Investigation on Sn grain number and crystal orientation in the Sn-Ag-Cu/Cu solder joints of different sizes

Polarized light microscopy and electron backscatter diffraction have been used to quantify the number of β-Sn grains and to examine the Sn crystallographic orientation in Sn-Ag-Cu/Cu solder joints, respectively. The effect of solder joint size on the Sn grain features was investigated due to the miniaturization of solder joints. The Sn-Ag-Cu solder joints of different sizes were found to contain only several β-Sn crystal grains and most solder joints were comprised of no more than three Sn grains. The solder joints showed a preferred crystal orientation. The c crystal axis of β-Sn grains tended to be at a small angle with solder pads. Specific orientation relationships were observed to be prevalent between neighboring β-Sn grains. The grain number, crystal orientation and misorientation were independent of solder joint size.