LED Solder Pad Segmentation for Crack Propagation Control
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Solution Overview
Problem
Flipchip type LEDs face high costs due to the use of expensive metal alloys for bonding and high-temperature packaging, and are prone to interface damage between solder pads and bumps, leading to separation issues.
Innovation Solution
A semiconductor light emitting device with a passivation layer, solder pads with separated regions, and solder bumps, where a crack blocking layer and inter-metallic compound layer are used to prevent crack propagation, and a barrier metal layer is disposed between the solder pads and electrodes to enhance bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal alloy such as AuSn is used as a bonding metal in flipchip type LEDs, then bonding strength is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive metal alloys (AuSn) with a cheaper solder material (Sn-Ni alloy) for the bonding process. While solder has lower melting point and is considered less durable than gold-based alloys, it provides sufficient bonding strength for LED applications at a significantly reduced cost, making the bonding material effectively 'disposable' after serving its primary function.
Solution Approach 2:
The patent changes the material composition parameters by using an Sn-Ni alloy with specific composition ratios instead of traditional AuSn alloys. This parameter change allows achieving adequate bonding strength while reducing manufacturing cost and enabling lower temperature processing.
2Strength
If a metal alloy with high melting point is used for bonding, then bonding strength is improved, but package material cost increases due to requirement of high-temperature resistant materials
Solution Approach 1:
The patent changes the thermal parameters by using a solder material with lower melting point (Sn-Ni alloy) instead of high-temperature metal alloys. This allows the use of standard, lower-cost package materials that do not require special high-temperature resistance properties, thereby reducing package material costs while maintaining sufficient bonding strength.
3Reliability
If solder pads are used in bonding regions, then electrical connection is improved, but interface damage and separation between solder pad and solder bump occur
Solution Approach 1:
The patent divides the solder pad into multiple separated regions rather than using a continuous pad structure. This segmentation prevents crack propagation across the entire interface - when stress or thermal expansion occurs, the separation between pad regions allows localized deformation without causing complete interface failure or separation between solder pad and bump.
Solution Approach 2:
The patent incorporates an inter-metallic compound layer (such as Cu-Sn alloy) at the interface between the solder pad and solder bump. This layer acts as a cushioning buffer that absorbs stress and prevents direct contact between the solder and the underlying structure, thereby preventing interface damage and separation before they can occur during operation.
4Strength
If barrier metal layer is added between solder pads and electrodes, then bonding strength is improved, but device complexity increases
Solution Approach 1:
The patent introduces a barrier metal layer (such as Cu or Cu alloy) as an intermediary between the solder pad and the electrode. This intermediate layer serves multiple functions: it strengthens the bonding interface, prevents unwanted chemical reactions, and improves electrical conductivity. While it adds a structural layer, the benefits in bonding strength and reliability outweigh the increased complexity.
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 effectively prevents damage and separation at the solder pad and bump interface, increasing bonding strength and reducing the risk of crack propagation, thereby enhancing the reliability and cost-effectiveness of the LED device.
Implementation Method 1
A crack blocking layer may be disposed in each isolation region
Implementation Method 2
An inter-metallic compound layer may be disposed on a surface of each solder pad with which a solder bump is in contact
Implementation Method 3
A barrier metal layer may be disposed between the solder pads and the first and second electrodes
Data Source
AI summary
A semiconductor light emitting device includes a multi-region solder pad. The semiconductor light emitting device includes a light emitting diode (LED) chip having a first surface on which first and second electrodes are disposed and a second surface opposing the first surface. A passivation layer is disposed on a surface of the LED chip such that bonding regions of the first and second electrodes are exposed through the passivation layer. A solder pad is disposed in each respective bonding region and has a plurality of separated regions. A solder bump is disposed in each respective bonding region and covers the plurality of separated regions of the respective solder pad. In the semiconductor light emitting device, separation between the solder pad and the solder bump may thereby be effectively prevented by ensuring that an interface between a solder pad and a solder bump is not entirely damaged.