With 20 times more operating life than standard film resistors, these components combat sulfur pollution to maximize reliability.
TTI.inc has submitted this post. Written by Bourns.
Sulfur pollution can adversely affect productivity in industrial environments, and is known to be influenced by several critical factors that include areas where oils, lubricants or fossil fuels are utilized. Sulfur is also an issue when affected materials are in the presence of rubber seals, gaskets, grommets or molded coatings, which are frequently part of the factory setting.
Sulfur pollution can be exacerbated in air-polluted industrial areas or locations with biological or volcanic gases. The applications particularly impacted by sulfur pollution encompass industrial motor controls, pump controls, welding equipment and the like. That is why it is highly recommended to source sulfur resistant components for most industrial designs in order to maximize reliability, increase equipment efficiency and extend application longevity.
Construction of film resistors
The film surface mount chip resistor is practically a standard in the electronics industry, and is widely used today due to its favorable economics and manufacturability. The basic structure of a chip resistor, shown in the image below, is composed of a ceramic substrate with layered terminations on each end of the ceramic chip.
The layers consist of internal terminations that typically comprise a printed silver (Ag) or silver palladium (AgPd) material. The resistive element or ink is then screened onto the ceramic chip and connects both sides of the Ag/AgPd terminals, creating the resistive circuit. An epoxy passivation layer is then applied over the resistive element, which partially covers the Ag/AgPd terminals, leaving a portion of the terminal exposed for final construction of the terminal outer layer application process. A protective nickel (Ni) covering is then sputtered onto the Ag/AgPd terminals to prevent any type of contamination. Finally, a matte tin (Sn) solder layer is applied to the terminals to complete the construction.
Comparing standard film resistors to sulfur-resistant film resistors
In standard film resistors, the internal Ag/AgPd terminal is only protected by the epoxy passivation layer. This makes it susceptible to the ingress of sulfur-based gasses. These gasses can diffuse and attack the silver in the Ag/AgPd internal terminal, which, depending on factors such as temperature, humidity and even air flow in the environment, begin the corrosion process and the formation of silver sulfide. Over time, the silver sulfide can crack the ceramic of the resistor package, causing the resistor to form an open circuit. Another possible consequence is that once the non-conductive silver sulfide has formed along the length of the terminal, it gradually increases with resistance as the conductive path is reduced, eventually resulting in another open circuit condition and ultimately, failure of the resistor.
Sulfur-resistant resistors can be used in the same application areas as standard film resistors; designers will see no difference. Their benefits in industrial systems, however, can be enormous in these mission critical applications, especially harsh industrial environments or certain geographic locations where conditions may not be optimal for system operation.
Advantages of sulfur-resistant film resistors
Bourns offers an advanced line of sulfur-resistant film resistors with features that deliver multiple design benefits. For example, their plating termination layers have a special structure in the area between the protective layers and the terminations in order to cover the silver (Ag) terminals to protect it against sulfurous gases.
Employing sulfur-resistant film resistors is particularly important in data-critical applications, and including them in an industrial design helps ensure the reliable transfer of data. Data has become ever more vital in the digital age where the need is paramount for uncorrupted data transmission and reception at the binary level in a wide range of applications, from a simple handheld device to an industrial supercomputer.
Although soft errors or repairable bits of data can be recovered through redundant systems and complex algorithms or error correction systems, the hard failure of any input or output interface port can still trigger a system failure. These hard failures can be caused by corrosion in a system such as a server farm exposed to harsh environments on a factory floor. It can be especially harmful in data systems located in regions of the world that have higher percentages of potentially corrosive gasses or biological and volcanic gasses, specifically in environments where known higher sulfur contamination exists.
In addition to gaseous-born states, sulfur can also be found in connectors, oils, lubricants, gaskets, rubber sealings, molded coatings, etc., which can lead to the formation of silver sulfide that corrodes the silver terminals in sensitive electronic components like a film resistor. There are now even recommendations on corrosivity levels for IT centers so as to try to eliminate the destructive effects corrosion can have in this environment.
With the use of Bourns sulfur-resistant film resistors, this corrosion-related type of hard failure can be substantially reduced or eliminated, resulting in improved system reliability, performance, robustness and reduction of downtime. This is one of the most important operating factors in industrial systems where subsystems such as memory modules are used heavily in server farms or in associated data/storage centers.
Performance test results
In order to test the performance of standard film resistor compared to a sulfur-resistant film resistor, Bourns tested the parts in a 2,400 cm3 glass desiccator vessel with ~40 – 60 grams of powdered sulfur. The vessel was heated to an elevated temperature of 105 ËšC to accelerate the effects of the sulfurization. The resistors were then measured at regular intervals to verify resistance. Under these test conditions, the results of the standard film resistor versus the sulfur-resistant film resistor showed the sulfur-resistant device had more than 20 times greater operating life than the standard device.
In the world of industrial and telecommunication electronics, this test result indicates that sulfur-resistant film resistors contribute to improving reliability. Increasing reliability and reducing field failures related to standard film resistor failure in sulfur contaminated environments also results in boosting both industrial productivity and operational efficiencies.
Effective solution for protection against downtime/field failures
Due to the rise in using industrial and telecommunication electronic equipment in a wide variety of environments, the need for specifying sulfur-resistant film resistors is becoming increasingly necessary. Reliability in these market segments is critical and failures can be extremely costly to the manufacturers, users and service providers.
Bourns’ extensive components design expertise allows the company to continually advance its sulfur-resistant film resistor components. Bourns’ full line of thin and thick film resistors are designed to meet the growing need for more ruggedized components that can operate reliably in certain harsh environments. For engineers, they are excellent solutions to help protect against system downtime and field failures safeguarding the industrial operators’ return on investment.
Visit Bourns Industrial Strength Surge Protection from TTI, Inc. to learn more.
