Abstract:
Method of fabricating LED assembly disclosed herein can provides a string of original colored high intensity LEDS usable for screen displaying or traffic signal lights molded by injecting harmless polyacrylic resin in a short time duration and at low temperature.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to method of fabricating LED assembly, and more particularly, to method of fabricating a string of original colored (E,G,B) high intensity LEDS (Light Emitting Diodes) to be displayed on a screen or used as a traffic light source. 
     2. Description of the Prior Art 
     In conventional method of fabricating LED assembly, an epoxy resin added with a hardener molded by baking at high temperature (90° C.˜110° C.) is a commonly adopted procedure. For example, in a cited case herein, which was patented by NO3 11269 in Taiwan, a fabrication method by plastic packaging was employed. The material used for fabrication was a plastic resin (an hardener was required to cure its softness at room temperature) applied to the micro structure of a semiconductor surface by coating or spraying, them the later fabricating steps were successively carried out after hardening of the plastic resin. As the package was performed by coating or spraying, the finished surface of the product was somewhat uneven. In addition, such a fabrication method provided by the cited case is only applicable for semiconductor packaging owing to the fact that it is unable to withstand ejecting pressure higher than 40 psi. 
     Since high intensity blue colored LED has come to practical use, it soon becomes a favorite of multi-media world. Further innovation on precision of light emission angle and uniformity in tint are asked that can not be attained with a conventional resin treatment. 
     Filling epoxy resin or silicone rubber in a LED assembly housing by heating at a temperature above 120° C. in an oven, the rate of yield scarcely exceeds 90% with disqualified results in disorganized disposal of elements, inadequate quantity of resin attachment, and unevenness of surface. Besides, a cracked resin package is not repairable and inadvertent spattering of resin in the front of surface an unit LED causes degrading of brightness. 
     High intensity blue or green LED lighting source should be reliably made watertight if it is to be installed outdoor. However, such an aim is hard to be attained by a conventional method of driving in an oven after instilling a resin with a low cost. 
     In order to overcome the shortcomings inherent to the conventional technique described above, the present inventor has delved into this matter with a long time efforts and came to realization of the present invention. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide method of fabricating LED assembly by using polyacrylic resin as a essential packaging material and applying a pressure above 40 psi to integrally form a watertight contour of a string of LED assembly by injection molding process so as to obtain a good looking, smooth surfaced appearance of the product. 
     It is another object of the present invention to provide method of fabricating LED assembly by using an innovative plastic resin injection machine to save 50% time needed in the whole stages of fabrication so as to minimize production cost internationally competitive with other leading countries in this field of technology. 
     In the method of the present invention, the time duration required for polyacrylic resin injection per round is only about 40 sec with temperature descending from 110° C. down to below 60° C. fully in compliance with internationally standardized LED fabrication specification and increase of 130 times production speed compared with general conventional method of fabrication. Besides, in case the housing of the LED assembly is cracked, it is 99% repairable by fusing plastic resin of the housing. 
     To enable a further understanding of the innovative and technological content of the invention herein, refer to the detailed description of the invention and the accompanying brief description of the drawings appended below. Furthermore, the attached drawings are provided for purposes of reference and explanation, and shall not be construed as limitations applicable to the invention herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings disclosed two illustrative embodiments of the present invention which serve to exemplify the various advantages and objects hereof, and as follows: 
     FIG. 1 is a view illustrating the first step of method of fabricating LED assembly according to the present invention; 
     FIG. 2 is a view illustrating the second step of method of fabricating LED assembly according to the present invention; 
     FIG. 3 is a view illustrating the third step of method of fabricating LED assembly according to the present invention; 
     FIG. 4 is a view illustrating the fourth step of method of fabricating LED assembly according to the present invention; 
     FIG. 5 is a view illustrating the fifth step of method of fabricating LED assembly according to the present invention; 
     FIG. 6A is a fragmentary cross sectional view of a conventional LED assembly; 
     FIG. 6B is another fragmentary cross sectional view of a conventional LED assembly; 
     FIG. 7 is a view of method of fabricating LED Assembly in another embodiment of the present invention; 
     FIG. 8 is a view illustrating the first step of method of fabricating LED assembly in another embodiment of the present invention; 
     FIG. 9 is a view illustrating the second step of method of fabricating LED assembly in another embodiment of the present invention; 
     FIG. 10 is a view illustrating the third step of method of fabricating LED assembly in another embodiment of the present invention; 
     FIG. 11 is a view illustrating the fourth step of method of fabricating LED assembly in another embodiment of the present invention; and 
     Table 1 is a comparison between properties of polyacrylic resin and epoxy resin. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the method of fabricating LED assembly of the present invention shown in FIG. 1 at first step, a plurality of unit LEDS  10  welded onto an electrical board  11  which has been already cut into a desired shape, then lead conductors  12  are welded to the electrical board  11  at a proper position. The unit LEDS are disposed according to a definite way so as to exhibit a lustrous and beautiful high quality mixed color later on. 
     In the second step shown in FIG. 2, the string of LEDS  10  buried in a framed gutter  13  and fixed therein, the gutter  13  shall be well fitted for the unit LEDS  10  in every respect such that the resin to be injected thereinto in the next step will not overflow thereby ensuring a good product quality. 
     In the third step shown in FIG. 3, the framed gutter  13  together with the LED assembly  10  is put in a mold cavity of a mold  14  which is to be closed both from right and left, and the LED assembly  10  is settled thereat. 
     In the fourth step shown in FIG. 4 polyacrylic resin  16  is injected into the framed gutter  13  from an injection port  15 , and a copper stick  17  is simultaneously inserted thereinto to stabilized the injection operation. It should be noted that an annular groove  18  will be formed at the rear part of the injected polyacrylic resin  16 . However, a rubber ring  19  (not shown) can be filled therein for preventing entry of water drips in a rainy day so as to protect the product from defection. 
     In the fifth step shown in FIG. 5, a finished product of LED assembly  21  is taken out from the mold  14  thus completing the whole fabrication steps. In the present invention, the time required for polyacrylic resin  16  injection per round is only about 30 sec. with temperature descending from 90° C. down to below 60° C. fully in compliance with internationally standardized LED fabrication specification, and the rate of yield attains as high as 99%. 
     For comparison, in a conventional fabrication method using epoxy resin or silicone rubber as a packaging material, and heating in an oven at a temperature above 120°, the rate of yield obtainable is below 90% accompanying with dissatisfactory structure of resin package, and unsmoothness of the finished product. 
     For a further comparison between the product fabricated according to a convention method and that according to the present invention, reference should be made to FIGS. 6A and 6B. As shown in FIG. 6A, the product molded with epoxy resin or silicone rubber is finished in such a state that the surface between adjacent unit LEDS is formed in an arcuate FIG. 22, an incident light  23  (from a lamp source or sun light) is reflected in diffusing state lacking uniformity in brightness and homogeneity in color. On the contrary, the fabrication method according to the present invention is employed in FIG. 6B wherein the product is molded with polyacrylic resin by injection process lasting for approximately 30 sec at a temperature descending from 90° C. to below 60° C. It should be noted that the product fabricated in a withstandable temperature and time duration has a resultant planar surface  24  between adjacent unit LEDS which acts as a reflecting mirror against an incident light (from a lamp source or sun light) so that there are no shortcomings as that of the product fabricated according to the conventional techniques. 
     FIG. 7 shows a view of method of fabricating LED assembly in another embodiment of the present invention. As shown in FIG. 7 this LED assembly is applicable as a traffic signal lamp for cross roads. It is characterized in that the LED assembly  25  containing red, green and yellow colors is screwed onto a screw socket  27  without using any luminary but only adding a light shade  26 . With this construction, by the aid of direct emission property of LED light, the light signal of one of the cross road at the instant of variation from yellow to red is not visible from the driver waiting at the other cross road so as to evade his/her too early starting thereby eliminating a possible traffic accident as that is apt to happen in case a conventional traffic signal lamp in a non-shaded luminary is installed on a cross road intersection. 
     In the first step of fabrication in another embodiment shown in FIG. 8, a plurality of unit LEDS  30  is welded onto an electrical circuit board  31  which has been already cut into a desired shape. 
     FIG. 9 shows the second step of method of fabricating LED assembly in another embodiment of the present invention, it differs from the step shown in FIG. 1 That lead conductors  32  are not connected to a circuit board  31  in advance, but are passed through the guide hole  33  in a preformed housing before connecting to the circuit board  31 . Afterward the circuit board  31  is pushed and engaged to an inner flange  34  of the housing to be fixed thereof, and then the LED assembly is buried in a framed gutter  35 . 
     FIG. 10 shows the third step of method of fabricating LED assembly in another embodiment of the present invention, the framed gutter  35  together with the LED assembly is settled in a mold  36 , in this case as the inner part of the framed gutter  35  is divided in two spacing by the circuit board  31 , a front room  37   a  and a rear room  37   b , so that the resin has to be injected thereinto through respective inlet ports  38   a  and  38   b.    
     FIG. 11 shown the forth step of method of fabricating LED assembly in another embodiment of the present invention, wherein a finished LED assembly  39  is taken out of the mold cavity after carrying out injection molding about 30 sec. from 90° C. to 60° C. with 99% rate of yield. 
     Table 1 is a comparison between properties of polyacrylic resin employed in the present invention and epoxy resin employed in prior techniques. 
     
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Epoxy 
                 Polyacrylic resin 
               
               
                 State 
                 (liquid plastic) 
                 (solid state) 
               
               
                   
               
             
             
               
                 Way of finishing 
                 Adding hardener 
                 Heating up to 200° C. 
               
               
                   
                 and anti-ultra 
               
               
                   
                 violet ray substance 
               
               
                 Objects to be packaged 
                 LED chip, IC chip 
                 Integrated LED, 
               
               
                   
                   
                 entirely water-proof IC 
               
               
                 Way of filling 
                 Coating, spraying, 
                 Squeezing by injection 
               
               
                   
                 implanting 
               
               
                 Injection pressure 
                 Almost nil if by 
                 Applying 
               
               
                   
                 coating or 
                 15 kgf-30 kgf high 
               
               
                   
                 implanting 
                 pressure to squeeze 
               
               
                   
                   
                 into mold 
               
               
                 Way of hardening 
                  85° C. for 4 hours; 
                 155° C. for 10 sec 
               
               
                   
                 100° C. for 2 hours 
                 after placed in mold 
               
               
                 Available waiting time 
                  25° C. for 4 hours; 
                 No time limit 
               
               
                   
                  40° C. for 5 hours 
                 (in any environmental 
               
               
                   
                 after mixing 
                 condition) 
               
               
                 Heat deformation 
                 122° C. 
                 135° C. 
               
               
                 occurring temperature 
               
               
                 Combustion 
                 Combustible 
                 Non-combustible 
               
               
                   
                   
                 UL94 
               
               
                 Dielectric constant 
                 3.12 at 1 KHz 
                 3.09 at 1000 KHz 
               
               
                 Volumetric resistance 
                 1.3 × 100,000 
                 1,000,000,000 
               
               
                   
                 Ohm-cm 
                 Ohm-cm and up 
               
               
                 Arc withstanding ability 
                 none 
                 130 sec 
               
               
                 Hardness 
                 114 R-Scal 
                 90 R-Scal 
               
               
                 Boiled water 
                 0.42% for 1 hour 
                 0.02% for 1 hour, 
               
               
                 absorption rate 
                 (0% at 23° C.) 
                 (0% at 23° C.) 
               
               
                 Temperature expansion 
                 6.0 × (−100,000) 
                 6.0 × (−100,000) 
               
               
                 coefficient 
               
               
                   
               
             
          
         
       
     
     In all, after having made careful consideration over the above detailed description of the present invention, it will be clearly understood that the present invention has several noteworthy features which are prominently superior to any conventional techniques, and are as follows: 
     1. The product has good appearance, smooth contour surfaces due to adequate resin attachment, well-organized disposal of components excellent water tightness and low production cost with nearly 100% rate of yield. 
     2. A noteworthy contribution to environmental protection that generation of poisonous gas due to heating resin material at high temperature for a long time that is the problem, inherent to conventional methods is eliminated because harmless polyacrylic resin is used with a very short time duration of heating under relatively low temperature in the present invention. 
     Those who are skilled in the art will readily perceive how to modify the invention. Therefore the appended claims are to be construed to cover all equivalent structures which fall within the true scope and spirit of the invention.