EFFECTS OF REFLOW ATMOSPHERE AND FLUX ON TIN WHISKER GROWTH OF Sn-Ag-Cu SOLDER
Authors: Alongheng Baated, et al. Company: Osaka University, Air Liquide, and Senju Metal Industry Co. Date Published: 10/4/2009
Abstract: Sn whisker growth behavior of Sn-Ag-Cu solder fillets, on lead-frames of quad flat packages (QFPs), on OSP printed circuits boards during 85°C/85% relative humidity (RH) exposure was evaluated. Three different concentrations of halogen activated flux (Sn-3.0wt%Ag-0.5wt%Cu) were soldered in an air and an inert N2 reflow atmospheres. The lead frames of QFPs were metalized with Sn plated Cu and Fe-42wt%Ni (alloy 42). Sn whiskers were observed on the surface of solder fillets of the QFPs joints reflowed with halogen flux in air atmosphere. Substantial amount of Sn oxides were formed for those solder fillets with whisker growth and the amount of Sn oxides increased with the halogen content. Sn oxide formation apparently enhanced whisker formation. The combination of air reflow atmosphere and high halogen flux was the worst for oxidation of solder fillet resulting in Sn whisker formation, regardless of electrode lead frame for Cu and alloy 42. In contrast, an inert N2 reflow atmosphere prevented the Sn whisker formation of Sn-Ag-Cu solder fillets, for all conditions of current work.