In-Ag Solid-Liquid Interdiffusion Bonding for LED Die Bonding
Date Issued
2011
Date
2011
Author(s)
Hsieh, Chih-Wei
Abstract
As the awakening of environment-friendly conscious, green-industries are attracting much attention in today’s society. We regard light emitting diode (LED) as the most potential lighting technique in the future due to its advantages: energy conservation, long life, high reliability and low pollution. However, LED is affected by temperature significantly. Both the light output efficiency and life will be cut down dramatically with increasing junction temperature. Therefore, precise thermal management is one of the most important issues of LED development.
This research focuses on the die bonding process in high-power LED packaging. There are three major methods for LED die bonding now: silver paste, lead-free solder and Au-Sn eutectic bonding. Each of them has pros and cons; no one can replace the others. In this study, we use “In-Ag solid-liquid interdiffusion bonding (SLID) technique” for LED die bonding because it allows LED chip to bond at low temperature; for the multilayer structure preparation, we use electroplating and electroless plating process because it costs less and uses simple equipments. After bonding, we execute the die shear test and the thermal resistance measurement. Moreover, we observe and analyze the micrograph and composition of the broken interface and the joint cross-section.
The results show that, both increasing the thickness of Ag deposits and lowering the bonding temperature could reduce the thermal stress induced by coefficient of thermal expansion (CTE) mismatch between materials and enhance the bonding strength. Although the bonding strength is worse than the three commercial techniques for LED die bonding, still, it already surpassed the MIL-STD 883G. On the other hand, the thermal resistance of In-Ag SLID is lower than the other three common LED die bonding methods. It indicates that In-Ag SLID is a technique of great thermal conductivity. Besides, the joint is nearly void-free, and mainly composed of Ag2In IMC and Ag.
To sum up, In-Ag SLID is a technique of low bonding temperature which enables LED chip to remain complete during the process. The thermal conductivity of the joint is outstanding, and it can help the heat dissipation of LED chip. But the bonding strength has to be further improved in order to enhance the joint reliability.
Subjects
LED
Thermal management
Die bonding
In-Ag SLID
Electroplating
Electroless plating
SDGs
Type
thesis
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