What are the main parameters of electronic components? What are their respective characteristics? (II)

What is the quality parameter of electronic components?

The quality parameter is used to measure the quality level of electronic components. It usually describes the characteristics of the component's characteristic parameters and specification parameters as a function of environmental factors, or defines the boundary conditions for which they cannot perform functions. The quality parameters common to electronic components generally include temperature coefficient, noise electromotive force, high frequency characteristics and reliability. From the perspective of the whole machine manufacturing process, the main quality parameters are mechanical strength and weldability.

(1) Temperature coefficient: The specification parameters of electronic components will change slightly with changes in ambient temperature. For every 1 °C change in temperature, the relative change in value is called the temperature coefficient in 1/°C. The temperature coefficient describes the stability of the characteristic parameters of the component under the change of ambient temperature. The smaller the temperature coefficient, the more stable its value is. The temperature coefficient also has positive and negative points, which respectively indicate whether the trend of component value changes increases or decreases when the ambient temperature rises. The temperature coefficient (symbol, size) of electronic components depends on factors such as their materials of manufacture, structure and production conditions.

When making electronic products that require long-term stable work or large changes in the temperature of the working environment, components with a small temperature coefficient should be used as much as possible. The ventilation and cooling of the products should be considered according to working conditions, and corresponding constant temperature measures should be taken.

(2) Noise electromotive force and noise figure: The internal noise of electronic equipment is mainly generated by various electronic components. We know that the free electrons in the conductor are always in the "unregular" thermal motion state at a certain temperature, so that a "regular" current whose direction and size change with time is formed inside the conductor. And the noise electromotive force is generated at both ends of the equivalent resistance of the conductor. The noise electromotive force is randomly changed and acts in a wide frequency range. Since this noise is generated by the thermal motion of free electrons, it is usually It is called thermal noise, and the effect of thermal noise increases as the temperature rises.

In addition to thermal noise, various electronic components generate other types of noise due to differences in materials, structures, and processes. For example, carbon film resistors generate noise due to discharge and surface effects between carbon particles. It is not available in the metal film resistor, so the noise acoustic electromotive force of the metal film resistor is smaller than that of the carbon film resistor), the shot noise generated by the carriers inside the transistor, and the like.

(3) High-frequency characteristics: When the operating frequency is different, the electronic components will exhibit different circuit responses, which are determined by the materials and process structures used in the manufacture of the components. In the general analysis of the circuit, the electronic components are usually considered as ideal components, but when they are in the high frequency state, many features that are not prominent will be reflected.

(4) Reliability and failure rate: Like any other product, the reliability of an electronic component refers to its effective working life, that is, the time it can normally complete a particular electrical function. The end of the working life of an electronic component is called failure.

(5) Mechanical strength and weldability: The mechanical strength of electronic components is one of the important quality parameters. People generally want electronic equipment to work in an ideal environment without vibration and mechanical shock. However, in fact, the vibration and impact of the equipment cannot be avoided. If the mechanical strength of the components selected by the equipment is not high, it will break during the vibration, causing damage and invalidating the electronic equipment. This is not uncommon.

(6) Other quality parameters: There are some specific quality parameters for various electronic components. For example, for capacitors, the magnitude of the insulation resistance, the energy loss due to leakage (represented by the loss tangent), etc. are all important quality parameters. For another example, the reverse saturation current Icbo, the penetration current Iceo, and the saturation voltage drop Uces of the transistor are all quality parameters of the triode.

(7) These specific quality parameters of electronic components have corresponding acceptance criteria and should be selected according to the requirements of the actual circuit.