Characterization of a New and Complete Lead-Free Thick Film Resistor System for the Hybrid Circuit Market

Abstract

The move to lead-free thick film technology, including resistors does not necessarily mean a move away from performance. There have been many recent developments in the area of lead-free glasses, thick film dielectrics, and conductor materials. However, the development of lead-free resistor materials has been slower to enter the market. This slower evolution is due, in part, to the need to develop a series of discrete compositions that are compatible with each other and cover a wide range of resistance values. There can be 8–10 individual members in such a series. The primary goal of this development was to achieve resistor performance on par with, or superior to an existing and popular premium lead based resistor system. This paper describes a new series of lead-free thick film resistor compositions that cover a complete range of decade values from 1 Ohm/square to 10 MegOhms/square. Each member is compatible and blendable with adjacent members to cover all possible resistivity needs. This system provides excellent environmental stability of laser trimmed resistors, tight TCR gap control, a wide processing latitude, and minimal termination effects with a wide range of lead-free conductor metallurgies including Au, Ag, Ag/Pt, and Ag/Pd. In this paper, we report the results of a characterization study that includes 1000 hours of laser trim stability in 85°C/85%RH, thermal ageing at 150°C, room temperature ageing, and thermal cycle stability at −50°C +150°C. Electrical properties are presented and include Power Handling, Quan-tech Noise, and Electrostatic Discharge stability. In addition, this paper investigates and documents: resistor length effects, fire and refire sensitivity effects, thickness behavior, and the use of lead-free encapsulation.