Patent Publication Number: US-2006006401-A1

Title: Flip chip light emitting diode

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the invention  
      The invention pertains to a flip chip light emitting diode structure. More particularly, the invention relates to a flip chip light emitting diode that is easy to be fabricated and capable of increasing the lifetime of the product.  
      2. Description of the Related Art  
      Referring to  FIG. 1 , a conventional light emitting diode structure includes a substrate  3 , an LED chip  1 , and an epoxy-compound resin  2 . The LED chip  1  is mounted on the substrate  3  and is electrically connected the substrate  3  by wires.  
      According to the above-mentioned structure, the overall volume of the conventional light emitting diode is too large. The size of the conventional LED is limited by its structure, therefore, it is very different to reduce the dimension of the LED to be thinner, smaller and lighter.  
      It is very also important how to obtain high heat dissipation LED. In particular, a white light emitting diode may be produced to generate high heat energy, therefore, the heat dissipation effect is very important. But, because epoxy-compound resin is a transparent paste, which has a poor thermal conductivity, the heat energy generated by LED chip when applied a higher current may not be dissipated. A conventional light emitting diode may not be manufactured to apply high current, such as lighting, back-lighting applications. Therefore, how to omit the epoxy-compound resin is very important in LED package technology.  
      However, when omit the epoxy-compound resin, the light generated by light emitting diode cannot be refracted, and the brightness of the light emitting diode is reduced drastically.  
     SUMMARY OF THE INVENTION  
      An objective of the invention is to provide a flip chip light emitting diode structure that the lifetime of the product can be prolonged effectively.  
      Another objective of the invention is to provide a light emitting diode structure that the brightness of the product can be increased.  
      Another objective of the invention is to provide a light emitting diode structure that the size of the LED can be produced to be lighter, thinner, and smaller than that of the conventional LED.  
      To achieve the above-mentioned objective, the invention includes a substrate, a LED chip, and a low refractive index layer. The substrate is formed of a substantially transparent material, which includes a top surface and a lower surface. The LED chip has a first surface and a second surface, the first surface of the LED is mounted on the lower surface of the substrate, the second surface is formed with a N-electrode and a P-electrode. The low refractive index layer is mounted on the top surface of the substrate, the refractive index of the low refractive index layer is lower than that of the substrate, and higher than that of the atmosphere.  
      Therefore, the light generated by LED chip  4  can be refracted, so that the brightness of the light emitting diode may be promoted, and can be produced to be lighter, thinner, and smaller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view showing a conventional light emitting diode structure.  
       FIG. 2  is the first schematic illustration showing a flip chip light emitting diode structure of the present invention.  
       FIG. 3  is the second schematic illustration showing a flip chip light emitting diode structure of the present invention.  
       FIG. 4  is the third schematic illustration showing a flip chip light emitting diode structure of the present invention.  
       FIG. 5  is the fourth schematic illustration showing a flip chip light emitting diode structure of the present invention.  
       FIG. 6  is a cross-sectional schematic illustration showing a flip chip light emitting diode structure connected to a printed circuit board.  
       FIG. 7  is a cross-sectional schematic illustration showing a flip chip light emitting diode structure coated with a fluorescent paste.  
       FIG. 8  is a cross-sectional schematic illustration showing a flip chip light emitting diode structure with a transparent lid. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Please refer to  FIG. 2 , a flip chip light emitting diode structure of the present invention includes a substrate  4 , a LED chip  5 , and a low refractive index layer  9 .  
      The substrate  4  is formed of a substantially transparent material, which includes a top surface  40  and a lower surface  42 .  
      The LED chip  5  has a first surface  50  and a second surface  52 , which is formed with an N-electrode  7  and a P-electrode  8 . The first surface  50  of the LED chip  5  is mounted on the lower surface  42  of the substrate  4 . Wherein the P-electrode  8  of the LED chip is coated with an insulation layer  6 , which is formed of Si O 2  film or Si 3  N 4  film. The N-electrode  7  and P-electrode  8  of the LED chip are formed with bonding pads, each bonding pads include a flip chip solder bump  10 .  
      The low refractive index layer  9  is mounted on the top surface  40  of the substrate  4 , the refractive index of the low refractive index layer  4  is lower than that of the substrate  4 , and higher than that of the atmosphere.  
      In the embodiment, the low refractive index layer is formed of Si O 2  film or Si 3  N 4  film. Therefore, the light generated by light emitting diode can be refracted via the low refractive index layer to increase the brightness of the light emitting diode.  
      Please refer to  FIG. 3 , it is the second schematic illustration showing a flip chip light emitting diode structure of the present invention. Wherein the low refractive index layer  9  is formed with a rough surface  11  by etching. Thus, the light generated by light emitting diode can obtain a better refractive through the rough surface of the low refractive index layer to increase the brightness of the light emitting diode.  
      Please refer to  FIG. 4 , it is the third schematic illustration showing a flip chip light emitting diode structure of the present invention. The light emitting diode comprises a substrate  4  and an LED chip  5 . The top surface  40  of the substrate  4  is formed with a plurality of lens  12  by etching. The lens  12  are formed of Zn O, Si O 2 , Si 3 N 4 , Zn Se, GaN or ITO etc.  
      Thus, the light generated by light emitting diode can obtain a better refractive through lens  12  to increase the brightness of the light emitting diode.  
      Please refer to  FIG. 5 , it is the third schematic illustration showing a flip chip light emitting diode structure of the present invention. The light emitting diode comprises a substrate  4  and an LED chip  5 . The top surface  40  of the substrate  4  is formed with a plurality of tiny posts  13  by etching. The tiny posts  13  are formed of Zn O, Si O 2 , Si 3  N 4 , Zn Se, GaN or ITO etc.  
      Thus, the light generated by light emitting diode can obtain a better refractive index through tiny posts  13  to increase the brightness of the light emitting diode.  
      Please refer to  FIG. 6 , it is a cross-sectional schematic illustration showing a flip chip light emitting diode structure connected to a printed circuit board. The flip chip solder bump  10  of the LED chip  5  is electrically connected to the electrode  15  of the printed circuit board  20  by SMT.  
      Please refer to  FIG. 7 , it is a cross-sectional schematic illustration showing a flip chip light emitting diode structure coated with a fluorescent paste. After the LED chip  5  is electrically connected to the printed circuit board  20 , a fluorescent paste  16  is coated over the LED chip  5  by printing to form white light emitting diode or mixture light.  
      Please refer to  FIG. 8 , it is a cross-sectional schematic illustration showing a flip chip light emitting diode structure with a transparent lid. After the LED chip  5  is electrically connected to the printed circuit board  20 , a transparent lid  17  is covered onto the LED chip to enable the light generated by LED chip with focusing purpose.  
      While the invention has been described by the way of an example and in terms of a preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications. Therefore, the scope of the appended claims should be accorded to the broadest interpretation so as to encompass all such modifications.