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A Novel Approach for Resolution of Test Cubes Issue in TestKompressTM EDT®

IP.com Disclosure Number: IPCOM000198994D
Publication Date: 2010-Aug-20
Document File: 4 page(s) / 70K

Publishing Venue

The IP.com Prior Art Database

Abstract

Scan and ATPG tools like TestKompress (by Mentor Graphics) use EDT technology to achieve compression of scan test data by controlling a large number of internal scan chains using a small number of scan channels. In this process, the tool creates a test cube filled with a few care bits and lots of pseudo-randomly-generated don't care bits to test a particular fault site. The creation of test cube is actually a combination of a large number of simultaneous equations in which too many care bits can make it impossible for the tool to solve the system of equations. Failure to simultaneously create all the care bits required to test a particular fault site results in test cube issue. This idea provides a solution when EDT is not able to compress all the test cubes generated. This can be used in cases where no patterns are generated due to test cubes problem. The idea involves insertion of one dummy flip flop in design with every flip flop back to back in a scan chain as a result of which don't care bits in test vectors for every scan flop increases. The faults that are left out due to test cubes issue as EDT aborted faults can be tested using this approach and the advantage of using this approach over the bypass approach is that the scan chain length in this is shorter (as compared to the bypass scan chain length) and hence there is reduction in tester memory required.

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A Novel Approach for Resolution of Test Cubes Issue in TestKompressTM EDT®

Abstract

Scan and ATPG tools like TestKompress (by Mentor Graphics) use EDT technology to achieve compression of scan test data by controlling a large number of internal scan chains using a small number of scan channels. In this process, the tool creates a test cube filled with a few care bits and lots of pseudo-randomly-generated don’t care bits to test a particular fault site. The creation of test cube is actually a combination of a large number of simultaneous equations in which too many care bits can make it impossible for the tool to solve the system of equations. Failure to simultaneously create all the care bits required to test a particular fault site results in test cube issue.

This idea provides a solution when EDT is not able to compress all the test cubes generated. This can be used in cases where no patterns are generated due to test cubes problem. The idea involves insertion of one dummy flip flop in design with every flip flop back to back in a scan chain as a result of which don’t care bits in test vectors for every scan flop increases.

The faults that are left out due to test cubes issue as EDT aborted faults can be tested using this approach and the advantage of using this approach over the bypass approach is that the scan chain length in this is shorter (as compared to the bypass scan chain length) and hence there is reduction in tester memory required.

Detailed Description of the idea

The first step is the addition of dummy flops in design in which one/two (or more) dummy flops are inserted per scan flop so that the scan chain length doubles/triples. This is done by modifying the library cell definition in which a sequential element is added just before the mux in the library cell (as shown in Figures 1). The scan...