Flexible PCB Dielectric Loss Reduction via Layered Polypropylene and Polyimide

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Solution Overview

Problem

Flexible printed circuit boards made of polyimide films experience significant high-frequency signal loss due to dielectric loss and have reduced heat resistance, leading to failures in high-temperature applications and increased manufacturing costs.

Innovation Solution

A method involving the stacking of base sheets with low dielectric constants, such as polypropylene, bonding sheets with lower melting temperatures, and heat-resistant sheets like polyimide on the uppermost and lowermost portions, along with the formation of anisotropic conductive layers or flame retardant sheets, to minimize dielectric loss and enhance heat resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a polyimide film is used as the base board of the flexible printed circuit board, then mechanical strength and heat resistance are improved, but dielectric loss occurs during high frequency signal transmission causing signal loss

Engineering Contradiction:

Improvemechanical strength and heat resistanceVSAvoiddielectric loss and signal loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The flexible printed circuit board is divided into multiple layers with different materials: a base sheet layer (polypropylene) for low dielectric loss, bonding sheets for adhesion, and heat resistant sheets (polyimide) for thermal protection. This segmentation allows each layer to perform its specific function optimally without compromising the others.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite structure combining polypropylene base sheet with low dielectric constant, polyethylene or polypropylene bonding sheets, and polyimide heat resistant sheets. This composite material approach integrates the advantages of each material: low dielectric loss from polypropylene, bonding capability from intermediate sheets, and heat resistance from polyimide.

Inventive Principle:

Principle #40Composite materials

2Loss of energy

If a film with low dielectric constant is used to minimize high frequency signal loss, then dielectric loss is reduced, but heat resistance is reduced causing the surface to melt at high temperatures

Engineering Contradiction:

Improvedielectric lossVSAvoidheat resistance

Core Design Contradiction:

Loss of energyVSTemperature

Solution Approach 1:

The solution moves from a single-layer structure to a multi-layer stacked structure, adding the dimension of layering. The heat resistant sheet is placed on the uppermost and lowermost portions of the stack, creating a protective thermal barrier while the low dielectric constant base sheet remains in the center for optimal signal transmission.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

Bonding sheets made of polyethylene or polypropylene are used as intermediary layers between the base sheet and heat resistant sheets. These bonding sheets facilitate adhesion between layers with different thermal and electrical properties, enabling the composite structure to function as an integrated unit.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Loss of energy

If a film with low dielectric constant and high heat resistance is used, then both dielectric loss and heat resistance problems are solved, but manufacturing cost increases

Engineering Contradiction:

Improvedielectric lossVSAvoidmanufacturing cost

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

Heat resistance is applied locally only where most needed - on the uppermost and lowermost portions of the flexible printed circuit board where thermal exposure occurs during SMC mounting processes. The base signal transmission layers maintain low dielectric constant materials, optimizing both performance and cost.

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 approach reduces high-frequency signal loss, increases heat resistance, and lowers manufacturing costs by using thin films for high-speed signal processing while maintaining mechanical strength and preventing overheating issues.

Implementation Method 1

preparing a bonding sheet having the melting temperature lower than the melting temperature of the base sheet; bonding by heating and pressurizing the laminate

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentUS11013128B2Method for manufacturing flexible printed circuit board and flexible printed circuit board manufactured by same

Publication Date: 2021.05.18 AMOSENSE CO LTD

AI summary

Disclosed is a method for manufacturing a flexible printed circuit board and a flexible printed circuit board manufactured thereby, which minimizes a dielectric loss due to a high frequency signal and preventing a loss of the high frequency signal. The disclosed method for manufacturing the flexible printed circuit board according to an embodiment of the present disclosure includes preparing a base sheet; preparing a bonding sheet having a melting temperature lower than a melting temperature of the base sheet; forming a laminate by stacking the base sheet and the bonding sheet; and bonding by heating and pressurizing the laminate.