Optical Module Flexible PCB Ground Pad Stacking
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Solution Overview
Problem
The existing optical modules with flexible printed circuit boards experience deterioration in frequency characteristics due to uneven soldering and wider board dimensions, leading to worsened workability and frequency performance.
Innovation Solution
The optical module design includes a flexible printed circuit board with an insulating substrate having a first and second surface, where the first wiring pattern features a signal line with ground pads positioned close to the signal-line portion, and the second wiring pattern includes a ground plane overlapping with the signal-line portion, ensuring stable ground and reduced electromagnetic radiation, while maintaining desired impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If pads are arranged in a horizontal row for electrical connection, then the flexible printed circuit board becomes wider, but the workability of soldering worsens and bonding becomes uneven
Solution Approach 1:
The patent transitions from a conventional horizontal row arrangement of pads to a three-dimensional stacked configuration where signal pads and ground pads are positioned on different layers. This vertical dimensionality change allows the circuit board to maintain compact width while achieving proper soldering workability through optimized pad positioning in the vertical direction.
Solution Approach 2:
The patent applies different pad configurations to different functional requirements: signal pads are positioned on the first surface for electrical connection, while ground pads are positioned on the second surface in a stacked arrangement. This local differentiation of pad qualities and positions optimizes both soldering workability and electrical performance without requiring increased board width.
2Area of stationary object
If pads are made thinner to reduce board width, then the board becomes narrower, but soldering workability worsens leading to uneven bonding
Solution Approach 1:
Instead of reducing pad thickness horizontally, the patent positions ground pads on the second surface directly below or adjacent to signal pads on the first surface, creating a vertical stacking arrangement. This maintains adequate pad dimensions for soldering while reducing the horizontal footprint of the circuit board.
3Reliability
If ground pads are positioned close to the signal-line portion, then frequency characteristics improve, but electromagnetic radiation and cross-talk increase
Solution Approach 1:
The patent positions ground pads on the second surface in vertical proximity to signal pads on the first surface, creating a three-dimensional grounding structure. This vertical arrangement provides effective ground reference for high-frequency signals while the stacked configuration naturally contains electromagnetic fields, reducing radiation and cross-talk compared to horizontal arrangements.
Solution Approach 2:
The ground pads are positioned to surround or enclose the signal-line portion in a nested configuration, with ground pads on both surfaces creating a shielded environment for the signal transmission path. This nested grounding structure improves frequency characteristics while containing electromagnetic radiation.
Data Source
AI summary
An optical module includes a photoelectric device and a flexible printed circuit board. The flexible printed circuit board includes an insulating substrate with a first surface and a second surface, a first wiring pattern on the first surface, and a second wiring pattern on the second surface. The first wiring pattern includes a signal line with a signal terminal portion at a tip and a signal-line portion narrower than the signal terminal portion, the first wiring pattern including a pair of ground pads at positions sandwiching the signal-line portion, at least part of the pair of ground pads avoiding being adjacent to the signal terminal portion. The second wiring pattern includes a ground plane overlapping with the signal-line portion and being connected to the pair of ground pads, the second wiring pattern including a signal pad connected to the signal terminal portion.