Darkside-20k is a global direct dark matter search experiment designed to reach a total exposure of 200 tonne-years free from instrumental backgrounds. The core of the detector is a dual phase Time Projection Chamber (TPC) filled with 50 tonnes of low-radioactivity liquid argon.
The entire TPC wall is surrounded by a gadolinium-loaded polymethylmethacrylate, which acts as a neutron veto, immersed in a second low-radioactivity liquid argon bath enclosed in a stainless steel vessel. The neutron veto is equipped with large area Silicon Photomultiplier (SiPM) array detectors, placed on the TPC wall. SiPMs are arranged in a compact design meant to minimize the material used for Printed Circuit Board (PCB), cables and connectors: Veto PhotoDetection Units (vPDUs).
A vPDU comprises 16 Tiles, each containing 24 SIPMs, together with front end electronics, and a motherboard, which distributes voltage and control signals, sums tiles channels, and drives the electrical signal transmission. The neutron veto will be equipped with 120 vPDUs.
The paper will focus on the production of the first four vPDUs, describing the assembly chain in the UK institutes, in order to underline the rigorous QA/QC procedures, up to the final characterization of the first completed prototypes. Tests have been extensively performed in liquid nitrogen baths either for the single Tiles and for the assembled vPDUs.