PCB Via Back Drilling to Eliminate Residual Stub Reflections

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Solution Overview

Problem

Existing back drilling methods for printed circuit boards result in signal reflection issues due to residual via plating stubs, which are difficult to detect and remove effectively, leading to signal integrity problems.

Innovation Solution

A multi-step back drilling process using varying drill angles and orientations to progressively remove via stubs, ensuring the via diameter at the top is larger than at the bottom, thereby minimizing residual stubs and reducing signal reflections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional back drilling is used to remove via stubs, then via stub removal is achieved, but residual plating remains causing signal reflection issues

Engineering Contradiction:

Improvesignal integrityVSAvoidvia stub removal completeness

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The back drilling process is segmented into multiple operations with different drill bit diameters. A first drill bit with diameter equal to the via diameter removes the majority of the via stub, while a second drill bit with smaller diameter removes residual plating. This segmentation allows complete stub removal without leaving harmful residues that cause signal reflections.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The drill bit diameter parameter is changed between drilling operations. The first operation uses a drill bit with diameter matching the via diameter (D1), and the second operation uses a smaller drill bit (D2). This parameter change enables progressive removal of via stub material, ensuring complete elimination of residual plating while maintaining signal integrity.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If larger drill bits are used to remove via stubs, then stub removal efficiency is improved, but damage to adjacent board layers increases

Engineering Contradiction:

Improvevia stub removal efficiencyVSAvoiddamage to adjacent layers

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The drilling operation is divided into two segmented steps using different drill bit sizes. The first step uses a larger drill bit (D1) matching the via diameter to efficiently remove the bulk of the via stub. The second step uses a smaller drill bit (D2) to precisely remove only the residual plating. This segmentation achieves high productivity while protecting adjacent board layers from damage.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first drilling operation performs partial removal of the via stub using a drill bit sized to remove the majority of material efficiently. The second operation completes the removal by eliminating the remaining residual plating. This partial action approach removes sufficient stub material to prevent signal reflections while avoiding excessive removal that would damage adjacent layers.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS12471215B2Printed circuit board with reduced via striping

Publication Date: 2025.11.11 DELL PROD LP

AI summary

A printed circuit board includes a dielectric material, a signal trace on a surface of the dielectric material, a signal layer within the dielectric material, a via including plating, and multiple back drill locations. The plating provides an electrical communication between the signal trace and the signal layer, and the via has a diameter. The back drill locations are along a length of the via beyond the signal layer. A first combined diameter of the back drill locations at a bottom of the back drill locations is equal to the dimeter of the via. A second combined diameter of the back drill locations at a top of the back drill locations is greater than the dimeter of the via.