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# Cross-Sectional Area Determination by Resistance Measurement With Compensation for Temperature and Contact Resistance

IP.com Disclosure Number: IPCOM000062110D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 51K

IBM

## Related People

Frushour, JE: AUTHOR [+2]

## Abstract

The cross-sectional area of printed circuit lines can be calculated if the resistance, resistivity and the length of the line are known. Test systems that measure line resistance on printed circuit lines using four point probes are limited when the test pads on a printed circuit board are too small to accommodate a four-point probe method. A resistance measurement that only uses two probes is error prone and less satisfactory due to a variation of probe contact resistance from one test to another and because the resistivity of the printed line under test is a function of temperature. A two-point resistance measurement technique in which special circuitry and test programs reduce these errors is accomplished in a test system that measures the cross-sectional area of printed circuit lines.

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Cross-Sectional Area Determination by Resistance Measurement With Compensation for Temperature and Contact Resistance

The cross-sectional area of printed circuit lines can be calculated if the resistance, resistivity and the length of the line are known. Test systems that measure line resistance on printed circuit lines using four point probes are limited when the test pads on a printed circuit board are too small to accommodate a four-point probe method. A resistance measurement that only uses two probes is error prone and less satisfactory due to a variation of probe contact resistance from one test to another and because the resistivity of the printed line under test is a function of temperature. A two-point resistance measurement technique in which special circuitry and test programs reduce these errors is accomplished in a test system that measures the cross-sectional area of printed circuit lines. The tester performs a resistance measurement on each net and the value obtained is multiplied by a compensating factor. The result is then compared to the resistance calculated from equation (1) shown below. R = p L/A + Rt + K (1) where A is the minimum cross-sectional area for the printed circuit line, L is the length of the net, p is the resistivity of the copper, Rt is the tester wiring resistance and K is the maximum probe contact resistance variation that will be encountered in testing the board. The tester automatically determines the value of the tester wiring resistance Rt prior to each board test by the use of a built-in calibration fixture. The test program, along with the special built-in calibration fixture, compensates for va...