LED Electrode Pad Ductility Layer for Stress Relief
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Solution Overview
Problem
The flip chip bonding technology for light emitting diodes (LEDs) leads to stress generation due to thermal expansion and contraction during the eutectic bonding process, resulting in cracks and reduced quality due to current leakage.
Innovation Solution
Incorporating a ductility layer between the eutectic layer and the semiconductor epitaxial structure in the electrode pad structure, which reduces stress and prevents cracking by using materials like Au, Ag, Al, Ni, Ti, and Pt, and optionally an adhesive layer to enhance connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If flip chip bonding technology is used for LED packaging, then the size of chip package is reduced and signal transmission path is shortened, but stress is generated in the LED due to thermal expansion and contraction of the substrate during eutectic bonding, causing cracks in metal pads
Solution Approach 1:
The electrode pad structure is segmented into multiple functional layers: a eutectic layer for bonding, a barrier layer to prevent material diffusion, and a ductility layer to reduce stress. This segmentation allows each layer to perform its specific function, resolving the contradiction between achieving strong bonding and preventing stress-induced cracking.
Solution Approach 2:
The electrode pad structure uses composite materials with different properties: the eutectic layer (Au, Au/Sn, or Sn/Ag/Cu) provides bonding capability, the barrier layer (Ni, Ti, or Pt) prevents diffusion, and the ductility layer (Au, Ag, Al, Ni, Ti, Cr, or Pt) reduces stress. This composite structure resolves the contradiction by combining materials with complementary properties.
2Reliability
If eutectic bonding process is performed with heating, then electrical connection between LED and substrate is achieved, but thermal expansion and contraction of the substrate generates stress that leads to current leakage
Solution Approach 1:
The ductility layer acts as an intermediary between the rigid substrate and the semiconductor epitaxial structure. It absorbs and redistributes the stress generated during thermal cycling, preventing stress concentration that would otherwise cause cracks and current leakage, while still allowing reliable electrical connection to be formed.
Solution Approach 2:
The invention changes the physical parameters of the electrode pad structure by introducing layers with different mechanical and thermal properties. The ductility layer has specific material properties that allow it to accommodate thermal expansion differences, changing the stress distribution parameters to prevent cracking during the heating process.
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 ductility layer effectively mitigates stress-induced cracking, maintaining the quality of the LED by ensuring reliable electrical connections and preventing current leakage.
Implementation Method 1
the light emitting diode and the substrate are heated in a reflow oven to achieve eutectic bonding and electrical connection between the light emitting diode and the circuit of the substrate
Implementation Method 2
during the eutectic bonding, the substrate is subjected to thermal expansion and contraction in the heating process, so stress is generated in the light emitting diode
Implementation Method 3
The ductility layer reduces the stress on the light emitting diode produced by thermal expansion and contraction of the substrate during the heating phase in the eutectic bonding process
Implementation Method 4
The barrier layer blocks the diffusion of the material of the eutectic layer in the eutectic bonding process
Data Source
AI summary
Provided is a light emitting diode (LED) mounted on a carrier substrate and including a semiconductor epitaxial structure and at least one electrode pad structure. The semiconductor epitaxial structure is electrically connected to the carrier substrate. The electrode pad structure includes a eutectic layer, a barrier layer and a ductility layer. The eutectic layer is adapted for eutectic bonding to the carrier substrate. The barrier layer is between the eutectic layer and the semiconductor epitaxial structure. The barrier layer blocks the diffusion of the material of the eutectic layer in the eutectic bonding process. The ductility layer is between the eutectic layer and the semiconductor epitaxial structure. The ductility layer reduces the stress on the LED produced by thermal expansion and contraction of the substrate during the eutectic bonding process, so as to prevent the electrode pad structure from cracking, and maintain the quality of the LED.