Conventional integrated circuit (IC) manufacturing requires each IC device be electrically tested at elevated and depressed temperatures (typically -60C to 160C) before shipment in order to properly classify the device performance (e.g. its clock speed). This final testing also determines general characteristics, such as whether a device is defective or meets minimal functional performance specifications. Thermal forcing systems are used in the semiconductor manufacturing process from product development in the engineering labs to final assembly & test on the production floor. Thermal forcing systems are benchtop direct contact systems for temperature testing integrated circuits and other Device Under Test (DUT) including high-Watt emitting devices.
Thermal forcing systems are usually integrated with automatic test equipment and handler in production. The thermal head (the heating and cooling block) must be robotically moved up and down as the ICs move past the test station on a belt system. This movement requires flexibility in the connecting process lines and controls of the thermal system. The thermal systems must perform fast, accurate, stable and cost effective temperature forcing on the DUT while taking up a minimal amount of space on the production floor. Thermoelectric heating and cooling systems have been used in the past but they are very inefficient and lack the cooling capacity required by the latest ICs. They also have a well-known problem of degradation in performance over relatively short operating times. Liquid chillers have also been used but are very large, have high maintenance requirements, and have potential for leaking liquid coolants in an environment that is not at all tolerant to leaks.
Aspen partnered with a major supplier of thermal forcing systems to develop a new approach based on direct expansion of refrigerant in the copper head that comes into contact with the DUT. This challenge required the development of a novel evaporator cold plate that is on the order of 50 x 50 mm, has internal features for enhanced heat transfer, and can absorb as much as 800 W of heat from the DUT. The evaporator cold plate had to be connected to the main unit via flexible refrigerant lines and the compressor and condensing unit had to be very small to fit into a 19” rack mount format. Aspen used our own miniature variable speed rotary compressor combined with a parallel flow microchannel condenser to achieve the very small rack mount unit required. The vapor compression system also includes an 8 to 10’ long flexible stainless steel suction line with a refrigerant control capillary tube to achieve the refrigerant flow to and from the remote evaporator. The system has been so successful, Aspen’s customer asked us to develop and supply larger capacity units as well. We now manufacture five different vapor compression engines for thermal forcing systems which are able to achieve very low temperatures and absorb high heat loads.