REDUCING SOLDER DEFECTS UNDER NITROGEN WITH VARYING OXYGEN CONCENTRATIONS
Author: H. Hsiao Company: BOCLH Date Published: 4/28/1997
Surface Mount International
Abstract: Numerous reports have documented improvements in fundamental aspects of soldering under nitrogen. It has been well established that nitrogen inerted soldering helps to widen the process window and improve first pass yield. The advantages gained from using nitrogen must justify the cost. Therefore it is important to determine the specific atmosphere requirement for realizing the benefits while optimizing the nitrogen consumption and the nitrogen supply mode. Production defect rate data were thus obtained as a function of the oxygen concentration in both reflow and wave soldering atmospheres. These soldering tests were conducted at assembly lines that make computer mother boards. Benefits in reflow soldering were demonstrated with oxygen levels below 1000 ppm. A small but continuous improvement in yield with decreasing oxygen concentrations was observed down to 25 ppm oxygen. The wave soldering data showed that majority benefits, > 60 % in dross reduction and > 50 % in total defect reduction, were realized with oxygen concentrations of less than 2000 ppm. Further improvements in decreasing number of opens continued with decreasing oxygen concentration to 400 ppm (> 90 ‘%o reduction), while the numbers of shorts remained similar when oxygen concentrations were under 2000 ppm. Based on these results, various nitrogen supply modes should be considered for the soldering processes, depending on availability and economics.