Multilayer FPCB Stepped Via Structure for Dry Film Filling
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Solution Overview
Problem
Multilayer circuit boards face challenges in filling the bottom of the fall structure between inner and outer conductive wiring layers due to the limitations of dry film thickness, which restricts the line width and line space of the outer conductive wiring layer.
Innovation Solution
A method involving a double-sided copper substrate with electrically conductive holes and stepped portions formed by pressing single-sided copper substrates together, allowing dry film to fully fill the fall structure without requiring increased thickness, thereby enabling reliable connection and preventing short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the dry film thickness is increased to allow the dry film to fully fill the bottom of the fall structure, then the filling completeness is improved, but the resolution deteriorates and the line width and line space are limited
Solution Approach 1:
The patent applies preliminary action by forming a plated through-hole with a bottom plated layer before applying the dry film. This pre-formed structure provides a foundation that allows the dry film to properly fill the fall structure without requiring excessive thickness, thereby maintaining resolution while achieving complete filling.
Solution Approach 2:
The patent introduces an intermediary element - the bottom plated layer formed within the plated through-hole. This plated layer acts as a mediator between the inner conductive wiring layer and the outer conductive wiring layer, enabling the dry film to fill the fall structure effectively without compromising resolution.
2Reliability
If the dry film thickness is increased to ensure complete filling of the fall structure, then the reliability is improved, but the line width and line space are restricted
Solution Approach 1:
The plated through-hole and bottom plated layer are formed in advance before the dry film application. This preliminary structuring ensures reliable electrical connection and mechanical support, allowing the use of thinner dry film that maintains both reliability and fine line dimensions.
Solution Approach 2:
The patent changes the structural parameters of the connection path by introducing a plated through-hole with bottom plating. This parameter change provides a more reliable connection path that does not depend on increased dry film thickness, thereby maintaining both reliability and acceptable line width.
3Ease of manufacture
If the dry film thickness is increased to fill the fall structure, then the manufacturing robustness is improved, but the device complexity increases
Solution Approach 1:
The plated through-hole structure is prepared in advance during the PCB manufacturing process. This preliminary action creates a robust foundation for subsequent steps, making the overall manufacturing process more reliable without adding significant complexity, as the plating process is a standard manufacturing step.
Data Source
AI summary
A flexible printed circuit board with multiple layers includes an inner wiring substrate and at least one outer wiring plate. Each outer wiring plate is connected to one surface of the inner wiring substrate, and defines at least one through hole which passes through the outer wiring plate to expose the inner wiring substrate. Each outer wiring plate further includes an adhesive plate connected to the inner wiring substrate. The adhesive plate includes a stepped portion extending towards a center of the through hole.