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SEMI G38-0996 © SEMI 1987, 2004 2 wind tunnel assemblies ar e presented for reference purposes only . 5.1.4 Still-Air Enclosure Assembly — The microcircuit shall be mounted i n a cubic enclosure of not less than 0.028 m …

SEMI G38-0996 © SEMI 1987, 2004 1

SEMI G38-0996 (Reapproved 1104)

TEST METHOD FOR STILL- AND FORCED-AIR JUNCTION-TO-

AMBIENT THERMAL RESISTANCE MEASUREMENTS OF

INTEGRATED CIRCUIT PACKAGES

This test method was technically reapproved by the Global Assembly and Packaging Committee and is the

direct responsibility of the Japanese Packaging Committee. Current edition approved by the Japanese

Regional Standards Committee on July 23, 2004. Initially available at www.semi.org September 2004; to be

published November. Originally published in 1987; previously published September 1996.

1 Purpose

1.1 The purpose of this test is to determine the thermal

resistance of integrated circuit packages using thermal

test chips.

2 Scope

2.1 This test method deals only with junction-to-

ambient measurements of thermal resistance and limits

itself to still- and forced-air convection testing

environments.

NOTICE: This standard does not purport to address

safety issues, if any, associated with its use. It is the

responsibility of the users of this standard to establish

appropriate safety and health practices and determine

the applicability of regulatory or other limitations prior

to use.

3 Referenced Standards

3.1 SEMI Standards

SEMI G32 — Guideline for Unencapsulated Thermal

Test Chip

SEMI G42 — Specification for Thermal Test Board

Standardization for Measuring Junction-to-Ambient

Thermal Resistance of Semiconductor Packages

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

4 Terminology

4.1 Definitions

4.1.1 The following definitions and symbols shall

apply for the purpose of this test:

4.1.2 ambient temperature (T

, in degrees Celsius) —

the ambient temperature is the temperature of the air at

a specified location in the vicinity of the

microelectronic device under test (DUT).

4.1.3 junction temperature (T

, in degrees Celsius) —

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. For purposes of this

test, the measured junction temperature is only

indicative of the temperature in the immediate vicinity

of the element used to sense the temperature.

4.1.4 power dissipation (P

, in watts) — the heating

power applied to the device causing a junction-to-

reference point temperature difference.

4.1.5 temperature-sensitive parameter (TSP) — 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.

4.1.6 thermal resistance — junction to specified

reference point, R

θJR

degrees Celsius/watt. The thermal

resistance of the microcircuit is the temperature

difference from the junction to some reference point in

the ambient divided by the power dissipation P

4.1.7 velocity (v

, in linear feet per minute (LFPM)) —

the velocity of the air at a specified location upstream

of the DUT.

5 Apparatus

5.1 The apparatus required for these tests shall include

the following as applicable to the specified test

procedures.

5.1.1 Thermocouple Material — Shall be copper

constantan (type T) or equivalent, for the temperature

range −100 to + 300°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.

5.1.2 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.

5.1.3 Controlled Temperature Chamber, Fluid Bath, or

Wind Tunnel — Capable of maintaining the specific

reference point temperature to within ± 0.5°C of the

reset (measured) value. Typical still-air enclosure and

SEMI G38-0996 © SEMI 1987, 2004 2

wind tunnel assemblies are presented for reference

purposes only.

5.1.4 Still-Air Enclosure Assembly — The microcircuit

shall be mounted in a cubic enclosure of not less than

0.028 m

(1.0 ft

). There shall be no radiation sources

other than the microcircuit under test in the enclosure.

The interior enclosure wall shall have a high reflectance

finish (emissivity < 0.1). The ambient temperature

should be measured by means of a thermocouple

mounted at a distance of approximately 2.54 cm (1.0 in)

beneath the DUT and 1.27 cm (0.5 in) from the test

board or socket.

5.1.4.1 The microcircuit shall be mounted in such a

manner that conduction cooling through the leads or the

test socket or both shall be small compared to the other

cooling mechanisms. No. 36 AWG wire should be

connected to the device test socket. The air flow (by

natural convection) should be unrestricted above and

beneath the device. An alternative approach would be

to use a mounting arrangement that approximates an

application environment. Such a reference mounting

configuration can be found in Specification, Thermal

Test Board Standardization for Measuring Junction-to-

Ambient Thermal Resistance of Semiconductor

Packages. Device mounting and test board positioning

inside the measuring chamber are depicted in Figure 1.

5.1.5 Wind Tunnel Assembly — A typical wind tunnel

design is shown with its dimensions in Figure 2.

5.1.5.1 The fan or blower should be placed

downstream of the DUT as depicted in Figure 2. A

static pressure differential measurement across a

calibrated nozzle is used to calculate the wind tunnel air

velocity, while a thermocouple is used to measure the

ambient temperature upstream of the DUT. Both of

these devices should be placed at a specified location

upstream of the DUT, as shown in Figure 2. The

thermocouple is located in the center of the wind

tunnel, 5.08 cm (2.0 in) from the test section and 2.54

cm (1.0 in) above the center plane of the DUT.

5.1.5.2 The microcircuit shall be mounted in such a

manner that conduction cooling through the leads or the

test socket, or both, shall be small compared to the

other cooling mechanisms. To minimize conduction

through the leads, No. 36 AWG wire should be

connected to the device test socket. The DUT should be

aligned so that the air front is parallel to the longer edge

of the package (air front hitting the package side). An

alternative approach would be to use a mounting

arrangement that approximates an application

environment. Such a referee mounting configuration

can be found in SEMI G42. Device mounting and test

board orientation inside the wind tunnel are depicted in

Figure 3.

5.1.5.3 Flow straighteners should be placed upstream

of the DUT, as shown in Figure 2. The flow

straighteners should provide a flat velocity profile

across the test section of the wind tunnel. This will

ensure that the DUT is exposed to a uniform velocity

across its entire cross section. A typical velocity profile

for well-developed turbulent flow is depicted in Figure

5.1.5.4 Calibrated hot wire anemometer or nozzle with

suitable pressure gauges (p

and p

) for measuring the

pressure difference across the nozzle is used to

calculate the wind tunnel air velocity. When using the

nozzle, the pressure differential across the calibrated

nozzle is measured using a liquid monometer, typically

in inches of water.

5.1.5.5 Hot wire anemometer capable of verifying the

air velocity profile with an accuracy of ± 5%. The

velocity sensor should disrupt the airflow as little as

possible.

6 Procedure

6.1 Measurement of Wind Tunnel Air Velocity, v

—

The air velocity measurement techniques are direct

method and indirect method.

6.1.1 Direct Measurement of Wind Tunnel Air Velocity

— The direct method is based on a measurement by a

hot wire anemometer in wind tunnel.

6.1.2 Indirect Measurement of Wind Tunnel Air

Velocity, vA — The air velocity measurement technique

is an indirect method based on a pressure differential

measurement across a calibrated nozzle. The actual

velocity of interest is derived from a calibration curve

relating the pressure differential of the nozzle to the

volume (or mass) flow rate of the air through the

nozzle. The required air velocity (in linear feet per

minute) is then calculated by dividing the volume flow

rate (in cubic feet per minute) by the cross sectional

area at the entrance of the DUT test section (in square

feet). The volume flow rate shall be determined to

within an accuracy of ± 10%.

6.1.2.1 Air Flow Profile — Hot wire anemometer

should be used to verify that the flow profile of the air

front, measured within 5.08 cm (2.0 in.) of the test

section, does not vary by more than 10% across the

center 90% of the test section. The DUT and mounting

board/socket should not be in the test section when the

flow profile is determined.

6.2 Direct Measurement of Reference Point

Temperature, T

— For the purpose of measuring the

still-air junction-to-ambient microelectronic device

thermal resistance in a chamber, the ambient

temperature (T

= T

) should be measured with a

SEMI G38-0996 © SEMI 1987, 2004 3

thermocouple beneath the DUT. For purposes of

measuring forced air junction-to-ambient thermal

resistance in a wind tunnel, the ambient temperature

should be measured with a thermocouple upstream of

the DUT in the section of the tunnel that experiences

fully developed flow.

6.3 Thermal Resistance, Junction to Specified

Reference Point, R

θJR

6.3.1 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 ambient temperature

and power dissipation in the device and a measurement

of the junction temperature are known. When making

the indicated measurements, the package shall be

considered to have achieved thermal equilibrium when

halving the time between the application of power and

the taking of the reading causes no error in the indicated

results within the required accuracy of measurement.

6.3.2 Indirect Measurement of Junction Temperature

for the Determination of R

θJA

— The purpose of the test

is to measure the thermal resistance of integrated

circuits by using particular semiconductor elements on

the chip to indicate the device junction temperature. In

order to obtain a realistic estimate of the operating

junction temperature, the whole chip in the package

should be powered in order to provide the proper

internal temperature distribution. During measurement

of the junction temperature, the chip heating power

(constant voltage source) shall remain constant while

the junction calibration current remains stable. It is

assumed that the calibration current will not be affected

by the circuit operation during the application of

heating power.

6.3.3 The temperature-sensitive device parameter is

used as an indicator of an average (weighted) junction

temperature of the semiconductor element for

calculations of thermal resistance. The measured

junction temperature is indicative of the temperature

only in the immediate vicinity of the element used to

sense the temperature.

6.3.4 The temperature-sensitive electrical parameters

generally used to indirectly measure the junction

temperature are the forward voltage of diodes and the

emitter-base voltage of bipolar transistors. Other

appropriate temperature-sensitive parameters may be

used for indirectly measuring junction temperature for

fabrication technologies that do not lend themselves to

sensing the active junction voltages.

6.3.4.1 Steady-State Technique for Measuring T

—

The following symbols shall apply for the purpose of

these measurements:

Measuring current in milliamperes.

Value of temperature-sensitive parameters in

millivolts, measured at I

, and corresponding to

the temperature of the junction heated by P

Calibration temperature in degrees Celsius,

measured at the reference point.

Value of temperature-sensitive parameter in

millivolts, measured at I

and specific value of

6.3.4.2 The measurement of T

, using junction forward

voltage as the TSP, is made in the following manner:

6.3.4.2.1 Step 1 — Measurement of the temperature

coefficient of the TSP (calibration).

6.3.4.2.2 The coefficient of the temperature-sensitive

parameter is generated by measuring the TSP as a

function of the reference point temperature, for a

specified constant measuring current, I

, by externally

heating the device under test in a controlled temperature

oven or fluid bath. The reference point temperature

range used during calibration shall encompass the

temperature range encountered in the power application

test (see Step 2). The measuring current is generally

chosen such that the TSP decreases linearly with

increasing temperature over the range of interest and

that negligible internal heating occurs in the silicon and

metal traces. For determining the optimum TSP

calibration or measuring current, V

vs. log I

curves

for two temperature levels that encompass the

calibration temperature range of interest should be

blotted. The optimum measuring current, I

, is then

selected such that it resides on the linear portion of the

two V

vs. log I

curves that were generated. A

measuring current ranging from 0.05 to 5 mA is

generally used, depending on the specifications and

operating conditions of the device under test for

measuring the TSP. The value of the TSP temperature

coefficient, V

, for the particular measuring

current used in the test, is calculated from the

calibration curve, V

vs. T

. At least three points

should be used to generate the voltage vs. temperature

curve for the determination of the TSP temperature

coefficient.

6.3.4.3 Step 2 — Power application test

6.3.4.3.1 The power application test is performed in

two parts. For both portions of the test, the reference

point temperature and the specified air velocity are held

constant at a preset value. The first measurement to be

made is that of the temperature-sensitive parameter

(i.e., V

, under operating conditions with the