Ultra-Stable Sintered Silver Die Attach for Demanding High-Power/Temperature Applications

Abstract

Abstract:A novel and simple processing step has been demonstrated to produce thermally stable sintered silver nanoparticles structures. Sintered silver has been investigated as a die attach to resolve the long-standing demand for a reliable material to enable high power/temperature electronics operating above 300 °C. However, it is now a well-known fact that such materials undergo massive microstructural evolution at 250 °C and above, creating doubts about their longterm reliability. Here an additional processing step utilizing oxidizing treatment is demonstrated to immobilize the silver atoms through formation of Ag2O. This technique stabilizes sintered silver up to 400 °C, taking advantage of the open pore network to facilitate treatment deep in the material interior.

Arresting high-temperature microstructural evolution inside sintered silver

“…It has been previously shown that sintered silver can be stabilised through exposure to steam, and it has also been revealed that placing the sintered silver in water before exposure to high temperatures provides the same effect [10] [11]. In the previous studies the treated samples have demonstrated stability up to at least 600 h at 300 °C, and up to at least 24 h at 350 °C and 400 °C.…”

“…Silver nanoparticle paste from NBE Tech, LLC, NanoTach® X-Paste was chosen for this work due to the numerous previous studies of this and similar systems [10]. The material is recommended for die sizes of up to 10×10 mm with a pressure-less sintering process, and peak sintering temperature of 255 Cº for 25 minutes.…”

“…The grain sizes were analysed by taking optical images of the samples and analysing the average grain sizes of the samples using ImageJ 1.46 and the Matlab® image processing toolbox. Detailed description of grain size calculations can be found in references [10], [13]. The measured average grain sizes were then investigated to estimate the limitations of the sintered silver stabilisation technique at each storage temperature.…”

“…One attempt to increase the thermal stability of sintered silver uses a gold mesh interposer [8], and another utilizes addition of SiC [9]. The method described in this work stabilizes sintered silver without addition of other secondary materials or complex manufacturing steps [10] [11]. Cleaning electronics by water dipping is a standard method used for electronics cleaning without any moisture absorption-related risks [12].…”