Manufacturing Process of multilayer FPC
The production of multilayer flexible printed circuit boards (PCBs) involves a precise and intricate process to ensure reliability and performance. The FPCs are in applications like consumer electronics, medical devices, and aerospace systems.
Below is a summarized workflow for multilayer flexible printed circuit boards:
Material Preparation
The process begins with selecting a flexible substrate, typically polyimide or polyester, due to its heat resistance and mechanical durability. Copper foil is laminated onto the substrate using adhesives or adhesiveless methods (e.g., sputtering). For multilayer designs, inner layers are pre-etched with circuit patterns via photolithography: photoresist is applied, exposed to UV light through a mask, and chemically etched to remove unwanted copper.
Layer Stacking and Lamination
Multiple layers (single/double-sided flex circuits) are aligned and bonded under high temperature (170–200°C) and pressure (200–400 psi) using prepreg (B-stage resin) as an adhesive. Critical steps include “black oxidation” or “browning” of inner copper layers to enhance adhesion and prevent delamination.
Drilling and Plating
Microvias and through-holes are drilled mechanically or with lasers, followed by copper plating to establish interlayer connections. Advanced techniques like laser drilling ensure precision for high-density designs.
Outer Layer Processing
Outer circuits are patterned and etched, similar to inner layers. A protective coverlay (polyimide film) or solder mask is laminated to insulate traces, with openings for solder pads. Stiffeners (e.g., FR4) may be added to reinforce specific areas.
Testing and Finishing
Electrical tests verify continuity, followed by surface finishing (e.g., ENIG) to prevent oxidation. Final inspection ensures quality before singulation.
This streamlined process balances flexibility and complexity, enabling compact, high-performance multilayer flexible printed circuit boards.
