WO2003027686A2

WO2003027686A2 - Method and apparatus for temperature control of a device during testing

Info

Publication number: WO2003027686A2
Application number: PCT/US2002/013441
Authority: WO
Inventors: Maxat Touzelbaev
Original assignee: Advanced Micro Devices, Inc.
Priority date: 2001-09-27
Filing date: 2002-04-29
Publication date: 2003-04-03
Also published as: WO2003027686A3; AU2002259063A1; TW564337B

Abstract

In the present method, a device under test (34) is maintained at a generally constant temperature. In furtherance thereof, a thermal head (30) is positioned adjacent the device (34), and a number of functional tests are run on the device (34), causing the power level of the device (34) to vary. The power level of the device (34) is monitored, and the power level of the thermal head (30) is varied so that the sum of the power level of the device under test (34) and the power level of the thermal head (30) remains generally constant.

Description

CONST NT NET HEATING POWER TECHNOLOGY

Maxat Touzelbaev

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to semiconductor technology, and more particularly, to maintaining substantially constant temperature of a semiconductor device under test.

2. Background 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 αf the device may vary greatly, causing the temperature of the device to fluctuate. In dealing with this problem, it is well known to provide a thermal head 10a surface 11 which may be brought into contact with the lid 12 of a device 14 under test, for example, a flip-chip mounted in a printed circuit board 16 (Figure 1), or in the case of an unlidded device, in contact with the device 14 itself (Figure 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 αf the device under test 14 with a programmed 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 αf the device under test 14 back to the chosen value. However, this approach requires an accurate measurement αf the temperature αf the device under test 14, which cannot realistically be achieved with a lidded device, and is also difficult even with an unlidded device. Thus, this approach has not proven entirely satisfactory.

Another approach, currently practiced by Schlumberger, Ltd. for unlidded devices uses an algorithm as follows:

where: T_d = temperature of device under test; T_c = temperature αf thermal head Pa = power dissipated by device under test;

K₀ = thermal stack up coefficient αf 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 Kβ is a constant, this has proven not to be the case, that is Kβ 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. 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, aid is equally effective in the case of lidded and unlidded devices.

DISCLOSURE OF THE INVENTION

The present invention is a method of maintaining a device under test at a generally constant temperature. In such method, a thermal head is positioned adjacent the device under test, and a number αf tests are run on the device, causing the power level of the device to vary. The power level of the device is monitored, and the power level of the thermal head is varied in response thereto so that the sum αf the power level of the device under test and the power level of the thermal head remains generally constant With this approach, the total power level or energy dissipated remains generally constant, so that the temperature of the device under test remains substantially constant

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 are shown and described embodiments 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.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic αf Hie invention are set forth in the appended claims. The invention itself, however, as well as said preferred mode of use, and further objects and advantages thereof, will best be understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein:

Figure 1 is a sectional view illustrating a typical prior art process, with a lidded device under test; Figure 2 is a view similar to that shown in Figure 1, but with an unlidded device under test; Figures 3 - 6 illustrate the process of the present invention; and Figure 7 is a flowchart illustrating the process of Figures 3 -6.

BEST MOP S ) FOR CARRYING OUT THE INVENTION

Reference is now made in detail to a specific embodiment of the present invention which illustrates the best mode presently contemplated by the inventor for practicing the invention.

Figure 3, similar to Figure 1, shows a thermal head 30 adjacent a device under test (DUT) 34, the thermal head 30 having a surface 31 in contact with the lid 32 of the device under test 34, for example, a flip-chip mounted on a printed circuit board 36. The thermal head 30 includes an electric heating element 38 adjacentthe surface 31 αfthethermalhead30 incontactwitlιthe lid 32. The output of the heating element 38 can be increased and decreased by respectively increasing and decreasing electrical current flow therethrough, and by flow of coolant 40, such as water, through a passage 42, all as described above.

Initially, by way of example, with the device under test 34 unpowered, that is, with no electrical tests being run thereon, and with no flow of coolant 40, a chosen constant electrical current (the magnitude of which is indicated by the length αf arrow A) is caused to flow in the heating element 38, to cause the heating element 38 to produce a level of power, dissipated as heat, the power level being determined by the formula P₀ = IV = I²R, where:

P₀ = thermal head power I = electrical current in thermal head heater V = voltage applied to thermal head heater = heater resistance. The electrical current level A in the heating element 38 may be chosen to determine a thermal head 30 power level P_oi wherein the temperature αf the head 30, Ud 32 and device under test 34 are, for example, 90° C. (see Block 1 of flow chart, Figure 7). In this situation, the total power (P_t) of the thermal head (P_Λ) and device under test Pa = 0) = P_ol.

Next, again without flow of coolant 40, the device under test 34 is powered to a given level P_di during, for example, the running of a functional test thereon (see Block 2 of Figure 7). The powering of the device under test 34 causes the device under test 34 to dissipate heat corresponding to the level of power Pai thereof, which, if added to the heat dissipated by the thermal head 30, would cause the temperature αf the device under test 34, the Ud 32, and the tliermal head 30 to increase, so that Hie device under test 34 would no longer be at the desired 90° C To maintain the device under test 34 temperature at 90° C. , power level of the device under test 34 is continuously monitored, and the power level of the thermal head 30 is varied, i.e. changed or adjusted (by changing tlie electrical current level through heating element 38) in response to Hie changed power level of tlie device under test 34 so that the sum αf the power level of the device under test and tlie power level of the thermal head remains generally at a constant P_b i.e., as the power level of the device under test 34 changes during testing thereof, the power level of the thermal head 30 is changed in accordance with the following algorithm: P_t= P_d + P₀ where

P_t = total power, held generally constant P₀ = thermal head power P_d= device under test power.

In the example given thus far, with the increase in power level of the device under test 34 (from zero to Pdi), electrical current in the heating element 38 of the thermal head 30 would in response be decreased to a magnitude indicated by the length of arrow B of Figure 4 to in turn reduce the power level of the thermal head 30 to P_o2, in accordance with the above formula, P_t (constant) = P_dι + P_ώ

With the total power P_t αf the device under test 34 and thermal head 30 remaining substantiaUy the same as in the previous state, substantiaUy the same amount of total heat is dissipated as in the previous state (Figure 3), so that the temperature αf the device under test 34 (along with thermal head 30 and lid 32) remains at substantially 90° C. (see also Block 3 of Figure 7). Next, for example, the device under test 34, during testing thereof, is powered to a given level P ₂ greater than zero but less than P_dι, i e., that as shown and described with regard to Figure 4 (see Block 4 of Figure 7). The reduced powering αf the device 34 causes Hie device 34 to dissipate less heat, which would cause the total αf heat dissipated by the thermal head 30 and the device under test 34 to decrease, which would in turn reduce the temperature αf the device under test 34 below tlie desired 90° C. In order to maintain the temperature αf the device under test 34 at 90° C, again with no coolant 40 flow, the electrical current through the heating element 38 αf the thermal head 30 is increased as indicated by the length αf arrow C (in response to the decrease in power of the device under test 34, which power level is continuously monitored as described above), to increase the power level of the thermal head 30 to P^ in accordance with the formula P_t (constant) = Pd2 + Pc3 so that the total amount of power P_b and thus heat dissipated, remains substantiaUy the same, in turn providing that the device under test 34 (along with the thermal head 30 and Ud 32) remain generaUy at 90° C (Block 5 of Figure 7).

The steps of Blocks 4 and 5 αf Figure 7 can be repeated for various devices under test power levels, as chosen. Also, it will be understood that various temperatures T can be chosen in block 1 σf Figure 7. Figure 6 shows the present invention in association with an unlidded device 34, wherein Hie thermal head 30 is adjacent the device under test 34 with the surface 31 thereof brought directly into contact with the device under test 34. It will be seen that the steps above can readily be appUed to this situation. It will be seen that the present approach maintains a device under test at a substantiaUy constant chosen temperature in a simple and effective manner, by merely monitoring the power level of the device under test and choosing an appropriate power level of the thermal head by only varying the level of electrical current through the heater thereof, i.e., no monitoring of temperature of the device under test is needed. It wiU further be seen that the method is simple, inexpensive and effective in use, and is readUy appUed to Udded and unUdded devices. The foregoing description αf the embodiment of the invention has been presented for purposes of iUustration and descriptioa It is not intended to be exhaustive or to limit the invention to tlie precise form disclosed. Other modifications or variations are possible in Uglit of tlie above teachings.

The embodiment was chosen and described to provide the best iUustration of the principles αf the invention and its practical appUcation to thereby enable one of ordinary skiU of the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legaUy and equitably entitled

Claims

CLAIMS;What is claimed is:

1. A method of maintaining a device under test (34) at a generaUy constant temperature characterized by: monitoring the power level of the device under test (34); and varying the power level of a thermal head (30) positioned adjacent the device under test (34) so that the sum αf power level of the device under test (34) and the power level of the thermal head (30) remains generaUy constant

2. The method of claim 1 wherein the step of varying power level of the thermal head (30) comprises varying electrical current in the thermal head (30).

3. The method αf claim 2 wherein the step αf varying power level of tlie tliermal head (30) is undertaken only by varying the electrical current in the thermal head (30).

4. The method αf claim 1 and further comprising the step αf providing that tlie device under test (34) is a Udded device under test (34).

5. The method of claim 1 and further comprising to step αf providing that the device under test (34) is an unlidded device under test (34).

6. A method αf maintaining a device under test (34) at a generally constant temperature characterized by: providing a power level of a thermal head (30) positioned adjacent the device under test (34); providing a power level of the device under test (34); changing the power level of the device under test (34); and changing the power level of the thermal head (30) so that the sum of the power level of the device under test (34) and the power level of the thermal head (30) remains generally constant

7. The method of claim 6 wherein the step αf changing the power level of tlie thermal head (30) comprises changing the electrical current level therein.

8. The method of claim 7 wherein the step of changing the power level of the thermal head (30) is undertaken only by changing the electrical current therein.

9. The method of claim 6 and further comprising the step αf providing that the device under test (34) is a Udded device under test (34).

10. The method of claim 6 and further comprising the step αf providing that the device under test (34) is an unlidded device under test (34).