Flexible Printed Circuit Pad Layout for Stable LED Reflow Welding
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Solution Overview
Problem
In liquid crystal display devices, especially in vehicle-mounted products, the traditional design of LED pads with different sizes for positive and negative electrodes leads to uneven stress during reflow welding, causing offset and large angles of LED lamp beads, resulting in backlight leakage and poor optics.
Innovation Solution
The flexible printed circuit design includes groups of LED pads with a first pad, a second pad, and a third pad, where the first and second pads receive a first voltage signal, and the third pad receives a second voltage signal, ensuring consistent stress on the tin paste and preventing offset and large angles by making the first and third pads equivalent in size and shape, and symmetrically arranging lead wires for even stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional LED pads with different sizes for positive and negative electrodes are used, then the structure is simple, but the stress distribution during reflow welding becomes uneven causing offset and large angles
Solution Approach 1:
The negative electrode pad is divided into two separate pads (first pad and second pad), each connecting to separate lead wires. This segmentation allows independent stress distribution and positioning, preventing the offset and large angle problems caused by uneven stress in traditional single-pad designs.
Solution Approach 2:
The patent uses asymmetric pad configuration where the first and second pads have different arrangements relative to the LED lamp bead, but both receive the same voltage signal. This asymmetric layout optimizes stress distribution while maintaining electrical functionality, resolving the contradiction between simple structure and welding precision.
2Reliability
If different sized pads are used for positive and negative electrodes, then the design is simple, but backlight leakage occurs due to offset and large angles
Solution Approach 1:
By segmenting the negative electrode into two pads with separate lead wire connections, the patent achieves more precise positioning and stress distribution. This prevents LED lamp bead offset and large angles, eliminating backlight leakage while maintaining reasonable design complexity.
Solution Approach 2:
The patent applies different pad configurations to different locations: the first and second pads are positioned to optimize stress distribution, while the third pad (positive electrode) maintains its traditional position. This local optimization improves optical performance without requiring complete redesign of the entire pad structure.
3Manufacturing precision
If first pad and third pad are made equivalent in size and shape, then stress distribution is even, but the number of pads increases from two to three
Solution Approach 1:
The negative electrode is segmented into two pads instead of using one large pad. This segmentation achieves even stress distribution comparable to using two equivalent pads, but with the advantage that both pads share the same voltage signal, simplifying the electrical design compared to using two independent positive and negative pads.
Solution Approach 2:
The first and second pads are both connected to the same voltage signal (negative electrode), effectively merging their electrical function while maintaining separate physical positions for optimal stress distribution. This merging approach achieves uniform stress distribution with fewer independent electrical connections than using three separately powered pads.
Data Source
AI summary
Embodiments of the present disclosure disclose a flexible printed circuit, a light bar, a backlight module and a liquid crystal display device. The flexible printed circuit includes a substrate and a plurality of groups of LED pads located on the substrate, wherein each group of the LED pads is configured to mount one LED lamp bead, each group of the LED pads includes a first pad, a second pad and a third pad, the firs pad, the second pad and the third pad are arranged sequentially in a first direction, the first pad and the second pad both receive a first voltage signal, the third pad receives a second voltage signal, and the first voltage signal is different from the second voltage signal.