Flexible Circuit Manufacturing Without Insulating Substrate
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Solution Overview
Problem
Existing methods for manufacturing flexible printed circuits for smart cards are costly and require additional steps, such as die-attach and wire-bonding, which increase complexity and material usage.
Innovation Solution
A process eliminating the insulating substrate by using a sheet of electrically conductive material and a thermoplastic-modified epoxy adhesive, allowing for the direct integration of chip modules into card bodies without additional adhesive films, enabling single- or double-sided flexible circuit production with adjustable thickness for chip connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If an insulating substrate is used to support the conductive layer, then the flexible circuit has structural stability, but the manufacturing process becomes more complex and costly with additional adhesive films required
Solution Approach 1:
The patent removes the insulating substrate from the flexible circuit structure, retaining only the essential components: the conductive layer and the adhesive layer. This extraction eliminates the need for additional adhesive films and substrate handling steps, directly reducing manufacturing complexity while maintaining structural stability through the adhesive layer alone
Solution Approach 2:
The adhesive layer is formulated with specific properties (thermoplastic-modified epoxy with controlled viscosity and glass transition temperature) to perform multiple functions: bonding the conductive layer, providing structural support, and enabling direct chip integration. This localized functional enhancement replaces the need for separate insulating substrate and adhesive film components
2Ease of manufacture
If additional adhesive films are deposited on the back of modules, then chip modules can be integrated into card bodies, but the number of manufacturing steps increases
Solution Approach 1:
The adhesive layer is designed to combine multiple functions into a single component: it bonds the conductive layer to the substrate, provides structural support, and serves as the bonding interface for direct chip integration. This merging eliminates the need for separate adhesive film deposition steps, directly improving manufacturing efficiency
Solution Approach 2:
The adhesive layer is pre-formulated with thermoplastic properties and controlled viscosity to enable direct chip integration at standard embedding temperatures. This preliminary preparation of the adhesive layer with integrated bonding capabilities eliminates the need for additional adhesive film deposition during the manufacturing process
3Productivity
If a thin insulating substrate is used to retain flexibility, then the flexible circuit can be continuously manufactured, but the substrate requires additional protective adhesive layers
Solution Approach 1:
The patent eliminates the insulating substrate entirely, retaining only the conductive layer and adhesive layer. This extraction maintains flexibility while removing the need for protective adhesive films, simplifying the overall structure and enabling continuous manufacturing without additional protective layers
Solution Approach 2:
The adhesive layer is formulated with specific rheological parameters (viscosity of 77-88 mPa.s at room temperature, glass transition temperature of 51.5°C ±5°C) to provide adequate bonding strength and structural support without requiring a thick insulating substrate. This parameter optimization enables substrate elimination while maintaining flexibility and continuous manufacturability
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 method reduces production costs and complexity by eliminating the need for additional adhesive films and substrate handling, improving yield and allowing for direct chip integration with precise adhesive thickness adjustment for efficient chip connection.
Implementation Method 1
an adhesive material formulated specifically to have thermofusible properties (hot-melt according to the Anglo-Saxon terminology) and which can be reactivated at the usual embedding temperatures
Data Source
Figure 1~2c
Figure 2d~2g
Figure 2h~2k
AI summary
The invention relates to a method for manufacturing a flexible circuit (3) for a chip card module (100). Said method comprises a step of producing electrically conductive contact pads (15) in a first sheet (11) of conductive material. A layer (8) of electrically insulating adhesive material is also used, either to adhere a second sheet (12) of electrically conductive material onto the first sheet of conductive material or to form an intermediate complex making it possible to perforate the layer of adhesive material before it is transferred onto the first sheet of conductive material. Regardless of which option is chosen, the method according to the invention makes it possible to avoid using a flexible substrate of plastic material (PET, PEN, polyimide) or composite material (glass/epoxy) to perform the structuring and metalization of the conductor tracks and contact pads used in the chip card modules. The adhesive material can be specially formulated to have intrinsic hot-melt properties compatible with an operation for inserting the electronic module into the recess of the chip card body without using an additional hot-melt adhesive. The invention also relates to a flexible circuit for a chip card manufactured using said method and to a chip card module comprising such a flexible circuit.