Thermal and Structural Analysis of a Suspended Physics Package for a Chip-Scale Atomic Clock

Power dissipation for chip scale atomic clocks (CSAC) is one of the major design considerations. 12 mW of the 30 mW power budget is for temperature control of the vertical-cavity surface-emitting laser (VCSEL) and the alkali-metal vapor cell, each must be maintained at 70±0.1°C even over large ambient temperature variations of 0°C to 50°C. The physics package of a CSAC device is composed of the cell, VCSEL and optical components. This package is heated to 70±0.1°C, but must be very well insulated to dissipate less than 12 mW. To create such a high level of insulation the physics package is enclosed in a gold coated vacuum package and is suspended on a specially designed Cirlex structure. The thermal performance of the suspended physics package has been evaluated by measuring the total thermal resistance from a mockup package with and without an enclosure. Without and enclosure the resistance was found to be 1.07°C/mW. With the enclosure the resistance increases to 1.71°C/mW. These two cases were modeled using FEA, which was found to match well. A FEA model of the real design of the enclosed, suspended physics package was then modeled an was found to have a thermal resistance of 6.28°C/mW, which meets the project requirements. The structural performance of the physics package was measured by shock testing the physics package mockup and recording the response with a high speed video camera. The shock testes were modeled using dynamic FEA and were found to match the measured displacements well. A FEA model of the real design of the physics package was created and it was found that the package will survive an 1800 g shock of any duration in any direction without exceeding the Cirlex yield stress, 49 MPa. In addition the package will survive a 10,000 g shock of any duration in any direction without exceeding the Cirlex tensile stress, 229 MPa.Copyright © 2007 by ASME