Research Of Preparation Process Of The Laminated PTCR Materials

In recent years, the electronic products have been smaller and more integrated,which promotes the development of microelectronics and surface-mountingtechniques （SMT）. So the resistor, the capacitance, the inductance and some sensitiveelements should be produced sheet to meet the need. The positive temperaturecoefficient （PTC） resistors, as a member of the sensitive elements, not only should besheet but also low room temperature resistance for the low voltage they work at. Theroom temperature resistance of traditional bulk positive temperature coefficient ofresistivity （PTCR） materials can not be further reduced. However, with the muchlower room temperature resistance and excellent PTCR behavior, the laminatedPTCR resistor has attracted many focuses for its great market potential and scientificmerit.In our study, sand ball milling and planet ball milling were used to grind the rawmaterials of the PTCR ceramic and the BaTiO₃powders which were prepared bysolid state method. The effects of particle sizes of raw materials and BaTiO₃powderson properties of PTCR ceramics were discussed. The pores in PTCR ceramicsprepared using sand ball milled raw materials were large and had a centralizeddistribution. But the pores in ceramics prepared using planet ball milled raw materialswere relatively small and widely dispersed. The resistivity and PTCR jump（lg（Rmax/Rmin）） of ceramics prepared using sand ball milled raw materials were largercompared with that of ceramics prepared by planet ball milled raw materials. Inaddition, compared with the ceramics made from planet ball milled BaTiO₃powdersthe resistance changed large after reoxidation for the samples made from sand ballmilled BaTiO₃powders. What is more, the abnormal growth of grains was found outin ceramics made from planet ball milled BaTiO₃powders, but not in ceramics madefrom sand ball milled BaTiO₃powders.Meanwhile, the effects of SiO₂on the properties of PTCR ceramics wereinvestigated. Suitable amount of SiO₂（0.2at.%） could help to largely decrease theroom temperature resistivity and didn’t affect the PTCR effects. But too much SiO₂ could block the pathway of oxygen in the grain boundary and made the PTCR effectspoor. At the same time, it could make the room temperature resistivity to increaseagain.