Hub-Module  Maximum Component Height
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                                         Original Rev.  22-Mar-2015
                                          Current Rev.  30-Mar-2015


The height available for Side 1 and Side 2 components on
ATCA circuit boards is described in section  2.2.4  of the
PICMG 3.0 specification.

All of the component height calculations start from the
6.61 mm  specification for the distance from Side 1 of the
PCB  (pcb top side)  to the Pitch Line that is adjacent to
the back side of the card.  Note that the top surface of the
PCB is always the same distance from this Pitch Line,
independent of the thickness of the PCB.

The only other basic specifications are:  the  6HP  30.48 mm
1.200 inch  unit cell spacing of the Pitch Lines   and   the
2.54 mm high component keep out zone between the tops of the
top side components and the next Pitch Line.


Thus for Side 1,  without a Side 1 cover plate,  one may use
components that are:  30.48 mm  -  6.61 mm  -  2.54 mm  =
21.33 mm tall.   If a Side 1 cover plate is used then its
thickness must be subtracted from  21.33 mm  to get the
maximum available Side 1 component height.


The available Side 2 component height depends directly on
the thickness of the PCB  and  on how much clearance one
wants between the Side 2 components and the required Side 2
Cover Plate.   Note that the back side of the Side 2 Cover
Plate may be immediately against the adjacent Pitch Line.

I assume that the Hub Module PCB will need to be in the range
of 22 layers, with 4  100 Ohm pair layers on the top and
bottom and 4  1 oz power layers in the middle.  Based on the
CMX stackup this will result in a PCB that is about  3.3 mm
thick.   I don't think that we can count on the Hub Module
PCB being thinner than this.   The standard thickness of the
required Side 2 Cover Plate is  1.0 mm.   Thus with zero
clearance one could use Side 2 components that are:
6.61mm  -  3.3mm  -  1.0 mm  =  2.31 mm  tall.

From this  2.31 mm  maximum Side 2 component height one must
subtract something for clearance of for a sheet of insulating
material.   Let's pick  0.25 mm  (10 mils)  for the thickness
of an insulating sheet  and  0.06 mm  (2 mils)  for clearance.

This gives a maximum Side 2 component height of  2.0 mm.

Note that in the above component height calculation,  zero
slack was assigned for PCB bow and twist.

-->  I will design the Hub Module with a  2.0 mm  maximum
     Side 2 component height.


The thickness of the plastic insulation in the Dell modules
and is some power supply modules is  10  to  12 mils.
A possible insulation is DuPont Nomex Aramid "paper".