Semiconductor testing at a wide range of temperatures during manufacturing test, with the DUT operating, was originally considered a Military Grade application. However, with the increase in Mobile devises, and the variety of environments they are used in, The IC’s and Semiconductors require more stringent testing at wider operating temperature ranges. The term Tri-Temp Test is used to describe this test requirement that can range from -55˚C to 135˚C.
Testing devices at varying temperatures generally meant using an Environmental Thermal Chamber. The limitations with this method are the controlling of the temperature by passing moving air over heating and cooling elements. The temperature changes were slow to respond, and it is difficult to maintain a constant temperature at various points in the chamber. This can be an expensive and inefficient method of temperature testing and will limit throughput in a manufacturing environment, due to slower temperature transitions. These types of Chambers also use a great amount of power and take up a large amount of floor space and generally have a larger price tag.
In contrast, Thermal Electric Cooler (TEC) with a precision Temperature Controller allows the ICs to be in direct contact to the thermal chuck or thermal platform. With highly thermal conductive materials such as copper or aluminum, used as the base plate for the chuck or thermal platform and the TEC chips directly connected to the base plates, the thermal conduction can be faster responding and bi-directional. This allows for temperature settings above and below ambient. The Bi-Directional drive capability of the Thermal Controller maintains accuracy and allows for fast temperature transitions. Using thermocouples to measure and maintain the Device Under Test temperature.
A thermoelectric cooler (TEC) module is a solid state device which can control heat flux using current. It is very useful in small scale temperature control, providing fast temperature response and ultra-high temperature stability. TEC temperature control equipment can also be very compact and efficient.
Selecting the correct TEC device or the appropriate Thermal Chuck or Platform requires Calculations that include parameters such as Th (Hot surface temperature in ˚C), Tc (Cold Surface temperature in ˚C), Qmax (Heat Load of Device under test in Watts) and Rth (Thermal resistance of the heat exchanger in ˚C/Watts).
Most TEC Manufacturers will supply graphs or tables to help in the selection of the appro-priate TEC, or forms for determining the Custom Thermal Chuck or Thermal Platform with multiple TEC’s.
One consideration with very low temperature conditions, such as -55℃, if the IC under test does not have good thermal insulation to ambient, it will become a heat source and have a thermal leakage effect. Condensation can form under low temperature testing, so it is important to create moisture free environment. There are various types of Air Drying methods that can be used.
The TEC controller requires precision measurements of the temperature of the Device un-der test and fast responding bidirectional drive capability. Some use a single thermocouple for measuring the DUT temperature. The better TEC controllers will require 2 Thermocou-ple measurements especially if they utilize proportional-integral-derivative control (PID) control.
A PID controller calculates an “error” value as the difference between a measured process variable and a desired setpoint. The controller attempts to minimize the error by adjusting the process control inputs. The PID controller calculation (algorithm) involves three sepa-rate parameters,: the proportional, the integral and derivative values, P, I, and D. P depends on the present error, I on the accumulation of past errors, and D is a prediction of future errors, based on current rate of change. The weighted sum of these three actions is used to adjust the process via a control element of the power supplied to the TEC.
Selecting the parameters for the PID controller manually can be very difficult. There are TEC Controllers that have an Auto Tune PID control that will automatically tune the PID. Some TEC controllers use a small signal and one-directional temperature transient to find PID pa-rameters. This auto tune method is OK for heater only temperature control, but not for TEC control. In order to match the thermal response of a TEC control system, Advanced TEC Controllers use a large-signal and bi-directional driving methods for PID auto tune. This method results in the best temperature control behavior, which is fast, precise, and stable. While some other TEC controllers require a set of PID parameters for every 20˚C, Chroma’s Advanced TEC Controllers need only a set of optimal PID parameters (usually auto tuned at 40~50 ˚C) to cover all operation from -50 to 150 ˚C. The PID Control Graphs below illustrate the differences of a conventional on/off control, and PID control not optimized and an Auto tuned PID control.
To create a complete thermal test system would include the Thermal Chuck or Platform, with the Thermal controller and a small dedicated covered area around the platform to in-sure a dry environment free of condensation. An example of this type of system is the Chroma 3110 Tri-Temp test system (pictured below).
By Using a 54130 TEC controller with a proper platform and the Chroma IC handling technologies, Chroma provides total Tri-temp solution for IC manufacturers. Chroma 3110 Is designed for signal site test for test laboratory and Chroma 3260 provides 6 test sites to increase the test throughput.
As shown, the DUT (Device under test) will be contacted by the “Chuck” which will be customized by different form factors. The TEC which bridges between “Chuck” and “Cold Plate” will be driven by the bidirectional current from the TEC controller. By using 2 thermocouples will check the temperature differences between Present Value“P.V.” and Set Value “S.V.”, then feedback to TEC to adjust the power. Chiller will be connected to “cold plate” in case the accumulated heat needs to be taken away. Air dryer will provide the necessary “dry air” to prevent the condensation on the test site, which hosts DUT.
In conclusion, Thermal Electric Coolers (TEC) constructed in a Thermal Chuck or Thermal Platform and controlled by a TEC Precision Controller, can be efficiently used in manuafac-turing and design verification testing. With improved overall performance, accuracy and lower costs and better throughput.
For more information on Chroma’s TEC Controller and Data Logger products, please visit our Thermoelectric test and Control product page.