PCB Backdrilling Stub Length Control via Electrical Detection
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Solution Overview
Problem
Conventional backdrilling methods for printed circuit boards (PCBs) face deviations in backdrilling depth due to thickness inhomogeneity, leading to increased stub length and loss in high-frequency signal transmission, as the backdrilling depth obtained from edge coupons does not accurately represent the actual depth across the PCB.
Innovation Solution
A method and apparatus that utilize a drill bit to generate electrical signals when contacting conductive layers, determining their locations and obtaining Z-coordinate information to calculate a medium thickness between these layers, allowing for precise backdrilling with a preset depth that includes a compensation value, thereby reducing the backdrilling stub length and improving signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If backdrilling depth is determined using conventional Coupon test results from PCB edge, then the measurement process is simplified, but the backdrilling depth accuracy deteriorates due to thickness inhomogeneity across the PCB
Solution Approach 1:
The patent replaces the mechanical sectioning measurement method with an electrical field-based detection method. The drill bit is equipped with a detection electrode that generates an electrical field to detect conductive layers, substituting the mechanical coupon sectioning process with an electrical field interaction method that provides real-time depth information during drilling.
Solution Approach 2:
The drill bit performs dual functions: it both drills the hole and detects the conductive layer positions simultaneously. The detection electrode integrated into the drill bit enables the drilling tool itself to measure the thickness and locate conductive layers, eliminating the need for separate coupon testing and sectioning processes.
2Productivity
If backdrilling depth is determined using pre-calculated theoretic depth, then the process efficiency is improved, but the stub length control precision deteriorates due to PCB thickness variations
Solution Approach 1:
The patent implements real-time feedback during the backdrilling process. The detection electrode continuously monitors the position of conductive layers, and the control system uses this feedback information to dynamically adjust the backdrilling depth, ensuring precise stub length control despite PCB thickness variations.
Solution Approach 2:
The detection electrode identifies the positions of conductive layers before the actual backdrilling operation begins. This preliminary detection allows the system to calculate and set the precise backdrilling depth in advance, combining the efficiency of pre-calculated methods with the accuracy of real measurements.
3Loss of energy
If PCB thickness is increased to meet high-frequency signal transmission requirements, then the signal loss is reduced, but the backdrilling depth deviation increases leading to greater stub length
Solution Approach 1:
The patent replaces conventional electrical detection methods with a magnetic field-based detection system. The detection electrode generates a magnetic field that penetrates the PCB substrate, enabling accurate detection of conductive layer positions even in thick PCBs where traditional electrical methods fail due to signal attenuation.
Solution Approach 2:
The patent changes the detection parameter from electrical field strength to magnetic field characteristics. By using magnetic field-based detection, the system can accurately measure conductive layer positions in thick PCBs without being affected by the increased thickness, thereby maintaining backdrilling precision despite the need for greater PCB thickness to reduce high-frequency signal loss.
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 enables high-precision backdrilling, reducing hole link loss in high-speed and high-frequency signal transmission by accurately determining the backdrilling depth, thus enhancing the integrity of transmitted signals.
Implementation Method 1
a drill bit of a drill performs a drilling motion from an initial location, and a drill generates a first electrical signal when contacting a first conductive layer of a printed circuit board
Data Source
AI summary
The present invention relates to a PCB drilling method including: performing a drilling motion from an initial location, and generating a first electrical signal when coming into contact with a first conductive layer of the PCB, determining a first conductive location according to the first electrical signal, and obtaining first Z-coordinate information continuing to perform the drilling motion after drilling through the first conductive layer, and generating a second electrical signal when coming into contact with a second conductive layer, determining a second conductive location according to the second electrical signal, and obtaining second Z-coordinate information; continuing to perform the drilling motion and drilling through the PCB to obtain a through hole; and performing backdrilling in the location of the through hole according to a preset depth, and the preset depth is a medium thickness between the second conductive layer and the first conductive layer plus a compensation depth.