Thick film resistor failure is never because of a failure with the resistive component but is normally resulting from exterior environmental things such as mechanical and electrical stresses and handling issues. Failures is often both classed as a degradation of performance or finish failure (ordinarily as an open as opposed to a short circuit).
Six widespread triggers of thick movie resistor failure are:
Thermal difficulties
Mechanical worry
Consistent overload
Surge
Environmental - steel migration
ESD
MECHANICAL FAILURES
Other than handling hurt bringing about substrate cracks and chips most mechanical damage is caused by possibly vibration or inappropriate mounting with the product. Micro cracking of your resistor materials because of vibration or compression / extension of your resistor resulting from inappropriate mounting may result in transform within the resistance value, damage to the resistive factor or part failure. In all instances the chance of failure is improved by presence of a number of of the stresses detailed below.
ENVIRONMENTAL Aspects
Even though a thick movie resistor is often coated to guard it from moisture and aggressive chemical features environmental components for instance humidity and contamination still demand thorough thought. Both could cause steel migration between the terminals in the resistor resulting in opportunity short circuit or possibly a alter in resistance price.
THERMAL ISSUES
Most mechanical failure modes of thick film resistors are propagated by heat. It is therefore vital to understand the heat dissipation Attributes in the resistor and substrate substance. A reduced electrical power resistor dissipates warmth through conduction as a result of its part potential customers or connections, even though a high electrical power resistor dissipates warmth through radiation.
When recent passes by way of a resistor it generates heat along with the differential thermal expansions of the several product Utilized in the resistor manufacturing course of action induces stresses in the resistor. Temperature Coefficient of Resistance (TCR) is the best recognized parameter utilized to specify a thick film resistor security, and defines the resistive factor's sensitivity to temperature modify. Energy Coefficient of Resistance (PCR) quantifies the resistance transform because of self-heating when electrical power is applied and is especially critical for resistors Employed in ability programs.
OVERLOAD Situations
A ongoing over-load of a resistor product degrades the insulation resistance and alterations the resistor parameters after a while. Voltage worry may cause conduction from normally non-conductive components within the resistor film leading to deterioration and sometimes failure on account of warm spots. It truly is therefore crucial to notice the resistor optimum specified voltage.
SURGE CONDITIONS
The main element factor in analyzing the surge survivability of the thick movie resistor would be the mass of a resistor aspect, that is specifically proportional to its thickness multiplied by its surface area location. The geometry of a resistor also has an effect on its surge stand up to ability. A larger surface spot brings about a better film mass, and in the end an improved surge effectiveness. The increased area region will allow additional heat dissipation which is crucial in electrical power resistor apps.
The ultimate issue contributing variable to a resistor surge functionality is how the part is resistor trimmed to establish the final resistance value. The tactic utilized for trimming can build weak places that lead to failure less than surge ailments.
ESD
Harm by using ESD is often a latent defect that may be hard to detect. The resistor might be partly degraded by ESD but keep on to accomplish its meant purpose. Nonetheless, the probability of premature or catastrophic failure in the resistor gadget are elevated, specifically When the device is exposed to a number of in transistor the stresses listed higher than.