Padding of Multicycle Broadside and Skewed-Load Tests

Abstract

Multicycle tests achieve test compaction by increasing the number of clock cycles between scan operations and reducing the number of tests. Tests in a compact multicycle test set typically have different numbers of clock cycles between their scan operations. This creates an opportunity to improve the test set by increasing the numbers of clock cycles between the scan operations of the tests, without increasing the number of tests and without exceeding a bound $L$ on the number of clock cycles. Motivated by this observation, this paper studies the padding of multicycle broadside and skewed-load tests for transition faults. After padding, all the tests have $L$ clock cycles between their scan operations. This paper makes several observations and defines new types of multicycle tests that are supported by commercial tools to allow padding to be performed without losing fault coverage. The new types of tests can be used for achieving a higher fault coverage, further test compaction, or an improved test set quality within the bound $L$ . This paper develops padding procedures and presents experimental results for benchmark circuits to demonstrate these effects.