Flexible Printed Circuit Edge Cutouts for Water Migration Prevention
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Solution Overview
Problem
Existing flexible printed circuits (FPCs) in electronic devices, such as portable computers and flip-type cell phones, face challenges in preventing the migration of water due to gaps between the water-tight film and resin strips, which can lead to liquid intrusion into the device.
Innovation Solution
The FPC design incorporates resin strips with cutouts in their edges near the tail end, increasing the effective length of the edges and forming notches or oblong chambers to slow down liquid flow, combined with a water-tight film overlay to enhance sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a water-tight film is applied to cover the tail exit of the FPC, then water migration is reduced, but gaps remain at the edges that allow liquid intrusion
Solution Approach 1:
The edge of the resin strip is segmented by forming cutouts that create multiple smaller gap sections instead of one continuous gap. This segmentation increases the effective length of the edge and disrupts continuous liquid flow paths, making it more difficult for liquid to penetrate through the water-tight film interface.
Solution Approach 2:
The solution moves from a two-dimensional gap closure to a three-dimensional structure by forming cutouts with depth into the resin strip. This creates oblong chambers and notches that extend the liquid flow path in the vertical dimension, significantly increasing the time required for liquid to penetrate through the edge gaps.
2Reliability
If the resin strips are made thicker to prevent liquid intrusion, then sealing is improved, but the FPC becomes more rigid and less flexible
Solution Approach 1:
Instead of increasing the overall thickness of the resin strip, the solution segments the edge region by forming cutouts. This creates localized deeper sections at the edges while maintaining the overall thin profile and flexibility of the FPC. The segmented structure provides enhanced liquid resistance without compromising the global flexibility needed for the hinge application.
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
This configuration significantly increases the time it takes for liquid to travel along the edges, effectively inhibiting water migration into the device, with demonstration showing a delay from five minutes to twenty minutes, and allows any remaining liquid to evaporate without causing damage.
Implementation Method 1
there may be gaps 110 at the edge of the water-tight film 108 that can create channels along the edges of the strips 104, increasing the possibility of intrusion of liquid into the gaps 110
Implementation Method 2
liquid to travel along the edges
Implementation Method 3
the tail exit of the FPC 100 may be covered with a water-tight film 108, such as Mylar®
Implementation Method 4
The conductive traces are configured to electrically couple the first unit at a tail end of the FPC with the second unit at an opposing end of the resin strips
Implementation Method 5
bonding the resin strips to a baseplate
Data Source
AI summary
A flexible printed circuit (FPC) is provided comprising a base plate and a pair of elongated resin strips disposed on the base plate. The resin strips comprise conductive traces embedded between the resin strips and configured to electrically couple a first unit of an electronic device at a tail end of the resin strips with a second unit of the electronic device at an opposing end of the resin strips. The resin strips have edges having cutouts formed therein adjacent to the tail end.