Generally, a footprint should include a field of the format
In the majority of cases, the pin quantity is self explanatory and is sufficient to describe the number of pins on the symbol.
However there may be cases where this numbering is insufficient. Where the number of footprint pins does not match the number of package pins, exceptions must be made.
Exception: Omitted pins, missing pin numbers are skipped
The LTC3638 comes in an
MSOP-16 package which has four missing pins, for increased voltage isolation.
In this case, the numbers for the missing pins are skipped and the normal pin numbers are assigned to the remaining pins.
To indicate this, the footprint should be named as follows:
xx= number of remaining pins
yy= number of remaining pins + number of removed pins
In the LTC3638 example above, this would result in:
The footprint pads should be numbered like so: