Metal Covered Polyimide Composite for Flexible Circuit Boards

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Solution Overview

Problem

Conventional methods fail to effectively prevent peeling at the interface between copper layers and tin plating in non-adhesive flexible laminates, primarily due to Kirkendall voids and impurity concentration, which are exacerbated by the use of multiple electroplating baths and complex plating systems.

Innovation Solution

A metal covered polyimide composite is developed with a tie-coat layer and metal seed layer formed on a polyimide film using electroless plating or drying methods, followed by a copper or copper alloy layer formed through electroplating, where the copper layer is divided into fewer zones to reduce impurity concentration and Kirkendall voids, and tin plating is applied to the copper circuit after etching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If multiple electroplating baths are used to form copper layers, then the copper layer thickness and conductivity are improved, but Kirkendall voids and impurity concentration increase causing peeling between copper and tin layers

Engineering Contradiction:

Improveadhesion strength between copper and tin layersVSAvoidpeeling resistance at copper-tin interface

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent merges multiple electroplating baths into a single electroplating bath to form the entire copper layer (10-50 μm thick). This eliminates the copper layer boundaries that would otherwise be created by multiple baths, thereby preventing impurity concentration and Kirkendall void formation at these boundaries, which causes peeling between copper and tin layers.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent segments the copper layer into multiple sub-layers (first copper layer 5-30 μm, second copper layer 5-20 μm, third copper layer 0.1-5 μm) within a single electroplating bath. This segmentation allows control of plating conditions to prevent impurity concentration while maintaining the benefits of a thick copper layer without creating harmful boundaries between separately plated layers.

Inventive Principle:

Principle #1Segmentation

2Manufacturing precision

If complex plating systems with multiple zones are used, then manufacturing precision is improved, but device complexity and impurity concentration increase

Engineering Contradiction:

Improvecopper layer thickness uniformityVSAvoidelectroplating system complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent applies local quality by creating different copper layer thicknesses in different regions through a simple single-bath electroplating process. The first copper layer has thickness 5-30 μm, the second has 5-20 μm, and the third has 0.1-5 μm, achieving precise thickness control without complex multi-zone systems by controlling plating conditions locally within the single bath.

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If copper layer boundaries are created by multiple electroplating baths, then the copper layer can be formed with controlled thickness, but impurities concentrate at boundaries creating Kirkendall voids

Engineering Contradiction:

Improvecopper layer thickness controlVSAvoidimpurity concentration and Kirkendall voids

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The patent maintains continuity of useful action by forming the entire copper layer (10-50 μm) in a single continuous electroplating process without interrupting to change baths. This continuous plating prevents the formation of copper layer boundaries where impurities would concentrate, eliminating the source of Kirkendall voids while maintaining precise thickness control through controlled plating parameters.

Inventive Principle:

Principle #20Continuity of useful action

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 significantly reduces Kirkendall voids and impurity concentration, enhancing adhesion strength and preventing peeling between copper and tin layers, while simplifying the electroplating process by using fewer baths and zones, thus improving the reliability of non-adhesive flexible laminates for electronic components.

Implementation Method 1

a tie-coat layer and a metal seed layer formed on a polyimide film by electroless plating or a drying method

Methodology Applied

Scientific EffectElectroless plating: Deposition (physical)

Implementation Method 2

a copper layer or a copper alloy layer formed thereon by electroplating

Methodology Applied

Scientific EffectElectroplating: Electroplating

Data Source

PatentUS8568899B2Metal covered polyimide composite, process for producing the composite, and process for producing electronic circuit board

Publication Date: 2013.10.29 JX NIPPON MINING & METALS CORP

AI summary

Provided is a metal covered polyimide composite comprising a tie-coat layer and a metal seed layer formed on a surface of a polyimide film by electroless plating or a drying method, and a copper layer or a copper alloy layer formed thereon by electroplating, wherein the copper plated layer or copper alloy plated layer comprises three layers to one layer of the copper layer or copper alloy layer, and there is a concentrated portion of impurities at the boundary of the copper layer or copper alloy layer when the copper layer or copper alloy layer is three layers to two layers, and there is no concentrated portion of impurities when the copper layer or copper alloy layer is a single layer. Additionally provided are a method of producing the composite and a method of producing an electronic circuit board.