PCB Inkjet Ink With Silane Adhesion for Polyimide Cover Layers
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Solution Overview
Problem
Existing UV curable inkjet inks for legend printing on PCBs face challenges in achieving adequate adhesion to various substrates, particularly polyimide-based cover layers, while avoiding yellowing and containing halogen-free components, especially with the shift to LED curing at 395 nm.
Innovation Solution
A radiation curable inkjet ink comprising di- or multifunctional alkoxysilanes functionalized with epoxide or oxetane groups, along with a photoinitiator system that includes acylphosphine oxide and aminobenzoate co-initiators, and a formulation that avoids thioxanthone, is used to enhance adhesion and prevent yellowing, suitable for LED curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional UV curable inkjet inks are used for legend printing, then curing is achieved, but adhesion to polyimide substrates and cover layers is insufficient
Solution Approach 1:
The patent employs a composite photoinitiator system combining acylphosphine oxide and aminobenzoate co-initiators, along with silane-based adhesion promoters, to achieve both strong adhesion to polyimide substrates and effective UV curing. This composite approach allows the ink to bond reliably to diverse substrates including polyimide cover layers while maintaining curability with LED lamps.
2Productivity
If thioxanthone photoinitiator is used, then curing sensitivity is improved, but yellowing of the legend ink occurs
Solution Approach 1:
The patent changes the chemical parameters of the photoinitiator system by replacing thioxanthone with acylphosphine oxide as the primary photoinitiator and adding aminobenzoate as a co-initiator. This parameter change maintains curing sensitivity while eliminating the yellowing side effect, achieving both efficient curing and color integrity of the white legend ink.
3Reliability
If halogen containing additives are used, then flame retardancy is improved, but ecological compliance is compromised
Solution Approach 1:
The patent extracts and removes halogen-containing additives from the ink formulation, replacing them with halogen-free alternatives. This extraction eliminates the harmful halogen content while maintaining the required flame retardancy properties, ensuring ecological compliance for PCB manufacturing.
4Strength
If adhesion promoters are added to improve adhesion, then bonding strength increases, but ink formulation complexity increases
Solution Approach 1:
The patent uses silane-based compounds that serve multiple functions: they act as adhesion promoters to bond the ink to substrates, serve as crosslinking agents to enhance the cured network, and contribute to the overall mechanical properties of the legend layer. This multi-functionality reduces formulation complexity while maintaining strong adhesion.
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 inkjet ink demonstrates improved adhesion to polyimide substrates and cover layers, maintains color integrity, and meets ecological requirements by being halogen-free, with effective curing using UV LEDs.
Implementation Method 1
UV curable ink jet ink... a photoinitiator system that includes acylphosphine oxide and aminobenzoate co-initiators... effective curing using UV LEDs
Implementation Method 2
di- or multifunctional alkoxysilanes functionalized with epoxide or oxetane groups... demonstrates improved adhesion to polyimide substrates and cover layers
Data Source
AI summary
A radiation curable inkjet ink comprising a polymerizable compound, a photoinitiator characterized in that the inkjet ink further comprises a di- or multifunctional alkoxysilane and a monofunctional alkoxysilane functionalized with a group selected from the group consisting of an epoxide and an oxetane.