化学镀镍工艺条件对陶瓷热敏电阻性能的影响

Influences of electroless nickel plating conditions on properties of PTC ceramic thermistor

化学粗化能使晶界剥蚀晶粒裸露,当化学粗化时间超过5min可以明显提高瓷片焊接强度。化学镀镍溶液pH值升高,镀层磷含量降低,同时可能生成Ni(OH)2沉淀夹杂在镀层中,从而使电阻升高;磷含量升高,热敏电阻耐电压强度下降;因此镀镍液pH值应控制在4 0～5 0。热处理温度在250℃即可将扩散到陶瓷的初生态氢原子去除,热处理温度过高或热处理时间过长使镍明显氧化从而破坏了瓷片的欧姆接触。电阻-温度特性曲线测定结果显示,经热处理的热敏电阻的R T曲线与银锌电极的R T曲线相似。

Chemical roughening could corrade crystal boundary and make crystal grain naked, therefore, welding strength of PTC ceramic was obviously enhanced after roughening over 5 minutes. With the raise of pH value of electroless nickel plating solution, content of phosphorus in deposit was lowered, and moreover, Ni(OH)_2 was probably precipitated and mingled with Ni-P deposit which resulted in ascension of resistance. The more phosphorus content in deposit, the lower endurance voltage strength of PTC ceramic was. Optimum pH value might be from 4.0 to 5.0. Nascent hydrogen atom formed on ceramic surface could be eliminated in heat treatment at low temperature of 250 ℃. Higher temperature or longer heat treatment time would cause nickel oxidation and destroy ohmic contact of thermistors. Results show that resistance to temperature curves of PTC ceramic is similar with that of silver-zinc electrode.