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Surface Temperature Measurements: Methods for Fastening Thermocouples

2023.06.07

Points of this article

・Methods for fastening the tip (junction) of a thermocouple to the package of an IC or other device include ① using polyimide (PI) tape or the like, and ② using an epoxy adhesive.

・The JEDEC standards recommend methods using an epoxy adhesive.

・Apart from the method of attaching the thermocouple tip, the arrangement of the wiring also affects the measurement results, and so the wiring itself is run along the surface of a heat source.

table of contents

・Methods for Fastening Thermocouples: Attachment Methods
・Methods for Fastening Thermocouples: Arrangement of Wiring

When measuring a surface temperature, the method used to fasten the thermocouple and the arrangement of the wires affect the measurement results. It is important to minimize the effect of the thermocouple fastening method.

Methods for Fastening Thermocouples: Attachment Methods

Methods for fastening the tip (junction) of a thermocouple to the package of an IC or other device include ① use of polyimide (PI) tape or something similar, and ② use of an epoxy adhesive. The JEDEC standards recommend a method using an epoxy adhesive.

The features of each are as follows.

Fastening method	Advantages	Disadvantages
Polyimide (PI) tape	・The thermocouple tip makes direct contact with the package surface ・Fastening is simple ・Removal is simple	・Separation, absence of contact are possible ・Because the tape itself has low thermal conductivity (1/1000 that of metals), convection to the outside air is impeded
Epoxy adhesive	・Little chance of separation (depending on temperature resistance) ・Small area needed for fastening ・Recommended by JEDEC	・Flows between thermocouple and package ・Fastening requires time

Methods for Fastening Thermocouples: Arrangement of Wiring

Apart from the method used to attach the thermocouple tip (junction), the arrangement of the wires also affects the measurement results. The wires must be kept close to the package until the PCB is reached. By doing so, the drop in temperature at the thermocouple junction due to heat dissipation from the wire is alleviated. This is also described as a wiring technique in the JEDEC standards. In other words, the key to accurate surface temperature measurements lies in minimizing heat dissipation caused by the thermocouple.

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Surface Temperature Measurements: Methods for Fastening Thermocouples

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