Alongheng Baated

Sn–Ag–Cu Soldering Reliability as Influenced by Process Atmosphere

To develop an optimal soldering process of Sn-Ag-Cu soldered joints, the influences of atmosphere and cooling speed during reflow treatment on soldering reliability have been examined through the use of Sn plated chip components and of Pd plated small outline packages (SOPs) on a printed circuit board (PCB) soldered with Sn-3wt.%Ag-0.5wt.%Cu, Sn-3.8wt.%Ag-0.75wt.%Cu and Sn-4wt.%Ag-0.9wt.%Cu solder pastes under air or N2 atmospheres. In the case of chip component joints, the solder compositions, cooling speed and atmospheres during reflow treatment slightly affect the dendritic microstructure. Those parameters rarely affect the wetting behavior and mechanical properties. In the case of SOP joints, however, the atmospheres during reflow treatment and fluxes strongly affect the appearances of fillet surfaces structure. Despite the types of solder fluxes, N2 process atmosphere obviously improved wettability of solder on lead-frame of the SOP.

Investigation of mechanism for spontaneous zinc whisker growth from an electroplated zinc coating

Zinc (Zn) whiskers are tiny hair-like electrically conductive filaments of Zn that sometimes grow from Zn coated surfaces (e.g., electroplated, hot dip). Zn coatings are commonly used as anti-corrosion coatings for iron (Fe) based structures. One of many common applications for Zn coated Fe is found on raised-floor tiles and support structures utilized in computer data centers. The formation of Zn whiskers threatens the reliable operation of electronic equipments due to the electrical shorting hazard they present. As with tin whiskers (much more broadly researched than Zn whiskers), the mechanism of formation is still not clear. This work investigated the Zn whisker growth mechanism for an electroplated Zn coating above carbon steel substrate from a raised floor tile using recent technology methods. Iron-zinc (Fe-Zn) Intermetallics and Zn oxides were identified by X-ray diffraction analysis (XRD). EDS (energy disperse spectroscopy) and EPMA (electron probe micro analysis) identified Fe-Zn intermetallic compounds on the surface of the Zn layer in addition to the interface between Zn coating and carbon steel substrate. Zn oxides formed primarily on the surface of Zn coating. Consequently, we speculate that Fe-Zn intermetallic compounds and Zn oxide formation can be the source of compressive stress effect on Zn whiskers growth on electroplated Zn coating above carbon steel substrate.

Sn-Ag-Cu Soldering Reliability Influenced by Process Atmosphere

To develop an optimal surface mount reflow soldering process with Sn-Ag-Cu, the influences of atmosphere and cooling speed on soldering reliability have been examined by using Sn plated chip components and of Pd plated small outline packages (SOPs) on a printed circuit board (PCB). Typical three Sn-Ag-Cu alloy pastes, i.e., Sn-3.0wt%Ag-0.5wt%Cu, Sn-3.8wt%Ag-0.75wt%Cu, and Sn-4.0wt%Ag-0.9wt%Cu, were used for reflow soldering in air or N2 atmospheres. In the case of chip component joints, the solder compositions, cooling speed, and atmospheres during reflow treatment slightly affect the dendritic microstructure of the solder fillets. In contrast, these parameters rarely affect the solder wettability both on boards/components and shear strengths of the solder joints. In the case of the SOP joints, however, the atmospheres in reflow treatment and the fluxes strongly affect the appearances of solder fillet surfaces structure. Despite the types of solder fluxes, N2 process atmosphere obviously improved wettability of the solders on the lead-frames of the SOP. Moreover, the scatter in shear strengths becomes smaller and the wetting of solders on the lead-frames becomes stabler in N2 atmosphere than in air atmosphere.