[SI-LIST] AW: Definitions in IPC-T-50

  • From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
  • To: SI-LIST <si-list@xxxxxxxxxxxxx>
  • Date: Thu, 17 Mar 2011 09:59:05 +0100

Hi Jack,

the definition is correct, but it is strongly related to the way the dk is 
measured (at least for low frequencies). Nowadays, other techniques are used to 
get material properties for higher frequencies and higher accuracy because it 
was shown that the "old way" wasn't accurate enough for todays electronic 
development.

I think the definition should be improved to also refer to the impact of the dk.

Maybe something like:
Dielectric constant of a material surrounding a conductor affects the electric 
fields of the signal. It reduces the wavelength and the velocity of 
propagation. Both effects increase along with the dielectric constant.  It can 
be measured as the ratio of capacitance of a two electrode setup separated by 
material under test vs. air.

BR
Gert


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Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im 
Auftrag von Jack Olson
Gesendet: Mittwoch, 16. März 2011 20:18
An: SI-LIST
Betreff: [SI-LIST] Definitions in IPC-T-50

Greetings,
IPC-T-50 (Terms and Definitions) is currently under revision, and as I was 
browsing the latest entries (ok, I have a boring life...) I noticed the 
definition they give for DIELECTRIC CONSTANT.

Dielectric Constant
The ratio of the capacitance of a configuration of electrodes with a specific 
material as the dielectric between them to the capacitance of the same 
electrode configuration with a vacuum or air as the dielectric.
See “Permittivity.”

While that may be technically accurate, I wonder if  it really helps the reader 
understand the significance of the term.

As a member of the standards development committee I can submit recommendations 
for the next publication, so is this a good definition or could we do better?

I suppose I should also include the following:

Effective Relative Dielectric Constant
The relative permittivity (See “Dielectric Constant”) of a mixed media 
configuration, such as air and the solid dielectrics used in microstrip, that 
has the equivalent electromagnetic wave propagation characteristics of a single 
dielectric medium.

Permittivity
The square root of the ratio of the electromagnetic wave propagation 
characteristics of free space to that of the dielectric medium. The 
permittivity, , of a material is, in general, a complex-valued (has real and 
imaginary parts) parameter. The real and imaginary parts of  are given by 
N and O. See "Dielectric Constant."
(the missing characters above look like a backwards "3")

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  • » [SI-LIST] AW: Definitions in IPC-T-50 - Havermann, Gert