Abstract:
A photoelectric device includes a ceramic substrate defining a cavity in a top thereof and having two electrode layers beside the cavity. A photoelectric die is received in the cavity. A first packing layer is received in the cavity and encapsulates the photoelectric die. The photoelectric die is electrically connected with the electrode layers via two wires. A reflective cup is mounted on the ceramic substrate and defines a receiving space above the top of the ceramic substrate and the first packing layer. A second packing layer is received in the receiving space and covers the first packing layer.

Description:
This application is a divisional application of U.S. application Ser. No. 12/879,206 field 10 Sep. 2010, and is based on and claims priority from China Patent Application No. 200910177043.6 filed 18 Sep. 2009. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a method of fabricating a photoelectric device, and relates more particularly to a photoelectric device, a method of fabricating the same, and a packaging apparatus for the same. 
     DESCRIPTION OF THE RELATED ART 
     Light emitting diodes (LEDs) in photoelectric devices have advantages such as low power consumption, high brightness, compact physical size, and extensive lifespan; thus, LEDs are considered to be the best light source for an eco-friendly, energy conservative next generation illumination system. If a lens is disposed on the light output surface of an LED, total reflection and light scattering phenomena can be minimized, and the light extraction efficiency of the LED can be improved.  FIG. 1  is a stereoscopic view showing an LED package  100  having a dual structure disclosed in U.S. Pat. No. 7,458,703. The LED package  100  includes a lower structure  110 , a lower lens  160 , and an upper lens  180 . The lower structure  110  comprises a package body  130  and a lead  120 . After being packaged, the lower lens  160  and the upper lens  180  are assembled together to form a structure with an hourglass shape, thereby laterally emitting light from the LED. However, the lower lens  160  and the upper lens  180  are molded independently from each other; thus, the cost of the LED package  100  is high, and a lot of manpower and extra assembly procedures are needed. 
     Therefore, a photoelectric device having a lens structure, a method of mass producing the photoelectric device, and a packaging apparatus for the photoelectric device are required. The photoelectric device may adopt a ceramic substrate of high thermal conductivity as its substrate so as to improve its heat dissipation efficiency. The method and the apparatus can effectively avoid the issue of the ceramic substrate being easily broken during device packaging so that the reliability and production yield of the photoelectric device can be improved. 
     SUMMARY 
     The present invention provides a method for fabricating a photoelectric device and a packaging apparatus for packaging a photoelectric device, and more particularly related to a method for fabricating a photoelectric device formed on a ceramic substrate and a packaging apparatus for packaging the photoelectric device. The proposed method and apparatus may avoid the breakage issue of the ceramic substrate during the packaging process, improving the reliability and yield of production of the photoelectric device. 
     The present invention provides a method for fabricating a photoelectric device, which comprises the steps of: providing a ceramic substrate, comprising a thermal dissipation layer on a bottom layer of the ceramic substrate, an electrode layer on the top surface of the ceramic substrate, and a reflective structure in cavities of the ceramic substrate; forming a plurality of photoelectric dies on a top surface of the ceramic substrate; forming a first packaging layer on top surfaces of the plurality of photoelectric dies; loading the ceramic substrate between a lower mold and an upper mold; and forming a plurality of lenses on a top surface of the first packaging layer by injection molding or transfer molding. 
     The present invention provides a photoelectric device, which comprises a ceramic substrate, a photoelectric die, a reflective cup, a first packaging layer, a second packaging layer, and a lens structure. The ceramic substrate comprises a thermal dissipation layer and at least two electrode layers electrically insulating from the thermal dissipation layer. The photoelectric die is disposed on a top surface of the thermal dissipation layer and electrically connects to the at least two electrode layers. The reflective cup is disposed on a top surface of the first electrode layer so as to form a first accommodation space, wherein the reflective cup comprises a slantwise surface. The first packaging layer is disposed on a top surface of the photoelectric die. The second packaging layer is disposed within the first accommodation space and is disposed on a top surface of the first packaging layer. The lens structure is attached in the accommodation space and is disposed on a top surface of the second packaging layer 
     The present invention provides another photoelectric device, which comprises a ceramic substrate, a photoelectric die, a plurality of reflective cups, a plurality of packaging layers, and a lens structure. The ceramic substrate comprises a thermal dissipation layer and at least two electrode layers electrically insulating from the thermal dissipation layer. The photoelectric die is disposed on a top surface of the thermal dissipation layer and electrically connects to the at least two electrode layers. The plurality of reflective cups is disposed on a top surface of the first electrode layer so as to form an accommodation space. The plurality of packaging layers is disposed within the accommodation space, wherein at least one of the plurality of packaging layers is disposed on the photoelectric die. The lens structure is attached on the ceramic substrate and covers the plurality of packaging layers 
     To better understand the above-described objectives, characteristics and advantages of the present invention, embodiments, with reference to the drawings, are provided for detailed explanations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described according to the appended drawings in which: 
         FIG. 1  is a stereoscopic view showing an LED package having a dual structure disclosed in U.S. Pat. No. 7,458,703; 
         FIG. 2  is a cross-sectional view showing a photoelectric device according to one embodiment of the present invention; 
         FIG. 3  is a flow chart showing the steps of a method for fabricating a photoelectric device according to one embodiment of the present invention; 
         FIGS. 4A to 4C  are cross-sectional views showing a method for fabricating a photoelectric device using an injection molding process according to one embodiment of the present invention; 
         FIGS. 5A to 5D  are cross-sectional views showing a method for fabricating a photoelectric device using a transfer molding process according to one embodiment of the present invention; 
         FIGS. 6A to 6D  are cross-sectional views showing a method for fabricating the lens structure of a photoelectric device using a printing process according to one embodiment of the present invention; and 
         FIGS. 7A to 7C  are cross-sectional views showing a method for fabricating the lens structure of a photoelectric device using a dipping and cooling process according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  is a cross-sectional view showing a photoelectric device  20  according to one embodiment of the present invention. The photoelectric device  20  adopts a ceramic substrate  210  as its substrate. The ceramic substrate  210  can be of high temperature co-fired ceramics or of low temperature co-fired ceramics. The ceramic substrate  210  is usually made of aluminum oxide; however, other material such as aluminum nitride (AlN), beryllium oxide (BeO), silicon carbide (SiC), glass, or diamond can be used to manufacture the ceramic substrate  210 . 
     Referring to  FIG. 2 , the photoelectric device  20  comprises a thermal dissipation layer  212 , a p-type electrode layer  214 , and an n-type electrode layer  216 , wherein the p-type electrode layer  214  and the n-type electrode layer  216  are able to electrically connect to an external power source (not shown). The thermal dissipation layer  212  may include any thermally conductive material, for example, metal. A photoelectric die  218  is disposed on the top surface of the thermal dissipation layer  212 . The patterns of the p-type and n-type electrode layers  214  and  216  can be formed using semiconductor processes, for example, including a vapor deposition process or sputtering deposition, a photolithographic process, an electroplating or chemical plating process, and an etching process. A reflective structure  230 , which is formed using ceramic or metal by, for example, a sputtering process or formed using non-metal by a molding process, can be formed on the top surface of thermal dissipation layer  212  and a central cavity of the ceramic substrate  210 , thereby increasing light reflectance. The photoelectric die  218  disposed on the top surface of the thermal dissipation layer  212  of the ceramic substrate  210  can be wire bonded or flip-chip bonded. The wires  220  in  FIG. 2  are used to electrically connect the pads of the photoelectric die  218  to the p-type and n-type electrode layers  214  and  216 . 
     During the packaging process, a first packaging layer  222  is filled into the accommodation space formed by the reflective structures  230  and the top surface of the photoelectric die  218  for enclosing the photoelectric die  218 . The first packaging layer  222  comprises phosphor powder mixed with epoxy resin, silicone resin, or a mixture thereof. The phosphor powder may absorb light from the photoelectric die  218  and generate light of different wavelength. A reflective cup  224  is formed on the top surface of the ceramic substrate  210 . The reflective cup  224  is usually made of opaque or highly reflective resin. The reflective cup  224  may include a highly reflective metal film  226  slantedly formed thereon to increase light reflectance, wherein the highly reflective metal film  226  is made of metal or highly reflective material. In addition, in the reflective cup  224 , a second packaging layer  228  can be formed to enclose the first packaging layer  222  and the wires  220  for further protecting the photoelectric die  218  from the damage caused by external force or by weather. The second packaging layer  228  is made of epoxy resin, silicone, or mixed with foresaid material with phosphor powder. Further, a lens structure  240  can be directly formed in the accommodation space of the reflective cup  224  so as to avoid the alignment issue or assembly issue related to prior art photoelectric devices. 
       FIG. 3  is a flow chart showing the steps of a method for fabricating a photoelectric device according to one embodiment of the present invention. In Step S 31 , a ceramic substrate is provided, wherein the ceramic substrate comprises a thermal dissipation layer on a bottom layer of the ceramic substrate, an electrode layer on the top surface of the ceramic substrate, and a reflective structure in cavities of the ceramic substrate. In Step S 32 , a plurality of photoelectric dies is formed on the top surface of the ceramic substrate. In Step S 33 , at least one packaging layer is formed on the top surfaces of the photoelectric dies. In Step S 34 , the ceramic substrate is loaded between a lower mold and an upper mold, and a buffer layer is disposed between the lower mold and the ceramic substrate for uniformly distributing the pressure that the lower mold acts on the ceramic substrate. In Step S 35 , a plurality of lenses are formed on the top surface of the at least one packaging layer. Steps S 31  to S 33  are as described above, and the details of the method steps are explained with  FIGS. 4A to 4C  hereinafter. 
       FIGS. 4A to 4C  are cross-sectional views showing a method for fabricating a photoelectric device using an injection molding process according to one embodiment of the present invention. In  FIG. 4A , a plurality of reflective cups  422  and a packaging layer  426  are formed on a ceramic substrate  412 , and a plurality of block members  424  are formed between the plurality of reflective cups  422 . In order to form a lens structure on the top surface of the ceramic substrate  412  using a molding process, a buffer layer  410  is disposed or formed on the top surface of a lower mold  414 , as shown in  FIG. 4A . Thereafter, the ceramic substrate  412  is loaded between the lower mold  414  and an upper mold  416 , which includes a mold surface  418  configured to form a plurality of lenses and a plurality of melt channels  420  corresponding to the plurality of block members  424 . 
     Next, the lower mold  414  and the upper mold  416  are closed and molten material is introduced. As shown in  FIG. 4B , an injection device  430  injects molten material through the melt channel  420  to nozzles  432 . When the molds  414  and  416  are closed and the molten material is injected, the lower mold  414  directly applies pressure on the bottom surface of the ceramic substrate  412 . If the ceramic substrate  412  is not flat, high local stresses may occur. Although the ceramic substrate  412  is of high hardness, the ceramic substrate is fragile so that bending stresses may easily break it. The buffer layer  410  is a solution for the flatness issue of the ceramic substrate  412 , or for the flatness issue of the lower mold  414 . The buffer layer  410  can uniformly distribute the pressure applied by the lower mold  414  to the surface of the ceramic substrate  412 . After the molten material which is introduced into cavities between the upper mold  416  and the packaging layer  426  is cooled and solidified, a mold opening step is performed so as to separate the lower mold  414 , the upper mold  416 , and the buffer layer  410 . The disposition of the buffer layer  410  can also reduce the impact of the pressure produced by mold closing and molten material injection so that the ceramic substrate  412  can avoid breakage when it undergoes pressure during the molding process, increasing the reliability of production and production yield of the photoelectric device. 
     After the molds  414  and  416  are opened, photoelectric devices having lens structures  440  are complete. Next, as shown in  FIG. 4C , cutting lines  434  are formed on the ceramic substrate  412  using a laser or by a molding process. Thereafter, a diamond knife, laser or water knife is used to cut the ceramic substrate  412  along the cutting lines  434  to obtain separated photoelectric devices  20  as shown in  FIG. 2 . Alternatively, the ceramic substrate  412  can be manually broken to obtain separated photoelectric devices  20 . 
     In the above embodiments, the block members  424  are disposed between the plurality of reflective cups  422  so as to form a plurality of photoelectric devices having lens structures. In another embodiment, a film layer, labeled in  FIG. 5D  as  524 , can be formed between the plurality of reflective cups  422  such that the electrode layers on the ceramic substrate  412  can be protected from damage when the molds  414  and  416  are closed and the molten material is injected. The film layer  524  can be stripped from the ceramic substrate  412 , and the remnant adhesive on the film layer  524  or the adhesive blocks in the runners can be simultaneously removed when the film layer is stripped. After the film layer  524  is removed, a plurality of separated lens structures  440  is formed on the ceramic substrate  412 . 
       FIGS. 5A to 5D  are cross-sectional views showing a method for fabricating a photoelectric device using a transfer molding process according to one embodiment of the present invention. As shown in  FIG. 5A , a plurality of reflective cups  522  and a packaging layer  526  are formed on the top surface of a ceramic substrate  512 , and a film layer  524  is formed between the plurality of reflective cups  522 . The disposition of the film layer  524  is for protecting the electrode layers (not shown) on the ceramic substrate  512  from damage when the molds  514  and  516  are closed and the molten material is injected. Similarly, in order to form a lens structure on the top surface of the ceramic substrate  512  using a molding process, a buffer layer  510 , as shown in  FIG. 5A , is disposed or formed on the top surface of a lower mold  514 . Next, the ceramic substrate  512  is loaded between the lower mold  514  and an upper mold  516 , which includes a mold surface  518  configured to form a plurality of lenses and a plurality of lateral melt channels  520 . 
     As shown in  FIG. 5A , a dummy mold  530  is disposed between the ceramic substrate  512  and the upper mold  516 . The dummy mold  530  includes a mold surface, which is configured to have a shape to form a plurality of lenses. The mold surface of the dummy mold  530  can be different from that of the upper mold  516 , thereby forming lens structures with different configurations. Alternately, the mold surface of the dummy mold  530  can be the same as that of the upper mold  516 , thereby obtaining smoother configurations of lens structures. Certainly, the mold surface  518  of the upper mold  514  can be further treated to become smoother by, for example, an electro-polishing process. Referring to  FIG. 5B , when the lower mold  514 , the upper mold  516 , and the dummy mold  530  are closed, a plurality of cavities communicating with each other are formed on the top surface of the packaging layer  526 . 
     Thereafter, an injection device injects molten material from the lateral melt channel  520 . Referring to  FIG. 5C , after the molten material introduced into cavities between the upper mold  516  and the packaging layer  526  is cooled and solidified, the lower mold  514 , the buffer layer  510 , the upper mold  516 , and the dummy mold  530  are removed. The film layer  524  can be stripped from the ceramic substrate  512 , and the remnant adhesive on the film layer  524  or the adhesive blocks in the runners can be simultaneously removed when the film layer  524  is stripped. After the film layer  524  is removed, a plurality of separated lens structures  540  is formed as shown in  FIG. 5D . In addition, the film layer  524  has a buffering effect; it can absorb the pressure that the upper mold  516  applies on the surface of the ceramic substrate  512 . After the ceramic substrate  512  is detached, photoelectric devices with lens structures are completed. Finally, cutting lines are formed on the ceramic substrate  512  using a laser or by a molding process, and a diamond knife, laser or water knife is used to cut the ceramic substrate  512  along the cutting lines to obtain separated photoelectric devices. 
       FIGS. 6A to 6D  are cross-sectional views showing a method for fabricating the lens structure of a photoelectric device using a printing process according to one embodiment of the present invention. In  FIG. 6A , a plurality of reflective cups  622  and a packaging layer  626  are formed on the top surface of a ceramic substrate  612 . In order to form a lens structure on the top surface of the ceramic substrate  612 , the ceramic substrate  612  is loaded between the lower mold  614  and an upper mold  616 . The upper mold  616  is configured to extend into the gaps between the plurality of reflective cups  622  to isolate the photoelectric dies  600 , and the upper mold  616  has a height sufficient to form a plurality of accommodation spaces respectively surrounding the photoelectric devices. 
     Referring to  FIG. 6B , an injection device  630  injects molten material into the accommodation spaces through nozzles  632  corresponding to the accommodation spaces. After the accommodation spaces are fully filled with molten material, and the filled molten material is cooled and solidified, the upper mold  616  and the lower mold  614  are separated as shown in  FIGS. 6C and 6D . After detachment, the material in the accommodation spaces may be formed into lens structures  640  on the photoelectric dies  600  due to internal cohesion of the material. Finally, cutting lines are formed on the ceramic substrate  612  using a laser or by a molding process, and a diamond knife, laser or water knife is used to cut the ceramic substrate  612  along the cutting lines to obtain separated photoelectric devices. 
       FIGS. 7A to 7C  are cross-sectional views showing a method for fabricating the lens structure of a photoelectric device using a dipping and cooling process according to one embodiment of the present invention. In  FIG. 7A , a plurality of reflective cups  722  and a packaging layer  726  are formed on the top surface of a ceramic substrate  712 . In order to form a lens structure on the top surface of the ceramic substrate  712 , the ceramic substrate  712  is loaded between the lower mold  714  and an upper mold  716 . The upper mold  716  comprises a mold surface  718 , which is configured to form lenses with desired shape and to hold liquid material  720 . 
     Referring to  FIG. 7B , after the lower mold  714  and the upper mold  716  are closed, the packaging layer  726  is dipped into the liquid material  720  held by the upper mold  716 . After the liquid material  720  is cooled and solidified, the lower mold  714  is separated from the upper mold  716 , which is removed thereafter, as shown in  FIG. 7C . After detachment, photoelectric devices with lens structures are completed. Finally, cutting lines are formed on the ceramic substrate  712  using a laser or by a molding process, and a diamond knife, laser or water knife is used to cut the ceramic substrate  712  along the cutting lines to obtain separated photoelectric devices. 
     The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by persons skilled in the art without departing from the scope of the following claims.