CN1874011A - A light emitting diode device - Google Patents

Abstract

The invention discloses a light-emitting diode device with low thermal resistance, which comprises a light-emitting diode chip capable of converting electric energy into electromagnetic waves, a group of metal lead frames, an insulating material for coating the metal lead frames and forming a cavity, an optical lens arranged above the cavity and fixed with the insulating material, a primary carrier for bearing the light-emitting diode chip and connecting the light-emitting diode chip and the lead frame in a welding way and simultaneously serving as a heat dissipation port of the light-emitting diode, and a high light-transmitting substance covering the light-emitting diode chip.

Description

A light emitting diode device

technical field

The invention relates to a light-emitting diode device, especially a light-emitting diode device with low thermal resistance, so that the light-emitting diode can operate under high power without causing failure or loss of service life due to excessive internal temperature of the device. The device can be used for indication, lighting, backlighting or decoration as a reliable LED light source.

Background technique

In a conventional LED device (as shown in FIG. 1 ), the LED chip 10 is placed in a groove on one electrode of a metal lead frame 11, the groove functions as a light reflecting surface, and gold or aluminum wires 14 are used to Lead the electrode of the light emitting diode chip 10 to the metal lead frame of the other pole to form a path. The light emitting diode chip 10 and the metal lead frame 11 are covered by transparent epoxy resin 12 and only two terminal pins are exposed. This light-emitting diode device has been widely used in light-emitting diode traffic signal lights, third brake lights of automobiles and indicator lights of electronic products.

Another widely used light-emitting diode device (as shown in Figure 2) places a light-emitting diode chip 10 on a printed circuit board 13, and uses gold wires or aluminum wires 14 to connect the electrodes of the light-emitting diode chip to the printed circuit board The electrodes are covered with epoxy resin 12 with good light transmission, and phosphor powder can also be added in the epoxy resin to generate white light.

These two light-emitting diode devices use bonding wires to connect chips and wires. Most of these bonding wires are gold wires, so they have certain ductility and strength, and are widely used in the semiconductor packaging industry. Because gold is expensive and the process The upper wire bonding occupies a considerable proportion of the cost in terms of equipment and production, so the wire bonding process has a certain burden on the entire packaging cost. At the same time, due to the area and optical considerations of the chip design, the diameter of the bonding wire can only be 0.8 to 1.5 mils, and the stress it can withstand is quite limited. Therefore, the fracture of the bonding wire has become one of the most important factors for the failure of LED packaging products. , especially after the lead-free soldering process has gradually become the mainstream in recent years, the higher soldering temperature increases the stress caused by the thermal expansion coefficient between the packaging materials, causing the product to fail due to the breakage of the bonding wire. Therefore, canceling the bonding wire will be the key to LED packaging A major improvement.

The disadvantage of these two light-emitting diode devices is that the thermal resistance from the chip to the pin is too high. Since the chip is the heat source of the device, the temperature of the chip will rise when the heat dissipation is insufficient, and the life will be shortened when the temperature is too high. , brightness decline, and even make the device invalid, so heat dissipation is a very important issue for light-emitting diode devices.

Generally speaking, the heat dissipation characteristics of an LED device are defined by the thermal resistance value. Since the LED chip is the only heat source for the device and the pins are its heat dissipation path, we usually use the PN junction surface of the LED chip to its connection. The thermal resistance of the pin is used to define the heat dissipation characteristics of the light-emitting diode device, which is represented by Rθ _JP , which means the thermal resistance from the junction to the pin, which can be expressed mathematically:

Rθ _JP ＝T _J -T _P /Q

T _J : the temperature of the junction surface of the LED chip;

T _P : the temperature of the pins of the LED device;

Q: The heat flux through this heat transfer path.

Since the light-emitting diode chip is the only heat source of the device, and except a small part of the electric energy passed through it is dissipated in the form of electromagnetic waves after being converted, most of the energy is converted into heat energy. We can simply use the power consumed by the light-emitting diode chip to represent the heat energy that needs to be transferred to the pins through the device, so the mathematical formula can be re-expressed as:

Rθ _JP ＝T _J -T _P /I _f ×V _f

I _f : the current of the LED chip;

V _f : the voltage of the LED chip.

Since the pin temperature is a parameter of the system, its value is determined by the heat dissipation characteristics of the system. Under a certain heat flux, the value is fixed when the system is determined, and has nothing to do with the heat dissipation characteristics of the LED device. Therefore, we can determine by From the above mathematical expression, it can be known that the higher the thermal resistance of the light-emitting diode device is, the higher the temperature of the P-N junction of the chip will be.

On the other hand, it is known from the conduction heat transfer that the thermal resistance of heat conduction and heat transfer can be simply expressed as:

Rθ＝L/K×A

L: the length of the heat conduction path;

K: thermal conductivity coefficient of heat conducting material;

A: The normal cross-sectional area of the heat conduction path.

Therefore, we can know that the longer the heat dissipation path of the LED device, the smaller the cross-sectional area of the path and the lower the thermal conductivity of the material, the greater the thermal resistance of the device. Therefore, in order to design a light-emitting diode device with low thermal resistance, it is necessary to make the heat dissipation path as short as possible, increase its heat dissipation area and select materials with high thermal conductivity.

The main way of heat dissipation of the above-mentioned light-emitting diode device is to dissipate heat from the chip through the bracket or the printed circuit board. The thickness of the copper-plated line on the circuit is only tens to hundreds of microns, and its heat dissipation cross-sectional area is too small, so the thermal resistance of this design is very large, generally between 500-1000K/W. When the power is slightly higher, it is easy to cause the LED chip to overheat. With the bracket as the way of heat dissipation, its material is mostly copper or iron, and its heat dissipation characteristics are quite good, but its cross-sectional area is too small, so its thermal resistance is about 150-250K/W, and the device can load The current is only around 30mA.

To solve this problem, there are other designs to improve the previous problem of insufficient heat dissipation cross-sectional area. As shown in Figure 3, the pin area is increased by adding pins, which can effectively reduce its thermal resistance, but because its heat dissipation path is still very long, its thermal resistance value is still as high as 50-75K/W .

Thereafter, a further invention such as U.S. Patent No. 6,274,924 (as shown in Figure 4) uses the lead frame 11 covered by insulating material 15, leaving a cavity in the middle of the insulating material, and inserting an additional heat from the cavity. Terminal piece (heat sink) 16, then light-emitting diode chip 10 is fixed on a sub-carrier (submount) 17, is fixed on this heat terminal piece again, and connects its circuit to positive and negative lead frame with gold wire. Due to the use of an additional thermal terminal, the invention can effectively reduce the length of the heat conduction path and increase the cross-sectional area of heat conduction, thereby reducing the thermal resistance of the LED device to 10-15K/W. However, from a manufacturing point of view, the additional thermal terminal increases the complexity of the manufacturing, increases the process steps, and also increases the overall height of the light emitting diode device. Another problem is that this package design uses a larger chip, and the increase in package area increases the stress caused by the difference in thermal expansion coefficient between materials, and the risk of bond wire breakage also increases greatly.

Contents of the invention

The technical problem to be solved by the present invention is to provide a light-emitting diode device, which not only has the characteristics of low thermal resistance, but also can take into account the simplicity of its manufacture and minimize the thickness of the light-emitting diode device, so as to achieve light, thin and short At the same time, it is necessary to shorten the distance of the welding wire or completely eliminate the welding wire to greatly improve the reliability of the product.

In order to solve the above technical problems, the technical solution of the present invention is to include a metal lead frame, which is divided into a positive lead wire support and a negative lead lead support by etching or punching, the support is fixed by an insulator, and there is a cavity in the insulator The cavity forms a crystal-fixing area, and the back side of the positive and negative lead wire supports is partly exposed in the cavity formed by the insulator. The light-emitting diode chip is placed on the sub-carrier formed by the silicon substrate in the way of flip-chip, and the circuit is printed on the sub-carrier, and the light-emitting diode chip is passed through the circuit on the sub-carrier and the positive lead wire support and the negative lead lead support by welding. Connected, high light-transmitting material is placed in the die-bonding area to cover the light-emitting diode chip.

As a further improvement of the invention, an optical lens is set on the high light transmittance material. The material of the lens can be epoxy resin, silica gel, glass, Teflon or other materials that meet the light transmittance requirements. Total internal reflection improves the brightness, and the light pattern can be changed according to its optical design to meet different optical requirements.

Another further improvement of the present invention is to use injection molding (injection molding) or compression molding (transfer molding) in the crystal-bonding cavity of the bracket combination formed by the positive and negative electrode wire brackets and insulators with high transparency. The optical material forms an optical lens.

Another further improvement of the present invention is to use a plurality of light emitting diode chips, which can be the same color light chip or different color light chip, and the connection structure can be series connection, parallel connection or common cathode and common anode. This can increase its brightness, or achieve the function of mixing light and changing color when using a different color light chip.

The light-emitting diode device of the present invention uses the chip sub-carrier to dissipate heat directly, which saves the traditional design of using thermal terminals or metal brackets under the sub-carrier to dissipate heat, which can effectively reduce the overall height. The wire bracket is connected by welding, which saves the welding process, which can greatly improve the manufacturing cost and product reliability. It has the characteristics of low thermal resistance, and simultaneously takes into account the simplicity of the process and high reliability. Due to its low thermal resistance, the light-emitting diode device can be used in high-power conditions, increasing the current used from the traditional 20mA to 350mA or higher, and because of the simplicity of the process, it can reduce material and manufacturing costs, and because Its high reliability can be applied to applications that have strict requirements on reliability, such as automobiles, aircrafts or large-size backlights, and can also be used in higher temperature environments and lead-free soldering processes.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

Fig. 1 is a schematic structural view of a through hole stent type light emitting diode;

2 is a schematic structural view of a surface-mounted light-emitting diode on a printed circuit board;

Figure 3 and Figure 4 are schematic diagrams of the structures of two existing low thermal resistance light-emitting diodes;

5 is an exploded schematic view of an embodiment of an optical lens installed in the present invention;

Fig. 6 is a combined schematic diagram of an embodiment of an optical lens installed in the present invention;

7 is a schematic structural view of an embodiment of a low thermal resistance light-emitting diode of the present invention;

8 is a top view of an embodiment of the present invention with multiple LED chips installed;

Fig. 9 is a side view of an embodiment of the present invention with a plurality of LED chips installed;

FIG. 10 is a schematic structural diagram of an embodiment of the present invention provided with an electrostatic protection circuit.

In the figure, 10. LED chip; 11. Metal lead frame; 12. Epoxy resin; 13. Printed circuit board; 14. Gold wire or aluminum wire; 15. Plastic insulator; 16. Thermal terminal piece; 17. Secondary carrier ; 18. The positive pole of the bracket; 19. The negative pole of the bracket; 21. Silica gel; 22. Optical lens; 23. A pair of back-to-back Zener diodes.

Detailed ways

Figures 5 and 6 show an embodiment of the present invention, which divides a metal support into a positive lead wire support 18 and a negative lead lead support 19 by means of a die, and uses 15 packs of plastic insulating material in an injection molding manner. Covering and fixing the above-mentioned lead frame to form a cavity, wherein the backs of the positive electrode lead frame 18 and the negative electrode lead frame 19 are exposed in the cavity. An optical lens 22 is set on the cavity with epoxy resin material by transfer molding and combined with the insulator 15, and there is a groove at the bottom, the optical lens 22 and the insulator 15 are fitted together So there is no way to escape from above or below the cavity. The light-emitting diode chip 10 is placed on the sub-carrier 17 made of the silicon substrate in a flip-chip manner. The sub-carrier is provided with a circuit and soldered to the exposed part of the lead frame in the cavity by tin-lead solder (Pb/Snsolder paste). The light emitting diode chip is connected with the wire supports 18 , 19 . Cover the LED chip 10 with silica gel 21 and fill the gap between the chip and the optical lens to form a low thermal resistance and high reliability LED device with no wire bonding process.

Fig. 7 is another embodiment of the present invention, which divides a metal support into a positive lead wire support 18 and a negative lead lead support 19 by means of a die, and wraps and fixes it with a plastic insulating material 15 in an injection molding manner. The lead frame above forms a cavity, wherein the backs of the positive electrode lead frame 18 and the negative electrode lead frame 19 are exposed in the cavity. The light-emitting diode chip 10 is placed on a sub-carrier 17 made of an aluminum nitride substrate in a flip-chip manner. The sub-carrier is provided with a circuit and soldered to the exposed part of the lead frame in the cavity by solder paste. The chip is connected to wire supports 18 , 19 . Covering the LED chip 10 with silica gel 21 forms a low thermal resistance and high reliability LED device with no wire bonding process.

Fig. 8 and Fig. 9 are another embodiment of the present invention, which is to separate the metal support into three positive lead wire supports 18 and one negative lead lead support 19 by means of a die, and use plastic insulating material in the form of injection molding. 15 covers and fixes the above-mentioned lead frame and forms a cavity, wherein the backs of the above-mentioned three positive electrode lead supports 18 and negative electrode lead supports 19 are exposed in the cavity. An optical lens 22 is set on the cavity with epoxy resin material by transfer molding and is combined with the above-mentioned insulator 15 and has a groove at the bottom. The optical lens 22 and the insulator 15 are fitted together so that Detach from above or below the cavity. Three light-emitting diode chips 10 that can emit red, green and blue light respectively are placed on a sub-carrier 17 made of a silicon substrate in a flip-chip manner. The sub-carrier is provided with circuits and soldered to the lead frame with solder paste. In the exposed part of the cavity, the light-emitting diode chip is connected to the lead brackets 18, 19, and the light-emitting diode chip 10 is covered with silica gel 21 and filled in the gap between the chip and the optical lens to form a wire-free process Light-emitting diode devices with low thermal resistance, high reliability, and can emit red, green, blue and mixed light colors.

Fig. 10 is another embodiment of the present invention, which divides a metal support into a positive lead wire support 18 and a negative lead lead support 19 by means of a die, and covers and fixes them with a plastic insulating material 15 by means of injection molding. The lead frame also forms a cavity, wherein the backs of the three positive lead supports 18 and the negative lead support 19 are exposed in the cavity. Set an optical lens 22 on the cavity with epoxy resin material by transfer molding, and combine with the insulator 15 and have a groove at the bottom, the optical lens 22 and the insulator 15 are fitted together So there is no way to escape from above or below the cavity. A light-emitting diode chip 10 that can emit blue light and a pair of back-to-back Zener diodes 23 are placed on a sub-carrier 17 made of an aluminum substrate by means of silver glue adhesion, and the light-emitting diode chip 10 and the Zener diode are connected by bonding wires 14 The diode 23 is connected to the sub-carrier 17 made of the aluminum substrate, wherein the pair of back-to-back Zener diodes 23 are connected in parallel with the LED chip 10 . The secondary carrier 17 made of the aluminum substrate is actually a metal core printing circuit board (MCPCB, metal core printing circuit board), and the metal core printing circuit board is soldered to the exposed part of the lead frame in the cavity by soldering , the light-emitting diode chip is connected to the wire brackets 18, 19, and then the light-emitting diode chip 10 is covered with silica gel 21 and filled in the gap between the chip and the above-mentioned optical lens, forming a low thermal resistance, high reliability and static electricity. Light-emitting diode devices for protective devices.

Claims (9)

1. a light-emitting diode assembly is characterized in that, comprising:

Conductive metal frames, this lead frame are spaced apart mutual disjunct positive wire frame and cathode lead frame;

Insulating material coating described conductive metal frames, and form cave, a chamber, and the back portion of described conductive metal frames exposes in the cave, chamber;

Single or multiple light-emitting diode chip for backlight unit place on the inferior carrier to cover crystal type, and this time carrier surface is provided with circuit, and described light-emitting diode chip for backlight unit is connected with conductive metal frames, and this time carrier is connected with conductive metal frames with welding or adhesive means;

On light-emitting diode chip for backlight unit coated with refractive index greater than 1.3, light transmission is higher than 80% translucent material and coating chip.

2. a kind of light-emitting diode assembly according to claim 1 is characterized in that, also comprises optical lens, described optical lens with ejection formation, change moulding or other molding mode and be arranged on top, cave, chamber and combine with described insulator; Described translucent material is filled between light-emitting diode chip for backlight unit and optical lens.

3. a kind of light-emitting diode assembly according to claim 1 is characterized in that, single or multiple light-emitting diode chip for backlight unit, and the material that is higher than 1W/m-K with the coefficient of heat conduction is attached on time carrier.

4. a kind of light-emitting diode assembly according to claim 1 is characterized in that, the substrate material of the inferior carrier of carries chips can be silicon, metal, metal alloy, pottery, aluminium nitride or its combination.

5. a kind of light-emitting diode assembly according to claim 1 is characterized in that, greater than 70%, its material can be optical plastic, epoxy resin, glass, silica gel, Teflon or its combination to this optical lens in the light transmission of wavelength 550nm.

6. a kind of light-emitting diode assembly according to claim 1 is characterized in that, the material of the translucent material of this coating chip can be optical plastic, epoxy resin, glass, silica gel or its combination.

7. a kind of light-emitting diode assembly according to claim 1 is characterized in that, this device has a plurality of positive wire framves, or has a plurality of cathode lead frames, or has a plurality of positive wire framves and cathode lead frame simultaneously.

8. a kind of light-emitting diode assembly according to claim 1 is characterized in that, this device has the carrier carries chips a plurality of times.

9. a kind of light-emitting diode assembly according to claim 1 is characterized in that, is provided with the electrostatic protection circuit in this device.

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