Electromagnetic noise suppression sheet, flat cable for high-frequency signals, flexible printed circuit board, and process for producing the electromagnetic noise suppression sheet

Abstract

An electromagnetic noise suppression sheet obtained by using combination of a conductive carbon and spinel ferrite particles having a cumulative 50% volume particle diameter of 1 to 10 μm, can exhibit an excellent transmission attenuation power ratio and a reduced return loss in a near electromagnetic field, and is suitable for high-density mounting. The electromagnetic noise suppression sheet of the present invention can be produced by the process of the present invention which includes the steps of applying a coating material in which the conductive carbon and the spinel ferrite particles having a cumulative 50% volume particle diameter of 1 to 10 μm are dispersed, to form a coating film having a thickness of 10 to 100 μm after dried, and subjecting the resulting coating film to thermoforming under pressure.

1 .- 4 . (canceled) 
     
     
         5 . A process for producing an electromagnetic noise suppression sheet, comprising the steps of:
 preparing a coating material in which a predetermined amount of a conductive carbon and a predetermined amount of spinel ferrite particles having a cumulative 50% volume particle diameter of 1 to 10 μm are dispersed such that contents of the conductive carbon and the spinel ferrite particles having a cumulative 50% volume particle diameter of 1 to 10 μm in the dried coating material are 3 to 10% by volume and 40 to 65% by volume, respectively;   applying the thus prepared coating material onto a substrate to form a coating film having a predetermined thickness;   drying the thus formed coating film; and   subjecting the thus dried coating film to thermoforming under pressure.