Via Stub Termination Pad for PCB Resonance Control

Solution Overview

Problem

The resonance of unused via stubs in printed circuit boards affects signal integrity as transmission frequencies increase, and existing methods like backdrilling are costly and inefficient.

Innovation Solution

A termination pad is added to the end of the via stub, and optionally along its length, to increase the effective impedance and shift the resonant frequency away from communication frequencies, using a method that determines the pad size based on the via stub length and signal frequencies.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If backdrilling or counter boring is used to remove via stub resonance, then signal integrity is improved, but manufacturing cost significantly increases

Engineering Contradiction:

Improvesignal integrityVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent extracts the harmful resonant portion of the via stub by backdrilling or counterboring to remove or shorten the unused via portion, thereby eliminating the antenna effect and resonance issues while maintaining via connectivity between layers

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces an intermediary structure (such as a via fence, via stub termination, or resistive material) to mitigate the resonance effect of the via stub without completely removing it, providing a cost-effective alternative to full backdrilling

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If backdrilling or counter boring is used to remove via stub resonance, then signal integrity is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvesignal integrityVSAvoidmanufacturing process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts the harmful resonant portion of the via stub by backdrilling or counterboring to remove or shorten the unused via portion, thereby eliminating the antenna effect and resonance issues while maintaining via connectivity between layers

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces an intermediary structure (such as a via fence, via stub termination, or resistive material) to mitigate the resonance effect of the via stub without completely removing it, providing a simpler manufacturing alternative to full backdrilling

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If via stub is left unused without treatment, then manufacturing cost is reduced, but resonance occurs at transmission frequencies

Engineering Contradiction:

Improvemanufacturing costVSAvoidresonance

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful via stub resonance into a beneficial or neutral element by treating the via stub with resistive material, grounding, or termination structures that dissipate or control the resonance energy, transforming the problem into a solution

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent introduces an intermediary structure (such as a via fence, via stub termination, or resistive material) to mitigate the resonance effect of the via stub without completely removing it, providing a cost-effective alternative to full backdrilling

Inventive Principle:

Principle #24Intermediary (Mediator)

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 reduces or eliminates resonance issues in printed circuit boards, enhancing signal integrity without significantly increasing manufacturing costs.

Implementation Method 1

A via stub 8 may act as an antenna, and thus may resonate at frequencies (and harmonics thereof) for which the length of via stub 8 is equal to one-quarter of the wavelength of such frequencies.

Methodology Applied

Scientific EffectResonance: Resonance

Implementation Method 2

A termination pad is added to the end of the via stub, and optionally along its length, to increase the effective impedance and shift the resonant frequency away from communication frequencies

Methodology Applied

Scientific EffectImpedance: Electrical Impedance Tomography

Data Source

PatentUS10605585B2Systems and methods for frequency shifting resonance of an unused via in a printed circuit board

Publication Date: 2020.03.31 DELL PROD LP

AI summary

In accordance with embodiments of the present disclosure, a circuit board may include a first trace formed in a first layer of the circuit board, a second trace formed in a second layer of the circuit board, a via, and a termination pad. The via may be configured to electrically couple the first trace to the second trace, the via comprising a via stub corresponding to a first portion of a length of the via not within a second portion of the via between a first location in which the first trace is electrically coupled to the via and a second location in which the second trace is electrically coupled to the via. The termination pad may be formed at an end of the via stub opposite at least one of the first location and the second location.