Reactive NanoTechnologies, Inc. (RNT), developer and manufacturer of its patented NanoFoil®, announced that it has developed a bonding solution using NanoBond® for ruthenium (Ru) sputtering targets bonded to metal backing plates that does not require the use of backside metallization (BSM). Ruthenium is a technology enabler for what is known as perpendicular recording in hard disk drives, allowing more bits of information to be recorded in a smaller space, thus increasing storage capacity.
Traditional indium reflow bonding of Ru sputtering targets to metal backing plates requires the use of BSM. BSM of the bonding face of a Ru target is usually achieved by sputter deposition of a multilayer coating that acts as a diffusion barrier between the Ru and the indium solder and also enhances adhesion of indium solder. BSM thus represents an extra processing step that can add to lead time and increase costs for sputter target bonding.
The NanoBond® process of sputtering targets uses NanoFoil® to provide a localized heat source that reflows pre-applied solder layers on the target and the backing plate. Since the heat is localized to the solder layers, the target and backing plate are bonded at room temperature. This in turn allows NanoBond® to be compatible with tin (Sn) based solders that have significantly higher melting temperatures compared to indium. Sn can be applied directly to the bonding surface of Ru targets with the aid of acid flux.
RNT has conducted aging studies demonstrating that there is no significant diffusion of Sn into Ru. The diffusion distance of Sn into Ru after aging at 100ºC for 120 hours, is less than 2 µm. The integrity of the bond was confirmed with ultrasonic scanning and strength testing. Bond coverage was measured to be 99 % and shear strength of 27 MPa was measured with failure occurring exclusively in the Sn solder.
“The NanoBond® process is robust in that has different benefits for different materials,” stated RNT’s Global Vice President of Sales, Mike O’Neill. “The ability to eliminate the need for a back side metallization is another instance where NanoBond® can simplify the sputter target bonding process.”