iMX7D module component height max

In the step-file of the colibri_module_with_maximum_component_height_3d_step_model.zip a max component height of 1.8mm on the bottom side (facing the carrier board) is specified,
but in the colibri_arm_som_imx7_datasheet.pdf and colibri_carrier_board_design_guide.pdf it is 2.2mm.

What`s correct ?

Thank you !

Hi Moscht

Thanks for your feedback. You are absolutely right!

Please consider the value in the Carrier Board Design Guide of 2.2mm as correct. We will change it accordingly in the STEP file.

BR Andrija

Hi Andrija !

Thank`s for your reply !

In 3D CAD the component height on the evaluation-board below the module is 0,55mm (RA4, RA5, …) and the module is around 2,75mm distance to the evaluation-board.
With a component heigth of 2,2mm on the Module there is 0,0mm space (so no space) between the components of the evaluation-board and the module (maybe more/less when considering tolerances).

So with the actual documentation there is not even possible to place a 0402 decoupling-capacitor below the module with the connector used on the evaluation-board (Tyco 1473005-1). Here we checked the board-design of the evaluation-board how this problem was solved there.
There we saw the decoupling-capacitors are placed&routed against the rules of the “Carrier Board Design Guide”, “Layout Design Guide” and state of the art of electronic design, LOL ^^

Is it possible to get a more detailed documentation of the component heights on the module (facing the carrier-board), to place parts below the module with this board connector ?

Thank you !

BR

Moscht

Hi @Moscht,

The board to board distance is actually 2.9mm, not 2.75mm. Please have a look into the (datasheet of the connector manufacturer. There, you will see that the space between the carrier board and the middle of the module is 3.4mm. Since the module is 1mm thick, we get a board to board spacing of 2.9mm. This gives us some tolerance for components with 0.55mm height.

Unfortunately, I do not have a detailed 3D drawing of the module. The CAE tool we are using for designing the modules does not feature a 3D export. Anyway, I really do not recommend placing higher components on the carrier board, since we cannot guarantee that in a future revision of the module that we are not placing higher components or move components around. The only thing we guarantee is that the module will not exceed the 2.2m on the bottom side as stated in the design guide.

Kind regards
Peter.

Hi Peter !

You are absolutely right, the nominal distance from the module to the board is 2.9mm.
We have measured from the lower edge of the slot of the board connector, which is the lowest possible position of the module in the slot of the connector and the module is held in this position only with the contacts of the plug.

For a product in a real life environment we have to consider a worst-case.
There we have to take the 2.75mm gap from the module to the board.
So with a 0402 MLCC, that has a typical height of 0.50mm (±0.05), there is already no gap (2.75-2.2-0.55=0.0mm).
If we consider further points like mechanical vibration/shock, solder paste below the MLCC, … possibly this lead to a contact of the parts.

For an evaluation board the consideration is ok, for a released product placed on the market we think not :slight_smile:

BR

Moscht

Hi @Moscht,

I fully understand your concerns. However, 2.2mm is already the worst case number. Components on the module are not allowed to higher than 2.2mm (including tolerances). Unfortunately, TE does not really specify the tolerances for the board-to-board height. the 3.4mm is just a control number. The 2.75mm cannot even be found in their datasheet. The PCB thickness itself is 1mm +/-0.1mm. The whole thing can be tight, but I have never had any report of an issue. We did fibration and shock tests on our own. The Results can be found here.