Browse Prior Art Database

Switching Device

IP.com Disclosure Number: IPCOM000039195D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 58K

Publishing Venue

IBM

Related People

Esplin, RN: AUTHOR [+4]

Abstract

Multilayered printed circuit cards and boards that are fabricated from glass cloth impregnated with epoxy resin are subjected to dielectric loss measurements. The measurements are used as an indicator of moisture in the various layers of the cards or boards. The magnitude of the capacitance and dielectric loss is measured between signal lines and adjacent power planes throughout the board. These measurements are typically made on an individual basis using a double pair of coaxial cables which are connected to the two plated through holes (PTHs) leading to the respective signal line to power plane being studied, and is connected to an instrument to measure dielectric loss and capacitance.

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Switching Device

Multilayered printed circuit cards and boards that are fabricated from glass cloth impregnated with epoxy resin are subjected to dielectric loss measurements. The measurements are used as an indicator of moisture in the various layers of the cards or boards. The magnitude of the capacitance and dielectric loss is measured between signal lines and adjacent power planes throughout the board. These measurements are typically made on an individual basis using a double pair of coaxial cables which are connected to the two plated through holes (PTHs) leading to the respective signal line to power plane being studied, and is connected to an instrument to measure dielectric loss and capacitance. Since there may be any number of such signal line to power plane groups to be studied, this individual measurement for each net is very time consuming. A device which will switch the various number of signal line to power plane groups over the frequency range of 100 Hz to 100 kHz, without introducing any added capacitance to the measurements, is described in the following. This switching is done automatically through the use of stepping motors which actuate spring- loaded probes. These, in turn, connect the capacitance measuring instrument to the desired signal line to power plane pairs. Because many multilayered electronic cards and boards are made from glass cloth impregnated with various types of epoxies which absorb moisture, it is important to know the status of moisture within the

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card or board, particularly so since the internal structure of the cards or boards is comprised of many closely spaced signal lines and power planes (copper) which are connected to the surface through copper PTHs. If moisture is entrapped or diffuses through the structure in the presence of foreign metallic ions, these ions can cause a serious shorting problem. Hence, dielectric loss studies as a dryness indicator can be used on any composite, subcomposite, or finished card or board where there is a need to know if there is sufficient dryness so tha...