A New Center-Tapped Medium-Power Microfilm Resistor

A new center-tapped microresistor with high power density capability, good stability, and a high degree of inherent reliability is described. The resistor consists of a 0.075 in²chip 0.022 in thick with two equal-value sputtered tantalum nitride photoetched resistors. Gold-plated copper leads are thermal pulse bonded to evaporated chrome/gold bonding pads. The resistive film is protected with an epoxy coating. Performance data include 10 000 h life at 70°C with 0.2 and 0.4-W dissipation with resistance changes generally under 1 percent. This is equivalent to 70 W/in²of substrate area and up to 1300 W/in²of resistive area. Also included are 10 000 h of 150°C thermal aging, temperature cycle, moisture performance and short time overload, and hot-spot temperature rise versus power dissipated. With heat sinking, short time overload of up to 3 W was successfully applied. Tolerance as manufactured is ±5 percent and stability is generally equivalent to M I L 10509 characteristic C. The product design, manufacturing process, fabrication equipment, and process controls are described. Included are a continuous sputtering machine, an autobonder, an autotester, and a "binstock" qualification procedure. Two unusual applications are described. In one, pairs of center-tapped resistors are used as stripline attenuators or as stripline terminations. They are useful at frequencies up to approximately 2 GHz, In the second application, they are used in an ultrahigh-speed computer. All signal conductors are treated as transmission lines and terminated with the microresistor. The computer size is such that just under 500 000 resistors are required. Operation of this computer leads to interesting conclusions regarding field failure rate and require- ments.