1、JEDEC PUBLICATION User Guidelines for IR Thermal Imaging Determination of Die Temperature JEP138 SEPTEMBER 1999 ELECTRONIC INDUSTRIES ALLIANCE JEDEC Solid State Technology Association Electronic Industries Alliance STD- IA JEPLIB-ENGL NOTICE EWJEDEC standards and publications contain material that h
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9、 Canada (1-800-854-7179), International (303-397-7956) Printed in the U.S.A. All rights reserved . JEDEC Publication No. 138 Page 1 USER GUIDELINES FOR IR THERMAL IMAGING DETERMINATION OF DIE TEMPERATURE (From JEDEC Board Ballot JCB-95-69, formulated under the cognizance of the JC-25 Committee on Tr
10、ansistors.) 1 Purpose The purpose of these user guidelines is to provide background and an example for the use of an infrared (IR) microscope to determine die temperature of electronic devices for calculations such as thermal resistance. 2 Terms and definitions The following definitions and symbols
11、are used throughout this document: TIM peak junction temperature (in degrees Celsius) TJ(AV) average junction temperature (in degrees Celsius) TC case temperature (in degrees Celsius) NOTE - Measured with a thermocouple that is attached as close as possible to the major heat flow path, usually on th
12、e bottom center of the device package or case for packaged parts. For wafers, this temperature is the die temperature. For surface-mount devices. this is the lead frame. TM mounting surface temperature (in degrees Celsius) NOTE - Measured with a thermocouple inserted in an access hole terminated nea
13、r the devicehtage interface. PD power dissipation (in watts) of a single junction under test or of the entire package. RJR thermal resistance between junction and a reference (such as ambient (ROJA) or case (RJc), measured in “CrW) emissiviy: A dimensionless factor that is a property of the material
14、 and its surface texture. NOTE - Emissivity (E) is represented by a number between O and 1 where E = O represents a perfect infrared reflector and E = 1 represents a perfect infrared absorber or “blackbody”. A blackbody is also a perfect radiator or emitter of infrared radiation. spatial resolution:
15、 The diameter of a spot, in micrometers, whose size is determined from the half-power points resulting from a point infrared source. JEDEC Publication No. 138 Page 2 3 Apparatus Some or all of the following list of equipment will be necessary to complete the procedure: 3.1 Infrared microscope A micr
16、oscope with a detector or array of detectors sensitive to infrared radiation is necessary. The microscope may be from any one of the three major families: single detector staring, single detector imaging, or array detector imaging. Each of the three families has price/performance advantages and disa
17、dvantages. The features and performance specifications of the IR microscope have a significant impact on the accuracy of the data collected. Spectral response The Indium Antimonide (InSb) detector with spectral response of 2-5 pm is used for applications where high spatial resolution specifications
18、are desired. Mercury Cadmium Telluride (HgCdTe) with spectral response of 5-15 pm has advantages for room temperature applications but is inferior to InSb for resolution of small features and sensitivity at temperatures above room temperature. Spatial resolution The necessary spatial resolution (spo
19、t size) specification depends on the individual application. If the length or width of the feature to be measured is less than the spot size, the resulting data for that point will not be the true peak temperature and will be erroneously low since the desired feature and its surrounding area will be
20、 averaged into one data point. Temperature resolution Temperature resolution is the ability to detect small changes in temperature. An accepted minimum standard for temperature resolution is 0.5 OC at 60 OC, but instruments are currently available that are capable of O. 1 OC temperature resolution.
21、Emissivity correction Emissivity is a dimensionless factor that is a function of the material and its surface texture. Emissivity can range from zero for a perfect reflector to one for a perfect emitter (blackbody). The maximum infrared energy which can be emitted from a body at any given temperatur
22、e is that of a blackbody. Therefore, the infrared energy density emitted from a blackbody is a measure of its temperature. The infrared microscope calculates temperature by either assuming that the DUT has high (near unity) emissivity or using an internal emissivity correction algorithm. if the IR m
23、icroscope does not have an emissivity correction algorithm, the device must be coated with a uniform high emissivity layer. This layer must be thin (25-50 pm) and of a known, high emissivity (E 2 0.95) such as flat black paint or lampblack. The uniform high emissivity layer can reduce peak junction
24、temperatures by as much as 2% (OK) due to alteration of the thermal characteristics of the die. The uniform high emissivity layer is typically permanent. , . JEDEC Publication No. 138 Page 3 3 Apparatus (contd) 3.1 Infrared microscope (contd) e) Background Reflections If the IR microscope has an emi
25、ssivity correction algorithm, then reflections from the background must be corrected for. This capability is unnecessary for instruments that rely on the uniform high emissivity layer since a surface with high emissivity has low reflectivity. f) Narcissus Effect Correction The Narcissus Effect is an
26、 error that results from the cold (liquid-nitrogen cooled) detector “seeing” its own reflection on a surface with low emissivity. This effect is predictable and can be negated in software. Note that this phenomena is only apparent when the cold detector is staring at a low emissivity surface perpend
27、icular to the axis of view. 3.2 Device holder The DUT is mounted on a device holder which provides the following: a) Ability to maintain die or case temperature at a stable known value, typically via a temperature controlled mounting surface. b) Access for at least one of two thermocouples, dependin
28、g on the following: Ideally and for most accurate measurement, a thermocouple is attached to the device case to acquire TC, the case temperature. For most wafers (where TC is the die temperature) and in many packaged part applications, this will be possible. In some cases, however, it is not feasibl
29、e to attach directly to the case. If it not feasible to attach a thermocouple directly to the case, provide an access hole to allow mounting surface temperature, TM, to be measured as close as possible to the bottom surface of the die or package. This value is then used as an approximation of Tc. Be
30、fore inserting the thermocouple, fill the access hole with thermal grease or thermal conducting epoxy to assure heat flow to the thermocouple bead. Air pockets in the access hole should be avoided. c) All interfaces such as die to adapter and adapter to temperature-controlled mounting surface must b
31、e coated with a layer of thermal grease or thermal conducting epoxy to assure good heat flow. This is particularly important in cases where TM is being used to approximate Tc. d) Allow for electrical connection so that the device can be brought to operating temperature. This can take the form of a P
32、CB assembly with socket and breakout connectors for packaged devices or a probe station for devices in die form. STD-EIA JEPL36-ENGL 1777 E 3234b00 Ob252 320 JEDEC Publication No. 138 Page 4 3 Apparatus (contd) 3.3 Thermocouple A thermocouple is used for measuring case or mounting surface temperatur
33、e. The thermocouple material can be copper-constantan (type T) or equivalent. The junction of the two thermocouple wires is welded to form a bead. The accuracy of the thermocouple and associated measuring system should be less than or equal to M.5 “C. 4 Procedure 4.1 Instrument calibration The calib
34、ration of an IR microscope is checked with a blackbody source. If the temperature of the blackbody is measured with a thermocouple, that temperature is converted to infrared radiance with a lookup table or calculated with Plancks Law. The derived radiance is compared to the radiance measured with th
35、e IR microscope to verify calibration. 4.2 Device preparation The DUT must be in precapped or decapped form to provide direct viewing of the die surface. If the uniform high emissivity layer method of emissivity normalization is used, the active area of the DUT is coated. 4.3 Test preparation a) The
36、 DUT is mounted in the device holder on the temperature controlled stage and a thermocouple connected to measure Tc or TM. b) All electrical connections necessary to stimulate the DUT to its operating conditions are made. c) The optics are focused and centered on the area of interest. Generally, max
37、imum infrared energy indicates focus on the primary heat generation element or junction. Focus is accomplished in some systems by initially performing a visual focus (if a visual camera is present) and then changing to the IR system. This method assumes that the visual and IR systems are parfocal. I
38、f a visual system is not present (or to provide additional capability), an IR focus can be performed on the DUT by viewing the raw radiance image and manipulating focus until the sharpest image appears. The raw radiance image can be viewed from either its analog (fastest display rate) or digital sig
39、nal. JEDEC Publication No. 138 Page 5 4 Procedure (contd) 4.4 Test procedure a) The case (or die for wafers) temperature is set to a known, stable value. b) All necessary emissivity and background correction operations are executed. For a system with automated emissivity, background, and Narcissus c
40、orrection, this procedure will take the following form 1,2: 1) Basic relationship - The basic equation for radiance (where the object is considered to be opaque) is: NM = ENT + (1 - &)NA, (1) where NM is the measured radiance, E is the emissivity, NT is the blackbody radiance at target temperature,
41、and NA is the blackbody radiance at ambient temperature. 2) Emissivity Calculation - By acquiring radiance measurements (with the device unpowered) at two temperatures (T1 and T2) which straddle the temperature at which you wish to test the device, you now know NM at two points (NM and NM). In addit
42、ion, from the calibration performed prior to the test (see 4. i), you know NT at the two temperatures at which you acquired NM (NT and N7-2). Substituting known values into equation 1, you have two equations in two unknowns (E and NA), and can solve for E as 3) Ambient Radiance Calculation - By acqu
43、iring a radiance measurement (with the device unpowered) at the desired case temperature Tc (NM) and using the known blackbody radiance at Tc (NT), the ambient radiance can be calculated as N=(Npyl3 -&N3)/(1 -E) (3) Calculating ambient radiance at the desired case temperature corrects for the backgr
44、ound reflections and Narcissus effect. c) The DUT is then operated at a specified electrical operating condition (power vs. time). Allow enough time for the junction temperature to stabilize. At the same time, limit the time such that the reference temperature does not vary. Record all of the necess
45、ary electrical conditions and test circuits for the calculations to be performed. d) The radiance, or temperature for corrected IR microscopes, is acquired and recorded. This data will be used to calculate thermal characteristics such as thermal resistance (RJR). For corrected systems such as descri
46、bed in step b, and using equation 1 and the known values, the blackbody radiance of the device is calculated as NT = (NM - ( 1 - &)NA)/& (4) Using Plancks law (or a power series expansion to this) gives the temperature of the device from the known blackbody radiance. STD.EIA JEPL38-ENGL L979 II 3234
47、b00 Ob25804 LT3 m JEDEC Publication No. 138 Page 6 5 An example: bJR Calculation The ability of a semiconductor device, such as a power transistor, to dissipate generated heat to the environment is critical for reliable operation of that device. In order to predict the reliability of a new device or
48、 analyze the failure of an existing device, thermal Characteristics must be determined. The figure of merit used to describe the thermal characteristics of a microelectronic device is thennal resistance. Thermal resistance allows the representation of thermal characteristics in electrical terms. The
49、 most general expression of thermal resistance is where &JA = Thermal resistance between junction and ambient (“Cm ReJc = Thermal resistance between junction and case (“CN) &cA = Thermal resistance between case and ambient (“CN). The calculation of RejC is used to quantify the thermal properties of a device and is defined as the difference between the junction and case temperatures divided by the power dissipation of the element. Two options for measuring TJ exist. i) Assuming that the spatial resolution of the IR microscope is sufficient to provide several measurements
