Multilayer PCB Via Impedance Matching Without Back Drilling
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Solution Overview
Problem
Conventional impedance matching designs in multilayer circuit boards face challenges in maintaining consistent characteristic impedance, leading to signal reflection and poor connection issues due to over or under drilling of stub portions, affecting high-frequency signal transmission quality and product yield.
Innovation Solution
The proposed impedance matching structure incorporates redundant conducting sections and grounding members in a capacitor structure, with the redundant conducting sections coupled to the transmission line and grounded conducting sections surrounding them, to achieve impedance matching through parasitic effects across multiple layers of the multilayer circuit board.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If back drilling is used to remove stub portions, then signal reflection is reduced, but manufacturing precision deteriorates due to over drilling or insufficient drilling
Solution Approach 1:
The patent applies preliminary action by pre-forming conductive plugs within the plating holes before final assembly. These plugs are positioned at controlled depths and serve as predetermined impedance matching structures, eliminating the need for post-manufacturing back drilling operations. The conductive plugs are inserted and secured in advance, ensuring precise positioning without requiring subsequent removal of stub portions.
Solution Approach 2:
The patent extracts the problematic stub portions by replacing them with conductive plugs of optimized length and positioning. Instead of removing material through back drilling, the solution extracts the harmful stub effect by substituting it with a precisely controlled conductive element that provides the desired impedance transformation without requiring material removal.
2Reliability
If characteristic impedance matching is prioritized, then signal transmission quality improves, but device complexity increases due to multiple design considerations
Solution Approach 1:
The patent applies parameter changes by systematically varying key parameters of the conductive plugs including their length, diameter, material composition, and positioning within the plating holes. By adjusting these parameters, the invention achieves impedance matching across different frequency ranges and transmission requirements, providing a flexible solution that adapts to various design needs without increasing overall structural complexity.
Solution Approach 2:
The patent applies local quality by implementing impedance matching structures at specific locations along the transmission path where impedance discontinuities occur. Rather than uniformly complexizing the entire transmission line, the invention places targeted conductive plugs only at critical interfaces and transition points, maintaining simplicity in non-critical sections while achieving overall impedance matching.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively adjusts the impedance values of the transmission line, ensuring consistent characteristic impedance and improving signal transmission quality, while avoiding issues of poor connection and local stub residuals, thus enhancing the yield and reducing costs.
Implementation Method 1
at least one grounding member, which is disposed adjacent to but separated from either or both of the conductive member of the transmission line and the at least one redundant conducting section in a capacitor structure for impedance matching
Data Source
AI summary
An impedance matching structure is disposed on a multilayer circuit board for matching an impedance of a transmission line for transmitting an electronic signal. At least one redundant conducting section is coupled to a conductive member of the transmission line between input and output terminals of the transmission line. The conductive member and the redundant conducting section are disposed in a corresponding plating hole. At least one grounding member disposed adjacent to but separated from either or both of the conductive member of the transmission line and the at least one redundant conducting section in a capacitor structure for impedance matching. The at least one grounding member includes a first grounding member penetrating through at least two layers of the multilayer circuit board.