Light Emitting Device Electrode Extended Sections for Solder Alignment
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Solution Overview
Problem
Conventional light emitting devices face issues with improper self-alignment and solder ball generation due to the shape of redundant reflow pads and separate electrodes, leading to voids in molten solder during the reflow process.
Innovation Solution
The light emitting device incorporates first and second extended sections on the substrate electrodes to guide the heat-melted connecting material, preventing solder ball formation and ensuring excellent self-alignment by controlling the surface tension of the connecting material, thereby maintaining a precise connection between electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a redundant reflow pad is provided along the outer circumference of the LED element to prevent solder ball generation, then solder ball formation is reduced, but improper self-alignment occurs causing improper positioning of the mounted light emitting element
Solution Approach 1:
The reflow pad is segmented into two distinct functional zones: an extended section that protrudes beyond the light emitting element's outer circumference to prevent solder ball generation, and a non-extended section that aligns with the element to provide self-alignment during mounting. This segmentation allows each zone to perform its specific function without interfering with the other.
Solution Approach 2:
Different regions of the reflow pad are given different geometric properties: the extended section has a larger area extending beyond the element to control solder flow and prevent balling, while the non-extended section maintains precise alignment with the element boundaries to ensure proper positioning. This local differentiation of pad geometry resolves the contradiction between solder ball prevention and self-alignment.
2Reliability
If separate first and second substrate electrodes are used corresponding to P-type and N-type electrodes, then electrical connection is achieved, but molten solder converges towards the second electrode forming excessive connecting thickness and generating voids
Solution Approach 1:
The first extended section is designed to extend beyond the light emitting element's outer circumference, creating an asymmetric configuration that prevents molten solder from converging towards the second electrode. This asymmetric extension balances the solder distribution between the first and second electrodes, preventing excessive thickness and void formation while maintaining proper electrical connection.
3Reliability
If the shape of the electrode on the insulating substrate is made identical to the electrode on the LED element side, then proper electrical connection is achieved, but solder paste bulges out around the electrode and forms solder balls during reflowing
Solution Approach 1:
The reflow pad is divided into functional segments with different geometries: the extended section that protrudes beyond the element to contain solder paste and prevent balling, and the non-extended section that matches the element shape for proper electrical connection. This segmentation allows the pad to simultaneously achieve both connection reliability and solder ball prevention.
Solution Approach 2:
The reflow pad extends in the planar dimension beyond the light emitting element's outer circumference, creating a two-dimensional configuration that accommodates both functions: the extended portion controls solder flow to prevent balling, while the aligned portion ensures proper electrical connection. This dimensional extension resolves the contradiction between connection quality and solder ball prevention.
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 effectively prevents solder ball generation and voids, ensuring high-quality products with improved self-alignment performance, even in mass assembly, by using extended sections to manage the heat-melted connecting material effectively.
Implementation Method 1
ensuring excellent self-alignment by controlling the surface tension of the connecting material
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Disclosed is a light emitting device (1) comprising a rectangular element (10) mounted upon a mounting substrate (20) via a heat-melted connecting material, wherein second substrate electrodes (3) are formed conforming to the recesses (2c) of a first substrate electrode (2) and a portion of the outer periphery of the first and second substrate electrodes (2,3) is provided with first extended sections (2b) that extend farther outward than the outer periphery (gs) of the aforementioned element (10). The aforementioned first extended sections (2b) are formed in at least one or more locations per one side of the outer periphery (gs) of the aforementioned rectangular element (10); the aforementioned first substrate electrode (2) is provided with second extended sections (2d) that are formed on at least one of both ends of the aforementioned recesses (2c) flanking the first extended sections (2b) of the aforementioned second substrate electrodes; and the aforementioned second extended sections (2b) extend farther outward than the outer periphery of the aforementioned element (gs).