Mechanical Requirement
Height of the component (including heat sink etc.)
Suitable package/footprint: Warning!! Some times packages with same
name have different varieties – for example, there are different types of
SOIC packages – narrow SOIC, wide SOIC, so we need to check the pitch
and width also while ordering the component – not just the name of the
package in the datasheet.
Area of the component
Footprint compatibility for future upgrades: we also need to check
whether the next higher capacity or higher performance version of the
same device is available with the same footprint so that we can upgrade
the capacity in future without changing the PCB layout. This is more
relevant to memory.