[SI-LIST] Re: Change of Decap package
- From: Istvan Novak <istvan.novak@xxxxxxxxxxx>
- To: naren.thesia@xxxxxxxxx
- Date: Sat, 07 Oct 2006 11:21:49 -0400
Naren,
A few more quick points: when you compare, the capacitance, resistance,
and inductance
and their potential frequency and bias dependies need to be considered.
As Steve pointed out,
inductance may not change much between 0402 and 0201, BUT: keep in mind
that what matters
for you is the loop inductance formed by the part, pads, escape traces
(if any), vias and planes.
If there is no change in the planes, via locations/sizes and you only
modify the escapes and pads to
accomodate the smaller part, inductance will slightly go up. This is
because with the same via
placement the loop size does not change, but the narrower body of the
smaller cap will increase
the inductive contribution. If you can move the vias proportionally
closer as you change to a
smaller case size (leaving the via pattern the same), inductance usually
goes down, because
you gain more by shrinking the loop. It depends on the PCB technology
available to you, and
the via/escape pattern you would otherwise use for the 0402 parts if
shrinking the loop by
moving the vias closer is an option for you or not.
Resistance (ESR) probably will go up because the smaller part has less
metal in it. Capacitance
may be more frequency and bias dependent, because the smaller part
probably will have
either thinner dielectric layers or a different (higher-Dk) ceramics) or
both. In generic applications
this may not be a big concern. If your application has sensitive analog
circuits (audio, RF,
low-noise PLLs) you may need to consider the potential piezo-electric
noise from the parts. For
the above reasons, smaller parts with the same capacitance will have a
higher chance of showing
piezoelectric problems.
Regards,
Istvan Novak
SUN Microsystems
Naren Thesia wrote:
>Hi All,
>
>
>In our dense design we want to replace all decoupling capacitor having 0402
>package (0.1 uF) with 0201 package (0.1 uF).
>
>
>
>Some of guys are not agree with that; saying that may degrade performance
>point of board.
>
>I agree it will increase Assembly & Rework cost but it should not have
>impact on performance.
>
>
>
>Anyone have any experience/thought to share regarding performance?
>
>
>
>Thanks in advance!
>
>
>
>Regards,
>
>Naren
>
>
>
>
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