Printed Wiring Board Solder Resist Curing Gradient
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Solution Overview
Problem
Conventional printed wiring board manufacturing methods often result in insufficient photocuring near the laminated base material, leading to recesses in the solder resist layer and potential short circuits or haloing phenomena, as the photocuring of the solder resist layer is insufficient in the vicinity of the laminated base material, causing unintended edge shapes and adhesion issues with solder bumps.
Innovation Solution
A method involving multiple solder resist precursor layers with varying photocuring abilities, where the portion closer to the laminated base material has a higher photocuring ability than the surface portion, ensuring sufficient curing from the surface to the base material contact area, and using specific resin compositions with adjusted concentrations and types of photopolymerization initiators and inhibitors to maintain intended opening shapes and prevent short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a uniform solder resist layer is applied and cured, then the surface portion is sufficiently cured, but the portion near the laminated base material remains insufficiently cured
Solution Approach 1:
The solder resist layer is designed with spatially varying properties: the portion near the laminated base material contains photopolymerization initiators at higher concentrations or with higher initiating ability, while the surface portion has lower concentrations. This local differentiation ensures sufficient curing at the base material interface while maintaining proper opening shapes at the surface.
Solution Approach 2:
The patent changes the concentration and type of photopolymerization initiators as a function of position within the solder resist layer. Specifically, the initiator concentration increases or initiating ability increases toward the base material contact portion, creating a gradient structure that optimizes curing at different depths.
2Strength
If the solder resist layer is uniformly cured, then adhesion is improved, but recesses form at the opening edges causing haloing phenomena
Solution Approach 1:
Different regions of the solder resist layer are given different curing characteristics: the base material contact portion uses high-initiator concentration formulations to ensure strong adhesion through complete curing, while the surface opening portions use lower initiator concentrations to prevent over-curing that would cause edge recession and haloing.
Solution Approach 2:
The patent applies partial curing enhancement by concentrating photopolymerization initiators specifically in the portion near the laminated base material rather than uniformly throughout the entire layer. This targeted approach provides sufficient curing where needed for adhesion without excessive curing at the opening edges.
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 ensures the solder resist layer is sufficiently cured from the surface to the base material contact, preventing short circuits and haloing, and maintaining the intended shape of the openings, thereby enhancing the reliability and integrity of the printed wiring board.
Implementation Method 1
the solder resist layer includes a photosensitive resin material... a photopolymerization initiator... irradiating light upon the solder resist precursor layers... such that the solder resist precursor layers from the first solder resist precursor layer to the n-th solder resist precursor layer are cured
Data Source
AI summary
A printed wiring board includes a laminated base material including an insulating layer and a conductor layer formed on the insulating layer, and a solder resist layer laminated on the laminated material and including photosensitive resin. The resist layer has surface portion and portion in contact with the laminated material, the conductor layer has pattern including conductor pads in contact with the resist layer such that the pads are positioned in openings in the resist layer, and the resist layer satisfies a first condition that a chemical species derived from a photopolymerization initiator has concentration higher in the portion in contact with the laminated material than concentration in the surface portion and/or a second condition that the chemical species derived from the initiator in the portion in contact with the laminated material has photopolymerization initiating ability higher than a chemical species derived from a photopolymerization initiator in the surface portion.