  In this paper we report on the characterization of SiPM tiles developed for
the R & D on the DUNE Photon Detection System. The tiles were produced by
Fondazione Bruno Kessler (FBK) employing NUV-HD-SF SiPMs. Special emphasis is
given on cryo-reliability of the sensors, i.e. the stability of electric and
mechanical properties after thermal cycles at room and 77K temperature. The
characterization includes the determination of the I-V curve, a high
sensitivity measurement of Dark Count Rate at different overvoltages, and
correlated noise. The single p.e. sensitivity is measured as a function of the
number of sensors connected to a single electronic channel, after amplification
at 77K using a dedicated cold amplifier.
