PCB Optical Isolation via Nonuniform Via Catch Pads
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Solution Overview
Problem
Conventional Printed Circuit Boards (PCBs) with uniform via catch pads allow light to transmit between sides, potentially triggering sensitive light sensors and causing unwanted effects, such as increased current consumption and noise, due to the lack of effective optical isolation.
Innovation Solution
The implementation of non-uniformly sized via catch pads that overlap or interpose between metallic features in adjacent metal layers, creating an obstruction to light transmission through the PCB, thereby achieving optical isolation between the sides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform via catch pads are used in PCB, then manufacturing is simple and consistent, but light transmission between sides occurs causing sensor triggering and electromagnetic noise
Solution Approach 1:
The patent applies asymmetry by making the via catch pads non-uniform in size across different metal layers. Specifically, catch pads in outer metal layers are made larger than those in inner layers, creating an asymmetric stack that effectively blocks light transmission through the PCB while maintaining manufacturing feasibility through systematic size variation.
Solution Approach 2:
The patent implements local quality by varying the size of catch pads at different locations and layers. The catch pad size is locally optimized based on its position in the stack - larger pads at outer layers provide maximum light blocking where needed most, while inner layer pads can be smaller. This localized differentiation achieves effective optical isolation without requiring all pads to be uniformly large.
2Object-affected harmful factors
If non-uniformly sized via catch pads are used to block light transmission, then optical isolation is achieved, but manufacturing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the via catch pad structure into multiple discrete metal layers, each with its own catch pad. This segmentation allows independent sizing and optimization of each layer's catch pad while maintaining overall manufacturing consistency. The systematic approach of having predetermined size variations across layers reduces the complexity burden compared to completely custom designs.
Solution Approach 2:
The patent utilizes parameter changes by systematically varying the size parameter of catch pads across different metal layers. This controlled parameter variation achieves the desired light blocking function while maintaining manufacturing feasibility through predictable, rule-based size changes rather than arbitrary complexities.
3Object-affected harmful factors
If larger catch pads are used to obstruct light, then optical isolation improves, but PCB area and component density are reduced
Solution Approach 1:
The asymmetric catch pad design concentrates the light-blocking function at outer layers where larger pads are placed, while inner layers use smaller pads. This asymmetric distribution achieves effective optical isolation without requiring all pads to be large, thereby preserving more PCB area for other components and traces compared to a uniform large-pad design.
Solution Approach 2:
Local quality optimization allows catch pads to be sized appropriately for their specific function and location. Outer layer pads are locally enlarged to provide maximum light blocking, while inner layer pads are locally reduced in size since they contribute less to light transmission blocking. This localized sizing achieves the required optical isolation with minimal impact on overall PCB area utilization.
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 design effectively reduces the transmission of light through the PCB, minimizing unwanted triggering of light sensors and electromagnetic noise, while allowing the use of inexpensive solder masks and enhancing electromagnetic shielding.
Implementation Method 1
The non-uniformly sized via catch pads may thus provide an obstruction to the transmission of light through otherwise transmissive dielectric regions of the PCB around the via
Data Source
AI summary
A Printed Circuit Board (PCB) includes a via extending through at least one layer of the PCB. The PCB may also include a first catch pad connected to the via and located within a first metal layer of the PCB. The first catch pad may have a first size. The PCB may further include a second catch pad connected to the via and located within a second metal layer of the PCB. The second catch pad may have a second size greater than the first size. The second catch pad may overlap horizontally with a portion of a metallic feature in the first metal layer to obstruct light incident on a first side of the PCB from transmission to a second side of the PCB through a region of dielectric material near the via.