Electronic component dealer teaches you how to choose electronic components

The selection of electronic components is very important. The failure of components is mainly concentrated in the following four aspects:
(1) Component reliability issues
The component reliability problem is the basic failure rate problem. This is a random nature failure. The difference from the quality problem is that the component failure rate depends on the working stress level. At a certain stress level, the failure rate of components will be greatly reduced. In order to eliminate components that do not meet the requirements for use, including unqualified electrical parameters, unsatisfactory sealing performance, unqualified appearance, poor stability, early failure, etc., screening tests should be conducted. The screening tests for major components of electronic products generally require:

The purchaser should provide the following test report. The high temperature test generally requires welding simulation test. The high temperature oven test generally does not meet the actual welding requirements. The test can be completed by channel test reflow (force front recommended: M series test type reflow) The actual welding production curve, so that the quality of the tested devices is more guaranteed!

1 The resistance is 100% tested at room temperature according to the technical conditions, and the rejects are rejected.
2 Ordinary capacitors are 100% tested at room temperature according to technical conditions, and reject non-conforming products.
3 connectors sample and test various parameters according to technical conditions.
4 Semiconductor devices are screened according to the following procedures:
Visual inspection → initial measurement → high temperature storage → high and low temperature impact → electric power aging → high temperature test (simulated welding test) → low temperature test → normal temperature test

The rejection rate should be calculated after the screening is completed.
Q=(n / N)×100%
Where: N - the total number of samples tested;
n - the number of samples rejected;
If Q exceeds the upper limit of the standard, all components of this batch are not allowed to go on the machine and shall be disposed according to relevant regulations.
(2) Manufacturing quality issues
The failure caused by the quality problem is independent of the working stress. Unqualified quality can be eliminated through strict inspection. In engineering applications, mature products of fixed-point manufacturers should be used, and products that are not certified are not allowed.

(3) Design issues
The first is to properly select the right components:
1 Try to use silicon semiconductor devices, with little or no semiconductor devices.
2 more integrated circuits, reducing the number of discrete devices.
3 switch tube MOSFET can simplify the drive circuit and reduce losses.
4 output rectifiers try to use diodes with soft recovery characteristics.
5 should choose metal, ceramic, glass packaged devices. It is forbidden to use plastic packaged devices.
6 The integrated circuit must be a class of products or military products that meet the quality standards of MIL-M-38510 and MIL-S-19500 standards B-1.
7 Use as few relays as possible when designing. If necessary, use a well-sealed sealed relay.
8 In principle, the potentiometer is not used, and the one that must be retained should be sealed.
9 The distance between the absorbing capacitor and the switching tube and the output rectifier should be very close. Because of the high frequency current flowing, it is easy to heat up. Therefore, these capacitors are required to have high frequency, low loss and high temperature resistance.

In humid and salt spray environments, aluminum electrolytic capacitors can cause corrosion, capacity drift, and increased leakage current. Therefore, in ships and humid environments, it is best not to use aluminum electrolytic capacitors. Since the electrolyte is decomposed when bombarded by space particles, the aluminum electrolytic capacitor is not suitable for use in the power supply of aerospace electronic equipment.

The electrolytic capacitor has good temperature and frequency characteristics, high and low temperature resistance, long storage time, stable and reliable performance, but the tantalum electrolytic capacitor is heavy, the volume ratio is low, the back pressure is not resistant, the high pressure type (>125V) is less, and the price is expensive.

About derating design: The basic failure rate of electronic components depends on the working stress (including electricity, temperature, vibration, shock, frequency, speed, collision, etc.). Except for some components with low stress failure, others have the characteristics of higher working stress and higher failure rate. In order to reduce the failure rate of components, derating design is required in circuit design. The degree of derating, in addition to reliability, also needs to consider factors such as volume, weight, and cost. Different components have different derating standards. Practice shows that the basic failure rate of most electronic components depends on electrical stress and temperature. Therefore, the derating is mainly to control these two stresses. The following are the common components of electronic products. Amount factor:

The power derating factor of the 1 resistor is between 0.1 and 0.5.
2 The power derating factor of the diode is below 0.4, and the reverse withstand voltage is below 0.5.
3 LEDs.