LED Package Lead Frame Pillars Reduce Silver Tarnishing
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Solution Overview
Problem
Silver used in LED packages is prone to tarnishing due to environmental agents, leading to reduced reflectivity, which is a common issue in polluted areas.
Innovation Solution
The LED package design minimizes the use of silver by employing a metal lead frame with raised pillars and a highly reflective molding material, where the pillars provide electrical contact while the molding material, such as silicone compounds, offers optical reflectivity, reducing the exposed silver surface and thus the tarnishing risk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver is used to provide electrical conductivity and optical reflectivity in LED packages, then electrical conductivity and reflectivity are improved, but silver is prone to tarnishing in polluted environments which reduces reflectivity over time
Solution Approach 1:
The patent extracts silver from the bottom surface of the well, removing it from areas where it would be exposed to environmental agents. The silver is retained only on electrical contact elements (lead frame pillars and traces) where it serves its electrical function, while the optical reflection function is transferred to a different material (molding compound) that is not susceptible to tarnishing.
Solution Approach 2:
The molding compound is given multiple functions: it provides structural support, electrical insulation, and optical reflection. By making the molding compound highly reflective, it assumes the optical reflection function previously performed by silver, while the lead frame silver is restricted to electrical contact functions only.
2Reliability
If silver is used extensively for both electrical contact and optical reflection, then electrical conductivity and reflectivity are maintained, but the exposed silver surface area increases leading to greater tarnishing risk
Solution Approach 1:
Silver is extracted from the bottom surface area and confined to only the necessary electrical contact elements. This dramatically reduces the quantity of exposed silver while maintaining electrical functionality, as the silver is now limited to lead frame pillars and traces rather than covering the entire bottom surface.
Solution Approach 2:
Different materials with appropriate properties are applied locally: silver is applied only where electrical conductivity is needed (contact elements), while the molding compound provides both structural and optical functions in areas where silver would be unnecessarily exposed to environmental agents.
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 design maintains optical reflectivity and electrical conductivity while minimizing silver tarnishing, ensuring consistent performance even in polluted environments.
Implementation Method 1
The molding material is a highly reflective material to reflect light from the LED and provide good optical characteristics for the LED package
Data Source
AI summary
Embodiments of the invention include a package for a light emitting diode (LED). The package includes a lead frame, an LED, and an optically reflective but electrically non-conductive molding. The lead frame has a first lead frame part and a second lead frame part electrically isolated from the first lead frame part, each lead frame part having at least one raised pillar. The molding is disposed over the lead frame except over the pillars of the lead frame. The LED is mounted on at least one pillar and is electrically coupled to at least one pillar. The molding serves the purpose of a highly reflective, electrically conductive material like silver without being subject to tarnishing.