Investigation Of Fabricating Techniques Of Multilayer PTCR Thermistor

In recent years, the rapid development of integrated circuits (ICs) and surface mounted technology (SMT) has registered an increase in demand for chip-mounted thermistors for overcurrent protectors. The realization of multilayer structures can make the resistance low in PTCR ceramics without affecting the temperature characteristics. The lower resistance at room temperature allows multilayer PTCR ceramics to be more sensitive to transient changes of temperature and current, thus broadening the applications of multilayer PTCR ceramics in electronic devices. In order to realize the multilayer structure, chip-type forming technology of PTCR ceramics such as roll-forming method, slip-casting method and gel-casting method were investigated and compared. Those chip-type forming technology are all based on aqueous system, which is harmless to people and environment. The properties of PTCR ceramics are very sensitive to sinter-system. By controlling the sinter-system, we can reduce the resistivity of PTCR ceramics without affecting other properties of PTCR ceramics seriously.A five-layer chip PTCR thermistor was fabricated by electrode-bonding method with R25℃ being 3.2Ω. The size of that five-layer chip PTCR is 8.0mm×5.0mm×1.96mm, with Tc being 65.9℃ and βbeing 2.3×105. The performance and reliability of multilayer PTCR thermistors could be improved by many methods such as improving the evenness of the surface of chip PTCR ceramics, strengthening the adherence of internal electrode to PTCR ceramics, and introducing glass-glazed insulating layer aside the areas of internal electrodes.