Electronics Assembly Knowledge, Vision & Wisdom
NanoCopper Based Solder-free Electronic Assembly
NanoCopper Based Solder-free Electronic Assembly
This paper explores a nanotechnology enabled copper-based electrical interconnect material that can be processed around 200 degrees.
Materials Tech

Materials Tech programs cover topics including:
Adhesives, Chemicals, Cleaning Solutions, Coatings, Components, Design, Embedded Technology, Fasteners, Finishes, Flex Circuits, Flip Chip, Fluxes, PC Fab, Solders, Solder Masks, Solder Paste and more.
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Authored By:
A. A. Zinn, R. M. Stoltenberg, J. Beddow, J. Chang
Lockheed Martin Space Systems Company
Advanced Technology Center
Palo Alto, CA USA

Summary
The Advanced Technology Center of the Lockheed Martin Corporation has developed a nanotechnology enabled copper-based electrical interconnect material that can be processed around 200C. The readily scalable Cu nanoparticles synthesis process uses a low cost solution-phase chemical reduction approach. A pilot plant is fully operational producing one lb per batch of nanomaterial. We have demonstrated assembly of fully functional LED test boards using a copper-nanoparticle paste with a consistency similar to standard solder. Further improvements have led to the assembly of a small camera board with a 48 pad CMOS sensor QFN chip and a 26 pin throughhole connector.

In addition, we have a fully functional nanocopper assembly line in place for process development using standard industrial off-the shelf equipment. We are currently working with a commercial assembly house to dial-in the board assembly process. The fused material shows a tensile strength that is already in the range of space qualified solder. Once fully optimized, the nanocopper-based (trademarked CuantumFuseTM) solder-like material is expected to produce joints and interconnects with up to 10 times the electrical and thermal conductivity compared to tin-based solders currently in use and with a bond strength comparable or better than eutectic SnPb. Applications in space and commercial systems are currently under consideration.

Conclusions
In summary, we have developed an all-copper electronic assembly material that can be processed at 200C. Through improvements in nanocopper synthesis, paste formulation, and processing techniques, a fully functional camera board was successfully assembled using only nanocopper paste. Coupled with the proven scalability of our unique nanocopper synthesis process, this demonstration illustrates the utility and potential of nanocopper as a replacement for SnPb and Pb-free solders.

The electrical conductivity of nanocopper is already 2-3 times higher than standard solder currently in use. Also, the tensile strength is approaching that of the best solders available. Nanocopper is still in the early development stages, yet improvements in strength, thermal conductivity, and electrical conductivity have been rapid. There is plenty of room for further improvement as the full materials properties potential of nanocopper have yet to be realized.

We are aggressively pursuing further improvements in all areas of perfomance. The fact that this material already performs simlar to or better than existing materials shows the exciting potential of nanocopper to be a robust alternative to the current library of lead-free solders.

Initially Published in the IPC Proceedings

Comments
The nano-particle copper material would seem to eliminate the problems with tin-based solder whiskers. What's the downside?
Maris Graube, Relcom, USA
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