Very compact, water-cooled SiPM module for PET/MRT applications

We present the technology for very compact hybrid circuits with one water cooled LTCC substrate, Silicon Photomultipliers and ASICs for Positron Emission Tomography / Magnetic Resonance Tomography Applications. The SiPM modules with an area of 32.8 by 32.0 mm² contain 12×12 SiPMs in a pitch of 2.5 mm². The readout of the 144 channels is done by four highly specialized ASICs. The water cooling channels inside the 11 layer LTCC substrate with 2.1 mm thickness provide cooling for the ASICs, the SiPMs, and thermal insulation between ASICs and SiPMs and allow a very compact design of the detector modules. The 12 SiPM arrays with a 2×6 geometry are wire bonded only at the edges of the SiPMs to the LTCC, enabling the use of nearly the whole detector area for detecting photons. At the opposite side of the substrate four ASICs for the readout electronic with 272 μm bump pitch are flip-chip bonded to the LTCC substrate and underfilled and a few SMD components are mounted. Substrates and all components are MRT compatible. It could be shown, that a completely sufficient cooling with room temperature water is possible. A reduced time to thermal stability of the detector module (10 seconds) compared to air cooling (130 seconds) and water cooled copper pipes at the backside of the ASICs (44 seconds) could be shown.