Motivation:
- Defective devices deviate from normal distribution and Increased variance causes the bell curve to be distorted.
- Using a single limit results in a loss of quality or a reduction in yield.
- To overcome this the data of each individual die needs to be looked at
- Explore the advantages of real time advanced measurement strategies:
- Lot-to-lot / die-to-die dispersion independence decision making
- ATE set-up dispersion independence
- Explore the advantages of real time data processing features and evaluate the applicability of advanced real time screening algorithms in production test with a focus on:
- Ability to on-the-fly recalculate decision limits
- Adaptive limit setting
- Test program independent limit setting
Project Objectives:
- Development of a die-to-die dispersion independent DSM Test Strategy based on the Current Ratios IDDQ methodology
- Evaluate DSM IDDQ application within production test constraints
- Development and realization of Setup and subcontractor independent test programs
Module and Test platform
- QD-1011 Advanced IDDQ measurement module>
- High speed IDDQ measurement architecture (100µs)
- On-board data processor memory (SRAM & EEPROM)
- Custom Firmware for Current Ratios IDDQ support
- Limits are calculated by the module based on first measurement and on base of 5 Parameters that are programmed into device EEPROM after product characterization, being Spec Limit, Upper Limit Slope, Upper Limit Intercept, Lower Limit Slope, Lower Limit Intercept
- Various test platforms
The Recipe:
- Use ATPG to generate 1000 IDDQ Vectors
- Collect IDDQ data for one device
- Build a histogram and verify Normal Distribution
- Perform Temperature analysis on one device from 0C to 100C to validate IDDQ vector quality
- Characterize split lot material
- Extract equations for Max and o in terms of Min
- Set Upper and lower limits
- Program the IDD modules by loading the parameters for the Current Ratios monitor firmware
- Run test on 100 devices to ensure that the modules are correctly programmed
- Send modules and test program to Production test facility
Test Vehicles:
- The strategy was validated using 2 devices running in production.
Conclusion:
A die-to-die and test set-up independent DSM strategy based on Current Ratios was developed & successfully implemented in a production test environment. SMA experienced a significant improvement of the production quality, test subcontractor independence and a reduction of the overall test time. These achievements were only made possible through the use of an advanced IDDQ measurement module.
References:
- Ackerman R. , Doing More with Less: A Recipe for Rapid IDDQ Development, Digest of papers of the 9th IEEE European Test Symposium ETS2004, pp. , 273-278, May 2004, Ajaccio, Corsica, France.