conventional device. Furthermore, the method can form a thin and single overcoat layer on the silicon resin6in a short time and with a simple manufacturing machine even if the surface of the silicon resin6is not flat.

Results of an exemplary experiment using a semiconductor light-emitting device made in accordance with principles of the disclosed subject matter as compared to a comparative device are described as follows.

COMPARATIVE EXAMPLE

A comparative example device includes: a base board2comprising a glass epoxy board; a reflector1configured of a resin; a blue LED chip4having a dominant wavelength of 455-460 nm mounted on a pair of electrodes and electrically connected to a power source; and a soft silicon resin6having 45 in shore hardness A disposed in a cavity of the reflector1.

Embodiment

An embodiment device further includes microparticles7of SiO2having a mean particle size of 4 to 8 micrometer and located on the soft silicon resin6of the comparative example. In this case, the microparticles7extend on substantially the entire surface of the silicon resin6by application of a brush, and excess microparticles7are blown off with an air gun.

Results of a sticking test will now be given with respect to the embodiment and the comparative example. When a plastic sheet is pressed to the comparative example, the plastic sheet easily attaches to the silicon resin6of the comparative example. However, the plastic sheet does not attach to the surface of the embodiment device when the plastic sheet is pressed to the embodiment.

Results of light intensity measurements can be described as follows. When a light intensity of the comparative example device is based on 100, a light intensity of the embodiment device is 96. Thus, the microparticles7of the embodiment device do not practically affect the light intensity of the embodiment light-emitting device.

Results of directional characteristics with respect to chromaticity using a goniometer will now be described with reference toFIGS. 5A-B. The vertical axis shown inFIG. 5(A)shows the x-axis in a CIE xy chromaticity diagram, and the vertical axis shown inFIG. 5(B)shows the y-axis in the CIE xy chromaticity diagram. The horizontal axes shown inFIGS. 5(A)and (B) show an inclined angle based on an optical axis (0 degree) of the semiconductor light-emitting device. For example, the optical axis for the devices shown inFIGS. 1-4Dand6is a vertical line extending from a center of each of the LED chips (4,24).

For instance, when the horizontal axes are 40 degrees, each of the vertical axes show chromaticity of light emitted in the inclined direction of 40 degrees from the optical axis of the device. The embodiment device exhibits smaller chromaticity variation than that of the comparative example. Thus, the disclosed subject matter can decrease optical variability that is caused between a difference in light-emitting color emitted from the optical axis and light-emitting color emitted in an inclined direction from the optical axis.

In addition, when the semiconductor light-emitting device is mounted on a circuit board at a peak temperature of 260 degrees centigrade in a reflow soldering process, the microparticles7and the silicon resin6prevent problems such as peeling and the like.

Thus, the disclosed subject matter can provide a semiconductor light-emitting device with high reliability that can reduce the optical variability caused between a difference in light-emitting color emitted from the optical axis thereof and light emitting color emitted in an inclined direction from the optical axis. In addition, a method for manufacturing a semiconductor light-emitting device in accordance with principles of the disclosed subject matter can reduce lead time with respect to that of a conventional manufacturing method because the microparticles7do not require a process for solidification.

While there has been described what are at present considered to be exemplary embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover such modifications as fall within the true spirit and scope of the invention. All conventional art references described above are herein incorporated in their entirety by reference.