Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-05-28
2001-04-10
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S758010, C324S765010
Reexamination Certificate
active
06215323
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to testing of integrated circuits, and in particular to method and apparatus for testing of integrated circuits at temperatures other than ambient temperature using Peltier type devices.
Integrated circuits (ICs) are typically designed to be fully operational within a specified range of temperatures. In some applications this range is wide enough to test the limits of the various technologies involved. The need to operate an IC at temperatures as low as −30° C. or −40 ° C., for example, often leads to additional complication and expense at the testing stage. Traditionally devices are pre-cooled and fed into a cold chamber surrounding the test head. The test chamber and test heads are maintained at the low temperature using liquid Nitrogen as a heat sink. This method suffers from a number of drawbacks. It requires plumbing low temperature liquid Nitrogen which needs careful controls because of the danger associated with liquid Nitrogen. This type of temperature control method also demands measuring the temperature of a large thermal mass which can be costlier and tends to compromise accuracy. Condensation, and in some instances ice formation, on the surfaces and test heads is also a source of potential problems whereby mechanical systems are disrupted, and electrical contacts are rendered high impedance or intermittent. To avoid inaccurate temperature control and unreliable test results additional provisions for controlling the atmosphere around the test device are required to reduce or eliminate condensation. Further, when an IC is brought into contact with the test head, care must be taken to limit the perturbation effect on the temperature of the low thermal mass IC caused by the temperature of the test head. These and other types of problems exist when the IC is to be tested at temperatures significantly higher than the ambient temperature. The high or low temperature testing can be made further complicated by the type of circuitry that is integrated on the IC. For example, certain ICs include magnetic sensitive devices (e.g., Hall-effect devices) that create additional problems associated with generating the magnetic fields using an electromagnet at the various temperatures.
There is therefore a need for a low mass test system with an accurate temperature control and a limited surface area for temperature testing.
SUMMARY OF THE INVENTION
The present invention provides method and apparatus for testing integrated circuits at low or high temperatures in a low thermal mass environment. Broadly, the invention uses heat transfer elements such as Peltier devices inside the test head area to transfer thermal energy from one surface to another. The use of Peltier devices and the very low thermal mass of the combined test head and device under test (DUT), allow for fast and accurate temperature control of the DUT leads without using liquid Nitrogen. In a specific embodiment, the present invention provides a test system with two or more temperature control chambers through which the DUTs are transported by an indexed conveyor belt. The DUT is first pre-cooled in a first chamber that is, for example, surrounded by pipes carrying a cooling liquid such as water at low temperature. The second chamber includes Peltier type devices that bring the temperature of the DUT to the target test temperature. The last chamber includes the test head probes that are also held at the test temperature by using Peltier type devices. Calibrated temperature sensors are embedded in the test head and probe assemblies to ensure accurate setting of the test temperature. The various chambers are preferably surrounded by an enclosure filled with, e.g., dried Nitrogen gas at room temperature and at slight positive pressure. This atmosphere eliminates condensation when performing low temperature testing, and allows the water pre-cool to go to a temperature below the normal dew point. The problems of condensation and the dangers of using liquid Nitrogen are thus eliminated by the method and apparatus of the present invention.
Accordingly, the present invention provides in one embodiment a low temperature testing system including a conveyor mechanism configured to carry a device to be tested; a first temperature control zone adapted to receive the device on the conveyor mechanism, and configured to bring the device to a first temperature; a second temperature control zone adjacent to the first temperature control zone and adapted to receive the device on the conveyor mechanism, the second temperature control zone including at least one Peltier type element as a heat exchanger to bring the device to a second temperature; and a test zone adjacent to the second temperature control zone, the test zone including a mechanical arrangement configured to receive the device to be tested and to hold the device to be tested in a known fixed position relative to a tester head, the test zone further including Peltier type elements attached to the mechanical arrangement to control the temperature of the test zone. To test devices having magnetic sensitive elements, the test zone of the testing system of the present invention further includes, in an alternative embodiment, magnetic field generating elements that are thermally isolated from the mechanical arrangement.
In another embodiment, the present invention provides a method for testing electronic devices at low temperatures including the steps of pre-cooling the integrated circuit to a first temperature in a first chamber; passing the integrated circuit into a second chamber; cooling the integrated circuit to a second temperature lower than the first temperature by the use of Peltier type elements inside the second chamber; passing the integrated circuit into a test chamber; cooling the test chamber to substantially the second temperature by the use of Peltier type elements; and bringing test head in contact to leads of the integrated circuit to carry out electrical testing of the integrated circuit.
The following detailed description along with the drawings provide a better understanding of the nature and advantages of the temperature testing methods and apparatus according to the present invention.
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Noels Barts
Rennies Jos
Melexis N.V.
Metjahic Safet
Sundaram T. R.
Townsend & Townsend & Crew LLP
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