[Cryptech Tech] Updated novena noise board

[Jacob]

>>> If the lack of feedback on the list is to be taken as approval, I'm ready
>>> to order real PCBs.

Sorry for the delayed action on my part. It wasn't a good month.
I attached my comments as a txt doc.

Jacob


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NOISE BOARD REV.03 COMMENTS BY JACOB, 28 MAY 2015 
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If I understand correctly, you had built a prototype based on the schematic and layout(?) that works.
It that is the case, some of my comments, refering to comp values, may seem a bit out of place.
Regardless, I have included all my comments below.

Please also note that the comments are not exhaustive - there may be other detrimental issues that I haven't discovered yet.

Schematic:

1. Capacitors with X5R composition are lower quality than X7R. I suggest to move all to the X7R type.
2. Due to the operational characteristics of Ceramic capacitors, it is common to select their voltage rating at least 80% higher than the max DC voltage they would encounter during service - for getting a reasonable life. Therefore, I recomment to change C12 to 10V voltage spec.
3. Al caps like C1, C9 (and possibly others) are rated at 1000 hrs. This is considered below par for IT equipment. I suggest minimum 2000 hrs life spec as with the Panasonic EEE-FK1E100R series.
4. The ORANGE LED off the -15V rail in the DC-DC supply is not specced out, but I doubt that you would see any light out on a regular led at 1mA current. I suggest to reduce R3 value to 1.5 KOHM to get 8 mA or so through it.
5. C7, C10 can be 0603. In tight space 0805 is taxing.

Layout:

1. There are no Ref Des silk in Gerbers. Also no comp outline in the Noise section.
2. I am not sure what the metal constructions (connected to AGND) on the periphery of the noise section (on all 4 sides) are. Are those for a shield mounting?
3. Why are the footprint of JP1 and JP2 not in-line? 
4. Missing fiducials for assembly
5. I would prefer to see wider traces going to PWR/GND pins
6. Should design in some openings in the soldemask of the connector pads. As it is now, there is a danger of shorts during assembly. 
7. Since only lab measurements will determine the amount of noise coupling between the noise section AGND and the board GND, I suggest to also have an optional inductor (choke) placed as an experimental bridge between the 2 grounds. That inductor will be assembled only if the current ground topology will be too noisy. In that case, one can scrape off the current copper bridge between the 2 grounds and connect the grounds via the inductor. A 0805 footprint will be good.
8.I have some issues with the acute angle of some of the traces, but not to such a concern to flag them out now.
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