Multilayer circuit boards are generally defined as 10-20 or more high-grade multilayer circuit boards, which are more difficult to process than traditional multilayer circuit boards and require high quality and robustness. Mainly used in communication equipment, high-end servers, medical electronics, aviation, industrial control, military and other fields. In recent years, the market demand for multi-layer circuit boards in the fields of communications, base stations, aviation, and military is still strong.
Compared with traditional PCB products, multi-layer circuit boards have the characteristics of thicker board, more layers, dense lines, more through holes, large unit size, and thin dielectric layer. Sexual requirements are high. This paper briefly describes the main processing difficulties encountered in the production of high-level circuit boards, and introduces the key points of control of the key production processes of multilayer circuit boards.
1. Difficulties in inter-layer alignment
Because of the large number of layers in a multi-layer circuit board, users have higher and higher requirements for the calibration of the PCB layers. Typically, the alignment tolerance between layers is manipulated at 75 microns. Considering the large size of the multi-layer circuit board unit, the high temperature and humidity in the graphics conversion workshop, the dislocation stacking caused by the inconsistency of different core boards, and the interlayer positioning method, the centering control of the multi-layer circuit board is more and more difficult.
Multilayer circuit board
2. Difficulties in the manufacture of internal circuits
Multilayer circuit boards use special materials such as high TG, high speed, high frequency, thick copper, and thin dielectric layers, which put forward high requirements for internal circuit manufacturing and graphic size control. For example, the integrity of impedance signal transmission adds to the difficulty of internal circuit fabrication.
The width and line spacing are small, open and short circuits are added, short circuits are added, and the pass rate is low; there are many signal layers of thin lines, and the probability of AOI leakage detection in the inner layer is increased; the inner core board is thin, easy to wrinkle, poor exposure, and easy to curl when etching machine; The high-level plates are mostly system boards, the unit size is large, and the cost of product scrapping is high.
3. Difficulties in Compression Manufacturing
Many inner core boards and prepreg boards are superimposed, which simply presents the disadvantages of slippage, delamination, resin voids and bubble residues in stamping production. In the design of the laminate structure, the heat resistance, pressure resistance, glue content and dielectric thickness of the material should be fully considered, and a reasonable multi-layer circuit board material pressing plan should be formulated.
Due to the large number of layers, the expansion and contraction control and size coefficient compensation cannot maintain consistency, and the thin interlayer insulating layer is simple, which leads to the failure of the interlayer reliability experiment.
4. Difficulties in drilling manufacturing
The use of high TG, high speed, high frequency, and thick copper special plates increases the difficulty of drilling roughness, drilling burrs and decontamination. The number of layers is large, the total copper thickness and plate thickness are accumulated, and the drilling tool is easy to break; the CAF failure problem caused by the densely distributed BGA and the narrow hole wall spacing; the oblique drilling problem caused by the simple plate thickness. PCB circuit board
Post time: Jul-25-2022