The fixing method and technique of K-type thermocouple wire temperature measurement point

Fixing the K-type thermocouple wire on the circuit board can monitor important temperature parameters during the soldering process. There are many ways to fix it. The purpose is to obtain reliable temperature data on key positions of circuit board components. The fixing method of K-type thermocouple wire has a significant impact on data quality.
Choose the K-type thermocouple wire fixing method
In different application scenarios, different K-type thermocouple wire fixing methods should be selected. The following are the issues that should be considered in specific applications:
To obtain a reading of the surface temperature, the K-type thermocouple wire junction should be in direct contact with the measured surface. If solder or adhesive is used, their quantity should be reduced.
Compare the selected fixed method with a reliable 'benchmark'.
Quick curing adhesive is easy to use, but it is suitable for low-temperature applications such as the A-side of wave soldering and repair processes.
The use of high-temperature solder and epoxy adhesive requires considerable skill and time, and should not damage the circuit board when removing them. But in reflow soldering, IR, and wave soldering, they can provide * * temperature curves that are suitable for testing circuit boards.
The paper clip fixation method can withstand the high temperature of the furnace repeatedly, but it is limited to the edge of the board and cannot ensure stable contact of the K-type thermocouple wire.
The screw fixing method is very firm and reliable even at high temperatures, but it can seriously damage the circuit board. Moreover, errors may occur due to heat transfer between the backside and the internal ground plane.
K-type thermocouple wire fixing method
In order to obtain reliable data from K-type thermocouple wires, it is necessary to understand the following two general rules:
The K-type thermocouple junction must have direct and reliable thermal contact with the monitored surface, otherwise an unknown thermal resistance will be generated between the K-type thermocouple junction and the measured surface. In this way, the temperature reading will be closer to the temperature of the material surrounding the K-type thermocouple wire, rather than the temperature of the measured surface. An extreme example is when the kapton tape relaxes at furnace temperature, the K-type thermocouple wire will detach from the measured surface and begin measuring the temperature of the surrounding air.
The material used to fix the K-type thermocouple wire junction to the measured surface should be minimal. This material will increase the heat capacity directly transmitted to the K-type thermocouple wire junction, as well as the thermal insulation of the measured surface in contact with this material. Both of these situations will cause the temperature of the K-type thermocouple wire to lag behind the true temperature of the plate surface when the furnace temperature rises or falls. When the temperature change rate is 2 ℃/s, there will be a lag of 5 ℃ to 10 ℃, which means that the temperature peak on the typical reflux temperature curve will be greatly reduced.