In WATS, a UUT report status may be Passed, Failed, Error or Terminated. When calculating Yield (First Pass Yield (FPY), Second Pass Yield, etc.), all none Passed (Failed, Error or Terminated) indicates poor Yield.
Example: 100 Units is tested, 90 Passed, 5 Failed and 5 Error. FPY is 90%.
Starting from WATS version 18.1, the algorithm calculating Yield and Statistics, will include Error and Terminated STEP STATUS into the calculation of the "Step Caused UUT Failed/Error/Terminated" flag.
All none Passed UUT Reports should have one (1) Step Caused UUT Failure/Error/Terminated as example below.
This seems straight forward, however there are some considerations to be aware of.
TestStand (TS) allow multiple options to handle test flow and execution. When a test is Failed, the "normal" procedure is that this step also fails the calling step(s) (Sequence Call) and the UUT Report. In addition to STEP STATUS, TS also add a flag/property named "StepCausedSequenceFailure".
- TS allow you to edit the option "Step Failure Causes Sequence Failure" (Run Options). When unchecked, step status may be Failed, but "StepCausedSequenceFailure" is FALSE.
- When a step/sequence/UUT is Error or Terminated, TS does NOT set the "StepCausedSequenceFailure" flag.
- TS allow you to Disable "Result Recording" of any step (may cause a step that is Failed, Error or Terminated not to be included in the WATS report).
- If a Sequence is Terminated (by operator or automatic), a step indicating where is was terminated may not be included in the report by default.
To handle these different scenarios, the WATS algorithm has a built in intelligence using a combination of STEP STATUS and the "StepCausedSequenceFailure" flag to "at best" flag the one step per UUT report that caused none Passed.
In most cases, WATS uses STEP STATUS to set the "Step Caused UUT Failed/Error/Terminated" flag. It is important to:
- Log steps that indicates Failed, Error, Terminated
- Set same status on all calling steps in the hierarchy (or use the "automatic" mode in the toolkit/API) .
For advanced users, the "StepCausedSequenceFailure" flag can also be utilized in the WSXF/WSTF converters and the client API.