The present invention relates to a circuit card (4.3; 4.4) which includes conductive patterns (1, 2, 5, 6) and a web (3) made of glass fibers, at least one non-conductive blocking element (11.1; 11.2) for blocking the growth of a conductive filament (12.1; 12.2) along a glass fiber is provided which connects a conductive pattern (1, 2) with a further conductive pattern (5, 6). The present invention also relates to a method for increasing the resistivity of a circuit card (4.3; 4.4) to the formation of conductive filaments (12.1; 12.2), the circuit card (4.3; 4.4) including conductive patterns (1, 2, 5, 6) and a web (3) made of glass fibers; the circuit card (4.3; 4.4) being provided with at least one non-conductive blocking element (11.1; 11.2) for blocking the growth of a conductive filament (12.1; 12.2) along a glass fiber, which connects a conductive pattern (1, 2) to a further conductive pattern (5, 6).