Designing mezzanine boards: spec questions


#1

I’m going through the specs (great work, btw!) in preparation for designing a mezzanine board, and have a couple of questions:

Mechanical drawings:

It would be very useful to also get distances from board edge to the vertical axis of each expansion board connector. Currently, distances are given to the horizontal axis and to the axis of the first pin. Many footprints are not anchored to the axis of the first pin, which makes positioning more difficult and prone to errors.

Mezzanine boards:

Page 27 reads: “The board to mezzanine module spacing is 7.0mm, or optionally 8.0mm (depending on the mezzanine module connectors used).”

So, which is it? 7mm or 8mm?

Also, it would be very, very helpful if you could provide the exact part numbers for recommended connectors, especially the high-speed one. Ideally I’d love to see an example reference mezzanine board in KiCad, containing just the board outline, holes, and two properly positioned connectors with footprints. This would go a long way towards accelerating development of mezzanine boards.

thanks,
–J.


#2

Hi J:

The choice of 7mm or 8mm is up to the mezzanine board designer. It depends on which mating connectors you use for the high speed and low speed connectors. The High speed is available in two different heights which will give you 7 or 8mm board to board spacing. The Low speed connectors will give you 7mm spacing if you use through-hole version of the connector, and will give you 8mm spacing if you use surface mount versions of the connector.

One dimension you will need for use with the 410c board that is not on the mechanical drawings is the distance between the last pin of the low-speed connector and the first pin of the audio expansion connector. It is 3.95mm.

As you pointed out, “Many footprints are not anchored to the axis of the first pin”, The problem is they can be anchored anywhere, there is no “standard” way of specifying, hence the board drawings give coordinates to pin one. When I designed a mezzanine board, I built my footprints so that the were anchored on the center of pin 1, and the centerline of the connector (the same as the mechanical drawings in the spec).

Sample part numbers for the connectors are in the main 96Boards spec.

Full Disclosure: I am a employee of Qualcomm Canada. Any opinions I have expressed in this or any other post, may not reflect the opinions of my employer.


#3

Thanks!

So, just to double check, perhaps someone has already been through this:

The high-speed connector is specified as 61082-061409LF in the schematics. That’s an FCI part, and 06 means 2x30 pins, while the subsequent “1” indicates receptacle height 1, or 3.7mm. To get 7mm of space between boards I assume I should go with plug type 3, which gives 7mm combined mating height according to the connector datasheet?

FCI datasheet

If so, that would be part no FCI 61083-063xxxx.


#4

Oh, and as for mechanical drawings, I agree that there is no defined standard for specifying connector positioning, I just thought it would be helpful if both dimensions were provided (to the centerline of the first pin and to the centerline of the entire connector).


#5

One more question (sorry for asking so many): you said “The Low speed connectors will give you 7mm spacing if you use through-hole version of the connector, and will give you 8mm spacing if you use surface mount versions of the connector.”

The Molex 87381-4063 connector specified in the Dragonboard 410c seems to have 4.5mm height. The 96boards CE specification doesn’t seem to mention connector height, or perhaps I missed it. I’m now looking at example pin headers to mate with it and the ones I’ve found have a base that is 1.5mm high (Samtec MTMM series). That would give a total height of 6mm using a THT pin header, not 7 or 8.

It would really help a lot if you could provide some example part numbers for mating connectors.

thanks!
–J.


#6

It is sad and angry.
Today June 27 2017 ( !! ) i have the same question as here from November 2015 ( !! )
and the answers are still missing !


#7

Hi @momo

I’ve answered your questions in your other thread:

If I may gently point out that the document I have referred you to was published in Feb 2015 :wink:

It is true that there are definitely things we can improve with the spec, especially for the mezzanine ecosystem, but we didn’t get it completely wrong! We also hope to publish better guidance for mezzanine makers shortly.

Daniel