Resistors For Harsh Environments
This product highlight will discuss Stackpole's resistors designed for various types of harsh environments. Harsh environments might include high humidity, high sulfur, or simply high temperature. Applications in these harsh environments typically will not be able to use standard resistors and will provide an opportunity to design in a custom or unique solution and increase our value to the customer as a resistive product solutions provider. This product highlight will briefly discuss each of the three harsh environments above and will discuss the surface mount and thru-hole series from Stackpole that may provide a solution.
High Moisture Environments
High humidity environments pose a significant threat to metal film SMD and thru-hole resistors. Our most popular thru-hole products, the RNF / RNMF metal films, the CF / CFM carbon films, and the RSF / RSMF metal oxides may all be susceptible to failing open circuit in the presence of moisture under low power. Even though the passivation or outer coating on these resistors acts as a protective barrier from the elements, the high speed manufacturing environment may still produce resistors with pinholes, voids, or other abnormalities in their coating. These abnormalities may allow moisture to reach the film element and, in the presence of low electrical potential, may cause corrosion or dissolution of the film element. The end result is the resistance value increases and eventually opens. For axial leaded resistor requirements up to 3 watts and for resistance values above 1K ohms, the MG / MGM series is a thick film metal glaze technology that is impervious to moisture. Since corrosion of metal films typically happens only under low power loading, it is the higher resistance values that are most susceptible. However, the MG / MGM series is significantly more expensive than the general purpose metal film and carbon film resistors they usually replace. The HDM series is a moisture resistant carbon film resistor which addresses these concerns for axial leaded resistor requirements for ¼ watt and ½ watt sizes in tolerances down to 1%. Because the HDM uses a carbon film technology, it is less expensive than the equivalent metal glaze thick film products available currently.
- MG / MGM is available in sizes from ¼ watt up to mini 3 watt, in resistance values from 1K up to 200M, and in tolerances as low as 1%. Pricing ranges from: $0.055 to $0.37 each.
- HDM is available in ¼ and ½ watt sizes, in resistance values from 1 ohm to 2.2 Meg, and in tolerances down to 1%. Pricing ranges from $0.012 to $0.025 each.
High moisture environments can also cause thin film based chip resistors to corrode or dissolve. Our RNCF precision nichrome thin film resistors are the main series of concern here. Stackpole's solution is the RNCS passivated nichrome thin film resistors. The RNCS utilizes a sub-layer of silicon oxide or silicon nitride to provide a moisture impervious barrier under the final epoxy passivation overcoat. 3000 hour biased humidity testing shows performance that is equal to or better than tantalum nitride based resistors at a fraction of the cost. The RNCS0603 and 1206 are also AEC-Q200 qualified.
- RNCS is available in sizes from 0402 to 2512, in tolerances down to 0.1%, TCR's as low as 15 ppm, and in resistance values from 10 ohms to 1 Meg. Pricing ranges from $0.016 to $0.23 each.
Sulfur Rich Environments
High concentrations of sulfur can react with the silver in the inner terminations of some types of chip resistors forming silver sulfide which is not conductive. The result of this microscopic activity is gradual positive resistance shifts eventually leading to the resistor opening up completely. Sulfur is common in automotive applications, industrial machinery, agricultural equipment and construction equipment. However sulfur can be found in any environment where there are oils or other lubricants used, gaskets, hoses, and other rubber based products as well as industrial environments and gases from coal fired power plants or heavy manufacturing. One method of dealing with this issue is to reduce the amount of silver in the inner termination, as with Stackpole's RMCS. The reduction of silver is offset by an increase in palladium, which is unfortunately more expensive. In addition, since silver is still present there is still the possibility of failure due to sulfur contamination. A more reliable long term approach would be to eliminate silver in the terminations. Stackpole's RMCG has a gold termination that is impervious to sulfur, but significantly more expensive than the other anti-sulfur resistive products. The RNCP is a thin film based high power chip resistor series which also has no silver present in the inner termination making it impervious to contamination due to sulfur. The RNCP is designed for high volume applications and is much lower cost than most other thin film resistors which are usually only for precision applications.
- RMCS thick film chip resistors are available in sizes from 0201 through 2512, in tolerances as low as 0.5%, and in resistance values from 1 ohm to 10 Meg. Pricing ranges from $0.0055 to $0.075 each.
- RMCG gold termination chip resistors are available in sizes from 0402 through 2512, in tolerances down to 1%, and resistance values from 1 ohm to 10 Meg. Pricing ranges from $0.019 to $0.20 each.
- RNCP high power anti-sulfur thin film chip resistors are available in sizes from 0402 through 1206, in tolerances down to 1%, and resistance values from 1 ohm to 100 Kohms. Pricing ranges from $0.0017 to $0.01 each.
High Temperature Environments
High temperatures (over 155°C) can damage film resistors, so most are unsuitable for these environments. Automotive, industrial, aerospace, and heavy equipment are typical applications where high temperatures can be encountered. Wirewound resistors are an outstanding choice for customers with high temperature requirements because they typically have operating temperatures up to 275°C or 350°C. Wirewound resistors come in a wide variety of thru-hole packages including conformal coated, ceramic housed, ceramic housed vertical mount, and aluminum housed. The last three are fireproof products. Wirewounds can also be offered in surface mount packages from 1 watt up to 4 watts. Individual series capabilities vary widely. Pricing also varies widely depending on the series of choice.
The RSF / RSMF is a unique metal oxide film resistor in the Stackpole lineup because it offers an operating temperature range up to 235°C for the larger sizes and 200°C for the ½ watt and 1 watt sizes. This makes it a good alternative to wirewounds when low inductance is required and will usually be less expensive as well.
- RSF / RSMF is available in mini ½ watt through 5 watt sizes, in tolerances down to 1% and in resistance values from 0.1 ohms up to 1 Meg. Pricing ranges from $0.02 to $0.415 each.
For current sense resistors, the CSS / CSSH series of metal plate ultra precision current sense chip resistors offer operation up to 225°C, and can be used up to 275°C with some precautions. Current sense resistors because they are used in the power supply portion of the circuit are regularly subjected to high temperatures. They will also experience significant self-heating since they are typically used at or near full power. This higher operating temperature greatly expands the possible applications that the CSS / CSSH can serve. The CSS / CSSH series is also AEC-Q200 qualified for all sizes except CSSH2512.
- CSS / CSSH is available in sizes from 0603 (0.33W) up to 2728 (4W), in tolerances as low as 0.5%, TCR down to 15 ppm, and resistance values from 0.25 milliohms up to 120 milliohms. Pricing varies from $0.175 to $0.50 each.
For more information about Stackpole products, contact Stackpole Electronics, Inc. at
Stackpole Electronics, Inc.
2700 Wycliff Road Suite 410,
Raleigh NC 27607
Stackpole Electronics Inc. is a leading global manufacturer of resistors supplying to the worlds largest OEMs, contract manufacturers and distributors. Headquartered in Raleigh, N.C., the privately held company began manufacturing in 1928 as part of Stackpole Carbon Company in St. Mary's, Pennsylvania. Now part of the Akahane Stackpole Manufacturing Group (ASMG), Stackpole has manufacturing facilities in Japan, Taiwan, China and Mexico; warehousing facilities in El Paso, Shenzhen and Japan; and international sales offices in Tokyo, Taipei, London, Hong Kong and Shenzhen.