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Liquid Thermal Interface Application

WINTER 2012  MAE 156B SPONSORED PROJECT

UNIVERSITY OF CALIFORNIA, SAN DIEGO

SPONSORED BY JAMES W. BABCOCK (Ph.D.), DELTA DESIGN

Background:

Semiconductor devices require many tests during their manufacturing process to characterize their quality and performance capability.  These tests are done at specific, controlled temperatures, for to monitor the performance of devices under test (DUTs) as the performance varies with the temperature.  The temperature controlled testing device is one of Delta Design’s enabling technologies.  The temperature control is accomplished by contacting the DUT with a proprietary Thermal Unit (TU), which can change its temperature very rapidly.  In order for this TU to effectively control the temperature of DUT, the thermal resistance between the TU and DUT must be as low as possible.  One method to lower this thermal resistance is to maintain a very thin film of water between the TU and DUT.  For very short tests, it is sufficient to place a drop of water between the TU and DUT before the testing, but for longer period of testings at higher temperatures, the water will evaporate and thermal resistance will increase.  A method of continuous replacement of the water would be very useful.  One possible method of doing this would be to periodically inject water through a passage in the TU to the TU-DUT interface.

Device Under Test (DUT) and Thermal Unit (TU)

Objectives: 

The objective of this project is to build a prototype of a water application system that would continuously supply just the right amount of water to the TU-DUT interface.  This system would consist of a method of supplying controlled amounts of water to the interface based on the thermal resistance between the TU and the DUT.  Too little water would give poor thermal contact and poor thermal control, which would cause overheating of the DUT and burnout the DUT. On the other hand, too much water could leak onto the DUT package or printed wiring board and may damage the electric circuits on the DUT.  This product is intended to be mass-produced, so it is important to keep the cost low as well.

Description of final design:

Features:

> Water Application Feedback System

Thermal Interface Management System

The Water Application Feedback system is the main system that we are creating for the project.  To maintain a low thermal resistance between TU and DUT,  the water film needs to completely cover the surface of DUT at any conditions.  The system controls supplying of  water into the TU-DUT interface based on the feedback signals of RTD sensors on the TU and the DUT, and the Power supplied by DUT.

> Water Supply Overflow Detecting System

Concept of Overflow Detecting System

Since the Water Application Feedback system cannot manage excess of water supply, there needs to be a system that can detect the overflow of water.  The Water Supply Overflow Detector is a simple circuit that can tell when water comes to the edge of the DUT.

> DUT Power Management and Protection System

The DUT power management and protection system is the system that prevents the power being supplied to the DUT when the temperature of the DUT is high.  

Summary of performance results:

To succeed the project, those systems above must work properly for supplying right amount of water into TU-DUT interface at variety of conditions.  Since the rate of evaporation of water changes dramatically above the boiling point (100 degree Celsius), we needed to take extra-care for testing performance above 100 degree Celsius.

[results]