Flexible Printed Circuit Signal Terminal Width for High-Frequency Integrity
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Solution Overview
Problem
High-frequency characteristics deteriorate at the connection portion between the connection terminal and the transmission line in flexible printed circuits used as a connection interface with external electric circuits due to differences in electric field profiles between the terminal and transmission line structures.
Innovation Solution
The flexible printed circuit design includes signal and ground electrodes on opposing surfaces, with signal terminals on both surfaces connected via holes, where the signal terminal width on the ground electrode surface is narrowed towards the transmission line side to align electric field profiles, reducing signal terminal influence and enhancing high-frequency performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If signal terminals are formed on both surfaces of the flexible printed circuit with standard width, then soldering workability is improved, but high-frequency characteristics deteriorate due to electric field profile mismatch
Solution Approach 1:
The patent applies local quality by making the signal terminal width non-uniform: the width at the connection portion (where it connects to the transmission line) is made narrower than the width at the soldering portion. This local variation in width allows the terminal to have different characteristics at different locations - a narrow width at the connection end to match the transmission line's electric field profile and reduce signal influence, while maintaining a wider width at the soldering end for good soldering workability.
2Device complexity
If the connection terminal structure is made similar to coplanar line, then manufacturing is simplified, but high-frequency signal integrity deteriorates due to electric field distribution differences
Solution Approach 1:
The patent applies parameter changes by modifying the width parameter of the signal terminal along its length. Specifically, the width is changed from a constant value to a variable value that is narrower at the connection end and wider at the soldering end. This parameter change allows the terminal to transition smoothly between the coplanar line structure (for manufacturing simplicity) and a structure that better matches the transmission line's electric field profile (for high-frequency signal integrity).
Data Source
AI summary
A transmission line has a signal electrode formed on one surface of a flexible printed circuit, and a ground electrode formed on the other surface of the flexible printed circuit. A connection terminal has signal terminals formed on both the surfaces of the flexible printed circuit and electrically connected to each other through a via hole, and ground terminals formed on both the surfaces of the flexible printed circuit and electrically connected to each other through the via hole. The signal terminal on the surface, on which the ground electrode is formed, is formed such that at least a width in an end portion on the transmission line side is narrower than a width of a part of the signal terminal on the surface, on which the signal electrode is formed, to be at the same position when the flexible printed circuit is seen in a plan view.