KR20110010990A - Planar light source device - Google Patents

Abstract

PURPOSE: A planar light source device is provided to improve luminous efficiency by maintaining relatively a low temperature of a light emitting diode chip. CONSTITUTION: A substrate comprises a metal layer(111) which has a thickness of at least 1.0mm. A plurality of light emitting diode chips(12) has a chip size of 0.0784~0.25mm^2. The plurality of light emitting diode chips are spaced apart from the adjacent chip according to at least twice of the length of the chip. A reflective cover layer(13) is arranged on the substrate and is formed in a plurality of inner holes. A plurality of transparent body parts are filled in the inner hole of the reflective cover layer.

Description

Planar Light Source Device {PLANAR LIGHT SOURCE DEVICE}

The present invention relates to a planar light source device, and more particularly, to a planar light source device including a plurality of light emitting diodes arranged in a matrix arrangement.

Referring to FIG. 1, Taiwan Patent Publication No. 289947 discloses a planar light source device including a substrate 92 and a plurality of light emitting diode chips 91 placed in a matrix arrangement on the substrate 92. Each light emitting diode chip 91 is smaller than 40 mils (1 mm) (especially between 8 mils (0.2 mm) and 14 mils (0.35 mm)). The LED chip 91 is directly connected to a circuit on the metal layer of the substrate 92 to enhance thermal conductivity and luminous efficiency.

In practice, however, the distance of the two adjacent light emitting diode chips 91 and the thickness of the substrate 92 substantially affect the heat dissipation and luminous efficiency of the planar light source device. This problem is not mentioned in the above Taiwan patent.

Accordingly, it is an object of the present invention to provide an improved planar light source device that can solve the difficulty of heat dissipation because the LED chip can maintain a relatively low temperature during operation.

According to the present invention, a planar light source device is provided with a planar light source device. A planar light source device according to the present invention includes a substrate having a thickness of at least 1.0 mm or more and including a metal layer; And a plurality of light emitting diode chips disposed in a matrix arrangement on the substrate and having a chip size of 0.0784 mm ² to 0.25 mm ² , wherein a distance from an adjacent chip is at least twice the length of the chip; It includes.

The present invention utilizes a small size light emitting diode chip that has a relatively high external quantum effect and does not tend to accumulate heat. In particular, the size of the light emitting diode chip is limited to the range of 0.0784 mm ² to 0.25 mm ² . In addition, the LED chips are separated from each other by a distance of at least twice the length or width of the LED chip. Therefore, the planar light source device according to the present invention may not only have high luminous efficiency but also operate without significantly increasing the temperature of the LED chip.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2, there is shown a planar light source device 1 according to a preferred embodiment of the present invention.

The planar light emitting device 1 includes a substrate 11, a plurality of light emitting diodes 12 arranged in a matrix arrangement on the substrate 11, a reflective cover layer 13 disposed on the substrate 11, and the An adhesive layer 15 and a plurality of transparent body parts 14 are formed between the substrate 11 and the reflective cover layer 13 to bond the substrate 11 and the reflective cover layer 13 to each other. Due to the traditional method of manufacturing white light emitting diodes, the transparent body portion 14 includes phosphor powder to produce white light. The planar light source device 1 may be used for illumination and may be used together with a heat dissipation structure for the purpose of heat dissipation.

In this embodiment, the substrate 11 includes a metal layer 111 and an insulating layer 112. The reflective cover layer 13 includes a plurality of inner holes 131 and a plurality of reflective wells 132 defined by the inner holes 131, respectively. When the reflective cover layer 13 is disposed on the substrate, the inner holes 131 are individually disposed together with the light emitting diode chip 12. The transparent body portion 14 is formed together with the inner hole 131 of the reflective cover layer 13 to surround each of the light emitting diode chips 12 together with the inner hole 131 of the reflective cover layer 13. Cheap

In addition, in the present embodiment, the planar light source device 1 is disposed between the insulating layer 112 and the reflective cover layer 13 and the reflection wells of the reflective cover layer 13 and the circuit layer 17. It further includes a reflective coating 18 formed on 132. The light emitting diode chip 12 is connected to the circuit layer 17 by the metal wire bonding or flip chip packaging technique. The light emitting diode chip 12 is electrically connected in a series or parallel state through the circuit layer 17 according to the design and demand of the circuit. In this embodiment, the reflective coating 18 is made of metal and formed on the reflective well 132 of the reflective cover layer 13 by electroplating, evaporation, and sputtering.

In another preferred embodiment, the reflective coating 18 is made of a thermosetting resin, a high temperature heat dissipating resin, or a ceramic material having a high reflectance. In addition, the reflective cover layer 13 may be made of a plastic material having a high reflectance or a metallic material to directly form a reflective layer on the reflective well 132 of the reflective cover layer 13. In this embodiment, the reflective cover layer 13 is made of aluminum.

Three experiments were conducted to simulate heat concentration and temperature distribution on the planar light source device 1.

Selection of Board Area

The substrate 11 is made of an aluminum sheet having a thickness of 0.5 mm as the metal layer 111 and an insulating material having a thickness of 0.1 mm as the insulating layer 112. Four substrate samples are obtained from the substrate 11. The area of the substrate sample is 100 mm ² , 400 mm ² , 625 mm ² , and 900 mm ^2, respectively. Each substrate sample has a light emitting diode chip 12 measuring 1 mm x 1 mm. Simulation tests were performed for each sample and the temperature of the chip 12 was measured from each sample. The results are shown in Table 1.

<Table 1>

Board width (mm ² ) 100
400
625
900
Chip temperature (℃)
117
104
99
98

3 shows a graph of the area of the substrate and the temperature of the chip obtained from the data in Table 1. The data show that the temperature of the chip no longer drops in areas where the area of the substrate is greater than 550 mm ² (assuming the temperature of the chip is approximately 101 ° C.). Therefore, the width of the substrate 550 mm ² was chosen for the next experiment.

Experimental Example

The first experimental example was performed using four sample groups at the same input power. The width of the substrate is 550 mm ² and is the same in all experiments. However, the size of the chip 12, defined as length x width, was varied in the experiment.

First group: chip size is 1 mm x 1 mm, distance of adjacent chips is 1 mm.

Second group: chip size is 0.7 mm x 0.7 mm, distance of adjacent chips is 0.7 mm.

Third group: chip size is 0.5 mm x 0.5 mm, distance of adjacent chips is 0.5 mm.

Fourth group: chip size is 0.34 mm x 0.34 mm, distance of adjacent chips is 0.34 mm.

Table 2 shows the results of the first to fourth groups of the samples.

<Table 2>

Chip size (mm x mm) Chip distance (mm) Chip temperature (℃) 1 x 1 One 103 0.7 x 0.7 0.7 101.5 0.5 x 0.5 0.5 101 0.34 x 0.34 0.34 99

4 is a graph showing chip temperature and chip size obtained from the data in Table 2. FIG. The graph shows that the smaller the size of the chip, the smaller the temperature of the chip. However, if the chip size is too small, it becomes difficult to assemble the chip 12 to the substrate 11. On the other hand, when the chip size is smaller than 0.0784 mm ² (0.28 mm x 0.28 mm), the length and width of the chip is smaller than 0.3 mm. An InGaN chip has a pair of round bonding pads formed for wire bonding, and each round bonding has a diameter of about 0.1 mm, so that when the two round bonding pads are formed on a chip, the length of the chip If less than 0.3 mm, the total length of the round bonding pads will exceed half the length and width of the chip 12.

In this case, the chip emitted from the chip 12 will be seriously covered by the round bonding pad. Considering the temperature of the chip and the covering of the solder pad properly, the size of the chip should be limited to 0.0784 mm ² or more.

Tables 2 and 4 show that as the chip size increases, the temperature of the chip increases. If the chip size is greater than 0.25 mm ² (400 mil ² ), the chip temperature increases significantly. Therefore, the chip size should not be larger than 0.25mm ² .

Experimental Example 2

According to the results of the first experimental example, the chips were selected for the second experiment 0.0784 mm ² (0.28 mm x 0.28 mm) and 0.25 mm ² (0.5 mm x 0.5 mm). The distance between the chips can be varied in the second experimental example, but the substrate area is equal to 550 mm ² .

Table 3 shows the results using chips of the size 0.784 mm ² (0.28 mm × 0.28 mm).

<Table 3>

Chip size (mm x mm) Chip distance (mm) Chip temperature (℃) 0.28 x 0.28 0 103 0.28 x 0.28 0.2 98 0.28 x 0.28 0.4 96 0.28 x 0.28 One 93.5 0.28 x 0.28 1.5 93

5 is a graph showing the relationship between the chip distance and the chip temperature obtained from the data in Table 3. The graph shows that the chip temperature decreases as the chip distance increases, and when the chip distance is 0.8 mm or more, the chip temperature decrease does not occur much. However, the greater the chip distance, the larger the required substrate area.

Thus, as the chip distance increases, the cost of the material for manufacture will further increase. In terms of cost, for a chip size of 0.784 mm ² (0.28 mm x 0.28 mm), the distance between adjacent chips should be about 0.8 mm. This is about 2.86 (0.8 / 0/28) times the chip length (0.28 mm).

Similarly, Table 4 shows the results using chips of the size of 0.25 mm ² (0.25 mm × 0.25 mm).

<Table 4>

Chip size (mm x mm) Chip distance (mm) Chip temperature (℃) 0.25 x 0.25 0.1 103.5 0.25 x 0.25 0.2 102.3 0.25 x 0.25 0.5 101 0.25 x 0.25 One 99.5 0.25 x 0.25 1.5 98.6 0.25 x 0.25 2 97.7 0.25 x 0.25 2.5 97.4 0.25 x 0.25 3 97.3

6 is a graph showing the relationship between the chip distance and the chip temperature obtained from the data in Table 4. The graph shows that when the chip distance is 1.5 mm or more, the chip temperature is not reduced much. However, as the chip distance increases further, the substrate area and manufacturing cost will increase significantly. In terms of cost, the chip distance should be about 1.5 mm at a chip size of 0.5 mm x 0.5 mm (0.25 mm ² ). This is about three times (1.5 / 0.5) of the chip length, which is 0.5 mm.

From the results of Tables 3 and 4, in order to minimize the temperature of the chip, the chip distance should be at least twice the length / width value of the chip.

Experimental Example 3

Experimental Example 3 was carried out using substrates of different thicknesses. The chip size used in the third experimental example is 0.0784 mm ² (0.28 mm x 0.28 mm). Table 5 shows the results of the experiment.

<Table 5>

Substrate
Thickness (mm) 0.5 0.72 1.5 2 3
Chip temperature (℃) 89 83 80.5 80 80

7 is a graph showing the relationship between the thickness of the substrate obtained from the data in Table 5 and the chip temperature. The graph shows that when the thickness of the substrate exceeds 0.9 mm, the chip temperature decreases little. Therefore, the thickness of the substrate should preferably be 1.0 mm or more to maintain a low chip temperature.

In the above-described experimental example, the chip size ranges from 0.0784 mm ² to 0.25 mm ² and when the thickness of the substrate is 1.0 mm or more when the distance between adjacent chips is at least twice the length of the chip. The chip temperature can be maintained at a relatively low level.

The substrate used in the experiment was made of aluminum. Since the material of the substrate should have less influence on the heat dissipation compared to the chip size or the distance between two adjacent chips, the substrate may be made of copper or other high heat dissipation material. In addition, each LED chip 12 may be connected in parallel with a zener diode for preventing static electricity.

The present invention utilizes a small size light emitting diode chip 12 that has a relatively high external quantum effect and does not tend to accumulate heat. In particular, the size of the light emitting diode chip 12 is limited to the range of 0.0784 mm ² to 0.25 mm ² . In addition, the LED chips 12 are separated from each other by a distance of at least twice the length or width of the LED chip 12. Therefore, the planar light source device 1 according to the present invention may not only have high luminous efficiency but also operate without significantly increasing the temperature of the LED chip 12.

Although the present invention has been described based on this in consideration of most preferred embodiments, the present invention is not limited to the disclosed embodiments and to the extent that various modifications can be made within the technical scope of the various solutions of the present invention. Of course, the interpretation can be made to the extent that all modifications and equivalents are included.

1 is a perspective view of a conventional planar light source device.

2 is a cross-sectional view of a planar light source device according to an embodiment of the present invention.

3 is a graph showing the relationship between the area of the substrate and the temperature of the chip.

4 is a graph showing the relationship between the size of the chip and the temperature of the chip.

5 is a graph showing the relationship between the distance of the chip having a size of 0.28 mm x 0.28 mm and the temperature of the chip.

6 is a graph showing the relationship between the distance of the chip having a size of 0.5 mm x 0.5 mm and the temperature of the chip.

7 is a graph showing the relationship between the thickness of the substrate and the temperature of the chip.

Claims (10)

A substrate having a thickness of at least 1.0 mm or more and comprising a metal layer; A planar light source having a plurality of light emitting diode chips arranged in a matrix arrangement on the substrate and having a chip size of 0.0784 mm ² to 0.25 mm ² , the distance of adjacent chips being at least twice the length of the chip; Device. The method of claim 1, And when the size of the chip is 0.0784 mm ² , the distance between two adjacent chips of the light emitting diode chip is at least 2.86 times the length of the light emitting diode chip. And when the size of the chip is 0.25 mm ² , the distance between two adjacent chips of the light emitting diode chip is at least three times the length of the light emitting diode chip. The method of claim 1, And when the size of the chip is 0.28 mm x 0.28 mm, the distance between two adjacent chips of the light emitting diode chip is at least 0.8 mm. The planar light source device of claim 1, wherein the metal layer is made of aluminum. The planar light source device of claim 1, wherein the metal layer is made of copper. The method of claim 1, A reflective cover layer disposed on the substrate and formed with a plurality of inner holes; Further comprising a plurality of transparent body portion respectively filled in the inner hole of the reflective cover layer, And each of the light emitting diode chips is received in an inner hole of the reflective cover layer and covered by the transparent body portion. The method of claim 7, wherein The reflective cover layer includes a plurality of reflective wells defining internal holes, Wherein each reflective well comprises a reflective coating. The method of claim 7, wherein And the reflective cover layer is made of aluminum. 8. The planar light source device of claim 7, further comprising an adhesive layer formed between the substrate and the reflective cover layer.

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