UV Inkjet Inks for Flexible PCBs
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Solution Overview
Problem
Existing methods for manufacturing flexible printed circuit boards (Flex PCBs) using UV curable inkjet inks face challenges in achieving good flexibility, chemical and heat resistance, scratch resistance, and adhesion on polyimide substrates while maintaining reliable inkjet printing at conventional temperatures without organic solvents.
Innovation Solution
A UV free radical inkjet ink composition with specific silane compounds and a balanced ratio of difunctional and polyfunctional monomers, combined with a corona treatment and thermal curing, is used to achieve excellent adhesion and scratch resistance on polyimide substrates, ensuring reliable printing at temperatures below 55°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If monofunctional monomers are increased to enhance flexibility and adhesion, then flexibility and adhesion are improved, but scratch resistance deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the functional monomer ratio (0.05-5% monofunctional, 95-94.95% polyfunctional) and silane compound concentration (0.1-10%) to achieve optimal balance between adhesion, flexibility, and scratch resistance. This quantitative parameter optimization resolves the contradiction by finding the precise compositional sweet spot where all three properties are satisfied simultaneously.
Solution Approach 2:
The patent uses composite materials by combining polyfunctional monomers with silane compounds containing epoxy or amine groups. The silane compounds act as adhesion promoters that form strong bonds with polyimide substrates while the polyfunctional monomers provide crosslinked network structures for scratch resistance, creating a composite curable composition that achieves all desired properties without relying on monofunctional monomers.
2Strength
If cationically curable inkjet inks are used to eliminate shrinkage and improve adhesion, then adhesion and flexibility are improved, but jetting reliability deteriorates due to UV stray light curing in nozzles
Solution Approach 1:
The patent extracts the problematic cationic curable system and replaces it with a free radical curable system using polyfunctional monomers. This extraction removes the UV stray light sensitivity that causes nozzle clogging while maintaining adhesion performance through the use of silane compounds and optimized polyfunctional monomer formulations that cure reliably with standard UV LED irradiation.
Solution Approach 2:
The patent uses free radical photoinitiators with short lifetimes that cure quickly upon UV exposure, preventing the ink from remaining curable in the nozzle. This approach uses inexpensive, short-lived curable species that complete their reaction immediately upon irradiation, eliminating the persistent reactivity problem of cationic systems while maintaining adhesion through silane-based chemistry.
3Strength
If high amounts of monofunctional monomers are used for adhesion and flexibility, then adhesion and flexibility are improved, but chemical resistance and heat resistance deteriorate
Solution Approach 1:
The patent creates a composite curable composition combining polyfunctional monomers with silane compounds containing epoxy or amine groups. The silane compounds provide chemical resistance through their stable cyclic structures that open upon curing to form strong crosslinked networks, while the polyfunctional monomers provide adhesion and flexibility. This composite approach achieves all four properties (adhesion, flexibility, chemical resistance, heat resistance) simultaneously without relying on monofunctional monomers.
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 method provides Flex PCBs with enhanced adhesion, chemical resistance, and scratch resistance on polyimide substrates, maintaining reliable inkjet printing and meeting the requirements for Flex PCB manufacturing without the need for organic solvents or high temperatures.
Implementation Method 1
curing the ink by exposure to actinic radiation
Implementation Method 2
a corona treatment and thermal curing
Data Source
Figure 1~2
AI summary
A manufacturing method for printed circuit boards (1, 10) including the steps of: a) inkjet printing a UV free radical curable inkjet ink on a substrate (2); b) UV curing the UV free radical curable inkjet ink on the inkjet printed substrate; and c) applying a thermal treatment on the UV cured inkjet printed substrate; wherein the UV free radical curable inkjet ink contains at least a colorant, a free radical photoinitiator; a duofunctional monomer or oligomer and a polyfunctional monomer or oligomer; and 1 to 15 wt% of a silane compound according to Formula (I): wherein, the linking group L represents a -CH2- group or an aliphatic chain having 2 to 10 carbon atoms optionally substituted in the aliphatic chain by a nitrogen or an oxygen; R1 represents a methoxy group; R2 and R3 independently represent a methoxy group or a C1- to C4-alkyl group; and R4 represents a functional group selected from the group consisting of an epoxy group, an amine group, a carbamate group, a trimethoxy silane group and an ureido group.