Editing STDF and text datalogs: Is this a safe practice in production?

We recently received a support ticket asking why a certain text datalog is not uploading into the yield management system database. After a review, we discovered that the text datalog had been changed slightly. For certain fields, the expected tab character became spaces. We later learned that engineers as well as operators and technicians can edit the text datalog files manually.

In certain factories, one can also edit STDF files given that an STDF editor is available.

While convenient, allowing any user to edit any datalog files would be a major QA issue, aside from possibly disrupting the automated STDF and text datalog processing into the yield management system database. Semiconductor companies must ensure that the integrity of the datalogs is maintained. If a mistake is made during processing, the procedure should be to repeat the processing with minimum waste of time and resources but still maintaining the integrity of the datalog files.

Unfortunately, the tester systems themselves may not be capable of restricting users to read-only mode for datalog files so the best a company may be able to do is disallow manual editing of any datalogs and make sure operators, engineers and technicians adhere to this policy. If manual editing has to be done, it should only be allowed for special occurrences and only certain persons knowledgeable about the file format and the potential effect of such editing on the automated data processing should be authorized to do it.

Editing a datalog file is not a safe practice in production and it could be a source of quality issues as well as data processing issues on the yield management system. Semiconductor companies should ensure policies and controls are in place to prevent such practice.