PCB multilayer circuit boards are usually defined as 10-20 or more advanced multilayer circuit boards, which are more difficult to process than traditional multilayer circuit boards and require high quality and reliability. Mainly used in communication equipment, high-end servers, medical electronics, aviation, industrial control, military and other fields. In recent years, the market demand of high-rise boards in communication, base station, aviation, military and other fields is still strong.
With the rapid development of China’s communication equipment market, the high-rise board market has a bright future.
At present, domestic PCB manufacturers that can mass produce high-level circuit boards mainly come from foreign-funded enterprises or a few domestic-funded enterprises. The production of high-level circuit boards requires not only high investment in technology and equipment, but also the experience accumulation of technicians and producers.
At the same time, the customer authentication procedure of multilayer circuit boards is also strict and complicated. Therefore, the threshold for high-level circuit boards to enter enterprises is high, and the industrial production cycle is long.
The average level of PCB has become an important technical index to measure the technical level and product structure of PCB enterprises. This paper briefly describes the main processing difficulties encountered in the production of high-level circuit boards, and introduces the control points of key production processes of multilayer circuit boards for reference.
Compared with traditional PCB products, high-level PCB has many characteristics, such as thick board, many layers, dense lines, many through holes, large cell size, thin dielectric layer, etc., and requires higher internal space, interlayer alignment, impedance control and reliability.
1. Difficulties in interlayer alignment
Due to the large number of layers in the high-level panel, users have higher and higher requirements for PCB layer calibration. Generally, the alignment tolerance between layers is controlled at 75 microns. Considering the large unit size of the high-rise board, the high temperature and humidity in the graphic conversion workshop, the dislocation overlap caused by the inconsistency of different core boards, and the interlayer positioning mode, it is more difficult to control the alignment of the high-rise board.
2. Difficulties in making internal circuits
The high-rise board is made of special materials such as high TG, high speed, high frequency, thick copper, thin dielectric layer, etc., which puts forward high requirements for internal circuit fabrication and graphic size control. For example, the integrity of impedance signal transmission increases the difficulty of internal circuit manufacturing.
And the width and line spacing are small, the open circuit and short circuit are increased, the short circuit is increased, and the qualified rate is low; There are more thin signal layers, and the probability of AOI leakage detection in the inner layer increases; The inner core plate is thin, easy to wrinkle, poorly exposed, and easy to curl when etching machine; High-level plates are mostly system plates, with large unit size and high product scrap cost.
3. Difficulties in compression manufacturing
Many inner core plates and prepregs are superimposed, and the defects such as sliding plate, delamination, resin void and bubble residue are easy to occur in stamping production. In the design of laminated structure, the heat resistance, pressure resistance, glue content and dielectric thickness of materials should be fully considered, and a reasonable pressing scheme for high-rise board should be formulated.
Because of the large number of layers, the expansion and contraction control and size coefficient compensation can’t be consistent, and the interlayer insulation layer is easy to cause the interlayer reliability test to fail.
4. Difficulties in drilling
Special copper plates with high TG, high speed, high frequency and thick thickness increase the difficulty of drilling roughness, burr and dirt removal. The number of layers, the cumulative total copper thickness and plate thickness, make the drilling tool easy to break; CAF failure caused by dense BGA and narrow hole wall spacing; Inclined drilling is easy to occur due to the thickness of the plate.
This article is collated by multi-layer pcb proofing, and this article does not represent the viewpoint of this site.
