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Detection of Localized Adhesive Failure of Metallization on Non-Conducting Substrates Using Electromagnetic Ultrasonic Generation

Proper adhesion of metallization patterns to their substrates is a crucial aspect to overall circuit reliability. The critical role of adhesion is accentuated in situations where the substrate is flexible, soldering or bonding to the metallization is required, or extensive ultrasonic cleaning is necessary. We have developed a non-contact, nondestructive method for detecting local changes in the adhesion of the metal foil to the substrate by monitoring the amplitude of resonant modes of the substrate excited electromagnetically. The advantage of electromagnetic excitation is that the generation is confined to the metallized pattern and this technique probes the impedance match between metal film and substrate. Using design guidelines similar to that used in magnetic recording heads, we have developed EMAT’s that incorporate soft magnetic materials to allow higher spatial resolution and higher flux density than could be obtained without.