Low Profile Copper Foil Laminates for High Frequency PCBs
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Solution Overview
Problem
Current low profile copper laminates for high speed and high frequency printed circuit boards face challenges in achieving sufficient peel strength and adhesion to the base material, leading to higher attenuation losses due to surface roughness and dielectric losses, which affect signal integrity.
Innovation Solution
A method involving a low profile copper foil with surface roughness between 0.25 to 3.5 microns, coated with a layer of low dielectric loss resin that is partially cured to form a B-staged resin coated copper sheet, which is then laminated with a resin sheet to enhance adhesion and reduce dielectric losses, thereby improving peel strength and signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If low profile copper foil with smooth surface is used, then conductor loss is reduced, but adhesion to base material deteriorates
Solution Approach 1:
The copper foil surface is pre-treated with corona discharge or plasma treatment before lamination, creating surface activation that enhances adhesion. This preliminary action modifies the surface energy and chemistry of the copper foil, allowing strong bonding without requiring increased surface roughness, thus maintaining low conductor loss while improving adhesion strength
Solution Approach 2:
An adhesion promoter layer or coupling agent is introduced between the low profile copper foil and the base material. This intermediary substance facilitates strong bonding at the interface without requiring the copper surface to be rough, thereby maintaining low conductor loss while achieving sufficient adhesion strength through the mediating layer
2Loss of energy
If low profile copper foil with smooth surface is used, then conductor loss is reduced, but peel strength deteriorates
Solution Approach 1:
The copper foil surface undergoes pre-treatment processes such as corona discharge, plasma treatment, or chemical etching that create surface activation without significantly increasing roughness. This preliminary modification enhances peel strength by improving interfacial bonding while maintaining the smooth surface required for low conductor loss
Solution Approach 2:
The surface properties of the copper foil are modified by changing parameters such as surface energy, chemical composition, or micro-structure through treatments like plasma or corona discharge. These parameter changes enhance peel strength without substantially increasing surface roughness, thereby maintaining low conductor loss while achieving required peel strength
3Reliability
If resin coating is applied to copper foil, then adhesion is improved, but dielectric loss increases
Solution Approach 1:
The resin coating is applied selectively only in specific regions or at controlled thicknesses on the copper foil surface, rather than uniform thick coating. This local application provides sufficient adhesion in critical bonding areas while minimizing the overall dielectric material volume, thereby reducing dielectric loss while maintaining adequate adhesion
Solution Approach 2:
The dielectric properties of the resin coating are optimized by selecting materials with lower dielectric loss tangents and by controlling coating thickness parameters. The resin formulation is modified to achieve the minimum necessary adhesion while minimizing dielectric loss, balancing adhesion improvement against dielectric loss increase
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
The approach results in laminates with improved peel strength, reduced dielectric losses, and enhanced signal integrity, capable of withstanding higher voltages and possessing higher dielectric strength, while maintaining low conductor loss.
Implementation Method 1
partially curing the layer of low dielectric loss resin to form a resin coated low profile copper sheet
Implementation Method 2
laminating the resin surface of the resin coated low profile copper sheet to a resin sheet to form a laminate
Data Source
Figure 1
Figure 2~2A
AI summary
Laminate precursors and laminates for use in high speed and high frequency printed circuit boards, and methods for their preparation.