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Defect Detection in Conformal Organic Coatings of Metal Foils by AC Impedance

IP.com Disclosure Number: IPCOM000039356D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Day, RA: AUTHOR [+3]

Abstract

A method of testing organic coatings on metal foils involves AC impedance measurements of the metal-coating-solution interfacial region of a sample submerged in an electrolyte solution. The described technique yields a quickly obtained, non-destructive, quantitative electrochemical parameter which is proportional to the defect area in a conformal organic coating of a metal foil. The method works as follows. At a given AC frequency, the interface will show an impedance corresponding to resistive, capacitive or a combination of these properties [*]. Generally, at a sufficiently high frequency all current will cross an interface as capacitive current, while at a sufficiently low frequency only resistive (faradaic) current will pass.

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Defect Detection in Conformal Organic Coatings of Metal Foils by AC Impedance

A method of testing organic coatings on metal foils involves AC impedance measurements of the metal-coating-solution interfacial region of a sample submerged in an electrolyte solution. The described technique yields a quickly obtained, non-destructive, quantitative electrochemical parameter which is proportional to the defect area in a conformal organic coating of a metal foil. The method works as follows. At a given AC frequency, the interface will show an impedance corresponding to resistive, capacitive or a combination of these properties [*]. Generally, at a sufficiently high frequency all current will cross an interface as capacitive current, while at a sufficiently low frequency only resistive (faradaic) current will pass. The magnitudes of the impedances and corresponding resistance and capacitance will be determined by the quality of the coating. In a defect-free coating, only capacitive properties will be observed over a wide frequency range, with the magnitude of the capacitance determined by the thickness and area of the sample (C = eu A/1). Leaks or uncoated areas introduce low impedance resistive pathways for faradaic current across the interface in parallel with the interfacial capacitance. The resistance to faradaic charge transfer across the interface will decrease in proportion to exposed copper area or effective current leakiness of poorly coated areas. Capacitance will also change with the amount of uncoated or poorly coated area, with larger values being obtained for more metal/solution interface. The interface may then be considered as an infinite number of ideal resistors and capacitors in parallel, or simply, as a single non-ideal resistor and capac...