- FAQ -
The PIC's Poor Life Expectancy

by


Harvey
 Twyman
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    Question:
      I've been informed that I won't be able to reprogram my EPROM based PIC Microcontroller more than 4 or 5 times. Is this true?

    Reply:
      This does seem to be the case according to my experiences I'm afraid. I have 2 theories:-

      • Over Exposure to UV Light
      • Electro Static Damage

        •  
    • Over Exposure to UV Light:

      • My theory for their short PROGRAM/ERASE LIFE CYCLE is due to the fact that they seem to have a SMALL WINDOW. If you look through the device's window you can see that the silicon is actually LARGER than the window itself.

      Ordinary EPROMs for example have a much LARGER window to allow the ULTRA VIOLET light to penertrate the WHOLE device.

      PICs seem to need a much LONGER time under the UV light to erase them. Therefore combine this with the fact of them having small windows I've come to the conclusion that PART of the PIC's memory is IN-THE-SHADE. Therefore THESE areas will need a much LONGER UV EXPOSURE to erase the data completely.

      However, the areas of the device that ARE in DIRECT LIGHT are getting DAMAGED due to OVER EXPOSURE causing SUN BURN effects. Hense the SHORT LIFE EXPECTANCTANCY.

      The Windows are made from QUARTZ glass which posess a FILTERING characteristic that only allows UV light through. This is designed to REDUCE the chance of ERASURE in normal daylight during programming etc. However if an UNCOVERED device is exposed to SUN LIGHT, erasure will start occuring in just a FEW MINUTES!
       

    • Electro Static Damage:

      • My observation is that PIC devices are EXTREMELY SENSITIVE to Electro Static Damage. Just walking across a room from the Programmer to your hardware with the device legs exposed to the air will STATICALLY charge them to DANGEROUS LEVELS!

      Thus when the device next comes into contact with an EARTH,discharge occurs and DAMAGES the device. The damage isn't necessarily FATAL initially but prolonged exposure to this treatment WILL be.
       

    • A Static Protection Technique:

      • During transportation of the device, KEEP the device's LEGS SQUEEZED into the PALM OF YOUR HAND. Your skin is always DAMP so this keeps the device pins safely DISCHARGED.