  This report shows the design and the performance of a large area Silicon
Photomultiplier (SiPM) module developed detection of fluorescent light emitted
from a 10 cm scale volume. The module was optimized for the planned ACME III
electron electric dipole moment (eEDM) search, which will be a powerful probe
for the existence of physics beyond the Standard Model of particle physics. The
ACME experiment searched for the eEDM with the world's highest sensitivity
using cold ThO polar molecules (ACME II). In ACME III, SiPMs will be used for
detection of fluorescent photons (the fundamental signal of the experiment)
instead of PMTs, which were used in the previous measurement. We have developed
an optimized SiPM module, based on a 16-channel SiPM array. Key operational
parameters are characterized, including gain and noise. The SiPM dark count
rate, background light sensitivity, and optical crosstalk are found to all be
well suppressed and more than sufficient for the ACME III application.
