With the rapid development of modern microwave communication technology, the design of microwave circuit components with high performance and high precision has become increasingly important. In microwave radio frequency (RF) modules, thin-film circuit technology has become a key design method with its unique advantages. In this paper, several thin film circuit components based on alumina substrate are introduced in detail, including thin film microstrip circuit, thin film filter, thin film load, thin film equalizer and thin film power divider. These components play an irreplaceable role in microwave circuits, and their design accuracy and performance directly affect the performance of the whole microwave system.

 

 

Applications of alumina substrate in circuit

 

1 Thin film microstrip circuit

Aluminum oxide ceramic substrate is used to design thin film microstrip circuit, the thickness of the gold layer can be up to 3.5um, and the metal wire bonding can be used to connect with the external circuit. The common plate thickness is 0.127mm, 0.254mm, 0.381mm, 0.508mm, and the transmission frequency can reach more than 40GHz. It meets the frequency band requirements of most microwave RF module modules, and the thin film circuit line accuracy of the thin film process is ±5um. The microwave RF field often uses ceramic substrates for microstrip transmission lines or circuit design with high precision.

 

2 Thin film filter

The frequency of the thin film filter made of alumina ceramic substrate can be as high as 40GHz, which is often used as a functional unit of frequency selection in various microwave module modules and systems. Thin film filter is processed by thin film technology, through sputtering, lithography, wet or dry etching, cleaning, slicing to obtain thin film filter substrate, common interfinger type, hairpin type, comb type, parallel coupling type, C-type and other structural filters can be designed based on alumina ceramic substrate processing, can be designed low pass high pass band pass band resistance and other different types of filters. Because the dielectric constant of the alumina ceramic sheet is greater than that of the general PCB substrate, the volume of the film filter made by the alumina ceramic sheet is smaller than that of the general microstrip filter, and the electrical parameters of the film filter made by the alumina ceramic sheet are good. It is usually fixed with conductive adhesive or gold tin eutectic.

 

3 Film load

The aluminum oxide ceramic substrate is used to design the thin film load, which is often used to match the terminal of the module assembly of the microwave circuit to absorb the excess reflected power. For the load, the machining accuracy of the resistance value is very important, and the greater the deviation, the worse the final load performance. Due to the controllable square resistance of the tantalum nitride film layer in the film process, the film load with high precision can be produced, and the film load volume is very small, which is a good choice for the miniaturization of component modules. It is usually fixed to the end of the circuit using conductive adhesive or gold tin eutectic.

 

4 Film equalizer

The thin-film equalizer is designed with alumina ceramic substrate, which is often used to adjust the broadband power flatness of microwave circuits. The output waveform of the device is adjusted by changing the square resistance of the integrated tantalum nitride film layer and the different resistance values of the graphic design, so as to balance the power signal at the front end to achieve the power flatness adjustment effect.

 

5 Film power divider

The thin-film power divider designed with alumina ceramic substrate is often used in the multi-channel communication network system. It has the function of power distribution according to a certain proportion, with one input and multiple output. Since the isolation resistor can be integrated into the thin film circuit using the tantalum nitride film layer to design a suitable resistance value, this can avoid the deterioration of the circuit performance due to the welding of the patch resistance of the microstrip power divider and the instability of the resistance value of the patch resistor, and the thin film power divider is easier to achieve the multi-stage ultra-wideband design, and the designed object is small in size, easy to integrate and good in performance.

 

In summary, alumina ceramic substrate plays a crucial role in the design of thin-film circuit components. From thin film microstrip circuit to thin film power distributor, these components not only meet the requirements of high precision and high frequency of microwave RF modules, but also realize the miniaturization and high performance of the components. Through the precise control of thin film technology, we can obtain thin film circuit components with excellent electrical parameters, which further improves the overall performance of microwave systems. In the future, with the continuous progress of microwave communication technology, thin film circuit components based on alumina ceramic substrates will continue to play a greater role in the microwave field, contributing to the development of wireless communication, radar detection and other fields.

With the rapid development of modern electronic technology, the design of microwave RF components and high-frequency circuits is becoming more and more complex, and the performance requirements of components are becoming higher and higher. In order to meet these needs, thin film technology, as an advanced microelectronic technology, plays an increasingly important role in the design of microwave components and high-frequency circuits. This article introduces several thin film components based on alumina substrate design, including thin film attenuators, thin film couplers, thin film Bridges, thin film resistors, and thin film capacitors. These components play an indispensable role in microwave RF components and high-frequency circuits with their unique properties and wide application fields.

 

 

1 Film attenuator

The design of thin film attenuator using alumina ceramic substrate is often used for large signal attenuation in microwave RF module, or for multi-stage adjustment of attenuation value in programmed attenuation circuit. It is also based on the reasonable design of the square resistance of tantalum nitride film layer and the film process design of alumina ceramic circuit. Thin film attenuators can achieve high flatness of attenuation value in ultra-wide band with stable performance.

 

2 Thin film coupler

Aluminum oxide ceramic substrate design film coupler, often used in microwave component system power detection or signal separation, can be designed into any weak coupling degree coupler, and can use tantalum nitride design integrated isolation load, the port can be designed into the form of surface paste package, directly welded in the circuit for work. It can be designed into a multi-stage form when it needs to be applied to a wide band.

 

3 Film bridge

The use of alumina ceramic substrate design film bridge, also called 3dB bridge, often used to separate the signal and make it have a 90° or 180° phase difference, lange bridge is a form of its application more, through the gold wire bonding to achieve the signal connection between the lines.

 

4 Thin film resistance

The use of alumina ceramic substrate design film resistor, often used in high-precision, low noise and high stability of the circuit, often integrated in the microstrip film circuit design and processing, can also be designed separately into a variety of resistance types of film resistor used, or designed into a resistance network, through the gold wire bonding to select the required resistance value.

 

5 Thin film capacitance

The thin-film capacitor is designed with alumina ceramic substrate, which is often used in high-frequency filtering. The thin-film capacitor with arbitrary capacitance can be designed for power supply. The performance is more stable than that of ordinary chip capacitor, and it is suitable for high-frequency circuit.

 

In summary, thin-film components designed on alumina ceramic substrates, such as thin film attenuators, thin film couplers, thin film Bridges, thin film resistors and thin film capacitors, have shown excellent performance and wide application prospects in microwave RF components and high-frequency circuits. These components not only have the advantages of high precision, low noise and high stability, but also can achieve high performance indicators in the ultra-wide band, which provides a strong support for the development of modern electronic technology. With the advancement of science and technology and the improvement of demand, thin film technology will continue to play a more important role in the design of microwave RF components and high-frequency circuits, and promote the continuous development and innovation of electronic technology.

Because of its excellent mechanical properties, thermal stability and chemical inertness, alumina substrate has shown wide application potential in electronic packaging, thermal management and high-performance structural parts. The preparation process involves complex process steps, in which casting process, as the core link, plays a decisive role in the performance of the final product. This paper aims to discuss the key control points in casting process, such as raw material formula, casting film strip thickness and sintering process parameters, analyze how these parameters affect the thickness uniformity, appearance quality and surface roughness of alumina ceramic substrate engineering application indicators, so as to optimize the preparation process and improve the overall performance of the product.

 

 

Raw material formulation and slurry characteristics

The raw material formula is the basis of alumina ceramic substrate preparation, which directly affects the viscosity, solid content and other key physical properties of the slurry. Suitable slurry formulation helps to achieve good casting effect and uniform film distribution. The viscosity of the slurry should be moderate, which can ensure good spreading and avoid cracks or deformation during the drying process.

 

 

Casting film thickness control

The thickness of the cast film strip is a key factor in determining the final thickness tolerance of the substrate. In addition to the slurry state, the height of the casting blade also directly affects the thickness of the dry film. The thickness distribution of the film can be optimized by precisely controlling the height of the blade and the velocity of the film (uniform linear motion), and the phenomenon of thick center and thin sides can be reduced. For the substrate requiring high precision, the casting machine with adjustable blade surface curve becomes a necessary choice.

 

 

Desticking sintering process parameters

Debonding sintering is a key step in the preparation of alumina ceramic substrate, which directly affects the density, strength and microstructure of the substrate. Reasonable sintering temperature and holding time are helpful to eliminate the internal pores and improve the mechanical properties and thermal stability of the substrate. At the same time, the atmosphere control in the process of debonding is also an important factor affecting the quality and performance of the substrate.

 

Casting process flow chart

 

In summary, the preparation process of alumina ceramic substrate is a complex system engineering involving multi-factors and multi-steps. The rational selection and optimization of key control points such as raw material formula, casting film thickness and sintering process parameters are very important to improve the thickness uniformity, appearance quality and surface roughness of the substrate. Through in-depth study of the mechanism of influence of these parameters, combined with advanced preparation technology and equipment, the overall performance of alumina ceramic substrates can be further improved to meet the stringent requirements in high-performance electronic packaging, thermal management and structural components. In the future, with the continuous progress of material science and preparation technology, the preparation process of alumina ceramic substrate will be more refined and intelligent, providing a more solid foundation for the development of related fields.