# Surface Temperature Measurements: Thermocouple Types

2023.02.22

・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 TJ: Calculation Example Using ΨJT“, TT is necessary for estimation of TJ using ΨJT. In order to obtain TT, 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（℃）
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.