Microwave Tech - Discussion on Production Technology of Microwave High Frequency Circuit Board

Discussion on Production Technology of Microwave High Frequency Circuit Board

1 Introduction

Microwave high-frequency circuit boards refer to microwave devices produced on specific microwave substrate copper clad laminates using common rigid printed board manufacturing methods. In the high-speed signal transmission line of the printed board wire, it can be divided into two categories at present: one is high-frequency signal transmission electronic products, this type of product is related to the electromagnetic wave of the radio, which transmits the signal by sine wave Products, such as radar, radio and television, and communications (mobile phones, microwave communications, optical fiber communications, etc.); the other is high-speed logic signal transmission electronic products, which are transmitted by digital signals, and are also related to electromagnetic waves. Related to square wave transmission, this type of products began to be mainly used in computers, computers and other applications, and now they have been quickly applied to home appliances and communication electronic products.

In order to achieve high-speed transmission, there are clear requirements for the electrical characteristics of the microwave high-frequency circuit board substrate material. In terms of improving high-speed transmission, in order to achieve low loss and low delay of transmission signals, a substrate material with a small dielectric constant and dielectric loss tangent must be selected. High-speed transmission substrate materials generally include ceramic materials, glass fiber cloth, polytetrafluoroethylene, and other thermosetting resins. Among all resins, PTFE has the smallest dielectric constant (εr) and dielectric loss tangent (tanδ), and has good resistance to high and low temperature and aging. It is most suitable for high-frequency substrate materials. It is currently used The largest amount of microwave high-frequency circuit board manufacturing substrate material.

According to the characteristics of microwave high-frequency circuit board manufacturing, this article has conducted a more comprehensive discussion on the material selection, structure design and manufacturing process of microwave high-frequency circuit board.

2 The characteristics of microwave high-frequency circuit board manufacturing

The characteristics of microwave high-frequency circuit board manufacturing are mainly manifested in the following aspects:

2.1 Diversification of substrates:

For a long time, domestically produced glass cloth reinforced polytetrafluoroethylene copper clad laminate has been the most widely used in China. However, due to its single species and poor uniformity of dielectric properties, it has become increasingly unsuitable for some occasions requiring high performance. After entering the 1990s, the RT/Duroid series and TMM series microwave substrate plates produced by Rogers Corporation in the United States have gradually been applied, mainly including glass fiber reinforced PTFE copper clad laminate, ceramic powder filled PTFE copper clad laminate and ceramic powder Filled with thermosetting resin copper clad laminate, although expensive, its excellent dielectric properties and mechanical properties still have considerable advantages over domestic microwave high-frequency circuit board substrates. At present, such microwave substrates, especially those with aluminum substrates, are being widely used.

2.2 Design requirements for high precision:

The graphics manufacturing accuracy of microwave high-frequency circuit boards will gradually improve, but due to the limitations of the printed board manufacturing process itself, this increase in accuracy cannot be unlimited, and it will enter a stable stage after a certain degree. The design content of the microwave board will be greatly enriched. In terms of types, there will be not only single-sided and double-sided boards, but also microwave multilayer boards. For the grounding of the microwave board, higher requirements will be put forward, such as the general solution to the metalization of the holes of the PTFE board and the grounding of the microwave board with an aluminum substrate. The plating requirements are further diversified, and special emphasis will be placed on the protection and plating of aluminum substrates. In addition, higher requirements will be put forward for the overall three-proof protection of the microwave board, especially the three-proof protection of the PTFE board.

2.3 Computer control:

Computer technology is rarely used in the production of traditional microwave high-frequency circuit boards, but with the wide application of CAD technology in design, as well as the high precision and mass production of microwave high-frequency circuit boards, a large number of them are used in the manufacture of microwave high-frequency circuit boards. Application of computer technology has become an inevitable choice. The design and manufacture of high-precision microwave high-frequency circuit board templates, the numerical control processing of the shape, and the batch production inspection of high-precision microwave high-frequency circuit boards are already inseparable from computer technology. Therefore, it is necessary to connect the CAD of the microwave high-frequency circuit board with CAM and CAT, and through the data processing and process intervention of the CAD design, the corresponding CNC processing files and CNC inspection files are generated for the production process of the microwave high-frequency circuit board. Control, process inspection and finished product inspection.

2.4 Specialization of high-precision graphics manufacturing:

Compared with traditional rigid printed boards, the high-precision pattern manufacturing of microwave high-frequency circuit boards is developing in a more specialized direction, including the production of high-precision template manufacturing, high-precision pattern transfer, and high-precision pattern etching. And process control technology, but also includes a reasonable manufacturing process route arrangement. According to different design requirements, such as whether the hole is metallized or not, the type of surface plating, etc., a reasonable manufacturing process method is formulated. After a large number of process experiments, the process parameters of each related process are optimized, and the process margin of each process is determined.

2.5 Variety of surface plating:

With the expansion of the application range of microwave high-frequency circuit boards, the environmental conditions for their use have become more complicated. At the same time, due to the large-scale application of aluminum substrates, the surface of microwave high-frequency circuit boards is coated and protected. And on the basis of tin-plated cerium alloy, higher requirements are put forward. The first is the plating and protection of the microstrip pattern surface, which must meet the welding requirements of microwave devices, and the process technology of electroplating nickel and gold is used to ensure that the microstrip pattern is not damaged in harsh environments. In addition to the solderability coating on the surface of the microstrip pattern, the most important thing is to solve the three-proof protection technology that can effectively protect without affecting the microwave performance. The second is the protection and plating technology of aluminum liner. If the aluminum liner is not protected, it will quickly be corroded when exposed to moisture and salt spray. Therefore, as the aluminum liner is widely used, its protection technology should attract enough attention. In addition, it is necessary to study and solve the electroplating technology of aluminum plates. The demand for electroplating silver, tin and other metals on the surface of aluminum lining plates for microwave device welding or other special purposes is gradually increasing. This not only involves the electroplating technology of aluminum plates, but also has microstrip patterns. Protection issues.