MIL- STD-883F 2004 TEST METHOD STANDARD MICROCIRCUITS - 第66页

MIL-STD-883F METHOD 1012.1 4 November 1980 2 c. Sui table el ectr ical equipment as requir ed to provide c ontrol led level s of c onditi oning power and t o make the speci fied meas urements . The ins trument used to el…

MIL-STD-883F

METHOD 1012.1

4 November 1980

METHOD 1012.1

THERMAL CHARACTERISTICS

1. PURPOSE

. The purpose of this test is to determine the thermal characteristics of microelectronic devices. This

includes junction temperature, thermal resistance, case and mounting temperature and thermal response time of the

microelectronic devices.

1.1 Definitions

. The following definitions and symbols shall apply for the purpose of this test:

a. Case temperature, T

, in °C. The case temperature is the temperature at a specified accessible reference point

on the package in which the microelectronic chip is mounted.

b. Mounting surface temperature, T

, in °C. The mounting surface temperature is the temperature of a specified

point at the device-heat sink mounting interface (or primary heat removal surface).

c. Junction temperature, T

, in °C. The term is used to denote the temperature of the semiconductor junction in the

microcircuit in which the major part of the heat is generated. With respect to junction temperature measurements,

J(Peak)

is the peak temperature of an operating junction element in which the current distribution is nonuniform,

J(Avg)

is the average temperature of an operating junction element in which the current distribution is nonuniform,

and T

J(Region)

is the temperature in the immediate vicinity within six equivalent radii (an equivalent radius is the

radius of a circle having the same area as contained in a junction interface area) of an operating junction. In

general T

J(Region)

J(Avg)

J(Peak)

. If the current distribution in an operating junction element is uniform then T

J(Avg)

J(Peak)

d. Thermal resistance, junction to specified reference point, R

θJR

, in °C/W. The thermal resistance of the microcircuit

is the temperature difference from the junction to some reference point on the package divided by the power

dissipation P

e. Power dissipation, P

, in watts, is the power dissipated in a single semiconductor test junction or in the total

package, P

D(Package)

f. Thermal response time, t

, in seconds, is the time required to reach 90 percent of the final value of junction

temperature change caused by the application of a step function in power dissipation when the device reference

point temperature is held constant. The thermal response time is specified as t

JR(Peak)

, t

JR(Avg)

, or t

JR(Region)

conform to the particular approach used to measure the junction temperature.

g. Temperature sensitive parameter, TSP, is the temperature dependent electrical characteristic of the

junction-under test which can be calibrated with respect to temperature and subsequently used to detect the

junction temperature of interest.

2. APPARATUS

. The apparatus required for these tests shall include the following as applicable to the specified test

procedures.

a. Thermocouple material shall be copper-constantan (type T) or equivalent, for the temperature range -180°C to

+370°C. The wire size shall be no larger than AWG size 30. The junction of the thermocouple shall be welded to

form a bead rather than soldered or twisted. The accuracy of the thermocouple and associated measuring system

shall be ±0.5°C.

b. Controlled temperature chamber or heat sink capable of maintaining the specified reference point temperature to

within ±0.5°C of the preset (measured) value.

MIL-STD-883F

METHOD 1012.1

4 November 1980

c. Suitable electrical equipment as required to provide controlled levels of conditioning power and to make the

specified measurements. The instrument used to electrically measure the temperature-sensitive parameter shall

be capable of resolving a voltage change of 0.5 mV. An appropriate sample-and-hold unit or a cathode ray

oscilloscope shall be used for this purpose.

d. Infrared microradiometer capable of measuring radiation in the 1 to 6 micrometer range and having the ability to

detect radiation emitted from an area having a spatial resolution of less than 40 micrometers (1.6 mils) diameter at

its half power points and a temperature resolution (detectable temperature change) of 0.5°C at 60°C.

NOTE: May be a scanning IR microradiometer.

e. A typical heat sink assembly for mounting the microelectronic device-under test is shown on figure 1012-1. The

primary heat sink is water cooled and has a thermocouple sensor for inlet and outlet water temperature as shown

in figure 1012-1a.

An adapter heat sink, as shown on figure 1012-1b is fastened to the top surface of the primary heat sink, and has a special

geometry to handle specific size packages, e.g., flat packs, dual-in-line packages (small and large size) and TO-5 cans.

This adapter provides a fairly repeatable and efficient interface between the package and the heat sink; the heat sink

temperature is determined from a thermocouple peened into the underside of the adapter-near the package.

The adapter also contains the socket or other electrical interconnection scheme. In the case of the flat pack adapter heat

sink, the package is dropped into a special slotted printed circuit board (PCB) to register the leads with runs on the PCB;

toggle clamps then provide a pressure contact between the package leads and the PCB runs. Dual-in-line and axial lead

packages plug into a regular socket.

The thermal probe assembly is shown on figure 1012-1b. In practice, the pressure adjustment cap is adjusted so the disk at

the probe tip contacts the bottom surface of the package (chip carrier) with a predetermined force. A silicone grease (about

25-50 mm thick) is used at this interface to provide a reliable thermal contact.

3. PROCEDURE

3.1 Direct measurement of reference point temperature, T

or T

. For the purpose of measuring a microelectronic device

thermal resistance or thermal response time, the reference point temperature shall be measured at the package location of

highest temperature which is accessible from outside the package. In general, that temperature shall be measured on the

surface of the chip carrier directly below the chip. The location selected shall be as near the chip as possible and

representative of a temperature in the major path of heat flow from the chip to the heat sink. The surface may be altered to

facilitate this measurement provided that such alteration does not affect the original heat transfer paths and, hence, the

thermal resistance, within the package by more than a few percent.

3.1.1 Case temperature, T

. The microelectronic device under test shall be mounted on a temperature controlled heat

sink so that the case temperature can be held at the specified value. A thermocouple shall be attached as near as possible

to the center of the bottom of the device case directly under the chip or substrate. A conducting epoxy may be used for this

purpose. In general, for ambient cooled devices, the case temperature should be measured at the spot with the highest

temperature. The thermocouple leads should be electrically insulated up to the welded thermocouple bead. The

thermocouple bead should be in direct mechanical contact with the case of the microelectronic device under test.

3.1.2 Mounting surface temperature, T

. The mounting surface temperature is measured directly below the primary heat

removal surface of the case. It is measured with a thermocouple at or near the mounting surface of the heat sink. A typical

mounting arrangement is shown on figure 1012-2. The surface of the copper mounting base shall be nickel plated and free

of oxides.

MIL-STD-883F

METHOD 1012.1

4 November 1980

The thermocouple hole shall be drilled into the mounting base such that the thermocouple lead is directly below the area on

the case of interest. It is recommended that the thermocouple be secured into the mounting base with a thermal conducting

adhesive (or solder) and that particular attention be paid to minimizing air voids around the ball of the thermocouple. A

thermal conducting compound (or adhesive) should be used at the interface of the mounting base and the device under test.

3.2 Thermal resistance, junction to specified reference point, R

θJR

3.2.1 General considerations

. The thermal resistance of a semiconductor device is a measure of the ability of its carrier

or package and mounting technique to provide for heat removal from the semiconductor junction.

The thermal resistance of a microelectronic device can be calculated when the case temperature and power dissipation in

the device, and a measurement of the junction temperature are known. The junction with the greatest power dissipation

density (watts/mm

) shall be selected for measurement since that junction will generally have the highest temperature on the

chip. If the leads to that junction are not accessible and another junction is measured then it cannot be assured that the

highest temperature on the chip will be measured. Direct measurement should be used in this case.

When making the test measurements indicated below, the package shall be considered to have achieved thermal

equilibrium when the measured temperature difference, junction to case, reaches approximately 99 percent of its final value.

The temperature difference at that time will change at a rate less than

d(T

- T

) < 0.03 (T

- T

)

dt t

where t is the time after application of a power dissipation increment. The total time required for stabilization will typically be

less than a minute.

3.2.2 Direct measurement of junction temperature for determination of R

θJR

. The junction temperature of the thermally

limiting element within the semiconductor chip can be measured directly using an infrared microradiometer. The cap or lid

shall first be removed from the package to expose the active chip or device. The cavity shall not be covered with any IR

transparent material unless the chip is extremely large and has an extremely poor heat conduction path to the chip carrier.

The location of the junction to be measured should be referenced to a coordinate system on the chip so it can be relocated

after coating the chip. The active area of the chip shall be coated uniformly with a thin layer (25-50 µm thick) of a known

high emissivity (∈ > 0.8), low thermal conductivity material such as black pigmented lacquer. The package shall then be

placed on a temperature controlled heat sink and the case or mounting surface temperature stabilized at the specified value.

The microelectronic device under test shall then be operated at its rated power dissipation, the infrared microscope

crosshairs focused on the junction and scanned back and forth slightly at that location to maximize the radiance

measurement. That radiance measurement and the chip carrier temperature shall then be recorded. The power to the test

package shall then be turned off and the chip carrier allowed to return to the specified case or mounting surface

temperature. The emissivity of the coating over the junction region shall then be measured and the radiance from the

operating junction region shall be converted to temperature using this emissivity value. (Note that this method assumes the

emissivity of the coating material does not change appreciably with temperature. This assumption shall be valid if the

results are to be accurate and repeatable.)

If the junction to be measured is not specified then the test shall proceed as above except that the IR microscope crosshairs

shall be scanned over the whole active area of the chip to find and maximize the radiance measurement at the highest

temperature junction region.

The minimum width or length of the junction area shall be greater than 5 times the half power diameter of the objective lens

and greater than 5 times the thickness of the coating on the chip surface if this method is used to measure T

J(Peak)

. For

junction element diameters between 5 and 1 times the half power diameter of the IR microscope objective lens, some

average junction temperature T

J(Avg)

, where T

J(Region)

< T

J(Avg)

< T

J(Peak)

, will be measured.