A brake between a servo motor and a gearbox is part of the drivetrain, not an accessory: if it winds up elastically under load, the position read at the motor is not the position at the output. Nexen built the Eclipse SBP so the holding path has no give in it.

Why zero backlash matters when the brake sits between motor and gearbox?

Because torque flows through the brake on its way to the load. The SBP transmits torque through flexible discs to the armature plate, a coupling with zero backlash up to 100% of holding torque, so the motor encoder reading stays honest even while the brake holds a heavy axis. Torsional rigidity keeps the system from winding up under peak loads - the error a flexible brake introduces into a positioning loop is removed before it reaches the controller.

When would you pick pneumatic release over electric?

When the machine already has a plant air system and the brake must stay simple. SBP releases at 4.1-8.3 bar and engages by springs the moment pressure is gone - the fail-safe direction for e-stop and holding duty. Static torque spans 2 to 125 Nm across the series, IP67 sealing suits washdown cells, and the integral flanges adapt the brake to any servo or AC motor brand, so the motor and brake are matched at purchase, not adapted in the shop.