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In order to cope with the increase of information to more huge
volume, signal speed to faster and higher rate and frequency to higher ranges
more refined functions are required than ever for printed circuit boards and in
this way a new issue in a term: "Impedance Control" *represents such an
important functional characteristic.
In printed circuits where high-speed signals flow, an
ill-matched impedance often causes to suspend the inherent operational functions
completely.
Factors regulating the "impedance" are "interlayer thickness",
"circuit width", "circuit thickness" and "dielectric constant", wherein
according to simulations by approximate expression the contribution (influence)
of the "interlayer thickness", to the malfunction accounts for 70% approx. Thus,
the "interlayer thickness allowance" for print circuit board materials proved to
be the key factor.
To put it concretely, reduction of the variation of impedance from the
conventional level of ±15% to ±5% will require improvement of the tolerance
of interlayer thickness to be 1/2 to 1/3 of the current level. The newly
developed multi-layer materials comply with this rigorous requirement.
| *Note: |
"Impedance control" : Impedance in an alternating
current on PCB
just like resistance in D.C. functions to hinder devices from
exhibiting their inherent performance characteristics by reflection of signals
when the impedance between mounted circuit elements and printed circuits is not
matched well.
Regulating impedance for matching to prevent such malfunctions
is called "Impedance control." |
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