Use mechanical techniques to maintain a 1.5 mm space between the module PCB and the expansion board.
Use conductive hardware to provide a ground path between the expansion board and the module thermal plate. The PCB should be using grounded studs.
Apply even force (0.1 newton-meter or 0.9 in-lbs, maximum) at each through-hole mounting locations (module inserts).
Thermal solutions that interface with the module thermal plate must be independently supported to prevent forces that can lift, twist, or crush the module during any movement-transition or vibration during actual, end-device use cases.