Preparation Technology Of Copper Electrode Paste For Zinc Oxide Varistor

Zinc oxide varistor is a kind of ceramic semiconductor element with transient voltage suppression function,which is made of zinc oxide as the main material and adding various metal oxides into the raw material.Because of its unique volt-ampere characteristics,it can be used to replace Ziner diode and some capacitor devices.It can be used in parallel with protective components.To protect the electrical components from the current surge and electrostatic discharge caused by the sudden increase of voltage in the circuit.At present,the conductive phase used for zinc oxide varistor slurry is mainly silver powder,which accounts for about 80% of the slurry composition.However,the price of silver powder as precious metal has remained high in recent years,and the cost of preparing silver powder as slurry is higher.The copper electrode paste for zinc oxide varistors was prepared by substituting base copper for widely used silver metal.The properties of the sintered copper film were tested by four-probe resistance tester,spiral tensiometer,small tin soldering pot,scanning electron microscopy and energy dispersive spectrometer.The results showed that:(1)Copper slurry was prepared by two methods of atomization and electrolytic reduction.After sintering at 600?C,the pore of the copper film prepared by atomization was observed under scanning electron microscopy.The porosity of copper film prepared by electrolytic reduction method is higher,but affected by its shape,the melting effect of branch tip is better.The resistance difference between them is small,15.5 m?and 14.8 m?,respectively.(2)Comparing the softening point and wettability of different cryogenic glasses,it was found that the melting temperature of the two glasses ranged from 500 ~600?C,and the wettability of GF-1 glass was better from the appearance observation.(3)The proportion of conductive copper slurry for zinc oxide varistor is determined.The proportion of conductive phase,glass powder,oxide and organic carrier is 72:6.4:1.6:20.The copper conductor slurry prepared by this ratio has good weldability,the lowest resistivity is 12.3 m?,but the adhesion of the copper film sintered at 600 C is low,the maximum is 2.4 N.(4)After adding silver into copper powder,silver acts as a bridge between copper powder,fills the gap between copper powder,improves the sintering activity of copper powder and reduces the film resistance.Different proportions of copper conductor slurries were prepared by using silver-coated copper powder with 10% silver content.The results showed that when the amount of silver-coated copper powder and copper powder was 1:2,the silver-coated copper powder had the best promotion effect on the sintering of copper powder.The adhesion of the film was improved obviously,and the highest was 4.5N.(5)Compared with the slurry doped with Ag-coated copper powder prepared by atomization and electrolytic reduction,the Ag-coated copper powder has the best effect on improving the sintering activity of the spherical copper powder prepared by atomization.The effect of the resistance of copper powder prepared by electrolysis is the most obvious,and the resistivity decreases by 27.2%.(6)By adding silver powder and silver-coated copper powder respectively in the copper conductor paste,it was found that the slurry with the silver-coated copper powder was more evenly distributed,and the effect of promoting the sintering of the copper powder was better.(7)Six kinds of copper films prepared by slurry A1-B3 were tested.The results show that the antioxidant performance of slurry doped with silver-coated copper powder is stronger than that of pure copper slurry.The greatest weight gain is slurry A1,reaching 4.42%,and the smallest weight gain is B2.The minimum is 3.2%.