An introduction to STDF

If you are new to the semiconductor industry then you may want to learn more about STDF. STDF stands for “Standard Test Data Format” and it was originally developed  between some of the largest test equipment vendors and semiconductor companies. 

STDF is a binary format defined by the STDF V4 specification and is different to the spreadsheets and tables you are probably used to working with.

ATDF is an ASCII version of STDF and is readable in any text viewer. The binary format is faster for the tester computer to write as there is no need to convert any number or letter formats. As test time effects the cost of the product, it is often better to use the format that takes the least time to write.

The formats are defined and explained in the relevant specifications. However, this blog offers a simplified introduction to the formats. The structure from here on is largely the same between STDF and ATDF. Our examples below are ATDF because a string of 1s and 0s is not very easy to understand.

It’s a good idea to remember that STDF is a stream of data. It starts with the lot level information records such as MIR and SDR. Then any number of tests, dice (devices or parts) and results can be added before the file is closed. The advantage is that the file can be directly written during the automated testing. Also, a partial file may still contain usable data.

The format is organised by defined record types. Each record type is defined in the specifications as to the type of data contained, the size limit of that data and the data type of the field. In general yieldHUB fields directly follow the STDF V4 specification.

Here is an overview of the format to demonstrate how it works. The format is made up of sets of records to organise the data. For a complete and fully compatible file, many record types must be present. Having records missing is one of the most common issues with STDF data.

Global meta data

• Global record for the file: FAR

• Global record for the lot: MIR

• Pin map record: PMR [when using MPR]

• Global site description: SDR

• Wafer configuration: WCR [when testing wafers]

Test data when testing wafers

For each wafer

• Record for first wafer: WIR
  

For each part

• Record for the die overall: PIR

For each test

• Results for parametric tests: PTR [one for each numeric limit test in your program]

• Results for functional tests: FTR [one for each pass/fail test in your program]

• Multi-pin parametric test result: MPR [contains an array of data where the test name and limits are the same for each result]

• Final result from die: PRR

• Final results from wafer: WRR

Test data without wafer settings configured

For each part

• Record for the part overall: PIR

For each test

• Results for parametric tests: PTR [one for each numeric limit test in your program]

• Results for functional tests: FTR [one for each pass/fail test in your program]

• Multi-pin parametric test result: MPR [contains an array of data where the test name and limits are the same for each result]

• Final result from part: PRR

Final global data

• Summary for each test in job plan: TSR

• Count of parts placed in each HW bin: HBR

• Count of parts placed in each SW bin: SBR

• Part count totals: PCR

• Overall summary: MRR

MPR Extended capability

With the yieldHUB platform, product and test engineers can extend the capability of MPR. This test record type was intended to be used with the pins of the device in cases, such as continuity testing or input leakage. However, this has been extended to be used for any repeated testing where the test name is the same and the limits are the same.

The key is to expand the Pin Map Record to cover all of the index required in each array. For example, pin numbers 1 to 99 could be used for a frequency sweep where the pin numbers correspond to frequency values. Whereas, pin numbers 100 to 199 could be used for a voltage sweep.

Additionally, these pin numbers could be used for any physically repeated structure on the die. In that case, yieldHUB’s unique capability to input XY locations for each “pin” allows the results to be mapped across the die, across the wafer and across the batch of wafers. You can read more about this in the case study here.

An example ATDF

You can see each record type starts on a new line. There are delimiters, ie. the “|” bar character between each field for the record type. The example above is for wafer sort and contains the WIR record. The second example below is for the final test. Final test datalogs don’t have a WIR record in the STDF file.

Please note: This blog is only intended to provide a simple introduction to STDF and ATDF data formats.