Patent Publication Number: US-2013242519-A1

Title: Printed circuit board

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to structure and layout of printed circuit boards and, particularly, to a structure and layout of a printed circuit board capable of reducing electromagnetic interference. 
     2. Description of Related Art 
     Most electromagnetic interference generated in a printed circuit board can be reduced by a ground connection. However, a poor layout of a ground layer may strengthen the electromagnetic interference. 
     For example, referring to  FIG. 1 , a printed circuit board  100 ′ of an electronic device, such as a Digital Versatile Disc (DVD) player, includes a power switch circuit (not shown) used for repeatedly charging and discharging. A copper foil (shown as the shadow)  20 ′ laid on the entire printed circuit board  100 ′ is connected to ground, to form a high current ground loop, which is capable of reducing any electromagnetic interference generated in the printed circuit board  100 ′. 
     The electronic components in the printed circuit board  100 ′, such as a Power Management IC, include a ground pin to form a ground loop, and then connect to the high current ground loop formed by the copper foil  20 ′ via the ground pin, thus eliminating or reducing the electromagnetic interference generated therein. However, an inductor used for repeatedly charging and discharging and included in the power switch circuit and connected to the printed circuit board  100 ′ by pads  303 ′ and  304 ′ does not include a ground pin. Therefore, the high-order harmonic distortion and noise generated by the inductor during the process of repeatedly charging and discharging can only be reduced or eliminated by the copper foil covered by the inductor. But because the path of a loop formed by the ground connection of the printed circuit board  100 ′ and the copper foil covered by the inductor is long, a portion of high-order harmonic distortion and noise may flow to other electronic components of the printed circuit board  100 ′ via the copper foil  20 ′ during the process that the high-order harmonic distortion and noise are conducted to ground, thus increasing the adverse influence of the electromagnetic interference on the other electronic components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with reference to the 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 disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a layout diagram of a printed circuit board in an electronic device of related art. 
         FIG. 2  is a layout diagram of a new printed circuit board in an electronic device, according to an embodiment. 
         FIG. 3  is the layout diagram of the printed circuit board of  FIG. 2 , showing an inductor soldered on the printed circuit board. 
     
    
    
     DETAILED DESCRIPTION 
     For use in an electronic device (such as DVD player),  FIG. 2  shows a layout of a printed circuit board  100  capable of reducing electromagnetic interference. The printed circuit board  100  includes an insulating layer, a conductive metal layer (shown as the shadow)  20 , a number of pads, such as pads  301 ˜ 304  for soldering connecting electronic components, and a number of printed conductors  40  for connecting electronic components.  FIG. 2  only shows a portion layout of the printed circuit board  100 , in the embodiment, the printed circuit board  100  includes a power switch circuit. 
     In the embodiment, the conductive metal layer  20  is attached on the insulating layer, and is connected to an internal ground of the printed circuit board  100  for providing a ground path for electronic components mounted on the printed circuit board  100 . In the embodiment, the conductive metal layer  20  is a grounded copper foil attached on the insulating layer and is for absorbing the electromagnetic interference generated in the printed circuit board  100 . In the embodiment, the insulating layer includes a number of exposed portions  601 ˜ 603  free of the conductive metal layer thereon, and pads  301 ˜ 304  and the printed conductors  40  are formed on the exposed portions of the insulating layer and are insulated from each other. Thus, the conductive metal layer  20  is separated from the pads  301 ˜ 304  and the printed conductors  40  to avoid short-circuits. A number of grounding holes  50  connected to the internal ground of the printed circuit board  100  are arranged in the conductive metal layer  20  for radiating heat energy and providing space for thermal expansion. 
     Referring to  FIG. 3 , the power switch circuit includes an inductor  70  for charging and discharging repeatedly. In the embodiment, the inductor  70  is a chip inductor and is connected to the power switch circuit by being mounted on the exposed portion  603  and being electrically connected to the two pads  303  and  304 . The two pads  303  and  304  are insulated from each other and a predetermined area between the two pads  303  and  304  is not covered by copper foil  20 . Thereby a spread path of a high-order harmonic distortion and noise generated by charging and discharging process of the inductor  70  is cut off to prevent high-order harmonic distortion and noise going to other components on the printed circuit board  100 . Therefore, the incidence or amount of the electromagnetic interference on the other electronic components is effectively reduced. 
     Moreover, it is to be understood that the disclosure may be embodied in other forms without departing from the spirit thereof. Thus, the present examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the disclosure is not to be limited to the details given herein.