Surface-Mounted LED with Thick Electrode Pads
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Solution Overview
Problem
Conventional Surface-Mounted Technology (SMT) packaging for LED light-emitting devices faces challenges in thermal resistance and stability, particularly during the reflow soldering process, where flip-chip designs lack a supporting substrate and struggle with electrode pad asymmetry leading to potential electric connection failures.
Innovation Solution
The solution involves directly mounting an LED epitaxial structure with thick P and N electrode pads and an insulator between them over a supporting substrate, eliminating the need for a package step and ensuring physical support and electrical isolation, thereby simplifying the fabrication process and enhancing reliability during reflow soldering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SMT packaging is used with a package body, then the LED chip is protected and mounted on PCB, but thermal resistance increases and device stability deteriorates during reflow soldering
Solution Approach 1:
The patent extracts and removes the conventional package body structure, directly mounting the LED chip with electrode pads onto the PCB substrate. This elimination of the intermediate package body reduces thermal resistance pathways and improves heat dissipation while maintaining mechanical stability through direct bonding structures.
Solution Approach 2:
The patent applies preliminary bonding structures and support layers to the LED chip before the reflow soldering process. These pre-applied structural elements ensure the chip maintains stability during subsequent high-temperature processing, preventing deformation or displacement that would occur without such preliminary support measures.
2Ease of manufacture
If flip-chip LED design is used without supporting substrate, then mounting is simplified, but electrode pad asymmetry causes potential electric connection failures
Solution Approach 1:
The patent intentionally designs asymmetric electrode pad structures where the anode and cathode pads have different dimensions, shapes, or positions. This asymmetric design compensates for manufacturing tolerances and alignment variations during mounting, ensuring reliable electrical connections by providing larger contact areas for the more critical connection points.
Solution Approach 2:
The patent incorporates support layers and bonding structures beneath the LED chip before the mounting process. These preliminary support structures compensate for potential misalignments or stress during reflow soldering, cushioning against forces that would otherwise cause connection failures and ensuring robust electrical bonding.
3Ease of manufacture
If growth substrate is retained in LED structure, then chip fabrication is simplified, but device cost increases and luminous effect deteriorates
Solution Approach 1:
The patent removes the growth substrate after the LED active layers are formed on it. The growth substrate serves only as a temporary platform for epitaxial growth, and its removal eliminates parasitic optical absorption and scattering that would degrade light output, while the transferred LED structure maintains the manufacturing advantages of growth-substrate-based fabrication.
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 approach reduces costs, improves the reliability of LED light-emitting devices by providing adequate support for the epitaxial structure, preventing short circuits, and allowing for the removal of the growth substrate, thus enhancing the luminous effect and stability during the SMT process.
Implementation Method 1
a LED epitaxial structure having two opposite surfaces, in which, the first surface is a light-emitting surface
Implementation Method 2
an insulator between the P and N pads to prevent the P and N electrode pads from short circuit
Data Source
AI summary
A surface-mounted light-emitting device is fabricated by epitaxial growth: forming the LED epitaxial structure over a growth substrate through epitaxial growth; chip fabrication: determining P and N electrode regions and an isolating region over the LED epitaxial structure surface and fabricating the P and N electrode pads and the insulator over the P and N electrode regions and the isolating region, wherein the P and N electrode pads have sufficient thicknesses to support the LED epitaxial structure, and the insulator is formed between the P and N electrode pads to prevent the P and N electrode pads from a short circuit; removing the growth substrate and unitizing the LED epitaxial structure to form the chip; and SMT packaging: providing the supporting substrate and directly mounting the P and N electrode pads of the chip over the supporting substrate through SMT packaging to thereby form the surface-mounted LED light-emitting device.