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Chapter 8 Appendices
132
EPROM Versions
8-1-3 Erasing Written Data in Windowed Packages
In an internal EPROM with windowed packaging, data is erased("0" → "1")
when UV light at 253.7nm permeates the window to irradiate the chip.
The recommended exposure is 10W · s/cm
2
. This coverage can be achieved
by using a commercial UV lamp positioned 2 to 3cm above the package for
15-20 minutes(when the illumination intensity of the package surface
is12000µW/cm
2
). Remove any filters attached to the lamp. By installing a
mirrored reflector plate in the lamp, illumination intensity will increase by
afactor of 1.4 to 1.8, decreasing the erasure time.
If the window becomes dirty with oil, adhesive, etc., UV light permeability will
decrease, causing the erasure time to increase considerably. If this
happens, clean with alcohol or another solvent that will not harm the
package. The recommended above provides sufficient leeway, with several
times the amount of time it takes to erase all the bits. However, this value
will reliably erase data over all temperature and voltage ranges, and should
not be altered. The level of illumination should be regularly checked and the
lamp operation verified.
Erasure begins when EPROM is exposed to light with a wavelength shorter
than 400nm. Since fluorescent light and sunlight have wavelengths in this
range, exposure to these light sources for extended periods of time could
cause inadvertant erasure. To prevent this, cover the window with an
opaque label.
Data is not erased at wavelengths longer than 400 to 500nm. However,
because of typical semiconductor characteristics, the circuit may
malfunction if the chip is exposed to an extremely high illumination intensity.
The chip will operate normally if this exposure is stopped. However, for
areas where it is continuous, take necessary precautions.
(PX-AP101C11-SDC, PX-AP101C11-FBC)