Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
2001-11-07
2004-09-21
Paschall, Mark (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S209000, C219S505000, C324S763010
Reexamination Certificate
active
06794620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to semiconductor technology, and more particularly, to maintaining substantially constant temperature of a semiconductor device under test.
2. Discussion of the Related Art
Semiconductor devices typically undergo a variety of electrical test procedures, including short-circuit tests, burn-in tests, and device functional tests to insure their proper operation. During for example functional testing, it is important that the temperature of the device under test be held at a chosen, substantially constant value. However, during such functional testing, the power level of the device may vary greatly, causing the temperature of the device to fluctuate. The most important parameter is junction temperature, or the temperature of active regions in the device (there may be some temperature non-uniformity within the device). In dealing with this problem, it is well known to provide a thermal head
10
a surface
11
which may be brought into contact with the lid
12
of a device
14
under test, for example, a flip-chip mounted on a printed circuit board
16
(FIG.
1
), or in the case of an unlidded device, in contact with the device
14
itself (FIG.
2
). The thermal head
10
typically includes an electric heating element
18
along surface
11
the output of which can be increased and decreased by respectively increasing and decreasing electrical current flow therethrough, and a passage
20
through which coolant
22
, for example, water, may flow. By changing electrical current flow and/or providing or cutting off coolant flow, the temperature of the thermal head
10
, and thus the temperature of the device under test
14
adjacent thereto, can be adjusted or varied. As the temperature of the device under test
14
varies due to changes in power level thereof as described above, the temperature of the thermal head
10
is caused to change to compensate for the changing temperature of the device
14
, in order to attempt to maintain the device under test
14
at a constant, chosen temperature.
One approach in attempting to maintain the device under test
14
at a substantially constant temperature is to compare the temperature of the device under test
14
with a desired temperature as the temperature of the device under test
14
varies due to fluctuation of power level thereof. A PID (Proportional Integral Derivative) controller is used to sense that difference and vary the temperature of the thermal head
10
in order to bring the temperature of the device under test
14
back to the chosen value. However, this approach requires an accurate measurement of the temperature of the device under test
14
, which cannot realistically be achieved with a lidded device if a temperature sensor is not incorporated in the device, and is also difficult even with an unlidded device. Additionally, in the case of a lidded device, because of the thermal capacitance of the lid, a substantial delay occurs in change of temperature of the device under test through change in the temperature of the thermal head. Thus, this approach has not proven entirely satisfactory.
Another approach, currently practiced by Schlumberger, Ltd. for unlidded devices uses an algorithm as follows:
T
c
=T
d
−K
&thgr;
P
d
where:
T
d
=temperature of device under test;
T
c
=temperature of thermal head
P
d
=power dissipated by device under test;
K
&thgr;
=thermal stack up coefficient of device (overall thermal resistance between the die and the thermal head).
In this approach, the device under test temperature T
d
is chosen and thermal head temperature T
c
is set in accordance with this formula. The power dissipated by the device under test
14
is monitored. Through use of this formula, the temperature of the thermal head
10
can be varied in an attempt to hold the device under test
14
at a substantially constant temperature. However, it has been found that while ideally K
&thgr;
is a constant, this has proven not to be the case, that is K
&thgr;
may vary from one test run to another, causing inaccuracies in the attempt to hold the device under test
14
at a substantially constant temperature. Additionally, for functioning of this system, substantial, rapid swings in thermal head temperature are required, in turn requiring expensive and complicated hardware.
Therefore, what is needed is an approach in maintaining a device under test at a substantially constant temperature which overcomes the problems set forth above, meanwhile being simple, inexpensive and effective, and is equally effective in the case of lidded and unlidded devices.
SUMMARY OF THE INVENTION
In maintaining a device under test at a generally constant temperature, the temperature change of the device under test is characterized as the device under test undergoes changes in power level in response to an electrical testing sequence. Additionally, the temperature change of the device under test is characterized in response to changes in power level of a thermal head. Using this information, power levels at the thermal head are selected for use during the electrical testing sequence, based at least in part on the characterization of the temperature change of the device under test in response to the electrical testing sequence, so that the device under test remains at a substantially constant temperature during the electrical testing sequence.
The present invention is better understood upon consideration of the detailed description below, in conjunction with the accompanying drawings. As will become readily apparent to those skilled in the art from the following description, there is shown and described an embodiment of this invention simply by way of the illustration of the best mode to carry out the invention. As will be realized, the invention is capable of other embodiments and its several details are capable of modifications and various obvious aspects, all without departing from the scope of the invention. Accordingly, the drawings and detailed description will be regarded as illustrative in nature and not as restrictive.
REFERENCES:
patent: 3710251 (1973-01-01), Hagge et al.
patent: 3922527 (1975-11-01), Witkin et al.
patent: 5205132 (1993-04-01), Fu
patent: 6489793 (2002-12-01), Jones et al.
Advanced Micro Devices , Inc.
Paschall Mark
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