Avner Drory wrote:

I like to know if anyone found that Dielectric Constant, for the same
material (e.g. FR-4), might be different when used for calculation of
Microstrip or for calculation of Stripline.

---------------------
A point not brought up yet in this discussion.  The dielectric constant is
an average of the dielectric of the glass (high) and of the resin (low).
For high resin, thin materials, such as 106 and 1080 glass styles, the
dielectric will be in the 4.2 - 4.3 range.  For thick, high glass styles,
7628, the value will be at the high end, 4.7 - 4.9.  The differences in
readings you are getting may be a result of the glass fabrics used in the
construction of the board.  Both 7628 and 1080 glass styles are commonly
used, and could easily be found in the same board construction.

Based on what you wrote, IMHO, you are getting different dielectric values
because the FR-4 has different dielectic values.. This is due to the
differing ratios of glass and epoxy between the different copper layers in
the board.


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