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Using XOR Chains to Observe Real Time Pin Leakage on Low Pin Count Testing and Boundary Scans for Preconditioning

IP.com Disclosure Number: IPCOM000074582D
Publication Date: 2005-Feb-23
Document File: 3 page(s) / 302K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method that uses a boundary scan cell to precondition the pad, and different strings of XOR chains to monitor real time pad leakage on low-cost and low-pin count testers. Benefits include testing without the need for a mapping between the pin and the tester.

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Using XOR Chains to Observe Real Time Pin Leakage on Low Pin Count Testing and Boundary Scans for Preconditioning

Disclosed is a method that uses a boundary scan cell to precondition the pad, and different strings of XOR chains to monitor real time pad leakage on low-cost and low-pin count testers. Benefits include testing without the need for a mapping between the pin and the tester.

Background

New designs and improvements in process technologies have made System-on-Chip (SoC) design approaches attractive. However, these improvements increase the cost, complexity, and challenge of testing pad leakage in low-cost and low-pin count testers.

Currently, pad leakage testing is performed by using more expensive tester equipment (i.e. with enough tester channels), using an embedded IO BIST engine to pre-condition and sample the pad, or by re-designing the IO pad with a voltage divider to measure the pad leakage current.

General Description

The disclosed method uses the existing boundary scan cell to pre-charge those I/O pads that are not directly connected to a tester channel. The test mode turns off all leakage paths in the IO (such as clamps, pull up/down etc.). The boundary scan is then used to tri-state these IO pads and start sampling the leakage results, via different strings of the XOR tree (depending on their IO type). The leakage results are characterized and tested on a low-pin count tester for HVM testing. The following are the detailed steps for the disclosed method:

 

  1. Disable the internal pull-up, pull-down, and clamps to stop the bias current before pad leakage testing.
  2. Use existing boundary scan chains to pre-condition those IO pads which have no direct contact to tester channel.
    1. Pre-charg...