1. Field of the Disclosure
The present disclosure relates to the field of temperature control, and more particularly, to providing an interface for maintaining a set point temperature through heating and/or cooling an electronic device or component, typically while the electronic device or component is under test.
2. Background Information
Solid state electronic devices or components, such as semiconductors, have varying performance characteristics based on temperature. Typically, for example, such electronic devices generate heat (i.e., self-heat) during operation, and thus as the internal temperature increases, the performance characteristics change. Also, solid state electronic devices may be used in different environments, possibly enduring a wide range of temperatures.
To ensure constant performance characteristics, it is desirable to maintain a relatively constant temperature of electronic devices. This is especially true when functionally testing electronic devices to ensure proper operation and compliance with design specifications. For example, an electronic device, referred to as a device under test (DUT), may undergo endurance procedures, such as short-circuit testing and burn-in testing, to observe various device characteristics. During such testing, the temperature of the DUT must be kept relatively constant at a predetermined test temperature, or set point temperature, in order for the results to be meaningful. In other words, the tester must be able to confirm that certain observed electrical characteristics are attributable to factors other than changing temperatures.
In order to maintain a constant temperature, known thermal control devices are cable of removing heat, e.g., through a heat sink, as well as adding heat, e.g., through an electric heater. A heat sink incorporates a fluid having a temperature much lower than the test temperature of the DUT. A heater is placed between the DUT and the heat sink, and power is applied to the heater to raise the temperature of the heater face, e.g., to the test temperature required for DUT testing. The heat sink offsets any excess heating, and also removes heat generated by the DUT during the testing process, to the extent this self-heating increases the device temperature beyond the test temperature. Power fluctuations may cause significant and relatively instantaneous self-heating, requiring the need for the thermal controller to quickly and accurately react to offset the unwanted increase in temperature.
The interface where the heat sink (or heater, if used) contacts the DUT is of particular importance for maintaining the DUT at a constant temperature. For example, when the surface of the heat sink (or heater) is not substantially co-planar with the surface of the DUT, there may exist a non-uniform heat transfer across the surface of the DUT, which results in undesirable thermal gradients at the DUT. To account for this, some conventional systems provide a thermal interface material between the surfaces of the heat sink (or heater) and the DUT. For example, a liquid (e.g., a mixture of water and alcohol) may be disposed between the heat sink (or heater) and the DUT. The liquid fills any air gaps between the heat sink (or heater) and DUT, thereby providing a more uniform thermal connection between the heat sink (or heater).
However, the use of liquids as thermal interface materials comes with other disadvantages. For example, device testing is often performed over a wide range of temperatures and pressures, including some below the freezing temperature of conventional thermal interface liquids. When a liquid between the heat sink (or heater) and DUT freezes, the thermal uniformity of the interface often becomes compromised, leading to undesired thermal gradients at the DUT. Moreover, the use of liquid as a thermal interface material also presents disadvantages at higher test temperatures. For example, at some testing conditions, the liquid thermal interface material converts portions of the surface of a ceramic heat sink (or heater) into a microscopic slurry, which then causes unwanted abrasion of the DUT.
Also, even though liquid is useful for filling air gaps between the heat sink (or heater) and the DUT, liquids do not eliminate thermal gradients altogether. This is because different thicknesses of liquid between the heat sink (or heater) and the DUT, which may occur at a microscopic level where the surfaces of the interface are not substantially co-planar, have different thermal resistivities. For example, as depicted in FIG. 1A, a DUT 10 and/or a heat sink (or heater) 15 may have non-planar surfaces 17, 18, which results in differing thickness of liquid 19 at the interface. The thickness of the liquid 19 may be, e.g., 0 μm at a first location 20 and, e.g., 50 μm at a second location 25. Because the thermal resistivity of the liquid changes with the thickness of the liquid, thermal gradients exist when power is applied to the DUT, as shown in FIG. 1B.
In addition to the material between the heat sink (or heater) and the DUT, the interface between the heat sink (or heater) 15 and the DUT 10 may also be affected by the structures to which the heat sink (or heater) 15 and/or the DUT 10 are attached. For example, the heat sink (or heater) 15 is commonly carried by a thermal controller 30, such as that shown in FIG. 2. The thermal controller 30 may comprise, for example, piping that carries different temperature fluids (e.g., heating and cooling water) to the heat sink 15 for maintaining the DUT 10 at the desired temperature. The thermal controller 30, including the heat sink (or heater) 15 and piping, is generally moveable in an axial direction normal to the DUT 10 (in the direction of arrow “A”). In this manner, plural DUT's may be moved past the thermal controller 30 (in the direction of arrow “B”), and the thermal controller 30 brought down into contact with each successive DUT 10 for testing.
However, the rigidity of the structure carrying the heat sink (or heater) 15 often causes the surfaces of the heat sink (or heater) 15 and DUT 10 to be out of alignment. That is to say, the rigidity of the thermal controller 30 makes it difficult to align the surfaces 17, 18 as substantially co-planar at the interface. Such a situation is depicted in FIG. 3, in which it is seen that the surface 18 of the heat sink (or heater) 15 is angled compared to the surface 17 of the DUT 10, such that the surfaces 17, 18 are not substantially co-planar at the interface. In such situations, not only is there a likelihood of a thermal gradient at the interface, but there may also be an uneven force (e.g., torque, moment, etc.) applied to the DUT 10. Particularly, when the testing of the DUT 10 requires an axial force (e.g., up to 100 pounds) be applied to the DUT 10, such uneven application of force due to non-co-planar surfaces can result in damage (e.g., cracking) to the heat sink (or heater) and/or DUT.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.