Fluxless Lead-Free Soldering Process Employing Vacuum Technology

概要

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Owing to the increase in environmental consciousness, various environmental regulations have been enforced in the recent past. In particular, the use of lead in soldering technology has been forbidden by RoHS directives. Furthermore, manufacturing or import of chemical substances such as flux, which are used in the soldering process, may be restricted in EU. It may be difficult to change production methods for complying with these regulations by simply changing the materials used or improving the methods themselves. This paper presents several examples of dramatic improvement in soldering process through the employment of vacuum technology. In processes employing this technology, voids in a solder could be removed by varying pressure during solder melting. Moreover, melting solder in a hydrogen atmosphere or formic atmosphere accompanied by pressure variation renders the soldering process fluxless. The two above-mentioned methods adapt to die bonding process of power device which has a wide bonding area. Finally, we describe in detail the application of hydrogen radicals to solder bumps which have a diameter less than 1 mm. We found that hydrogen radicals not only reduce the oxide films of the solder but also inhibit the reoxidation.