Flux-Resin Interface for Moisture-Resistant PCB Coating Repair
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Solution Overview
Problem
Urethane resin coatings on circuit boards can be compromised by residual flux, leading to incomplete curing and peeling issues, especially at high temperatures, and pose challenges in repair due to high adhesion.
Innovation Solution
A package structure with a coating resin containing 10% to 50% isocyanate, which reacts with a flux having a hydroxyl group to form a reactant at the interface, eliminating the need for flux cleaning and enabling easy peeling during repairs by softening at the glass transition temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If urethane resin coating is applied to protect circuit board from moisture and dust, then water resistance and moisture resistance are improved, but the coating resin cannot be easily peeled off during repair
Solution Approach 1:
The patent applies a flux coating to the circuit board before applying the urethane resin coating. This preliminary flux layer serves as an intermediate that will later enable easy peeling of the resin coating during repairs, while still maintaining the water and moisture resistance function of the urethane resin.
Solution Approach 2:
The flux acts as an intermediary layer between the circuit board and the urethane resin coating. This intermediate layer provides the necessary interface that allows the resin to adhere properly for protection while enabling controlled peeling during repair operations without damaging the underlying circuit board.
2Manufacturing precision
If flux is washed off from circuit board to prevent curing interference, then curing completeness is improved, but additional processing steps and cost are increased
Solution Approach 1:
Instead of removing the flux as a harmful contaminant, the patent utilizes the flux's hydroxyl groups as beneficial reactive sites that promote complete curing of the isocyanate groups in the urethane resin. The previously problematic flux residue becomes the key to achieving complete curing without additional cleaning steps.
Solution Approach 2:
The flux on the circuit board performs a dual function: it remains as a residual layer that enables later peeling, and simultaneously serves as a curing promoter by reacting with the isocyanate groups. This self-service approach eliminates the need for separate flux removal and curing promotion steps.
3Strength
If conventional urethane resin is used for high adhesion, then bonding strength is improved, but repairability is worsened
Solution Approach 1:
The patent segments the bonding interface into two distinct layers: the flux layer providing strong adhesion to the circuit board, and the urethane resin layer providing protection and controlled peeling capability. This segmentation allows each layer to fulfill its specific function without compromising the other.
Solution Approach 2:
The flux layer creates localized adhesion properties at the circuit board interface, while the urethane resin maintains its protective qualities in the upper layer. This local differentiation of properties enables strong bonding where needed while preserving ease of removal where the resin needs to be peeled.
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
This configuration ensures complete curing of the resin without flux cleaning, enhances repairability by allowing easy removal of the coating resin without damaging components, and reduces the workload and cost.
Implementation Method 1
a coating resin that contains 10% to 50% by weight of isocyanate and covers the circuit board, the electronic component, and the bonding metal; a flux that contains a compound having a hydroxyl group and remains on the surface of the bonding metal; and a reactant of the coating resin and the flux, the reactant being formed at an interface between the flux and the coating resin
Implementation Method 2
setting the reactant at least to the glass transition point temperature of the flux to soften the reactant and peel off the coating resin around the electronic component
Data Source
AI summary
A package structure including an electronic component 2 mounted on a circuit board 1 with a bonding metal 3, wherein a flux 4 contains a compound having a hydroxyl group and remains on the surface of the bonding metal 3, a coating resin 5 contains 10% to 50% by weight of isocyanate, and a reactant 8 of the coating resin 5 and the flux 4 is formed at an interface between the flux 4 and the coating resin 5. Water resistance and moisture resistance can be obtained without cleaning the flux 4. The coating resin 5 can be easily peeled off at a temperature not lower than the glass transition point temperature of the flux 4.