High-impedance, femtoampere-level circuits are highly sensitive to electrostatic and electromagnetic interference (EMI). Even weak electric fields can couple into high-impedance nodes and cause significant interference when in close proximity to the circuit. Simply waving your hand near the test fixture, for example, can disrupt the low leakage measurement. To help reduce the effects of electrostatic and electromagnetic fields, fully enclose all exposed high-impedance traces with a shield. The shield serves to reduce external dc and ac signals from coupling into the high-impedance nodes by shunting the signals to analog ground. Keep the shield installed to reduce unwanted pickup and prevent contaminants from entering sensitive nodes. Shield cans and surface mount shield clips are readily available from manufactures.