What makes a resistor fail

Surges are large voltages or currents instantaneously applied to circuits. Well-known examples include lightning and static electricity. Surge voltage applied to a resistor may affect the resistance characteristics due to excessive electrical stress or result in damage worst-case scenario.

Increasing the chip size will lengthen the distance between electrodes and provide greater surge resistance, but requires a larger mounting area. ROHM's anti-surge chip resistors feature improved the power handling characteristics and a revised element shape to achieve higher rated power than conventional types.

Chip resistors are mounted on boards using solder, enabling use under a variety of environments. A difference in the degree of contraction thermal expansion coefficient due to temperature between the alumina substrate used as a base in thick-film resistors and FR-4 glass epoxy resin typically adopted in mounting boards.

This difference can result in excessive stress during repeated temperature cycling, leading to cracking at the solder fillet at the junction between the materials. Because of stress generated due to chip contraction, a longer distance between electrodes or larger chip size is considered disadvantageous.

However, there is often a tradeoff relationship between electrical characteristics such as chip size, rated power, and maximum element voltage. Some Users Seek to improve junction reliability in order to prevent solder cracks without compromising specifications such as rated power, or would like to increase rated power by increasing chip size without reducing junction reliability.

Adopting a wide terminal structure lengthens the heat dissipation pathway, improving rated power. Utilizing the wide-terminal LTR series will make it possible to prevent solder cracks and increase the rated power. In addition, high surge resistance is achieved, providing improved reliability. See Damage to thick-film resistors due to surges. Wire-would resistors are constructed by winding a resistive wire around an insulated form and covering the end product with an insulating material.

Film - Film resistors are made by forming a thin layer of resistive material onto an insulated form. The most commonly used film resistors can be divided into types according to the materials used: carbon-film, metal-alloy and metal-oxide.

One popular metal film resistor is manufactured by applying a metal film onto a cylinder of ceramic. One of the commonly used materials for these resistors is 'cermet'. Cermet is a combination of ceramic and metal materials, hence the name 'cermet.

One of the latest film resistor technologies is the manufacture of thick and thin film resistors, which are used in microelectronic and hybrid circuits. Thick film resistors are formed by stenciling a resistive metallic paste or ink onto a base in much the same way that silk screening is done. Usually the resistive materials are considered proprietary. Thin film resistors are formed by vapor deposition of a thin layer of resistive material onto a base. Thick and thin film resistors are normally trimmed to a specific value by etching away resistive material using lasers, sandblasting, etc.

Most composition and wire-would fixed resistors are packaged in a cylindrical form with axial leads. Thick and thin film resistors are manufactured in a variety of shapes and sizes. Film resistor networks are packaged in plastic dual-in-line packages DIP , single-in-line packages SIP , flatpack packages and round metal packages identical to those in which integrated circuits are packaged.

Individual resistors may be packaged in chip and pellet form. A chip, as used in microelectronics, is any small usually square or oblong piece of material that contains a circuit or component. Thick film resistors are commonly used in hybrid circuits where they are deposited directly onto the circuit substrate.

A substrate is a tiny platform on which circuitry is deposited. Thick and thin film resistors have found many applications in the development of microelectronics because they can be made smaller than other comparable value resistor types. Film resistors are often used in critical positions in circuitry. Power Resistors - Power resistors are required to carry large quantities of current and subsequently dissipate a lot of heat.

Consequently they are usually larger than those that are designed to carry smaller current quantities. Power resistors are usually encapsulated in materials that aid in the dissipation of heat and are usually designed so they can be mounted to a heatsink or equipment chassis to facilitate heat removal by conduction.

Common power resistors may be composition, wire-wound, or film resistors. Variable Resistors - A variable resistor is commonly referred to as a 'pot'; meaning a potentiometer.

A potentiometer contains an element of continuous resistive material with a sliding contact that traverses the element in a circular or straight line, depending on the potentiometer style.

It is normally adjusted by a shaft connected to a dial or thumbscrew, or by a screw-driver or adjustment tool.

Variable resistors may be wire-wound, composition or film resistors. Small, precision, adjustable resistors are called 'trim-pots' and are used for fine adjustments in low current applications. Variable resistors that are constructed to carry large values of current or power are called 'rheostats' and are commonly used for adjusting motor speeds and oven and heater temperatures.

Resistors usually have markings indicating value, tolerance and sometimes composition and reliability rating. Reliability rating is given as a failure-rate in percentage failure per hours of operation. These values may be written on the resistors or may be provided in color code as shown on the carbon composition resistor in Figure 1.

Figure The color code is usually provided by four or five color bands represented by the variation in color shades in the black and white photo around the body of the resistor. Add these two values of resistances. This is the approximate value of the burnt resistor. Yes, you can use it. It will give you an ability to source in more current.

To avoid the size of the resistor getting large due to high wattage, you can use SMD resistor. This will not only save space on your PCB but your PCB will look descent as compared to the through hole resistor of same power rating. It is common practice to use a Zero-Ohm chip resistor as a jumper because it is a component that can be handled by the same machine that places all of the other similarly-sized components.

Manufacturers typically give a maximum voltage for a particular resistor range, such as V for a mW resistor. A resistor is taken as a passive element since it can not deliver any energy to a circuit. Instead resistors can only receive energy which they can dissipate as heat as long as current flows through it. An ammeter is always connected in series with the circuit component you are measuring. A voltmeter is used to measure potential energy difference, voltage in volts or millivolts across a circuit component.

A voltmeter is always connected in parallel with the circuit component you are measuring. An ammeter is placed in series in the branch of the circuit being measured, so that its resistance adds to that branch. An ammeter is connected in series with the circuit to be measured. The ideal ammeter will have zero resistance so as not to disturb the circuit. Answer: To measure the total current, the ammeter must be placed at position 1, as all the current in the circuit must pass through this wire, and ammeters are always connected in series.

That being said, there are some resistor constructions, like the bifilar wire wound used for low-capacitance and low-inductance special resistors that could short out internally. In high-energy circuits, it's important to either use a fuse in line, or specify a fusible resistor, which is tested to always become open under fault currents. About permanent changes in resistance: these are more likely in older-style carbon composition resistors.

They are made of a mix dried slurry of clay and carbon particles. If heated near their melting point, some of the carbon atoms can migrate and change the bulk resistivity of the mix. The metal film resistors that are overwhelmingly used now don't suffer this effect but they can ignite if hot enough. The following users thanked this post: kalel. Zero Super Contributor Posts: Country: Generally speaking resistors fail open circuit, but a high value resistor, with a voltage across it exceeding its maximum voltage rating, can fail short by arcing over, which can drastically reduce the resistance value.

Quote from: Hero on July 28, , pm. Tomorokoshi Super Contributor Posts: Country:.