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Surface Temperature Measurements: Thermocouple Types

2023.02.22

Points of this article

・When measuring the surface temperatures of mounted semiconductor components, often the most practical approach is to use a thermocouple.

・In this article, type K thermocouples in class 1, and AWG 38 wiring, are used.

As indicated in the article “Estimating T_J: Calculation Example Using Ψ_JT“, T_T is necessary for estimation of T_J using Ψ_JT. In order to obtain T_T, the package top center temperatures of individual semiconductor components must be measured.

To measure the surface temperatures of electronic components, there are ① contact methods using thermocouples, and ② methods in which a radiation thermometer, a thermal imaging device, or the like is used to measure the energy radiated from an object surface. However, when measuring the surface temperatures of individual components mounted on a board, often ①, the methods using thermocouples, are more pragmatic. Hence in what follows we will explain important points relating to surface temperature measurements using thermocouples.

Thermocouple Types

There are various types of thermocouples (IEC standard thermocouples), these types being represented by symbols such as B, R, S, N, K, E, J, T, and C. Each of these types has its own range of measurable temperatures and characteristics. The table below presents the features of type K and T thermocouples, which are often used in measurements of electronic components and other equipment.

IEC code	Jacket color	Constituent materials		Class	Temperature range（℃）	Tolerance（℃）
IEC code	Jacket color	＋ lead	－ lead	Class	Temperature range（℃）	Tolerance（℃）
Type　K	Green	Nickel-chromium alloy Thermal conductivity （to 19 W/mk）	Nickel-aluminum alloy Thermal conductivity （to 30 W/mk）	1	－40 to ＋375	±1.5
				2	－40 to ＋333	±2.5
				3	－164 to ＋40	±2.5
Type T	Brown	Copper Thermal conductivity （to 385 W/mk）	Copper-nickel alloy Thermal conductivity （to 19 W/mk）	1	－40 to ＋125	±0.5
				2	－40 to ＋133	±1.0
				3	－67 to ＋40	±1.0

In these articles, a type K thermocouple used in order to suppress insofar as possible heat dissipation from the thermocouple. Moreover, a Class 1 thermocouple for which the tolerances of the thermocouple itself are small, and AWG 38 wiring (the JEDEC Standard recommends AWG 36 to 40), were selected for use.

【Download Documents】 Thermal Design of Semiconductor Components in Electronics

Thermal design has become a new issue in the design of electronic equipment in recent years, as thermal countermeasures have been the focus of attention. Although heat has been an important consideration for some time, the requirements for electronic equipment have changed in recent years, making it necessary to review conventional thermal countermeasures. This handbook describes thermal design based on the assumption that ICs and transistors are basically used in electronic equipment.

Surface Temperature Measurements: Thermocouple Types

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