Method for improving EMC of keyboard soft board

Abstract

A method for improving the EMI compatibility of the keyboard soft board is disclosed. A low-pass filter is installed on the scan lines of the keyboard soft board to remove high-frequency noise signals produced by the soft board circuit, achieving the EMC requirement. The low-pass filter is formed between the input terminal of the scan line and the touch pad. An inductance is selectively installed and between the touch pads. A capacitance is formed between the touch pad of the scan line and a ground network. The method of forming the capacitance is to form ground pads on the ground network corresponding the scan line touch pads. The method of forming the inductance may be achieved through a reversed U-shaped inductor.

1 . A keyboard with improving EMC, comprising from top to bottom direction: 
 a return line layer with a plurality of pads on a front face thereof;    an insulation layer;    a scan line layer with a plurality of pads on a front face thereof;    at least one ground pad on a rear face of the scan line layer and opposite to one of the pads of the scan line layer; and    an elongate-shaped trace formed on the front face of the scan line layer and connected with one of the pads of the scan line layer;    wherein the ground pad forms a capacitor with corresponding pad of the scan line layer and the elongate-shaped trace forms an inductor providing a filter circuit with the capacitor.    
   
   
       2 . The keyboard with improving EMC as in  claim 1 , wherein the diameters of the pad and the ground pad are preferably between 3 mm and 4 mm.  
   
   
       3 . The keyboard with improving EMC as in  claim 1 , wherein the elongate-shaped trace is of U shape.  
   
   
       4 . The keyboard with improving EMC as in  claim 1 , wherein the elongate-shaped trace is of reverse U shape.  
   
   
       5 . The keyboard with improving EMC as in  claim 4 , wherein the interval between the reversed U-shaped inductors is preferably about 0.3 mm.  
   
   
       6 . The keyboard with improving EMC as in  claim 1 , wherein the elongate-shaped trace is formed at an input end of the scan line layer.  
   
   
       7 . A keyboard with improving EMC, comprising from top to bottom direction: 
 a return line layer with a plurality of pads on a front face thereof;    an insulation layer;    a scan line layer with a plurality of pads on a front face thereof;    at least one ground pad on a rear face of the return line layer and opposite to one of the pads of the return line layer; and    an elongate-shaped trace formed on the front face of the scan line layer and connected with one of the pads of the scan line layer;    wherein the ground pad forms a capacitor with corresponding pad of the return line layer and the elongate-shaped trace forms an inductor providing a filter circuit with the capacitor.    
   
   
       8 . The keyboard with improving EMC as in  claim 7 , wherein the diameters of the pad and the ground pad are preferably between 3 mm and 4 mm.  
   
   
       9 . The keyboard with improving EMC as in  claim 7 , wherein the elongate-shaped trace is of U shape.  
   
   
       10 . The keyboard with improving EMC as in  claim 7 , wherein the elongate-shaped trace is of reverse U shape.  
   
   
       11 . The keyboard with improving EMC as in  claim 10 , wherein the interval between the reversed U-shaped inductors is preferably about 0.3 mm.  
   
   
       12 . The keyboard with improving EMC as in  claim 7 , wherein the elongate-shaped trace is formed at an input end of the scan line layer.