thick film resistor
Thick film resistors consist of a solid carrier material onto which the resistor material is applied in a thickness of 0.01 mm. As a rule, a thin ceramic disc or foil made of aluminum oxide is used as the substrate. In the additive process, the resistance material is applied as a paste to this substrate. The thick-film technology works with pastes made of metal oxide or carbon-based material, which is sintered with the carrier substrate at a temperature of over 800 °C. The thick-film resistors are then cut from the substrate. The thick-film resistors are cut by laser. They can be covered with a thin glass layer for protection.
The outer ends of the thick film resistors are surrounded with a conductive material that wraps around the top and bottom of the ends of the resistor. By having a conductive area on top of and also underneath the resistor, they can be soldered to circuit boards with the surface facing up and also down. In cases where the frequency is very critical or where the shortest possible running times are important, the thick-film resistor is soldered to the circuit board with the surface facing downwards.
Since the manufacturing process for thick film resistors is simpler than that for thin film resistors and, in addition, the carrier and resistor materials are cheaper, thick film resistors can be produced relatively inexpensively.
Thick film resistors are manufactured in a wide variety of resistor values and sizes as SMD devices or as part of a hybrid resistor network. Resistance ranges are much higher than thin film resistors, ranging from 20 ohms/cm2 to 500 kilo-ohms/cm2 . In terms of resistance values, thick film resistors are available with resistance values in the double- digit teraohm range. The size of thick film resistors is specified in a dimensional code and determines their rated power. Thick film resistors are also realized as power resist ors.
The size code corresponds to dimensions in milliinches (mils). For example, the dimensional code 0402 represents a size of 40 mils x 20 mils. Important characteristics of thick-film resistors include temperature coefficient, which for precision thick-film resistors is about 50 ppm/°C, stability of resistance value after 2,000 hours is 0.5%, and electrostatic discharge( ESD) resistance is 2,000 V. A disadvantage is the high inherent noise caused by the granular structure of the thick-film technology.