A Temperature Controlled Hybrid Substrate for Use as a Building Block in Precision Instrumentation Design

A hybrid module containing a temperature controlled substrate has been constructed for use as a universal building block in precision instrumentation design. The module itself is a standard 1.1" × 0.8" × 0.3" twenty-pin hybrid package enclosing a 0.25" × 0.65" aluminum oxide substrate with low thermal coupling to the ambient. Power is applied to a resistive heater deposited on the underside of this thermally floating "platform" to raise its temperature to approximately 67°C. The platform is stabilized at this elevated temperature by a temperature sensor and reference element located on the platform and by simple proportional control electronics located external to the module. The top of the platform has sufficient free area to mount up to six chip resistors and two chip capacitors, or it may be custom printed with a thick film resistor array. Fifteen of the twenty package pins are free for connection to the temperature stabilized camponents. The paper discusses the design of the controller and presents experimental data which shows that it is possible to reduce the temperature variation of the platform to within 1% to 2% of an ambient change over an ambient range of 0°C to 60°C. The design of the module is sufficiently flexible to be used as a universal circuit design building block in high performance instrumentation. Nearly an order of magnitude reduction in the temperature coefficient of some standard instruments should be possible using this technique.