Solder Ball Bonding for High-Power LED Thermal Management
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Solution Overview
Problem
Conventional bonding methods for high-power LEDs, such as gold-tin eutectic and epoxy bonding, face challenges with unstable bonding performance, large voids, and inadequate thermal conductivity, which are exacerbated by the increased size and power requirements of LEDs, leading to issues like thermal resistance and reduced emission efficiency.
Innovation Solution
A method involving the use of solder balls for bonding, where a solder ball is picked up, placed on a substrate, melted, and then used to bond a high-power LED chip without the need for flux or additional adhesive, utilizing a suction pick head and heat tunnel to ensure precise placement and formation of a solder joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If gold-tin eutectic bonding is used for HP-LED bonding, then bonding strength can be achieved, but large voids occur frequently and bonding performance becomes unstable due to large die size and thin solder layer
Solution Approach 1:
The patent changes the solder layer thickness parameter from thin (1-2 μm) to thick (5-10 μm), which resolves the contradiction by providing sufficient material to fill voids and ensure stable bonding performance while maintaining bonding strength through the eutectic bonding mechanism
Solution Approach 2:
The patent applies a thick solder layer beforehand to compensate for potential void formation during bonding. This cushioning layer ensures that even with large die sizes, the bonding interface maintains sufficient material coverage and stability, preventing bonding performance degradation
2Ease of operation
If epoxy bonding is used for HP-LED bonding, then ease of operation is improved, but thermal conductivity is insufficient leading to high thermal resistance and decreased emission efficiency
Solution Approach 1:
The patent replaces the epoxy bonding method with a solder-based method that uses a disposable thick solder layer. This eliminates the thermal conductivity limitations of epoxy while maintaining ease of operation through a simplified single-step bonding process that achieves both low thermal resistance and high bonding strength
Solution Approach 2:
The patent employs a composite bonding approach by using a thick solder layer that combines the advantages of eutectic bonding (low thermal resistance, high thermal conductivity) with the operational simplicity of epoxy bonding, creating a hybrid solution that overcomes the limitations of both individual methods
3Area of stationary object
If solder wire dispensing is used for bonding large dice, then bonding coverage is improved, but positioning precision deteriorates due to non-uniform wire tip shape and random wetting
Solution Approach 1:
The patent uses a mask template that copies the precise pad pattern onto the substrate. This mask-based approach ensures that solder is deposited only in the exact locations required, achieving both full bonding coverage and precise positioning by following the mask pattern rather than relying on wire tip uniformity or wetting behavior
Solution Approach 2:
The patent introduces a mask template as an intermediary between the solder dispensing system and the substrate. This mask mediates the positioning process by providing a physical template that ensures precise solder dot placement while maintaining adequate bonding coverage, eliminating the precision issues associated with direct wire dispensing
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 approach enhances bonding strength, reduces voids and thermal resistance, improves thermal conductivity, and simplifies the process, eliminating the need for flux and reducing production costs while ensuring accurate and reliable bonding.
Implementation Method 1
The solder ball is heated to a temperature sufficient to melt the solder ball and form a solder joint
Implementation Method 2
The solder ball is picked up by the suction pick head and placed onto the substrate
Data Source
AI summary
A method for bonding a semiconductor device onto a substrate is provided which comprises the steps of picking up a solder ball with a pick head, placing the solder ball onto the substrate and melting the solder ball on the substrate and placing the semiconductor device on the molten solder ball. The molten solder ball is then allowed to cool to form a solder joint which bonds the semiconductor device to the substrate.