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Background

Cohu, Inc. designs various types of testing manifolds for semiconductors. One of the manifolds tests semiconductors under extreme temperatures. One specific application is for aerospace industry where semiconductors are tested under temperatures as low as -55 C. The current system is an open cycle system in which liquid nitrogen (LN2) and compressed dry air (CDA) are mixed to the desired testing temperature and then exhausted after the cold gas mixture passes through the testing loads. This project's objective is to reduce the consumption of LN2, CDA, and power in order to reduce the cost of testing.

 Current System Diagram

Objectives

• Sealed closed cycle system capable of recirculating mixed gases

• Compatible with sponsor's current setup in terms of sensor mountings and tubing system

• Maintain heater temperature at -55℃ ± 5℃under variable test load power at steady state

• Temperature measurement accuracy of 1℃

• Use a 600-800 W heat source to emulate various testing loads.

 Final System Diagram

  Testing Results

   Problems Encountered

 Possible Future Improvements

• • One RTD malfunctioning when power supply is plugged

  • Very small leakage in the system due to the compressor

    • Typically occurs at 193 kPa (28 psi)

  • Compressor significantly warmed up the recirculated gas

    • Recirculated gas was only about -5℃ at the exit of the sump

  • Clearly seen from the different level of frosting of the compressor inlet/outlet

• • Compressor

    • Better sealing to reduce gas leak

    • Decrease heating of gas to increase system efficiency

  • Sump

    • Smaller sump (3-5L) will be sufficient and will decrease heat loss

    • Rectangular box for better mounting in the system

  • Mixing Manifold

    • Integration of the mixing manifold and recirculated flow control manifold

    • To reduce system complexity and system cost

  • Cover Box

    • Liftable lid for easy system maintenance