Abstract:
An LED assembly can effectively prevent static electricity from accumulation, comprises an LED module, a grounded support and two fasteners extending through the LED module into the support. The LED module comprises a printed circuit board having a metal substrate and two insulating layers formed on the substrate, and a plurality of LEDs mounted on the printed circuit board. Each fastener has a plurality of teeth extending downwardly through the insulating layer to abut against a top face of the substrate, to thereby electrically connect a top face of the insulating layer and the substrate.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an LED assembly, and more particularly to an LED assembly comprising an electrostatic-leading structure for preventing static electricity accumulation thereon. 
         [0003]    2. Description of related art 
         [0004]    LEDs have been available since the early 1960&#39;s. Because of their relatively high light-emitting efficiency, LED usage has increased in popularity in a variety of applications, such as residential, traffic, commercial, and industrial settings. In such applications, for sufficient light output, a plurality of LED modules is incorporated in a housing which supports mounting of the LED modules thereon, and also as a heat sink dissipating heat generated by the LED modules to an atmosphere ambient. Generally, most conventional LED modules are silicon printed circuit boards with multiple LEDs fixed thereon. 
         [0005]    Recently, there has been proposed an LED module substituting a metal printed circuit board for the conventional board, to improve heat dissipation therefrom, thereby allowing increased density of arrangement of the LEDs on the printed circuit board, thus enhancing overall light output per LED module. The metal printed circuit board requires electrical insulation from the LEDs, preventing electrical communication therebetween. Among the many attempts at insulating the metal printed circuit board from the LEDs, one example thereof sequentially forms a first insulating layer, an electrically conductive layer, and a second insulating layer on the metal printed circuit board. The first insulating layer insulates the metal printed circuit board from the electrically conductive layer, which is directly connected to electrode leads of the LEDs, supplying current thereto, the second insulating layer overlays the electrically conductive layer to prevent contact between the electrically conductive layer and other electrical terminals, which may disturb normal operation of the LEDs if in electrical connection with the electrically conductive layer. A plurality of screws with insulating washers sleeved thereon extends through the metal printed circuit board to thereby attach the LED modules to the housing. 
         [0006]    When the LED module is tested under a high voltage value by a testing device for determining electrical parameters thereof, or after being utilized for a long period as a light source in an LED lamp, there arises a probability that static electricity may be unexpectedly generated on an external surface of the second insulating layer. Since the washers, often of electrically insulating plastic material, are present between the screws and the external surface of the second insulating layer, the external surface of the second insulating layer can be substantially insulated from the screws. The static electricity on the external surface of the second insulating layer cannot be evacuated by the screws to ground, but will remain and accumulate gradually. A significant electrostatic discharge (ESD) may therefore occur in the LED module when accumulated static electricity reaches a critical value, and current may flow into the LEDs from the electrostatic discharge, resulting in malfunction or damage to the LEDs. 
         [0007]    What is needed, therefore, is a method for mounting an LED module on a support which can overcome the described limitations. 
       SUMMARY OF THE INVENTION 
       [0008]    A method for mounting an LED module on a support comprises providing an LED module, a support and a plurality of fasteners, each comprising a head, a pole extending downwardly from a bottom of the head, and a plurality of teeth protruding downwardly from the bottom of the head and surrounding the pole, inserting the fasteners through a printed circuit board of the LED module into the support, rotating each fastener to cause the teeth thereof to scrape parts of insulating layers off a metal substrate of the printed circuit board, whereby a top face of the substrate is exposed and in direct contact with the teeth of the fastener. Accordingly, an electrically conducting pathway between a top face of the insulating layers and the top face of the substrate is formed via the fasteners, and electrostatic electricity generated on the top face of the insulating layers can flow to the support through the pathway. Therefore, malfunction or damage to the LEDs by electrostatic discharge is avoided. 
         [0009]    Other advantages and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Many aspects of the present apparatus can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present apparatus. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0011]      FIG. 1  is an assembled, top view of an LED assembly in accordance with an embodiment of the present invention. 
           [0012]      FIG. 2  is an exploded cross-section of  FIG. 1  taken along line II-II, wherein two screws are detached from an LED module of the LED assembly. 
           [0013]      FIG. 3  is a view similar to  FIG. 2 , but one of the two screws is screwed into the LED module and a support of the LED assembly is removed. 
           [0014]      FIG. 4  is a view similar to  FIG. 3 , with configurations of the two screws varied. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  is a top view of an LED assembly to which the present invention is directed. The LED assembly comprises an LED module  10 , a support  20 , and a pair of screws  30  extending through the LED module  10  into the support  20  to thereby fix the LED module  10  onto the support  20 . The LED module  10  comprises a rectangular printed circuit board  12  and a plurality of LEDs  14  uniformly arranged thereon. 
         [0016]    Also referring to  FIG. 2 , the printed circuit board  12  constitutes a substrate  120  and a plurality of layers  122 ,  124  formed thereon. A pair of straight through holes  126  are defined in the printed circuit board  12  between the LEDs  14 , receiving the screws  30  therethrough and fixing the LED module  10  on the support  20 . The substrate  120  is substantially of a heat conducting material, such as copper, aluminum or an alloy thereof. The plurality of layers  122 ,  124  comprises a first insulating layer  122 , an electrically conductive layer (not shown), and a second insulating layer  124  sequentially plated on the substrate  120 . A thickness of the substrate  120  is about 1.5 mm, and a total thickness of the three layers  122 ,  124  is approximately 0.1 mm which is exaggerated in  FIGS. 2-4 . The first insulating layer  122  covers an overall top face of the substrate  120 , to thereby completely insulate the electrically conductive layer from the substrate  120 . The electrically conductive layer is patterned on the first insulating layer  122  avoiding positions of the LEDs  14 , and away from through holes  126 . The electrically conductive layer directly connects electrode leads (not shown) of the LEDs  14 , providing current from a power source (not shown) thereto. The second insulating layer  124  is formed on an outermost side of the printed circuit board  12 , preventing the electrically conductive layer from contacting other electrical terminals (not shown). Since there is no electrically conductive layer formed adjacent to the through holes  126 , the second insulating layer  124  directly joins the first insulating layer  122  at the places shown in  FIGS. 2-4 . 
         [0017]    Each screw  30  is integrally of metal and consists of a head  32  and a pole  34  extending downwardly from a bottom face thereof. The head  32  has a portion recessed downwardly in a top face thereof, thereby forming two crossed slots  38  (as viewed from  FIG. 1 ). A plurality of teeth  36  protrudes downwardly from the bottom face of the head  32  and surrounds a top end of the pole  34 . Each tooth  36  is triangular with a relatively sharp end. A plurality of spiral threads (not shown) around a circumferential face of the pole  34  interferingly engage internal threads in threaded holes (not shown) in the support  20 , thus interferingly fixing the LED module  10  on the support  20 . 
         [0018]    Also with reference to  FIG. 3 , when mounting the LED module  10  on the support  20 , the screws  30  are prepared to be readily inserted through the through holes  126  in the printed circuit board  12  with the teeth  36  thereof abutting a top face of the second insulating layer  124  of the printed circuit board  12 . As a rotation of each screw  30  impels it downwardly toward the support  20 , the teeth  36  of the screws  30  scrape annular parts of the second insulating layer  124  and the first insulating layer  122  of the printed circuit board  12  surrounding each through hole  126 . Before the teeth  36  reach the top face of the substrate  120 , an annular part of the top face of the substrate  120  surrounding each through hole  126  is substantially exposed. Meanwhile, rigidity of the substrate  120  prevents the ends of the teeth  36  from penetrating deep into the substrate  120 , and the screws  30  are impeded from moving downwardly any further. At this time, the heads  32  of the screws  30  project out of the second insulating layer  124 , establishing an electrical connection with the top face of the second insulating layer  124 , and the poles  34  of the screws  30  are threaded in the support  20 , thereby firmly fixing the LED module  10  on the support  20 . 
         [0019]    By removing the annular parts of the first insulating layer  122  and the second insulating layer  124  near the screws  30  from the substrate  120 , the head  32  of the screw  30  is in direct contact with the substrate  120  and electrical connection with the top face of the second insulating layer  124  of the printed circuit board  12 . Static electricity produced on the top face of the second insulating layer  124 , is conductable via the screws  30  to the substrate  120  which is grounded beforehand. Thus, malfunction of or damage to the LEDs  14  due to electrostatic discharge is avoided. 
         [0020]    Further, to ensure that the annular parts of the first and second insulating layers  122 ,  124  surrounding the through holes  126  can be completely cleared, the screws  30  can be continuously rotated downwardly to scrape a top portion of the substrate  120  under large force, after engaging the top face of the substrate  120 . Thickness of portion scraped off the substrate  120  varies, commensurate with the force applied, with preferably, in the present invention, the thickness of the scraped portion being about 0.2 mm. 
         [0021]    Alternatively, the screws  30  can be replaced with other elements as long as the same functionality is provided. Practicable among such elements, as shown in  FIG. 4 , is a fastening assembly  30   a  replacing the former integrally formed screw  30 . The fastening assembly  30   a  comprises a screw (not labeled) which has a head  32   a,  a pole  34   a  extending downwardly from a bottom face of the head  32   a,  and a metal annulus  31   a  detachably sleeved on the pole  34   a  of the screw. The annulus  31   a  has a circumference corresponding to that of the head  32   a  of the screw. A plurality of teeth  36   a  projects downwardly from the bottom face of the annulus  31   a.  The teeth  36   a  perform the same function as those of the former screws  30 , that is, scraping the first and second insulating layers  122 ,  124  off the substrate  120  of the printed circuit board  12 . Note that the screw and the annulus  31   a  of the fastening assembly  30   a  actually equal two corresponding separated parts of the prior screw  30 , respectively. It is believed that the present invention and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.