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Browse Prior Art Database

Use of Squid System to Locate Resistance Leakage in Electronic Packages

IP.com Disclosure Number: IPCOM000049447D
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 4 page(s) / 43K

Publishing Venue

IBM

Related People

Chaudhari, P: AUTHOR [+4]

Abstract

The SQUID (Superconducting Quantum Interference Device) is the most sensitive magnetic flux detector in frequency ranges from DC to a few kHz known today. It has been used for the detection of magnetic fields produced by ultra small currents, such as the electric currents generated by the activity in the human heart, brain, and so on.

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Use of Squid System to Locate Resistance Leakage in Electronic Packages

The SQUID (Superconducting Quantum Interference Device) is the most sensitive magnetic flux detector in frequency ranges from DC to a few kHz known today. It has been used for the detection of magnetic fields produced by ultra small currents, such as the electric currents generated by the activity in the human heart, brain, and so on.

As in biological applications, the second derivative gradiometer arrangement for the detection coil is chosen for the present work. This greatly enhances signal to noise ratio and allows room temperature measurements on samples larger than the inner diameter of the cryogenic dewar in which the detection system resides. A map of the current flow pattern in a circuit board is obtained by scanning it with the sensing coil. The diameter of the detection coil in commercially available SQUID gradiometers has a typical value of about one inch. The spatial resolution of such a system is determined, but not limited, by the size of the sensing coil if proper analysis of the SQUID output is made.

Here, we present the results of the experiment demonstrating the feasibility of the above technique as applied to an electronic package, and we propose a systematic approach to analyze the SQUID's response to such scanning to achieve a spatial resolution much better than the diameter of the detection coil.

In Fig. 1, an experimental arrangement is shown for detecting and locating signal and leakage current in an electronic circuit board by using an AC signal generator 17 connected to the sample and a commercial SQUID second derivative gradiometer 15. During the experiment, the sample 10 is moved in a plane parallel to that of the SQUID detection coil 11. The response of SQUID 16 as a function of position is read out through gradiometer 15 and SQUID electronics 14 by a lock in amplifier 12 and/or a spectrum analyzer 13.

Generator 17 impresses an AC voltage upon sample 10, and the SQUID response as a function of the position of the sensing coil axis 11 is monitored with lock-in amplifier 12 and a spectrum analyzer 13 in parallel. The results of such measurements on a laminated structure of an electronic circuit board with a simulated high resistance leak (HRL) between two parallel wires are shown in Figs. 2, 3 and 4.

In the SQUID, output voltage response is shown as a function of SQUID position. An AC voltage V of 5 Volts (rms) at 143 Hz is applied to two parallel signal lines in a laminated structure of a circuit board. The high resistance leakage between them is simulated by a resistor R connected as shown. The motion of the sample with respect to a position of the axis of the detection coil is also indicated schematically. It is clear from Fig. 2 that at the excitation frequency of 143 Hz, the displacement currents (due to the capacitive coupling of the signal leads to the power planes) are a major contribution to the SQUID output. Nevertheless, a...