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Is the "M" the last character in the Footprint Name? If so, it was built using the IPC-7351 "Most" Environment.
n IPC-7351
Density Level A: Maximum (Most) Land Protrusion – For
low-density product applications, the 'maximum' land pattern condition has been
developed to accommodate wave or flow solder of leadless chip devices and
leaded gull wing devices. The geometry furnished for these devices, as well as
inward and “J” - formed lead contact device families, may provide a wider
process window for reflow solder processes as well.
n IPC-7351
Density Level B: Median (Nominal) Land Protrusion – Products
with a moderate level of component density may consider adapting the 'median'
land pattern geometry. The median land patterns furnished for all device
families will provide a robust solder attachment condition for reflow solder
processes and should provide a condition suitable for wave or reflow soldering
of leadless chip and leaded Gull Wing type devices.
n IPC-7351
Density Level C: Minimum (Least) Land Protrusion – High
component density typical of portable and hand-held product applications may
consider the 'minimum' land pattern geometry variation. Note: IPC and IEC are both considering dropping the "Most" Envirnoment in the near future. It will still be available for PC boards that require hand-soldering. It has been proven that the "Nominal" Environment passes all the stress tests that the "Most" Environment does. So there is no longer a future need for the "Most" Environment. The "Least" environment will become the new Standard Footprint pattern coming up in the near future.
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