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Intermetallics evolution and its reliability effects on micro-joints in flip chip assemblies

Ye Tian, Heng Fang, Ning Ren, Chao Qiu, Fan Chen, Suresh Sitaraman

Microelectronics International

ISSN: 1356-5362

Article publication date: 3 February 2020

Issue publication date: 11 June 2020

150

Abstract

Purpose

This paper aims to assess precise correlations between intermetallic compounds (IMCs) microstructure evolutions and the reliability of micro-joints with a Cu/SAC305solder/Ni structure using thermal shock (TS) tests.

Design/methodology/approach

This paper uses 200-µm pitch silicon flip chips with nickel (Ni) pads and stand-off height of approximately 60 µm, assembled on substrates with copper (Cu) pads. After assembly, the samples were subjected to air-to-air thermal shock testing from 55 to 125 per cent. The transfer time was less than 5 s, and the dwell time at each temperature extreme was 15 min. To investigate the microstructure evolution and crack growth, two samples were removed from the thermal shock chamber at 0, 400, 1,200, 2,000, 5,800 and 7,000 cycles.

Findings

The results showed that one (Cu, Ni)6Sn5/(Ni, Cu)3Sn4 dual-layer structure formed at the Ni pad interface of chip side dominates the micro-joints failure. This is because substantial (Ni, Cu)3Sn4 grain boundaries provide a preferential pathway for the catastrophic crack growth. Other IMCs microstructure evolutions that cause the prevalent joints failure as previously reported, i.e. thickened interfacial (Cu, Ni)6Sn5 and Ni3P layer, and coarsened IMCs inside the solder matrix, only contributed to the occurrence of fine cracks. Moreover, the typical interfacial IMCs spalling triggered by thermally induced stress did not take place in this study, showing a positive impact in the micro-joint reliability.

Originality/value

As sustained trends toward multi-functionality and miniaturization of microelectronic devices, the joints size is required to be constantly scaled down in advanced packages. This arises a fact that the reliability of small-size joints is more sensitive to the IMCs because of their high volume proportion and greatly complicated microstructure evolutions. This paper evaluated precise correlations between IMCs microstructure evolutions and the reliability of micro-joints with a Cu/SAC305solder/Ni structure using TS tests. It found that one (Cu, Ni)6Sn5/(Ni, Cu)3Sn4 dual-layer structure formed at the Ni pad interface dominate the micro-joints failure, whereas other IMCs microstructure evolutions that cause the prevalent joints failure exhibited nearly negligible effects.

Keywords

Acknowledgements

This work was supported by the National Natural Science Foundation of China under Grant U1704147. Support is also from Science and Technology Program of Henan Province under Grant 182102410048. The authors also acknowledge the valuable supports from The Youth Backbone Teacher Training Program of Henan University of Technology, and the Nano-Packaging and Interconnect Laboratory at the Korea Advanced Institute of Science and Technology.

Citation

Tian, Y., Fang, H., Ren, N., Qiu, C., Chen, F. and Sitaraman, S. (2020), "Intermetallics evolution and its reliability effects on micro-joints in flip chip assemblies", Microelectronics International, Vol. 37 No. 3, pp. 117-124. https://doi.org/10.1108/MI-07-2019-0048

Publisher

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Emerald Publishing Limited

Copyright © 2020, Emerald Publishing Limited

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