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PICList Thread
'UV Pic problem (use a hairdryer!!!)'
1996\12\18@172400 by Tim Kerby

picon face
I have also had this problem on two 16c74 (not 74A) chips.
When new they took 10 mins to erase but now they take oner 1 hour.
Microchip claim it is the eraser and the uv bulbs at £20 each need to be
replaced every few hours.
Personally, I think they are passing off the blame but I have found a
solution.  I have been using an industrial turbine to blast the eraser with
cool air while it erases, keeping the chips cool.  I had noticed that the
chips were heating up and this gave me the idea.  My erase time is now under
30 mins with the same chips.  Whatever it does it certainly helps - try a
hairdryer on cold setting, my turbine is only slightly more powerful.  I
would be very interested to know how the devices erase - to heat generates
by the light or by light alone.

Hope this helps - some comment from microchip would be nice

Note: this message is totally serious unlike some I have recently seen about
16c84 code protection.
     Try it.  It might help.

Tim


A happy Christmas to all who read this.

1996\12\19@001218 by tjaart

flavicon
face
Tim Kerby wrote:
>
> I have also had this problem on two 16c74 (not 74A) chips.
> When new they took 10 mins to erase but now they take oner 1 hour.
> Microchip claim it is the eraser and the uv bulbs at #20 each need to be
> replaced every few hours.
> Personally, I think they are passing off the blame but I have found a
> solution.  I have been using an industrial turbine to blast the eraser with
> cool air while it erases, keeping the chips cool.  I had noticed that the
> chips were heating up and this gave me the idea.  My erase time is now under
> 30 mins with the same chips.  Whatever it does it certainly helps - try a
> hairdryer on cold setting, my turbine is only slightly more powerful.  I
> would be very interested to know how the devices erase - to heat generates
> by the light or by light alone.
>

I built a UV eraser with a 6W Philips tube and have used it so many
times
on a 16c71 that the paint has started to fade. I have often wondered why
people complain about the erase times for the windowed parts, but you
have
just answered that question. The light is housed in a polished
aluminimum
box and runs very cool. I have never had to wait longer than 2 minutes
for
a PIC to erase.

--
Friendly Regards

Tjaart van der Walt
______________________________________________________________
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'UV Pic problem (use a hairdryer!!!)'
1997\02\03@235215 by Brian Boles
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face
The following is from our EPROM guy here.....


If anything, a hot chip will erase faster.  We use a 250 deg.C bake to
test the retention of our EPROM cells.  If a wafer is subjected to a
450 deg.C bake, it will erase the chip without any light at all.
Erasing occurs when enough energy is imparted to the stored electrons
on the floating gate to cause them to leave the poly 1 lattice.  The
e-field created by the stored charge then propels the electron back to
the silicon surface.  As erasing continues, the e-field gets weaker.
This creates an erase time profile that is an exponential decay. All
that maters is that you have enough energy from heat or light to
continue to remove electrons from the poly 1 lattice.


The actual effect you are be witnessing may be due to the UV bulb. I
believe that keeping the bulb cool will increase the light intensity thus
generating more lumens and thus erasing faster.

Rgds, Brian.

1997\02\04@000849 by Mike

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face
>If anything, a hot chip will erase faster.  We use a 250 deg.C bake to
>test the retention of our EPROM cells.  If a wafer is subjected to a
>450 deg.C bake, it will erase the chip without any light at all.
>Erasing occurs when enough energy is imparted to the stored electrons
>on the floating gate to cause them to leave the poly 1 lattice.  The
>e-field created by the stored charge then propels the electron back to
>the silicon surface.  As erasing continues, the e-field gets weaker.
>This creates an erase time profile that is an exponential decay. All
>that maters is that you have enough energy from heat or light to
>continue to remove electrons from the poly 1 lattice.

How often can a chip be subjected to 250 Deg ? I'm asking this in
reference to normal 27C256 EPROMs as well as PICs.

>The actual effect you are be witnessing may be due to the UV bulb. I
>believe that keeping the bulb cool will increase the light intensity thus
>generating more lumens and thus erasing faster.

=========================================================================

Does this mean we could erase OTP parts (the plastic ones) by heat alone
as long as we don't melt the plastic ? ? ? ? ? ? ?

=========================================================================

Before I had a ordinary UV eraser - I used a UV Suntan lamp which also had
a series connected IR source. The output was prodigious - by inverting it
over the EPROM it would take about 10 seconds to erase and the chip was also
sizzle hot - I now see that it erasure was probably also due to the IR !

Rgds

Mike
.....erazmusKILLspamspam@spam@wantree.com.au
Perth, Western Australia

1997\02\04@081901 by Miller, Steve

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face
Brian wrote:

>If anything, a hot chip will erase faster.  We use a 250 deg.C bake to
>test the retention of our EPROM cells.  If a wafer is subjected to a
>450 deg.C bake, it will erase the chip without any light at all.
>Erasing occurs when enough energy is imparted to the stored electrons
>on the floating gate to cause them to leave the poly 1 lattice.  The
>e-field created by the stored charge then propels the electron back to
>the silicon surface.  As erasing continues, the e-field gets weaker.
>This creates an erase time profile that is an exponential decay. All
>that maters is that you have enough energy from heat or light to
>continue to remove electrons from the poly 1 lattice.


>Rgds, Brian.

Does this mean that we can subject OTP parts to 842 degrees F (450 C)
and erase them?
I do some work with PICs and a lot of work with ZILOG.  I go through a
ton of ZILOG OTPs in development.  I would be happy to be able to erase
and reuse just a fraction of these chips.
If this is possible, please post the bake times required.  Thanks.

----- Steve

1997\02\04@171016 by William Chops Westfield

face picon face
   >  We use a 250 deg.C bake to
   >test the retention of our EPROM cells.  If a wafer is subjected to a
   >450 deg.C bake, it will erase the chip without any light at all.

   Does this mean that we can subject OTP parts to 842 degrees F (450 C)
   and erase them?

Sure, except that if you do this with a finished chip instead of a wafer,
the package will burn and the leadwires (or their connecting "solder") will
melt.

:-)
BillW

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