UV Curable Resin Prepregs for Flexible Circuit Barrel Crack Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current flexible multilayer manufacturing processes for printed circuit boards using polyimide foil layers face issues such as reliability problems with plated through holes, inadequate metallization, and barrel cracks due to thermal expansion differences, and require complex and costly manual processing steps.
Innovation Solution
Replacing polyimide foil layers with prepregs comprising a UV curable resin layer and a thermally curable resin layer, where the UV curable resin is partially cured using a mask with transparent and opaque portions to control curing, and then laminated with a core layer under heat and pressure, resulting in a semi-flexible core that is not substantially bonded to the cured UV resin portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyimide foil layers are used in flexible multilayer manufacturing, then the laminate structure is formed, but reliability problems occur with plated through holes and barrel cracks due to thermal expansion differences
Solution Approach 1:
The patent changes the material parameters by replacing polyimide foil with a composite prepreg system containing UV curable resin and thermally curable resin. The UV curable resin portion is cured before lamination to create a non-substantially bonded interface, reducing thermal expansion stress and eliminating barrel cracks while maintaining structural integrity
Solution Approach 2:
The invention uses a composite prepreg material combining UV curable resin and thermally curable resin with semi-flexible core layers. This composite structure allows differential bonding behavior where the UV cured portion remains partially unbonded, creating a stress-relief interface that prevents reliability failures
2Reliability
If polyimide foil layers are used, then laminate structure is achieved, but plasma cleaning is required for plated through holes
Solution Approach 1:
The patent changes the surface chemistry parameters by using UV curable resin that can be selectively cured to create bonding interfaces. This eliminates the need for plasma cleaning because the UV cured resin provides adequate surface preparation and adhesion without requiring additional plasma treatment steps
3Ease of manufacture
If FR4 material layer is used instead of polyimide foil, then cost is reduced, but the layup can only be bent a few times before damage
Solution Approach 1:
The invention creates a composite structure using UV curable resin and thermally curable resin with semi-flexible core layers. The UV cured portion that is not substantially bonded to the core layer acts as a stress-relief interface, allowing the laminate to maintain flexibility and withstand repeated bending while using cost-effective materials
Solution Approach 2:
The patent applies local quality by creating different bonding characteristics in different regions. The UV curable resin portion is cured to create a non-substantially bonded interface locally, while other portions maintain full bonding. This localized unbonded region provides flexibility and stress relief without compromising overall structural integrity
4Manufacturing precision
If manual processing steps are used for flex-rigid laminates, then precise assembly is achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies preliminary action by pre-curing the UV curable resin portion before the lamination process. This pre-curing creates a stable, non-substantially bonded interface that maintains precise alignment and positioning during subsequent lamination steps, eliminating the need for complex manual adjustment and PTFE inlay placement
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 approach reduces reliability issues like barrel cracks and eliminates the need for plasma cleaning, simplifies the lamination process, and allows for the production of flexible multilayer laminates with improved peel strength and reduced manufacturing complexity.
Implementation Method 1
directing UV light at the mask for a period of time sufficient to cure the UV curable resin layer underlying the UV light transparent portion of the mask
Implementation Method 2
applying heat and/or pressure to the lay-up to form a laminated layup
Data Source
Figure 1
Figure 2~3
Figure 4~6
AI summary
Prepregs (100) having a UV curable resin layer (102) located adjacent to a thermally curable resin layer (104) wherein the UV curable resin layer includes at least one UV cured resin portion (125) and at least one UV uncured resin (127) as well as methods for preparing flexible printed circuit boards using the prepregs.