Study on oxygen contamination during atomisation of solder powders for microelectronics

Solder paste used in electronics for interconnects in micro circuitry is the most important component, being seen as the governing factor for miniaturisation. As a result, the quality levels of solder paste are being constantly upgraded. Solder balling is a type of prominent defect generated during soldering operation encountered mostly due to the presence of oxide film on the solder powder surface. This phenomenon becomes particularly conspicuous when a fine solder powder is used in order to enhance the printability. This paper encompasses the results of studies carried out on oxygen pick up in Pb–Sn solder powders during melting, atomisation and powder storage stages for fine pitch solders. Hydrogen annealing has been conducted on the inert gas atomised solder powders before storage to avert oxygen pickup and the results have been compared with as atomised powders. It was found that, hydrogen annealing is a mandatory process to overcome problems arising out of oxides.