Several device technologies are available to designers and each of them makes sense for a certain subset of applications depending on cost-benefit analyses. But when the application requires stability over time and load, initial accuracy, minimal change with temperature, resistance to moisture, and a number of other characteristics, the choices are more limited.
The purchase price of each resistor technology generally falls along the lines of thick films being the least expensive, thin films being more costly, and foil being more costly yet. But as we all know, purchase price and “cost of usage” are two very different things. The inexpensive device that fails can wind up costing many times more in terms of replacement costs before shipment, failures in operating systems after shipments, scrubbed missions, and future business.
Thin film resistors are more precise than thick film resistors. They are also more costly. This technology is best suited for applications requiring greater precision, as in analog circuits where the stability of specific values is important, rather than just the mere presence or absence of a signal. Here, the designer makes both economical and performance analyses and determines that the requirements for precision and stability are satisfied by the more-costly thin films with acceptable risk and consequences of failure for the application. Microhm NAP series, NR series are typical thin film resistors for your choice.
In some applications, however, the consequences of failure are so costly that only the use of very high precision, very high reliability resistors, such as foil devices, can be justified. For example, telemetry equipment in remote earth locations may be extremely expensive to access and repair, and lives could be lost if the signal goes down. Systems in space must work as required with the greatest degree of confidence; there is no replacement opportunity and the cost of getting the system into operating locations is astronomical. Automatic test equipment performing hundreds of almost instantaneous tests on semiconductors as they come off the production line must perform with precision and reliability or hundreds of thousands of dollars’ worth of materials could be lost. Medical equipment cannot give false or undependable readings and still safeguard people’s health and lives. Microhm' foil resistors, such as MPR series, MVR series, NMS 2818, NMS4527 are of high reliability and stability , aims at these fields.
