1. Symmetrical structure of the single flexible board
Conventional structure, with a single flexible board in the middle of the stack.
Advantages: partial cover film pressing, good pressing bonding force, good process realization, good transparency, and uniformity of the inner layer. Good bending performance.
2. Laminating and stacking multiple flexible boards
The flexible boards are pressed with pure glue, which requires two pressings, one with pure glue, and one with PP after combining with the rigid board. Two pressings require different pressing auxiliary materials. Same, the conditional parameters are different.
Advantages: Multi-layer wiring of the flexible board increases the wiring space of the flexible board layer.
Process difficulties: different dielectric layers have an impact on the quality of the drilling, and the complexity of the two-time pressing process increases. The thickness of the flexible board is increased, and the bending effect is improved.
3.HDI structure
Laser blind hole + hole filling, HDI process, multiple pressing, NF PP and flow glue PP mixed press process
Advantages: increase product integration.
Process difficulties: multiple pressing, laser blind holes, PLASMA removal of glue, hole filling process. HDI process is long.
4. Book structure
Asymmetric pressing of multiple flexible boards.
Advantages: There are many layers of flexible board wiring, which can reach 12 layers, the wiring space of the flexible board is increased, the air gap structure between the flexible board, and the bending effect of the flexible board assembly is optimized.
Process difficulties: the length of the flexible board is different, the pressing fixture is pressed, the circuit is pressed, the etching is affected, and the process flow is complicated.
5. Flying tail structure
Two electroplatings, flexible board electroplating, using black hole + VCP process; rigid board electroplating using sinking copper + pattern electroplating.
Advantages: The flexible board has a plug-in finger design, which is convenient for plugging and conducting. The process of opening the lid is to first open the lid to leak the golden fingers and then immerse the gold together with the rigid board.
6. Asymmetric structure from top to bottom
The flexible board is located on the outer layer.
Advantages: It can meet the design and special bending of the outer flexible board.
Process difficulty, GAP filling design after opening the PP window on the flexible surface, flatness after pressing. Outer flexible board cover film + solder mask process, flexible board ink application.
7. Left and right asymmetric structure
Rigid board thickness is absolute.
Advantages: It can meet different layers of wiring in the rigid board area, and the design of different assembly thicknesses of the rigid board.
Process difficulties, two rigid board pressing, drilling, solder mask, two different depth mechanical control depth opening. The thin area of the rigid board needs to be electroplated, circuit, solder mask, and then external pressure bonding process, different areas, different depths of mechanical control depth opening process.
8. Unilateral asymmetric structure
The rigid board has two or more welding surfaces and two or more bending areas to meet the requirements of three-dimensional assembly.
Advantages: Each sub-rigid board welding area has pressing, drilling, electroplating, wiring, solder mask, opening process, and surface treatment. After finishing pressing together, the outer layer still needs the same process, the process is extremely complicated, and it is designed for industrial, military, and aerospace applications.
