  The Backward Angle Neutron Detector (BAND) of CLAS12 detects neutrons emitted
at backward angles of $155^\circ$ to $175^\circ$, with momenta between $200$
and $600$ MeV/c. It is positioned 3 meters upstream of the target, consists of
$18$ rows and $5$ layers of $7.2$ cm by $7.2$ cm scintillator bars, and read
out on both ends by PMTs to measure time and energy deposition in the
scintillator layers. Between the target and BAND there is a 2 cm thick lead
wall followed by a 2 cm veto layer to suppress gammas and reject charged
particles. This paper discusses the component-selection tests and the detector
assembly. Timing calibrations (including offsets and time-walk) were performed
using a novel pulsed-laser calibration system, resulting in time resolutions
better than $250$ ps (150 ps) for energy depositions above 2 MeVee (5 MeVee).
Cosmic rays and a variety of radioactive sources were used to calibration the
energy response of the detector. Scintillator bar attenuation lengths were
measured. The time resolution results in a neutron momentum reconstruction
resolution, $\delta p/p < 1.5$\% for neutron momentum $200\le p\le 600$ MeV/c.
Final performance of the BAND with CLAS12 is shown, including electron-neutral
particle timing spectra and a discussion of the off-time neutral contamination
as a function of energy deposition threshold.
