Project Background

Cohu is a leading company in semiconductor chip testing, using automation to reduce costs and test as many devices as possible. Chips are picked up and placed into a testing socket where they're terminally controlled using a thermal control unit and fluid metering valve, ensuring temperatures between -55°C to 175°C. Multiple devices are tested in parallel, requiring thermal units to be located close together, but this may cause performance issues due to limited space and environmental temperature.

Primary Issue: Current flow valves don't work well under high temperatures

• • Solenoid actuator experiences demagnetization

  • High temperatures cause sustained damage to other electrical components within flow valve

Goal: Redesign flow valve by separating the actuator mechanism (currently actuator mechanism: solenoid) from the actual valve mechanism

Proposed Solution: Remove electronics driving the actuator from high temperature testing environment and enable a remote (mechanical) connection between actuator and valve 

Purpose: Expand the capabilities of Cohu’s testing capabilities to accommodate broader testing temperature range for semiconductors

Executive Summary

Semiconductors have a wide variety of applications in contemporary industrial-sector and commercial products, including in many extreme environments. Some examples of high performance semiconductors are found in automobiles where they are exposed to high temperatures adjacent to combustion engines. 

Cohu Inc., the sponsor of this design project, is an industry leader in semiconductor testing and validation. The current semiconductor chip testing systems utilized by Cohu depend on liquid cooling for the thermal regulation of computer chips during testing. However, the existing advanced flow control valves that regulate the flow rate of the refrigerants are likely to fail at higher temperatures. These flow valves utilize solenoid actuators that experience demagnetization at higher temperatures, inhibiting their functionality. Similarly, at high temperatures the electronics that drive these valves can experience damage. The testing environment needed to test high performance semiconductors requires elevated temperatures that are unsuitable for the existing AFC valves.

The objective of this design study is to develop a flow valve that isolates the sensitive electronics from the extreme temperatures in the testing environment. The proposed solution decouples the valve body from the actuator and connects both subsystems with a flexible mechanical linkage. The actuator can be operated from outside the test chamber in suitable temperatures while the redesigned flow valve is built to withstand the increased temperature range in the test environment. Furthermore, this advanced actuator is designed to automatically respond in real time to control feedback during the semiconductor testing process. As more cooling is necessary, the flow valve will open to increase the refrigerant flow rate while closing as less cooling is needed. 

In this proposed design solution, four main subsystems can be identified:

1. Valve Body

2. Mechanical Linkage

3. Actuator

4. Feedback Control System

The proposed design solution integrates a stainless steel valve body capable of interfacing with the existing AFC valve port. An armature behaves as a linear actuator within the housing, regulating the flow of fluid through the valve as it opens and closes against the inlet. The armature is driven by a bowden cable acting as a mechanical linkage to the actuator. This flexible cable can be extended up to one meter from the test environment to protect sensitive electronics from the extreme temperatures experienced within the testing chamber. A feedback control system spins a stepper motor which uses a rack and pinion to develop linear motion in the bowden cable.