The CSR series is a range of metal film precision resistors in the MELF (Metal Electrode Leadless Face) package format. Unlike the flat rectangular ceramic body of a conventional SMD chip resistor, a MELF resistor uses a cylindrical ceramic substrate onto which a continuous, homogeneous metal film is deposited across the full outer surface of the cylinder. Resistance trimming is achieved by cutting a helical groove into the resistive film using a laser, a process that distributes the current path evenly around the circumference of the component and avoids the localised current concentration that can occur at trim cuts in flat chip resistors. This construction gives the CSR series substantially better pulse load handling than flat chip types of equivalent case size, as well as improved thermal distribution and long-term stability under sustained load.
Three package sizes are offered: CSR0102 (MicroMELF), CSR0204 (MiniMELF), and CSR0207 (MELF), with power ratings of 1/4W, 1/3W, and 1/2W to 2W respectively — the specific rating depending on the variant and mounting conditions. The resistance range spans 1Ω to 10MΩ, and six tolerance grades are available: ±0.1%, ±0.25%, ±0.5%, ±1%, ±2%, and ±5%. TCR grades of ±10, ±25, and ±50 ppm/°C cover the spectrum from tight-tolerance precision circuit requirements through to cost-effective general-purpose precision applications. The steel termination end-caps are plated with nickel and matte tin, providing reliable solderability and compatibility with standard no-clean and water-wash flux processes.
A defining characteristic of the MELF package is its environmental robustness. The cylindrical ceramic body and the protective lacquer overcoat that encases the resistive film provide superior resistance to moisture ingress, humidity, and contaminant-driven degradation compared to the flat-body chip resistor, where the resistive element is closer to the board surface and potentially more exposed. This robustness makes the CSR series particularly well suited to automotive, industrial, and outdoor electronics applications where components are exposed to prolonged humidity cycles, condensation, and wide temperature swings. The mechanical structure of the cylindrical package also provides greater resistance to vibration and thermal shock than equivalent flat chip types.
Within the RARA precision resistor family, the CSR occupies the same metal film technology category as the leaded MFR and high-precision MFD series, offering the stability and noise characteristics of metal film construction in a fully surface-mountable, lead-free format. It complements the thin film chip AR and SM series — which offer tighter tolerance and lower TCR in a flat SMD package — by providing higher pulse load capability, better environmental sealing, and a wider tolerance range in a board-mountable format. The CSR is colour-band marked per IEC 60062, is RoHS compliant, and is qualified to MIL-STD-202 and JIS-C 5201 test standards.
