Application of the hottest high frequency special

2022-08-03
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The application of high-frequency special coating technology in microwave circuits I. Introduction the electronic equipment using its main raw materials in harsh environments has higher and higher requirements for the "three proofing" performance of the circuit in the electronic equipment. Therefore, how to improve the "three proofing" performance of the circuit itself, especially how to improve the "three proofing" performance of the microwave circuit, is very important for every designer of the microwave circuit, Is an urgent problem. The main research results of the high-frequency special coating materials introduced in this paper should be published in mater Horiz. It is used in microwave circuits with operating frequency above 100 MHz to improve the adaptability of microwave circuits to high temperature, high humidity and harsh environment. Aiming at the problem that special coating materials may affect the performance of microwave circuit board, a method of introducing "correction factor" into microwave circuit design is proposed to solve the above problems. At the end of the paper, reliable data about the application technology of high-frequency special coating materials to enhance the adaptability of 362 MHz crystal oscillator and amplifier circuit to the harsh environment of high temperature and humidity are provided

II. Main technical indexes of high-frequency special coating materials

during the development of high-frequency special coating materials, a variety of materials were analyzed and studied. Finally, a surface treatment agent (transitional coating) f-1002 was successfully developed. Through the application of elastic-plastic silicone coating, the coating has stronger adhesion to the circuit substrate. Its main technical indexes are as follows:

(1) main electrical performance index dielectric coefficient ε (1 MHz) 2.8 dielectric loss TG δ (1MHz)2.7 × 10-3 volume resistivity ρν (Ω × cm)2 × 1015 (2) the adhesion of the coating to the circuit substrate shall not crack or delaminate after 20 times of impact at - 55 ℃ ~ + 125 ℃

III. microwave

circuit design method for coating problems

in order to provide reliable data for the coating technology of high-frequency special coating materials to enhance the adaptability of microwave circuits to the harsh environment of high temperature and humidity, the author of this paper designed a 362mhz crystal oscillator and amplifier circuit on f4b (polytetrafluoroethylene fiberglass board) substrate

The

circuit is an LC oscillation circuit controlled by a crystal. The change of the oscillation frequency of the LC oscillation circuit will cause the change of the crystal oscillation frequency. The harsh environment of high temperature and high humidity causes the change of oscillation frequency of LC oscillation circuit, which is reflected in the change of crystal oscillation frequency. Since the amplification circuit has little impact on the oscillation frequency of crystal oscillator due to the impact of environmental change, the change of crystal oscillation frequency becomes an important parameter to show the adaptability of circuit and circuit board to the harsh environment of high temperature and high humidity

The actual circuit diagram of the crystal oscillator is shown in Figure 1. Generally, the influence of coating on the circuit consists of the following parts. (1) It is coated on the transistor to affect the inter pole distributed capacitance of the transistor; (2) Coated on the chip capacitor, affecting the capacitance value; (3) Coating on the microstrip inductor will affect the value of the microstrip inductor

(2) and (3) mainly increase the distributed capacitance. Since the circuit operates at 362 MHz and the frequency is not too high, in this example, only the influence of the coating on the inductance is considered, and the influence on the capacitance and the inter pole distributed capacitance of the transistor is ignored

the design formula of microstrip inductance is quoted: l is the length of microstrip line, and the unit is cm

after coating with special coating materials, the design of the microstrip inductor will correct the slipping phenomenon of the tensile testing machine in the application process

where Δ L is the correction factor of inductance length, which can be obtained by test

in the 362 MHz crystal oscillation circuit, the oscillation frequency of the crystal oscillation circuit is reduced after the circuit is coated with special coating materials. By adjusting the adjustable capacitance in the circuit, the total capacitance C0 in the circuit changes Δ C, so that the oscillation frequency of the crystal oscillation circuit is restored to F0, which is calculated inversely by equation (1) Δ l。

once the correction factor is obtained through the test Δ l. In the later design of 362 MHz crystal oscillation circuit, under the same coating process specification, the correction factor can be used in the design process Δ l. The change of circuit performance after coating is greatly reduced

IV. 362 MHz crystal oscillation, amplification

Evonik's new materials make this idea possible. The wet heat comparison test of the circuit

1. design of the test

this test is to conduct multiple wet heat tests on the same 362mhz crystal oscillator and amplification circuit with f4b as the substrate, without coating high-frequency special coating materials and coating high-frequency special coating materials, and after comparing a large number of test data, Obtain reliable data on the application technology of high-frequency special coating materials to enhance the adaptability of 362 MHz crystal oscillator and amplifier circuit to the harsh environment of high temperature and humidity

2. test conditions

one cycle is 24 hours, and the circuit under test shall be continuously cycled for 10 times

(1) cycle steps

this test takes 24 hours as a cycle, every week

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