|Publication number||USRE42112 E1|
|Application number||US 11/652,468|
|Publication date||8 Feb 2011|
|Filing date||11 Jan 2007|
|Priority date||25 Jul 2003|
|Also published as||CN1577903A, CN100382340C, DE102004001312A1, DE102004001312B4, US7042022, US20050017259|
|Publication number||11652468, 652468, US RE42112 E1, US RE42112E1, US-E1-RE42112, USRE42112 E1, USRE42112E1|
|Inventors||Kwan-young Han, Do-hyung Kim, Seung-Man Yang, Chung-Hoon Lee, Hong-San Kim, Kwang-Il Park|
|Original Assignee||Seoul Semiconductor Co., Ltd.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (30), Non-Patent Citations (4), Referenced by (4), Classifications (15), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
(a) Field of the Invention
The present invention relates to a chip light emitting diode and a fabrication method thereof.
(b) Description of the Related Art
Chip light emitting diodes (LEDs) are generally employed as display devices and for backlighting. Recently, their use range has been increased to include various applications such as light sources for mobile phones and personal digital assistants (PDAs).
The conventional chip LED 50 has drawbacks in that optical paths of emitted light rays are limited because the resin package 56 has a rectangular cross section, causing a narrow viewing angle of the chip LED. Further, the intensity distribution of the emitted light is concentrated at the position of the chip. Therefore, many chip LEDs are required to light a certain area, resulting in high manufacturing cost in some applications such as for backlighting.
Further, heat generated from the conventional chip LED 50 during operation is concentrated in the edges, resulting in thermal or mechanical deformation of the diode.
When the thickness of the resin package is reduced for overall compactness of the conventional chip LED, a metal mold of the resin package should be more precisely formed for the edges, which may result in high manufacturing costs. Further, when the thickness of the resin package happens to be not uniform, stress may be concentrated at a thin part, so the adhesive strength is deteriorated causing poor reliability of the chip LED.
In view of the prior art described above, it is an object of the present invention to provide a chip light emitting diode (LED) having a wide viewing angle and a fabrication method thereof.
It is another object of the present invention to provide a chip LED in which the light intensity is substantially uniform on either side in order to illuminate a larger area with high brightness.
It is another object of the present invention to provide a chip LED in which the heat generated is distributed uniformly to avoid thermal and mechanical deformation and to prevent stress from centralizing on one side.
It is still another object of the present invention to provide a fabrication method of a chip LED, in which a simple metal mold structure can be employed to reduce fabrication costs.
To achieve these and other objects, as embodied and broadly described herein, a chip light emitting diode includes:
a metal pad and a lead spaced away from each other on a printed circuit board;
a light emitting chip mounted on the metal pad;
a wire connecting the light emitting chip and the lead; and
a resin package sealing the light emitting chip and at least a part of the metal pad, the lead, and the wire, the resin package having at least one curved projecting part.
The curved projecting part has a cross section which is substantially semicircular, or substantially or partially elliptical or parabolic. The curved projecting part preferably has a cross section which is comprised of a plurality of straight lines, an angle being formed between adjacent lines.
According to another aspect of the present invention, a fabrication method of a chip light emitting diode comprises the steps of:
mounting a light emitting chip on a metal pad formed on a printed circuit board;
connecting the light emitting chip to a lead formed on the printed circuit board;
providing the printed circuit board within a mold having a cavity, the cavity corresponding to at least one projecting part of the chip light emitting diode; and
forming a resin package sealing the light emitting chip and at least a part of the metal pad and lead by injecting resin material into the cavity of the mold, the resin package having at least one curved projecting part.
Both the foregoing general description and the following Detailed Description are exemplary and are intended to provide further explanation of the invention as claimed.
The accompanying drawings provide a further understanding of the invention and, together with the Detailed Description, explain the principles of the invention. In the drawings:
The present invention will be described in detail with reference to the accompanying drawings.
The resin package 160 has a curved projecting part 161 which has a cross section that is substantially semicircular. The cross section is elongated to form a cylindrical outer surface of the resin package 160. A suitable epoxy resin may be injected and molded into the resin package 160 using a metal mold (not shown) with a curved cavity.
Light rays R emitted by the chip 130 are refracted on the gently curved surface with different refractive angles. This causes light intensity distribution to become uniform and the viewing angle to be wide.
As shown in the enlarged sectional view of
As shown in
The resin package 160 of the chip LED 100 has no sharp edge, but rather it has a gently curved surface without limitation of the light path. This causes the light efficiency to be increased, as confirmed by experimental results shown in TABLE 1 which were obtained by the inventors through many experiments. TABLE 1 shows only average values of the light intensity and brightness according to the chip LED 100 and the conventional chip LED 50.
Average light intensity
Chip LED according to the
first preferred embodiment
Conventional ship LED
The experimental results of TABLE 1 were measured under the condition that the light emitting chips 100, 50 had the same dimensions of 304 μm in width, 304 μm in depth, and 100 μm in height, and input currents of 5 mA in light intensity measurement and 15 mA in brightness measurement.
Referring to TABLE 1, the chip LED 100 according to the present invention is enhanced in light intensity by 6 mcd and in brightness by 280 cd/m′ on average with respect to the conventional chip LED 50. Therefore, it is noted that the chip LED 100 has more light efficiency than the conventional one.
The curved projecting part 161 of the resin package 160 is described having a cross section of a semicircle referring to
Referring now to
It is also possible to provide a chip LED 400 with a resin package 460, as shown in
The present invention is not limited to the above-described embodiments. A curved projecting part of the resin package may have a cross section that is partly elliptical, parabolic, or circular, or any modification thereof. A surface of the resin package may have fine striations to scatter light, resulting in further widening of the range of viewing angle.
The resin package according to the present invention may be easily adapted to chip LEDs having a two-top structure.
Referring next to
The resin package 660 of the chip LED 600 has two curved projecting parts 661, 662. Both curved projecting parts 661, 662 are spaced out by spacer 663 with an interval 1 therebetween. The interval 1 may be selected from a range of 0.1 to 0.4 times the bottom length b in the cross section.
In the chip LED 600 according to the second preferred embodiment, light rays emitted by the chip 130 are transmitted and refracted on the two curved surface of the projecting parts 661 and 662. Then, the refracted rays diverge to provide a large viewing angle. This may enhance the lighting effect of both sides on a predetermined area.
Although the resin package 660 of the chip LED 600 according to the second preferred embodiment is described to have two projecting parts 661, 662, it is also possible to form more than two projecting parts in a resin package.
Light rays emitted by the chip 130 in the chip LED 700 or 800 are transmitted and refracted in the projecting parts 661, and they diverge with a large viewing angle. This may enhance the lighting effect as compared to the conventional chip LED 50 in FIG. 1.
It is also possible that the surface of the resin package according to the second preferred embodiment may have fine striations to scatter light, resulting in further widening of the range of viewing angle.
Referring next to
The PCB 110 is then mounted on a mold having a cavity (S4). The cavity corresponds to the projecting part(s) according to one of the first preferred embodiment and the second preferred embodiment.
Next, a solid epoxy mold compound is heated to 170-1800 and injected into the mold. The resin package 160 is formed on the PCB 110 with the shape described in the first or second preferred embodiment (S5). The resin package is formed to seal the light emitting chip. It is possible that the resin package is formed to seal either a part of the metal pad and lead, or the entire surface of the metal pad and lead.
Practically, a plurality of chip LEDs are formed on one PCB, which for example has a size of about 80 mm×50 mm. Therefore, each chip LED on the PCB is individually cut off (S6).
As described above, light rays emitted from the light emitting chip diverge radially and uniformly in a chip LED according to the present invention, to further widen the viewing angle. The lighting efficiency of the chip LED is also improved, so the number of chip LEDs is reduced in application to backlighting to light a certain area.
Heat generated from the chip LED according to the present invention is also uniformly distributed on the surface, to prevent the chip LED from deforming thermally or mechanically. Further, stress is not concentrated on one side, to enhance the adhesive characteristics between the resin package and the PCB, especially in compact chip LEDs.
Since a mold with a curved projecting part is easily manufactured, as compared to a resin package with a rectangular cross section, a relatively simple mold structure for a resin package reduces fabrication costs.
It will be apparent to those skilled in the art that various modifications and variations can be made to the device and method of the present invention without departing from the spirit and scope of the invention. The present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
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|U.S. Classification||257/99, 257/433, 257/E33.066, 257/100|
|International Classification||H01L29/22, H01L27/15, H01L33/54, H01L33/64, H01L33/56, H01L33/62|
|Cooperative Classification||H01L2224/48091, H01L33/54, H01L33/486, H01L2924/1815|