Browse Prior Art Database

Short Circuit Detection

IP.com Disclosure Number: IPCOM000089690D
Original Publication Date: 1977-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Deskur, KJ: AUTHOR

Abstract

Buried shorts between two circuit elements of a laminated multilayer printed-circuit (PC) board, if not detected, often result in the scrapping of the final board assembly. The detection techniques schematically shown in Figs. A-F permit location of such shorts so that they can subsequently be isolated from the rest of the board circuity and/or repaired, if possible. The techniques are particularly useful for detecting high resistance shorts.

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Short Circuit Detection

Buried shorts between two circuit elements of a laminated multilayer printed- circuit (PC) board, if not detected, often result in the scrapping of the final board assembly. The detection techniques schematically shown in Figs. A-F permit location of such shorts so that they can subsequently be isolated from the rest of the board circuity and/or repaired, if possible. The techniques are particularly useful for detecting high resistance shorts.

In A, constant current DC power supply 1 is connected across two of the board's plated-through holes (PTHs), e.g., PTHs 2 and 5, that are interconnected by PC conductor 6 and intermediate PTHs 3, 4.

Positive probe 7 of high-impedance, sensitive null detector, e.g., meter M, probes each PTH 2-5 while negative probe 8 is in electrical contact with another board element, e.g., power plane 9. If a short circuit exists between any of the PTHs 2-5 and plane 9, a null reading is obtained in M when the particular shorted PTH is probed. For example, with a short Rs between PTH 4 and plane 9, meter M indicates a positive polarity when PTH 5 is probed, negative polarities when PTHs 2 and 3 are probed, and a null when PTH 4 is probed, thereby pinpointing the location of Rs. Should the short occur between plane 9 and an intermediate point on conductor 6, which lies between two adjacent PTHs, it is detectable by the resultant reverse in polarity of the readings of M when the adjacent particular PTHs are probed.

In B, a calibrated linear potentiometer 10 is connected across two adjacent PTHs 3 and 4 and its arm 11 connected to probe 7. Arm 11 is adjusted until a null is obtained in meter M. From the known resistance parameters RT, R1, R2 and length L of conductor 6 between PTHs 3 and 4, the position along conductor 6 of short Rs between conductor 6 and plane 9 can be calculated from the following relationships, to wit: R1/R2 == L1/L2, where R1+R2 = RT, and L1+L2 =
L.

In C, the position P of short Rs between power planes 9, 9a is determined by first connecting power supply 1 to diametric corners A1, A2 of plane 9a and manipulating probe 7 relative to the surface of plane 9a until meter M indicates a null, which signifies that probe 7 is at some point on the zero potential line X1. Probe 7 is then further manipulated to identify other points along line X1, each of which produce a null reading. Meter M reads a positive polarity (+) for points to the right of line X1 and a negative polarity (-) for points to the left of line X1. Wit...