Thick film resistor failure is rarely a result of a failure from the resistive factor but is generally on account of exterior environmental variables like mechanical and electrical stresses and managing problems. Failures is often both classed for a degradation of overall performance or total failure (normally as an open up in lieu of a short circuit).
Six frequent leads to of thick film resistor failure are:
Thermal problems
Mechanical pressure
Continuous overload
Surge
Environmental - metallic migration
ESD
MECHANICAL FAILURES
Aside from managing injury bringing about substrate cracks and chips most mechanical destruction is due to either vibration or inappropriate mounting with the machine. Micro cracking of your resistor content brought on by vibration or compression / extension from the resistor resulting from inappropriate mounting may result in change from the resistance price, harm to the resistive element or part failure. In all conditions the risk of failure is amplified by presence of one or more of the stresses outlined underneath.
ENVIRONMENTAL Elements
Even though a thick film resistor is commonly coated to protect it from humidity and aggressive chemical elements environmental elements like moisture and contamination nevertheless demand watchful thought. The two could potentially cause metal migration in between the terminals in the resistor resulting in possible quick circuit or possibly a change in resistance value.
THERMAL Concerns
Most mechanical failure modes of thick movie resistors are propagated by heat. It can be for that reason important to understand the warmth dissipation Homes of your resistor and substrate content. A small electricity resistor dissipates heat by means of conduction by its ingredient qualified prospects or connections, when a high electricity resistor dissipates warmth by way of radiation.
When recent passes by way of a resistor it generates warmth as well as the differential thermal expansions of the several materials Employed in the resistor producing course of action induces stresses during the resistor. Temperature Coefficient of Resistance (TCR) is the best regarded parameter used to specify a thick film resistor steadiness, and defines the resistive component's sensitivity to temperature change. Energy Coefficient of Resistance (PCR) quantifies the resistance adjust as a consequence of self-heating when electric power is utilized and is particularly crucial for resistors Utilized in power applications.
OVERLOAD Problems
A ongoing about-load of the resistor product degrades the insulation resistance and changes the resistor parameters as time passes. Voltage pressure could cause conduction from Typically non-conductive components within the resistor movie leading to deterioration and sometimes failure due to hot spots. It truly is hence vital that you notice the resistor highest specified voltage.
SURGE CONDITIONS
The crucial element aspect in determining the surge survivability of the thick movie resistor would be the mass of a resistor factor, that's directly proportional to its thickness multiplied by its surface area region. The geometry of the resistor also affects its surge stand up to ability. A bigger area spot results in a better movie mass, and in the long run an enhanced surge efficiency. The elevated surface area region enables a lot more heat dissipation which is vital in energy resistor apps.
The ultimate issue contributing factor to some resistor surge capability is how the part is resistor trimmed to determine the final resistance capacitors value. The strategy useful for trimming can develop weak spots that bring about failure less than surge problems.
ESD
Hurt via ESD is really a latent defect that can be difficult to detect. The resistor can be partially degraded by ESD but continue to execute its intended perform. Having said that, the chances of untimely or catastrophic failure of your resistor product are enhanced, notably In the event the unit is exposed to one or more of your stresses stated earlier mentioned.