FPC Ground Structure for LCD EMI Reduction
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Solution Overview
Problem
As liquid crystal displays (LCDs) increase in size, they become thicker and more costly due to longer driving parts, leading to increased manufacturing costs and reduced efficiency, and high voltage and frequency applications weaken the electromagnetic interference (EMI) characteristics, particularly in 2-PCB structures with flexible printed circuits (FPCs).
Innovation Solution
Incorporating a ground member electrically connected to the bottom chassis and exposed outside within the FPC, which includes an insulating film, circuit wire, conductive ground layer, and contact holes, strengthens the ground structure and reduces EMI levels by allowing EMI to flow to the outside.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a 2-PCB structure with FPC is used to reduce driving part length, then manufacturing cost and efficiency improve, but EMI level increases
Solution Approach 1:
A ground member is introduced as an intermediary element within the FPC structure. This ground member extends from the first driving circuit board through the FPC to the second driving circuit board, providing a dedicated reference potential path that mediates electromagnetic interference between the two PCBs and reduces EMI levels while maintaining the compact 2-PCB configuration
Solution Approach 2:
The ground structure parameters are modified by extending the ground member through the FPC connection rather than using traditional separate ground connections. This parameter change in the grounding architecture creates a continuous low-impedance ground path that reduces EMI without requiring additional external grounding components
2Area of moving object
If driving part length is increased to accommodate larger LCD, then display size increases, but manufacturing cost increases
Solution Approach 1:
The driving circuit is segmented into two separate driving circuit boards (first and second PCBs) connected via FPC. This segmentation allows the driving circuits to be positioned closer to the LCD panel, reducing the overall driving part length and associated manufacturing costs while maintaining full display area functionality
Solution Approach 2:
The FPC enables a three-dimensional routing configuration where the ground member extends vertically through the FPC thickness and horizontally between PCBs. This dimensional approach allows compact integration of grounding functionality without increasing the horizontal footprint or driving part length
Data Source
AI summary
An LCD comprising an LCD panel on which an electrode pad is provided; a light source irradiating light to a portion of the LCD panel; a bottom chassis accommodating the light source; a driving part connected to the electrode pad and applying a driving signal to the LCD panel; a driving circuit part controlling the driving part and comprising a first driving circuit board connected to the driving part and disposed on a lateral side of the bottom chassis and a second driving circuit board connected to the first driving circuit board and disposed on portion of the bottom chassis; and an FPC connecting the first driving circuit board to the second driving circuit board and comprising a ground member electrically connected to the bottom chassis, and exposed to the outside. Accordingly, the present invention provides a liquid crystal display decreasing an EMI level of the FPC.