Flexible Circuit Guide Member for Flat Lamination
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Solution Overview
Problem
Flexible printed circuits face issues due to copper thickness differences, leading to raised hole rings, film breakage, and bubble cavities during lamination and etching, which complicates production.
Innovation Solution
A flexible printed circuit design featuring an intermediate layer with a substrate and embedded guide member connecting copper line layers, surrounded by protective layers, ensuring flat surfaces and preventing film breakage and hole damage, using PI materials and light-sensitive overlay films for improved reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper plating is performed on through-holes to connect line layers, then electrical connection between layers is achieved, but copper thickness difference causes hole ring elevation and surface non-flatness
Solution Approach 1:
A flatting layer (planarization layer) is introduced as an intermediary between the copper plating layer and the overlay film. This flatting layer fills the elevation caused by hole ring copper plating, providing a flat surface for subsequent lamination processes while maintaining the electrical connection function of the copper plating.
Solution Approach 2:
The solution addresses the surface elevation problem by adding a vertical dimension element - the flatting layer - which compensates for the height difference created by copper plating, transforming the non-flat surface into a flat surface for the overlay film lamination.
2Reliability
If copper plating layer is raised on original copper, then through-hole connection is formed, but thickness difference causes dry film breakage during lamination
Solution Approach 1:
The flatting layer serves as a mediator between the raised copper plating and the dry film overlay. It eliminates the thickness difference that would otherwise cause dry film breakage during lamination, allowing the lamination process to proceed smoothly while maintaining the through-hole connection.
3Reliability
If copper plating creates thickness difference, then electrical connection is achieved, but etching process becomes difficult and holes may break
Solution Approach 1:
The flatting layer acts as a protective intermediary during the etching process. It covers the raised copper plating and prevents etching solution from attacking the copper, thereby preventing hole breakage while maintaining the electrical connection through the copper plating.
4Ease of manufacture
If lamination is performed over thickness difference, then overlay film application is attempted, but bubble cavities form easily
Solution Approach 1:
The flatting layer provides a uniform lamination surface that eliminates thickness differences. This allows the overlay film to be laminated smoothly without forming bubble cavities, while the underlying copper plating structure remains intact for electrical connection.
Data Source
AI summary
The present disclosure discloses a circuit board including an intermediate layer and two protective layers wrapped on opposite sides of the intermediate layer, the intermediate layer including a substrate layer in the middle, the substrate layer having a through hole, wherein the intermediate layer further includes a first line layer and a second line layer respectively provided on opposite sides of the substrate layer, a first overlay layer and a second overlay layer respectively provided on opposite sides of the substrate layer and a guide member embedded in the through hole and connecting the first and second line layers, the first line layer being embedded in the first overlay layer and the second line layer being embedded in the second overlay layer. The flexible printed circuit of the present disclosure can avoid the risk of dry film breakage when laminating the overlay film and hole breakage defect when etching.