Rigid-Flexible PCB Groove Design for Adhesive Flow
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Solution Overview
Problem
Printed circuit boards (PCBs) with flexible and rigid regions face challenges in minimizing resin introduction into flexible regions, which reduces flexibility and can lead to stress concentration at the interface, potentially causing substrate breakage.
Innovation Solution
The PCB design incorporates a first substrate with a groove in the flexible region and a second substrate with an adhesive layer that extends into the groove, minimizing resin introduction and maintaining flexibility by allowing the adhesive to flow and cure within the groove, thus reducing stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If resin is introduced into the flexible region to form adhesive layers, then bonding strength between substrates is improved, but flexibility of the flexible region deteriorates and stress concentration occurs
Solution Approach 1:
The flexible region is segmented into multiple thin insulating layers (first insulating layer, second insulating layer, third insulating layer) with wiring layers in between. This segmentation allows the structure to maintain bonding strength through multiple adhesive interfaces while preserving flexibility by distributing stress across multiple thin layers rather than one thick resin layer.
Solution Approach 2:
Different regions of the PCB have different structures: the rigid region has a multilayer structure for strength, while the flexible region uses thin insulating layers to maintain flexibility. The adhesive layers are strategically placed only where needed for bonding, minimizing resin introduction in the flexible region while maintaining necessary bonding strength.
2Strength
If multilayer structure is formed in rigid region to reduce mounting stress, then structural strength is improved, but resin introduction into flexible region increases causing flexibility loss
Solution Approach 1:
The multilayer structure is segmented into distinct rigid and flexible regions. The rigid region contains the multilayer structure with adequate resin for strength, while the flexible region is carefully designed with minimal resin introduction, using thin insulating layers to maintain flexibility while still providing necessary structural support.
Solution Approach 2:
The PCB structure is locally optimized: the rigid region has a multilayer structure with sufficient resin content for mounting stress resistance, while the flexible region uses thin insulating layers (5μm to 20μm) to minimize resin introduction and maintain flexibility. This local differentiation allows each region to have the properties it needs without compromising the other.
Data Source
AI summary
A printed circuit board includes a rigid region and a flexible region; a first substrate disposed on the rigid region and the flexible region and comprising a first insulating layer and a first wiring layer comprising a first groove in the flexible region; and a second substrate disposed on the first substrate in the rigid region and comprising a first adhesive layer, a second insulating layer and a second wiring layer.