Flush Flexible Circuit Board via Additive Electroplating
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Solution Overview
Problem
Current flexible circuit boards have a raised and uneven surface due to the subtractive process, making it difficult to bond with other components and risking hollow bubbles at the adhesive layer-copper interface.
Innovation Solution
A flexible printed circuit design with a substrate layer, an embedded line layer, and protective layers on both sides, where the line layer is flush with the substrate surface, eliminating gaps and bubbles, and utilizing a light-sensitive overlay film and insulating layers for enhanced bonding and thermal reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the subtractive process is used to create copper lines on the substrate, then the copper lines can be formed on the flexible circuit board, but the surface becomes raised and uneven
Solution Approach 1:
Instead of removing material to create copper lines (subtractive process), the patent uses an additive process where copper lines are built up on the substrate through electroplating. The copper foil is laminated to the etched substrate, and copper is deposited to form the conductive lines, inverting the traditional approach to achieve a flush surface.
Solution Approach 2:
The patent moves from a two-dimensional surface pattern approach to a three-dimensional embedded structure. The copper lines are not just surface patterns but are built up in depth through electroplating, with the copper extending from the surface into the substrate cavity, creating a flush, embedded appearance.
2Ease of manufacture
If the subtractive process is used, then copper lines can be formed, but hollow bubbles form at the adhesive layer-copper interface
Solution Approach 1:
The patent inverts the traditional lamination sequence. Instead of laminating copper foil to the substrate and then etching, the substrate is etched first to create cavities, then copper foil is laminated to the etched substrate, and finally copper is electroplated to fill the cavities and form the conductive lines. This inversion eliminates trapped air and ensures complete adhesive coverage.
Solution Approach 2:
The substrate is pre-etched to create cavities before lamination. This preliminary action prepares the substrate surface to receive the copper foil and subsequent electroplating, ensuring that the adhesive layer can fully contact both the substrate and copper without trapping air bubbles.
3Ease of manufacture
If the surface is raised and uneven, then copper lines can be formed by subtractive process, but bonding with other components becomes difficult
Solution Approach 1:
The patent inverts the traditional approach by using additive electroplating instead of subtractive etching. This creates a flush, level surface where the copper lines are embedded in the substrate rather than raised above it, making the surface suitable for bonding with other components.
Solution Approach 2:
The copper lines have different properties at different depths: they are embedded in the substrate at the surface level for flush bonding, but extend into the substrate cavity to provide electrical connectivity. This local differentiation of properties allows both flush bonding and functional connectivity.
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 solution results in a flat surface for easy component bonding, prevents cavities and bubbles, and enhances thermal reliability by ensuring a seamless lamination process.
Implementation Method 1
the substrate layer is a light-sensitive overlay film
Implementation Method 2
a adhesive layer fixed between the insulating layer and the substrate layer and connecting the insulating layer and the substrate layer as one
Data Source
AI summary
The present disclosure discloses a circuit board including a substrate layer, a line layer fixed to the substrate layer and two protective layers wrapped on both sides of the substrate layer to cover the line layer, wherein, the line layer is embedded in the substrate layer and the surface of the line layer is flush with the surface of the substrate layer. The surface of the flexible circuit board is neat and can be easily bonded to other components, and during processing, because the surface of the line layer and the substrate layer are flush, when the protective layer is laminated to the substrate layer, there is no gap between the protective layer and the substrate layer, and the protective layer and the line layer, so there are no cavity bubbles between the line layer and the protective layer, and it has a high thermal reliability level.