The Introduction Of 8 Layer Enig Fr4 Multilayer PCB

 

1. The difficulty of interlayer alignment

Because of the many layers of multilayer PCB board, the calibration requirement of PCB layer is higher and higher. Typically, alignment tolerance between layers is controlled at 75um. It is more difficult to control the alignment of multilayer PCB board because of the large size of the unit, the high temperature and humidity in the graphics conversion workshop, the dislocation overlap caused by the inconsistency of different core boards, and the positioning mode between layers.

2. The difficulty of inner circuit production

The multilayer PCB board adopts special materials such as high TG, high speed, high frequency, heavy copper, thin dielectric layer and so on, which puts forward high requirements for inner circuit production and graphic size control. For example, the integrity of impedance signal transmission increases the difficulty of inner circuit fabrication. The width and line spacing are small, the open circuit and short circuit increase, the pass rate is low; with more thin line signal layers, the inner AOI leakage detection probability increases. The inner core plate is thin, easy to wrinkle, poor exposure, easy to curl etching; multilayer PCB is mostly system board, which has larger unit size and higher scrap cost.

3. Difficulties in lamination and fitting manufacturing

Many inner core boards and semi-cured boards are superimposed, which are prone to defects such as slide plate, lamination, resin void and bubble residue in stamping production. In the design of laminated structure, the heat resistance, pressure resistance, glue content and dielectric thickness of the material should be fully considered, and a reasonable material pressing scheme of multilayer plate should be made. Due to the large number of layers, the expansion and contraction control and size coefficient compensation are not consistent, and the thin inter-layer insulating layer is easy to lead to the failure of inter-layer reliability test.

4. Drilling production difficulties

The use of high TG, high speed, high frequency, thick copper special plate increases the drilling roughness, drilling burr and drilling stain removal difficulty. Many layers, drilling tools are easy to break; CAF failure caused by dense BGA and narrow hole wall spacing is easy to lead to inclined drilling problem due to PCB thickness.