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Pass SEMI Checksum Despite Misreading of SEMI OCR

Explanation of incorrect checksum behavior in OCR for Wafer ID and how to fix

15/09/2024

Details

Matter:

When reading a SEMI OCR, SEMI checksum is passed even though it is obviously misread.

Probable Causes:

  • SEMI checksum can be passed if it misreads more than one character, which is SEMI checksum spec.
  • Next, SEMI checksum is passed even though it is misread, which actually occurred.
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There are no actual images, but these are other examples:

  • Incorrect: CP4FU248SEF7(SEMI checksum passed)
    Correct: CL4FU248SEE7
  • Incorrect: MLF4U152WAD7(SEMI checksum passed)
    Correct: M6E4U152WAD7

Solution:

  • If you specify "SEMI with Virtual" instead of "SEMI" in the "Checksum" field, the acceptance of Virtual checksum will be reliable.
  • By setting the "Character Threshold" item to a higher value, you can strictly judge against erroneous characters.