STDF (Standard Test Data Format)

Notes

Originally defined by Teradyne and now a de facto industry standard; STDF V4 remains the version everyone parses.

Overview

STDF, short for Standard Test Data Format, is a binary file format in which automatic test equipment records the results of testing each chip, from lot and wafer details down to individual measurements and the bin each part is sorted into. Originally developed by Teradyne, it became a de facto standard across tester makers and test data software. STDF files are the raw input for yield analysis, outlier screening and adaptive test.

How it works

An STDF file is a stream of typed records, each with defined fields. It opens with records describing the file and the lot, such as the tester and test program, and for wafer test a record describing the wafer layout. Each wafer and each part then has records that mark its start, carry its results and close with a part result giving pass or fail, hardware and software bin numbers and, at wafer sort, its x and y position. Parametric test records hold a measured value against its limits, functional test records hold pass or fail details, and multiple-pin records hold a value per pin. Summary records at the end give counts per bin and part totals.

Records are written as testing proceeds, so a file cut short may still hold usable data, and a binary format is quick for the tester to write, which matters when test time costs money. The trade-off is that files cannot be read by eye; an ASCII counterpart, ATDF, carries the same structure, and many open and commercial tools read STDF directly. Missing records are among the most common practical problems.

The current base is version 4, with a 2007 revision. Teradyne granted SEMI a royalty-free licence to the format so that industry groups could extend it, and an extension for logging memory fail data was developed through a SEMI working group.

Examples

• A wafer sort STDF file whose part results, with die coordinates and bins, are turned into a wafer map.
• Parametric results from final test fed into an outlier screen that rebins parts far from the population.
• Bin summaries compared across testers to spot one tester yielding lower than the others.
• An STDF file converted to ATDF so that an engineer can inspect a suspect record in a text editor.

Why it matters

Test data, yield and outlier screening engineers rely on STDF daily, as do the ATE software engineers who generate it and the data platform teams who load it into databases. It is the shared language between testers from different makers and the analytics that decide what ships, so a missing or wrong field can make a wafer map or an outlier screen wrong too.

Related terms

• Outlier screening
• PAT
• Adaptive test
• Binning

Where it appears on the Hub

Used on 10 pages of the Hub. In each group, the pages that mention it most come first.