Multi-layer High Frequency Circuit Board

Multilayer high frequency PCB is a more complex PCB structure that consists of multiple layers of circuit boards. In a multilayer HF PCB, components can be arranged and connected on multiple layers. The upper and lower layers are connected to each other through jacks and pads. Multilayer high-frequency PCBs are usually used for complex circuits such as base stations, wireless communications, aviation systems, etc.

A. Difficulty of Inter-layer Alignment.

Due to the number of layers of high-level boards, customer design side of the PCB layers of the alignment requirements are increasingly stringent, usually inter-layer alignment tolerance control ± 75μm, taking into account the design of high-level board unit size is larger, the graphics transfer workshop environment temperature and humidity, as well as the inconsistency of the different core board layer up and down the misalignment brought about by the superposition of the inter-layer positioning methods and other factors, making the high-level board inter-layer alignment control is even more difficult.

B. Difficulty of Inner Layer Line Production.

High-level board using high TG, high-speed, high-frequency, thick copper, thin dielectric layer and other special materials, the inner layer of line production and graphic size control puts forward high requirements, such as the integrity of impedance signal transmission, increasing the difficulty of the inner layer of line production. Line width line spacing is small, open short circuit increased, micro-short increased, low pass rate; fine line signal layer is more, the inner layer of AOI leakage rate increased; inner core plate thickness is thin, easy to wrinkle resulting in poor exposure, etching over the machine is easy to roll the board; high-level board most of the system board, unit size is larger, in the finished product scrap cost is relatively high.

C. Pressing The Production Difficulties.

Multiple inner core board and semi-cured sheet stacked, press production is prone to slip, delamination, resin voids and bubble residue and other defects. When designing the laminated structure, it is necessary to fully consider the heat resistance of the material, the voltage resistance, the amount of glue filling and the thickness of the medium, and to set a reasonable program for press-fitting of high-level boards. The number of layers is large, and the control of rise and shrinkage and the amount of size factor compensation can not maintain consistency; the thin insulation layer between the layers is likely to lead to interlayer reliability test failure problems. Figure 1 is a thermal stress test after the emergence of burst board delamination defects Figure.

D. Drilling Production Difficulties

The use of high TG, high-speed, high-frequency, thick copper-type special plates, increasing the difficulty of drilling roughness, drilling burrs and de-drilling dirt. The number of layers, the cumulative total copper thickness and board thickness, drilling easy to break the knife; dense BGA, narrow hole wall spacing caused by the CAF failure; due to the thickness of the board can easily lead to oblique drilling problems.

E. Multilayer High Frequency Circuit Board Production Process.

Cutting - Drilling - Hole treatment (plasma treatment or chemical potion activation treatment) - Chemical copper immersion - Full-plate plating - Dry film - Inspection - Graphic plating - Etching - Etching inspection – Solder proof - Text - Tin spraying - CNC appearance - Electrical test - Final inspection - Packaging - Shipping.

F. High Fequency Circuit Board Application Fields.

1. a, 5G communication, telecommunication equipment and other communication products;
2. b, Power amplifiers, low noise amplifiers, etc.;
3. c, Passive components, such as power dividers, couplers, duplexers, filters, etc.;
4. d, High-frequency electronic devices in the fields of automobile collision avoidance systems, satellite systems, radio systems, etc.

Multi-layer high frequency PCB board its processing difficulty, its quality and reliability requirements, widely used in communications equipment, high-end servers, medical electronics, aviation, industrial control, military and other fields.

Compared with the product characteristics of conventional PCB boards, multi-layer high-frequency PCB boards have thicker boards, more layers, more dense lines and holes, unit size is larger, thinner dielectric layer and other characteristics, the inner layer space, interlayer alignment, impedance control and reliability requirements are more stringent. What are the difficulties in the production of multilayer high-frequency PCB boards?