Failure Mechanism Analysis of Resistor
According to the materials used for the resistor body, common non-wound resistors can be classified into four types, alloy type; film type; thick film type; and synthetic type. For fixed resistors, its main failure modes are open circuit, electrical parameter drift, etc.; For potentiometer, its main failure modes are open circuit, electrical parameter drift, and noise increase. The service environment will also cause the maturing of resistors, which has a great impact on the life of the electronic pcba.
Oxidation: the Oxidation of resistor body will increase the resistance value, which is the main factor to cause the maturing of resistors. In addition to the resistors made of precious metals and alloys, other materials are damaged by oxygen in the air. Oxidation has a long-term effect. When the influence of other factors gradually decreases, oxidation will become the main factor, and the high temperature and high humidity environment will accelerate the oxidation of the resistor. For precision resistors and high-value resistors, the fundamental measure to prevent oxidation is the seal protection. BQC recommends that sealing materials should use inorganic materials such as metals, ceramics, glass, etc. The organic protective layer cannot completely prevent moisture permeability and air permeability, and It can only delay the oxidation and adsorption.
The maturing of binder: For organic synthesis resistors, the aging of organic binders is the main factor affecting the stability of resistors. Organic binders are mainly made up of synthetic resins. In the manufacturing process of resistors, pcba processing enterprises change the synthetic resin to high polymerization degree through heat treatment. The main cause of polymer aging is oxidation. The free radical formed by oxidation causes a hinge of the polymer molecular bond, thereby causing the polymer to further solidify, become brittle, and thus lose elasticity and mechanical damage. The curing of the binder shrinks the volume of the resistor, the contact pressure between the conductive particles increases, the contact resistance becomes smaller, and the resistance value decreases, but the mechanical damage of the binder also increases the resistance value. Usually, the curing of the binder occurs before the mechanical damage, so the resistance value of the organic synthesis resistor exhibits the following regularity: some decreases at the beginning, then turns to increase, and there is an increasing trend. Since the aging of the polymer is closely related to temperature and light, the synthetic resistor accelerates aging under high temperature and strong light.
The maturing of resistors under electrical load: applying the load to the resistor will accelerates its aging. Under DC load, electrolysis can damage the thin film resistor. The electrolysis occurs between the grooves of the groove resistor. If the resistor matrix is a ceramic or glass material containing alkali metal ions, the ions move under the effect of the electric field between the grooves. In a humid environment, this process becomes more intense.
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