High-level circuit boards are generally defined as 10 layers - 20 or more layers of high-layer circuit boards, which are more difficult to process than traditional multi-layer boards, and have high quality and reliability requirements, mainly used in communication equipment, high-end servers, medical electronics. , aviation, industrial control, military and other fields. In recent years, the demand for high-end boards in the fields of application communications, base stations, aviation, and military is still strong. With the rapid development of China's telecom equipment market, the high-end board market is promising.
At present, PCB manufacturers that can mass produce high-level circuit boards in China mainly come from foreign-funded enterprises or a few domestic-funded enterprises. The production of high-level circuit boards requires not only high technology and equipment investment, but also the accumulation of experience of technicians and production personnel. At the same time, the procedures for importing high-level board customers are strict and cumbersome. Therefore, high-level circuit boards enter the enterprise with high threshold and realize industrialization. The production cycle is longer.
The average number of layers of PCB has become an important technical indicator to measure the technical level and product structure of PCB companies. This paper briefly describes the main processing difficulties encountered in the production of high-level circuit boards, and introduces the control points of the key production processes of high-level circuit boards for your reference.
Main production difficulties
Compared with the characteristics of conventional circuit boards, high-level circuit boards have the characteristics of thicker plates, more layers, denser lines and vias, larger cell size, thinner dielectric layers, etc., inner space, interlayer alignment, Impedance control and reliability requirements are more stringent.
1. Difficulties in alignment between layers
Due to the high number of high-level circuit boards, the alignment of the customer's design end to the PCB layers is more and more strict. Usually, the inter-layer alignment tolerance is controlled by ±75μm. Considering the high-level board unit size design, the graphic transfer workshop environment temperature and humidity And the factors such as misalignment and interlayer positioning caused by the inconsistency of different core layers, make the interlayer alignment control of the high-rise board more difficult.
2. Difficulties in the production of inner layers
The high-rise board adopts special materials such as high TG, high speed, high frequency, thick copper and thin dielectric layer, which puts high requirements on the inner layer circuit production and graphic size control, such as the integrity of impedance signal transmission, which increases the difficulty of inner layer circuit fabrication. The line width is small, the open circuit is increased, the short is increased, the pass rate is low; the signal line of the fine line is more, the probability of the AOI leak detection is increased; the thickness of the inner core plate is thin, and the fold is easy to cause poor exposure, etching It is easy to roll when passing the machine; most of the high-rise boards are system boards, the unit size is large, and the cost of scrapping the finished product is relatively high.
3. Pressing and making difficulties
A plurality of inner core sheets and prepregs are superimposed, and defects such as sliding sheets, delamination, resin voids, and bubble residues are easily generated during press production. When designing the laminated structure, it is necessary to fully consider the heat resistance, withstand voltage, the amount of glue and the thickness of the material, and set a reasonable high-level plate pressing program. The number of layers is large, the amount of expansion and contraction control and the compensation of the size factor cannot be consistent; the interlayer insulation layer is thin, which easily leads to the failure of the interlayer reliability test.
4. Difficulties in drilling
High-level circuit boards use high-grade TG, high-speed, high-frequency, thick copper special plates, which increase the difficulty of drilling roughness, drilling burrs and drilling. The number of layers is large, the total copper thickness and plate thickness are accumulated, the drilling is easy to break the knife; the dense BGA is more, the CAF failure problem caused by the narrow hole wall spacing; the plate thickness is easy to cause the oblique drilling problem.