PCB Back-Drilled Hole Structure for Stub-Free High-Speed Signals
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Solution Overview
Problem
Existing PCB designs face challenges in achieving higher signal transmission rates due to the presence of back-drilled stubs, which increase transmission loss and hinder the development of PCBs beyond 224Gbps.
Innovation Solution
A method involving physical and chemical means to form back-drilled holes, specifically forming a first back-drilled hole and then using etching to create a second back-drilled hole that removes the stub, thereby reducing signal loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional PCB design with plated through holes is used, then manufacturing simplicity is maintained, but back-drilled stubs remain causing signal loss
Solution Approach 1:
The hole structure is segmented into three distinct types: plated through holes for complete penetration, first back-drilled holes extending only to the first dielectric layer, and second back-drilled holes created through etching. This segmentation allows each hole type to serve its specific function optimally, with the stub portion isolated and removed in the second back-drilled hole, thereby reducing signal loss while maintaining manufacturing feasibility
Solution Approach 2:
The harmful back-drilled stub portion is extracted and removed from the first dielectric layer by creating a second back-drilled hole through etching. This extraction eliminates the source of signal loss and reflection, allowing the plated through hole to function effectively for high-speed signal transmission without the detrimental stub extension
2Reliability
If back-drilled stubs are removed completely, then signal quality improves, but manufacturing process complexity increases
Solution Approach 1:
The first back-drilled holes are formed in advance during the drilling process before the etching step, extending to the first dielectric layer to establish the correct depth boundary. This preliminary action prepares the structure for the subsequent etching process that creates the second back-drilled hole, ensuring precise stub removal while maintaining manufacturing efficiency through process sequencing
Solution Approach 2:
The first dielectric layer serves as an intermediary medium that contains the second back-drilled hole created by etching. This intermediary structure allows the stub removal process to be performed chemically rather than mechanically, improving precision and reducing manufacturing complexity while ensuring complete stub elimination for enhanced signal transmission quality
3Speed
If higher signal rates like 224Gbps are targeted, then transmission speed improves, but existing PCB designs fail due to stub effects
Solution Approach 1:
Different hole regions are assigned different qualities and functions: plated through holes provide complete electrical connection, first back-drilled holes are precisely controlled to extend only to the first dielectric layer with specific depth, and second back-drilled holes are created with exact dimensions through etching to remove only the stub portion. This local quality differentiation ensures high-precision signal transmission paths for 224Gbps and higher rates while maintaining manufacturing feasibility
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
The method effectively reduces signal loss by 25% to 30% and improves signal quality by eliminating back-drilled stubs, enabling PCBs to operate at higher speeds.
Implementation Method 1
forming a second back-drilled hole in the first dielectric layer by etching to remove the back-drilled stub
Data Source
Figure 1~3a
Figure 3b~3d
Figure 3e~3g
AI summary
Provided in the present disclosure is a preparation method for a printed circuit board, the preparation method comprising: forming a layer structure body comprising a plated-through hole, wherein the plated-through hole penetrates through the layer structure body; forming a first back-drilling hole at the position, corresponding to the plated-through hole, of one side of a first surface of the layer structure body, wherein the first back-drilling hole extends to a first dielectric layer of the layer structure body, and the plated-through hole forms a back-drilling stub in the first dielectric layer; and forming a second back-drilling hole in the first dielectric layer by means of etching so as to remove the back-drilling stub, wherein one end of the second back-drilling hole is connected to the first back-drilling hole, and the other end of the second back-drilling hole is connected to the plated-through hole. Further provided in the present disclosure are a printed circuit board and an electronic device.