The effects on residual stress in multilayer NTC thermistors during soldering process and bending test (I. soldering pro
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TECHNICAL PAPER
The effects on residual stress in multilayer NTC thermistors during soldering process and bending test (I. soldering process) Nam Chol Yu1 • Yong Ho Ri1 • Chol Man Kim1 Received: 10 April 2020 / Accepted: 16 April 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A new three-dimensional finite element model to characterize the residual stress distribution in multilayer NTC thermistor during soldering process has been developed. During the soldering process, the effects of inner silver electrode number and lateral margin length on mechanical residual stress are studied. Throughout the weldbonding and heating process, the maximum and minimum principal stresses in the active region of the thermistor ceramic are not zero, which implies that most of the thermistor ceramic is not stress-free. Numerical results show that the increasing of the lateral margin length could effectively decrease the maximum tensile stress.
1 Introduction NTC(Negative Temperature Coefficient) thermistors are used in many electrical and electronic products such as mobile phone, personal computer and peripheral device, battery pack (secondary battery),liquid crystal display etc. They could be applied in temperature measurement, control and compensation of many instruments, time delay, voltage regulation and surge suppression. In most temperature sensing applications the NTC thermistors are made of spinel manganite (Maclen 1979; Vakiv 2001). For more reliable intended sensor applications, NTC thermistors are composed of multivalent transition metal oxides such as NiO, Mn3O4, Co3O4, Cu2O3 and Fe2O3, which are forming a complex spinel (Mn, Co, Fe, Cu)3O4 structure (Altenburg 2001; Buchanan 2019). Thick film thermistors based on complex spinel (Mn, Co, Fe, Cu)3O4 powder with binding glass have been known for more than two decades now (Altenburg 2001; Fritsch 1998). Thick film geometries were investigated not long after that, and custom design thermistors for miscellaneous sensors were introduced (Tutunea 2018; Talic and Cerimovic 2015). Nanometric thermistor paste was developed in the last decade using the complex spinel mentioned & Nam Chol Yu [email protected] 1
School of Science and Engineering, Kim Chaek University of Technology, P.O. Box 60, Kyogu, Pyongyang, Democratic People’s Republic of Korea
above (Ikegami 1980; Aleksic´ 2017), than characterized and applied for printing of different types of thermistors (Yadav 2019). They come in a variety of sizes. The thermistors obtained are usually called: disc, small chip, thick film and thin film thermistors. The thick film thermistor has several types such as sandwich, multilayer, segmented and interdigitated and the calculating methods of resistivity and B value by these types were described in (Aleksic´ 2007). Among these multilayer NTC thermistors are layered composite structures consisting of alternating layers of metal inner electrodes and NTC thermistor ceramics sandwiched between two ceramic co
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