Microwave Circuit PCB

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, lines and holes are more dense, unit size is larger, the media layer is thinner and other characteristics of the inner space, the interlayer alignment, impedance control, as well as the reliability of the requirements are more stringent. What are the difficulties in the production of multi-layer high frequency PCB board?

a, Interlayer Alignment Difficulties

Due to the number of layers of high-level boards, the 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 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 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 plate; 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. More layers, cumulative total copper thickness and plate thickness, drilling easy to break the knife; dense BGA more than narrow hole wall spacing caused by the CAF failure problem; due to the thickness of the plate can easily lead to oblique drilling problems.