Via Hole Impedance Adjustment in Multilayer PCB Ground Layers
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Solution Overview
Problem
The through via hole in multilayer printed wiring boards tends to have lower impedance due to being surrounded by solid conductors of the ground layers, leading to impedance mismatch issues.
Innovation Solution
The multilayer printed wiring board design includes a via hole with a first land inside the wiring layer opening and second lands inside the impedance adjustment layer openings, where the distance from the solid conductor to the via hole is greater than from the wiring layer to the via hole, and recesses in the second lands facilitate impedance adjustment, allowing the via hole to have increased impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the through via hole is surrounded by solid conductors of the ground layers, then the via hole is well grounded and shielded, but the impedance of the via hole decreases
Solution Approach 1:
The patent applies local quality by creating different distance relationships between the via hole and solid conductors at different locations. Specifically, the distance from the via hole to the solid conductor in the first direction is made different from the distance in the second direction, creating asymmetric local characteristics that increase via hole impedance while maintaining grounding and shielding effectiveness.
Solution Approach 2:
The patent changes the geometric parameters of the via hole structure by adjusting the distances to surrounding solid conductors in different directions. This parameter modification directly increases the via hole impedance to match the characteristic impedance of conductive lines, thereby reducing impedance mismatch and improving signal transmission quality.
2Object-affected harmful factors
If the distance from the solid conductor to the via hole is increased, then the via hole impedance increases, but the grounding effectiveness may be reduced
Solution Approach 1:
The patent maintains grounding effectiveness by ensuring that solid conductors are still present around the via hole, but optimizes the local distance relationships. By making the distance in the first direction different from the distance in the second direction, the patent achieves impedance increase while preserving the shielding and grounding functions through the remaining close proximity of solid conductors in other directions.
Data Source
Figure 1A~1B
Figure 1C
Figure 2~3
AI summary
The invention provides a multilayer printed wiring board with a via hole of increased impedance. A multilayer printed wiring board P includes ground layers L1 and a via hole V1. The ground layers L1 include a wiring layer L11 and a first impedance adjustment layer L12. The wiring layer L11 includes a solid conductor L111 having an opening L112 and a passage L113, and a conductive line L114 is provide inside the opening L112 and the passage L113. The adjustment layer L12 includes a solid conductor L121 with an opening L122. The via hole V1 is provided in the ground layers L1 and the insulating layers L2 such that the via hole V1 is located inside the opening L112 and the opening L122 and connected to the conductive line L114. The distance R1 is smaller than the distance R2, where the distance R1 is the distance in the Y-Y' direction from the outline α1 of the opening L112 to the via hole V1, and the distance R2 is the distance in the Y-Y' direction from the outline α2 of the opening L122 to the via hole V1.