Flexible PCB Cover Layer Thickness Reduction via Dual-Resin Vacuum Bagging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional flexible printed circuit boards have a thick cover layer that limits the reduction in size of electronic components, necessitating a method to decrease the thickness of the cover layer to achieve smaller flexible printed circuit boards.
Innovation Solution
A method involving a two-layer cover film with a first resin layer and a second resin layer, where the second resin layer softens at a lower temperature than the first, is used to reduce the thickness of the cover layer by vacuum bagging the laminated structure at a temperature higher than the softening point of the second resin layer, ensuring reliable coating of the conductive pattern.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a conventional single-layer cover film is used, then the manufacturing process is simple, but the cover layer thickness cannot be reduced sufficiently
Solution Approach 1:
The cover film is divided into two distinct resin layers: a first resin layer (polyimide) providing heat resistance and mechanical strength, and a second resin layer (epoxy) providing excellent adhesion to the conductive pattern. This segmentation allows each layer to be optimized for its specific function, enabling thinner overall coverage while maintaining performance.
Solution Approach 2:
The patent uses a composite structure combining polyimide and epoxy resin layers. The polyimide layer provides thermal stability and mechanical properties, while the epoxy layer ensures strong bonding to the conductive pattern. This composite approach achieves reduced thickness with enhanced overall performance compared to single-material solutions.
2Volume of moving object
If the cover layer thickness is reduced, then the size of the flexible printed circuit board is reduced, but the reliability of coating the conductive pattern is compromised
Solution Approach 1:
The second resin layer (epoxy) is specifically designed with superior adhesion properties to ensure reliable coating of the conductive pattern. This local optimization of material properties at the critical interface between cover layer and conductive pattern maintains coating reliability even when the overall cover layer thickness is reduced.
Solution Approach 2:
The patent utilizes the different softening temperatures of the two resin layers (epoxy softens at lower temperature than polyimide) to control the coating process. By heating to a temperature range that softens the epoxy layer without degrading the polyimide, reliable coating is achieved at reduced thickness through precise thermal parameter control.
3Reliability
If a two-layer resin structure is used, then the coating reliability is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The two-layer resin film is pre-assembled with the epoxy layer positioned to contact the conductive pattern before the lamination process. This preliminary configuration ensures that during vacuum bagging, the epoxy layer automatically bonds to the conductive pattern without requiring additional positioning steps, simplifying the overall manufacturing process despite the dual-layer structure.
Solution Approach 2:
The manufacturing process exploits the phase transition (softening) of the epoxy resin at its specific softening temperature. By controlling the heating process to reach this transition point, the epoxy layer becomes sufficiently fluid to flow and adhere to the conductive pattern, then solidifies upon cooling to create a reliable bond. This phase transition mechanism simplifies the bonding process compared to requiring additional adhesives or complex curing procedures.
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 allows for a more reliable coating of the conductive pattern with a reduced cover layer thickness, effectively decreasing the size of the entire flexible printed circuit board while maintaining high-density electronic component mounting.
Implementation Method 1
a second resin layer that is laminated to an inner side of the first resin layer and that softens at a lower temperature than does the first resin layer
Implementation Method 2
a pressure bonding step of vacuum bagging the laminated structure and the cover film at a temperature higher than a softening temperature of the second resin layer
Data Source
AI summary
According to an aspect of the present disclosures, a method of making a flexible printed circuit board, which includes a base film having an insulating property, a conductive pattern disposed on either one or both surfaces of the base film, and a cover layer covering a conductive-pattern side of a laminated structure inclusive of the base film and the conductive pattern, includes a superimposing step of superimposing a cover film on the conductive-pattern side of the laminated structure, the cover film having a first resin layer and a second resin layer that is laminated to an inner side of the first resin layer and that softens at a lower temperature than does the first resin layer, and a pressure bonding step of vacuum bagging the laminated structure and the cover film at a temperature higher than a softening temperature of the second resin layer.