Bob,

You are correct, the dielectric constant of a material does not change 
between microstrip, embedded microstrip or stripline configurations.

Avner,

Some general words of caution:

Dielectric constant does change depending on resin and reinforcement 
type, resin content, frequency, temperature and humidity. Typically, 
dielectric constant decreases as frequency increases. 

On microstrips, the fact that there is air on one side of the 
transmission line lowers the effective dielectric constant. Solder 
mask coatings counteract this effect to some degree.

Please call off-line if you would like to discuss further.

Luis Rivera
[log in to unmask]
CompuRoute, Inc.
Dallas, TX
(214) 340-0543


> 
> 
>   Avner--
>          If I am wrong, I hope someone out there will make me smarter, but
>    the dielectric "CONSTANT" is just that--constant for that type of material.
>    IMOP, when calculating impedance of microstrip or stripline, the dielectric
>    constant of a material doesn't change, less the material's unique tolerance
>    range REF: IPC-D-275 Table 3-2. Therefore, unless proven wrong, the constant
>    DOES NOT change, but the impedance value WILL vary depending on which 
>    formula you are using depending on you pwb construction. Hope that helps.
>    If wrong, please correct me via E-mail,
> 
>                              Bob Vanech
> E-Mail : [log in to unmask]
>    
> 
>