In-House Testing at CSS
Testing is a critical aspect in both the development and production of mixed-signal ASICs. At CSS, we typically develop the test program and conduct both prototype evaluation testing and production testing for all custom ASICs "in-house". This is a little unusual since most ASIC development houses subcontract this work. This has been our policy from the start and we feel it provides our customers real advantages. The advantages include the following:
- Faster ASIC prototype evaluation: Our wafer probers are literally at our design engineer's fingertips. When a new ASIC arrives from the foundry, an in-depth analysis of its performance starts immediately - by the person best qualified for this work - the ASIC designer.
- Efficient ASIC performance feedback: Wafers are tested at CSS not only in the pass/fail mode - we also gather parametric data for in-depth analysis of the ASIC performance on each processed wafer. By testing for "Key Process Parameters" in-house, at the wafer level, we are able to quickly check to assure that the process is maintaining our required "6-Sigma" performance level.
- Reduced cost: Mixed-Signal ASICs are difficult (and usually expensive) to test - primarily due to the analog circuits. Analog testing can take a long time and on an expensive general purpose tester this gets very costly. Our custom PC-based testers are not as expensive as large general purpose testers - so wecan afford to spend all the time necessary to thoroughly test analog circuits without the usual high cost.
At CSS the ASIC test program development starts during the initial design. Our design engineers subscribe to the "design-for-test" principle. Using simple multiplexers and efficient serial interfaces, access to internal ASIC nodes is made available. This allows for very efficient test program developments.
Following the design, while the ASIC prototype is in initial fabrication, the test development engineers at CSS complete a test program for evaluation of the ASIC at the wafer level. This program is set-up to allow for more in-depth analysis of the ASIC performance than would be practical for an off-site tester.
After the ASIC prototype has completed evaluation, the production test program is completed. The in-depth analysis parts of the program are removed and the program is optimized for efficient production testing. However, the program still includes the parametric tests mentioned earlier as well as the standard pass/fail tests. Both wafer testing (wafer sort) and package testing are included in the production level test program.
We feel this approach results in very real benefits for our customers. In essence, it provides CSS the ability to provide the testing capabilities our customers needs in an efficient and cost effective manner.
ASIC test development is just part of the ASIC development process. For a more complete outline of the CSS approach to ASIC development, click on this link to our website: Custom ASIC Development - The Process.