Do you know the difficulties in the production process of PCB multilayer boards? There are many exquisite things in PCB design, whether it is design principles or device mix and match, there are strict requirements. So what are the difficulties in the factory process of multilayer boards?
PCB multilayer circuit boards are generally 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 server, medical electronics, aviation, industrial control, military and other fields. In recent years, the market demand for high-layer boards in communications, base stations, aviation, military and other fields is still strong.
The average level of PCB has become an important technical index to measure the technical level and product structure of PCB enterprises. This article briefly describes the main processing difficulties encountered in the production of high-layer circuit boards, and introduces the control points of the key production processes of multi-layer circuit boards for reference.
Compared with traditional PCB products, high-layer PCBs have the characteristics of thicker boards, more layers, dense lines, more through holes, larger unit sizes, and thin dielectric layers. The requirements for internal space, interlayer alignment, impedance control, and reliability higher.
1. Difficulties in interlayer alignment
Due to the large number of layers in high-level panels, users have higher and higher requirements for the calibration of PCB layers. Typically, 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 positioning method between layers, etc., the centering control of the high-rise board is more difficult.
2. Difficulties in making internal circuits
High-layer 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 production and graphic size control. For example, the integrity of impedance signal transmission increases the difficulty of internal circuit fabrication.
The width and line spacing are small, the open circuit and short circuit increase, the short circuit increases, and the pass rate is low; there are many thin line signal layers, and the AOI leakage detection probability of the inner layer increases; the inner core board is thin, easy to wrinkle, poor exposure, and easy to curl when etching the machine; High-level plates are mostly system boards with large unit sizes and high product scrap costs.
3. Difficulties in compression manufacturing
Many inner core boards and prepreg boards are superimposed, and defects such as slippery boards, delamination, resin voids, and air bubbles are prone to occur during stamping production. In the design of the laminated structure, the heat resistance, pressure resistance, glue content and dielectric thickness of the material should be fully considered, and a reasonable plan for pressing high-rise boards should be formulated. Due to the large number of layers, the expansion and shrinkage control and size factor compensation cannot be kept consistent, and the thin interlayer insulation layer is likely to cause the failure of the interlayer reliability test.
4. Difficulties in drilling
The use of high TG, high speed, high frequency, and thick copper special plates increases the difficulty of drilling roughness, drilling burrs and drilling dirt. The number of layers is large, the cumulative total copper thickness and plate thickness are easy to break when drilling; there are many dense BGAs, and the CAF failure problem is caused by narrow hole wall spacing; the problem of inclined drilling is easily caused by the thickness of the plate. The above are the difficulties in the production process of PCB multilayer boards
