Segmented Via Trimming for PCB Signal Integrity
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Solution Overview
Problem
Existing methods for forming through holes in printed circuit boards (PCBs) result in excessive conductive material, leading to signal distortion and increased costs due to the 'stub effect' and limitations in backdrilling processes, which are inaccurate and time-consuming, especially when dealing with multiple stubs and complex designs.
Innovation Solution
A method involving dual diameter through hole edge trimming, where a first hole is drilled followed by a second hole of larger diameter, forming a ledge, and then electroless and electrolytic copper plating is applied, with excess material trimmed using laser ablation or mechanical drills to create electrically isolated segmented via structures, reducing unnecessary conductive material and improving signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single large diameter hole is drilled for through hole formation, then the manufacturing process is simple, but excessive conductive material is formed causing stub effect and signal distortion
Solution Approach 1:
The through hole is divided into multiple segments by drilling holes of different diameters at different depths. A first hole is drilled with a first diameter, then a second hole is drilled within the first hole with a second diameter that is larger, creating a ledge. This segmentation prevents continuous conductive material formation and eliminates the stub effect while maintaining manufacturing feasibility.
2Reliability
If backdrilling is used to remove stubs, then signal integrity is improved, but the process is inaccurate and time-consuming
Solution Approach 1:
The ledge is created in advance during the drilling process itself, before copper plating occurs. The dual diameter hole structure is formed beforehand to prevent excess conductive material formation, eliminating the need for subsequent backdrilling operations and reducing production time while maintaining signal integrity.
3Manufacturing precision
If sequential processing is used for via structures with short stubs, then manufacturing precision is improved, but costs increase substantially
Solution Approach 1:
The hole drilling and ledge formation operations are merged into a single integrated process. By drilling the second hole within the first hole to create the ledge structure, the patent combines multiple functions into one operation, achieving precise via structure formation without requiring sequential processing steps, thereby reducing complexity and cost.
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 approach effectively minimizes signal degradation and increases PCB density by electrically isolating conductive material, reducing production time and costs compared to traditional sequential lamination processes, while maintaining reliability and accuracy.
Implementation Method 1
applying an electroless copper to an inner surface of the first hole and the second hole
Implementation Method 2
applying an electrolytic copper to the inner surface of the first hole and the second hole
Implementation Method 3
trimmed using laser ablation
Data Source
AI summary
Cost effective and efficient methods to maximize printed circuit board (PCB) utilization with minimized signal degradation are provided. The methods include electrically isolating a segmented via structure by controlling the formation of a conductive material within a plated via structure by utilizing different diameter drills within a via structure for trimming the conductive material at the via shoulder (i.e., the rim of a drilled two diameter hole boundary). The trimmed portion may be voided in the via structure for allowing electrically isolated plated through-hole (PTH) segments. One or more areas of trimmed rims within the via structure are used to form multiple stair like diameter holes to create one or more voids in the via structure. As a result, the formation of conductive material within the via structure may be limited to those areas necessary for the transmission of electrical signals.