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Detection of Circuit Board Via Defects by Acousto-Electric (Micro-Phonic) Means

IP.com Disclosure Number: IPCOM000044598D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 90K

Publishing Venue

IBM

Related People

Hollis, RL: AUTHOR [+2]

Abstract

Using ultrasonic excitation to open and close cracks in circuit modules being tested, to modulate DC electrical currents in a fashion subject to detection, permits testing for incipient faults which would survive ordinary electrical tests. Fig. 1 shows a module (00) under test by probes 1 and 2 and acoustic transducer 3. Probe 1 is DC biased by source 4; oscillator 5 provides an AC signal at 1-10 MHz. Oscillator 5 and probe 2 provide inputs to lock-in amplifier 6 which provides a constant phase AC component indicative of a fault. A drop of water 7 may be used to ensure acoustic coupling from transducer 3 to the module under test. Fig. 2 shows a typical via connector; of main interest is the possibility of a crack occurring between the two plated layers (Fig.

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Detection of Circuit Board Via Defects by Acousto-Electric (Micro-Phonic) Means

Using ultrasonic excitation to open and close cracks in circuit modules being tested, to modulate DC electrical currents in a fashion subject to detection, permits testing for incipient faults which would survive ordinary electrical tests. Fig. 1 shows a module (00) under test by probes 1 and 2 and acoustic transducer
3. Probe 1 is DC biased by source 4; oscillator 5 provides an AC signal at 1-10 MHz. Oscillator 5 and probe 2 provide inputs to lock-in amplifier 6 which provides a constant phase AC component indicative of a fault. A drop of water 7 may be used to ensure acoustic coupling from transducer 3 to the module under test. Fig. 2 shows a typical via connector; of main interest is the possibility of a crack occurring between the two plated layers (Fig. 3), using longitudinal (z-polarized) acoustic waves passing through the via connector. As the sinusoidally varying stress waves, szz, pass by the crack, it will tend to open and close. This will cause the via connector's electrical resistance to change since the contact area between the plated layers will vary with the sign and amplitude of szz . The suitability of this acoustic technique for crack detection must be evaluated experimentally; however, an estimate will be made here of the crack opening and closing expected for commercially available acoustic transducers and lenses. The actual geometry of the copper lines and via con...