Cleaning The Sensor Window - Teledyne Linea 2K CL User Manual

An important note on window blemishes
When flat field correction is performed, window cleanliness is paramount. The figure below shows
an example of what can happen if a blemish is present on the sensor window when flat field
correction is performed. The blemish will cast a shadow on the wafer. FFC will compensate for this
shadow by increasing the gain. Essentially FFC will create a white spot to compensate for the dark
spot (shadow). As long as the angle of the incident light remains unchanged then FFC works well.
However when the angle of incidence changes significantly (i.e. when a lens is added) then the
shadow will shift and FFC will makes things worse by not correcting the new shadow (dark spot)
and overcorrecting where the shadow used to be (white spot). While the dark spot can be
potentially cleaned, the white spot is an FFC artifact that can only be corrected by another FFC
calibration.

Cleaning the Sensor Window

Even with careful handling, the sensor window may need cleaning. The following steps describe
various cleaning techniques to clean minor dust particles to accidental finger touches.
Use compressed air to blow off loose particles. This step alone is usually sufficient to clean the
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sensor window. Avoid moving or shaking the compressed air container and use short bursts of
air while moving the camera in the air stream. Agitating the container will cause condensation
to form in the air stream. Long air bursts will chill the sensor window causing more
condensation. Condensation, even when left to dry naturally, will deposit more particles on the
sensor.
When compressed air cannot clean the sensor, Dalsa recommends using lint-free ESD-safe
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cloth wipers that do not contain particles that can scratch the window. The Anticon Gold 9"x 9"
wiper made by Milliken is both ESD safe and suitable for class 100 environments. Another ESD
acceptable wiper is the TX4025 from Texwipe.
• An alternative to ESD-safe cloth wipers is Transplex swabs that have desirable ESD properties.
There are several varieties available from Texwipe. Do not use regular cotton swabs, since
these can introduce static charge to the window surface.
Wipe the window carefully and slowly when using these products.
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56 • Additional Reference Information
Linea CL Series Camera