United States of America as Represented by the Secretary of the Air Force

Mcdonnell Douglas Corporation

Maryanne Sovak

Jeffrey S Mott

Peter L Tihanyi

Hubert J Vollmer

Sonnia C Rojas

Method of bonding a chip to a Cu heat sink comprises depositing a layer of Ni upon the sink, depositing a layer of Pt over the NI, and thereafter annealing the sink in a partial vacuum containing a reducing gas. After the annealing step, a metallic wetting layer of Au and a layer of In are sequentially deposited upon the Pt, and the chip is soldered to the heat sink by means of a flux free soldering process. The pure Pt is very dense and stable, does not have microholes therein which would otherwise allow the Cu ions to penetrate the Pt. For a BeO heat sink, a Ti layer is deposited over the sink rather than Ni, and a layer of Pt is thereafter deposited over the Ti layer. The Ti, Pt and BeO interact to form a good bond of high thermal conductivity, which also blocks ion migration upwardly toward the solder and the electronic chip.

LED soldering method utilizing a PT migration barrier

An element is soldered to a heat sink by a flux-free technique in which flux-free solder is first deposited onto the heat sink surface, then the element is placed into position on the surface, then the heat sink is placed into and held at a constant temperature in a pressure controlled chamber to a level below the melting point of the solder while undergoing a plurality of cycles of introduction and purging of an oxygen stripping gas. Then the heat sink is raised to a temperature sufficient to cause a solid to liquid phase change to the solder layer in the presence of the oxygen stripping gas which is marked by optically detecting the change by monitoring the reflectivity change characteristic of the phase transition then holding the solder in a liquid state for a second interval of time sufficient to allow the majority of the solder oxidation at the interface between the solder and the element to be removed by the action of the oxygen stripping gas, and then rapidly cooling the heat sink and the element to room temperature.

Growing community of inventors

Shenorock, NY, United States of America

Maryanne Sovak