Scan-Based Testing: The Only Practical Solution for Testing ASIC/Consumer Products

Over the last 2-3 years, there has been a major change in the IC industry from being predominantly “functionalbased testing” to being predominantly “scan-based testing” (for new design starts). As recently as 2-3 years ago, the topic of panels was “Is scan-based testing feasible for all products?” The question has now changed to “Can we completely avoid functional testing?” I believe the same trends that are driving companies toward scan-based testing will also drive them to completely avoid functional-based testing. The advantages of structural testing cannot be fully exploited unless at-speed functional testing is avoided. The issues that are driving companies away from functional testing include: • Cost of the ATE required to apply at-speed functional tests. (full speed, full-pincount) The motivation to use “cheap, DFT testers” is quickly growing and is tightly linked to scan-based testing. Additionally, multi-DUT testing (enabled by scan testing) can dramatically reduce the cost of testing. • Test development time & effect. It may take months of test development activity to fully debug and optimize functional tests. Most products cannot accept this time-to-market impact. • Lack of a migration path to built-in self-test (BIST). Some companies are moving toward logic BIST and would like test methods (like scan testing) that can be extended to provide a BIST solution. • Functional testing often requires empirical learning (often based on feedback from the field) that takes months to develop. For many products, this long development time is not acceptable. • Lack of fast/accurate fault diagnostics. In the future, all test methods MUST provide support for defect localization. Many companies that have experience with scan-based testing have found that the vast majority of defects can be detected with structural testing – but there are still a small percentage of faults that apparently require functional test. In order to completely avoid functional testing, the industry will develop a suite of structural test methods that enable scan-based testing to meet product quality and reliability requirements. In the future, the number of faults detectable only with functional testing will be driven so low so that the additional cost of functional test will not longer be justified.