Oxidation of the resistor body will increase the resistance value, which is the most important factor causing the aging of the resistor. Except for resistors made of precious metals and alloys, other materials are destroyed by oxygen in the air. Oxidation is a long-term effect. When the influence of other factors is gradually weakened, 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-resistance resistors, the fundamental measure to prevent oxidation is seal protection. The sealing material should be made of inorganic materials such as metal, ceramics, glass, etc. The organic protective layer cannot completely prevent moisture and air permeability, and can only delay the oxidation and adsorption.
Aging of Resistor Binder
For organic synthesis resistors, the aging of organic binders is the main factor affecting the stability of resistors. Organic binders are mainly synthetic resins. In the manufacturing process of resistors, thermosensitive polymerizate of synthetic resins is converted into high polymerization degree by 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 occurs, 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.
Aging of Resistors under Electrical Load
Applying a load to the resistor accelerates its aging process. Electrolysis can damage the thin film resistor under DC load. Electrolysis occurs between the grooves of the grooved resistor. If the resistive substrate is a ceramic or glass material containing alkali metal ions, the ions move under the action of the electric field between the grooves. In a humid environment, this process is carried out more intensely.
The above are several reasons for the failure of aerospace resistors, and the changes in resistors have a major impact on the aviation industry. Many aerospaces currently customize resistors and shunts to ensure the safety of aerospace programs.
