Temperature control for high power burn-in for integrated circuits

A temperature control system for high power burn-in of integrated circuit chips which includes an individual heat sink at each of the integrated circuit chips to dissipate heat generated by the integrated circuit. A heater for each chip is provided and is temperature controlled so that heat may be added by the heater as a function of the heat generated by the integrated circuit chip. A temperature sensor is provided in close thermal contact with the integrated circuit chip to sense the temperature of the integrated circuit chip. A closed loop temperature controller is used to vary the amount of current provided to the heater to maintain a desired range of temperature. Thermal contact between the temperature sensor and the integrated circuit chips is insured by utilizing a spring to urge the sensor toward the integrated circuit chip.

BACKGROUND OF THE INVENTION 
The present invention relates to controlling the temperature of an 
integrated circuit chip that is undergoing a high power burn-in test by 
using a heat sink that dissipates heat generated by the integrated 
circuit, in combination with a controlled heater to add heat. A sensor in 
contact with the integrated circuit chip is used to provide a signal to 
control the heater to maintain the integrated circuit chip at a desired 
temperature range. 
The procedure of burn-in of integrated circuits is well known, and various 
structures are provided for such burn-in. U.S. Pat. No. 4,900,948 shows an 
apparatus for providing burn-in of integrated circuits on burn-in boards. 
A thermal control system for controlling the temperatures of high power 
semiconductor devices that are being burned in is shown in U.S. Pat. No. 
5,515,910. This device uses a liquid cooling. 
In some instances, it is desirable to measure and control the temperature 
of each semiconductor device. U.S. Pat. No. 5,164,661 shows a device that 
uses two temperature sensors, one of which senses the temperature of the 
heat exchange device and the other senses the temperature of the 
integrated circuit under test. 
Various other test systems for component testings are well known, including 
life tests in burn-in chambers. The process of burning in a semiconductor 
chip typically consists of applying a load to the electronic components on 
the integrated circuit chip being tested at elevated temperatures. This 
allows identification of weak or faulty components for insuring quality 
control for reliable ultimate use of such integrated circuits, such as in 
a computer system. 
SUMMARY OF THE INVENTION 
The present invention relates to a temperature control system for high 
power burn-in testing that permits maintaining an integrated circuit chip 
under test at a substantially uniform temperature. Specifically, the 
integrated circuit chip under test is plugged into a burn-in socket on a 
mother board in a test oven. The integrated circuit chip is placed into 
heat conducting relationship to a plate heater, which in turn is in 
thermally conductive relationship to a heat sink. The integrated circuit 
temperature is sensed with a suitable temperature sensor, such as a 
thermistor, which is held in intimate contact with the integrated circuit. 
The signal from the thermistor controls a power source to the heater so 
that when the temperature is below a certain level, the heater will be 
energized to provide heat to maintain the integrated circuit chip at a 
desired temperature profile. The heat sink will dissipate heat from both 
the heater and the integrated circuit chip. 
The temperature sensor is in a housing that is spring loaded to hold the 
temperature sensor against the integrated circuit chip to insure that it 
is an intimate, heat conducting relationship to the integrated circuit 
chip. 
The present device is quite easily controlled to maintain the temperature 
of individual integrated circuit chips in a burn-in system within a 
desired range.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A mother board or burn-in board for burning in of integrated circuits is 
illustrated generally at 10, and is of selected size to fit within a 
burn-in oven 11. The mother board 10 mounts a plurality of chip sockets 16 
which are connected to the necessary controls 15 through edge connectors 
17 for powering components on an integrated circuit chip 12 which is being 
tested. The integrated circuit chip 12 has a number of pins, some of which 
are shown schematically at 14. The pins plug into one of the burn-in board 
sockets 16 that are attached to the mother board 10. Each socket 16 is 
positioned on the board 10 in a desired arrangement with several other 
sockets, so that a large number of integrated circuits can be tested at 
one time. The details of construction of the burn-in board, the mother 
board and the mother board sockets 16 are shown in prior patents and are 
not shown in great detail. However, it is to be understood that each of 
the circuits on the integrated circuit chip 12 will be connected for 
powering and cycling the components as desired for the test involved. 
As can be seen in FIGS. 1 and 2, the integrated circuit chip 12 shown has a 
layer 18 and this chip has posts 20 thereon which may be for a heat sink 
in use. A thermal control assembly 22 is in thermal contact with the layer 
18, and thus in close thermal contact with the integrated circuit chip 14. 
Clearance is provided for the posts 20. A heat sink assembly 24 as shown 
includes a heat conductive, resilient foam layer 28 positioned to directly 
engage the layer 18 to provide for thermal transfer from the integrated 
circuit chip 12 to a base plate 28, which has an internal a boss portion 
29 backing the thermal foam 26. The base plate 28 is made of high heat 
conducting material such as a metal. A flat surface resistance heater 
plate 32, or other type of electrical heater is positioned against the 
base plate 28 across the surface that faces outwardly from the integrated 
circuit chip 14. Thus there is quite a wide surface area for heat transfer 
between the base plate and the heater. On the opposite side of the heater 
plate 32 there is a heat sink 34, that has a lower plate member 36 and a 
number of fins 38 to dissipate a substantial amount of heat from both the 
heater plate 32 and the integrated circuit chip 12. 
As shown, the heater plate 32 is clamped to the base plate 28 and to the 
heat sink 34 by screws 40 which thread into the base plate to clamp the 
heater tightly against both the heat sink and the base plate. These 
components form the heat sink assembly 24. 
A temperature sensor housing 44 is positioned to fit into a central opening 
45 formed in the heat sink 34, heater 32, base plate 28 and thermal foam 
layer 26. The sensor housing 44 is made of material having low thermal 
conductivity (a heat insulator) and has an internal passageway 46 which at 
its lower end mounts a thermistor or other temperature sensor 48. The 
temperature sensor 48 protrudes slightly outwardly from the end of housing 
44, so that when the housing is positioned in the opening 45 and under 
spring load, the sensor will engage the surface of plate 18 so that the 
temperature sensor is in good thermal contact with the integrated circuit 
chip itself and in particular the heat conducting layer 18. The 
temperature sensor housing 44 is urged toward the base plate with a spring 
50 backed with a washer 52 and a cap 54 that is held on the heat sink 34 
with suitable countersunk screws 56. A head 44A on the temperature sensor 
housing seats in a recess in the base plate under load from spring 50. 
Some integrated circuit chips have a temperature sensor integral therewith. 
The integral temperature sensor can be used for control on the temperature 
instead of sensor 48. 
The temperature control assembly 22 is clamped down onto the integrated 
circuit chip, to compress the foam layer and hold the base plate 28 and 
the entire thermal control assembly in good thermal contact with the 
integrated circuit chip 12 through the use of screws 60 which pass through 
apertures in the heat sink, the heater and the base plate, and then can 
thread into the mother board 10 to clamp the thermal control assembly 
tightly onto the integrated circuit chip. When the screws 60 are 
tightened, the thermistor or other sensor indicated at 48 is urged into 
intimate contact with the plate 18 of the integrated circuit chip 12. The 
spring 50 will yield slightly so that the temperature sensor or thermistor 
48 is loaded against the layer 18 under a spring load. The resilient heat 
conductive foam layer 26 will compress to conform to the surface of the 
integrated circuit chip and the deposited components. 
When the countersunk screws 56 are tightened, the spring 50 will be urged 
against the head portion 44A of the sensor housing, so that the housing 44 
is held in position under spring pressure. 
In order to control the amount of heat that is being provided by the 
heater, and thus control the temperature of the integrated circuit chip 
12, a simplified schematic for a controller circuit is shown in FIG. 3 at 
64. The amount of current provided to the heater represented schematically 
at 66 is controlled by a temperature controller operation amplifier 68 
which essentially is a comparator having one input at a reference voltage 
level, which can be adjustable. The reference represents the reference or 
desired temperature. A voltage signal based on the signal from temperature 
sensor 48 (or an integral sensor) is connected to the other input of the 
amplifier 68. Differentials between the two inputs will cause the 
amplifier 68 to vary the output to control the current in the heater 66. 
Either a pulsed current or an analog current can be provided to the 
heater. 
The heater plate 32 may have two separate resistances connected in 
parallel, but they are represented schematically in FIG. 3. 
Preferably the temperature controller 64 is mounted on the mother board 10, 
or quite close to the heater that it is controlling. There is a separate 
temperature controller for each of the integrated circuit chips being 
tested. One voltage reference source, however, can be used for several 
different temperature controllers. 
If desired, a separate board can be used for mounting the temperature 
controllers, and they can be connected to the burn-in board or mother 
board 10 during use. 
In operation, when the integrated circuit chip is powered through socket 
16, the heat sink 34 will remove most of the heat from the integrated 
circuit 12. In order to maintain a substantially constant temperature, 
heat is added by the heater 32, and the amount of heat that is added is 
dependent on the heat generated by the integrated circuit chip. This will 
vary from one integrated circuit to another. The amount of heat added by 
the heater may also vary because of variable heat loss from one heat sink 
to another. Thus, the individual controller for each of the temperature 
control assemblies is important. 
The temperature sensor makes contact with the integrated circuit chip and 
senses its temperature. A closed loop temperature controller as shown in 
FIG. 3 is used to control the heat provided by the heater. 
The spring 50 insures good thermal contact between the temperature sensor 
48 and the integrated circuit layer 18. 
The thermal control unit is held in place by clamping the thermal control 
assembly 22 relative to the mother board. The thermal foam layer is not 
always used, but provides some resiliency for reducing thermal impedance, 
so that there is good thermal contact. 
While one type of fastener (screw 60) is shown for holding the thermal 
control assembly 22 in position on the integrated circuit 14, other types 
of fasteners can be used as desired. 
The size of the heat sink 34 can be varied to accommodate the amount of 
power that needs to be dissipated by the integrated circuit chip, and the 
heater size also can be varied as desired. 
The integrated circuit chip is called a "device under test" and may be 
abbreviated as DUT for convenience. 
Although the present invention has been described with reference to 
preferred embodiments, workers skilled in the art will recognize that 
changes may be made in form and detail without departing from the spirit 
and scope of the invention.