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Freescale Semiconductor
Application Note
© Freescale Semiconductor, Inc., 2007. All rights reserved.
This application note addresses a common challenge
encountered during circuit board testing with Freescale
microprocessors in newer technologies, such as 130 nm and
smaller processes. The discussion includes a detailed
description of the issue of testing power rails for shorts with
devices in these newer technologies, an explanation of why
it occurs, and the factors that affect it.
It is common practice for board testing houses to test for
shorts on the power rails by measuring the resistance from a
power rail to the ground rail. In older technologies, this is a
reasonable approach. However, this application note
explains why this approach can be problematic when used
with devices in newer technologies.
First, however, it is beneficial to understand the goal in
performing this type of test. Freescale tests all production
devices prior to shipment, including functional tests,
opens/shorts tests, and AC and DC specifications. All
production devices shipped by Freescale meet reliability
requirements and have a guaranteed expected lifetime. By
definition, all production devices shipped by Freescale are
“good parts.” Therefore, testing for power rail shorts is
needed only on the circuit board itself. If bare boards are
tested before assembly to verify that there are no issues in the
board manufacturing process, testing for shorts after boards
are assembled ensures that no shorts were introduced on the
board during assembly. If a high degree of confidence in the
Document Number: AN3372
Rev. 0, 06/2007
Contents
1 Interactions Between Ohmmeters and Core Circuits . .2
2 Leakage Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
2.1 Diode Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
2.2 Leakage Current and Geometry . . . . . . . . . . . . . . .4
2.3 Leakage Current and Process . . . . . . . . . . . . . . . . .5
2.4 Leakage Current and Temperature . . . . . . . . . . . . .6
3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
4 Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Challenges in Testing for Power Rail
Shorts with New Technologies
by Michael Everman
Networking and Computing Systems Group
Freescale Semiconductor, Inc.
Austin, TX
