Over Cleaning Causes Measurement Errors
The operator should should stay with the system and monitor the display during the clean cycle. Once the cleaning is complete, the operator should stop the cleaning process. The operator needs to avoid “over-cleaning” the Test Solvent.
The resistivity probe has a measurement limit of about 60.35 Mohm-cm, whereas the DI-Columns can clean to a much higher resistivity value. So if left unattended, the system could clean the Test Solvent well above the 60.35 Mohm-cm sensor limit and the actual starting resistivity would then be unknown and hence the actual contamination measurement could be incorrect. Recall, the contamination is calculated based upon the starting resistivity, and if the starting value is not accurate the calculation would also be not accurate.
For example, if the DI Columns clean the Test Solvent to 100 Mohm-cm, the system will think it is at 60.35 Mohm-cm (the maximum the sensor measures). Then any contamination extracted that lowers the resistivity from 100 to 60.35 is not measured, and this is a dead-band in the measurement which will under-report the actual contamination extracted from the board.
