Locating hold time violations in scan chains by generating patterns on ATE
First Claim
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1. A method for determining if a scan chain is blocked under all environmental conditions comprising the following steps;
- setting an environmental variable of a device under test wherein the environmental variable comprises at least one of temperature and supply voltage;
repeatedly applying a non-constant sequence pattern to the device under test;
sweeping the environmental variable through a range while repeating the steps preceding;
recording a value of the environmental variable which enables a match of an input sequence to the device under test and an output sequence from the device under test, whereby no changes in the output sequence distinguishes the scan chain as broken, an exact match of the input sequence and the output sequence distinguishes the scan chain as good, and variability in matching input sequences and output sequences distinguishes the scan chain as potentially having defects causing hold time violations in at least one scan cell in the scan chain; and
determining a number of scan cells in the scan chain having defects causing hold time violations by,setting the environmental variable to a value determined to cause a potential hold time violation; and
thenapplying a pattern of 2n ones, 2n zeroes and n ones to an input of the scan chain, wherein n is the length of the scan chain; and
observing an output of the scan chain and comparing a number of clocks to a number of bits between transitions, whereby the number of scan cells causing hold time violations is equal to the number of clocks that a transition occurs before n clocks.
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Abstract
A method for determining that failures in semiconductor test are due to a defect potentially causing a hold time violation in a scan cell in a scan chain, counting the number of potential defects, and, if possible, localizing, and ameliorating hold time defects in a scan chain.
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Citations
6 Claims
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1. A method for determining if a scan chain is blocked under all environmental conditions comprising the following steps;
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setting an environmental variable of a device under test wherein the environmental variable comprises at least one of temperature and supply voltage; repeatedly applying a non-constant sequence pattern to the device under test; sweeping the environmental variable through a range while repeating the steps preceding; recording a value of the environmental variable which enables a match of an input sequence to the device under test and an output sequence from the device under test, whereby no changes in the output sequence distinguishes the scan chain as broken, an exact match of the input sequence and the output sequence distinguishes the scan chain as good, and variability in matching input sequences and output sequences distinguishes the scan chain as potentially having defects causing hold time violations in at least one scan cell in the scan chain; and determining a number of scan cells in the scan chain having defects causing hold time violations by, setting the environmental variable to a value determined to cause a potential hold time violation; and
thenapplying a pattern of 2n ones, 2n zeroes and n ones to an input of the scan chain, wherein n is the length of the scan chain; and observing an output of the scan chain and comparing a number of clocks to a number of bits between transitions, whereby the number of scan cells causing hold time violations is equal to the number of clocks that a transition occurs before n clocks. - View Dependent Claims (2, 3)
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4. A method for determining the number of scan cells in a scan chain having a defect causing a hold time violation comprising the steps following:
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setting an environmental variable to a value determined to cause a potential hold time violation; applying a pattern having i) background of logic zeros followed by a foreground of logic ones, and ii) a background of logic ones followed by a foreground of logic zeros; observing the output of the scan chain and comparing a number of clocks to a number of bits between transitions, whereby the number of hold time violations is equal to the number of clocks a transition occurs before n wherein n is the length of the scan chain. - View Dependent Claims (5)
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6. A method for localizing a hold time fault in a scan chain of a device under test using automated test equipment, comprising:
using the automated test equipment, detecting a hold time fault in the scan chain of the device under test, determining a safe voltage value for loading and unloading the scan chain, and localizing the hold time fault in the scan chain by applying recurring hexadecimal 3'"'"'s, 6'"'"'s, 9'"'"'s, and C'"'"'s to an input port of the scan.
Specification