Thick film resistor failure isn't caused by a failure on the resistive aspect but is normally due to external environmental factors including mechanical and electrical stresses and managing challenges. Failures is often possibly classed as being a degradation of overall performance or full failure (usually being an open up rather than a brief circuit).
6 widespread causes of thick movie resistor failure are:
Thermal troubles
Mechanical worry
Constant overload
Surge
Environmental - steel migration
ESD
MECHANICAL FAILURES
Aside from managing injury bringing about substrate cracks and chips most mechanical problems is caused by both vibration or inappropriate mounting of the device. Micro cracking in the resistor product due to vibration or compression / extension with the resistor as a consequence of inappropriate mounting can result in modify during the resistance benefit, damage to the resistive element or ingredient failure. In all cases the potential risk of failure is enhanced by existence of a number of from the stresses listed beneath.
ENVIRONMENTAL Components
Even though a thick film resistor is often coated to protect it from moisture and aggressive chemical factors environmental elements like dampness and contamination nonetheless call for cautious thing to consider. Both of those might cause metallic migration among the terminals of your resistor leading to opportunity limited circuit or possibly a alter in resistance benefit.
THERMAL Difficulties
Most mechanical failure modes of thick film resistors are propagated by heat. It really is hence significant to be aware of the warmth dissipation Homes in the resistor and substrate materials. A reduced electric power resistor dissipates heat through conduction by means of its component sales opportunities or connections, although a substantial electric power resistor dissipates warmth by way of radiation.
When latest passes by way of a resistor it generates heat and the differential resistors thermal expansions of the various substance Employed in the resistor production approach induces stresses from the resistor. Temperature Coefficient of Resistance (TCR) is the greatest regarded parameter utilized to specify a thick film resistor steadiness, and defines the resistive element's sensitivity to temperature improve. Electric power Coefficient of Resistance (PCR) quantifies the resistance improve as a result of self-heating when energy is applied and is especially critical for resistors Employed in ability applications.
OVERLOAD Situations
A ongoing over-load of the resistor product degrades the insulation resistance and variations the resistor parameters over time. Voltage worry could cause conduction from Usually non-conductive products from the resistor film bringing about deterioration and occasionally failure as a consequence of scorching spots. It really is therefore important to observe the resistor optimum specified voltage.
SURGE Ailments
The main element ingredient in analyzing the surge survivability of the thick movie resistor is the mass of a resistor factor, and that is directly proportional to its thickness multiplied by its floor place. The geometry of a resistor also impacts its surge face up to capacity. A larger floor space ends in a greater movie mass, and ultimately an improved surge effectiveness. The elevated floor space will allow extra heat dissipation which is crucial in ability resistor apps.
The ultimate element contributing element to a resistor surge capability is how the element is resistor trimmed to determine the final resistance price. The method used for trimming can create weak places that bring about failure less than surge situations.
ESD
Injury through ESD can be a latent defect which can be difficult to detect. The resistor can be partly degraded by ESD but keep on to conduct its intended function. However, the chances of premature or catastrophic failure on the resistor unit are greater, especially Should the gadget is subjected to one or more with the stresses shown over.