Inkjet Curable Polyimide Acrylate Coating for Flexible PCB Adhesion
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Solution Overview
Problem
Existing photocurable compositions for flexible printed circuit boards lack flexibility and adhesion to both plastic substrates and conductive circuits, and do not provide adequate withstand voltage characteristics after thinning.
Innovation Solution
A curable composition for inkjet is developed, comprising a soluble polyimide resin, a photocurable acrylate compound, a photopolymerization initiator, and a thermosetting resin. The photocurable acrylate compound includes difunctional (meth)acrylate compounds with alkylene or alkoxy chains, bisphenol epoxy (meth)acrylate compounds, and (meth)acrylate compounds with hydroxyl groups, which are combined with the soluble polyimide resin to enhance flexibility and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a general photocurable composition is used to protect the circuit board, then the circuit is protected from oxidation and corrosion, but the coating film lacks flexibility and does not achieve excellent adhesion to both circuit metal and plastic substrate
Solution Approach 1:
The patent uses a composite material system consisting of polyimide resin, acrylate monomer, and photopolymerization initiator. The polyimide resin provides adhesion to both plastic substrate and conductive metal, while the acrylate monomer and photopolymerization initiator enable UV curing to form a flexible crosslinked network. This composite approach resolves the contradiction by combining materials with complementary properties to achieve both adhesion and flexibility simultaneously.
Solution Approach 2:
The patent adjusts key parameters including the ratio of polyimide resin to acrylate monomer, the molecular weight of polyimide, and the concentration of photopolymerization initiator. By optimizing these parameters, the coating film achieves the right balance between adhesion strength and flexibility. For example, controlling the polyimide resin content within specific ranges ensures sufficient adhesion while maintaining the flexibility needed for flexible circuit board applications.
2Reliability
If a general photocurable composition is used to protect the circuit board, then protection is provided, but after thinning the coating film does not achieve better withstand voltage characteristics
Solution Approach 1:
The patent changes the chemical composition parameters of the coating material to achieve high withstand voltage characteristics even at reduced thickness. By using polyimide resin with specific molecular weight and incorporating acrylate monomers that form dense crosslinked networks upon UV curing, the coating maintains excellent electrical insulation properties at thinner depths, thus resolving the contradiction between withstanding voltage and coating thickness.
3Reliability
If conventional coating methods are used, then protection is applied to the circuit board, but material waste and liquid waste from lithography process increase
Solution Approach 1:
The patent replaces conventional lithography processes with direct UV curing technology. Instead of using light-sensitive resins that require chemical development and produce liquid waste, the invention uses UV-curable compositions that directly polymerize upon UV exposure to form the protective coating. This substitution eliminates the lithography process entirely, thereby eliminating the generation of waste liquids while maintaining the protective function.
Solution Approach 2:
The UV-curable composition performs self-polymerization upon exposure to UV light, forming the protective coating directly without requiring separate development steps. This self-service mechanism eliminates the need for additional chemical processing steps that would generate waste, thereby reducing substance loss while maintaining effective protection.
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 curable composition achieves excellent flexibility, withstand voltage characteristics after thinning, and maintains solder heat resistance, ensuring strong adhesion to both plastic substrates and conductive layers.
Implementation Method 1
a photopolymerization initiator, and a thermosetting resin. The photocurable acrylate compound includes a difunctional (meth)acrylate compound containing an alkylene chain or an alkoxy chain
Data Source
AI summary
The invention provides a curable composition for inkjet, a cured product, and a flexible printed circuit board. The curable composition for inkjet includes a soluble polyimide resin, a photocurable acrylate compound, a photopolymerization initiator, and a thermosetting resin. The curable composition for inkjet has excellent flexibility, and has a withstand voltage of greater than 2 kV even when the thickness is less than 20 μm.