Journal of SMT Article

A Nanocopper Based Alternative to High Temperature Solder

Authors: S. Hamasha, A. Sharma, B. Schnabl, L. Cheng, L. Desir, K. Bretz, L. Wentlent, A. A. Zinn, J. Beddow, K. Schnabl, E. Hauptfleisch, D. Blass, and P. Borgesen
Company: Binghamton University, Lockheed Martin, and Auburn University
Date Published: 4/1/2017   Volume: 30-2

Abstract: Alternatives to high temperature solder remain limited. The CuantumFuseTM material under development by the Advanced Technology Center at the Lockheed Martin Corporation appears to be the only one to offer the potential for a drop-in replacement of solder as far as SMT assembly equipment and processes are concerned. The Cu nanoparticle paste is printable with the consistency of solder paste and the particles fuse together at 200°C in a conventional full convection reflow oven. This is motivating ongoing studies of the associated reliability. The challenge is that the resulting Cu joint is nano-crystalline and nano-porous, lending it some unique properties, and that the microstructure is not thermally stable. However, the joint does remain solid up to higher temperatures than envisioned in any microelectronics application.

Assessment of the reliability of existing joints, not to mention the optimization and prediction of the reliability of new versions of the material, will require much more than just accelerated testing. Different versions of the nano-Cu material are being characterized in terms of creep rates and mechanisms as well as the behavior in both thermal and isothermal cycling. Microstructures are characterized by FIB polishing, to preserve porosity structures, followed by optical microscopy, SEM, and TEM. Generalization of results requires us to distinguish between competing effects of the distributions of grain sizes and pores on creep. Experiments were extended to include nano-porous Au samples with much larger grain sizes to help resolve that.

We conclude that counteracting effects of grain sizes and pore distributions on ductility, strength and fatigue resistance may offer opportunities for optimization of nano-particle based joint structures. So far we argue that comparisons of the present nano-Cu material to solder in accelerated thermal or isothermal cycling will tend to be extremely conservative.


Key words: Nano-particles, high temperature, reliability

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