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Method of Diagnosing Intermittent Logic Built-In Self Test Pattern Sequence Dependencies

IP.com Disclosure Number: IPCOM000031167D
Original Publication Date: 2004-Sep-15
Included in the Prior Art Database: 2004-Sep-15
Document File: 4 page(s) / 339K

Publishing Venue

IBM

Abstract

The disclosed invention describes a novel method of diagnosing intermittent logic built-in self test (LBIST) signatures in very large scale integration (VLSI) devices that occur in any Nth loop of the first test sequence being executed.

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Method of Diagnosing Intermittent Logic Built -In Self Test Pattern Sequence Dependencies

The need exists to be able to quickly diagnose intermittent logic built-in self test (LBIST) signatures that occur in any Nth loop of the first test sequence being executed. An intermittent signature that only occurs the first time the test is executed is often a result of an array or logic block not being properly initialized. The problem with diagnosing fails of this nature is that once the test has been executed, the fail will no longer occur, and further diagnostics is not possible. As chips become more complex devices, with more and more arrays mixed with other logic blocks that need to be initialized, the need increases to diagnose problems dealing with initialization.

    The disclosed invention consists of two main procedures. The first procedure is used to determine all the failing stumps channels on the device (Fig. 1). The second procedure is used to find all the failing latches within each failing stumps channel (Fig. 2
). The steps in each procedure are itemized below.

Find all failing stumps channels (refer to Fig. 1)
1) Power the device on (i.e., to 1.3V)
2) Disable compression of all stumps channels into the multiple input shift registers (MISRs) by setting misr_mask latches = 1
3) For each stumps channel on the device:

a) Enable compression of the stumps channel into the MISR by setting misr_mask_x latch = 0 b) Execute the LBIST test twice (this will result in a stable ("golden") signature)

c) Read and record the stable signature as a reference point

d) Power the device off (i.e., to 0.0V)

e) Power the device on (i.e., to 1.3V) (This should cause the instability to occur again if this stumps is causing the fail). f) Execute the LBIST test once (This will result in an unstable ("non-golden") signature if this stumps is causing the fail)
g) Read and record the signature
h) Repeat steps (d) - (g) 5-10 times
i) Compare all signatures from (c) and (g).

     If any of the signatures mismatch, the intermittent fail is being caused by this stumps channel.

Go to 'Find all failing latches' for this stumps channel.

     If all the signatures match, the fail is not being caused by this stumps channel.
j) Disable compression of the current stumps channel into the MISR by setting misr_mask_x latch = 1

Find all failing latches (refer to Fig. 2) (Note: T...