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Sintered Silver for LED Applications

  • H. ZhangEmail author
  • K. Suganuma
Chapter

Abstract

In the general illumination industry, LED is increasingly becoming a mature technology which possesses a series of advantages such as excellent performance, environmental-friendly properties, and economical operation cost.

In this chapter, various LED die-attach materials are introduced and compared. A conclusion is drawn after the discussions, that is, as an advanced technique for LED die attachment, sintered Ag matches well with the requirement of ultra-high-power LED die-attach and therefore attracts intensive research focus from industry and academia.

As a promising LED die-attach material, sintered Ag allows LED modules working at higher temperature with less energy loss and higher material robustness. Although its cost can be prohibitive—as much as four to five times more expensive than epoxy die-attach materials or solder materials, sintered Ag paste is commercially available in many high-end applications.

The reliability issues and corresponding countermeasures of sintered Ag for die-attach materials have also been discussed. Because sintered Ag materials are being widely used in the packaging of power devices, the cases and results included in this chapter are not limited to LED applications; emerging usage of sintered Ag in wide bandgap (WBG) power semiconductors will also be covered.

In the last section, a low temperature/pressure Ag-Ag direct bonding method for a high-temperature die-attachment structure has been introduced. The process uses “nano-volcanic eruption of Ag” caused by stress migration at 250 °C and therefore named as stress-migration-bonding (SMB) process. The bonding achieved a die-shear strength over 80 MPa, and neither joining paste nor solder is required. Only a pre-sputtered Ag thin layer on the surface of dummy chips and DBC substrates can realize bonding with a low pressure (1.0 MPa) provided by a simple bonding jig at 250 °C.

The formed Ag joint has an interface thickness of less than 3 μm, whose density is similar to that of bulk Ag. This feature realizes the ultra-high bonding strength as well as an ideal electric/thermal performance. The SMB technique is well compatible with the current die-attachment process for power devices. This breakthrough achievement will bring a bright future to the development of next-generation power devices with ultra-high performance and reliability.

Keywords

LED Wide bandgap (WBG) power semiconductors Die-attach Silver (Ag) sintering paste Stress migration bonding (SMB) Silver (Ag) nano volcanic eruption 

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Authors and Affiliations

  1. 1.Osaka UniversitySuitaJapan

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