Core Cavity Noise Isolation Structure for Chip Packages

Solution Overview

Problem

High frequency electromagnetic energy leakage into chip cavities due to impedance mismatch and return loss issues in thick core packaging, exacerbated by the larger core thickness, which affects mechanical reliability and increases costs.

Innovation Solution

A noise isolation structure is implemented in the chip package with a void in the bottom build-up layers having a sectional area that varies in different distances from the core region, and multi-layer relief structures with progressively smaller openings or additional conducting structures to reduce electromagnetic coupling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a thicker core is used in chip packages, then manufacturing cost is reduced and mechanical reliability is improved, but electromagnetic energy leakage into the cavity increases due to impedance mismatch and return loss

Engineering Contradiction:

Improvemechanical reliabilityVSAvoidelectromagnetic energy leakage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The relief structure is divided into multiple segments along the signal path, with each segment providing localized impedance control. The segmented approach allows better management of electromagnetic energy distribution and reduces overall leakage into the cavity while maintaining the thick core structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The relief structure implements local quality changes by varying the ground area and impedance characteristics at specific locations along the signal path. This localized impedance control mitigates electromagnetic energy leakage at critical points without requiring changes to the overall thick core design.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If a thicker core is used in chip packages, then manufacturing cost is reduced, but electromagnetic energy leakage into the cavity increases due to larger core thickness

Engineering Contradiction:

Improvemanufacturing costVSAvoidelectromagnetic energy leakage

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The relief structure is divided into multiple segments along the signal path, with each segment providing localized impedance control. The segmented approach allows better management of electromagnetic energy distribution and reduces overall leakage into the cavity while maintaining the thick core structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The relief structure implements local quality changes by varying the ground area and impedance characteristics at specific locations along the signal path. This localized impedance control mitigates electromagnetic energy leakage at critical points without requiring changes to the overall thick core design.

Inventive Principle:

Principle #3Local quality

3Reliability

If traditional relief structures are used, then return loss characteristics are improved, but electromagnetic coupling into the cavity is not adequately mitigated at high frequencies

Engineering Contradiction:

Improvereturn loss characteristicsVSAvoidelectromagnetic coupling

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The relief structure is divided into multiple segments along the signal path, with each segment providing localized impedance control. The segmented approach allows better management of electromagnetic energy distribution and reduces overall leakage into the cavity while maintaining the thick core structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The relief structure implements local quality changes by varying the ground area and impedance characteristics at specific locations along the signal path. This localized impedance control mitigates electromagnetic energy leakage at critical points without requiring changes to the overall thick core design.

Inventive Principle:

Principle #3Local quality

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 design effectively minimizes electromagnetic coupling between the cavity and BGA balls, improving signal integrity and reducing noise interference, while maintaining mechanical reliability and cost-effectiveness of thick core packages.

Implementation Method 1

The void directly below the core of the package allows electromagnetic energy to couple out of signal nets and into the cavity structure

Methodology Applied

Scientific EffectElectromagnetic coupling: Electromagnetic Induction

Data Source

PatentUS11688675B1Core cavity noise isolation structure for use in chip packages

Publication Date: 2023.06.27 XILINX INC

AI summary

Various noise isolation structures and methods for fabricating the same are presented. In one example, a substrate for chip package is provided. The substrate includes a core region, top build-up layers and bottom build-up layers. The top build-up layers are formed on a first side of the core region and the bottom build-up layers are formed on a second side of the core region that is opposite the first side. Routing circuitry formed in the bottom build-up layers is coupled to routing circuitry formed in the top build-up layers by vias formed through the core region. A void is formed in the bottom build-up layers. The void is configured as a noise isolation structure. The void has a sectional area that is different in at least two different distances from the core region.