Patent Publication Number: US-2010129598-A1

Title: Optical film

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 97146031, filed Nov. 27, 2008. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an optical film, and more particularly relates to an optical film which has satisfactory quality and is easy to adjust. 
     2. Description of Related Art 
     With progress in semiconductor technologies, a light emitting diode (LED) now has advantages of high luminance, low power consumption, compactness, low driving voltage, mercury free, and so forth. Therefore, the LED has been extensively applied in the field of displays and illumination. On account of the extended applications of the LED, demands on colors of a light source supplied by the LED are diversified by degrees. In addition to the above, high quality requirements for correlated color temperature (CCT) and color rending index (CRI) in the LED have been growing. 
     Taiwan patent no. M318797 is directed to a method of forming an optical film.  FIG. 1  is a schematic view of a conventional LED package structure having an optical film. The LED package structure  100  includes a substrate  110 , an LED chip  120 , a lens  130 , and an optical film  140 . The substrate  110  has a cavity  112  and a circuit layer  114 . The LED chip  120  is disposed on the substrate  110  and is electrically connected to the circuit layer  114  on the substrate  110  through wire bonding. The optical film  140  is disposed above the cavity  112  of the substrate  110 , and the lens  130  is disposed on the optical film  140 . Here, the optical film  140  is formed by well mixing phosphor powder with transparent adhesive liquid or a transparent plastic material in an appropriate proportion and shaping the mixture as a film. 
     The phosphor powder in the optical film  140  excited by light emitted from the LED chip  120  generates secondary light beams. The secondary light beams can be mixed with the light emitted from the LED chip, so as to form other light beams with specific wavelengths. Hence, diverse light beams can be emitted by the LED package structure  100 . Nonetheless, during the fabrication of the optical film  140 , it is not apt to evenly mix the phosphor powder or to prevent precipitation of the phosphor powder. As such, the optical film  140  with poor quality may deteriorate CCT and CRI performance of the light emitted by the LED package structure  100 . In other words, the optical film plays a dominant role in determining light source performance in the LED package structure. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an optical film having a plurality of phosphor layers stacked together. 
     The present invention is directed to another optical film having a plurality of patterned phosphor layers arranged in array. 
     In the present invention, an optical film including a plurality of phosphor layers stacked together is provided. Each of the phosphor layers is excited by an exciting light source and respectively emits a secondary light beam, and the secondary light beams emitted by the phosphor layers are in different wavelength ranges. In a preferred embodiment of the present invention, the optical film is capable of peeling off or separating from an object (e.g. a substrate, a tape, and so on). 
     According to an embodiment of the present invention, the optical film further includes a first substrate on which the phosphor layers are stacked. 
     According to an embodiment of the present invention, a wavelength of the exciting light source is shorter than a wavelength of each of the secondary light beams. 
     According to an embodiment of the present invention, the first substrate is a transparent substrate. According to other embodiments of the present invention, the first substrate is a reflective substrate. 
     According to an embodiment of the present invention, the phosphor layers include at least two of a red phosphor layer, a green phosphor layer, and a yellow phosphor layer. 
     According to an embodiment of the present invention, one of the phosphor layers located bottommost entirely covers a surface of the first substrate. 
     According to an embodiment of the present invention, the optical film further includes a second substrate covering one of the phosphor layers located topmost, such that the phosphor layers are interposed between the first substrate and the second substrate. 
     According to an embodiment of the present invention, when the first substrate is a transparent substrate, the second substrate can be a transparent substrate or a reflective substrate. According to other embodiments of the present invention, when the first substrate is a reflective substrate, the second substrate can be a transparent substrate. 
     In the present invention, another optical film including a plurality of patterned phosphor layers arranged in array is provided. Each of the patterned phosphor layers is excited by an exciting light source and respectively emits a secondary light beam, and the secondary light beams emitted by the patterned phosphor layers are in different wavelength ranges. 
     According to an embodiment of the present invention, the optical film further includes a first substrate on which the patterned phosphor layers are stacked. 
     According to an embodiment of the present invention, a wavelength of the exciting light source is shorter than a wavelength of each of the secondary light beams. 
     According to an embodiment of the present invention, the first substrate is a transparent substrate. According to other embodiments of the present invention, the first substrate is a reflective substrate. 
     According to an embodiment of the present invention, the patterned phosphor layers include at least two of a patterned red phosphor layer, a patterned green phosphor layer, and a patterned yellow phosphor layer. 
     According to an embodiment of the present invention, the patterned phosphor layers cover different regions on a surface of the first substrate, and the patterned phosphor layers entirely cover the surface of the first substrate. 
     According to an embodiment of the present invention, the optical film further includes a second substrate. The second substrate covers the patterned phosphor layers, such that the patterned phosphor layers are interposed between the first substrate and the second substrate. 
     According to an embodiment of the present invention, when the first substrate is a transparent substrate, the second substrate can be a transparent substrate or a reflective substrate. On the contrary, when the first substrate is a reflective substrate, the second substrate is a transparent substrate. 
     According to an embodiment of the present invention, the patterned phosphor layers have a matrix arrangement. 
     According to an embodiment of the present invention, the patterned phosphor layers have a delta arrangement. 
     According to an embodiment of the present invention, the patterned phosphor layers have a honeycomb arrangement. 
     In light of the foregoing, the optical film of the present invention has a plurality of stacked phosphor layers or a plurality of patterned phosphor layers arranged in array. Each of the phosphor layers excited by the exciting light source respectively emits one secondary light beam, and the secondary light beams emitted by the phosphor layers are in different wavelength ranges. The secondary light beams in different wavelength ranges can be mixed and then can become the light beams in specific wavelength ranges. Moreover, it is easier to adjust the optical film having a plurality of phosphor layers, and therefore the light beams formed thereby have diverse wavelength lengths. 
     In order to make the aforementioned and other features and advantages of the present invention more comprehensible, several embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings constituting a part of this specification are incorporated herein to provide a further understanding of the invention. Here, the drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic view of a conventional LED package structure having an optical film. 
         FIGS. 2A to 2E  are schematic flowcharts illustrating a fabricating process of an optical film according to an embodiment of the present invention. 
         FIG. 3  is a schematic view illustrating another coating method with use of phosphor powder according to the embodiment of the present invention. 
         FIGS. 4A to 4D  are schematic flowcharts illustrating a fabricating method of an optical film according to another embodiment of the invention. 
         FIGS. 5A and 5B  are top views illustrating patterns on two types of patterned phosphor layers according to an embodiment of the present invention. 
         FIG. 6  is a schematic view of an LED package structure according to still another embodiment of the present invention. 
         FIG. 7  is a schematic view of an LED package structure according to yet still another embodiment of the present invention. 
         FIG. 8  is a schematic view of an LED package structure according to yet still another embodiment of the present invention. 
         FIG. 9  is a schematic view of an LED package structure according to yet still another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIGS. 2A to 2E  are schematic flowcharts illustrating a fabricating process of an optical film according to an embodiment of the present invention. First, referring to  FIG. 2A , a first substrate  210  is provided. In the present embodiment, the first substrate  210  can be a transparent substrate or a reflective substrate. In addition, the first substrate  210  can be a rigid substrate or a flexible substrate. 
     Next, referring to  FIG. 2B , phosphor powder and a volatile solvent are well mixed, and the first substrate  210  is coated with the mixture. In the present embodiment, a coating method of the first substrate  210  with the phosphor powder includes evenly distributing the mixture of the phosphor powder and the solvent onto the first substrate  210  by printing, as shown in  FIG. 2B . 
     After that, referring to  FIG. 2C , a phosphor layer  200   a  is formed by the residual phosphor powder after the solvent is evaporated. Based on actual demands, the steps depicted in  FIGS. 2B and 2C  can be repeated, so as to form a plurality of phosphor layers  200   a,    200   b,    200   c,  for example. Note that the order of forming the phosphor layers  200   a,    200   b,    200   c  and the thickness of the phosphor layers  200   a,    200   b,    200   c  are not limited in the present invention and can be changed upon actual requirements. In the present embodiment shown in  FIG. 2D , only three phosphor layers  200   a,    200   b,  and  200   c  are illustrated for the purpose of exemplary explanation. The thickness of the phosphor layers  200   a,    200   b,  and  200   c  preferably ranges from 0.5 μm to 1 mm in the present embodiment. 
     Referring to  FIG. 2E , after the aforesaid steps are completed, a second substrate  220  can be selectively disposed on the topmost phosphor layer  200   c,  such that all of the phosphor layers  200   a,    200   b,  and  200   c  are interposed between the first substrate  210  and the second substrate  220 . The second substrate  220  serves to protect the phosphor layers  200   a,    200   b,  and  200   c  from being damaged. In the present embodiment, the second substrate  220  is, for example, a reflective substrate or a transparent substrate. Besides, the second substrate  220  can be a rigid substrate or a flexible substrate. It should be noted that when the first substrate  210  is a transparent substrate, the second substrate  220  can be either a reflective substrate or a transparent substrate. By contrast, when the first substrate  210  is a reflective substrate, the second substrate  220  can be a transparent substrate. 
     Alternatively, the phosphor layers  200   a,    200   b,  and  200   c  can be peeled off or released from the first substrate  210  after said steps are completely performed according to the present embodiment, so as to form the optical film  200  having a plurality of phosphor layers  200   a,    200   b,  and  200   c.  To be more specific, without the first substrate  210  and the second substrate  220 , the optical film  200  simply consisting of the phosphor layers  200   a,    200   b,  and  200   c  is more advantageous in terms of thickness, weight, and volume. In a preferred embodiment of the present invention, the optical film  200  is capable of peeling off or separating from an object (e.g. a substrate, a tape, and so on). 
       FIG. 3  is a schematic view illustrating another coating method with use of the phosphor powder according to the present embodiment of the present invention. Referring to  FIG. 3 , the first substrate  210  can be coated with the phosphor powder not only by printing as shown in  FIG. 2B  but also by spraying the phosphor powder. Note that the thickness of the phosphor layers can vary upon the actual demands no matter the coating method is performed by printing or by spraying. In the present embodiment, the thickness of the phosphor layer preferably ranges from 0.5 μm and 1 mm. 
     Afterwards, referring to  FIG. 2E , the optical film formed by performing the aforesaid manufacturing process includes a plurality of phosphor layers  200   a,    200   b,  and  200   c  stacked together. Each of the phosphor layers  200   a,    200   b,  and  200   c  is excited by an exciting light source and respectively emits one secondary light beam, and the secondary light beams emitted by the phosphor layers  200   a,    200   b,  and  200   c  are in different wavelength ranges. In general, a wavelength of the exciting light source is shorter than a wavelength of each of the secondary light beams. According to the present embodiment, the phosphor layer  200   a  is a red phosphor layer, the phosphor layer  200   b  is a green phosphor layer, and the phosphor layer  200   c  is a yellow phosphor layer, for example. Each of the phosphor layers  200   a,    200   b,  and  200   c  respectively has different phosphor powder. In the present embodiment, the wavelength within which the phosphor layers  200   a,    200   b,  and  200   c  can be excited ranges from 380 nm to 700 nm, for example. 
     The thickness of the phosphor layers  200   a,    200   b,  and  200   c  in the optical film  200  poses an impact on optical properties of the optical film  200 . Therefore, the optical properties of the optical film  200  can be changed by controlling the thickness of the phosphor layers  200   a,    200   b,  and  200   c.    
     The optical film  200  of the present embodiment can include a first substrate  210  for enhancing the structural strength of the optical film  200 , such that the optical film  200  can be used with ease. The bottommost phosphor layer  200   a  entirely covers a surface of the first substrate  210 . In addition to the first substrate  210 , the optical film  200  can further include a second substrate  220 , so as to better protect the optical film  200  from being damaged. The second substrate  200  covers the topmost phosphor layer  200   c,  such that the phosphor layers  200   a,    200   b,  and  200   c  are interposed between the first substrate  210  and the second substrate  220 . Materials of the first substrate  210  and the second substrate  220  and conditions on which said materials can be used have been discussed hereinbefore, and therefore no further descriptions are provided herein. 
       FIGS. 4A to 4D  are schematic flowcharts illustrating a fabricating method of an optical film according to another embodiment of the invention. Referring to  FIG. 4A , the fabricating method of the optical film in the present embodiment is similar to that depicted in  FIGS. 2A to 2D , while the main difference therebetween lies in that a patterned mask layer  310  is disposed on the first substrate  210  before the first substrate  210  is coated with the phosphor powder, so as to partially expose portions of a surface  212  of the first substrate  210 . 
     As indicated in  FIG. 4B , the exposed portions of the surface  212  of the first substrate  210  are coated with the phosphor powder, so as to form a patterned phosphor layer  300   a.  The other portions of the surface  212  of the first substrate  210  that are covered by the mask layer  310  do not contain any phosphor powder. 
     With reference to  FIG. 4C , the mask layer  310  is moved to expose portions of the surface  212  of the first substrate  210 . Note that the portions of the surface  212  of the first substrate  210  where the patterned phosphor layer  300   a  is formed are covered by the mask layer  310 . 
     Next, the step depicted in  FIG. 4B  is repeated by coating the first substrate  210  with another phosphor powder, so as to form another patterned phosphor layer  300   b.  In the present embodiment, the steps depicted in  FIGS. 4B and 4C  can be repeated continuously without restraint, and thereby a plurality of patterned phosphor layers  300   a,    300   b,  and  300   c  arranged in array as shown in  FIG. 4D  can be formed. In  FIG. 4D , only three different patterned phosphor layers  300   a,    300   b,  and  300   c  are illustrated for the purpose of exemplification. 
     Similar to the manufacturing method of the optical film described in the previous embodiment, steps of the manufacturing method of the optical film in the present embodiment can also include selectively forming a second substrate  220  to cover the patterned phosphor layers  300   a,    300   b,  and  300   c  and to further dispose the patterned phosphor layers  300   a,    300   b,  and  300   c  between the first substrate  210  and the second substrate  220 . In an alternative, according to other embodiments, the patterned phosphor layers  300   a,    300   b,  and  300   c  can be peeled off or released from the first substrate  210 , so as to form an optical film  300  which includes a plurality of patterned phosphor layers  300   a,    300   b,  and  300   c  arranged in array. 
     Referring to  FIG. 4D , the optical film  300  formed by applying the aforesaid manufacturing method includes a plurality of patterned phosphor layers  300   a,    300   b,  and  300   c  arranged in array. Each of the patterned phosphor layers  300   a,    300   b,  and  300   c  is excited by an exciting light source and emits a secondary light beam, and the secondary light beams emitted by the patterned phosphor layers  300   a,    300   b,  and  300   c  are in different wavelength ranges. According to the present embodiment, a wavelength of the exciting light source is shorter than a wavelength of each of the secondary light beams. For instance, the patterned phosphor layer  300   a  of the present embodiment is a patterned red phosphor layer, the patterned phosphor layer  300   b  of the present embodiment is a patterned green phosphor layer, and the patterned phosphor layer  300   c  of the present embodiment is a patterned yellow phosphor layer. The thickness of the phosphor layers, areas covered by the phosphor layers, and positions where the phosphor layers cover are not limited in the present invention and can be changed based on actual demands. However, only three patterned phosphor layers  300   a,    300   b,  and  300   c  are illustrated in  FIG. 4A  for the purpose of exemplification. 
     Referring to  FIG. 4D , the optical film  300  of the present embodiment can include a first substrate  210  on which the patterned phosphor layers  300   a,    300   b,  and  300   c  are stacked. In the present embodiment, the patterned phosphor layers  300   a,    300   b,  and  300   c  cover different regions on the surface  212  of the first substrate  210 . 
       FIGS. 5A and 5B  are top views illustrating patterns on two types of patterned phosphor layers according to an embodiment of the present invention. Referring to  FIGS. 5A and 5B , the patterned phosphor layers  300   a,    300   b,  and  300   c  are formed according to the patterns on the mask layer  310 , and therefore the patterned phosphor layers  300   a,    300   b,  and  300   c  have different patterns. For instance, the patterned phosphor layers  300   a,    300   b,  and  300   c  can have a matrix arrangement as indicated in  FIG. 5A , a honeycomb arrangement as indicated in  FIG. 5B , or a delta arrangement. 
     In the above embodiments, structures and manufacturing methods of the two types of optical films are respectively discussed. In the embodiment hereafter, the application of the aforesaid optical films to an LED package structure is elaborated with reference to drawings. 
       FIG. 6  is a schematic view of an LED package structure according to still another embodiment of the present invention. Referring to  FIG. 6 , an LED package structure  400   a  of the present embodiment includes a substrate  410 , an LED chip  420 , and an optical film  430   a.  The substrate  410  has a cavity  412  and a circuit layer  414 , and the cavity  412  exposes a portion of the circuit layer  414 . The LED chip  420  is disposed on the bottom of the cavity  412  and is electrically connected to the circuit layer  414 . Here, the LED chip  420  and the circuit layer  414  are electrically connected by performing a wire bonding process or a flip chip process. 
     According to the present embodiment, the optical film  430   a  is referred to as the optical film  200  described in the above embodiment, for example. The optical film  430   a  includes a plurality of stacked phosphor layers. The stacked phosphor layers excited by an exciting light source emit secondary light beams in different wavelength ranges, and the secondary light beams in different wavelength ranges can be mixed to form the light beams in specific wavelength ranges. 
     In  FIG. 6  of the present embodiment, only one LED chip  420  is illustrated for exemplification. Nevertheless, the number of the LED chip  420  and the wavelength of the light emitted by the LED chip  420  can be adjusted upon actual demands and are not limited in the present invention. Notably, the wavelength of the light emitted by the LED chip  420  is taken into account, and so are the light beams which are in different wavelength ranges and are emitted from different phosphor layers excited by the exciting light source. As such, it is rather easy to adjust the light emitted by the LED package structure  400   a.  In addition to the above, CCT and CRI performance of the light emitted by the LED package structure  400  can also be better regulated because the optical film  430   a  is rather apt to be adjusted. 
       FIG. 7  is a schematic view of an LED package structure according to yet still another embodiment of the present invention. As shown in  FIG. 7 , the LED package structure  400   b  of the present embodiment is similar to the LED package structure  400   a  of the previous embodiment. The main difference therebetween lies in that an optical film  430   b  of the present embodiment further includes a first substrate  432   a.    
       FIG. 8  is a schematic view of an LED package structure according to yet still another embodiment of the present invention. As shown in  FIG. 8 , the LED package structure  400   c  of the present embodiment is similar to the aforesaid LED package structure  400   a.  The main difference therebetween lies in that an optical film  430   c  in the LED package structure  400   c  of the present embodiment is, for example, the optical film  300  having a plurality of patterned phosphor layers arranged in array. 
     In  FIG. 8  of the present embodiment, only one LED chip  420  is illustrated for exemplification. However, in a preferred embodiment, the LED chip  420  can be arranged corresponding to patterns on the optical film  430   c,  so as to form a plurality of sub-regions in which light beams can be mixed and can have different wavelengths, which is not limited in the present invention. 
       FIG. 9  is a schematic view of an LED package structure according to yet still another embodiment of the present invention. As shown in  FIG. 9 , the LED package structure  400   d  of the present embodiment is similar to the LED package structure  400   c  of the previous embodiment. The main difference therebetween lies in that an optical film  430   d  of the present embodiment further includes a first substrate  432   a  and a second substrate  432   b.  The first substrate  432   a  and the second substrate  432   b  serve to protect the optical film  430   d  from being damaged during fabrication thereof or consumers&#39; utilization thereof 
     According to the above embodiments depicted in  FIGS. 6 to 9 , the LED chip  420  is taken as an example for describing the present invention. However, the above descriptions do not pose a limitation on the present invention. Namely, an LED package structure including a lens can also be disposed in the cavity  412 , so as to form a package in package (PIP) structure. Besides, the LED chip  420  can also be replaced by other appropriate light emitting devices. 
     In light of the foregoing, the optical film of the present invention has a plurality of phosphor layers, and the phosphor layers are excited by the exciting light source and emit the secondary light beams in different wavelength ranges. The secondary light beams in different wavelength ranges can be mixed and then can become the light beams in specific wavelength ranges. Since the optical film is rather apt to be adjusted, the light beams formed thereby are allowed to have diverse wavelength lengths. Moreover, in some embodiments of the present invention, the light beams emitted by the LED package structure can have different CCTs and better CRIs when the optical film of the present invention is applied to the LED package structure. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.