Conductive Layer Integrated FPC Adhesion and Warpage Control
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Solution Overview
Problem
Conductive-layer-integrated flexible printed circuits (FPCs) face challenges in maintaining long-term electromagnetic shielding effectiveness during repeated bending or sliding, primarily due to inadequate adhesion between the electromagnetic shielding material and the insulator film, which affects flexibility, flame retardance, electrical insulation reliability, and warpage.
Innovation Solution
A conductive-layer-integrated FPC structure comprising an electromagnetic-shielding conductive layer, a photosensitive resin composition layer with carboxyl-group-containing resin, photo-polymerization initiator, and thermosetting resin, laminated in a specific order, with the photosensitive resin composition layer containing fine particles like phosphorus, aluminum, or magnesium, and thermosetting resin with an optimal epoxy-to-carboxyl group ratio for improved adhesion and insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an electromagnetic shielding material is integrated into an FPC, then electromagnetic shielding effectiveness is improved, but adhesion between the shielding material and insulator film deteriorates
Solution Approach 1:
A photosensitive resin composition layer is introduced as an intermediary between the electromagnetic shielding conductive layer and the insulator film. This intermediate layer contains carboxyl-group-containing resin that chemically bonds to both the metal particles in the shielding layer and the insulator film, creating strong interfacial adhesion while maintaining electromagnetic shielding effectiveness.
Solution Approach 2:
The photosensitive resin composition layer is formulated as a composite material containing carboxyl-group-containing resin, thermosetting resin, photo-polymerization initiator, and fine particles (phosphorus, aluminum, or magnesium). This composite structure provides both adhesion to the shielding layer and flame retardance, while the carboxyl groups specifically target bonding to metal surfaces.
2Object-affected harmful factors
If the FPC structure is optimized for electromagnetic shielding, then shielding performance is improved, but flexibility and warpage resistance deteriorate
Solution Approach 1:
The photosensitive resin composition layer is designed as a thin film that maintains flexibility while providing adhesion. The resin composition is formulated to cure into a flexible network structure that accommodates bending and folding of the FPC without cracking or delaminating, thus preserving both flexibility and adhesion to the shielding layer.
Solution Approach 2:
The molecular structure and crosslinking density of the photosensitive resin composition are optimized to balance flexibility and adhesion. By controlling the types and ratios of resins (carboxyl-group-containing and thermosetting), the network structure is tuned to provide sufficient bond strength to the shielding layer while maintaining chain mobility for flexibility and resistance to warpage.
3Reliability
If adhesion promoters are added to improve bonding, then adhesion is improved, but flame retardance deteriorates
Solution Approach 1:
Multiple functions are merged into a single photosensitive resin composition layer: adhesion promotion (via carboxyl groups), flame retardance (via phosphorus, aluminum, and magnesium fine particles), and flexibility. This eliminates the need for separate adhesion promoter layers that would compromise flame retardance, as the adhesion and flame retardance functions are integrated at the molecular level within the same layer.
Solution Approach 2:
The photosensitive resin composition is formulated as a multi-functional composite where carboxyl-group-containing resin provides adhesion, thermosetting resin provides structural integrity, and fine particles of phosphorus, aluminum, or magnesium provide flame retardance. The synergistic combination of these components achieves both strong adhesion and excellent flame retardant properties simultaneously.
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 solution enables FPCs that are flexible, resistant to flame, and reliable in electrical insulation, with enhanced adhesion between the electromagnetic-shielding conductive layer and the photosensitive resin composition layer, effectively addressing warpage issues and maintaining electromagnetic shielding performance.
Implementation Method 1
a photo-polymerization initiator
Data Source
AI summary
A conductive-layer-integrated flexible printed circuit includes: (A) an electromagnetic-shielding conductive layer; (B) a photosensitive resin composition layer; and (C) a wiring-pattern-equipped film, (A) the electromagnetic-shielding conductive layer, (B) the photosensitive resin composition layer, and (C) the a wiring-pattern-equipped film being laminated in this order, and (B) the photosensitive resin composition layer being formed from a photosensitive resin composition containing at least (a) carboxyl-group-containing resin, (b) a photo-polymerization initiator, and (c) thermosetting resin.