Advantech SOM-Express Design Guide
Chapter 8 Heat Sink Recommended Design 105
Figure 8-4: SOM-Express Module Heat-Spreader
The interior holes at coordinates (40, 40) and (80, 40) are tapped through holes with
a M2.5 thread. The interior holes do not receive standoffs. These holes may be
sealed on the module side by an adhesive backed foil, or they may be blind tapped
holes with a minimum thread depth of 2.5mm. They are intended to allow additional
attachment points to the heat-spreader from outside the module.
8.7 Component Height – Module Back and Carrier Board Top
Parts mounted on the backside of the module (in the space between the bottom
surface of the module PCB and the Carrier Board) shall have a maximum height of
3.8mm (dimension ‘B’ in Figure 8-5)
With the 5mm stack option, the clearance between the Carrier Board and the bottom
surface of the module’s PCB is 5 mm (dimension ‘A’ in Figure 8-5). Using the 5mm
stack option, components placed on the Carrier Board topside under the module
envelope shall be limited to a maximum height of 1mm (dimension ‘C’ in Figure 8-5),
with the exception of the mating connectors. Using Carrier Board topside
components up to 1mm allows a gap of 0.2mm between Carrier Board module
bottom side components. This may not be sufficient in some situations. IN Carrier
Board applications in which vibration or board flex is a concern, then the Carrier
Board component height should be restricted to a value less than 1mm that yields a
clearance that is sufficient for the application.
If the Carrier Board uses the 8mm stack option (dimension ‘A’ in Figure 8-5), then the
Carrier Board topside components within the module envelope shall be limited to a
height of 4mm (dimension ‘C’ in Figure 8-5), with the exception of the mating
connectors. Using Carrier Board topside components up to 4mm allows a gap of
0.2mm between Carrier Board topside components and module bottom side
components. This may not be sufficient in some situation. IN Carrier Board
applications in which vibration or board flex is a concern, then the Carrier Board
component height should be restricted to a value less than 4mm that yields a
clearance that is sufficient for the application.
Figure 8-5: Component Clearances Underneath Module
