Packaging effects on the sensing performance of RTDs on an AlN substrate of a wafer heater

This study investigates packaging effects on the sensing performance of resistance temperature detectors (RTDs) on an AlN substrate of a wafer heater. The study utilizes a solder packaged RTD (PRTD1) as a conventional case and a thermal paste immersed RTD (PRTD2) as a traction free case with the AlN substrate. A high precision measurement study and a robust FEA thermal-structural study are conducted to explore packaging effects. The measurement finds that sensed results by the PRTD1 are even 2.5 °C or 0.9 Ω higher than those of the PRTD2. The thermally-induced strain in the Pt thin-film of the PRTD1 may explain this difference. The FEA study determines that the non-negligible axial strain of 0.002 occurs in the Pt thin-film with the heated surface of the AlN substrate isothermal at 250 °C. This study demonstrates that the straightforward analytical method may reasonably predict the shift of the electrical resistance, induced by the thermally-induced strain, of the RTD. The discrepancy is found to be smaller than 10 % compared with the sophisticated measurement.