A fixed composition resistor normally fails in an open configuration when overheated or too demanding due to shocks or vibrations. Excessive humidity can cause an increase in resistance. A resistive composition resistor can wear after extensive use and worn particles can cause high resistance short circuits.
Resistors may not work open or short, along with changing their value under environmental conditions and outside performance limits. Examples of resistance failures include:
Productive defects causing intermittent problems. For example, improper caps on wires or metal resistors can weaken and lose contact, and resistor-to-head resistances can change resistor values.
Surface mounting resistors delaminate when similar materials, such as between the ceramic substrate and the resistive layer, are bonded.
Nihrom thin film resistances in integrated circuits attacked by passive glass phosphor, corrosion and resistance increase.
SMD resistors with silver metallisation of contacts that suffer an open circuit fault in a sulfur-rich environment due to the accumulation of silver sulfides.
Copper dendrites that grow from copper (II) oxide present in some materials (such as the layer that facilitates the adhesion of metallization to a ceramic substrate) and rack precision bridge.
Potentiometers and trimmers:
Potentiometers and trimerizers are three-terminal electromechanical parts that contain a resistance path with an adjustable wiper contact. Together with the normal resistance failure modes, mechanical wiper and resistive layer wear, corrosion, surface contamination and mechanical deformations can lead to intermittent wiper resistance changes, which is a problem with the audio amplifiers.
Many types are not perfectly sealed, with contaminants and moisture coming into that part; a particularly common contaminant is the soldering flux. Mechanical deformations (such as damaged wiper contact) may occur by overturning the casing during welding or mechanical stress during assembly. Excessive stress on the conductors may cause substrate cracking and open failure when the crack penetrates the resistive path.