Chapter 2 Test Specification Process

1. Chapter 2 Test Specification Process

2. Device Specification Sheet • Purpose • Design Specification • Determine functionality of design • Test List Generation • Insure device lives up to spec sheet claims • Communication • Verify that device is appropriate for the end application • Flexible Document • Ownership - catalog or custom? • Allows changes to specifications • Avoid ambiguities • Late Changes in Specification Sheet Indicates Poor Organization

3. Device Specification Sheet • Structure • Feature Summary • Quick look at functionality of chip • Principles of Operation • Detailed device function • guaranteed by functional or parametric test program • Absolute Maximum Ratings • Failure limits of chip • not critical to a test engineer • Electrical Specifications • Core of parametric tests • Test conditions are listed as notes • MAX, MIN, TYP, guaranteed by design

4. Device Specification Sheet • Structure • Timing Diagrams • Critical to test program development • Manually generated for frequency synchronization • Application Information • Aids customer in designing end application • Functional block diagram • shows top level representation of device function • Characterization Data • Data collected during testing i.e. parameter histograms • Circuit Schematics / Die Layout • Device functional pin representation and layout

5. Generating the Test Plan • To Plan or Not to Plan? • Shoot From the Hip Approach • Non-optimized • May cause a device to be Non-testable • Planned Testing • Allows early interaction between design and test engineers • Identification of non-testable functions • Synchronization of clocking schemes • Tester hardware identification • identify tester hardware deficiencies

6. Generating the Test Plan • Purpose of a Test Plan • Less Formal than a Device Data Sheet • Test Engineers Roadmap to Generate Test Program • Official Communication Tool • Test engineer • Design engineer • Product engineer • Customer

7. Generating the Test Plan • Structure of a Test Plan • Device Background not Found in Data Sheet • Special Test Requirements • Explanation of the Purpose of Each Test • Assumptions regarding particular test and why • Hardware Setup Diagram for each Test • All Documentation should be Tester Independent • Tester Specific Information should be added as a separate section

8. Generating the Test Plan • Design Specifications vs. Production Test Specifications • Production Testing is very Time Critical!! • Not all Design Parameters need to be Tested in Production • Identification of Critical Test Parameters • Minimum Testing to Reduce Test Time while Insuring Device Functionality

9. Generating the Test Plan • Converting the Spec Sheet into a Test Plan • Infinite Permutations of Possible Tests Indicated by Data Sheet • Caution is necessary due to signal interactions • How does the Test Engineer know which Tests are needed in Production Testing?? • For each sentence in the device description, there should be at least one test that verifies the claim • Max. and Min. electrical specifications must all be verified • Worst case failure modes are often used to limit the number of tests required to verify the device function • Extensive testing of a device will reveal more tests which need to be added or can be omitted

10. Components of a Test Plan • Test Program Structure • Coded Version of the Test Plan • Waveform creation / Tester initializations • Calibrations • Continuity • DC parametric tests • AC parametric tests • Functional tests / Digital patterns • Digital timing tests • Test sequence control • Test limits • Binning control

11. Components of a Test Plan • Test Code and Digital Patterns • Test Code • Controls order and timing - does not create timing signal • instrument settings • signal generation • signal measurements • Digital Patterns • Consists of groups of data called vectors • drive data for each pin • expect data for each pin • Vectors are sent out at a regular rate “bit cell rate” • Tight frequency control is critical • Allow looping and branching of vectors

12. Components of a Test Plan • Binning • Grading of Devices into “Bins” • Performed by handler • Pass or Fail • Continuity Fail - could indicate handler error • Different grades of device based upon performance • 100 MHz chip vs 120 MHz chip • Fast Binning • Device is rejected as soon as it fail first test • Reduces test time

13. Components of a Test Plan • Test Sequence Control • Sequencers • C program coded • Graphical user interface controlled • Waveform Calculations and Other Initializations • Pre-computed Waveforms • Performed only once when the program is loaded • tl_init function in Teradyne architecture • Reset of tester Instrumentation to Default State • Focussed calibrations • Checkers

14. Components of a Test Plan • Focussed Calibrations • Tester does not have Sufficient Accuracy for a Test • Determines the Inaccuracy of a Fast Instrument using Slower, more Accurate Instrumentation • Software compensation allows a more accurate result. • Not absolutely perfect - still has the inaccuracy of the more accurate instrumentation • Software Calibration due to DIB Design • DIB Checkers • Checks for Faulty Op-Amps, Comparators, and Relays often placed on the DIB • Avoids running thousands of devices on a bad DIB board

15. Components of a Test Plan • Characterization Code • Used for Characterization of First Production Devices • Very Thorough Testing to Identify and Correct Marginal Portions of the Design • Simulation Code • Added to Test Program to Allow Mathematical Routines to be Verified • Offline Debugging of Test Code • Avoids wasting valuable tester time

16. Components of a Test Plan • Debuggability • Debugging Consumes 20% of a Test Engineers Week • Test code bugs • Hardware errors • Correlation errors • Intermittent failures • DIB errors • Broken tester modules • Design Debugging • Ability to modify code to isolate a device function • Run experiments for designers or customers to verify device