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Moisture Concentration Monitor for Epoxy/Composite Materials

IP.com Disclosure Number: IPCOM000039140D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Lawrence, WH: AUTHOR [+3]

Abstract

Monitoring of the moisture content of epoxy layers sandwiched between layers of metal foil in a circuit board composite is essential in resin development and process quality control. A method which permits an intermittent measurement of the moisture in epoxy layers works as follows. Small polar groups or molecules, such as water, respond to an applied electric field by reorienting so as to oppose the applied field. This behavior is the source of the relatively high dielectric constant of a polar material such as water (E = 80.3), compared to a non-polar material such as carbon tetrachloride (E = 2.2). At a sufficiently high frequency of the applied electric field, however, the polar groups of any molecule will be unable to respond to the applied field.

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Moisture Concentration Monitor for Epoxy/Composite Materials

Monitoring of the moisture content of epoxy layers sandwiched between layers of metal foil in a circuit board composite is essential in resin development and process quality control. A method which permits an intermittent measurement of the moisture in epoxy layers works as follows. Small polar groups or molecules, such as water, respond to an applied electric field by reorienting so as to oppose the applied field. This behavior is the source of the relatively high dielectric constant of a polar material such as water (E = 80.3), compared to a non-polar material such as carbon tetrachloride (E = 2.2). At a sufficiently high frequency of the applied electric field, however, the polar groups of any molecule will be unable to respond to the applied field. At such a high frequency the dielectric constant (or capitance) will decrease to a value determined only by electronic and atomic polarization. The difference in capitance measured at frequencies sufficiently low such that all dipolar groups respond to the applied field, and that at a high enough frequency such that no dipolar groups respond to the field is the total dipole contribution to cap itance. This method is applied by measuring the capitance at a low temperature using a high frequency AC signal. Under the conditions of this measurement the capitance determined should be independent of moisture concentration, as small polar groups will have insuff...