A Thermal Model of the LabPET II ASIC

The LabPET II detection module is the building block of PET scanners for ultra-high-resolution imaging of small to mid-sized animals and the human brain. For optimal performance, it must be operated at a stable temperature. The detection module is composed of four APD-LYSO detector arrays with two flip-chip ASICs mounted on the backside of an interposer generating 550 mW each. Currently, the scanner architecture includes an air cavity around the electronics and smaller cavities close to the detectors. Cooling down the front-end electronics located in these small cavities becomes problematic as the number of modules increases to address the different targeted configurations of the LabPET II scanners from mouse to human brain geometries. A basic knowledge of the heat distribution is necessary to develop an efficient thermal management in all cases. The aim of this work is to build a model of the LabPET II ASIC and associated PCB for enabling heat flow simulations and circumscribe the thermal management requirements. The Flow Simulation module (SolidWorks), was used to build the thermal model. The ASIC and the interconnection with the PCB were reproduced accurately while some adjacent structures were simplified to ease the simulation burden. The model was applied to simulate three different configurations of printed-circuit boards carrying the ASICs and other components where a fan is turned on/off to create a forced airflow. Each simulation was compared to some experimental measurements. A temperature difference of less than 5 degree Celsius between the simulations and experimental measurements is noticed, giving confidence that the thermal model of the ASIC is valid and transferable to different mechanical assemblies.