THE SIMULTANEOUS DETERMINATION OF SULFITE AND SULFATE IONS IN ENGLEHARD GOLD PLATING BATHS USING ION CHROMATOGRAPHY
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-16
The APDAC TAB organization is concerned with the bumping of wafers using an Englehard gold sufite system where 22pm ofgold are plated electrolyticalIy in about 22 minutes. The Englehard system consists of gold complexed with sulfite plus borate and hydroxide as elec- trolytes. As the bath is used the sulfite is oxidized to sulfate during electrolysis and/or contact with air. Ini- tially we analyzed the bath only for gold content by inductively coupled plasma spectroscopy (ICP) and for sulfite concentration by iodometric titration. However we now know that bath performance is a function of the buildup of sulfate in the system causing an increase in conductivity and "spikes" (single crystal growth) in the gold finish, therefore it became necessary to develop a procedure to determine the concentration of the sulfate in the bath.