Hardware manual

Rev. 3.0, 09/98, page 263 of 361
14.3.4 Erasing of Data
The windowed package enables data to be erased by illuminating the window with ultraviolet
light. Table 14.7 lists the erasing conditions.
Table 14.7 Erasing Conditions
Item Value
Ultraviolet wavelength 253.7 nm
Minimum illumination 15W⋅s/cm
2
The conditions in table 14.7 can be satisfied by placing a 12000µW/cm
2
ultraviolet lamp 2 or 3
centimeters directly above the chip and leaving it on for about 20 minutes.
14.4 Handling of Windowed Packages
(1) Glass Erasing Window: Rubbing the glass erasing window of a windowed package with a
plastic material or touching it with an electrically charged object can create a static charge on the
window surface which may cause the chip to malfunction.
If the erasing window becomes charged, the charge can be neutralized by a short exposure to
ultraviolet light. This returns the chip to its normal condition, but it also reduces the charge stored
in the floating gates of the PROM, so it is recommended that the chip be reprogrammed afterward.
Accumulation of static charge on the window surface can be prevented by the following
precautions:
① When handling the package, ground yourself. Don’t wear gloves. Avoid other possible
sources of static charge.
② Avoid friction between the glass window and plastic or other materials that tend to accumulate
static charge.
③ Be careful when using cooling sprays, since they may have a slight ion content.
④ Cover the window with an ultraviolet-shield label, preferably a label including a conductive
material. Besides protecting the PROM contents from ultraviolet light, the label protects the
chip by distributing static charge uniformly.
(2) Handling after Programming: Fluorescent light and sunlight contain small amounts of
ultraviolet, so prolonged exposure to these types of light can cause programmed data to invert. In
addition, exposure to any type of intense light can induce photoelectric effects that may lead to
chip malfunction. It is recommended that after programming the chip, you cover the erasing
window with a light-proof label (such as an ultraviolet-shield label).