Light emitting diode

A light emitting diode includes a base, a light emitting chip, and a wavelength converting layer. The base is formed with a recessed portion that has a bottom wall surface, and a side wall surface extending upwardly from the bottom wall surface and cooperating with the bottom wall surface to define a receiving space. The light emitting chip is provided on the bottom wall surface of the receiving space, and has a top chip surface disposed below a top surface of the base, and a peripheral chip surface extending downwardly from the top chip surface and being substantially parallel to and forming a gap with the side wall surface of the recessed portion. The wavelength converting layer is filled in the receiving space in the recessed portion so as to cover the top chip surface and the peripheral chip surface of the light emitting chip.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese Application No. 096115904, filed on May 4, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a light emitting device, more particularly to a light emitting diode.

2. Description of the Related Art

As shown inFIG. 1, a conventional light emitting diode includes a base11formed with a recessed portion111, a light emitting chip12provided on a bottom wall surface of the recessed portion111and having a top chip surface and a peripheral chip surface, and a fluorescent layer13filled in the recessed portion111so as to cover the top chip surface and the peripheral chip surface of the light emitting chip12. The fluorescent layer13contains phosphor particles131for converting a part of blue light emitted from the light emitting chip12into yellow light, so that the mix of blue and yellow light results in white light. However, since light (L2) emitted from the peripheral chip surface travels in the fluorescent layer13longer than light (L1) emitted from the top chip surface, the light (L2) is more likely to be converted into yellow light than the light (L1), thereby making the light obtained from the conventional light emitting diode yellowwish.

U.S. Pat. No. 5,959,316 discloses another conventional light emitting diode (seeFIG. 2) that eliminates the aforementioned drawback by first covering the top chip surface and the peripheral chip surface of the light emitting chip12with a transparent spacer14, and then disposing the fluorescent layer13to cover the transparent spacer14. Since the fluorescent layer13has a uniform thickness, light emitted from different parts of the light emitting chip will be eventually converted to obtain output light that is less yellowish.

Moreover, U.S. Pat. Nos. 6,576,488, 6,417,019 and 6,650,044 disclose methods such as electrophoresis and stenciling to manufacture still another conventional light emitting diode (seeFIG. 3) including the fluorescent layer13that has a uniform thickness and that is disposed to directly cover the top chip surface and the peripheral chip surface of the light emitting chip12. However, these methods can only be applied to the light emitting chip12that is mounted to the base11via chip bonding process (seeFIG. 4) rather than wire bonding process. Furthermore, these methods lead to higher manufacturing costs, thereby impeding the popularity of the conventional light emitting diode.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a light emitting diode that can avoid color deviation of light obtained therefrom.

Accordingly, a light emitting diode of the present invention comprises a base, a light emitting chip, and a wavelength converting layer. The base has a top surface and is formed with a recessed portion that is indented from the top surface. The recessed portion has a bottom wall surface having a periphery, and a side wall surface extending upwardly from the periphery of the bottom wall surface to the top surface of the base and cooperating with the bottom wall surface to define a receiving space. The light emitting chip is provided in the receiving space and is disposed on the bottom wall surface of the recessed portion such that a geometric center of the light emitting chip coincides with that of the bottom wall surface of the recessed portion. The light emitting chip has a top chip surface that is disposed below the top surface of the base, and a peripheral chip surface that extends downwardly from the top chip surface to the bottom wall surface of the recessed portion, and that is substantially parallel to and that forms a gap with the side wall surface of the recessed portion. The wavelength converting layer is filled in the receiving space in the recessed portion so as to cover the top chip surface and the peripheral chip surface of the light emitting chip.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown inFIGS. 5 and 6, the preferred embodiment of a light emitting diode according to the present invention comprises a base21, a light emitting chip22, and a wavelength converting layer23.

The base21has a top surface219, and is formed with a recessed portion210that is indented from the top surface219. The recessed portion210has a bottom wall surface211having a periphery216, and a side wall surface212extending upwardly from the periphery216of the bottom wall surface211to the top surface219of the base21and cooperating with the bottom wall surface211to define a receiving space215.

The light emitting chip22is provided in the receiving space215and is disposed on the bottom wall surface211of the recessed portion210such that a geometric center of the light emitting chip12coincides with that of the bottom wall surface211of the recessed portion210. The light emitting chip22has a top chip surface220that is disposed below the top surface219of the base21, and a peripheral chip surface221that extends downwardly from the top chip surface220to the bottom wall surface211, and that is substantially parallel to and that forms a gap24with the side wall surface212of the recessed portion210.

The wavelength converting layer23is filled in the receiving space215in the recessed portion210so as to cover the top chip surface220and the peripheral chip surface221of the light emitting chip22.

The recessed portion210is rectangular in this embodiment, i.e., the side wall surface212thereof has a pair of parallel first surface parts213and a pair of parallel second surface parts214that extend between the first surface parts213, and the side wall surface212is substantially perpendicular to the bottom wall surface211. In this embodiment, as shown inFIG. 6, since the light emitting chip22is diced from a wafer that has a uniform thickness and is diced along the thickness direction of the wafer, the light emitting chip22is also rectangular. As further shown inFIG. 7, the peripheral chip surface221of the light emitting chip22has a pair of parallel first surface portions222that are disposed parallel to the first surface parts213of the side wall surface212, and a pair of parallel second surface portions223that extend between the first surface portions222and that are disposed parallel to the second surface parts214of the side wall surface212. Each of the first surface parts213has a first length (WL1) transverse to the second surface parts214. Each of the second surface parts214has a second length (WS1) transverse to the first surface parts213. Each of the first surface portions222has a third length (WL2) transverse to the second surface portions223. Each of the second surface portions223has a fourth length (WS2) transverse to the first surface portions222. The first length (WL1) has a difference with the third length (WL2) that is less than 0.6 millimeters, and the second length (WS1) has a difference with the fourth length (WS2) that is less than 0.6 millimeters. In this embodiment, the difference between the first length (WL1) and the third length (WL2) is 0.4 millimeters, and the difference between the second length (WS1) and the fourth length (WS2) is also 0.4 millimeters.

As shown inFIG. 5, the base21is one of a metallic substrate (e.g., a lead frame), a printed circuit board, a ceramic substrate, a plastic substrate, and any other substrate made of materials that can be suitably processed. The recessed portion210is processed in different ways according to the material from which the base21is made.

The light emitting chip22can be one that is configured for wire bonding or flip chip bonding. In this embodiment, by virtue of a pair of metallic electrodes (not shown) thereof electrically connected to an external power source, the chip22is driven to emit blue light with a wavelength between 400 nm to 470 nm.

In this embodiment, the wavelength converting layer23is a fluorescent layer containing a transparent plastic such as silicone or epoxy resin, and phosphor particles231for converting the blue light emitted from the top chip surface220of the light emitting chip22into yellow light that has a wavelength between 520 nm and 570 nm. In other embodiments of the invention, the light emitting diode can comprise a chip that emits ultraviolet light having a wavelength between 300 nm to 400 nm, and a fluorescent layer that includes phosphor particles emitting red light having a wavelength between 590 nm and 650 nm, green light having a wavelength between 500 nm and 530 nm, and blue light having a wavelength between 440 nm and 480 nm to result in white light.

Since the semiconductor material of the light emitting chip22has a refractive index greater than that of the transparent plastic of the wavelength converting layer23, if photons generated from the active layer of the light emitting chip22move outwardly of the top chip surface220and the peripheral chip surface221of the light emitting chip22at an angle greater than the critical angle of total reflection, the photons will be totally reflected inwardly of the light emitting chip22instead of passing through the light emitting chip22into the wavelength converting layer23. Therefore, photons pass through the top chip surface220mostly in directions within a first angular range θ1(seeFIG. 8), and pass through the peripheral chip surface221mostly in directions within a second angular range θ2(seeFIG. 8).

Since the wavelength converting layer23has a uniform thickness at the part covering the top chip surface220of the light emitting chip22within the first angular range θ1, the characteristics of the converted portion of light through the wavelength converting layer23within the first angular range θ1will be substantially the same. As the side wall surface212of the recessed portion210of the base21is disposed parallel to the peripheral chip surface221of the light emitting chip22, most light within the second angular range θ2and emitted from the light emitting chip22into the wavelength converting layer23will undergo multiple reflections inside the wavelength converting layer23between the side wall surface212of the recessed portion210and the peripheral chip surface221of the light emitting chip22, or will be absorbed by the materials of the wavelength converting layer23and the light emitting chip22for transformation into another form of energy. Therefore, the effect of light emitted from the peripheral chip surface221upon light emitted from the top chip surface220can be effectively reduced without incurring higher manufacturing costs.