LED Soldering Method Utilizing a PT Migration Barrier.
Patent, Filed 22 Dec 87, patented 4 Apr 89,
DEPARTMENT OF THE AIR FORCE WASHINGTON DC
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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. PAT-CL-228-124. jes
- Metallurgy and Metallography