Speaker
Description
Silicon sensor based particle detectors operated in an hadronic radiation environment need to be cooled to counteract the radiation induced leakage current and prevent thermal runaway. To achieve this most efficiently, a low thermal resistance is required between the detector modules and the cooling structures. In many cases dry thermal contacts are sufficient, but especially for large area contact so-called thermal interface materials (TIM) - of which many products are available on the market - are the preferred choice. However, in the use case for detector cooling there are many requirements, such as no liquid, no heat cure, low thermal impedance, no compression force, radiation hardness, making it more difficult to find a suitable TIM. An example use case is the cooling of the CMS Phase-2 Outer Tracker PS modules. Its entire underside of 5 x 13 cm must be thermally coupled to the mechanics. The current candidate materials are room temperature curing two component thermal gap fillers.
The contribution will outline the measurements and highlight the results to qualify gap filler materials to the radiation dose expected for the lifetime of the CMS Outer Tracker. Three different types have been tested thermally and mechanically in this campaign.
The thermal test setup determines the thermal conductivity of a test sample by measuring the temperature gradient with a controlled amount of heat flow through a sample. The development and calibration of this custom thermal conductivity measurement setup is detailed in a separate contribution to this conference.
Mechanical tests are needed to ensure structural integrity of the thermal interface even when under some extent of thermal stress. Since the gap fillers can not be considered glues in classical sense, the standard lap shear and peel tests can't be used for qualification. Resembling the style of an ISO 4587 lap shear test, and an ISO 25217 mode-1 fracture test, test samples were made with a large 5 x 5 cm adhesion overlap using plasma cleaned carbon fibre plates to have a surface comparable to its intended use case. The testing method developed for this study will be presented and motivated.
After testing of unirradiated samples, they have been irradiated to 600 kGy. The measured mechanical and thermal properties will be presented and the results before and after irradiation will be compared. We found that the gap filler material hardens significantly, however its thermal and adhesive properties are maintained. The hardening reduces the cohesion failure, leading to an increased mechanical strength.
| Collaboration / Activity | Generic R&D |
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