Ceramic thick film resistors have long been the main force in electronic applications, but they rely on brittle substrates that are susceptible to cracking or delamination. With this in mind, Burns, Inc. offers a steel based alternative for applications that require high power, thermal efficiency, and mechanical robustness.
Ceramic thick film resistors are reliable prior to cracking or delamination, but the risk of cracking or delamination increases significantly with reduced equipment and increased power density. Deflection, vibration, or thermal cycling of circuit boards can impair their performance and reliability, resulting in potential field failures.
Traditional ceramic thick-film resistors are inexpensive and widely available, but their substrates are brittle and have low reliability in harsh environments. Stainless steel provides a rigid but slightly compliant substrate that absorbs mechanical stresses caused by circuit board bending, vibration, and handling during assembly, reducing the risk of cracking or delamination.
Steel based thick film (TFOS) resistors offer a mechanically robust and thermally efficient alternative to demanding high stress designs in which even a small amount of circuit board bending, vibration or thermal cycling can cause degradation of ceramic resistors.g.
Bourns introduced the first TFOS resistor TFOS30-1-150T in mid-2025 (Figure 1). Elements manufactured with TFOS have excellent thermal conductivity, high power density and strong mechanical durability, making them suitable for demanding applications. Many power or high energy circuits have limitations on the ability of the element to absorb, dissipate, and withstand energy impulses to avoid cracking, drift, or premature failure.
Figure 1: Bourns' TFOS30-1-150T uses a stainless steel substrate that is more reliable than thick film ceramic resistors. Picture courtesy of Bourns)
Steel substrates provide excellent heat dissipation for improved power dissipation and higher power density in smaller packages. Apply a high integrity dielectric layer over the cleaned stainless steel substrate to prevent conduction of electrical energy through the steel.
By transferring power handling and robustness into resistors, designers can reduce radiator usage, reduce part count, and improve field reliability. In short, according to Bourns, designers can achieve higher performance in smaller spaces without additional cooling hardware.
During manufacturing of TFOS components, thick film conductor and resistor patterns are drawn on the dielectric layer using a screen printing process. Each time after passing, the material is burned and solidified in a high temperature furnace to ensure adhesion and a robust conductive and resistive path. Finally, the conductors and resistors are covered with a protective glaze to provide mechanical protection, environmental resistance and electrical insulation from the substrate.
High Level Design Considerations
TFOS resistors offer high power and pulse processing capabilities in a compact form to maintain performance advantages under demanding conditions. This allows engineers to meet stringent reliability and thermal management requirements without compromising overall dimensions.
TFOS30-1-150T is compliant with the AEC-Q200 standard and is suitable for automotive applications such as battery storage systems, motor drives, inverters, fuel cell vehicle sensor panels, and other applications where high power, thermal management, and mechanical robustness are critical.
Bourns notes in an application note [1] on the use of this element in fuel cell stack sensor boards that TFOS is well suited for this application because it handles high power densities. It can adapt to the precharge and discharge circuit of fuel cell vehicles, and ensure efficient energy management even under variable frequency operation. Its low inductance and tight tolerances ensure accurate measurement of voltage, current and temperature in the fuel cell stack.
TFOS30-1-150T is available in 4.000 "L x 2.756" W (101.60 mm x 70.00 mm) custom termination options, including pads, push-on connectors, suspension leads, and termination cables. Bourns notes that this flat, solid steel base plate can be fabricated in a variety of shapes and sizes, up to 406 mm x 406 mm, to fit a variety of custom layouts or mounted directly on a radiating surface. Designers can also specify additional ohmic values, resistance tolerances, and integration of multiple resistors.
It has a resistance of 150 Ohms and a tolerance of ± 10% and is optimized for accuracy. It is rated at 260 W when mounted on a radiator and up to 900 W when cooled by a fan, making it ideal for applications requiring significant heat dissipation. The TFOS30-1-150T has an extended operating temperature range of - 55 ° C to+125 ° C and, according to Bourns, can withstand extremely high element temperatures up to 350 ° C.