Tuesday 10 April 2012

Chip Resistors


Chip resistors are passive resistors with a form factor of an integrated circuit (IC) chip. Typically, they are manufactured using thin-film technology. There are two basic configurations for chip resistors: single resistor and resistor chip array. Single chip resistors are standard, passive resistors with a single resistance value. Resistor chip arrays contain several resistors in a single package. For both configurations, performance specifications include resistance range, tolerance, temperature coefficient of resistance (TCR), power rating, operating direct current (DC) voltage, current rating and operating resistors. For resistor chip arrays, the number of resistors in the package is also an important parameter to consider. 
Chip resistors are made from many different materials. Carbon-composition resistors consist of powdered carbon, an insulating material, and a resin binder. Cermet resistors are made of ceramic and metallic materials. Carbon film, ceramic composition, metal alloy, metal foil, tantalum, and wirewound chip resistors are also commonly available. Metal-film resistors are produced by depositing a resistive element onto a high-grade, ceramic rod. They are similar, but not identical to metal-oxide resistors. Thick-film chip resistors are made by stenciling a resistive metallic paste or ink onto a base in a process similar to silk screening. By contrast, think-film chip resistors are formed by vapor-deposition and then trimmed to a specific value. 
Chip resistors differ in terms of categories, applications, features and packing methods. Categories include fusible, current sensing, high current, high frequency, high voltage, power, precision, surge and telecom chip resistors. Chip resistors for automotive, aerospace, medical or military applications are also available. In terms of features, some chip resistors feature a heat sink or electrically-isolated case. Others are air-cooled, water-cooled, or non-inductive. Chip resistors with a fireproof case or non-flame coating are also available. Devices with an electrically-isolated case or NEMA enclosure are also available. Packing methods for chip resistors include tape reel, rail, bulk pack, tray, and shipping or stick magazine. 
Organizations such as Underwriters Laboratories (UL), the International Electrotechnical Commission, and the Canadian Standards Organization (CSA) maintain standards for a variety of passive resistors. Chip resistors that are destined for sale in European Union (EU) nations must meet the Restriction of Hazardous Substances (RoHS), End-of-Life Vehicles (ELV), and Waste Electrical and Electronics Equipment (WEEE) directives. RoHS compliant chip resistors contain only minimal levels of lead, cadmium, hexavalent chromium, polybrominated biphenyl and polybrominated diphenyl ether. ELV compliant devices contain only minimal amounts of lead, cadmium and mercury.





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