Novel Technique for Precision Soldering Based on Laser-Activated Gold Nanoparticles

This paper introduces a novel technique for repairing defective soldering joints in densely packed printed circuit boards and multichip modules. The new technique is not based on conventional soldering methods or tools, but rather on the remarkable properties of gold nanoparticles. Gold nanoparticles are deposited on the surface of the solder pad or joint that must be reworked, and a low-power laser with a wavelength in the range of 500-800 nm is directed to the area where the gold nanoparticles are present. The nanoparticles absorb the electromagnetic radiation at such wavelengths very effectively, and intense surface plasmons are generated in the nanoparticles. The surface plasmons cause the nanoparticles to heat up, where the temperature can reach several hundred degrees of Celsius. This in turn causes the solder that is in contact with the nanoparticles to melt, while other solder joints in the vicinity remain unaffected. The narrow wavelength range of 540-572 was determined to be the optimal range of wavelengths for the present application.