Bart,
> - a better internal construction: that is a lower profile, reversed
> geometry capacitors like 0306 or even 0204 and e.g. X2Y-caps which exhibit
> 'inductance cancelation' by opposing currents ?
Yes.
> - geometry data of the capacitor, like cover thickness.
> That would be no problem. It's -of course- known to us. I must study how
> to publish this data, in datasheet?, on the website? or available on
> request? .....
Giving typical values on the data sheet and supplying more info (guaranteed
min/max values) on request would be a great start.
> - Minimizing the cover thickness: we specify thickness of our products, a
> series of capacitors in a given size have a specified thickness.
> For capacitors with a low capacitance, the numbers of needed layers is not
> sufficient to obtain the required thickness.
> So we add, symmetrically at the bottom and the top side, cover layers
> (just dielectric layers) until the required thickness is reached.
> This is obviously not an advantage for having low inductance.
You are correct. On the other hand, the required capacitance value
does not necessarily have to span a large range. For bypass
applications, there are design methodologies (and I am in that camp),
where the preferred capacitance value is always the highest available
capacitance in the chosen case style. This automatically minimizes
the cover thickness at the manufacturer, and minimizes the
need for additional lower-frequency capacitors. There are viable
design alternatives, where specific capacitance values are required.
In that case the higher-than-minimum inductance means that the
series resonance frequency of the part (in the typical mounting scenario)
will be somewhat lower. However, exactly these design options count
on a specific resonance frequency of the capacitor. If the cover thickness
of the capacitor is well controlled, this will help to reduce the
uncertainty
of the inductance in the application due to tolerances in the vertical
PCB dimensions.
> - Honestly I think that the situation having a set of "standardized" small
> test boards with known geometry and containing the main connection options
> is having more chances to be realized. Boards would be availble to vendors
> and users (in fact we already did so with the small board having the 50
> Ohm trace on it used for measurements in the Wiltron universal fixture).
> I'm willing to promote this in our organization. I think it is beneficial
> for both the customers and the manufacturers.
>
> Istvan, since you are in this area and having the experience, could and
> are you willing to provide us with a proposal for such a set of boards?
> e.g. size, substrate material, thickness, copper thickness, pad layout,
> via diameter and number of vias, interface(e.g. connectors) to e.g. VNA
> for each case style/size?
> Problem will be to get all manufacturers, vendors and users in the same
> direction....
Lets think about it. Our purpose to put together the "Measurement of
power distribution networks" TecForum at DesignCon was exactly with
these thoughts in mind: to start and promote a dialog among manufacturers
and users that eventually will be a win-win for all parties. Will anyone
from
your company be present at DesignCon East (Boston, June 23-25, 2003)
Regards,
Istvan Novak
SUN Microsystems
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