Abstract: A method has been formed for direct solder "bumping" of wafers, chips and interconnection pads or traces on hard to solder surfaces such as aluminum and indium tin oxide. It has been discovered that conventional solders modified by the addition of a light reactive metal can be jetted in the form of microdroplets onto a hard to solder substrate and that the modified droplets will wet and bond to the surface of the hard to solder substrate. This makes it possible for the first time to create solder bumps on bare uncoated hard to solder substrates such as aluminum and indium tin oxide without the need for first applying a different surface which conventional solder will wet.

Abstract: A compact printhead assembly is designed for employment in a soldering operation without the need for fluxes and without conducting the operation in a confined chamber. A self-contained printhead assembly has an internal reservoir and internal heating elements for raising the temperature above the melting temperature of solder or other liquid to be dispensed in microdroplets from a working surface at one end of the printhead housing. A jetting device containing an electro-mechanical transducer is pulsed to produced droplets at an exit orifice located at the working surface. Inert gas is preheated by the housing and delivered to the working surface to establish an oxygen-free atmosphere around the exit orifice and between the working surface and a substrate located a working distance away, whereby microdrops can be formed and deposited without harmful oxidation.

Abstract: A method and apparatus for producing solidified solder balls and for ejecting generally spherical-shaped drops of liquid solder through a controlled atmosphere to impact on a surface to be wetted is disclosed. The apparatus comprises a preload reservoir to hold and maintain solder in a liquid state, an ejection chamber to hold and maintain the solder in a liquid state, a connection between the preload reservoir and the ejection chamber to allow liquid solder in the preload reservoir to be transferred to the ejection chamber while maintaining the oxides in the preload reservoir, a device to pressurize the ejection chamber with an inert gas and an ejection device operatively connected to receive liquid solder from the ejection chamber and to eject generally spherical-shaped drops of liquid solder to a specific location on a surface to be wetted. Structure is included to provide an atmosphere of inert gas between the ejection device and the specific location on a surface to be wetted.