Double Back-Drilled PCB Vias for mmWave Phased Array Routing
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Solution Overview
Problem
The development of mmWave phased array antennas for 5G radio technology faces challenges in manufacturing due to the complexity of transition structures, particularly vias, between layers in printed circuit boards (PCBs), which are difficult to produce accurately and cost-effectively, especially with high layer counts and fine pitch ball grid array packages.
Innovation Solution
The mmWave phased array antenna employs interconnected back-drilled vias with prepreg buildup layers and microvias to form electrical connections between beamforming ICs and radiating elements, allowing for precise impedance matching and cost-effective high-volume manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional PCB fabrication methods with plated through hole vias and microvias are used for high layer count structures, then trace routing capability is improved, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The via structure is segmented into two parts: a plated through hole via for coarse routing and an additional microvia layer for fine pitch routing. This segmentation allows each via type to perform its specialized function, achieving both coarse and fine routing capabilities without requiring all vias to be complex microvias, thereby reducing overall manufacturing complexity while maintaining versatility
Solution Approach 2:
The microvia is positioned within or adjacent to the plated through hole via structure, creating a nested arrangement where the fine pitch microvia routes are integrated with the coarser PTH via structure. This nesting allows the combination of both via types to work together in a compact configuration, achieving complex routing patterns without proportionally increasing fabrication complexity
2Ease of manufacture
If plated through hole vias are used for all connections in high layer count PCBs, then manufacturing process is simplified, but fine pitch ball grid array routing becomes challenging or impossible
Solution Approach 1:
Different via types are applied locally to different routing requirements: plated through hole vias are used for general-purpose coarse routing where larger tolerances are acceptable, while microvias are used locally at fine pitch BGA locations where high precision is required. This local differentiation allows the manufacturing process to achieve high precision where needed without applying complex microvia fabrication everywhere, thus maintaining ease of manufacture overall
3Manufacturing precision
If microvias are used throughout the PCB structure for fine pitch routing, then routing precision is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The via system is segmented into PTH vias for general routing and microvias specifically for fine pitch areas, allowing precision to be achieved only where required rather than uniformly across the entire PCB. This selective application of microvias reduces material costs and fabrication complexity while maintaining the necessary routing precision for fine pitch BGAs
Data Source
AI summary
A mmWave antenna that has particular application to be used in a 5G radio. The antenna includes a RGB structure having a plurality of layers. The RGB structure includes a first via hole formed into the layers through one side of the RGB structure and filled with a first via and a second via hole formed into the layers through an opposite side of the RGB structure and filled with a second via, where the first and second vias are electrically coupled by an interconnect. Prepreg buildup layers are formed on the one side of the PCB structure and prepreg buildup layers are formed on the opposite side of the PCB structure. A beamforming IC is formed on the prepreg buildup layers on the one side of the PCB structure and an antenna radiating element is formed on the prepreg buildup layers on the opposite side of the PCB structure.