Low Temperature Metal Stack for LED Die Attach
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Solution Overview
Problem
Conventional die attach materials, such as silicone and AuSn 80/20 alloys, are inadequate for high-light-output LED applications due to poor thermal conductivity and compatibility issues with plastic packages, leading to reliability and performance limitations, especially at higher drive currents and elevated temperatures.
Innovation Solution
A metal die attach stack comprising a bonding layer with a high tin content (>40%) and gold (<10%), along with a nickel layer, which is thermally stable up to 260°C, allowing for lower reflow temperatures and enhanced thermal properties without damaging plastic packages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional AuSn 80/20 alloy die attach is used, then good mechanical strength and thermal conductivity are achieved, but high reflow temperature (305°C) damages plastic packages
Solution Approach 1:
The patent changes the compositional parameters of the die attach alloy by reducing gold content from 80% to 60-70% and increasing silver content to 30-40%, creating a new alloy system with lower melting point that maintains bonding reliability while enabling lower reflow temperatures compatible with plastic packages
Solution Approach 2:
The patent creates a composite die attach structure using a multi-layer metal stack including Cu/Sn/Au or Cu/Sn/Silver alloy combinations, where each layer performs specific functions (thermal conduction, bonding, oxidation resistance) to achieve both low-temperature processing and high-reliability attachment
2Ease of manufacture
If silicone die attach material is used, then ease of application is improved, but poor thermal conductivity limits LED performance at high drive currents
Solution Approach 1:
The patent replaces the silicone-based polymer die attach material with a metal-based bonding system (Cu/Sn/Au or Cu/Sn/Silver alloy stacks), substituting a mechanically-applied polymer system with a thermally-conductive metal bonding system that provides superior thermal management while maintaining manufacturability through controlled deposition and bonding processes
3Illumination intensity
If larger LED die are used to increase light output, then illumination intensity is improved, but higher drive currents require better thermal conductivity that silicone cannot provide
Solution Approach 1:
The patent extracts the thermal management function from the silicone die attach material and assigns it to a dedicated metal thermal conduction layer (Cu/Sn/Au or Cu/Sn/Silver alloy stack), allowing the die attach system to simultaneously provide mechanical bonding and superior thermal conduction pathways that efficiently remove heat from high-power LED junctions
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
The solution improves thermal conductivity and reliability of LED packages, enabling higher light output at lower currents while maintaining stability and compatibility with plastic packages, reducing thermal resistance and reflow temperature requirements.
Implementation Method 1
a bonding layer on the light emitting diode that contacts the package surface and provides mechanical attachment of the light emitting diode to the package surface
Implementation Method 2
The metal stack includes a bonding layer on the light emitting diode that contacts the package surface and provides mechanical attachment of the light emitting diode to the package surface
Data Source
AI summary
A light emitting diode structure includes a diode region and a metal stack on the diode region. The metal stack includes a barrier layer on the diode region and a bonding layer on the barrier layer. The barrier layer is between the bonding layer and the diode region. The bonding layer includes gold, tin and nickel. A weight percentage of tin in the bonding layer is greater than 20 percent and a weight percentage of gold in the bonding layer is less than about 75 percent. A weight percentage of nickel in the bonding layer may be greater than 10 percent.