Thick film resistor failure isn't attributable to a failure of your resistive element but is normally due to exterior environmental elements for instance mechanical and electrical stresses and managing challenges. Failures is usually both classed for a degradation of performance or entire failure (typically being an open rather than a short circuit).
Six frequent leads to of thick movie resistor failure are:
Thermal concerns
Mechanical anxiety
Frequent overload
Surge
Environmental - metal migration
ESD
MECHANICAL FAILURES
Besides handling damage resulting in substrate cracks and chips most mechanical damage is attributable to possibly vibration or inappropriate mounting with the device. Micro cracking on the resistor product a result of vibration or compression / extension in the resistor as a consequence of inappropriate mounting can result in improve from the resistance worth, harm to the resistive component or element failure. In all conditions the chance of failure is greater by presence of one or more of the stresses mentioned beneath.
ENVIRONMENTAL Variables
Even though a thick movie resistor is usually coated to guard it from humidity and intense chemical aspects environmental things like moisture and contamination nevertheless demand cautious thing to consider. Both equally may cause metal migration among the terminals from the resistor leading to opportunity small circuit or simply a change in resistance value.
THERMAL ISSUES
Most mechanical failure modes of thick film resistors are propagated by warmth. It truly is therefore vital to understand the warmth dissipation properties on the resistor and substrate product. A reduced power resistor dissipates heat by using conduction through its ingredient prospects or connections, though a high power resistor dissipates heat by means of radiation.
When current passes by way of a resistor it generates warmth plus the differential thermal expansions of the several substance Utilized in the resistor production procedure induces stresses inside the resistor. Temperature Coefficient of Resistance (TCR) is the best identified parameter accustomed to specify a thick film resistor balance, and defines the resistive factor's sensitivity to temperature improve. Electricity Coefficient of Resistance (PCR) quantifies the resistance modify because of self-heating when electrical power is applied and is particularly important for resistors used in energy apps.
OVERLOAD Ailments
A steady about-load of a resistor unit degrades transistor the insulation resistance and modifications the resistor parameters over time. Voltage worry could cause conduction from Usually non-conductive resources while in the resistor movie resulting in deterioration and occasionally failure due to sizzling places. It is hence crucial that you notice the resistor utmost specified voltage.
SURGE CONDITIONS
The important thing aspect in deciding the surge survivability of a thick movie resistor may be the mass of the resistor element, and that is specifically proportional to its thickness multiplied by its surface area space. The geometry of the resistor also affects its surge stand up to functionality. A bigger floor space brings about a greater film mass, and in the end an enhanced surge performance. The increased floor space permits much more warmth dissipation which is very important in energy resistor purposes.
The final issue contributing issue to a resistor surge functionality is how the element is resistor trimmed to establish the final resistance price. The method useful for trimming can produce weak places that induce failure underneath surge situations.
ESD
Injury through ESD is actually a latent defect which might be tricky to detect. The resistor could be partly degraded by ESD but carry on to carry out its meant purpose. Having said that, the likelihood of untimely or catastrophic failure of your resistor product are greater, notably In the event the gadget is exposed to one or more from the stresses outlined earlier mentioned.