Cooling of multi chip module by the use of two-phase flow in liquid channels

The use of silicon microstrip detectors are gaining a lot of interest for instance within X-ray imaging. Approximately 1200 parallel diodes are made on a typical 60 mm times 60 mm silicon detector. The signal level from one of this diodes is in the order of 5 fC. The detectors must therefore be very intimate combined with a "first level" of read-out electronics, consisting of a low noise charge amplifier and some control and read out system. This readout electronic must be implemented on separate silicon chips. We are now trying to use the silicon microstrip detector itself as a Multi Chip Substrate for the read out electronics. The VLSI circuits will probably be located along one or two edges of the square detector briquette. One major problem is the cooling of this module. The microstrip detector needs a very stable and well controlled temperature for an optimal function. This paper will be concerned with the use of two-phase liquid/vapour channels integrated into the mechanical support structure for the detector. The liquid evaporates when it is absorbing heat from the VLSI circuits. We thereby obtain a two-phase liquid- vapour transport in the channels. The paper will present our work on two fundamental topics. One is the temperature distribution along the two phase channel. The other important task is the initiation of nucleate boiling. For the experimental part we have used Fluorinert liquid, FC-87 with a boiling point of 31/spl deg/C at normal atmospheric pressure.