2004 Volume 7 Issue 3 Pages 230-238
Recently, there is a tendency for low impedance to be adopted by various electronic circuits, and such demand is also appearing in the field of thick-film resistors. The CB (Carbon Black) has been used for a long time as a main conductive particle which is dispersed in resin system thick-film resistors. Only the resistor of negative TCR is obtained, because CB particles have rather large negative TCR, even if we intend to obtain low resistance in response to this demand by increasing CB fraction. On the other hand, the RuO2 particle which is adopted in the glass system thick-film resistor has positive TCR, and its electric resistivity is 4 digits smaller than CB particles. Therefore, it was presumed that the low resistivity having zero TCR may be acquired, if an appropriate fraction of CB particles is mixed with RuO2 particles. On the basis of this thinking, we tried to develop a new resin system thick-film resistor of low resistivity with zero TCR by using a mixture of RuO2 and CB. As a result of an experiment, zero TCRhot and a low resistivity of 100 Ω/_??_, which was the initial purpose, was obtained by using the RuO2/CB=12vol.%/3vol.% mixture, and the impedance was steady up to 10 MHz. It was also confirmed that optional TCR from negative to positive range is freely obtained by changing the blend ratio of CB and RuO2. Next, the current noise index and the equivalent elements of impedance were measured in order to examine the characteristics of contact point, and then the correlation among these was discussed. It was especially shown that the contact resistance of the conductive particles are the main source of the current noise. The resistor of this type is expected to be used in the multilayer printed wiring circuit as embedded resistors in addition to general use, because the TCR is freely controllable between negative and the positive value.