Stub-less Plated Through-Holes via Segmented Metallization
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Solution Overview
Problem
The increasing demand for smaller and faster electronic devices has led to the issue of unwanted conductive stubs in printed circuit boards (PCBs), which radiate noise under high-frequency applications, necessitating the removal of these stubs to improve signal integrity.
Innovation Solution
A method involving the formation of stub-less plated through-holes in PCBs, where a multilayer structure is created with insulating and conductive layers, and a secondary material layer is used to create a void within the through-holes, allowing for segmented metallization and the removal of stubs through back drilling and electroplating processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional via formation methods are used, then manufacturing process is simple, but conductive stubs remain in vias causing noise radiation
Solution Approach 1:
The via formation process is segmented into multiple distinct stages: initial via drilling, shadow layer deposition, secondary material layer deposition, selective etching to create voids, and electroplating. This segmentation allows each stage to be optimized independently, ensuring complete stub removal while maintaining manufacturing feasibility through controlled, step-by-step material addition and removal.
Solution Approach 2:
The shadow layer and secondary material layer are deposited before the electroplating stage, serving as preliminary structures that guide subsequent material deposition. The shadow layer prevents unwanted plating in certain areas, while the secondary material layer creates voids that prevent stub formation. These preliminary actions ensure that when electroplating occurs, the desired via structure is achieved without stubs.
2Reliability
If stubs are removed through back drilling, then signal integrity improves, but manufacturing precision requirements increase
Solution Approach 1:
The shadow layer acts as an intermediary barrier between the via opening and the electroplating process. It selectively allows plating in certain regions while blocking it in others, enabling precise control over the plated through-hole structure without requiring extremely precise mechanical drilling depths. The secondary material layer similarly serves as an intermediary that creates controlled voids to prevent stub formation.
Solution Approach 2:
The process utilizes changes in material properties and deposition parameters to achieve precise via structure control. By controlling the thickness and composition of the shadow layer and secondary material layer, and by adjusting electroplating parameters (current density, plating time, electrolyte composition), the via depth and stub removal are precisely controlled without relying solely on mechanical drilling precision.
3Object-affected harmful factors
If multiple layers are added to prevent stubs, then noise radiation is reduced, but device complexity increases
Solution Approach 1:
The shadow layer and secondary material layer serve multiple functions simultaneously: they act as barriers to prevent unwanted plating, create controlled voids to eliminate stubs, and guide the electroplating process to form the desired via structure. This multi-functionality reduces the need for separate dedicated layers for each purpose, thereby limiting the increase in overall device complexity while effectively reducing noise radiation.
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 effectively eliminates stubs, reducing noise interference and enhancing signal integrity in high-frequency applications, enabling the production of high-speed digital and RF-designed PCBs.
Implementation Method 1
electroplating a first conductive layer into the through-hole over the shadow layer; and electroplating a second conductive layer over the plated first conductive layer in the through-hole
Data Source
AI summary
The disclosure provides a multilayer structure for a printed wiring board (PWB). The multilayer structure may include a plurality of insulating layers interleaved with a plurality of conductive layers comprising at least one inner conductive layer. The multilayer structure may also include one or more stub-less plated through-holes through the plurality of insulating layers and the plurality of conductive layers. The multilayer structure may include at least one secondary material layer formed on the at least one inner conductive layer. The secondary material layer defines a void that creates a discontinuity in the plated through-hole to achieve segmented metallization of the plated through-hole. The disclosure also provides a method of forming the multilayer structure.