Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-07-19
2003-11-18
Karlsen, Ernest (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C219S209000, C702S130000
Reexamination Certificate
active
06650132
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus which can be used to maintain the temperature of a device such as a semiconductor integrated circuit device during a testing operation. In particular, the invention relates to a technique in which the device can be cooled and/or heated during testing in order to control the temperature of the device despite the varying levels of heat generated by the operation of the device.
BACKGROUND OF THE INVENTION
Control of DUT (“device under test”) temperature in testing operations has been practiced for some time. During burn-in, for example, the DUT is placed in an environment with an elevated temperature, typically an oven, and signals applied for a prolonged period in order to promote failure of the device which would otherwise occur only after extensive use. The burn-in process uses the elevated temperature to accelerate what would otherwise be a very long-term process within the DUT. In an oven-type burn-in operation, a large number of devices are loaded on burn-in boards which are placed in the oven and tested together.
In other tests, it has been proposed to control the temperature of the DUT so as to simulate possible ambient temperatures during normal use. In such cases, a bulk temperature control is not appropriate because the temperature of each individual DUT can vary significantly over short periods of time. Also, it is not possible to change the temperature of the DUT reliably or quickly during the test process. A number of proposals have been made for more accurate control of DUT temperature variation during testing is to affect the accessed maximum speed of the device in normal use, known as “speed binning.” Inaccuracy in this assessment can lead to failure of a device in normal use.
U.S. Pat. No. 5,297,621 discloses a liquid bath in which devices are immersed during testing. The liquid in the bath is inert and comprises a mixture of two liquids having boiling points above and below the desired temperature. By varying the mixture of the two liquids, the liquid in the bath is arranged to have a boiling point which is at the desired operating temperature of the DUT (“set point temperature”). Heat generated by the DUT is dissipated by convection within the bath and by nucleate boiling of the liquid on the DUT. Heat transfer from the DUT to the liquid is facilitated by placing a heat sink in contact with the DUT.
U.S. Pat. No. 4,734,872 discloses a system in which a stream of temperature-controlled air is directed at the DUT. The air is drawn into a chiller where its dew point is lowered. The chilled air is then passed to a heater which raises the temperature of the air to a desired level to control the temperature of the DUT. Measurement of the DUT temperature and air stream temperature are used to control the heater and hence the temperature of the air impinging on the DUT.
U.S. Pat. Nos. 4,784,213 and 5,205,132 disclose a variant on the system disclosed in the '872 patent described above. In both of these cases, the air stream is split into a cooled stream and a heated stream. The two streams are then mixed in appropriate proportions to produce a single stream directed at the DUT and having the desired temperature.
U.S. Pat. No. 5,309,090 discloses the heating of a DUT by applying a signal/power to certain structures in the DUT so as to generate heat by their operation and so heat the DUT evenly. This method does not allow the DUT to be cooled in the same way.
Recent developments in high-performance microprocessor design have lead to an increase in power consumption and dissipation from about 10 Watts to 60-70 Watts. Furthermore, the increase in component density within a microprocessor chip and the adoption of modem chip packaging structures has lead to devices which have extremely low thermal inertia, i.e. devices which will heat up and cool down very quickly. CMOS technology used in such chips is characterized by having a power consumption and dissipation which varies depending on the activity of the device. When in normal use, the chips will have cooling devices such as fans mounted nearby or even on the chip package so as to dissipate the heat generated by the operation of these devices. However, during functional testing, these cooling devices are not present and the power dissipated during very high speed functional testing is sufficient to raise the temperature of the device quickly to a level which could permanently damage the device.
The prior art methods of temperature control all rely on a direct measurement of DUT temperature during testing to provide feedback control to the heat exchanger. This approach suffers from a number of problems. It is difficult to make a reliable, consistent temperature measurement at the surface of a device when testing in a high volume manufacturing environment because of the variability in contact resistance encountered. Even with a good temperature measurement, extrapolation of device internal temperature in a high inertia package is problematic. With any feedback system, there is always the problem that the device must change its temperature before the measurement can be made and the thermal response time of the chip can be as low as 30 ms whereas that of the heat exchanger is often in the region 100-200 ms. Therefore, at best, such an arrangement can only smooth temperature variation and can lead to temperature undershoot which is also undesirable.
It is an object of the present invention to provide methods and apparatus which allow temperature control of devices during test, particularly cooling during test.
SUMMARY OF THE INVENTION
One aspect of the present invention provides a method for controlling the temperature of a DUT during a testing operation, comprising: a) measuring a parameter related to power consumption by the DUT during testing; and b) using the parameter related to power consumption to operate a temperature control device to compensate for temperature change due to changes in power consumption by the DUT during testing.
Another aspect of the invention provides an apparatus for controlling the temperature of a DUT during testing, comprising: a) means for measuring a parameter related to power consumption by the DUT during testing; b) a temperature control device which operates to control the temperature of the DUT during test; and c) means for controlling operation of the temperature control device according to the measured parameter related to power consumption.
The power supply (device power supply or “DPS”) supplies current to the DUT and measuring this current and, optionally, the voltage allows an almost instantaneous indication of the power consumption of the DUT. Since substantially all of the power consumed by the device appears as heat, and the relatively low thermal inertia of such devices, such a measurement also is indicative of heat dissipation by the device and hence its tendency to change temperature. This approach allows the temperature control signal to be generated well in advance of what would be possible using a direct temperature measurement since the parameter being measured exists before the DUT has even changed its temperature. In high performance IC testers, the current consumption (I
DD
) of the DUT is routinely measured. It is this measurement which can be used to provide the parameter related to power consumption/dissipation of the DUT. The amount of temperature elevation for a given current consumption will depend on a number of factors such as IC package type, form factor, set point temperature etc. In many cases, the effect will be non-linear but can be determined by calibration for a given device type. Where the device has a relatively high thermal inertia, it is desirable to calibrate the performance by including temperature sensors in a test device to allow correlation of I
DD
with the device internal temperature. The use of I
DD
measurement is particularly advantageous since this is a parameter which can be accurately and rapidly measured even during high volume testing applications.
The pa
Delta Design, Inc.
Karlsen Ernest
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