Multilayer Board Stackup for Stable RF Signals Under Bending

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Solution Overview

Problem

Multilayer boards used for radio frequency signal transmission often experience impedance mismatching and signal conductor separation when bent, leading to changes in radio frequency characteristics due to variations in joining material layer thickness and adhesion strength.

Innovation Solution

A multilayer board configuration with a signal conductor on one insulator layer surface and a lower relative permittivity second joining material layer on the opposite surface, where the adhesion strength between the first insulator layer and first joining material layer is higher than between the insulator layer and second joining material layer, reducing stress-induced thickness changes and preventing gap formation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a multilayer board is bent in the stacking direction, then the second joining material layer changes in thickness due to large stress, but this causes changes in radio frequency characteristics of the transmission line

Engineering Contradiction:

Improvebending flexibilityVSAvoidradio frequency characteristic stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies local quality by assigning different relative permittivity values to different joining material layers. Specifically, the second joining material layer (closer to the signal conductor) has a lower relative permittivity than the first joining material layer. This local differentiation compensates for thickness changes during bending, maintaining stable radio frequency characteristics despite the board's flexibility.

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If a multilayer board is bent in the stacking direction, then large stress is applied to the boundary between the insulator layer and the joining material layer, but this may cause peeling and gap formation

Engineering Contradiction:

Improvebending flexibilityVSAvoidadhesion strength at boundary

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

The patent implements local quality by creating different adhesion strength characteristics at different boundaries. The boundary between the first insulator layer and the first joining material layer has higher adhesion strength than the boundary between the first insulator layer and the second joining material layer. This differentiated adhesion design prevents peeling and gap formation at critical interfaces during bending operations.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If the thickness of a joining material layer changes from a predetermined thickness, then impedance mismatching occurs in the transmission line

Engineering Contradiction:

Improvejoining material layer thickness controlVSAvoidimpedance matching

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies parameter changes by utilizing the relative permittivity characteristic of the joining material layers. By setting the second joining material layer to have a lower relative permittivity than the first, the system compensates for thickness variations that occur during bending, thereby maintaining consistent impedance matching in the transmission line despite manufacturing tolerances or deformation.

Inventive Principle:

Principle #35Parameter changes

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 configuration maintains stable radio frequency characteristics and mechanical structural strength against bending by minimizing changes in the transmission line's radio frequency characteristics and preventing signal conductor peeling.

Implementation Method 1

a relative permittivity of the second joining material layer is lower than a relative permittivity of the first joining material layer

Methodology Applied

Scientific EffectRelative permittivity: Dielectric Permittivity

Implementation Method 2

an adhesion strength between the first insulator layer and the first joining material layer is higher than an adhesion strength between the first insulator layer and the second joining material layer

Methodology Applied

Scientific EffectAdhesion: Adhesive

Data Source

PatentUS12004290B2Multilayer board

Publication Date: 2024.06.04 MURATA MFG CO LTD

AI summary

In a multilayer board, a transmission line includes layers including a first insulator layer, a first joining material layer in contact with a first surface of the first insulator layer, and a second joining material layer in contact with a second surface of the first insulator layer. A signal conductor of the transmission line is on the first surface of the first insulator layer, a relative permittivity of the second joining material layer is lower than a relative permittivity of the first joining material layer, and an adhesion strength between the first insulator layer and the first joining material layer is higher than an adhesion strength between the first insulator layer and the second joining material layer.