Data processing: measuring – calibrating – or testing – Measurement system – Statistical measurement
Reexamination Certificate
2002-09-01
2004-09-14
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Statistical measurement
C702S117000, C702S118000, C702S182000
Reexamination Certificate
active
06792385
ABSTRACT:
BACKGROUND OF THE INVENTION
In the past, the “board test coverage” provided by a particular test suite was often measured in terms of “device coverage” and “shorts coverage”. Device coverage was measured as the percentage of board devices with working tests, and shorts coverage was measured as the percentage of accessible board nodes.
Device
Coverage
=
#
Tested
Devices
Total
#
of
Devices
Shorts
Coverage
=
#
Accessible
Nodes
Total
#
of
Nodes
The above model of board test coverage was developed at a time when testers had full nodal access to a board (i.e., access to the majority (typically 95-100%) of a board's nodes). Boards were also less dense, less complex, and somewhat more forgiving due to their lower frequency of operation. In this environment, the above model was acceptable.
Over the last decade, boards have migrated towards limited access. In fact, it is anticipated that boards with access to less than 20% of their nodes will soon be common. Some drivers of access limitation include:
Increasing board density (devices/square centimeter is increasing)
Fine line and space geometry in board layouts (i.e., smaller probe targets)
Grid array devices of increasing pitch density
High-frequency signals that demand precise layouts and offer no probe targets
Board node counts that are several times greater than the maximum available on any tester
The above changes have made application of the “old” model of board test coverage difficult at best, and meaningless in many cases.
Usefulness of the “old” model of board test coverage has also been impacted by the advent of new and radically different approaches to testing (e.g., Automated Optical Inspection (AOI) and Automated X-ray Inspection (AXI)). Many of the new test approaches are very good at testing for certain defects, but limited in terms of the number of defects they can test. Thus, more and more often, it is becoming erroneous to presume that a device with working tests is a sufficiently tested device. As a result, a board is often submitted to different test processes, which in combination define the “test suite” for a particular board (see FIG.
2
).
Given the above state of characterizing board test coverage, new methods and apparatus for characterizing board test coverage are needed.
SUMMARY OF THE INVENTION
According to one exemplary embodiment of the invention, a method for characterizing board test coverage commences with the enumeration of potentially defective properties for a board, without regard for how the potentially defective properties might be tested. For each potentially defective property enumerated, a property score is generated. Each property score is indicative of whether a test suite tests for a potentially defective property. Property scores are then combined in accordance with a weighting structure to characterize board test coverage for the test suite.
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patent: 5995652 (1999-11-01), Chiu et al.
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patent: 6167390 (2000-12-01), Brady et al.
patent: 6400996 (2002-06-01), Hoffberg et al.
patent: 2003/0018631 (2003-01-01), Lipson et al.
“ITC 1996 Lecture Series on Unpowered Opens Testing,” K.P. Parker, Proceedings, International Test Conference, p. 924 (1996).
“Real-World Board Test Effectiveness: What Does It Mean When a Board Test Passes?”, E.O. Schlotzhauer and R.J. Balzer, Proceedings, International Test Conference, pp. 792-797 (1987).
“Opens Board Test Coverage: When is 99% Really 40%?”, M.V. Tegethoff, K. P. Parker, K. Lee, Proceedings, International Test Conference, pp.333-339 (Jun. 1996).
Hird Kathleen J.
Parker Kenneth P.
Ramos Erik A.
Agilent Technologie,s Inc.
Hoff Marc S.
Suarez Felix
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