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Research Papers

# Thermal Conduction Switch for Thermal Management of Chip Scale Atomic Clocks (IMECE2006-14540)

[+] Author and Article Information
A. D. Laws

Y. J. Chang

V. M. Bright

Y. C. Lee

J. Electron. Packag 130(2), 021011 (May 15, 2008) (6 pages) doi:10.1115/1.2912187 History: Received February 20, 2007; Revised October 03, 2007; Published May 15, 2008

## Abstract

We report the first use of a bimetallic buckling disk as a thermal conduction switch. The disk is used to passively alter the thermal resistance of the package of a chip scale atomic clock. A vertical-cavity surface-emitting laser and a cesium vapor cell, contained in the clock, must be maintained at $70±0.1°C$ even under an ambient temperature variation of $−40°Cto50°C$. A thermal test vehicle has been developed to characterize a sample package with a thermal conduction switch. Three cases are presented for the temperature control of the test vehicle under different load placements and environmental conditions: (1) a heating load with a good conduction path to the switch in a vacuum package; (2) the same loading as in Case 1, but packaged in air; and (3) a heating load insulated from the switch, in a vacuum package. At $38°C$, the switch snaps upward to reduce the package’s thermal resistance. As a result, the heating power needed to maintain a constant temperature, $63.9±0.1°C$, is increased from $118to200mW$ for Case 1. Such a significant change of the thermal resistance demonstrates the effectiveness of the thermal switch. However, the switch becomes less effective with air filling the gap, as in Case 2, and the switch is not effective at all if the heating load does not have a good conduction path to the switch as in Case 3. The steady state response of this novel thermal conduction switch has been well characterized through experimentation and finite element analysis.

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## Figures

Figure 1

Illustration of the 1cm3 CSAC designed to utilize waste heat by using a bimetallic snap based thermal conduction switch

Figure 2

Illustration of heat transfer path and estimated allowable heat rates to meet the ultimate clock power requirements of less than 30mW

Figure 3

(a) A bimetallic snap disk taken from an Airpax 5003 series thermostat. (b) Illustration of the insulating, snapped down, and conducting, snapped up, states of the bimetallic snap based thermal conduction switch.

Figure 4

Illustration of a thermal test vehicle for characterizing the bimetallic snap based thermal conduction switch

Figure 5

Experimental results from the thermal conduction switch test vehicle for the side and corner resistors in room temperature air (25±1°C) and 60mTorr vacuum (25±1°C)

Figure 6

Experimental and FEA results for the center resistor in room temperature air (25±1°C)

Figure 7

Experimental and FEA results for the center resistor in 60mTorr vacuum (25±1°C)

Figure 8

2D axyisymmetric, coupled field, contact model of the bimetallic snap based thermal conduction switch test vehicle

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