Light Emitting Device Wire Bonding Stress Reduction
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Solution Overview
Problem
Conventional light emitting devices of the chip-on-board (COB) type face issues with wire disconnection and reduced working efficiency due to stress on the electrically conductive wire caused by resin expansion and external pressure, which can lead to unreliable bonding and increased risk of disconnection.
Innovation Solution
A light emitting device design featuring a substrate with electrically conductive layers having a second region positioned higher than the first region, where the light emitting elements are connected via an electrically conductive wire sealed by a light-transmissive resin molded portion with centrally projected cylindrical lens portions, reducing the overlap area between the resin and the bonding portion and thus minimizing stress on the wire.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the electrically conductive wire is bonded to raise the electrically conductive layer to eliminate steps, then wire bonding efficiency is improved and disconnection is reduced, but the device complexity increases due to the need for additional processing steps
Solution Approach 1:
The electrically conductive layer is raised in advance before wire bonding to eliminate steps and create a flat bonding surface. This preliminary action prevents wire disconnection and improves bonding efficiency by ensuring proper wire contact with the bonding target.
Solution Approach 2:
The electrically conductive layer is divided into different height regions (raised portion and non-raised portion) to serve different functions: the raised portion provides a flat bonding surface for wire connection, while the non-raised portion maintains the original electrical connection function.
2Reliability
If the resin molded portion completely covers the light emitting elements and wires for sealing, then protection is improved, but stress on the electrically conductive wire increases due to resin expansion and external pressure
Solution Approach 1:
The resin molded portion is segmented to provide different coverage levels: it covers the light emitting elements for protection but intentionally leaves the raised electrically conductive layer exposed or partially exposed to reduce stress on the bonded wire while maintaining adequate sealing.
3Ease of manufacture
If the second region of the electrically conductive layer is positioned at the same level as the first region, then manufacturing is simplified, but wire bonding efficiency decreases due to step formation
Solution Approach 1:
The second region of the electrically conductive layer is raised in advance to create a step-free bonding surface. This preliminary elevation eliminates the need for complex wire bonding maneuvers around steps, thereby improving bonding efficiency and working efficiency.
4Illumination intensity
If the cylindrical lens portions are made larger to improve light distribution, then optical performance is improved, but the overlap area with the bonding portion increases, causing more stress on the wire
Solution Approach 1:
The resin molded portion is designed with locally differentiated properties: in the region overlapping the raised electrically conductive layer, the resin coverage is reduced or eliminated to minimize stress on the wire, while in other regions, the cylindrical lens portions maintain their light-distributing function with adequate size.
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 enhances the reliability of the light emitting device by reducing the likelihood of wire disconnection and improving bonding efficiency, while also allowing for uniform stress distribution on the electrically conductive wire, thereby maintaining the integrity of the device under thermal expansion and external pressure.
Implementation Method 1
a sealing member formed by linking a plurality of semicylinder-shaped cylindrical lens portions made of resin
Data Source
AI summary
A light emitting device includes light emitting elements. A substrate includes electrically conductive layers each having a first region in which the light emitting elements are arranged and a second region connected to the first region and provided at a position higher than the first region. An electrically conductive wire electrically connects the light emitting elements arranged on the electrically conductive layer and the second region of the adjacent electrically conductive layer. A resin molded portion is formed of a light-transmissive resin that seals the light emitting elements and the electrically conductive wire. The resin molded portion has a shape in which centrally projected cylindrical lens portions is aligned, and in each of the cylindrical lens portions, the light emitting elements is arranged in a line shape. The second region is arranged between the light emitting elements in the light emitting element array.