Variable Bond Strength Adhesive for FPC Rework Stress Control
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Solution Overview
Problem
In liquid crystal display apparatuses, the separation of flexible printed circuit boards (FPCs) with LEDs mounted on them from double-faced adhesive sheets during rework applies excessive stress to soldered joint portions, leading to potential cracking and defective illumination.
Innovation Solution
The use of double-faced adhesive sheets with varying bond strengths, where the bond strength is lower on one end and higher on the other, allows for controlled peeling of the FPC without excessive stress on the LED terminals, preventing joint cracking and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the FPC is stuck to the double-faced adhesive sheet with uniform bond strength, then the FPC is firmly fixed during normal use, but excessive stress is applied to the LED joint portions during rework causing separation or cracking
Solution Approach 1:
The adhesive sheet is designed with different bond strengths at different locations: the first adhesive region (near LED mounting position) has lower bond strength to protect joint portions during rework, while the second adhesive region (away from LED mounting position) has higher bond strength to ensure firm fixation during normal use. This local differentiation resolves the contradiction between firm fixation and rework safety.
2Ease of repair
If the FPC is separated from the adhesive sheet for rework, then defects can be repaired, but the FPC deforms and excessive stress is applied to the LED terminals
Solution Approach 1:
By making the bond strength location-dependent, the patent enables easy separation at the first adhesive region (lower bond strength) for rework while the second adhesive region (higher bond strength) remains intact, preventing FPC deformation and excessive stress on LED terminals during the separation process.
Solution Approach 2:
The adhesive sheet is segmented into multiple adhesive regions with different bond strengths. This segmentation allows controlled separation at specific locations (first adhesive region) while maintaining attachment at other locations (second adhesive region), enabling rework without damaging the LED joint portions.
3Stability of the object's composition
If the FPC is firmly fixed during normal use, then stable illumination is achieved, but rework becomes difficult and may cause deformation
Solution Approach 1:
The adhesive sheet provides different fixation characteristics at different locations: strong fixation at the second adhesive region ensures stability during normal use, while the weaker first adhesive region allows easy separation for rework, resolving the contradiction between stability and repairability.
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 reduces the number of defective units, ensures stable illumination, and prevents uneven luminance by balancing stress during rework and normal use, enabling cost-effective manufacturing of high-quality display images.
Implementation Method 1
the FPC is stuck to a predetermined position of the backlight unit via the double-faced adhesive sheet (double-faced tape)
Data Source
AI summary
An illumination device includes a light source member, a flexible wired board the light source member mounted thereon and a wiring provided thereon, and a structure to be stuck to the wired hoard via sticking members at a plurality of sticking surfaces, wherein one end of the wiring provided on the wired board is electrically connected to and terminated at the light source member, and the other end of the wiring is provided with a connecting path to be electrically connected to the outside, and wherein the bond strength of the plurality of sticking surfaces is set in such a manner that the bond strength of the sticking surface located on the one end side of the wiring is lower than that of the sticking surface located on the other end side of the wiring.