PCB Registration Coupon for Backdrill-to-Metal Clearance
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Solution Overview
Problem
Existing registration systems for printed circuit boards (PCBs) face challenges in achieving precise alignment of drills relative to inner layers due to layer-to-layer tolerances, which can lead to reduced backdrill-to-metal distances and increased risk of conductive anodic filament (CAF) growth.
Innovation Solution
A registration system utilizing a coupon with a plurality of cutouts based on a chirp waveform or Barker sequence, which allows for robust autocorrelation and accurate alignment in noisy environments, enabling precise registration of drills relative to inner layers of PCBs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional registration systems are used for PCB drilling, then the process is simple, but the alignment precision is insufficient due to layer-to-layer tolerances
Solution Approach 1:
The patent introduces a registration coupon as an intermediary element with known geometric patterns (circles, squares, or grids) that serves as a reference marker between the drilling system and the PCB inner layer. This coupon contains features that can be precisely detected by the imaging system, enabling accurate registration despite layer-to-layer tolerances in the PCB manufacturing process.
Solution Approach 2:
The patent replaces mechanical alignment methods with an optical imaging and image processing system. A light source illuminates the registration coupon, and a camera captures images of the coupon features. Image processing algorithms then determine the precise position and orientation of the coupon relative to the PCB, enabling accurate drill registration without complex mechanical alignment mechanisms.
2Manufacturing precision
If layer-to-layer tolerances are present in PCB manufacturing, then manufacturing is feasible, but backdrill-to-metal clearance is reduced
Solution Approach 1:
The patent performs preliminary registration by first imaging the registration coupon and calculating its precise position and orientation before initiating the drilling process. This preliminary action establishes an accurate reference frame that compensates for layer-to-layer tolerances, allowing the drilling system to compensate for manufacturing variations and achieve precise backdrill-to-metal clearance.
3Reliability
If registration accuracy is improved, then CAF growth risk is reduced, but the complexity of the registration process increases
Solution Approach 1:
The registration coupon is designed with self-aligning features that automatically provide registration information when imaged. The coupon's geometric patterns (circles, squares, or grids) create distinct image signatures that can be automatically detected and processed by algorithms, eliminating the need for complex manual alignment procedures or additional calibration steps.
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 proposed solution enhances the accuracy of backdrill to power plane registration, maximizing backdrill-to-metal clearance and reducing the risk of CAF growth, while also allowing for smaller antipads and potentially eliminating the need for resin fill.
Implementation Method 1
projecting light through the plurality of cutouts
Data Source
AI summary
In one or more embodiments, a coupon with a plurality of cutouts based on a chirp waveform may be used to align a drilling machine to a PCB. Light may be passed through the coupon and a camera may capture the light. A processor may perform zero padding, calculate a two-dimensional (2D) fast Fourier transform (FFT) of the image, multiply by a pre-calculated complex conjugate 2D FFT of the coupon, then calculate a cross correlation based on an inverse 2D FFT. Embodiments may find the best fitting coordinates of the peaks and use the coordinate as a correction factor for referencing a drilling machine to ensure drills are centered and/or aligned relative to power plane pads or antipads.