As one soldering expert at Fraunhofer Institute said during a discussion: Everything breaks, it is just a matter of how many cycles.
The key thing is to remove the mechanical stress from the solder joints and the points you listed are not going to help you very much in solving the mechanical strength.
Some sources of mechanical stress:
- Pushing and bending on buttons, knobs, connectors. SMD USB mini connectors where very sensitive...
- Vibration and dropping on the floor
- Thermal expansion/contraction
- Ageing, plastic materials releases softeners and other chemicals. Annealing. Even 1% can make a huge difference if the distance is long enough.
At first it might sound like a good idea to fix every single connector and pushbutton soldered on the PCBA to the housing. But you must also consider the operating conditions, for instance operating temperature range, and the materials that are used in the enclosure. Plastic materials might have a much larger thermal expansion than the PCB laminate. Sometimes it is better to have on fixed point, like all connectors along one edge, and let all the other thing be floating with a flexible connection.
I have seen some pushbutton extenders that had mechanical stops that touched the PCB surface to offload the tactile switch. Looked like a table where the bottom surface interfaced the switch and the 4 legs limited the movement.
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