Thick film resistor failure is never caused by a failure on the resistive element but is mostly because of exterior environmental things such as mechanical and electrical stresses and handling difficulties. Failures might be possibly classed for a degradation of general performance or finish failure (usually being an open up rather then a brief circuit).
Six popular will cause of thick film resistor failure are:
Thermal troubles
Mechanical pressure
Continual overload
Surge
Environmental - metal migration
ESD
MECHANICAL FAILURES
Besides managing hurt leading to substrate cracks and chips most mechanical hurt is brought on by possibly vibration or inappropriate mounting on the device. Micro cracking in the resistor content attributable to vibration or compression / extension from the resistor as a result of inappropriate mounting can lead to change while in the resistance benefit, harm to the resistive element or ingredient failure. In all instances the potential risk of failure is elevated by existence of one or more of your stresses mentioned down below.
ENVIRONMENTAL Elements
Whilst a thick movie resistor is often coated to guard it from dampness and intense chemical factors environmental factors such as dampness and contamination even now demand cautious thing to consider. Both equally may cause steel migration among the terminals of the resistor bringing about opportunity small circuit or maybe a improve in resistance benefit.
THERMAL Challenges
Most mechanical failure modes of thick movie resistors are propagated by warmth. It truly is for that reason crucial to be aware of the heat dissipation Homes of your resistor and substrate material. A minimal ability resistor dissipates heat by using conduction through its ingredient qualified prospects or connections, whilst a significant electric power resistor dissipates heat by way of radiation.
When existing passes via a resistor it generates heat and the differential thermal expansions of different material Employed in the resistor manufacturing process induces stresses during the resistor. Temperature Coefficient of Resistance (TCR) is the greatest regarded parameter accustomed to specify a thick movie resistor stability, and defines the resistive ingredient's sensitivity to temperature modify. Electricity Coefficient of Resistance (PCR) quantifies the resistance alter due to self-heating when ability is used and is especially essential for resistors Employed in electrical power programs.
OVERLOAD Disorders
A constant above-load of a resistor product degrades the insulation resistance and improvements the resistor parameters after a while. Voltage anxiety might cause conduction from Usually non-conductive components within the resistor movie resulting in deterioration and occasionally failure because of sizzling spots. It is actually for that reason important to observe the resistor utmost specified voltage.
SURGE Situations
The true secret ingredient in pinpointing the surge survivability of a thick film resistor may be the mass of the resistor factor, that is immediately proportional to its thickness multiplied by its area spot. The geometry of a resistor also affects its surge face up to capacity. A larger area region leads to an increased film mass, and finally an enhanced surge effectiveness. The greater surface area spot permits much more warmth dissipation which is crucial in ability resistor applications.
The final issue contributing factor to a resistor surge ability is how the part is resistor trimmed to establish the final resistance price. The strategy employed for trimming can build weak places that induce failure less than surge conditions.
ESD
Problems by using ESD is usually a latent defect that may be tough to detect. The resistor may be partly degraded by ESD but proceed to execute electronic components its meant function. Even so, the chances of untimely or catastrophic failure on the resistor gadget are improved, notably if the system is subjected to a number of from the stresses mentioned higher than.