Piranha HN RoHS User Manual
Teledyne DALSA
03-032-20135-00
61
Appendix C: CCD Handling
Instructions
Electrostatic Discharge and the CCD Sensor
Cameras contain charge-coupled device (CCD) image sensors, which are metal oxide semiconductor
(MOS) devices and are susceptible to damage from electrostatic discharge (ESD).
Electrostatic charge introduced to the sensor window surface can induce charge buildup on the underside
of the window that cannot be readily dissipated by the dry nitrogen gas in the sensor package cavity.
When charge buildup occurs, surface-gated photodiodes (SGPDs) may exhibit higher image lag. Some
SGPD sensors, such as the IL-P4 and the IT-P4 used in the Piranha2 cameras, may also exhibit a highly
non-uniform response when affected by charge buildup, with some pixels displaying a much higher
response when the sensor is exposed to uniform illumination. The charge normally dissipates within 24
hours and the sensor returns to normal operation.
WARNING:
Charge buildup will affect the camera’s flat-field correction calibration. To avoid an
erroneous calibration, ensure that you perform flat-field correction only after a charge buildup has
dissipated over 24 hours.
Protecting Against Dust, Oil and Scratches
The CCD window is part of the optical path and should be handled like other optical components, with
extreme care.
Dust can obscure pixels, producing dark patches on the sensor response. Dust is most visible when the
illumination is collimated. The dark patches shift position as the angle of illumination changes. Dust is
normally not visible when the sensor is positioned at the exit port of an integrating sphere, where the
illumination is diffuse.
Dust can normally be removed by blowing the window surface using a compressed air blower, unless the
dust particles are being held by an electrostatic charge, in which case either an ionized air blower or wet
cleaning is necessary.
Oil is usually introduced during handling. Touching the surface of the window barehanded will leave
oily residues. Using rubber fingercots and rubber gloves can prevent oil contamination. However, the
friction between the rubber and the window may produce electrostatic charge that may damage the
sensor. To avoid ESD damage and to avoid introducing oily residues, only hold the sensor from the edges
of the ceramic package and avoid touching the sensor pins and the window.
Scratches can be caused by improper handling, cleaning or storage of the sensor. Vacuum picking tools
should not come in contact with the window surface. CCDs should not be stored in containers where they
are not properly secured and can slide against the container.
Scratches diffract incident illumination. When exposed to uniform illumination, a sensor with a scratched
window will normally have brighter pixels adjacent to darker pixels. The location of these pixels changes
with the angle of illumination.
