Multilayer PCB Optical Path Protrusion Design

The patent applies local quality by forming conductor circuits with different configurations in different regions: in regions close to optical paths, conductor circuits are formed with increased line width or as ground patterns to reduce electromagnetic interference, while in other regions standard conductor circuits are used. This localized adaptation allows efficient space utilization near optical paths while maintaining optical signal transmission reliability through reduced interference.

The patent applies preliminary action by forming a flatting layer between the outermost insulating layer and the optical path protrusion region. This flatting layer is formed in advance to compensate for surface irregularities and prevent waviness from propagating to the optical path surface. By preparing the surface beforehand, the optical path can protrude for improved optical coupling while maintaining manufacturing precision and surface flatness.

The patent applies parameter changes by carefully selecting and optimizing the composition and thickness parameters of the solder resist layer. The solder resist layer is formulated with specific resin compositions and controlled thickness (typically 5-20 μm) to achieve sufficient optical transmittance for optical signal transmission while maintaining adequate adhesive force to prevent layer separation. This parameter optimization allows the solder resist layer to fulfill both optical and mechanical requirements.