Fujitsu FIM24721 Series Application Note page 12

Recommended mounting condition of Micro ICR
The Micro ICR includes precision optics. If package of the receiver is deformed
by excess load, the Micro ICR may be degraded in its characteristics or
damaged.
In order to prevent the degradation or damage, the receiver should be mounted
on flat area ( flatness < 15um, surface roughness < 12.5um ) larger than
package bottom area including package flanges by M1.2 screws with
0.376kgf*cm torque.
FUJITSU OPTICAL COMPONENTS CONFIDENTIAL
12
12
PS-15-349-01