Re: [psas-avionics] Strong opinion on 0603 vs 0402 for LGR, and future boards?

[Doug Ausmus]

I didn't see anyone bring this up, and I'm not sure which dielectrics and
types are being used, and at risk of stating what is likely trivially
obvious to the electronics designers in this august group , but when
using MLCC and going to smaller size capacitors (X5R and X7R, others) don't
forget to re-check the dielectric voltage-dependence curves. For your chip
film caps, this is far less an issue.

Here is some info and references, just in case some of your non-electronics
designers want to check it out:

Although this article is testing with higher valued caps, here's a nice
graph showing how the smaller chip sizes increase this effect over larger
sizes:
http://www.edn.com/design/analog/4402049/2/Temperature-and-voltage-variation-of-ceramic-capacitors--or-why-your-4-7--F-capacitor-becomes-a-0-33--F-capacitor
(Figure 1 and Table 2)
(From the following original article:)
https://www.maximintegrated.com/en/app-notes/index.mvp/id/5527

Most everyone is aware of the DC bias dielectric effects, but note that AC
waveforms have some dielectric effects as well, but exert their effects in
the opposite direction, to a point and are, of course, frequency dependent
(I am not sure if these AC dielectric effects are also size-dependent or
not, but it would be logical they might be):
http://catalogs.avx.com/SurfaceMount.pdf
(PDF page 128, [doc page #127]... Figures 2, 3)

:-)
Doug



On Sun, Oct 9, 2016 at 11:18 PM, Andrew Greenberg  wrote:

> > Are there any places where we need to be concerned about wattage?
>
> Yep! There are two cases that we won't switch packages: one where
> wattage is a problem (so far, no cases of this on the LGR board) and one
> where the capacitance value is too high for an 0402 (anything greater
> than about 1 uF). In these (and other cases I'm sure I missed) we'll
> leave the larger packages. Other than that, the "jelly bean" parts can
> be switched to 0402.
>
> OK, everyone seems to agree it's a "go", so now OreSat's default package
> size is now 0402. I think this makes sense.
>
> Andrew
>
> --
> ---
> Andrew Greenberg
>
> Electrical and Computer Engineering
> Portland State University
> http://www.ece.pdx.edu/
> a...@ece.pdx.edu  C: 503.708.7711
> ---
>
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Re: [psas-avionics] Strong opinion on 0603 vs 0402 for LGR, and future boards?

[Andrew Greenberg]

> Are there any places where we need to be concerned about wattage?

Yep! There are two cases that we won't switch packages: one where
wattage is a problem (so far, no cases of this on the LGR board) and one
where the capacitance value is too high for an 0402 (anything greater
than about 1 uF). In these (and other cases I'm sure I missed) we'll
leave the larger packages. Other than that, the "jelly bean" parts can
be switched to 0402.

OK, everyone seems to agree it's a "go", so now OreSat's default package
size is now 0402. I think this makes sense.

Andrew

-- 
---
Andrew Greenberg

Electrical and Computer Engineering
Portland State University
http://www.ece.pdx.edu/
a...@ece.pdx.edu  C: 503.708.7711
---

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[psas-avionics] Strong opinion on 0603 vs 0402 for LGR, and future boards?

[Andrew Greenberg]

Hey everyone,

Glenn added a reflectometer to the LGR, and in doing so, he introduced a
bunch of 0402 components to an existing 0603 board. I've been itching to
move to 0402 just because it gives so much more room for routing, and
it's something I think we should move towards, especially for future
boards. The SDR GPS boards, for example, already use mostly 0402.

Any strong opinions? It'll take about 20 minutes to switch the whole
board to 0402, I'm tempted. Any strong reasons not to, and make that our
standard?

Pros:
- Way better passives packing for future boards
- Vaguely better RF performance, maybe
- Standardizes on a single size to have around

Cons:
- Harder to hand place, but definitely doable.

Would love to hear thoughts!

Andrew

-- 
---
Andrew Greenberg

Electrical and Computer Engineering
Portland State University
http://www.ece.pdx.edu/
a...@ece.pdx.edu  C: 503.708.7711
---

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