Applications requiring femtoampere-level performance are extremely sensitive to contamination. Contaminants in the form of solder flux, salts, oils, organic acids, and more can form conductive paths over PCB traces and allow small currents to leak into input traces or other sensitive nodes, severely degrading performance. Proper handling and cleaning is required to achieve femtoampere level input bias performance in a PCB featuring the OPA928.

The following list of best practices helps prevent a PCB from contamination:

• Always wear a pair of clean, powder-free gloves or finger cots when handling the PCB.
• Always hold the PCB by the edges when handling is required.
• Avoid touching the surface of the PCB and other component packages, especially near sensitive nodes or input traces.
• Be cautious when breathing, speaking, and sneezing to prevent moisture or saliva from contacting the PCB.
• Do not allow direct airflow onto the board. Moving air can blow dust and moisture onto sensitive nodes. Airflow also introduces moving charges that manifest as a small current at the input.
• When not in use, place the PCB in an ESD bag or other enclosure to prevent dust and other contaminants from settling on the board.
• If configuring through-hole components in sensitive nodes, handle the components by the wire leads only.

A rigorous cleaning protocol is required after PCB assembly to remove all contaminants that can degrade input bias performance of the OPA928. Repeat the cleaning procedure any time the board is soldered or modified near sensitive nodes, or if contamination of these nodes is suspected.