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Method for multi-die tester touchdown optimization (MDiTTO)

IP.com Disclosure Number: IPCOM000006383D
Publication Date: 2001-Dec-28
Document File: 6 page(s) / 94K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for multi-die tester touchdown optimization (MDiTTO). Benefits include improved test pattern generation.

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Method for multi-die tester touchdown optimization (MDiTTO)

Disclosed is a method for multi-die tester touchdown optimization (MDiTTO). Benefits include improved test pattern generation.

Background

              During wafer testing, unnecessary touchdowns waste tester resources. By optimizing the test pattern and allowing die to be tested more than once, fewer touchdowns are required. With improved tester utilization, fewer testers are required to test the same quantity of die.

              Conventionally, only the results from the conventional automatic pattern generation tools are known with certainty, as the algorithms are embedded in vendor-supplied software. However, all conventional generated test patterns are comprised of non-overlapping touchdowns. This technique can be described as tiling (see Figure 1, Example Test Pattern with 21 Touchdowns). The use of a mathematical programming technique is unlikely because the search through possible touchdowns is extremely simple in this scenario. A row or column of adjacent touchdowns (tiles) is shifted so that as few touchdowns as possible are required to test the row or column of die. This local optimization is repeated on the next row or column. This approach does not, however, yield the optimal pattern overall. As implemented, this approach does not provide the option to leave a die untested when doing so would be more profitable (that is, the costs to test the die is more than the result is worth).

      Conventional optimization techniques create patterns in which the touchdowns must be adjacent and exclusive.

      Conventional algorithms permit only rectangular cards in a fixed orientation.

General description

              The disclosed method is a technique for generating the test pattern of sort wafers that covers all yieldable die (or the most profitable subset) with the minimum number of touchdowns (see Figure 2, Example Test Pattern with 20 Touchdowns). This technique is only applicable when multiple die may be tested with a single touchdown.

Key elements include:

·        A test pattern may test a single die more than when the exact limit to the number of tests is a function of the invasiveness of the test.

·        The Cartesian coordinate pair of each yieldable die on a wafer is treated as a member of a target set. Each possible touchdown is defined as a set of Cartesian coordinate pairs matching the coordinates of yieldable die that would be tested if that touchdown were used. An Integer Program (IP) is used to select the set of touchdowns which maximize the number of tested die times a “die value” minus the number of touchdowns times a “touchdown cost.”

Advantages

              The disclosed method provides several advantages over conventional solutions. The test pattern consists of the guaranteed minimum number of touchdowns for the dice tested and probe-card specified. This number is empirically about 10% fewer than conventional solutions.

              The disclosed method enables the user to determine with a profit factor (such as the relationship between testing...