PCB Backdrilling Qualification Using Test Coupons for Via Stripping

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Solution Overview

Problem

Existing PCB manufacturing techniques fail to properly detect via stripping issues during the backdrilling process, which can lead to impedance discontinuities and signal degradation, and current methods like micro-section analysis are reactive and can damage the PCB.

Innovation Solution

The use of test coupons with specific test points on printed circuit boards to evaluate backdrilling capabilities, coupled with vector network analyzers and time domain reflectometers, allows for non-destructive detection of via stripping by analyzing insertion loss and resonance in the electrical properties of backdrilled vias.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Difficulty of detecting and measuring

If micro-section analysis is used to detect via stripping issues, then detection capability is provided, but the PCB is damaged

Engineering Contradiction:

Improvevia stripping detectionVSAvoidPCB integrity

Core Design Contradiction:

Difficulty of detecting and measuringVSStrength

Solution Approach 1:

The patent replaces the mechanical micro-section analysis method with electrical measurement methods (vector network analyzer and time domain reflectometer) to detect via stripping issues. This substitution allows non-destructive detection by measuring electrical properties (insertion loss, resonance, impedance) instead of physically cutting and examining the PCB cross-section.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces test coupons as intermediary elements that contain test vias connected to test points on the PCB surface. These test coupons serve as mediators between the electrical measurement equipment and the actual PCB vias, enabling indirect detection of via stripping issues without damaging the production PCBs.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If backdrilling is performed to remove via stubs, then signal integrity is improved, but via stripping issues may occur

Engineering Contradiction:

Improvesignal integrityVSAvoidvia stripping

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent implements a feedback mechanism where electrical measurements (insertion loss, resonance frequency, impedance) are taken from test coupons after backdrilling, compared against reference values for proper backdrilling, and used to determine whether the backdrilling process parameters need adjustment. This closed-loop feedback enables detection and correction of via stripping issues.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent performs preliminary testing on test coupons before mass production to qualify the backdrilling process. By evaluating test coupons with known via configurations and comparing measurements against established references, the system prepares and validates backdrilling parameters in advance, preventing via stripping issues before they affect production PCBs.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If test coupons are used to evaluate backdrilling capabilities, then detection accuracy is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvevia stripping detection accuracyVSAvoidtesting system complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent creates simplified copies of the actual PCB via structure in the form of test coupons. These test coupons contain test vias that replicate the electrical characteristics of production vias but are designed specifically for testing purposes with accessible test points. This copying approach enables precise measurement without requiring complex access to internal via structures.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent segments the testing function from the production PCB by using separate test coupons. This segmentation allows the testing system to be independent and specialized, using dedicated test points and measurement configurations optimized for detecting via stripping, without complicating the production PCB design or requiring complex integrated testing solutions.

Inventive Principle:

Principle #1Segmentation

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 method enables early detection of via stripping issues, preventing signal degradation and ensuring that backdrilling is within specified tolerances, thereby improving PCB quality and reducing the risk of post-manufacturing failures.

Implementation Method 1

analyzing insertion loss and resonance in the electrical properties of backdrilled vias

Methodology Applied

Scientific EffectInsertion loss measurement: Electrical Resistance

Implementation Method 2

analyzing insertion loss and resonance in the electrical properties of backdrilled vias

Methodology Applied

Scientific EffectResonance: Resonance

Data Source

PatentUS20260013037A1Printed circuit board vendor backdrilling capability qualification

Publication Date: 2026.01.08 DELL PROD LP

AI summary

A printed circuit board, comprising a via configured to provide electrical connectivity between layers of the printed circuit board and having at least a portion of the via removed within a tolerance of a variable. The printer circuit board further includes a test coupon configured to detect a via stripping issue associated with the via, wherein the via stripping issue occurs when the portion of the via is removed outside of the tolerance of the variable.