It wasn’t until the 1980s that surface-mount technology (SMT) gained in popularity and use. Until then, through-hole technology was the go-to option for more than 30 years. Once SMT became available, smaller boards were possible, however, SMT isn’t always the answer. Devices utilizing SMT cannot be used directly with breadboards; they are not appropriate for large, high-power or high-voltage applications; and they aren’t suitable when there is mechanical stress. In these cases, and more, through-hole technology still shines.
Through-hole mounting uses leads that are inserted into holes drilled on PCBs and are then soldered to pads on the other side of the board by automated insertion machines or by hand placement. The resistors used are plated through-hole (PTH) with long, pliable leads that are either hand-soldered onto a board or inserted into a breadboard. The leads, once placed, are then trimmed.
Wirewound and axial packages are the two types of through-hole resistors, with axial packaging representing the most commonly used. This resistor size is based on its power rating. The axial leads are at each end of the cylinder or box-shaped component. They are used for short distances and they have a low or flat profile on the board. Wirewound resistors are usually more expensive, higher-end components used based on their higher power rating or inherent maximum temperature range. These resistors are made from carbon, metal, or metal-oxide film. A thin film of conductive material is wrapped in a helix and covered by an insulating material. Most are carbon-film or metal-film composition.
Wirewound resistors have a metal wire wound around a ceramic, plastic, or fiberglass core. The wire ends are soldered or welded to caps at the ends of the core and the resistor assembly is covered with a layer of enamel or paint for protection.
The Vishay wirewound RWR78N13R7FPB12 is a fixed single through-hole resistor for military use. Demonstrating high reliability, the RWR78N13R7FPB12 is MIL-PRF-39007 qualified. Features of the RWR78N13R7FPB12 include: a high-temperature silicone coating, a complete welded construction, and availability in non-inductive styles (type N) with Ayrton-Perry winding for lowest reactive components.
The CCR218RKB from TE Connectivity is a fixed single through-hole resistor constructed using solid ceramic composition, which is the traditional medium for absorbing high-energy pulses, in cases of high in-rush current. These resistors have excellent pulse withstanding capabilities and are very stable. This series is ideal for circuitry-associated performance in high-voltage power supplies, R-C snubber circuits and in-rush limiters.
Figure 1: Dimensions of the CCR218RKB from TE Connectivity. (Source: TE Connectivity)
These resistors feature low cost and high performance, a wide range of resistance values, and they are available on tape in two size options.
Yageo’s CFR1WSJT-52-10K fixed single through-hole carbon film resistor series is manufactured with a homogeneous film of pure carbon on high-grade ceramic rods. After a helical groove has been cut in the resistive layer, tinned connecting leads of electrolytic copper are welded to the end-caps.
Table 1: Temperature coefficient for the CFR series carbon film resistors. (Source: Yageo)
Through-hole mounting provides strong mechanical bonds, but the drilling required makes the boards more expensive to produce. When using multi-layered boards, they also limit the available routing area for signal traces below the top layer since the holes need to go through all layers. As a result, through-hole mounting is usually reserved for bulkier or heavier components or those that require great strength in support such as plug connectors.