Microstrip Grounding Structure for Low-Inductance High-Frequency PCBs
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Solution Overview
Problem
High frequency circuit boards experience degradation in characteristics at several GHz or more due to increased ground inductance when using through-holes in thick dielectric substrates for grounding, which also leads to mechanical weakness and warping.
Innovation Solution
A grounding structure for high frequency circuit boards featuring a dielectric substrate with a through-hole having a smaller opening on one surface and a larger opening on the opposite surface, connected to a grounding conductor layer, a back surface ground electrode, and a microstripline upper electrode with varying line widths to reduce ground inductance and improve high frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the dielectric thickness is increased to reduce warping, then the mechanical strength is improved, but the ground inductance increases and high frequency characteristics degrade
Solution Approach 1:
The grounding structure is segmented into multiple functional layers: a first grounding conductor layer in the through-hole, a back surface ground electrode, and an upper ground electrode. This segmentation allows each layer to contribute differently to mechanical support and electrical grounding, enabling the dielectric substrate to maintain both strength and low inductance at high frequencies.
Solution Approach 2:
The invention transitions from a simple planar ground connection to a three-dimensional multi-layer grounding structure. The upper ground electrode extends toward the signal transmission layer, creating a vertical dimension that reduces ground inductance while the thick dielectric substrate maintains mechanical strength, thus resolving the contradiction between mechanical strength and high frequency performance.
2Strength
If a through-hole grounding structure is used in a thick dielectric substrate, then mechanical strength is improved, but ground inductance increases at high frequencies
Solution Approach 1:
The upper ground electrode acts as an intermediary element that bridges the back surface ground electrode and the signal transmission layer. This intermediary structure provides a low-inductance ground path for high frequency signals while the thick dielectric substrate continues to provide mechanical strength, thus eliminating the harmful effect of high ground inductance.
Solution Approach 2:
The grounding structure implements local quality optimization by concentrating the low-inductance ground path in the upper ground electrode region where high frequency signals are present, while the thick dielectric substrate maintains its mechanical strength function. This localized optimization allows different regions to perform their specialized functions without compromising overall performance.
Data Source
Figure 1A~1C
Figure 2A~2B
Figure 3A~3C
AI summary
A grounding structure of the high-frequency circuit board includes a dielectric substrate, a back surface ground electrode, an upper ground electrode, and a microstripline upper electrode. The dielectric substrate has a first surface and a second surface, and is provided with a first through-hole. A first opening of the first through-hole at the first surface is smaller than a second opening of the first through-hole at the second surface. A first grounding conductor layer is provided in the first through-hole. The back surface ground electrode is provided at the second surface and is connected with the first grounding conductor layer. The upper ground electrode is provided at the first surface and is connected with the first ground conductor layer. The microstripline upper electrode is provided at the first surface.