PROCESS FOR IDENTIFYING THE LOCATION OF A BREAK IN A SCAN CHAIN IN REAL TIME

• US 20080141085A1
• Filed: 12/12/2006
• Published: 06/12/2008
• Est. Priority Date: 12/12/2006
• Status: Active Grant

• Current Assignee: Advantest Corporation
• Original Assignee: Inovys Corp. (Advantest Corporation)
• Inventors: Ishii, Takehiko, Chan, Gerald S., Dokken, Richard C.
• Granted Patent: US 7,568,139 B2
• Time in Patent Office: Days
• US Class Current: 714/726
• CPC Class Codes: G01R 31/318525 Test of flip-flops or latches
• CPC Class Codes: G01R 31/318569 Error indication, logging circuits

Abstract

A process for identifying the location of a break in a scan chain in real time as fail data is collected from a tester. Processing a test pattern before applying it on a tester provides a signature enabling a method for a tester to identify a scan cell which is stuck during the time the tester is operating on a device under test rather than accumulating voluminous test data sets for delayed offline analysis.

Claims

1. A method for determining the position of a blockage, B, in a scan chain, M, of N scan cells, wherein B is a number ranging from zero through N, wherein zero represents no blockage at all, and one is the first cell shifted out in a scan chain and N is the last cell shifted out in a scan chain, the method comprising the steps of

annotating a record for each scan cell with at least one of Z no fails, V all fails, T for toggling and S for stuck;

determining that a scan chain is blocked if the last cell in the scan chain is annotated S,

determining that a scan chain is not blocked if every cell in the scan chain is at least one of Z, V, and T, in which case B is set to zero,

computing B the number of consecutive cells from the first scan cell in a chain annotated at least one of Z, V, and T until encountering an initial scan cell annotated S;

wherein a scan cell record is annotated to be toggling T if the number of low failures is less than the number of low strobes and the number of high failures is less than the number of high strobes,

wherein a scan cell record is annotated to be stuck S if the number of low strobes is greater than zero and the number of low failures is equal to the number of low strobes and a number of high failures is equal to zero,

wherein a scan cell record is annotated to be stuck S if the number of high strobes is greater than zero and a number of high failures is equal to the number of low strobes and the number of low failures is equal to zero,

wherein a scan cell record is annotated to be zero Z if there are no failures,

wherein a scan cell record is annotated to be V if every strobe results in a failure, and

wherein strobes are presented H'"'"'s and L'"'"'s in the test patterns that are output from the ATPG tools as ASCII files.

2. A method for determining the position of a blockage, B, in a scan chain, M, of N scan cells, wherein B is a number ranging from zero through N, wherein zero represents no blockage at all, and one is the first cell shifted out in a scan chain and N is the last cell shifted out in a scan chain, the method comprising the steps of

determining that a scan chain is blocked if the record for a last cell in the scan chain is annotated S;

computing N minus B, the number of consecutive cells from the record for a last scan cell in a chain annotated S until encountering a record for a final cell not annotated S; and

recording an S into a record for a scan cell on one of the following conditions;

if the number of low strobes is greater than zero and the number of low failures is equal to the number of low strobes and a number of high failures is equal to zero, and

if the number of high strobes is greater than zero and a number of high failures is equal to the number of high strobes and the number of low failures is equal to zero.

3. The method of claim 2 further comprising the steps of annotating a record for each scan cell with at least one of Z no fails, V all fails, T for toggling and S for stuck;

and

determining that a scan chain is not blocked if every cell in the scan chain is at least one of Z, V, and T, in which case B is set to zero.

4. The method of claim 2 further comprising the step of annotating a record for a scan cell as follows:

annotating a record for a scan cell to be toggling T if the number of low failures is less than the number of low strobes and the number of high failures is less than the number of high strobes,

annotating a record for a scan cell to be stuck S if the number of low strobes is greater than zero and the number of low failures is equal to the number of low strobes and a number of high failures is equal to zero,

annotating a record for a scan cell to be stuck S if the number of high strobes is greater than zero and a number of high failures is equal to the number of high strobes and the number of low failures is equal to zero.

5. The method of claim 2 further comprising the step of annotating a record for a scan cell as follows:

annotating a record for a scan cell to be zero Z if there are no failures,

annotating a record for a scan cell to be V if every strobe results in a failure

6. The method of claim 2 further comprising

computing B the number of consecutive cells from the first scan cell in a chain annotated at least one of Z, V, and T until encountering an initial scan cell annotated S.

7. The method of claim 2 wherein strobes are presented as H'"'"'s and L'"'"'s in the test patterns that are output from the ATPG tools as ASCII files and wherein the combined number of H'"'"'s and L'"'"'s per scan cell is equal to the number of scan patterns V.

8. A method for enabling a tester to identify the location of a break in a scan chain in real time as fail data is collected on the tester, the method comprising computing a blocked chain analysis signature for each scan cell in a scan chain comprising the step of accumulating the number of low strobes and the number of high strobes in a scan pattern set wherein a high strobe is presented as H and a low strobe is presented as L in the test patterns that are output from the ATPG tools as ASCII files, comparing the number of high strobe failures and the number of low strobe failures with the analysis signature, and assigning a scan cell into one of the categories following:

always low, always high, and sometimes low and sometimes high.