LMP7704: an abnormal issue for the IC LMP7704MA/NOPB procured

Hi Jimit,

1) Can you please provide a complete schematic showing the input voltage signal into the LMP7704, the voltage supply voltages/connections, input and feedback components and the output load? If possible, please also share the Gerber plots or layout plots of the design.

2)  Are these PCB production boards assembled through a standard solder re-flow process, or engineering prototypes soldered by hand? How many devices have been tested showing this behavior?  If this is only one device, can you replace the device with a fresh unit?  

3) Has the PCB board undergo a standard cleaning protocol after soldering/assembly?

- Amplifier applications requiring picoampere range performance are very sensitive to PCB board contamination. Contaminants in the form of solder flux, oils and other impurities can form conductive paths over the sensitive PCB traces that allow small currents to leak from the input traces or other sensitive nodes. Leakage currents from solder flux contamination can disturb the input current measurement.  

- At our site, our boards undergo a standard cleaning protocol after the fabrication, soldering and assembly process prior shipping to customers, providing picoampere level performance. The PCB boards must be re-cleaned anytime devices are soldered into the PCB or modified near the input amplifier sensitive nodes. The recommended cleaning procedure requires access to an ultrasonic deionized (DI) water bath and run the ultrasonic cleaner for 20 minutes at 45°C. 

- If an ultrasonic bath is not available, then a manual cleaning procedure is possible: Use a toothbrush to scrub contaminants from the top layer bottom layers using DI water. Flush the scrubbed areas with fresh DI water, tilting the board to allow runoff to flow away from the input areas. Remove all moisture from PCB prior measurement.

- You may consult with your PCB manufacturer about the recommended solder flux cleaning procedure.

Thank you and Regards,

Luis

Hi Luis,

The designed board is standard 2 Layer board in which we are feeding the current from 1uA to 100pA. We have some samples of earlier procured LMP7704 and it is showing the proper output with the same input and over the same board. For reference PFA picture.

HI Panjak,

To be able to assist you, please attach the schematic file the LMP7704 circuit to this E2E post, using the "Insert" button at the bottom menu. I am unable to access the file since the firewall blocks access to the external drive link you have provided.

Please also confirm the PCB board went through a thorough solder flux removal process after assembly, since this is a common issue when measuring currents in the picoampere range. 

Thank you and Regards,

Luis

Dear Luis,

Yes PCB has gone through the solder mask cleaning process followed by ethanol cleaning of the PCB. This Portal only allow us to upload the image/file through URL.

Hi Pankaj,

We aren't able to view this link, you will need to post the schematic image to e2e.

Regards,
Mike