S. Xun, D. Van Heerden, T. Weihs, Reactive NanoTechnologies, Inc, Hunt Valley, MD
This paper describes a process which uses a composite reactive preform to hermetically seal cavities for microelectronic, optoelectronic and other applications. The composite preform consists of a multilayered reactive foil embedded in a solder preform. The reactive foil consists of thousands of alternating nanoscale layers comprised of elements with large negative heats of mixing, such as Al and Ni. When the reaction is activated in the foil using a small electrical or thermal stimulus, the heat generated melts the adjoining solder layers and permanently joins the package lid to the base forming a hermetic seal. The seal is achieved without exposing the components to high reflow temperatures.The composite preforms are fabricated by uniaxial pressing of solder and reactive foil preforms. This process creates a fully dense, robust, composite preform which can readily be tailored to a wide variety of existing cavity or package designs. We show that by using these composite preforms to seal packages helium leak rates of less than 1 x 10-10 atm-cc/sec can be achieved. This process provides an attractive alternative to more expensive sealing methods such as laser welding and eliminates the need for costly fabrication equipment.
Summary: This paper describes a process which uses a composite reactive preform to hermetically seal cavities for microelectronic, optoelectronic and other applications. The composite preform consists of a multilayered reactive foil embedded in a solder preform. The reactive foil consists of thousands of alternating nanoscale layers comprised of elements with large negative heats of mixing, such as Al and Ni. When the reaction is activated in the foil using a small electrical or thermal stimulus, the heat generated melts the adjoining solder layers and permanently joins the package lid to the base forming a hermetic seal. The seal is achieved without exposing the components to high reflow temperatures.
The composite preforms are fabricated by uniaxial pressing of solder and reactive foil preforms. This process creates a fully dense, robust, composite preform which can readily be tailored to a wide variety of existing cavity or package designs. We show that by using these composite preforms to seal packages helium leak rates of less than 1 x 10-10 atm-cc/sec can be achieved. This process provides an attractive alternative to more expensive sealing methods such as laser welding and eliminates the need for costly fabrication equipment.
