I'm building an EEG circuit and as such there are approximately 128 channel leads. At the moment I'm just running standard wires but to improve space and neatness I'm going to print these on a flex PCB which will terminate in a board-to-board connector. When looking at the pitch sizes I'm tempted to use the 0.35 mm, however I am concerned due to the lower space between traces this will lead to a decreased signal-to-noise ratio and convolution.
Would it be less risk to go with a higher pitch i.e. a 0.5 mm or even a 1 mm or should a 0.35 mm be fine?